texts: Intel 8051 UART mode 0 doesn't work in Proteus (clock impulses on TXD occur constantly, MCU recieves bytes itself)

texts:
I think that I've read everything about 8051's UART but I can't understand what goes wrong even in this simpliest example. According to literature in mode 0 MCU transmits byte only when we write it into SBUF, and only there 8 clock impulses occur in TXD line; MCU reads byte when TXD voltage changes.
In this example (only indicator is connected to P1) I write nothing to SBUF, but pediodically TI, then RI interrpupt occur, TXD voltage constantly changes and I constantly recieve 0.
Clock frequency is 12 MHz. What can be a reason?
Thank everyone for any effort!

;====================================================================
; MCU: 80C51
; Compiler:  ASEM-51 (Proteus)
;====================================================================

$NOMOD51
$INCLUDE (8051.MCU)

;====================================================================
; RESET AND INTERRUPT VECTORS
;====================================================================

      ; Reset vector
      org   0000h
      jmp   Init

      ; Serial port interrupt vector
      org   0023h
      call  SERIAL_PORT_HANDLER
      reti

;====================================================================
; MAIN CODE BLOCK
;====================================================================

      org   0150h
Init:
      setb  ES
      setb  EA
      mov   SCON,       #00010000b ; UART Mode 0,
                       ; accept messages with any 9th bit,
                       ; enable recieving,
                       ; don't recieve 9th bit,
                       ; clear interrupt flags

Loop:
      jmp   Loop

;====================================================================
; SERIAL PORT INTERRUPT HANDLER
;====================================================================

SERIAL_PORT_HANDLER:
   jb       TI,     _SENT

_RECEIVED:
   mov      P1, SBUF ; Move to indicator
   clr      RI
   jmp      _AFTER_SERIAL_PORT_HANDLING

_SENT:
   clr      TI

_AFTER_SERIAL_PORT_HANDLING:
   ret

;====================================================================
      END


texts: Torque control of a BLDC motor acting as a generator

texts:
I'm trying to build a dyno for electric motors. The dyno consists of two motors: a motor under test (MUT) and a load motor. The two motors are connected together through a shaft. On the shaft there's a torque sensor mounted.

For a load motor, I'm using a Revolt 160 Pro (12kW) with a SEVCON GEN4 controller. The idea is to run the motor from a battery or a power supply (connected to the SEVCON controller). When the load motor is acting as a generator, the three phase terminals of the load motor are gonna be switched to a circuit with a dump load to dissipate all the generated power.

My question is: let's say that I have an 8Nm clockwise input on the MUT and a 4Nm clockwise input on the load motor (since I want to load the MUT with 4Nm). The net result on the shaft it's going to be 4 Nm (clockwise referred to the MUT). Therefore, the load motor is going to act as a generator. When it's acting as a generator, the SEVCON controller and power supply are no longer part of circuit, the load motor is just connected to a circuit with a dump load. How can I control the load motor (now acting as a generator) so now it loads the MUT with exactly 4Nm? Do I need to have a variable and controllable dump load to achieve this application?

EDIT:
This is a rough schematic of the circuit of the dynamometer on the load side. There's two circuits, one used for the motor when it acts as a generator and another one used when the motor acts as a motor (and therefore it's controlled by a SEVCON controller). My question was how to control the motor when it acts as a generator, i.e. how to control the generator's load on the shaft.


texts:
I have a 12V computer fan that I want to hook up to my Raspberry Pi. It has a 7V sensor, 12V power and ground. I know that the Pi can only supply 5v so I’m just wondering how to hook it up to the Pi and be able to control the fan through GPIO pins.

I do have a 12V Power supply


texts: I work for a plastics molding company and we manufacture containers that we need to verify do not have holes in them. I am looking design a fixture that will apply a very high voltage (about 15-30KV) to the surface of the product to see if the electricity finds a path through the material.  I then want to sound an alarm if a path is detected.  I'm struggling to find a way to detect the current flow without blowing out (due to the high voltage) the electronics. I am a quality engineer, not an EE but I am a life long electronics hobbyist.  I have considered making a rudimentary optocoupler, putting a neon or xenon bulb in a box with a photocell but I am hoping for a more elegant solution. What would you suggest?


texts: Mass producing my electronics/raspberry-pi idea - What are the steps?

texts:
Could somebody tell me what the rough steps would look like? I think I have a good idea. I have put things into practice, and it's working and so on, but it's very ugly.

I guess, first I would have to build a prototype which looks much more like the final product and is not as ugly and so on. But what are the steps exactly, how do I best build a prototype and then move to mass production?

PS: 'Mass production' might be a bit misleading here: I just want to have 500 pieces at first. I just have no idea where to start and how the process looks like.


texts: Compliance of user replaceable lithium cells?

texts:
I seem to remember that in the EU, lithium cells may not be sold to consumers and may not be user-replaceable in consumer devices.
This vague idea seems to be supported by the fact that I cannot recall a single product that used e.g. user-replaceable 18650 cells.
Can somebody explain the basics of EU regulations regarding user-replaceable lithium cells?


texts: Flash Write protection to prevent access to firmware

texts:
I am reading up on ways to provide security to software images on boot devices. In this regard, I was reading up that if bootloader resides on Flash then using flash memory write protection, the bootloader memory addresses can be prevented from overwritten by malicious software.

However I want to know what is the scope of such protection mechanism? Can someone who has physical access to the flash simply erase/re-flash this region?
Thanks


texts: What circuit element must be removed to have the VTh equal to the voltage between two points using Thevenin's Theorem?

texts:
The question that I'm trying to understand is provided below:

The Thevenin's equivalent of the circuit "around" 6 ohms has a VTh equal to the voltage between a & b,
(a) With the 6 ohms and all sources (independent and dependent) removed.
(b) With the 6 ohms removed between a & b.
(c) With the 6 ohms remain connected between a & b.

Diagram:

I assume that the answer is b. When I removed the 6-ohm resistor, both \$v_{a}\$ and \$v_{b}\$ are 10 V; the resulting \$v_{Th}\$ would be zero. I think that this is how you find the Thevenin equivalent looking into terminals a and b.
Also, if my answer is going to be letter A, I think that it is unnecessary for determining the voltage. My further readings suggest that turning off the independent sources is only considered when calculating for resistance.
What I thought about letter C is that it is the wrong answer since I cannot apply Thevenin's theorem without turning off anything at all.
Do we have the same thoughts?


texts:
I am trying to calculate the quality factor for the response curve of a series RLC circuit. I measured the voltage across the capacitor at several frequencies and calculated its ratio to the forcing voltage. The curve I obtained is as follows:

How is it possible to find quality factor when there no points where the curve reach -3db on the left side of the peak?


texts: Can specific pipeline latency arithmatic block be inferred when using * or / operator in VHDL?

texts:
When using the * or / in VHDL, the synthesis tool shall infer the appropriate IP block to carry out that operation. If we open the actual GUI for that IP block we can find a lot of options e.g select whether to implement the function using hardware DSP blocks or only device logic, pipeline latency e.t.c. Is there a way to specify such things in VHDL at all?

Dividers are the slowest of the 4 operations (+, -, *, /). Using the / operator in VHDL means that we want a divider that can complete its task in a single cycle. This would generate a lot of logic and reduce Fmax of the design. How do I tell the synthesis tool to infer a divider that has pipeline latency of e.g 5 cycles in this case, without instantiating the actual divider from the IP catalogue.


texts: How fast can small electromagnet change it's power?

texts:
I have an idea to have a button, which houses two opposite facing magnets, so that they push apart, and provide tension for the button when you press it. I would like the button to have two steps - so press it a bit, and get more pressure from the button, and when you get past a certain threshold, it releases the pressure, allowing you to depress the button fully.

I want the sensation to be like snapping a brittle match, not like bending a soft metal rod.

So, my question is... if I can control the flow of electricity to the magnets, how quickly can the force between the magnets change? Does it change as fast as the electric input? Does it build up and slow down? Is this measurable? Is there any way to increase the speed at which the magnet can change?

Edit

Just to clarify - I don't only want to have a switch that can have two steps. I want to have a switch that can be programatically altered, so that the tension matches a profile defined on some arbitrary algorithm that regulates the current. I would like it to be able to switch profiles instantaneously, and dynamically.


texts:
I performed an experiment using an LVDT where I used a generator voltage of 4.84V. I determined the secondary voltage at the beginning position, obtaining 2.48V and at the end (displacement os 22.5 cm) 2.12V.
Now I have to compute the sensitivity in mV/V/mm.
I thought that this was given by
$$S=\frac{\Delta V_{sec}}{V_{prim} \Delta x}$$

which leads me to 0.3306 mV/V/mm.

Now apparently this is wrong and I should obtain a value around 4... My guess is that the expression I'm using, even if its dimensions are correct is not right. I read on this: http://www.gatewaycoalition.org/files/bioengg_Instrumentation/site/LinearVariableDifferentialTransformer.html
that they basically multiply the output and the input and divide by the excitation voltage times the displacement. But in that case, the units are not right. Can someone help me?
Thanks!


texts:
I have implemented the attached circuit for -2V indication. LED D6A is turning ON by giving just VCC_5V(=+5V). LED is working independent of VCC_2VN(= -2V). Please correct me and suggest the proper circuit.
Srikanth Kacchu


texts: Controlling AC motor with TRIAC or relay?

texts:
I have an old Marklin crane that uses two 16V AC motors for rotating left/right and raise/lower the hook.
Using an Arduino, an HC11AA1 for Zero-Cross detection and a TRIAC (BT137 driven by a MOC3052), I can use a knockoff Nunchuck to speed control one of the motors in one direction - All well and good.
Now, I need to control the motor in the opposite direction as well as the other motor in both directions. As I see it, I have two options:
1) Control three more TRIACS
2) Use three relays (one for switching between up/down and left/right and one each for up/down and left/right) to distribute the signal from the first TRIAC
The price is roughly the same, but do you see any pros and/or cons of the two options?


texts:
I have problems understanding what does this instruction do
MOV number,#(4+3)SHL(4)SHR(4)
googling gave me this "operand1 SHL operand2" which is different than the instruction i wrote above . Can somebody please explain it to me
I also have problems understanding what does this code do

using 1
MOV R0,#1
MOV AR0,#2 /* what do we use AR0? since I have always used the instruction mov rn,#immediate and this one is new to me */
SETB RS0
MOV R0,#3


texts:
I am a grade 12 student, working with electromagnets for a physics project. My equation requires me to measure the current of a 20-25 cm bare copper wire 18 gauge. The power supply would be an aaa battery (1.5v) and a rechargeable aaa battery (1.2v). How much current can I expect from this battery (completely new, haven't even taken it out the box)with neodymium magnets (which conduct) on both the positive terminal and the negative (one on each side of the battery basically). I haven't really dealt like this with anything before but I want an approx value so that I can test this equation out.

Thank you.

Edit: The circuit would be 20-25cm long


texts: Solid state relay voltage current rating

texts:
I am looking to use a solid state relay like this one . This relay has a peak load voltage of 350v and continuous dc current rating of 110mA.

My question - if I wanted to control 12v @ 1A DC through this SSR, will it be able to handle it?

350v @ 110mA = 38.5W and 12v @ 1A = 12W, since 12W is less than 38.5W it should work, correct?


texts: Extract information from video through HDMI input processing

texts:
I need to develop a prototype of a device that does the following:

Take an HDMI input
For each frame extract a small region of the screen.
It's a small bar indicating some changing value.
Convert this bar length into an int value, say 0-256.
This can be done in linux once the region is extracted
Pass through the HDMI onto the display

Could you please suggest which processor/development board/capture card or any other device that can accomplish this task. I was looking at DaVinci processors and they look like they are capable of this.


texts: How could I get something to oscillate at 2295 Hz?

texts:
I am curious on making things oscillate. I would love to do this with one chip, but if there was a chip that oscillated at 2295 Hz, I have no idea where it is. So the question is, how could I use an LC or RLC circuit to oscillate ate 2295 Hz? I have looked at the formulas and looked for calculators and can't see a way to go backwards like I'd like easily.

Or is there any other circuit that can be used to oscillate at this frequency?


texts: Can a Schmitt trigger be used to start up a multivibrator?

texts: That is, suppose we have a monostable multivibrator and when the DC power is connected, the voltage initially rises rapidly from 0 to V(in). In reality there is a nonzero rise time when you turn on DC power. So the idea is use a schmitt trigger to generate a voltage impulse during the rising time after the power switch is closed and before the maximum DC voltage is reached that will start up the oscillator.


texts: Two separate power supplies for a single project...can they be conglomerated somehow?

texts: I have two separate components, one of which needs a 5V 500mA-1A power supply, the other of which needs a 12V 5A power supply. Is there any way to combine a single power supply somehow so that I only need to plug one thing into the wall in order to power both components?


texts:
I have designed and built a motor controller circuit. The circuit has a microcontroller on which gets commands from a PC using an FT232R. Currently the FT232R is powered from the board's +5V supply. This +5V supply is generated using a regulator which converts the +24V power input to the board. The +24V input also powers the H-Bridge which drives the motor.

Everything works fine, except when it doesn't - sometimes, whilst stopping and starting frequently under a heavy load, the PC blue screens. I think this has something to do with the ground level rising due to heavy load on the motor - which the USB end of the PC doesn't like very much.

My solution is to first switch to USB bus power (the only thing it needs to run is the FT232R) to eliminate any fluctuation in the supply.

I also want to protect the USB ground from the main board ground, however they still need to be linked. I was thinking of using an inductor to connect the power planes to prevent spikes from the stop start action.

Is this a good idea or is there a better method?

I have decoupling caps (1u and 100u) on both the power input and regulated +5V as well as 10n and 10u on the major IC's and 10n and 100n on smaller IC's. The question is asking how to connect a noisy power plane to a quiet one with out making the quiet plane noisy.


texts:
I need to develop a controller board for some peripherals which communicate at 9600 baud with 1 start bit, 9 data bits, no parity and one stop bit.

I am not sure that I am up to coding a serial port driver or even modifying an existing 8 data bit driver to handle 9, so - does anyone know of an MCU which comes, off the shelf, with a serial port driver which can handle 9 data bits?

I strongly prefer SD card support, and Ethernet  / Wifi would be nice (I don't care too much about BlueTooth or USB, so long as they don't significantly increase price).

Needs to be able to run 24/7 in an embedded device.

I prefer something with FreeRTOS or similar and a good development IDE including debug facilities.

Am I asking too much or does such a beast exist?


texts: I make project for temperature controller with pid and tmp36 , will my design work?

texts: I design a close loop system with pid controller and feedback with tmp36 sensor


texts: Measuring extremely high impedance, extremely high voltage sources

texts:
I'm working on a geiger-counter, and trying to get an accurage measurement of the high-voltage Tube Bias.

The issue I'm having is that the impedance of the high-voltage source is really, really high, I'd guess somewhere in the range of 100-500 MΩ.

Right now, I have 4 10MΩ resistors in series with my scope probe, which is set at 10X (I've measured the scope input impedance to be 10MΩ). This should produce a effective 50X probe, with a 50MΩ input impedance. Then, since the Input impedance of the prove is still enough to significantly draw-down the high-voltage rail, I'm using a sampling scope to capture the voltage as I touch the scope probe to the high-voltage rail.

Unfortunately, I'm still getting voltages that are far higher then they should be (it should be ~500V. I'm measuring ~1.2 KV). However, as this is a spark-fun product, and the circuit that I have so far studied has been extensively studded with truly WTF inducing design decisions, I am having trouble determining if the incorrect voltage measurement is due to the circuit not behaving as designed, or measurement error on my part.

Are there any other simple ways I can measure a high voltage source with an extremely high source impedance, to cross-check my results?


texts: How to drive a 12V common cathode 7-segment display with 5V signals and BJT transistors?

texts:
I'm having trouble designing a driver for a large (5") 12V common cathode 7 segments display using a 74HC595 shift register and BJT transistors. Below are the schematics for the component (display) I want to drive.

(source: soldafria.com.br)

I have a working driver for a similar 12V common anode display using the shift register and 8 NPN transistors (BC547) (see schematics below). I've even seen folks replacing the transistors by darlington arrays sych as ULN2003 and ULN2803.

But I can't seen to find the equivalent circuit for common cathode displays.

My first (failed) attempt at it is shown below.

The problem seem to be that the 5V signal is not enough to turn off the PNP transistor. I would have to raise the signal to 12V to turn the transistor off, but I don't have that voltage coming from the microcontroller or the shift register.

So, how can I drive common cathode displays? Can anyone point me in the right direction, please?


texts: I have Ethernet PHY from Marvell (88E1111-B2-BAB1I000) and Ethernet transformer (S558-5999-AT-F). By mistake the MDI P&N connection got interchanged on the transformer side. Will it work?


texts:
I am simulating somewhat complex behavioral sources in LTspice - and am having difficulty getting a set of parameters to be accepted. See schematic below of a bidirectional buck/boost converter. I think it is rejecting my ".param D=..." line because it contains the table parameters. Can anyone give me a suggestion on how to resolve this? I need to "pre-calculate" the D parameter based on the step values of V1 and V2. If I just define V1 and V2 with no step/table , the simulation works fine.

Thanks for any suggestions!


texts: Level vs edge triggering, usefulness of level triggering

texts:
Many processors / µCs / dev-platforms (BeagleBoard, Arduino,...) use interrupts.
These can be triggered by the detection of:

HIGH level
RISING edge
CHANGING level (either FALLING or RISING edge)
FALLING edge
LOW level

Now either of two things must be true:

FALLING and LOW (/ RISING and HIGH) are virtually the same
When a LOW (/HIGH) level is applied over a non-trivial time, the controller is stuck repeating the interrupt service routine over and over

Both of these don't make sense to me:

The first cannot be true, since it would be totally useless to make the difference in the first place then.

So if the second one is true: how could this be useful? What application is there that is not better off with a combination of RISING and FALLING instead of HIGH?

Research so far:

This question is just a stub, so it didn't help: https://electronics.stackexchange.com/questions/92833/what-is-the-difference-between-level-triggering-and-edge-triggering
This one is also not too useful as it is about when those interrupts are triggered, not the implications of the differences: What does edge triggered and level triggered mean?
This one mainly elaborates on the differences in detection of the different trigger events: Why edge triggering is preferred over level triggering?


texts: How to split Analog and Digital GND planes for a TQFN device

texts:
This question is in reference to Mixed signal PCB layout for PSoC.

If I am using a microcontroller which has separate analog and digital supply inputs and GNDs, what should do with the grounds?

Should I connect all GND pins (both analog and digital) to the thermal pad? Or should I only connect the digital GNDs to the thermal pad and connect the analog GND to its own GND plane?


texts:
I am looking into building my own battery management system, and I am beginning to understand the concerns of overcharging/discharging, overheating, and equal use of each of the cells. I am planning to build a battery management system that uses around 120 3.7V 18650s to power a 24V DC motor, so I am planning to put 6 in a battery and have 20 batteries. At this stage this is all I know.

My question is this: should I be concerned about uneven discharge or charging within a 6-cell battery? I know the battery management system takes care of these problems from one battery to the next, but I don't know if this would be an issue within a battery.

On a slightly more vague note, any other recommendations on (1) sites where I can learn more about building this system and (2) routes I could take for this project.


texts: AD5933 analogs for 4-terminal measurements

texts:
I'm going to do bioimpedance measurements, and it seems that AD5933 chip (http://www.analog.com/media/en/technical-documentation/data-sheets/AD5933.pdf) has many useful features for this. However, every paper on bioimpedance measurement (e.g. Ishai et. al, Meas. Sci. Technol. 24, 102001) suggests to use 4-point scheme (i.e. 2 electrode for known current injection and 2 electrode for potential measurement). After examining AD5933 datasheet I find it difficult to use this part in 4-terminal setup, since AD5933 stabilizes voltage on the sample and measures current, while in 4-terminal setup it is necessary to have this the other way around.

May be there are any other reasonable chips, which are able to do 4-terminals, with the same capabilities for signal processing as AD5933?


texts: limit switches to control motor direction

texts:
I am trying to use two limit switches and two DPDT relays to control the direction of the motor.  When the power is applied the motor should rotate one direction (direction for this question isn't important).  Also, at this point (initialization) neither switch will be energized. The motor will rotate and move until it energizes the second limit switch (labeled Switch 2).  At this point, the direction of the motor should reverse.  The motor and hardware will then move towards switch one.  Once the motor reaches switch one it should stop completely (not reverse direction again). Below is my basic wiring diagram.

I wired it up and when I supply power the motor rotates.  However, whenever switch 2 is energized I can hear relay 2 energize and de-energizes quickly but no motor rotation.

Also, I am trying to implement a latching relay when the motor reverses direction.  I do not know if my problem is occurring there.

Finally, I am having problems trying to figure out how to have the motor stop once switch 1 is energized.

Any help with my two problems (reversal of direction, and stop when switch 1 energized) would be greatly appreciated.


texts: Trying to build a symmetrical power supply from a VDC input without the problems of virtual ground

texts:
I have built this circuit

to supply a few ICs. The problem is that at some point in time the load on the positive site is bigger than on the negative side. So the virtual ground moves towards the positive rail drawing current on the negative part, heating the LM337 excessively. Another problem is that this circuit has a huge amount of noise that is not filtered in any way and passes to the remaining circuit. An amplifier being supplied by this will show a huge amount of buzz and hum.

Due to the limitation of space for this project, I cannot have a real symmetrical power supply

I have researched other circuits like this one but all seem to have the same problem of the ground varying and not becoming stable.

Searching deeper I found this circuit using the TLE2426. I do not need huge current needs but 3 things I need and that is a circuit that does not change the ground when I have different loads on the positive or negative sides of it, low noise and with the minimum number of components... and I am not sure this circuit can handle an amplifier using the IC TEA2025B as a load.

Another problem with the power supply on the picture is that when I increase the amplifier volume, the LM337 starts to heating fast.

Is there any way to do a virtual ground that is stable, low noise and with the minimum number of components?


texts: Data communication in power harvesting project

texts:
I want to design a wearable gadget for elderly to detect falling. This gadget should work by energy harvesting. Now I want to find the best effitient way of power consumtion to send data to a station for emergency alert. Does anyone have any experience to help me choose the best way to communicate? I myself think about ultra-low power bluetooth module but I don't know the best ultra-low power bloutooth module. Can anyone help me?
Thanks in advance.


texts:
I'm in the process of designing a tiny embedded system, it has quite a bit
of sensors and it is controlled by 2 MCUs.

On previous versions of the test boards, I used 2mm pitch size headers for connecting the main board to a programming board. For the new version of the board, we definitely can not put these headers anymore.

I had the idea of using tiny 0.35 ~ 0.4 mm pitch connectors to interface both boards. I never tried to deal with this type of connectors before and I was wondering if they would be a good option for repetitive use,  which will happen when programming and testing the device.

I've found the processes of connector hunting quite hard as there is a HUGE selection of parts and I cannot find the wire that I'm looking for. I think I may have to custom order a FPC wire too?

I’m wondering if anyone had a similar experience or suggest a different method for interfacing the boards?

Thanks


texts: Provide extra current to a power supply output cover current surge of load at turn-on

texts:
Searching the previous questions I can find ones similar to this but nothing that answers this specifically.

I have a power converter which makes 115VAC/400Hz from 115VAC/60Hz and provides 2.5 amps.  My problem is my load has an inrush of 5 amps for 100ms.

My question is:  What size/type of capacitor and inductor would I need on the output of my power converter to compensate for the extra 2.5amps @ 100ms?

I will accept a different solution.


texts:
I'm making a very simple terminal. It consists of ATMEGA328, which outputs text on an LCD represented by the fonts read from the EEPROM (24LC).

Each character of the font consists of 9 bytes (each bit representing "color"). All the characters are stored one after another. Here's an example of the letter 'B':

I'm calculating the memory location of each character in order to avoid using an cross reference table the following way:

ASCII_VALUE_OF_THE_CHARACTER * 9 = character_memory_location;

So far so good, but the problem is: I cannot load all the fonts into a character array, because the ATMEGA328 has only 2kB of SRAM.

I decided to read the EEPROM directly each time I need to draw a string, but that leads me to my second problem - reading the EEPROM to death.

The datasheet states "More than 1 Million Erase/Write Cycles", but that doesn't seem to be much at all, considering just to render the text from my post would take 1,432 read cycles and would kill the memory in no time, so I believe I'm heading towards the wrong direction.

I could use some 'hacks' and pre-load or cache most frequently used characters into SRAM or use some kind of simple compression algorithm, or add multiple EEPROM's to balance the load, but I would much prefer a proper clean solution.

What would be the proper solution to solve this problem in order to keep the hardware working for as long as possible? Thanks!


texts: radio energy harvesting on WIFI questions

texts:
I am building up a radio harvesting circuit on WIFI signal, but I fail. Actually I am very new to antenna and RF aspects.I have several questions about the circuit.

First of all, I follow this schematic diagram from this article - http://www.hindawi.com/journals/apec/2010/591640/

Equipment that I have used:
6X 1N5819 DO-41 1A/40V diodes
17X 1pf ceramic capacitors
5X 0.1uH 0307 Axial-Lead Inductor
1X 2DBI 2.4-2.5GHz wifi pcb internal ipex antenna , like this:[IMG]
1X UNI-T UT33C DMM
[IMG]

C1 is made up of 11X 1pf capacitor in series.
L1 is made up of 5x 0.1uH inductor in parallel.
C2=C3=C4=C5=C6=C7=1pf capacitor

The result I have encountered:

When I place the antenna vary the distance between 1cm to 3meters in any direction from my home wifi router, zero volt across Test point 3 with ground point , even zero volt test point 1,2 with ground point measured by the DMM.

I doubt at some area that I may misunderstand:

What is MS in the schematic diagram that illustrated in the research ?
Do I use wrong type of capacitor or diode or inductors? Since I have found some capacitors, inductors and diodes that specifically used in RF.
Do I need earth the antenna ? Actually, the ground point of antenna I have connected to the earth poin that near to C7 which is also connected to DMM negative(COM) pin. And I just follow this IPEX instruction:
[IMG]
Is the antenna too weak ? Since I have only 2DBI gain of antenna, however, I wonder why I even can not get 0.1mV when I place the antenna very very close to the home wifi router.

Apart from this, a very strange phenomenon occur in this circuit:
When I change the diodes to 1N4004 and keep other equipment unchanged, and placing the antenna near to a charging mobile phone or wifi router (on top of the device), there is a reading, like 30-50 mV shown in DMM.
I wonder is this reading due to the AC charging current?

I hope someone can help me.
Thanks all

(Since I dont know how to place the diagram to the post here. So I may provide the post on other forum for reference, Please forgive me to do this. Sorry.
http://www.electronicspoint.com/threads/problem-on-radio-energy-harvesting-circuit-is-cockcroft-walton-circuit-fail.275060/ ==> picture inserted by Wouter)


texts: Capacitor in parallel with relay coil backfires on contacts

texts:
I've got a smoothing capacitor(2,2uF) C1 in parallel with relay coils inside a fullwave diode bridge.

When the circuit is closed through contacts in pre-relay RLY1 it first gives me, almost everytime because of capacitive reactance in circuit (Ce of C1 and C2), an arc over the contacts of the pre-relay, when circuit is closed.
But if I place a resistor R1 in front of capacitor C1 to limit the inrush charge current of the smoothing capacitor it will in very short backfire into the resistors R2 & R3 and destroy them. Leading to no zener voltage.

Placing a diode in parallell with resistor R1 for bypassing of the charge current in one direction will end up in almost the same way with destroyed resistors R2 & R3, but not until after almost 1000 tries.

Why is this happening and how can I stabilize the circuit so the smoothing capacitor isn't giving me an arc in either the pre-relay contacts neither backfire into the resistors?
Because of C2 there's around 45-50VDC left inside the diode bridge.
Any ideas?

simulate this circuit – Schematic created using CircuitLab

Edit schematic: Added R4, an ICL NTC for inrush current limit.

Second edit:

Below answer helped me on the way, thanks! As you pointed out @SpheroPefhany, D6 should be the other way around pointing cathode away(changed in schematics) from smoothing capacitor C1. I've tested some new things to increase the effect over R4(changed to 220Ω) with a TRIAC bypassing(edited as Figure 1) and also found another idea regarding the use of a TRIAC(Figure2 in orange dashed box) or DIAC(in blue dashed box) in series with the zener D5, without the R4 in the circuit.
However, to ensure the heat won't destroy the circuit, it needs to switch fast enough to decrease the heat during opening. Is this a working approach or have I missed something?

See updated schematics.

simulate this circuit


texts: Simplification of the boolean expression

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The following is the logic circuit:

I have to simplify the following:

(((AB)')'+(B+C)+(AB)'(B+C)')C

=(AB+B+C+(A'+B')(B'C'))C

=(B+C+A'B'C'+B'C')C

=BC+C+A'B'C+B'C

=C+A'BC'+B'C


texts: Straight vs Null Modem Serial cable confusion

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I have a cable having a DB 9 male at one end and a female at another end. I will be using this cable to connect  BeagleBoard Xm ver C1 to the serial port of my PC. I understand the pins with respect to the following image:

Now this document says that I must have a Straight-through Serial cable....

  The BeagleBoard-xM provides a female DB9 port and requires a serial
  cable to connect the console to your host system. Use a
  straight-through (not null-modem) cable.

I have checked that as per the above image, pins are shorted like this: 1-1, 2-2,3-3, 4-4, 5-5 and so on.

Does that means my cable is a straight-through cable as required?

Another resource is here that explains the type of cable I must have:

Serial Port-Related

    Why is there no output? Why is it not possible to type into the serial port?
        For original BeagleBoard, purchase the recommended serial adapter. The BeagleBoard-xM utilizes a straight-through DB9 male-to-female serial cable.
        Ensure that you are connecting:
        RX to pin 2
        TX to pin 3, and
        GND to pin 5.

Based on this am I using the correct cable?


texts: Can the board inside a hobby servo be repurposed to drive an external DC motor

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Motor controller boards tend to be pricey, L298's a bit of hassle for the occasionally hobbyist, and both take up 2 IO pins per motor.

I've had the idea to hack off the control pcb from inside a servo, replace the pot with a trimpot, and solder this to a DC motor in situ on a device I want to control (consider the device would be hard to mechanically modify to accommodate a servo).

My understanding of servo innards are shown here. vIn and Ground are implied only. The signal is compared with the signal from the potentiometer (motor position normally), and the generated error code is used for the PWM driving a H-bridge around the internal motor. What I am proposing is taking the internal motor out, and connecting an external one there.

The intent is that you'd use 1 I/O control pin for a bidirectional servo, and a speed controlled servo modified for continuous rotation. It already has FET's needed to handle motor current. Then taking the controlled motor outside of the servo casing or substituting it with a similar motor.

The motors in question are small toy motors - nothing large, or with major loads.

This sounds cheaper and easier to connect than a motor driver. Is this going to work?

Opening my first servo, a working supertec, the servo motor is soldered into the PCB. Desoldering it would be possible.


texts:
What I know is with a current source, the current through the resistor should be the same as the source. But here I have two current sources so would this affect the value? I need to work out current through each of the resistors.

simulate this circuit – Schematic created using CircuitLab


texts: When to use common-mode and/or differential mode filters?

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I read this article, but it is not clear to me in which cases should either common-mode or differential mode filters (or both of them) be used (from the point of view of reduction of noise at the inputs of a differential ADC)?

Also differntial ADCs may have high CMRR   that should be able to suppress common mode noise by their own? Thus, perhaps the common mode filter may be not neccesary?


texts:
Here is my attempt to find fan-out for TTL inverter circuit.

As you can see, I did analysis for high input (low output) and used condition for saturation of output transistor Q3 to find max. number of gates which can be connected.
When input signal is low, output will be high, aprox. Vout = Vcc - Vd2 - Vbe4. Which condition should I use to find max. number of gates which can be connected in this case?


texts: Slip ring (wound rotor) 3 phase motor, what VFD should I use?

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I'm trying to solve some puzzles around the electronics of an amusement ride. It's basicly an old carousel with a wave-like pattern (3 tops/downs along the circle) that i'm restoring. (So that you know the application) I've been researching some while now and would like to have answers instead of doubting myself over and over, spending too much time on it when I can just ask.

I've got a 3 phase slip ring (wound rotor) motor with the following plate:

HP: 2
V st. 220 / 380
A st. 5.9 / 3.4
V rot. 53
A rot. 19
RPM: 1385
Freq.: 50 Hz

(ofcourse I'm in Western Europa and using the 230V now)

I found out that I could make this a normal ac motor by shorting the slip rings (just connecting them together) so that I can use a VFD and connect it in delta. (Please correct me if i'm wrong on anything)

1) Is just shorting it ok? I read something about putting little resistors between? Why would that be better?

2) Do I need a dv/dt filter? (it sounds like overkill to me?) The length of the cable from vfd to the motor will be max 10 meters.

3) Risk here is that the insulation could fail. How do I measure this and what values should I get? (ofcourse all of them giving the same value)

4) Now the plate gives me that it's actually a 1.3kW motor. Now to select an VFD I assumed I would need a 1,5kW VFD. But I got told that I would need a 2,2kW VFD due to that it is a slip ring motor, is this true? And what ac motor should i buy when i decide to replace the old one? Would 1,5kW VFD still be sufficient?

5) Would a VFD with built-in brake unit (resistor) of 50% nominal current be good enough?

6) If I calculate the slip % it is 1500 - 1385 = 115, thus slip = 115/1500 * 100 = 7,67%. In this article they say this is a high slip motor and therefor I should use sensorless vector instead of a V/F VFD?

7) I don't know how I came up with this info, but somewhere I read I should ground the rotor in some special case. I was shocked and now i'm just becoming insecure. Am I true that this is weird? And you should just ground the stator.

8) Some company told me I should use a linear curve instead of an S-curve in my application. I thought the S-curve was the way to go.. So which is it and why?

If anyone can answer one or more of these questions, please do so. Even if you're not sure, just give your opinion so that I can see how many people think what. Thanks a lot!


texts:
When each address in memory(RAM) stores 8bits of data. 8086 have access to 2^20 address locations making it as (2^20)*8 = 1MB. When it has 16bit data bus and accessing only 8bit data then what is the use of 16bit data bus.

Q1) Does it access two address locations and increment IP(instruction pointer) by two.

Q2) Can it use two banks of memory simultaneously and increment IP by one as shown in below image.

 Is it true if not why


texts: Why is it that disk storage has increased exponentially over the years, while disk access times barely improved?

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If you look at how much we are able to store on our disks these days, you'd be appalled to notice that the time required to access information from the disks have grown very insignificantly compared to the improvement in time required to access DRAM memory, for instance. Or even CPU speeds.

Why is it that we can store much much more than we used to on HDD's, but the time it takes to access or write has not been catching up over the years?


texts: circuit explanation for detecting different gases by mq2 with raspberry pi

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I am able to get the readings from mq2 sensor but don't know how to detect different gases by it.

Can anyone help me in getting the circuit explanation of detecting different gases by using mq2 sensor when connected to raspberry pi?


texts: Easiest way to create electric light source from scratch

texts: Is it possible to make lightbulbs or any other electric light source without using high tech equipment? Is there something that could be created in small workshop?


texts:
A few months ago I bought some new speakers and an amp for my Jeep.  I made a little face plate with an ALPS potentiometer  to control the volume and it has an iPod dock (no head unit, just the pot).

A couple days ago I finally was able to order a Raspberry Pi, and I want to make my own head unit for my car that supports 192/24 for my vinyl rips (iPod only outputs 48/16).

Can I use a HDD to store my music on?  I know that the gyro effect on the HDD spinning can cause some serious problems if the drive is twisted around a different axis than the platters (because the head of the HDD can scratch the disk).

If I securely mount a HDD in my jeep will it break?  When I go off road the jeep probably does up to ±4g of acceleration for short times in random directions.  Can a spinning HDD tolerate that?

I will use a SSD if I have to, but even a small and (relatively) slow SSD for my 100GB of music will cost A LOT of money where as a 256GB HDD cost about $10 on eBay.

A more complicated option would be to cache my current playlist to the SD card on the RPi and install an accelerometer.  I could monitor the accelerometer and make it stop reading from the disk when the acceleration goes more that 1.2g or so.


texts:
I have a surge-protected outlet from a renowned brand.

On the back it is written
10A 230v
Up voltage = 0.8KV
Spd class III.

The 8 outlets are Shucko format.

I do not understand that up voltage.
Does it mean that the global load on the 8 outlets must be up to 230x10= 2.300W and a single outlet can bear up to 800W?

Please note, it has also a TV protection for coaxial antenna cable. Maybe that up voltage is related to that secondary protection?


texts:
I'm new to ARM and a bit confused with all the diferent series.

I need to build a low power gateway (ethernet, wifi...), so I guess a cortex-M or cortex-R will be the good starting point.
But it didn't find any dev board with say a cortex-m3 (wich seems to be quite popular) supporting linux.

It seems possible linuxM3, so I wonder why there is no linux project around an mbed or a LPCXpresso for example ?

Can anyone point me to the dev board I seek, or explain me why "cortex m"+linux doesn't comme with more answers ?


texts: Is it ok to use the PCB as part of the structure of a product?

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The industrial and product designers I'm working with keep on coming back to the idea of using the PCB as an integral part of the physical structure of our products.

We have wall-mounted products and I am quite uncomfortable with this. My argument against is that: "It is not a good design principal, the PCB should generally only be supporting its own weight and not unnecessary things like the frame"

They argue that the parts being supported are relatively light.
This even includes supporting a thin frame of stainless steel using double-sided tape directly to an empty (no tracks or components) part of the PCB, or to plastic PCB clips that are taped to the frame.
Today they challenged my argument by saying "what design principal? show us where it says this"

These types of solutions can come up often from industrial designers because it solves a lot of cost problems for them, and also pushes some of the structural responsibility down to the PCB design.

In my opinion, products designed to "hang" off PCBs are typically proven and tested for mounting by the product designer. For example, a large GPU heat-sink is heavier than anything we plan on placing.
However, If we are "hanging" our own parts of PCBs we are entering a whole world of design that I don't know enough about.

Perhaps someone can point me to some answers on these types of issues. It would be good to get some material on the forces that a PCB can take before solder starts cracking, etc.
Or maybe someone has seen a production-product that uses the PCB as part of the structure?
We are a small business, but our products are mass-production grade and we will need to pursue standards approvals such as CE.


texts: Question about analog and digital ground planes

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I am using a microcontroller with an integrated DAC. On my 4 layer PCB, I have connected the digital and the analog ground planes below the microcontroller.
The microcontroller and the DAC are supplied by a 3.3V regulator.
The DAC amplifier is supplied by a 5V regulator.

See the following picture?

Which ground plane (GND or AGND) should the 5V regulator be referenced to?
Which ground plane should the DAC amplifier supply (and its decoupling capacitor) be referenced to?


texts:
I developed a PCB for a project using STM32WB55 and after getting it manufactured I am trying to connect it to the computer using a Micro USB cable in order to run the code on it.
However, when I connect it to the PC I cannot see the COM port for it. It seemly doesn't detect the COM port. All I can see is the DFU in FS Mode under Universal Serial Bus which I am not that sure what it is or how to make use of it. ( see picture below. Sorry for it being in French)

I want to run the code on the PCB by using the bootloader, however in order to do that in to use the STM32Cube IDE tool, I need to see the COM port.
What do you think I should do?
I have tried using th STM32Cube Prog but I am not too sure how to use it and I have all my codes in STM32CubeIDE. Is there a way to code using the STM32CubeIDE using bootloader?


texts: Designing a radio frequency PCB with wireless communication

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Sorry the last post I had was not specific enough! I am new to designing a PCB for my project. The goal is to develop a radio frequency PCB that has power and radio sources that can perform wireless communication. I am very new to this. I have a lot of questions regarding how should I get started or even what software I would need to code for the PCB. Are there any videos/ tutorials that can help me get started? Some relevant examples will be great!

Thanks so much for your time!

Edit: I added a schematic (brianstorm of my thoughts) that explain what I am trying to do.. I am trying to measure the data (voltage) from the sensors and hoping to wire that with the PCB. But the goal is having the wireless communication and transmit the data. I was reading using maybe NRF24L01 Transceiver Module that might save me a lot rather then designing my own RF? (I'd need to design an antenna which I am not experienced with..)


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I have a 8.4V, 5000mAh NiMH hump pack running 2 PC cooling fans, each of which draws ~5A.

When I turned on the system (battery voltage ~9V), the fans ran fine for a moment, but then the voltage output from the battery begins dropping. After ~5 seconds, it stabilized at ~7V. After about 5-10 more seconds, I switched off the system and the battery voltage rose back up to 8.4V (not sure how fast, my analog voltmeter doesn't respond quickly). I did the same thing again - same result.

However, when I ran only 1 fan, the battery voltage remained near 8.4V.

What is happening to my pack? And how do I fix it?

Battery history:
The battery is ~5 months old with < 50 charges on it. I have been using a smart charger that has an auto-cutoff. First ~10 charges were at 1C, but now I charge at 0.1C or less. It may have been overcharged a few times and at least once it got to ~7V or less.


texts:
Lets say we have this circuit:

tpd(AND)=5 ns, tpd(OR)=5ns, tpd(NOT)=3ns, and tcd of all gates =1ns

FlipFlops: tpcq=1ns, tccq=1ns, tsetup=1ns thold=1ns

First I want to check this circuit for hold-time violations. And then I want to calculate the latency.

What exactly is tccq and tpcq of FlipFlops?
I understand that tcd+tccp > thold for the hold-time to be not violated. First I would look for the shortest path. This would be from the FF "D" to the FF "F".
The tccq of which FF (D or F or both?) do I have to take in consideration?


texts: RF Design - Antenna Feed-line Parameters

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I am implementing a BLE device with a chip antenna.  The device has already been impedance matched to 50Ω and is ready to be connected to the feedline and antenna.  The antenna datasheet has a recommended layout for edge-mounting and prefers a 50Ω co-planar wave-guide.

Using calculators such as this or this both give me the same CPWG impedance when provided with the relative dielectric constant for FR-4 at 2.45GHz (approx. 4.2), track width of 2.5mm, gap width of 0.75mm and dielectric thickness of 1.6mm.

None of the calculations I've come across seem to care about the length or shape of the CPWG (apart from gap/trace width) so my question is:  Am I right to simply link the antenna to the device as directly as possible so long as the above conditions are met?  What is the effect of the overall length of the CPWG?


texts:
WHat should I do when I am sending data using USB, when the callback in my firmware gives me USB BUSY?

Once, I received USB Busy state, I could no longer send data to my host from my firmware, but my host could still send data to my firmware and I am able to read it.

What should I do to clear the USB Busy state? and why is it in USB busy?


texts: TPS61196 LED Driver chip for high Voltage Backlight applications: What to do for proper backlight driving?

texts:
I need to design a Backlight Driver which has to have high brightness.

These are the equipments I have in the design:

My Backlight String combined of 2 parallel of 28 serial LEDs(2 * 28 = 56 LEDs)
My LED Driver Chip is TPS61196
My supply is 24V 15A 350W SWİTCH MODE ADAPTOR
My switching N-Channel Transistor is IRL640A

These are the features I need to cover:

I need to draw at least 350 mA from one channel(28 LEDs)
I need to adjust the Duty cycle 20% @ 120 Hz
When I draw 350 mA from 28 LEDs, output voltage will rise to about 28 * 3V = 84V + ~1V(Headroom) = 85V
I use 2 channels currently(each channel drives 28 LEDs in series) so 350 mA * 2 = 700 mA current needed to be boost
I will apply synchronised PWM dimmnig to 2 channels @ 120 Hz with 20% duty cycle

So designed this circuit (I took my reference design as TPS61196 EVM module). I followed the design guide carefully. Double checked the calculations. Yet, the circuit does not work. No strobe at all! Here is the schematic:You can download the SmartPDF file of both the schematic and the PCB here.

I tested the circuit in anyway I thought. Short circuits, wrong soldering, misplacement of components etc. checked for anything might be wrong, but everything was as in my design. So, I do not know what to do next. Maybe somebody here might have used the same chip and encountered the same problem. I am desperate here.

Only clue I have is this. I thought maybe, boost regulator is not working properly so I used another LED string which works with estimated 12V supply(When I apply 12V it lights up) and set the supply voltage to 12V. Because the initial IFB pin was 3.5V. Then I increased the supply voltage to 24V and I saw the initial IFB pin is increased as well to 16V. I could not see anything about this issue in the datasheet. I hope someone can help.


texts: The maximum current can flow when relay in closed state

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So many data sheets focus mainly on the parameters when contact is switching, such as the "maximum switching voltage", "maximum switching current". But what's the maximum current the contact can afford when the relay is already closed?

update:

I've noticed some manufacture give this parameter, such as, in Omron's data sheet for G8P

The "rated carry current" should be the current the contact can afford when closed, right? And you see, here it's just equal to the max. switching current. But some data sheet won't give this parameter directly, so can I assume that current shouldn't exceed the max. switching current?


texts: Test circuit for EU1640BCH12T / R Water proof ultrasonic sensors with Arduino?

texts: I have EU1640BCH12T/R waterproof ultrasonic sensors, which I have got from this link. These are standalone raw sensors without breakout board and not a module like HC-SR04. Being a new electronics hobbyist, I want to test these sensors with Arduino for distance sensing. I tried replacing transmitter and receiver of the original HC-SR04 module with my these ultrasonic ones but I am getting very ambiguous outputs from the circuit. Please suggest what circuit do I need to make to test these raw waterproof ultrasonic sensors?


texts: how to determin max current for an unknown stepper motor?

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I have a box of stepper motors and I can't remember where I got them from, nor can I find the datasheet for them.
They are named: 16HY0417N (or possible H instead of N at the end). I think they are from MOON (we usually buy stepper motors from them). They might have been customized for us (connector mounted) but maybe it's possible to read out the current from the model number?
I need to know the max Current and rated Voltage.


texts: ambient light rejection in absorbance sensor

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I'm making a sensor to measure light absorbance in a sample where the geometry varies over time.

I found a very nice transimpedance amplifier, the AD8304 designed for use with PIN photodiodes with a nice and wide dynamic range and logarithmic response which matches the physics of light absorption.  Here is an recommended application circuit from the datasheet:

Vref and Vout will feed the corresponding inputs on an SPI analog-to-digital converter.

The light source will be pulsed (sequenced through several wavelengths, actually), and the ADC measurements will be synchronized with the source pulses.  Pulses will be on the order of 100us in duration and the sequence will repeat at 2kHz.

I'd like to remove the error introduced by ambient light, which can be detected during the intervals while the source is turned off.  I think I can remove the ambient light by adding a parallel inductor which "learns" the ambient power level.  Can I use a solid-state switch to make the inductor only track the ambient level, as shown?

My idea is that the transistor acts as a switch -- while the source is turned off, the transistor disconnects the TIA and the RLC circuit charges until the current is all passing through the inductor.  When the source turns on, the inductor holds its current, subtracting it from the photodiode signal, and the remaining (non-ambient) current passes through the transistor to the TIA.

Will this work?  What parameters of the transistor and inductor do I need to pay special attention to?

On further consideration, I think that the node is supposed to be at VSUM, not ground, when the inductor current is constant.  So I think I should connect the inductor to (buffered) VSUM, as follows:

Finally, here's an adaptation of a current-mode sample-and-hold circuit:


texts: Altium silk screen carried over into copper layer

texts:
My PCB vendor informed me today that a silk screen feature that is carried over into the copper layers, lands on traces and causes shorts (yellow box on the right).

The yellow box is a connector and I got the Altium library from Samtec directly, I just wonder if it is a real problem, if it is how do I remove the silk screen.


texts: How to detect obstacles (Tripwire with Laser, IR or similar)

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Supposing I have a glass sheet 50cm x 30cm, with 10 holes (2 lines x 5 columns), with metal/plastic (i can chose) pins inside it. They can be flush (hidden in the hole) or salient (extending 2mm above, like a flat screw tip).

I'd like to be able to detect which pins are salient. But I can't have anything on top or behind the glass. It must be transparent (except for the pins) and totally free from components except on the borders. I'd have a 5mm clearance above the glass or less (I'd like to keep it really slick).

I considered a few solutions, but would like opinions about them. I believe I could use laser diodes + photo diodes, or IR leds + IR receivers. Any other ideas?

I could have 1 emitter per line and column, but it would have shadowing problems. Or 1 per hole/pin, which would be much more complex and expensive (not to say the alignment or elements).

I thought about using one emitter for each column, slightly off the column axis, with 2 detectors (one for each hole/pin). Not sure if it is possible to find cheap leaser diodes with wider enough angle. But may be possible with IR.

Not sure if IR reflections would be a problem, since I'd have at least 5 emitters.

Avoiding shadowing is a plus, not not absolutely required.

Any ideas?
Thanks a lot.

Update: I believe it is possible to do it using cheap IR emitters and receptors. However I'd have to use one pair for each switch:

I used red and green colors only to help visualizing the idea. Those are both IR emitters.

Opinions?


texts:
A recent question on here asking about how to calculate the accuracy of a circuit got me thinking about calibration in general.

In particular, as EEs we routinely use volts and amperes as a unit and yet these are both rather vague and hard things to quantify.

It used to be that a volt was defined by a "standard cell" kept locked up in a vault somewhere, but that changed to using the "Josephson voltage standard" which is a complex system that uses a superconductive integrated circuit chip operating at 70–96 GHz to generate stable voltages that depend only on an applied frequency and fundamental constants.

The latter is not exactly something one could throw together in a basement, or even in the test engineering departments in most companies.

The Ampere is worse. It is defined in SI as "That constant current which, if maintained in two straight parallel conductors of infinite length, of negligible circular cross-section, and placed one metre apart in vacuum, would produce between these conductors a force equal to 2×10−7 newtons per metre of length."

I have NO IDEA how anyone could measure that.

The ohm used to be defined by a specific height and weight of mercury, but that was abandoned in favor of being a derived unit from 1V and 1A.

This all brings me to wonder how much of what we use is calibrated to someone else's meter. And how many of those meters are calibrated to yet someone else's... and on and on. Seems like one big house of cards.

Is there some sort of intermediate standard of measures or equipment you can buy to use as calibrated references for 1V, 1A, and 1R? (Obviously you only need any two of those.)

Bonus question: Is there some sort of certification sticker one should look for when buying a meter or other equipment that indicates it is indeed tested to the actual SI values vs tested against, say, a Fluke?


texts: Why should the smallest bypass capacitor be placed nearest to the IC?

texts:
I have found and read many papers about bypass capacitors, but there is still one thing I am really struggling with. Let's say I have an IC and I place 3 bypass capacitors (eg. 10µ, 1µ and 100n). I am familiar with the idea that the smallest should be placed nearest, but I am still not certain why. From the papers I caught these 2 reasons:

The smallest capacitors are faster; thus, they can react fastest.
The goal of the smallest capacitor is to "filter" higher frequency noise. (This one is the one where I struggle.)

From what I've read, the reason to place the smallest closest is that high frequencies are affected by the length of the trace more than smaller frequencies. Is there someone who could explain this part to me?

Edit:
When I consider the typical graph of capacitor impedance based on frequency (the V shape graph), does it mean that the point of lowest impedance will be due to the inductance of LONG traces shifted left thus not filtering the high frequencies?


texts:
I am using FODM124 optocoupler. And I want to work in Saturation mode.
How to choose VF,IF,CTR and how to calculate Rf??
Bcoz i am seeing different IF's in the datasheet for different Vce's?
What exactly Vce relates with??

Please clarify.

With Regards,
Chaithra


texts: A question about sizing capacitor to mitigate the ripple of a DC-DC converter output

texts:
As a part of a circuit, I want to power an opamp LM311 with a 5V DC single supply. The whole circuit will be supplied by a 24V DC supply. To avoid another power supply I want to use this 24V to 5V DC-DC converter to power the opamp. I guess this converter doesn't require any heat sink. The opamp will draw around 5mA from this converter. Here is the data-sheet of the converter.

Below is the ripple of 5V output of this converter in AC coupling without loading. The ripple is around 1.7kHz with 40mV peak to peak:

And here below is the ripple in again in AC coupling without loading but this time I used a 1000uF 25V electrolytic capacitor. In this case the ripple is around 80Hz with around 10mV peak to peak:

Question:

I used a 1000uF capacitor in parallel with the converter and reduced the ripple as you see above in the scope outputs. But still there is ripple. Is this ripple acceptable? What is the criteria? I mean for a 5V supply is 10mV pk-pk ripple by using the 1000uF cap fine for this application(powering an opamp)? And if I use 5000uF or more I guess the ripple reduces more. But what is the limit here for the capacitor value? Is there a methodology I can summarize as a rule of thumb?


texts: JFET colpitts oscillator - very unstable

texts:
I've designed, simulated and build this simple JFET colpitts oscillator and I couldn't get it to work with real parts. I didn't have BF256B jfet model so I simulated it using some generic one. The circuit oscillates at correct frequency but amplitude varies with time and sometimes it doesn't oscillate at all. I tried to make it oscillate at lower frequencies to see if it would be stable there so I replaced L1 with 10µH inductor, C2 with 2.2nF cap and C1 with 10nF cap and I couldn't get it to oscillate at all (I also tried 2.2nF C1). This is my first time using JFET so I might be doing something fundamentally wrong. Does anyone see any possible issues with this design?

simulate this circuit – Schematic created using CircuitLab


texts: Four Half Bridge Load Sensors outputs highly fluctuating values

texts:
I have four half bridge strain gauge load sensors connected in a wheat-stone bridge configuration. I have fed the output of the sensors to the ADC (ADS1230) which is a 20 bit analog to digital converter.I have used ATMEGA16 microcontroller that takes the input from the ADC and displays to the LCD. But I am not getting constant reading .i.e ADC value is highly fluctuating and there is no way i can measure the weight accurately. I had also twisted the wires coming out from the loadcell. Here is the link to the load cells that I have used.

And the schematics as follows:

simulate this circuit – Schematic created using CircuitLab


texts:
Is there a amplifier that will always put out the same value? The values are ac not dc
Example 1: 1 volt  signal in=> 5 volt signal out.
Example 2: 3 volt signal in=> 5 volt signal out.
Example 3: 5 volt signal in=> 5 volt signal out.
Example 4: 10 volt signal in=> 5 volt signal out.
In other words, no matter the input voltage the output will always be the same even if the voltage is higer or lower than the output.
EDIT
The amplifier is for a radio recivier where a decoder needs a certain voltage. I just used these values for simplicity.


texts: Sources and References for Motor Selection

texts:
So, I was wondering if there is a book/textbook which discusses the issue of selecting the proper motor for a job. The type of it (induction, synchronous, DC, etc.) and mainly the nominal power of it.

I am at a stage where I understand the driving method for each type and I can design a proper driver, but I really have little clue on how to select the right motor.

I am not looking for a solution on a specific problem, but a general approach on how to analyze each problem and select the right type of machinery, based on the torque, speed and power required. I know that this is more of a "mechanical engineer" problem, but if anyone knows a source (no matter the size), I would like to know.

EDIT

Just to clarify: I am not looking for a way to decide the motor based on the requirements, but on a way to define those requirements. For example, lets say we want to choose a motor for a garage door. First of all, we have to know the way that the door opens. Is it on a rail and the motor has transform rotational movement to linear? or it wraps around an axis, as in "classic american garage door"? How much the door weights? How fast we want it to open? different gear boxes are needed, different torques and speeds in each example.


texts: How much Analog would a Beginner Electronics person need to know?

texts:
So most electronics books seem to deal with Digital...however messing around with the Arduino and such theirs been a few Analog projects and such......and I don't really know much about Analog (besides the conversions)......How much analog would someone "really" need to know. And are there any "Basic" Electronics books that cover it? or is that more of an advanced thing...

If it is a more advanced thing, maybe are there some specific Analog topics someone Like me would find useful? (Trying to Advance my embedded knowledge mainly).


texts: Am I doing something wrong or is there something wrong in this PMOS SPICE model?

texts:
I am trying to create a PMOS in Multisim based on a SPICE model.
The component itself is a DMC2400UV-7 from Diodes Incorporated (MOSFET  N/P-channel array for 20V.)
The NMOS simulation didn't give me problems and it works as expected, but the PMOS when testing it as a switch does nothing, however, I see a voltage change in the base.
My testing circuit is this:

The full SPICE model is as follow:
*---------- DMC2400UV Spice Model ----------

*NMOS
.SUBCKT DMC2400UV_NMOS 10 20 30
*     TERMINALS:  D  G  S
M1 1 2 3 3  NMOS  L = 1E-006  W = 1E-006
RD 10 1 0.1925
RS 30 3 0.001
RG 20 2 68
CGS 2 3 3.272E-011
EGD 12 0 2 1 1
VFB 14 0 0
FFB 2 1  VFB 1
CGD 13 14 6.7E-011
R1 13 0 1
D1 12 13  DLIM
DDG 15 14  DCGD
R2 12 15 1
D2 15 0  DLIM
DSD 3 10  DSUB
.MODEL NMOS NMOS  LEVEL = 3  VMAX = 1E+006  ETA = 0.01  VTO = 0.9058
+ TOX = 6E-008  NSUB = 1E+016  KP = 3.223  U0 = 400  KAPPA = 15.35
.MODEL DCGD D  CJO = 1.94E-011  VJ = 0.1108  M = 0.3101
.MODEL DSUB D  IS = 1E-009  N = 1.905  RS = 0.02633  BV = 25  CJO = 5.066E-012  VJ = 0.1753  M = 0.2672
.MODEL DLIM D  IS = 0.0001
.ENDS

*PMOS
.SUBCKT DMC2400UV_PMOS 10 20 30
*     TERMINALS:  D  G  S
M1 1 2 3 3  PMOS  L = 1E-006  W = 1E-006
RD 10 1 0.4041
RS 30 3 0.001
RG 20 2 14.3
CGS 2 3 4.178E-011
EGD 12 30 2 1 1
VFB 14 30 0
FFB 2 1  VFB 1
CGD 13 14 5.7E-011
R1 13 30 1
D1 13 12  DLIM
DDG 14 15  DCGD
R2 12 15 1
D2 30 15  DLIM
DSD 10 3  DSUB
.MODEL PMOS PMOS  LEVEL = 3  U0 = 400  VMAX = 1E+006  ETA = 0.001
+ TOX = 6E-008  NSUB = 1E+016  KP = 1.095  KAPPA = 49.86  VTO = -0.8823
.MODEL DCGD D  CJO = 1.311E-011  VJ = 0.2302  M = 0.2576
.MODEL DSUB D  IS = 3E-009  N = 1.688  RS = 0.5  BV = 25  CJO = 6.498E-012  VJ = 0.3007  M = 0.2934
.MODEL DLIM D  IS = 0.0001
.ENDS

*Diodes DMC2400UV Spice Model v1.0 Last Revised 2014/11/18

For the NMOS I copied from *---------- DMC2400UV Spice Model ---------- to .ENDS and for the PMOS from *PMOS to .ENDS
Finally, the net definition is this one:

My ultimate intention is to fabricate 8 tristate pins (as the last image) to drive a high voltage Charlieplexed LED array.

Maybe I'm skipping something, maybe the SPICE model considers a symbol with 6 pins and not two of 3 pins.


texts: Cheap 1" LCD suitable for use with microcontroller?

texts:
What cheap LCD pixel displays are available which are 1" or smaller which could be interfaced to a microcontroller? (AVR, PIC24, etc.)

I'd like to make an interactive keyfob.

The important factor is small size, 1.5"^2 maximum.

I've seen small colour displays in LCD keychains which look ideal - but, it looks as though they use some custom controller logic which only talks USB.

Something like these 16x16 monochrome LCDs would be ok, if I could find a display controllable with SPI (this device has a custom epoxied blob).

http://img.skitch.com/20090406-8dargu3hrnwdnfpgdu35k3tu78.jpg

Any ideas?


texts: What are the required Eye Specifications for SGMII+?

texts:
I am performing Signal Integrity Analysis for SGMII+ TX and RX lines operating at a frequency of 2500Mbps. Please let me know the minimum eye specifications such as eye height and eye width required to validate the same. Also, can you please let me know what is the expected voltage swing of the signals?
I am unable to find any related details in the specification nor mentioned in SoC or PHY datasheets.


texts: How much Program Memory does PIC24FJ1024GB610 have?

texts:
PIC24FJ1024 got 1024KBytes of Program Memory.

In the PIC24's Data Sheet in Chapter 4, mentions that the Program memory runs from 0x000000 to 0x7FFFFF which is 8,388 KByte.

Can someone explain why this duality?


texts: What would happen if water splashed on a 12v power supply when under load?

texts:
If I am running a 40A 12v power supply at approximately 32A, and a large quantity of water splashes onto it, what physical effects will occur in a worst case scenario.  I'm sure I can expect short circuits within the PSU and for my fuse to blow.  Will any sparking occur?  If so, could they make it out of the PSU case?  And could they persist for long periods or would the power stop flowing upon the first spark?

For the purposes of this question assume hard water with electrically conductive contaminants.  Assume further that the PSU is hooked up to a power switch with a 45A fuse hooked up to a 110v / 15A outlet.

For clarification: This did not actually occur.  I've just been playing around with a PSU doing some experiments and the question occurred to me when my daughter walked into the room with a cup of water.


texts: I know that relays are used for heating element or any electronic other device with high wattage/high current. But for my application, I am using a Nichrome wire as a heating element and only want to provide power of 100mW, for that I need a current of approximately 71mA current(which I already calculated). I will be using a microcontroller to control it and will be turning it on and off at regular intervals. I was planning to use BJTs as my current driver circuits but then someone suggested me about relays. The maximum current that the MCU pin can provide is 50mA. I could only find applications with high wattage that use relays for example in automotive applications. Can someone suggest me if using relays would work for my application? Or if they would work which I think they will, would it be better than using BJT as a current driving circuit?


texts: Is it possible to make a 150 Hz resonant circuit from RF toroids?

texts:
I want to make an LC filter resonant at 150 Hz using a 2.5 uF 400 V CBB61 capacitor and inductor. They are shown in the image below.

The toroid core looks like an RF toroid core but I don't know the AL. The toroid core length is slightly less than 30 mm and its outer diameter is 17 mm.

From calculation I need 450 mH inductor to make a resonant circuit with 2.5 uF capacitor at 150 Hz. So I planned to make 450 mH inductor from some of this core.

Is it possible to make an inductor from this core (or many of this type of core) that has optimum resonant circuit at 150 Hz (3rd harmonic frequency of 220 V / 50 Hz power system)?

If not, what kind of inductor should I use?

Its use is to make an shunt path for 3rd harmonic current.


texts:
Let me know if this is the wrong place for this, but I am looking to program an FPGA (Spartan 6, I believe) using a microcontroller.

Right now the way I am thinking about doing this is I will load the FPGA program in a .hex file onto the microcontroller memory and load it serially into some sort of JTAG IC which will then subsequently program the FPGA.  My question is does this JTAG IC theoretically exist, and if so, what should I be looking for?  I am not entirely familiar with JTAG, so maybe that is the source of my confusion.

Thanks in advance!


texts: We would like to design an FM transmitter module for Arduino boards. Therefore, we are in need of a trimmer capacitor that can be controlled digitally. Do digital trimmer capacitors exist or do you have other ideas how to design such a module?


texts: Arduino Runing On && Charging NiMH batteries

texts:
I have a project I'm working on that will have an Arduino running on 2 or 4 rechargeable NiMH AA batteries. I say 2 because I might boost up the voltage to what's needed. My problem is that this project will sometimes be plugged in and I would like the batteries to be able to charge during that time. These batteries will each have a capacity of around 2000-2400 mAh.

I must have done half a days amount of research on this topic and although I feel much more informed I still don't know how to proceed. Based on what I've read the most important thing is a constant current, with < .1c trickle charge for NiMH batteries and ~2c 1.2cSource linked below for a fast charge.

First off, is there a way to make a crude 'dumb' charger with say an external 12v power supply and the Arduino reading the battery voltage and shut off accordingly? If so where should the voltage be read at along the circuit for it to properly read.

I'd like to know that last bit the most, because regardless of what charging mechanism in the end is selected, I wish to know whether the Arduino can read the battery voltage while the batteries are plugged in.

Also, should I in the end use an IC like http://www.digikey.com/product-detail/en/BQ2002PN/296-9326-5-ND/379871 and let it take care of the entire situation. If so is the one I have selected a good one for this particular application?

Edit

I have tried to continue research and attempt to present a circuit. I will say this is the most complicated circuit I have attempted to design. Besides the couple dozen schematics I had looked at, I mostly used the following:

http://www.ti.com/lit/ds/symlink/lm317l.pdf

http://www.learningelectronics.net/circuits/float-charger-for-nimh-cells.html

And was using the following for battery charging information:

http://www.ti.com/lit/an/snva557/snva557.pdf

I now have a general understanding of the LM317 and adjustable voltage regulators in general (a big thanks to the above LM317 datasheet), but the additional complications slightly confuse me. To be specific Figure 7 in the datasheet I understand, but Figure 8 (which gave the most to this schematic) I only slightly understand the resistors with the transistor, and how it ties in with the adjustment on the regulator. Perhaps because of that the 6V used in the figure title somewhat eludes me, as does the ICHG.

The second link, I mostly used for the placement of the LED's which I am not sure will actually turn on/off accordingly. But it also mentions how the resistors stop the charge after a voltage set with the trim Pot, and I question whether mine also does that; I think so, but I'm not sure.

With that said if any of my confusion could be explained I feel that would help me to adjust the schematic accordingly. I would still like to incorporate this with an Arduino in the end, but that can be a next step.

simulate this circuit – Schematic created using CircuitLab


texts: PCB 4-Layer Cap Construction, Prepregs Mechanical strength

texts:
I am trying to construct a 4-Layer board for RF application. I have decided to use Rogers RO4350 material due to the high frequency signals on the top layer. I have also considered to combine Rogers and FR4 material since the high frequency signals will be only on the top layer (less expensive). The most suitable stackup for the moment is:

Rogers RO4350B of 4mil (0.101mm) thickness

Rogers Prepreg RO4450B of (30mil to 40mil) thickness

Rogers RO4350B of 4mil (0.101mm) thickness

As you can see RO4350 dielectrics are quite thin so we need the prepreg to add mechanical strength on our board. My question is: Since we use a prepreg in the middle instead of a thick core, will the above stackup have an appropriate mechanical strength or a thick core should be used instead of prepreg?


texts: Does the power drop on a diode become entirely heat?

texts:
Let's consider this simple circuit with:

A DC voltage source (for instance of 24V)

3 Diodes in series (with total $$ 0.65\times3 \approx 2 V $$ of voltage drop)

A resistor of $$10\Omega$$

This device gives 22V of voltage to the resistor starting from a 24 voltage source.
Now,
I) The resistor receives 22V, so the current on it is equal to 2.2A. The power it absorbs is equal to $$2.2A \times 22V = 48.4W$$
II) The DC voltage source provides 24V, and the current on it is always 2.2A. So the power it provides is equal to $$2.2A \times 24V = 52.8W$$
Obviously the remaining power (52.8 - 48.4 = 4.4W) goes to the 3 diodes.
So, my question is: does this power entirely become heat (so 4.4W of heat) because of the diode parasitic resistances? Or some part of it is stored in some ways inside the diodes?


texts: How to understand voltage change between different phases of BLDC?

texts:
Actually, it is a question about an application note of BLDC from here.

（on page 30 of that material）

The question is about calculation of potential of M. What I learned from book is that the voltage of inductance is proportional to the speed of current change. So, I do not think it is
a constant value, like HV/3?? Which parts do I misunderstand??


texts: Is this a proper use of a PNP transistor?

texts:
I'm attempting to use a transistor to switch on and off an SSR, which in turns switches on and off a solenoid. I originally used an NPN transistor (2N222), but this caused problems when the MCU reboots, because all the IO pins are pulled high. While trying to theorize (using my very limited knowledge in the area) on how I might use a PNP transistor to switch on/off the +5V going to the NPN transistors, it struck me that I might simply use a PNP to drive the SSR directly. This would avoid the reboot issue, because the transistor would be "switched off" while the IO was driven high (right...?):

Is this an appropriate use of a PNP transistor? Is this a (probably-obvious-to-most-but-clever-to-me) valid solution?

Based on Russell's answer, I think it's not (at least, not how it's drawn here), because the MCU output is only 3.3V, not 5V.


texts: Question about the equivalent circuit of an induction motor

texts:
This is the given equivalent circuit for the above parameters (from the problem's solution):

The resistance is R2[(1-s)/s].

However, my textbook shows that the resistance is instead R2/s for the equivalent circuit of an induction motor:

What is the significance in the discrepancy between R2/s and R2[(1-s)/s]?


texts: Struggling to understand zero cross detecting circuit

texts: I'm considering using this zero-cross detector circuit in a design but I'm struggling to understand exactly how Q1 is activated. The description says "Q1 turns on and feeds current from C1 to the opto via R4, whenever the mains voltage (divided by (R1+R2)/R3) is lower than the voltage across C1." I understand this, but it doesn't explain how the gate of Q1 is activated. In order for the optocoupler to indicate a zero crossing, the gate must be activated only when a zero-crossing occurs, so its reasonable to assume that it has something to do with the capacitor discharging, but how it actually happens is still eluding me. Can anyone venture an answer?


texts:
I am developing the BLDC motor controller board and I have problems with low-side gate driving. I am using MC33035 BLDC motor controller. PWM for speed control is fed into low-side MOSFETs. High-side MOSFETs are used for commutation. I have one ground-referenced shunt for current protection.
I found out that low-side MOSFETs have oscillations on turn on and I can't get rid of them.  (High-side MOSFETs don't have such problems)

I tried to increase the gate resistor (30Ohm, 56Ohm, 100Ohm, 200Ohm)- did not help. I tried to put ferrite in series with the gate resistor it helped a little, but not enough. I tried to put a capacitor between the drain and the gate. I tried 470,900,2200pf capacitors, but this did not help. I tried to put the capacitor between gate and source, but this did not help.
And I found out that oscillations increase as PWM is fed to low-side MOSFET. First PWM edge does not have gate oscillations.
Maybe my driver is a bad choice? Because all low-side gate PWM currents have to go through a single shunt, although I have a solid ground plane, maybe parasitic elements are just too big and cause oscillations.
But maybe you guys know what can I try to get rid of this oscillations.
Schematic of one leg:

Top side PCB:

UPDATE 1:
I tried to decrease the gate resistor value, but oscillations become worse.
100Ohm + Ferrite

10Ohm + NO ferrite


texts: Can you set the PWM output of an Atmel AVR to a specific frequency and have control over duty cycle?

texts:
I'm trying to drive an LED at 38kHz with a low duty cycle like 10% from an Atmel ATTiny88.  The chip is currently running at 8MHz, but could be adjusted for this portion of code, if need be.

Using the Timer1 with PWM I seem to either have the option to have decent control over the frequency, or I can only use the prescalers to adjust frequency and have control over the duty cycle.  I have not found a way to have both the tight control over frequency and also be able to adjust the duty cycle.

Is there a solution that would allow for this, or is it not possible on these microcontrollers?


texts:
I am working on dc to dc boost converter using IC LED5000.
schematic design and components as per E-Design suite from ST microelectronics.
specifications are
Vin- 12V DC
Vout- 36V, 100mA
FSW- 800KHz
when i supply 12v vin my output not boosting upto 36v it is only 11to12v as vin same.
IC switching at 820KHz ok .
any suggestion..?


texts: Deriving transfer function for effect of \$f_T\$ on BJT CE amplifier

texts:
I'm working to characterize the power NPN-based power stage in the DC Lab Power
Supply I'm designing.
I got a really helpful
answer
from gsills to a prior question I asked on that topic; now I'm just trying to
follow along step-by-step to be able to derive the results for myself, so I can
apply the same reasoning to other possible pass devices. Also, it's a good opportunity for me to solidify my understanding of BJT small signal analysis.
The place I'm having trouble is in deriving the transfer function for the
common-emitter (CE) small signal model to determine the location of the pole
due to the transition frequency (\$f_T\$) of the pass device. From gsills' answer:

What about the poles? First let's look at the pole caused by \$\beta\$
rolloff to \$f_T\$. In the model, eliminate all the capacitors and write
the transfer function. It's kind of big, but there is just one pole, which
after solving for the root gives the pole frequency for \$\beta\$ rolloff.
$$f_{p-\beta } = \frac{f_T \left(r_b+(\beta +1) \left(r_e+R_E\right)+R_4\right)}{\beta  \left(r_b+r_e+R_4+R_E\right)}$$

Here's a redrawn small-signal model with all the capacitors removed (also
I changed \$R_4\$ to the perhaps more conventional \$R_s\$:

I guess where I'm struggling is there are no capacitors to bring in a \$1/sC\$
element, so I don't see how to end up with something where frequency is
a factor. I'm kind if imagining there's some sort of \$\beta(s)\$ expression
that gets substituted, but I can't really discern an approach that seems like
it will get me there. I do note that \$f_{p\beta}\$ is proportional to \$f_T/\beta\$, the best case beta rolloff pole, and also that the rest of the numerator exactly matches the denominator of the DC gain of the model. But that's all I've got.
How can I get from here to an \$f_{p\beta}\$ expression like the one gsills
provided?


texts: I need information on  "the protection of distribution system through effective grounding techniques." I want to know the possible protection schemes for neutral as fault current or return current rises too much make it conductive. What will be the best protection for neutral?


texts: Paralleling Mosfets: Can I use a common gate resistor, or do I have to use a separate one for each mosfet?

texts:
When calculating gate resistor for a single mosfet, first I model the circuit as a series RLC circuit. Where, R is the gate resistor to be calculated. L is the trace inductance between the mosfet gate and the output of the mosfet driver. C is the input capacitance seen from the mosfet gate (given as \$C_{iss}\$ in mosfet data sheet). Then I calculate the value of R for appropriate damping ratio, rise time and overshoot.

Do these steps change when there are more than one mosfets connected in parallels. Can I simplify the circuit by not using separate gate resistor for each mosfet, or is it recommended to use separate gate resistors for every mosfet? If yes, can I take C as the sum of gate capacitors of each mosfet?

simulate this circuit – Schematic created using CircuitLab

In particular, I am aiming to drive a H-bridge made of TK39N60XS1F-ND. Each branch will have two paralleled mosfets (8 mosfets at total). The mosfet driver section will consist of two UCC21225A. The working frequency will be between 50kHz and 100kHz. The load will be primary of a transformer with an inductance of 31.83mH or more.


texts: Why does adding a capacitor to the adjust pin of a voltage regulator improve PSRR?

texts:
When looking into the datasheet of an voltage regulator, they often recommend adding a capacitor from the ADJ pin to ground, to improve ripple rejection.

It can also often lead to an significant increase in PSRR when doing so, according to their performance graphs:

But why?
It seems kinda unintuitive to me. Adding a huge capacitor at the feedback pin makes me think that the changes in the output voltage will take longer time for the regulator to measure(i.e slower control loop), because the capacitor has to be charged/discharged first. But this doesn't seem to be the case.

What am i missing?


texts: If Conventional Current is wrong, how can I trace the flow of current in a schematic?

texts:
If Conventional Current is backwards, how do I look at something like this schematic and trace the flow of current?  I'd like to follow the design linearly from positive to negative.

When the battery is on, does current go to 8, then 4, then through R1 and so on?

Does the current get "back around" to the side of the capacitor, 1, and the speaker eventually (though fast)?

How can this be so if in reality electrons flow from negative to positive?

Edit:  If the current were water here, how would I see that physically on the wiring, as if they were pipes?


texts: Verilog "optimizes" my code to run slower

texts:
I am using a Lattice LC4256V-5T144 CPLD and their ispLever Classic software. Simulation says this chip can run the 20-bit counter at 227 MHz; my requirement is 200 MHz. I have found that if the clock enable is used, code only runs at 182 MHz, which is too slow. I can design the circuit to avoid using clock enable, but the software always "optimizes" it to use the clock enable, and thus slows it down. There is plenty of space in the CPLD.

The counter is OK, my problem is latching the counter value upon the rising edge of an independent OneKHz signal derived from a 10MHz timebase. I use a 2-FF synchronizer for it.

QUESTION: When setting latch, how can I force Verilog to use logic on the D input rather than "optimizing" it to use the clock enable?

Here's the relevant Verilog code:

wire counterInput, OneKHz;  // defined and driven elsewhere in the module
                            // counterInput is 10kHz to 200 MHz
reg [19:0] counter, latch;  // latch is read via SPI elsewhere in the module
reg latchEn1, latchEn2;     // 2-FF synchronizer for OneKHz
reg latchEnable;            // also sets Ready (which is cleared by SPI read)

// latchEn1 and latchEn2 form a 2-bit shift register of OneKHz, so
// (latchEn1 & !latchEn2) means a rising edge on OneKHz happened
// on posedge of counterInput one clock earlier.

always @ (posedge counterInput)
begin
    counter <= counter + 1'd1;
    latchEn2 <= latchEn1;
    latchEn1 <= OneKHz;
    latchEnable <= (latchEn1 & !latchEn2);
    latch <= latchEnable ? counter : latch; // THIS LINE IS THE PROBLEM
//  latch <= (latchEnable & counter) | (!latchEnable & latch); // also fails
//          (that line also fails if I write out each bit)
end


texts: Bit shifting and PORT value on PIC18F4520

texts:
I am working on a PIC18f4520.
To do my test, I have connected a led to the pic. The following items are the steps I would like to do :

Save the value of the port set for the LED (which blinks according to the ISR subroutine I wrote, and can be look at in this case as a clock signal). For this I did :

unsigned char portValue;   // initialization
TRISBbits.TRISB5 = 0;      // LED on RB5 set as output

portValue = PORTBbits.RB5; // operation in the main while loop

Left shift the bits of portValue by one but with the insertion of the RB5 value. To illustrate :

--> if RB5 = 1, I would have portValue = 0b0000 0001
--> at t+1, RB5 = 0 then portValue = 0b0000 0010
--> at t+2, RB5 = 1 then portValue = 0b0000 0101
--> and so on (RB5 taking 1 or 0 and no other value)

With what I have wrote so far I can only do a left shifting. But I can't find a way to "add" the RB5...

Does something like

portValue = portValue<<(&PORTBbits.RB5);

could work ?
Bit shifting operations are quite new to me so my questions can be odd.

Anyhow, thanks in advance !


texts: Will it harm my 9v rechargeable battery if the +ve and -ve terminals are connected to each other

texts:
By mistake, the positive and negative terminal of a 9v rechargeable battery were connected to each other by me, and when I noticed it, I quickly removed it and the battery became hot a little. Did it caused any harm to my battery, Or should I use the battery or is it damaged now? Will it explode if I put it to charging now?
Link to battery


texts: Stable current source with discrete components

texts:
The purpose of this is to compare and learn different circuit topologies, not use of the shelf solutions which obviously provide cheaper, simpler and better results. Considering this requirement (no use of ICs, not even a matched pair), the parameter ranges given below and that the load should be connected to the voltage source:

Can we get better temperature stability and input voltage regulation by an order of magnitude (e.g. < 100uA)? To focus on the main goal, let's disregard the temperature coefficient of the metal film resistors.

The load regulation of the circuit on the left is already good enough. I've used different BJTs on the right do avoid depending on any form of matching between the discrete components.

The parameters are: 10 <= Vin <= 30, 0 <= Temp. (C) <= 50, 0 <= RL <= 1200, Isource ~ 5mA

Manually adjusting the central value with a trimpot is fine, let's not add this concern either.

Note: the ranges below are simulated by fixing all but one parameter.


texts: Getting a higher voltage from TL431 in a crowbar circuit

texts:
I want to protect a circuit from overvoltage using crowbar circuit, the input voltage shouldn't get above 50 V.

TL431 output is 36 V max, can a zener diode in series like schematic below protect the TL431? (is the circuit below correct)

Should I add the triac gate trigger voltage to the set voltage?

simulate this circuit – Schematic created using CircuitLab
BT139 datasheet
TL431 datasheet


texts: How do I work out energy stored in a capacitor bank?

texts:
I would like to know how to work out energy stored in a capacitor bank ?
I have done my own working outs and have reached an answer of 0.192J, I don't know if this is correct ?


texts:
I am confused on the terms Open, Short, and Closed when talking about circuits. As far as I know:

a) Open circuit means the wires are cut off so there will be no current flow, but there is voltage.
b) Closed circuit means the wires are connected so there will be flow of current, but there is no voltage
c) Short circuit also refers closed circuit.

Is my knowledge (a,b,c) about the question correct?

There is also another thing which confuses me:

d) Voltage is the force that makes the current flow. How can there be current but no voltage or voltage but no current? (from formula: \$V = I \cdot R\$)

Please explain a, b, c and d so it won't bother me anymore if I am going to solve circuits..


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I am trying to power my servomotor only for a short period of time (controlled by my MCU). I have seen I could use a switching regulator (3 pins). The thing is that I am working with really low power. The battery provides 3.6V to 4.2V; My MCU works with 3.3V and my motor needs 3.5V to 6.4V.

Do you have a solution to power my motor with this kind of switching regulator?


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Calculate the current shown by the ammeter.

simulate this circuit – Schematic created using CircuitLab

How do we solve this using delta-wye transformations?


texts: Reason for 27 MOhm resistors on Analog Discovery oscilloscope

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I am looking at the schematic diagram of a BNC adapter for Analog Discovery 2 oscilloscope inputs, and I see 27 MOhm resistors R3 and R4 (see the figure).
What is the point of these resistors?


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I am using an 8ohm ,0.5w speaker like this BMS16-16 .
I also have LM386 which suggest to use a 10 ohm resistor in seris with a 0.05micro capcitor .I am trying to understand how this together is suppose to be 8 ohm or what is the inductive of the speaker.


texts: Where can I connect the unused input to preserve the logic expression?

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So there is an unused input for the bottom NAND gate (even though it is not shown in the picture) and the question wants us to connect it while preserving the logic expression. I know when we connect it to the ground, the lower NAND gate never outputs 0. So I assume we are not going to connect it to the ground. But when we connect it to the +5V supply or E, we can get 0 or 1 as an output. Connecting it to E makes it work like it is a two-input NAND gate. I know I have to choose one of them but which one. I would appreciate it if I can get an explanation of what I should do when I come across these kinds of problems.
By the way I assumed we needed to connect it to E and made these answers (I would appreciate feedback to these also):
WIRING DIAGRAM

CIRCUIT SCHEMATIC

TRUTH TABLE
For the truth table I used this logic expression:
!((A&B)&(C&D)&(!(D&E)))


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i am making a pocket power supply and hoping to use it as voltmeter as well using 3 position SPDT switch to choose between power supply, off or voltmeter.

  [power supply - off - voltmeter]

how do i achieve this and make the middle position of the switch to power it off or should i just use a separate switch for the display?


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I stripped a DB9 extension cable which I will use to connect to a DB9 connector on one end and an RJ45 on another. I need to make connections to pin 2, 3, and 5 on the DB9 side.

When I stripped the DB9 wire, I was surprised to find 5 wires, since there are 9 pins in a DB9 connector. Why are there 9 pins but only 5 wires?

One of the wires is unshielded. Why is that? The other wires are red, brown, orange, and black. Which pins do these go to?


texts: Is input noise in a dual OpAmp device common to both channels?

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I'm designing an input buffer stage for a low voltage, noise sensitive application. These buffer stages consist of dual package OpAmps, with each individual OpAmp buffering the + or - input to a differential amplifier.

I'm comparing similar OpAmps for their noise specs, mainly their input noise voltage (spec given in nV / sqrt(Hz)), which I understand to be related to the white noise spectral density, and their 0.1 - 10Hz input voltage noise (spec given in nVp-p), which I understand is mainly related to 1/f noise. My application is low frequency, ~1-1kHz and will be effected by both of these figures.

My question is, is the noise from these sources common and directly related for the two OpAmps within the single package? In this case, will the noise then be removed by the differential measurement by the following amplifier stage?


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I have the question "For the circuit shown find the value of the current I"

From the previous question before this I worked out V = 60,

Therefore V = IR

And so I = V/R = 60/10 = 6A.

Is this correct ?


texts: what is this component and the brand name ? P527 DGM

texts: Im studying this board's circuit. But cannot find what's this P527 DGM component is. Could anyone tell me? Thanks