texts: Help building a scheme (involves L293D H-bridge)

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I'm making a bluetooth-controlled fire truck for my son based on an old wire-controlled truck I bought at a yard sale. It didn't have its wire-remote.

I already got Arduino Nano to drive 2 motors using a L293D (wheels forwards-backwards, steering left-right). It is being controlled from my phone via HC-05. Works like a charm.

Here's my problem. There are three wires sticking out that control the truck's siren and water pump. By using a battery pack, I tested different combinations and found two that make the truck do what I want. When I connect battery '+' to purple and '-' to black wire, siren sounds. When I connect battery '+' to purple and '-' to orange wire, water pump works.

My question is, how do I control (switch on and off) these two functions using another L293D? See attached picture. I need to understand which of Outputs 1,2,3,4 should be connected to Purple, Black and Orange and enabled for it to work.

Appreciate your help! It was far easier with the two motors :)


texts:
I had my first very exciting and successful go at an oscilloscope today. The question which arose at the end of my first experience has to do with the accuracy I was expecting. My microcontroller was programmed to output signals such as a HIGH signal for 80us, LOW for 50us, HIGH for 25ms, etc. I used a 16MHz crystal with my ATMega8.

When I recorded the output with the scope, I noticed that the measurements were not exact. For example, when I'd expect a 80us HIGH signal on the scope, it would look something like 77us. The signals which lasted longer times (i.e. 25ms) seemed more accurate.

My question is simply: is this what I should expect? I mean, the device I hooked up to my microcontroller requires specific signals for specific amounts of time, and I programmed my microcontroller to deliver it those signals for the lengths of time it requires. Everything works great, I just can't seem to understand why this discrepancy exists. For reference, the sensor is the DHT-11 temperature sensor. If the microcontroller is actually not delivering the precise signals, why is my sensor responding correctly?

Here are some of my guesses:

The sensor can tolerate some amount of error, which is why it works. I can't seem to identify and put that error into perspective based on the data sheet.
The crystal is not perfectly accurate. We are dealing with microsecond resolution here, so it is possible.
Other components like resistors and capacitors introduce error.
The clock on the oscilloscope is not perfect either - albeit much better than the crystal used for my microcontroller

Perhaps there is something else going on which I am not aware of.

Note that the timings I used above are just examples, and may differ from the data sheet and what I actually used in my code.


texts: ICL 7673 circuit Hysteresis Resistor values

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I'm using the ICL 7673 circuit from datasheet "without external PNP transistors".

Please help with deciding Rf and Rs resistor values for 0.5V hysteresis.

Any help is much appreciated.

Please see picture below.

You can see below ( a simplified version) showing that this circuit is actually quite different from a regular hysteresis circuit.

Regular hysteresis = comparator + positive feedback resistor network

ICL 7673 hysteresis = comparator + positive feedback resistor network + switch

So this hysteresis circuit works only for the condition Vs > Vp


texts: Could I replace headphones NIMH battery with Lithium Ion phone battery of the same voltage?

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Is it possible to replace a battery for headphones? I would like to replace a 052030 li po battery with a Nokia BL-5C Lithium Ion battery. The li po battery is rated at 130 mAh with 3.7v. The Lithium Ion battery, on the other hand, is 1 Ah with 3.7v.

Thank you for your help.


texts:
I am making 3V to 500V DC converter for a GM (Geiger-Müller) tube kind of application. Basically the tube needs to see 500V across it.
I read this relevant thread here :
5V to 160V DC converter
and I have a couple of queries:

Would the LT1073 circuit be suitable for this application.What
would be the maximum voltage felt by the LT1073 at the SW1 pin ? SW1
pin MAX is mentioned as 50V. Is this independent of the supply
voltage?
Suppose I use the common low cost MC34063 , would 3V be the
absolute minimum I could go down to? Suppose I use a flyback
topology instead of a boost converter,would I be able to get by
using the internal switch of the MC34063 instead of an additional
external switch? I suppose the external switch is needed more for
the HV rather than the current drawn.


texts:
I have very simple loop to read serial port and write to client

// telnet defaults to port 23
Server server(23);

void setup() {
    Serial.begin(9600);// opens serial port, sets data rate to 9600 bps

    // initialize the ethernet device
    Ethernet.begin(mac, ip, gateway, subnet);

    // start listening for clients
    server.begin();
}

void loop() {
    if (Serial.available() > 0) {
        char byte = Serial.read();
        server.write(byte);
    }
}

problem happens if serial port is open (on computer side) after ethernet connection is established, no data is transmitted

What gives?
thank you


texts: How can I reduce noise caused by shift register updates?

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I have a couple of designs using 74HC595BQ-Q100,115 shift registers.  Some are using the SO-16 package, some the DHVQFN16.  Some have five shift registers, some have three.  ALL have a significant noise spike when the data is loaded to the output register.  I am completely sure that it's not the update itself. Series resistors limit the rise and fall times of the control signals to values that are slow but within the chip data sheet, and if I disable the output update, the noise does not happen even though I'm re-writing the shift register.

I've gone as far as internal engineers at Nexperia who confirm that the SR itself is causing the noise "oscillating during update".  The footprints for both packages don't support getting the bypass caps any closer than I currently am, and I've tried bypasses from 1nF to 10uF, multiple caps.. I can't afford the room for X2Y caps here, and no guarantee that that would solve the problem.

The outputs go to an LED display through series resistors.  All that is within package ratings, and I can't change the output current demand.  I have seen that the noise goes away if I completely disconnect the outputs, but even 4.7K resistors in series produce almost as much noise as the 68 ohm resistors currently used.

The frequency of interest is in the 100's of kHz so shielding materials work particularly poorly down there.  I've tried Mu metal, Finemet, flexible ferrite.. Nothing makes a noticeable change.

As you can see, I'm forcing all the current in both VCC and GND paths to go through the capacitor pads, not even allowing a "T" connection.

I've actually toyed with the idea of using a programmed ARM here, I can get one in a very similar package, internal clock, and even at the same price!  However that's a bit of a project with no guarantee of success.


texts: Measuring the quality factor RLC circuit

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I am trying to get the Q factor for this circuit but I don't know how to simulate it properly.

I did a frequency sweep from 1 Hz - 30 MHz.
The oscillating frequency is 16 MHz.
I can't get the bandwidth around that frequency.

How should I simulate it to get the obvious shape of the Q factor for the RLC circuits?

NOTE: The diagram is wrong, L1 = 21.23mH

EDIT: With the I probes set on R,L or C I get only a fixed value for everything.


texts: Thevenin Voltage and Resistance Calculations

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In order to calculate R_th, you have to made all voltage and current sources equal to 0 (creating open circuits at current sources and shorts at voltage sources), so you will wind up with only resistors. That means that:

$$R_{th}=[(R_1+R_2)^{-1}+1/R_3+1/R_4]^{-1}$$

The dependent voltage source has a transresistance, so it adds on to the value of R_th. This is not being accepted as my answer though. I tried with and without the transresistance, even though it shouldn't be removed.


texts:
Before anyone say something negative about my post, yes, i have already read a lot of other posts before i public this question (well maybe not A LOT) but still i have doubts.
I'd be really glad if someone can guide me, first i'll explain what i want to achieve and what i know.
My purpose is to make an edge detector with pure VHDL (HLS is a valid option) an FPGA with Vivado Design Suite (with pure i mean without using any external help like pre built IP cores or toolkits form xilinx, etc), im between a Zybo fpga with zynq 7000 msoc, or an kintex with enough RAM to load a low quality image.
I already have some VHDL knowledge but i have never worked with image processing with a FPGA.
Here i go.

IS it even possible to make a real time color image processing in FPGA without using any external Software or Hardware, like MATLAB, and to be able to read an image from a camera and after the processing, display it on a screen with VGA connection or something like that?      AND of course, synthesizable.

First, which is the best (in terms of difficulty and performance) format file to load an image to fpga BRAM. I have read some posts saying that .bin, .hex, .mif and .coe, but which is the right one? I pretend to read a grayscale image, and after that, a color image.

Could someone give me an example (some explaining would be perfect) in vhdl to read a .coe/hex/etc file? Or link me to a good source of knowledge on how to do that.

Is there any book about image processing with fpga  with some examples?

and thats it.
I would really be grateful if someone could guide me.


texts: Reading and Sending Values to a 104 pc I/O relay board

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I am wondering how to send values to a 104 PC I/O board. There are several on the market that use a similar approach. Information surrounding the one I have in my possession can be found here. I have the R104-88 model(8 inputs and 8 outputs). From my understanding I have to select which base address I want to use with the jumpers. Using the jumpers I have selected the base address to be 300H.  So if I were to read 302H I would be getting the inputs from pins 0, 1 , 2, and 3. The problem is that not matter what the inputs are, I always read FFH from address 302H. I am using inpout32.dll to read the addresses. The code I am using to do this using python is below. I am running Windows XP as my OS.

import ctypes
print ctypes.windll.inpout32.Inp32(0x302)

Is there a better way do this? What am I missing? Do I have to configure the Hardware some how? I am at a loss of what to try next. Apologies if this is not the correct forum to ask. The question kinda falls under electronics, stackover flow and super user.

Edit:

The setup I am using is a 104 PC. The I/O board just fits on top of the 104pc and power supply.


texts: Do resistors turn electricity into heat?

texts: When wiring resistors to a battery, it generates heat and in the worst case, sets on fire but when it is used to limit current, for example in series to an LED, do they still generate heat ?


texts: Choosing capacitors for a linear voltage regulator

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I'm trying to use an LM1117 linear voltage regulator to convert to 3.3v (input voltage will be 9 or 5 volts; not yet decided). The datasheet suggests using 10uF tantalum capacitors on the input and output. While I could just go with the suggestion, I find most of the tantalum capacitors that are available are considerably more expensive than other capacitors, and in a SMT form factor (I'd prefer through-hole). I'm thinking of using aluminum or ceramic caps instead.

This excerpt from the datasheet specifies what ESR ranges are acceptable:

  8.2.2.1.3 Output Capacitor
  The output capacitor is critical in maintaining regulator stability, and must meet the required conditions for both
  minimum amount of capacitance and equivalent series resistance (ESR). The minimum output capacitance
  required by the LM1117 is 10 µF, if a tantalum capacitor is used. Any increase of the output capacitance will
  merely improve the loop stability and transient response. The ESR of the output capacitor should range between
  0.3 Ω to 22 Ω. In the case of the adjustable regulator, when the CADJ is used, a larger output capacitance (22-µF
  tantalum) is required.

As I understand it, ceramic caps have a very low ESR. Could I just add a 0.3 Ω to 22 Ω resistor in series with a ceramic capacitor? I've read what ESR is and isn't, and I don't understand it one bit, so right now it's just a range of numbers I'm trying to match. However, ceramic caps tend to have smaller capacitance, so it might not be as easy to get 10uF ceramic caps.

If I recall correctly, aluminum caps have a much higher ESR (though exactly what "higher" means I'm not sure). Additionally, it can be difficult to get a datasheet for a capacitor simply because they're such common components (I'm in China and purchasing online, but don't read Chinese). So I'm not sure how to make sure I'm within the ESR range specified.

Finally I should note that I don't have any of these components yet, but I'll probably get an assortment of capacitors when I do order.

So my question: What capacitors can be used in this situation, and with what value resistors (if any)? Note that I'm interested in the theory, not just this single situation, but not being experienced with capacitors some specific examples could be helpful.

Related: ESR and CSR of Capacitor


texts: Understanding the guaranteed data consistency within CAN network

texts:
I am reading the CAN spec and it says the following about data consistency:

  Data Consistency: Within a CAN network it is guaranteed that a message is simultaneously accepted either by all nodes or by no node. Thus data consistency of a system is achieved by the concepts of multicast and by error detection

Is my understanding that when no node accepts the message that the transmitter will send the message again and that the error count will increment correct?

Does the transmitter know that all nodes accepted the message based upon the acknowledge bit by the receivers? How does the transmitter know that all nodes sent this acknowledge bit on the bus and not just some of the nodes?


texts: De-soldering and Re-soldering Lithium battery to PCB

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Ive got a Lutron Homeworks 4 Processor that is c. 15 years old, it has failed where there has been a power outage to the processor and the lithium battery on the PCB has not been able to provide power to retain the processors memory. Apparently this is a common issue with the systems.

I need to de solder the battery from the PCB and the solder a new battery in its place.

The battery spec is : https://www.manomano.co.uk/catalogue/standard-battery/lithium-battery-sl360-pr-aa-36v-24ah-pr-7402307?model_id=7402307

Below ive attached some photos of the PCB from both sides showing the battery etc.

Ive never undertaken something like this before and was looking for some tips / pointers, my main concern is damaging the PCB and heating the battery past its 100C temp limit whilst soldering.

Here are the photos:

originals


texts: What is common mode voltage exactly in current sense amplifier ? how to select a current sense amplifier based on common mode voltage?

texts:
I understood the average difference between the input and output voltages is called common voltage .But still i have a doubt when it comes to current sense amplifier. i a m confused like is it the voltage drop across the shunt resistor .which we will feed as input to the current sense amplifier.

i am using 36V 2500 mAh battery pack its maximum voltage is 42 v when the battery is fully charged and its minimum 30V when the battery is fully discharged.

Iam using a 6.6 mohm shunt resistor it will give maximum voltage drop of 100 mv for max 15 Amps of current . is this voltage drop is called as common mode voltage.

The current sense amplifier iam plannin to use is AD8207 whose input supply is 3.3v . so when i search in google about choosing the current sense amplifier i saw that when we use High side bidirectional current sensing amplifier the common mode voltage should be equal to the bus voltage Why. and the AD8207 current sense amplifier whose common mode voltage is equal to my nominal battery to load bus voltage that is 36v but it is not equal to my maximum bus voltage 42 v . so can i use AD8205 as current sensing amplifier in my circuit.

What is bus voltage is it the nominal voltage of Battery pack given to the load or maximum voltage of battery pack given to the load.

So according to my understanding the common mode voltage is the voltage drop between the shunt resistor and it is extremely low compared to the bus voltage and why we need a current sense amplifier whose common mode voltage is equal to the bus voltage .

My battery to Load specification:

Battery pack nominal voltage : 36v
maximum discharge voltage : 42v
minimum discharge voltage : 30v
Nominal current : 2.5 A
maximum current that can be used in the bus (between battery to load): 15 A
shunt resistor value based on 100 mv dropout voltage : 6.6 mohm

What is exactly a common mode voltage? and based on my bus voltage and my common mode voltage.Can i use AD8207 in my application.

based on above battery to load specification can i use AD807 current sensing amplifier with 3.3 v of input voltage and  20 V/V of gain.

Please find the attached datasheet of AD8207 :enter link description here


texts:
I've been in the PIC-world for 12 years but only been using PIC10/12/16. For the next (one of-)project I will need a PIC with USB Host-mode, which means 24 or 32. Both architectures are ridiculously complex compared to the 8-bit baseline, so no matter which I choose I will have a lot to learn.

That said, what I want to do is to connect a USB keyboard to my device, retrieve the scancodes from the pressed keys, and then transfer the result to 20 output pins for a millisecond or two, clear all outputs, rinse and repeat. No screens, communications or other processing, just bitbanging the 20 output pins (using a truthtable of my own, depending on which keycode is grabbed from the keyboard).

This is just a very brief outline of the project, as I haven't figured out all the gory details yet. I might need 1-3 input pins for reset, calibrate, or whatever. Just in case. A 28-pin chip will probably not do since USB seems to require a bunch of pins itself, so I guess a 44-pin TQFP or similiar will do fine.

Question: Should I go for a PIC24 or a PIC32 here? What are the pros/cons of these two for my given scenario?


texts: Analog readings vary by higher current draw

texts:
I have a circuit, where an Atmega328pb and an WS2812-LED-Strip is powered by a 3,7V battery which voltage is boosted by a step up converter to 5,1V.
To indicate low battery, It reads the unboosted battery voltage (Analog Pin directly connected to positive of battery) and blinks if the voltage is below my threshold and shuts down at a lower threshold.
Now I connect a lab bench power supply instead of a battery and set the voltage to my threshold (max current is set to more then enough), to simulate low battery. It works as expected, until I increase the brightness of the LED-Strip. Now it just shuts down like the voltage is 100 or even 300mV lower. The same sees the battery protection in my circuit and cuts power at full brightness even if the supply voltage is 300mV above the threshold.
I know that voltage drops if the resistance is too high for the supply, but the power supply still shows the correct voltage and the amps are far away from the max current I set.
I couldn't test it with a battery for now, but I think it'll be the same.
My question is, how to solve this problem. Can I somehow still get accurate readings? Or is there a software trick to do this?


texts:
I guess I've been somewhat ignorant when it comes to the finer details of pcb layout. Lately I've read a couple of books that try their best to lead me on the straight and narrow. Here is a couple of examples of a recent board of mine, and I have highlighted three of the decoupling caps. The MCU is a LQFP100 package and the caps are 100nF in 0402 packages. The vias connect to ground and power plane.

The top cap (C19) is placed according to best practices (as I understand them). The other two are not. I haven't noticed any problems. But then again the board has never been outside the lab.

I guess my question is: How big a deal is this? As long as the tracks are short, does it matter?

The Vref pins (reference voltage for the ADC) also have a 100nF cap across them. Vref+ comes from an onboard TL431 shunt regulator. Vref- goes to ground. Do they require special treatment like shielding or local ground?

EDIT

Thanks for great suggestions! My approach has always been to rely on an unbroken ground plane. A ground plane will have the lowest possible impedance, but this approach may be too simplistic for higher frequency signals. I've made a quick stab at adding local ground and local power under the MCU (The part is an NXP LPC1768 running at 100MHz).
The yellow bits are the decoupling caps. I'll look into paralleling caps. The local ground and power are connected to the GND layer and the 3V3 layer where indicated.

The local ground and power are made with polygons (pour). It's going to be a major rerouting job to minimize the length of the "tracks". This technique will limit how many signal tracks can be routed under and across the package.

Is this an acceptable approach?


texts: Help driving 9V circuit with a 5V RTC clock interrupt pin (active low)

texts:
I am using this RTC clock module (http://datasheets.maximintegrated.com/en/ds/DS3231.pdf). The DS3231 has alarm function that can be programmed twice a day. When the alarm goes off it makes the interrupt pin an open collector (according to the data sheet). The particular board I am using can be found on eBay  , and here is the schematics for the board I am using https://edwardmallon.files.wordpress.com/2014/05/rtc-goodparts.jpg?w=640  as you can see, the interrupt pin "SQW" is not pulled high by default). I have already verified on a 3V circuit (with arduino) that the interrupt pin works as expected. For my use case, I am using the DS3231 from the battery Vcc , and not steady 3.3V vcc from a regulator.

What I am trying to achieve is to utilize the alarm function to drive a 9v circuit.
I have a few questions:

1) My first attempt is to use the IRF9510 P channel MOSFET. The result is MOSFET is always on . Pull up 9V resistor is used at the gate. Gate-Ground voltage is 0.19v when interrupt is active low. Gate-Ground voltage is 3.5v when alarm is not triggered (interrupt is not open collector) , which explains why the MOSFET is on, but I don't understand why, as the pin should be high impedance when not active low ? (note my battery is at 8.65V, spec sheet says maximum input range to be 5V and 5V + 3.5V is 8.5V quite close to 8.65V)

2) My second attempt is to use a small 3v cr2032 battery and a P-channel MOSFET (I have also tried the same setup with a PNP transistor and that works too). The active low interrupt can drive a 2V+ signal to another N-channel MOSFET gate. (ofcourse, the common ground are established.) That N-channel MOSFET has its source connected to 9V.
Setup 2) works except for the current consumption for the 3V cr2032 battery. I measure 0.11mA when the interrupt is not activated, and 0.4mA when interrupt is low. Given 200mAh
typical capacity, this only amounts to approximately 1/2 a month of runtime (assuming average 0.55 mA draw)
I should mention, both the MOSFET-MOSFET setup and PNP-MOSFET setup draws about the same amount of currents, (MOSFET-MOSFET is better, at 0.1mA when not activated and 0.25mA when active low)

3) for setup 2) there are only a handful of pull-up resistors and gate resistor pairs that result in a working system. I have tried many combinations and my conclusion is anything from 1k ~ 4.7k works very reliably.  The current draw is a function of the resistors used but at higher resistance value, the N-channel mosfet (the second mosfet) will not turn on appropriately, why is that?

any suggestions ?
thanks


texts: Getting Waveforms with Negative Voltage Component on a Bridge Rectifier

texts:
I am trying to simulate a Bridge Rectifier with 1N4005 diodes and an AC power source. The circuit looks like this: link here

I am getting a waveform that drops below zero V, is this behavior acceptable for a circuit like this? Thank you.


texts: Altium 18 - Pad on board edge in 3D-VIEW/3D-PDF

texts: Is there a way to show a half cut plated-hole/pad in 3D-VIEW/3D-PDF on the PCB edge with the board-outline?


texts: What is the typical PCB fabrication process in a professional PCB house?

texts:
I have been etching my own boards as part of my hobby interest into electronics, and I can't help but wonder how exactly is the typical printed circuit board manufactured? Unfortunately, details on the process are extremely scarce online.
I am aware that a similar question already exists, but it doesn't really explain anything at all and the answer to the question hinges on a youtube video that has since been removed.

I have been trying to piece together the process from information available online and from my own experience, with my current assumption (about single and double sided boards) being the following:

Hole drilling for holes, leads and vias on the bare dielectric substrate (e.g. FR4) followed by cleaning.
Activation for electroplating (applying a thin conductive layer) and rinsing.
Copper electroplating and rinsing.
Surface polising and cleaning.
Photoresist application, UV exposure and photoresist development (removal of either exposed or unexposed resist, depending on chemicals used).
Copper etching, rinsing and photoresist removal.
Solder mask application, UV exposure, development (removal of either exposed or unexposed solder mask, depending on chemicals used) and curing.
Optional tin and/or gold plating of exposed copper followed by cleaning.
Silkscreen printing, ink curing.

Is the order of steps at all correct? What solvents are used for cleaning? What chemicals are used for surface activation for electroplating? Which electrolytes are used for electroplating? Which etching chemicals are employed? Is the solder mask and photoresist applied as a dry film or as an UV curable ink, or is a photolithography technique used at all?

Yeah, I'm curious about everything.


texts: FT230X direct interfacing with 5V uC like PIC24FV &/ PIC18

texts:
I am working on a project in which I am using PIC24FV32KA304. And I want to use FTDI FT230x usb to uart chip for communication with PC.

Datasheet of FTDI chip mentions that TTL input is 5V tolerant. So from this I understand that input to RX pin of FT230x can handle 5V.

My question is will it convert voltage level of TX to 5V? Can I directly interface RX, TX of FT230x with my 5V uC or do I need to use level converter?


texts: Restoring old SR-50 Calculator, odd Charger Voltage

texts:
I have an old Texas Instruments pocket calculator, for fun decided to get it working again. It is strictly a NiCd powered calculator, no alkaline recommended.

The charger is the 9130, says output 6 VAC, 175 mA. Tested with unloaded output measures 9 VAC, with a 20k ohm per volt VOM. Before I crack open the power supply case, is this "correct?" I don't like the sound of AC charging NiCds. Should be some kind of filtering in there that might need repair.

The SR-50 takes 3 NiCds, no circuitry in the very basic battery pack, will use new NiCds.  Maybe I should get a new charger.  The battery pack is required for operation of the calculator.

What is a good way to test the charger under load?


texts: Run Energia from SRAM / Memory (CC3200 Launchpad)

texts:
In the code composer Studio it is possible to "flash"/load your program straight into the LaunchPads SRAM memory and run it without touching the flash.

Is there a way to do the same in Energia?

PS: I am familiar with Arduino but not with CCS.


texts: constant voltage source & sink for charging & discharging batteries

texts:
I'm attempting to build a simple circuit that will apply a constant voltage to a Lithium-Ion battery. If the applied voltage is greater than the battery, it should source current at a constant voltage, if the applied voltage is less than the battery, it should sink current at a constant voltage.

The circuit I've tried so far is attached in the image(s) below. I like this circuit because it allows me to control the voltage applied just by dialing a pot. It works well for sourcing current (image 1), however, as soon as the applied voltage drops below that of the battery, it flattens out (image 2). That is to say, the circuit cannot sink current at constant voltage.

I would like to build a circuit that can do both, as indicated by the cartoon graph in image 3. I would like to get behavior indicated by the dashed curve.

Does anyone have any suggestions for this?

Thanks!


texts: LDO regulator stability with bypass capacitor

texts: I'm working on a dac which use a Te7022 as usb receiver, it will be powered by the mic5205 LDO so I search for  articles about stability with LDO and got this: http://www.ti.com/lit/an/snva167a/snva167a.pdf. It's quite easy to understand until section 7 "Additional Poles From Ceramic “Bypass” Capacitors". I think the author forgot to include the Esr of the bypass capacitor in the equation.A single          0.1uf X7R capacitor will     often have an   esr about 20mohm so 10 capacitors in parallel is effectively about 3mohm and it's also parallel with the tantalum so isn't Rout in the equation  3mohm instead of 0.43ohm?


texts:
I'm working on a project to determine the water clarity, using a MCU with a turbidity sensor. I have tested sensors such as: Cheap Dishwasher sensor, and while it works for changes in turbidity in dirty water, it isn't great with clean water.

For example, the water I am testing in the ocean could have enough clarity to see down 20ft. The value returned on the sensor is about the same as if the clarity is 50ft, or 60ft. It is able to easily determine the difference between 2ft and 10ft, when there is a huge difference in suspended particles.

I am using an Atmega ADC with a 10bit resolution. I know I would be better off with an external ADC, and making my own sensor with a photoresistor/transistor and IR emitter. My question is, is there anything I can do with the sensor design to force the curve to be affected more in the clean water side that the dirty? If not, is my best bet to just ensure I have a high resolution ADC with very little noise?

Thank you very much


texts: So I have 4 systems with mini itx power supplies and am looking to purchase power bricks from the manufacturer. What confuses me is the power bricks are 102 Watts while the PSU can do 160W with a max of 200W. This is probably obvious question but since the power brick can only do 102 watts that means the PSU can only provide 102W, and if this is the case why would the manufacturer bundle the two together?


texts: Hi-voltage required for 100% SoC in LA banks?

texts:
Talking large banks of expensive true-deep-cycle cells, not the stuff you see in mass retail channels. Maybe the 6v golf cart batts from Sam's, at the "value" low end.

I think end-of-life ratings are based on the battery losing 20% AH capacity, and 500 50% discharges would be optimistic in real life, even for top-shelf true marine grade AGM like Odyssey or Lifeline.

Premise: getting such Lead chemistry banks up to ** true 100% full *** SoC as often as possible, is necessary for them to last even close to their rated lifespans. This cannot practically be done from fossil fuel engine-based charging, except for commercial trucking or ships motoring along most of every day.

Particularly true for AGM, but FLA as well.

In regular usage, I've seen recommendations like "at least once a week" to "every 3-4 partial charge cycles".

Assume daily cycling use, SoC always kept > 50%, no solar nor shore power available for weeks at a time, and regular but short-session high voltage (2-3 hrs, 200A @ 14.4V+, assume that's optimal) bulk charging a few times a week from engine generation.

The goal is to minimize starting up the engine(s) for the sole purpose of charging the banks, and certainly not running them for many hours just for low-amp floating purposes.

My question is: How close would an alternative source ** at 13.6V input current ** get to that "100%" level, assuming huge AH capacity available and hooked up say for 12-hour sessions?

Would the answer "X" be significantly different for FLA vs AGM chemistry?

Say X = "98-99.5% SoC", would it still be necessary to regularly supplement these 13.6 floats with long sessions of higher-voltage floating?

If so, what sort of pattern would be the minimum to ensure longevity from this factor. For example assuming daily cycling from "X" down to 60% SoC, maybe 50% once a week, then daily bulk(CC) + absorption (CV) recharge for 2-3 hours at 14.4V from fossil fuel.

Then, every day additional 8 hours of float at 13.6V, all with no loads.

How often, if at all, would I need to do additional many-hours floating at the higher voltage?

If this extra step will only get me from say 400 cycle lifetime to 420, it's likely not cost-effective to buy an expensive DC-DC charger to boost the long-float voltage up to 14.4V.

But if it's a difference of 100 cycles, it would be worth it.


texts:
Is there any VHDL 93 or 2002 code that is incompatible with VHDL 2008?

In other words, if I have a bunch of files made for older vhdl standards, will a 2008 simulation/compilation work just fine?

Phrased differently, is there ANY reason NOT to use the a simulator/compiler in vhdl 2008 mode?


texts: Differential equation from a Wheatstone bridge with Inductor

texts:
I've been given the following circuit and been asked to give the differential equation showing the relationship between \$u_e(t)\$ and \$u_a(t)\$

The differential equation should be in the form
$$\scriptstyle u_{a}^{\prime}(t) + k_1\cdot u_{a}(t)= k_2\cdot u_{e}(t) + k_3\cdot u_{e}^{\prime}(t) + k_4\cdot u_{e}^{\prime\prime}(t)$$

Some of the coefficients can be zero.

I can see that I'm going to have to integrate the inductor term in order to get an expression for the current, but I'm getting really confused about where I need to start and how to proceed.

I tried applying Kirschoff's laws as far as I could but I don't see how to fit them into each other to get a meaningful result.


texts:
I am trying to measure the current draw of a digital hobby servo (futaba 3050) to estimate its applied torque.

To implement this I am using a shunt resistor setup with an IC that will send a proportional current through its output (P3) which will then be drawn through a  resistor (R2) giving a output voltage that will be measurable by the MCU.

(The setup is shown in the schematic below, using a 0.2ohm shunt resistor and the IC ZXCT1009FTA by 'Diodes Incorporated')

simulate this circuit – Schematic created using CircuitLab

After having implemented this on a PCB I have been testing the circuit and I have a few questions regarding my results.

When first testing the circuit I used a simple power resistor to draw a fixed current through the wire called "Servo Supply" in the schematic. And while varying the current from my lab bench power supply through the power resistor the voltage on "ADC measurement" changed proportionally to the current as expected.

After passing this simple first test I then moved on to the real test, actually running a servo as load. But unfortunately I ran into trouble. I probed the voltage at "ADC measurement" pin. And the result from running the Servo (keeping it at a fixed position but applying small torque) can be seen in the first image.

When then applying more torque the measured voltage is kept at the same level but kept high for a longer time. Actually making the current measurement behave like a PWM. Here is another image with more torque applied to the servo.

After searching for more information about doing current measurements on servos I read about this behaviour which I assume is originating from that the servo is controlled with a PWM signal?

So to summarize into the actual question:
How will I go about to measure the current (torque) of the servo in a good way? I read about measuring the average current draw for example by adding a capacitor (at the ADC pin I assume), but I feel unsure about how I would choose said capacitor?

Or could I just do ADC measurements and take the average over a full PWM period?

Thankful for any input/help. If there's any additional info needed I am happy to extend the question.

Best regards, Mattias


texts: What kind of connector can be used for 1.5 mm jack

texts:
I recently bought this product. The jack is of 1.5 mm in this. I have tried to use all kinds of wires inside this jack but none of them fit properly. The standard male to male wires are also too loose for it. Right now currently I have made some temporary solution to it by looping a single stand wire and then putting it inside the jack but it would be better for my project to use something that is standard are more reliable like a male to male wire.
So any suggestions on what kind of male connector I can use for this??


texts: Drive FET/transistor based on 2 different resistances

texts:
simulate this circuit – Schematic created using CircuitLab

Basically I have an issue where a security manufacturers power supply has built in eol resistors for monitoring a battery or mains fault.

The problem is that these resistors are the wrong value for an install and can't be changed, they're built in and won't be able to be modified as it will void warranty.

The circuit is quite simple. There is 2 4K7 resistors in series connected to 0v, these are then connected to an input pin with a pullup resistor to 5V. There is a transistor in parallel with one resistor that essentially shorts it out if no faults.

So on an input there is a path to 0v with either 4K7 or 9K4 resistance.

Now how do I go about having these 2 states drive a FET or transistor ?

Sorry for the stupid question however while I understand some basics on how they work I have never designed anything like this.

Is it as simple as a resistor voltage divider say with a FET where 1 resistance value is within gate threshold voltage and the other not or would I need something like a comparator or a zener clamp ?

Edit:

Have added a schematic, what is is in the box on the left is built into the supply and cannot be altered. The terminal essentially then connects straight to an input but the problem is that the resistance isn't correct for this security panel.

Based on what MikeP has said on the right is what I believe may vaguely work given a gate threshold of 2V.

Unfortunately do not have the 5VDC rail available to play with either. Only the 13.7VDC rail from the supply itself, I may have to play around with this as essentially it is monitoring itself and if running down on battery that voltage rail will sag so my external circuit may switch off before the power supplies monitoring determines batteries are too low.

Next questions would be does that FET require any sort of protection or pull-up/downs and also is there any way to easily invert it so it turns on or off the same as the built in transistor rather than opposite ?

Depletion mode seems hard to find...

Thanks so far.


texts: What is the function of the diode in the image?

texts: I am buildind a circuit like this, but I am confused about D1, is it necessary?


texts:
I need to wire this switch, but I have no idea how. I thought I was buying a normal 3P rocker switch :)
The power source is 12v battery and the load is LED flashlight.


texts: Limit of internet speed over air medium calculation?

texts:
What is the maximum internet possible limit via air medium.How do we calucate maximum speed limit of data transfer via air .

Is there any formula for this ?


texts: View High Voltage AC Signal on Oscilloscope

texts:
I would like to capture a high voltage AC signal on an oscilloscope.

Input signal: 160V @ 400Hz

Output signal: ~40V @ 400Hz

Oscilloscope: TDS3014C

I intend to use a voltage divider: 100k ohm (1/2 watt) resistor and 27k ohm (unknown power rating).

My calculations:

I = V/R = 160V / (127k ohm) = 1.26 mA

Vout = Vin * R2 / (R1 + R2) = 160V * 27k ohm / (100 k ohm + 27 k ohm) = 34.0 V

P_r1 = I^2 * R1 = (1.26 mA)^2 * 100k ohm = 159 mW
P_r2 = I^2 * R2 = (1.26 mA)^2 *  27k ohm =  43 mW

Is using this voltage divider a good method to view the 160V (400Hz) signal?

If not, what do you recommend?


texts: Driving a tiny speaker via pwm, amplified with a BJT - in reverse?

texts:
I'm playing around with a micro and a small buzzer (passive). I built up an simple emitter-follower buffer to reduce the load on my uC, but I accidentally installed the transistor backwards on the board. It worked great, although when I noticed my mistake and flipped it around (with the emitter side tied to gnd, and the load coming off the collector), the sound was greatly reduced, about the same as driving the buzzer directly from the gpio.
I'm trying to understand what's happening. The volume is much MUCH louder with the transistor 'flipped' (as in the diagram). Current from collector -> GND is 50mA, and I get the same reading from the speaker - > the emitter. I(b) is too small for me to read with my meter.
What did I just build?

simulate this circuit – Schematic created using CircuitLab

Update:
After looking at the datasheet from the buzzer, and wiring it up as below, the volume output from the speaker is equally loud in either transistor orientation. Oddly enough, if I remove the flyback diode, then I lose a lot of volume in 'normal' orientation, but not in reverse.
I'll also note that I tried a few other tiny speakers, and didn't observe this behaviour. So, something about the particulars of the buzzers I was using.

simulate this circuit


texts:
I'm building a 150 Hz sine wave circuit using op amp 741, capacitors and resistors. The amplitude of the output would be a bit less than 5 Vrms. Now I want to connect the circuit output to electro optic[EO] crystal so it would operate, the crystal (works as a phase shift and also as an isolator so current can be neglible) works at 600 Vrms.

I'm looking for a small transformer that can work @150 Hz and step up 5 Vrms to 600 Vrms,

Is that a feasible requirement? How can i implement it? I look all over for transformers that will do the job but no luck.


texts: I have a micro-controller which calculates and decides about the current each minute. Then for one minute the circuit must hold that current constant. Then it should control the current via a buck circuit including MOSFET and a hall-effect current sensor. How to do it with AVR? it seems I need a control design(control theory). If there is an IC doing that automatically, it is very appreciated (I mean that I give it the required current in analogue or digital and it generates appropriate PWM).


texts: Which of the two connections is best for reducing losses?

texts:
I have a choice between the following two set-ups for a project. Option One is to have the motor controller mounted close to the batteries but further away from the motor. Option Two is to have the motor controller mounted closer to the motor but further away from the batteries.

I am wanting to know if there is any specific advantage in connecting everything in either Option One or Option Two in regards to cable losses? (Is it better to have the controller closer to the motor or is it better to have the controller closer to the batteries?).

I understand that there will be several factors which will affect the losses within the cables in either option such as cable length, cable gauge, temperature etc.

simulate this circuit – Schematic created using CircuitLab


texts:
I have made low pass filter both on Breadboard and in Proteus.Both of them have different problems.
I have kept voltage gain at "3".
In breadboard,voice output in the earphone is lower than input.In input I have a microphone When I blow air by mouth, It give me rough voice hearing by earphone.
In case of simulation in Proteus,When I applied above 333 Hz freq, output in speaker is still beep.
I cant understanding what is this happening..
Please help me...I am beginner.


texts: Is it really a bad idea to leave an MCU input pin floating?

texts: I've heard that leaving a pin floating on an MCU when configured as an input (vs. the default output) is bad for the pin, and can eventually cause it to fail prematurely. Is this true? N.B. in my instance the pin is floating somewhere between 0.3V and 1.3V due to an incoming video signal. This sometimes falls in the no man's zone of 0.8V - 2.0V when operating from 3.3V.


texts: Why this LVDS transceiver doesn't specify the differential input polarity?

texts:
I've been looking to implement a LVDS transceiver in my project where i can hook up to Displayport AUX differential pair.
I've discovered a suitable part, SN65MLVD200A in the following design guideline document (although many alternatives in the TI SN65 series can and might be better to use)
https://www.intel.com/content/dam/www/programmable/us/en/pdfs/literature/an/an_745.pdf
https://www.ti.com/lit/ds/symlink/sn65mlvd204a.pdf
My question is why there is no polarity specified in the differential inputs marked A and B in the datasheet.
Considering that polarity doesn't matter because of the symmetrical internal logic of the transceiver, wouldn't this mean that the outputs marked D and R in the datasheet will swap when the differential input polarity is swapped?
Kind regards


texts:
I would like to ask how reliable are these relay modules. Is it possible to use them in industrial application that will run non-stop for months? If not, what alternatives can I use?
mechanical relay
solid state relay


texts: Charging circuit for bulk 1.2v 1200mah ni-cad batteries

texts:
I am seeking advice about how to construct a charging circuit for 1.2v 1200mah ni-cad batteries. I have around 60-70 of these batteries and I want to create a bulk charging circuit so I can charge 5 or more (preferably 10 or so) at once while still being able to charge only 1 at a time if that is all that needs to be charged.

I found this schematic:

and a descriptive post here: http://www.electro-tech-online.com/threads/help-me-build-a-simple-nicad-charger.90780/#post-714659

about the math behind the charging for the original posters circumstances, but I am wondering if I can simply parallel the load to multiple batteries to charge many at once. I am sure the LM317 can handle 10 batteries at 120ma charge rate.

Overall question: Is it possible to use that schematic and parallel the load to multiple batteries? Also is this math correct as per the following details:

Battery         -> 1.2v 1200mah
Charge rate     -> 0.1C*1200mah = 120ma
Charge time     -> (1.4 * 1200mah) / 120ma = 14 hours
R1              -> 1.25v / 0.120ma = 10.416Ω
DC supply input -> (1.2v * 1cell) + 2v = 3.2v or higher

How many watts should R1 be in this situation? Is it also safe to increase the charge rate from 0.1C to 0.2C or 0.3C? I don't have any way to monitor the batteries temperature. These batteries were manufactured in 2011 so they are pretty new (if it makes a difference).


texts: How can I model this common mode choke in circuit in LTspice?

texts:
How can the common mode choke in below diagram used in LTspice? By an inductor or transformer? How should be the circuit drawn in LTspice?

I want to use this to filter out CM noises for single ended coaxial cable.


texts: What is happening with voltage on capacitor?

texts:
Capacitor is fully charged and switch is closed. What is the value of voltage on capacitor (\$U_c\$)?

Example

\$U_c=0\textrm{ V}\$. I understand this on this way: capacitor is fully charged, and there is no current. So \$U=R\cdot I\$ is giving us always \$0\$ because \$I=0\$.

Voltage on \$R1\$ is \$ U1=R1\cdot I\$.

Example

\$U_c=R1\cdot I1\$.

Voltage on \$R1\$ is \$U1=R1\cdot I1\$.

I am confused now. Why now voltage on capacitor is not 0 either, if capacitor is fully charged(and current is 0).

What is the difference between these two circuits?
Can someone explain me this a simple as possible?


texts: Allowed error in baud rate between pic and Bluetooth module

texts:
I'm trying to connect a dsPIC33FJ128MC804 - 16 bit pic - with a Bluetooth module
the problem is i have few baud rates of Bluetooth to choose between them , searched the net but could not find the allowed baud rate error due to baud rate generator register takes only integer values as you know , so what is the maximum allowed error ?
Edit: i read the related section of data sheet and family reference to UART but i do not think i found any information regarding this point.


texts:
I am trying to refurbish an electronic personal locator beacon (for rescue callouts for stranded hikers/sailors/pilots).

To do so to spec most devices require a GPS signal test (activation). There is a BNC output to couple directly to a receiver for analysis that emergency is being squawked.

But to avoid a false emergency, the device must be shielded.

Is there a standard construction or recommended material for shielding 406.1MHz transmitter? Would a metal box with BNC feed through be sufficient?


texts:
I am facing issue using SPI with a PIC18LF27K42 in order to drive a micro SDcard.

I am not very confortable with these "new" PIC18LF27K42 and i am trying to fix this issue since several weeks without success.

Currently i can drive the micro SDcard with a PIC18LF14K50 and all functions are working fine.

And the problem is that when i am trying to initialize the SD card by sending the command GO_IDLE_STATE (CMD0) i should have a R1= 0x01 response. But get always 0x00 as response. So i cannot go further in the SD card initialization.

With the PIC18LF27K42 i am suspecting the following potential issues

PIC initialisation
SPI functions

Thank you for your help and guidance.

Compiler : XC8 v1.45
IDE      : MPLABX v5.15
external 4MHz quartz

I am using the following pin

RA5 (pin 7)  : SPI_CS   : the Slave Select pin is controled by the software

RC2 (pin 13) : SPI_SDO

RC3 (pin 14) : SPI_SCK

RC4 (pin 15) : SPI_SDI

PIC initialisation

/* Initializing PORTA */
PORTA   = 0;
LATA    = 0;
ANSELA  = 0;
TRISA   = 0b11010000;

/* Initializing PORTB */
PORTB   = 0;
LATB    = 0;
ANSELB  = 0
TRISB   = 0b11111111;

/* Initializing PORTC */
PORTC   = 0;
LATC    = 0;
ANSELC  = 0;
TRISC   = 0b00010011;

/* map peripherals */
PPSLOCK = 0x55;
PPSLOCK = 0xAA;
PPSLOCKbits.PPSLOCKED = 0x00;

/* Peripheral Input Selection */
SPI1SDIPPS  = 0x04;

/* Peripheral Output Selection */
RC2PPS = 0b011111;    /* OUTPUT : SPI_SDO  */
RC3PPS = 0b011110;    /* OUTPUT : SPI_SCK  */

PPSLOCK = 0x55;
PPSLOCK = 0xAA;
PPSLOCKbits.PPSLOCKED = 0x01; // lock PPS

SPI initialisation and functions

void SPI_Init (void){
    SPI1CON0bits.EN = 0;   // disable SPI for reset and reconfiguration

    SPI1CLK     = 0x00;    // select the clock Frequency (4MHz)
    SPI1BAUD    = 0x07;    // set the SCK freq. to 250KHz with a 4MHz clock
    SPI1TWIDTH  = 0x00;    // set 8 bits width data transfert

    SPI1CON0 = 0x03;       // SPI as Master, MSB first, BMODE = 1

    SPI1CON1 = 0x00;    // SPI1 Polarity and Sampling control
    SPI1CON2 = 0x03;    // TXR = 1, RXR = 1, Slave Select disabled
    SPI1INTE = 0x00;    // disable all interrupt
    SPI1INTF = 0x00;    // clear all flags
    __delay_ms(200);
    return;
}

unsigned char SPI_Read (void){
    SPI1STATUSbits.CLRBF = 1;   // clearing the RXFIFO and TXFIFO buffers, related to
                                // SPI1RXB and SPI1TXB registers respectively
    SPI1TCNTH = 0;
    SPI1TCNTL = 1;         // One byte transfert counter
    SPI1CON0bits.EN = 1;   // enable SPI1 peripheral
    SPI1TXB = 0xFF;        // write the data into the output buffer
    while (SPI1CON2bits.BUSY); // wait until Reception is completed
   SPI1CON0bits.EN = 0;    // disable SPI1 peripheral

   return (SPI1RXB);       // return with byte read
}

void SPI_Write (unsigned char data_out){
    SPI1STATUSbits.CLRBF = 1;   // clearing the RXFIFO and TXFIFO buffers, related to
                                // SPI1RXB and SPI1TXB registers respectively
    SPI1TCNTH = 0;
    SPI1TCNTL = 1;
    SPI1CON0bits.EN = 1;   // enable SPI1 peripheral
    SPI1TXB = data_out;    // write the data into the output buffer
    while (SPI1CON2bits.BUSY);   // wait until Transmition is complete
    SPI1CON0bits.EN = 0;   // disable SPI1 peripheral

    return;
}


texts:
I have a refrigerator that stopped working. A few years ago the board was burnt near a relay contact therefore I looked at the board as the primary culprit. I am trying to test the relays to determine if these are broken but have no experience with this and the information I got was not very helpful. For the relay 832A-1C-S I tested the resistance (the two bottom pins) and I got 153.8 ohms. Does this mean (according to specs; link below) that this relay is not working? For the 812H-1A-S I am not sure if there is anything I can test with a multimeter. Any help will be appreciated.

The datasheets for these relays are:
https://www.mouser.com/datasheet/2/378/832a-257239.pdf
http://www.songchuan.com/db/pictures/AdminModules/PDT/PDT090410001/201191914401494858.pdf


texts:
I recently got a eye diagram from one of the supplier which looks not quite the same as the other one I used to see.

so from this I think this is a pass as it has plenty of margin from the Mask, but my question is about the amplitude of the eye, the way it exceed the top and bottom limit in an unusual way.

I was thinking about it has something to do with a booster, but any HDMI guru here have see eye diagram similar to this before can point me if it has something to do with the circuit of the HDMI connector?

Thanks


texts: Identifying components in an electric fencer output board

texts:
I'm just looking at an electric fencer output board at the moment, it's not plugged into the fencer, I'm just testing the components are it has a fault. I'm having trouble with these here though, they read ol for resistance, no capacitance, nothing in diode mode, so scratching my head on what on earth they are, as they have no kind of marking either. They just have a white end, and straw coloured other end, but seem to have no electrical properties according to my multimeter, so not sure if they are just damaged or what.

Edit
Here is the circuit


texts:
I am reading some books trying to understand how physically they rotate in the same direction as the positive sequence components but in the reverse sequence. How can that even be. If a machine rotor under normal load conditions is rotating CCW with ABC sequence. How can the machine continue to rotate in CCW direction but with ACB sequence.
The book:

My confusion is from the below page. How the phase sequence is reversed? As I understood from page#58 above as highlighted in red "The connections from a, b, c to a, c, b or vice versa can generally be made by completely interchanging phases b and c for both the equipment and the connections." Does this mean that they interchange the phases! it cannot be this. So, how phase sequence is reversed?

Protective Relaying: Principles and Applications, Fourth Edition
By J. Lewis Blackburn
2014 by Taylor & Francis Group, LLC
International Standard Book Number-13: 978-1-4398-8812-4 (eBook - PDF)


texts:
I'm trying to come up with the state-space equations for this circuit, but I think I'm making a mistake when writing KVL through a loop with a current source.

simulate this circuit – Schematic created using CircuitLab

Is it valid to write for the top loop:

V_L + V_C = 0

where V_L is the voltage across the inductor and V_C is the voltage across the capacitor.

Only writing KVL for the bottom loop doesn't give me enough equations to solve for the state space variables (VL, VC, and V2C)


texts: How does forward biasing of both junctions in BJT leads to saturation?

texts:
As far as I know, for an NPN-BJT, when both (base-emitter and base-collector) are forward biased; we consider the operation to be in saturation mode. Here, the transistor functions as a short circuit between emitter and collector.
[SEE IMAGE BELOW]

However, I expect quite different.

With the electric field directions as shown above;
I expect that a large number of electrons present in the emitter would now easily cross the emitter-base junction due to a reduced depletion region and supporting electric field.
Similar should be the case for the collector-base junction. (Electrons from collector would now be arriving at base)
So now, we have electrons coming in from emitter to base, and collector to base junction.
We therefore expect the direction of currents to be base to collector, and base to emitter.
Overall, we have a large current passing to the base, which is supplying current to emitter and collector.
Now, this is nowhere similar to a short circuit situation.
Where have I gone wrong?
Also, please explain the actual physical mechanism of the functioning of this BJT in saturation mode.


texts:
Short Version
Can I make a serial connection from an Arduino to a device with an FTDI connector?

Long Version
I have a wifi shield for an Arduino that is misbehaving. I know their is an FTDI connector on the shield that you can use to do diagnostics on the chip but I do not have an FTDI cable at the moment.

Is the FTDI connector just a serial interface or is it something different?

If it is serial would it not be possible for me to actually write an application for the Arduino that would issue commands over the FTDI connector for diagnostics purpose?


texts:
I'm designing a rather big PCB which will have 64 nokia 5110 LCDs arranged in an 8x8 matrix and will all be controlled by a single microcontroller.

Each screen will have an 8-bit shift register as a buffer, to compensate for the mismatch between the microcontrollers ~50MHz max SPI clock and the LCDs 4MHz. Therefore, there will be 64 shift registers in series at 50MHz on an approximately 30cm x 30cm PCB.

My question is then, what are the problems I should account for in such a design? Assuming I place each screens shift register behind it, I would have really long (approximately 250cm) zig-zagging traces for the clock and data lines.

This seems pretty ridiculous, but at the same time I've had no problem working with breadboard and jumper wires at close to those frequencies, the only difference being the wire length.

I could also clump all the shift registers near the microcontroller so the longest lines will be the ones leading into the screens at the lower frequency, but the traces would still be pretty long.

I'd appreciate any help and suggestions to avoid having many failed PCB designs.


texts: In this amplifier circuit we are using a voltage divider bias. Why can we consider that voltage produced by R2 is actually providing voltage to the base. What is R1 doing?


texts: Derivation of time constant for single source, single capacitor RC circuit

texts:
Take a circuit comprised of resistors, a single capacitor, and a single step response voltage source. Then:

Every single voltage and current in the circuit, except at the voltage source, will have a *e^(-t/tau) dependency.
Where tau, the time constant, is the capacitance times equivalent resistance seen by the capacitor.

Why are 1 and 2 true? I understand why it is true for a resistor connected in series with a capacitor but not why this can be generalized, especially since not every RC circuit can be simplified into a resistor in series with a capacitor.


texts: I have a solar panel with below specifications. I have some questions

texts:
As in picture Vmp = 17.40V and Imp = 0.58A implies Power =
17.40*0.58 ≈ 10W.

Does it provide 0.833A (10/12) at 12 volts?

What does "Max. System Voltage 800VDC" mean in the picture ?


texts: Required velocity of each wheel in 3-wheel omni bot

texts:
I'm using a 3-wheeled omni bot which can move in any horizontal direction (example: https://www.robotshop.com/en/3wd-48mm-omni-wheel-mobile-robot.html).

Given an object velocity (velocity at which the entire bot should move) and an angle it should move in (degrees), how can I determine the required speed of each wheel?

I tried the following, but have experienced some strange results:

const int wheel1Deg = (90 - (90 - angle)) %  360;
const int wheel2Deg = (90 - (210 - angle)) % 360;
const int wheel3Deg = (90 - (330 - angle)) % 360;

Setpoint = cos ( wheel1Deg * PI / 180.0 );
.....etc


texts: Are the maximum battery voltage and the open circuit voltage (equivalent circuit ) of the battery the same?

texts:
If you model the battery equivalent circuit with Rint circuit, Are the maximum battery voltage and the open circuit voltage of the battery the same?
And can we interpret the range in which the terminal voltage decreases due to the resistance of the circuit when the current flows as the available voltage range of the battery?
Ex. battery info.
Max output voltage : 900 Vdc
Output voltage range : 650 - 900 Vdc


texts:
I have this electrical system: a switch connected to a 120V 60Hz 21W light bulb. I wanted to add two outlets one for a LED, another one for something else like a laptop or a fan.

I tried to plug in series like this:

But only the LED comes on.

I tried with a 15W bulb and now both are working. Why is that?


texts: Lets say we have a single plate that has a charge of +Q on it. A plate with charge -Q is infinite distance away. Will the plate with +Q have a capacitance associated with it? Why or why not? I was thinking that because the distance between the plates is infinity, the capacitance is zero, but according to my TA, that is not the case. There is always some sort of "absolute" capacitance for the plate with +Q (a capacitance will exist between the plate and air?). Can someone help me out in understanding this?


texts: what is the meaning of the pipe symbol "|" in front of a variable

texts:
I am analysing some verilog code and found something like

wire z = |a & b;

while simultation the code behaves just like

wire z = a & b;

so i was wondering what is the meaning of the | (pipe) symbol? Does it have any impact on the simulation/synthesis?


texts: May a warm reset by pulling down the reset pin of the SoC cause the file system corrupts?

texts:
In my embedded Linux system, I made a hardware switch to pull down the reset pin of the SoC(TI DM365). When the system is running, I can push the button to reboot the system. I want to know whether this behavior is safe to my file system or it will cause a corruption. I use Linux version 2.6.32 + jffs2 in my system. If yes,  can someone explain why the corruption happens? Very appreciated!

Is pulling down the reset pin as risky as cycling the power of the system which may causes the FS corrupts?


texts:
in this PSU schematic, you can see on the right, close to the two schottkey diodes, a coupled inductor L15, marked as SQR1257.

You can also read the note close to it: "2_1: 25uH / 4_3: 21uH"

the only datasheet that I could find is this: http://inductor.com/media/catalog_pdf/product/sqr1242-sqr1257-sqr1277.pdf

The marking on the actual inductor is 275 (I only got a picture of it, so I cannot measure it).
Link to the pic: http://cdm.link/app/uploads/2014/03/ms20kit1.jpg

But I can't find on the datasheet this marking, and 21uH or 25uH is not an option either.

So what do you think this inductor is?

also, as bonus question, what's the purpose of the MOSFET on this circuit? to me looks like it acts as switch to switch off the PSU (from the KILL signal by the CPU or by the mechanical switch), am I right?

UPDATE:

I found those infos about that inductor, and it is a custom wound one.
I could not find on Mouser a coupled inductor with 25uH + 21uH, do you think I could just use one with 22uH on both coils?
for example this: https://www.vishay.com/inductors/list/product-34359/


texts:
Assuming no load, how does continuously changing the distance between the plates of a capacitor (in a sinusoidal fashion for simplicity) affect the output voltage? Does electromagnetic induction come into play in this scenario?
I understand there will be an immediate change in the output voltage since $$ V = Q/C = \frac{Q}{\varepsilon}\frac{d}{A} $$ and clearly the permittivity constant will change sinusoidally itself.
But what about the fact that there is a time-changing electric field? We must have a perpendicular time-changing magnetic field as a result. Does this magnetic field affect the voltage across the plates?
If not, I believe that would mean the energy spent in changing the distance would be dissipated purely thermally.
(For clarity, this is not a question from an assignment or such.)


texts:
I've recently bought some cheap TowerPro SG-50 rc servos from ebay. They seem to work quite well, and despite their small size they are quite strong.

But how "strong" are they actually. The datasheet specifies:

  Stall Torque: 0.8 kg / cm

What does that mean. I guess that stall torque is the amount of torque that needs to be applied  in the reverse direction of the rotation, before the servo stalls. But what does the unit kg / cm mean?


texts:
I have connected 6v to the power jack of my arduino, and when I tested the output voltage from the Vin, it turns to be 5.3v with no connection and 4.8 with some connections to the I/O pins.

IS that normal?
Because I was trying to supply a 6v motor through H-bridge, but the voltage at the motor decreased down to 3v!

Is it possibly because of a protection diode in both the arduino and the H-bridge?
Is it possible that these diodes can pull down the voltage from 6v to around 3.1 v ?


texts: Raspberry Pi vs Arduino ADK (with phone tethering)

texts:
I was doing some research for my capstone project next year. Basically it is an autonomous rover, designed to scout out outdoor areas and send back video/pictures to a website.

So far, our initial design for control system involved Arduino ADK connected to an Android phone. The phone is intended to be the brain and we can use all the sensors that comes with it, while the arduino will be used to control the motors and for realtime feedbacks.
We are using a phone for this because individual components like gps, cellular module, etc. for arduino will end up costing us a lot more. For communication, we are going to use cellular network of the phone due to it's long range.

Our professor liked the idea, but he suggested that we should look in to using a raspberry pi instead of Arduino, so that we could use some programs and hardware (analysis/data logging) meant for linux, giving the project a more practical purpose in the future. Essentially making the RPi the brain, and just use the sensors on the phone to supply data.

I'm not that experienced with Rpi, so not sure how things will turn out. So I have a few questions:
-Can an android phone be tethered with the Rpi, and simply use it as a 3g modem, and use the data from the onboard sensors?
-While RPi is not meant for realtime functions, what kind of lag should be expected from this? if it is less than 100ms, i figure it should be fine.
-While the GPIO on the RPi is limited in number, can it be used to run a motor controller? It can also be paired up with a simple arduino uno which in turn can have have the motor controller, but will it be a waste of resources?

I am still doing my research and will have plenty of questions in the future. For now these noobish questions will be enough to start with.


texts: How does the frequency information of RF signal is carried over optic converted output?

texts:
I have an RF input signal in the frequency range of  1000MHz to 2000MHz with the power level of 0dBm+/-1dBm throughout the band, this signal needs to be converted to optic signal using RF to optic converter.

I have studied that, based on the input RF signal the RF to optic converter laser diode bias current will be adjusted and accordingly the optical signal intensity will be varied.

Now the question here is how does the frequency information will converted into optical form, Means how the frequency information will be modulated and taken through the converted optical signal?


texts:
A step-up transformer turns a lower alternating voltage to a higher one, while stepping down the current. This is due to the conservation of energy (energy to into the first coil must equal to the power coming out of the second coil).

I'm using a 12v DC to 240v AC inverter to power my soldering iron from a 12 volt DC battery. From what I've understood, soldering irons work by letting the high voltage current pass through the metal tip of the iron. This current then heats the metal to the high temperature required. Somewhere inside the inverter, a transformer is used to step up the voltage.

But if the power provided by the 12 volt DC battery (which goes into the first coil of a transformer) is the same as the power provided by the 240 volt inverter output (coming out of the secondary coil), why do I need the inverter at all? Essentially I'm turning electrical energy into heat, so if I were to connect the DC voltage supply directly into the iron wouldn't the iron heat the same way since the amount of power is being turned into heat?

The same question applied also for incandescent light bulbs: Since they work by heating a filament (which then emits light), should't they also work with lower voltage supplies as long as the provided current is higher? Then the power would again the the same.


texts:
After always being interested in learning more about electronics, I figured LED-strips would be a great start.

I'd like to power a 4 meter WS2812B-LED-strip (60 LEDs/m). These run on 5V and draw about 60mA per LED. That's 14.5A, or 75W. However, I've yet to find any power supplies for these figures, only imported industrial ones - which feels a bit scary with my limited knowledge.

I've understand that powering it through the Arduino is a bad idea, but what's the simplest and cheapest solution for powering it? I do have a bunch of old supplies for laptops and whatnot lying around.


texts:
My PWM control is having issue,I don't know why...

So I'll briefly describe my PWM specs;

a 4-bit Input named value,

Input clock 50MHz,

a single bit output PWM_out,

Duty cycle is equal to 1/16 of input clock and

it changes when the value input is changed.

like, Value = 0000, Duty Cycle=0%

Value = 0001,Duty Cycle=6.25%

Value = 0010,Duty Cycle=12.5%

Value = 0010,Duty Cycle=18.75%

.... etc

when value changed,duty cycle should be increased by 6.25%

Here is my code and output doesn't seem correct;

module pwm_c(clk,value,PWM_out,counter);
input clk;
input [3:0] value;
output PWM_out;
reg PWM_out;

output reg [3:0]counter;

//parameter rst=1;

always@(posedge clk)
    begin
        if(!rst)
            counter <= 4'd0;
        else
            counter <= counter + 4'd1;
    end

always@(counter or value)
    begin
        if(value == 4'd0)
            PWM_out = 1'b0;
        else if(value == 4'd1)
            PWM_out = (counter >=4'd1) ? 1'b0:1'b1;
        else if(value == 4'd2)
            PWM_out = (counter >=4'd2) ? 1'b0:1'b1;
        else if(value == 4'd3)
            PWM_out = (counter >= 4'd3) ? 1'b0:1'b1;
        else if(value == 4'd4)
            PWM_out = (counter >= 4'd4) ? 1'b0:1'b1;

        else if(value == 4'd5)
            PWM_out = (counter >= 4'd5) ? 1'b0:1'b1;
        else if(value == 4'd6)
            PWM_out = (counter >= 4'd6) ? 1'b0:1'b1;
        else if(value == 4'd7)
            PWM_out = (counter >= 4'd7) ? 1'b0:1'b1;
        else if(value == 4'd8)
            PWM_out = (counter >= 4'd8) ? 1'b0:1'b1;

        else if(value == 4'd9)
            PWM_out = (counter >= 4'd9) ? 1'b0:1'b1;
        else if(value == 4'd10)
            PWM_out = (counter >= 4'd10) ? 1'b0:1'b1;
        else if(value == 4'd11)
            PWM_out = (counter >= 4'd11) ? 1'b0:1'b1;
        else if(value == 4'd12)
            PWM_out = (counter >= 4'd12) ? 1'b0:1'b1;

        else if(value == 4'd13)
            PWM_out = (counter >= 4'd13) ? 1'b0:1'b1;
        else if(value == 4'd14)
            PWM_out = (counter >= 4'd14) ? 1'b0:1'b1;
        else if(value == 4'd15)
            PWM_out = (counter >= 4'd15) ? 1'b0:1'b1;

        else
            PWM_out = 1'b0;
    end

endmodule

Although I've asked a friend who knew a little more about Verilog than me,
He said,
I have to divide the input value by 16,per value is equal to 16 clocks of input clock.
I don't quite understand how to implement this...
I don't understand how to divide value input,'cause in my thoughts that's 4 manual switches or wires..
How do you divide something that's controlled manually?

Please anyone help me...Thanks...

edit;
adding all and each suggestions,still not the result I expect.the third picture is by far I tried to get as close as I wanted,but if you look at the value,It still doesn't divided by 16 and PWM_out starts to have output from value=3 not value=1...

edit2;
So I asked my friend once more,and it suggested that value has to 16 times of clk,which means I have to make value changes after full 16 pulses of clk,but I just haven't have the faintest idea to implement this.

maybe I wasn't cleared enough...down below is what I transit in my brain of above's suggestion..

value has to be full 16 cycles of clk before change,and then PWM_out to output...like,value=0,PWM_out=0 and value changes after 16 pulses of clk, value=1,PWM_out=1,value changes after 16 pulses of clk...so on and so on... each time it change the PWM_out is wider and wider like, value =0,PWM_out=0, changes after 16 pulses of clk,value=1,PWM_out=1(equal to almost one pulse of clk) , value=2,PWM_out=2(equal to one pulse of clk)...so on.

the PWM_out should be close to the third picture,but should be from tighter to wider and the value has to match the full 16 cycles of clk.

edit3:
Okay,so I think maybe I take the third picture's wave result to draw out what I described in edit2...maybe the drawn picture would much better to help to think...drawn picture in Fifth Picture.


texts: A friend who is an electrical engineer (heavy current) told me to earth my satellite dish and its fixing pole against lightning, using a thick copper cable (6 sq.mm) and an earth spike.   He also said the earth cable must have gentle bends and no sharp bends where it fits around rooftop/wall edges etc.   Does this have to do with increasing the impedance of the cable thereby reducing its effectiveness?


texts: Use of Potato semiconduter iC in data acquisition systems

texts:
I recently came across this interesting technology: http://www.potatosemi.com/

It seems that have managed to reduce the high-frequency noise using their technology. I don't know much about noise reduction or high-frequency operation but I am curious
1)Can we use these chips for data acquisition from strain gauge sensors to achieve low noise?
2)If no What are other brief uses of such technology?

Sorry, I know that it is a very broad Question but it looks very interesting tho and I am unable to understand.
Thank You


texts: RGB to YPbPr (YCbCr) conversion and bright picture issues

texts:
I'm working on a specific RGB to YPbPr (component) converter. It is supposed to connect old consoles to a modern flat 240p supportive TV. However I have an issue with luma Y output part. Here is the schematic of the current version I created:

YPbPr formula is R 0.299 + G 0.587 + B 0.114 and resistors R1-R3 are supposed to do this part

Sometimes the picture is too bright on the top, especially if the picture is black, the picture gets bright on the top and gets even brighter after time. I noticed when I put R6 75ohm resistor as pictured, the brightness decreases a little as it should, however if I lower the resistor value even more, the picture gets screwed up overall.

Right now I'm clueless on how to fix it. Does anyone have any ideas?? I can take a photo of the brightness issue if needed. Many thanks in advance

EDIT: here's the real photo of the effect (some reflection is shown but the main issue is still visible)


texts: Setting the HSE clock frequency of an STM32

texts:
I am programming an STM32 (manual here). Page 83 has a diagram indicating that the HSE Clock frequency is between 4 and 26 MHz.

The paragraph on HSE clocks starts on page 84, but does not give any information regarding setting the clock to a specific frequency. I have had a look at the RCC registers (starting from page 91) and could find how to turn on/off several clocks, and set various prescalers. I haven't found any register dealing with setting and reading the HSE clock frequency.

How can I read/write the HSE clock frequency?


texts: I know that breathing in solder fumes is not really good for you. I happen to have some respirators lying around. Could I use this instead of a fume extractor? It might save me some money if I could just use the respirator?


texts: Does anyone make a ZIF socket for Xbee?  It seems like a needed item, since you need to program each Xbee with X-CTU before installing it in it's final circuit.  But, I can't seem to find one.


texts: Fourier coefficient and resolution in simulators

texts:
I post below two fourier graphs of the same signal, simulated for two different transient durations:
The time domain function is a sine with 60Hz frequency.

Transient duration 40ms gives the following fourier graph:

Transient duration of 300ms gives the following Fourier graph:

I had expected the fundamental frequency used to calculate the coefficients to be 60Hz, the main frequency of the time domain function.
But the simulator uses the transient duration as a period to compute first the fundamental frequency and then calculates the Fourier coefficient.
Is that convenient event though the sine function is periodic?
In the simulator window, there is something called Resolution/Frequency; what is the link between this resolution and the formula used to calculate the coefficients of a Fourier series?
NB: the simulator is Simplis/Simetrix for power electronics.


texts: No electricity but have a Ford Econoline van with a 12v Auxiliary "Power Point" Outlet (and more)

texts:
I'm trying to figure out if I can get power to my desktop PC from a source other than electrical. I know nothing about electricity. I have the following:

12v Auxiliary "Power Point" Outlet in my van
APC Back-Up UPS XS Series, 1500 VA, 865 WATT

I actually forgot I had the UPS, so basically what I have are empty batteries: I would need to recharge the UPS in some alternative way that is not electric. Thanks.


texts:
I didn't know whether to place this question here or on stackoverflow, but I finally decided to post it here.

I want to build a simple system that would be able to work with basic peripherals (UART, keyboard, VGA monitor).
I would like to use MPU instead of MCU as a ´main unit´, so there would be more memory for processing data. This ´main´ chip would use a single SDRAM to store its data.

For the VGA output, I want to use an Atmel AVR chip, that would request data from another memory, which would contain screen data in 8-bit RGBS format.
Here is where I get to problems.

I don't need much of VGA memory (less than 512KB), therefore I want to use SRAM memory, which is also simple to access compared to SDRAM. The VGA resolution I chose uses 25 MHz pixel clock, which means that I have only ~40ns time to retrieve a single pixel from SRAM to DAC. That's good as most of the memories that match my search input (>=4Mbit memory, <40ns access time) can do this.

Back to the MPU memory, I would like to ask my first question: when is it necessary to send a refresh command to SDRAM? Do I have to do it, or is it possible to get a memory that would need any external magic to refresh it?

Now I get to the problem how to access that SRAM VGA memory from the main chip, as it is almost always accessed by my VGA controller (not mentioning that I need yet another chip for mapping this memory nicely to MPU´s address space). I thought of reserving some pins of the VGA controller for MPU´s requests for SRAM access, which would mean that some video frames would have to be skipped leaving this SRAM accessible to MPU without interruptions.

I'm stuck here. I could only think of these possible solutions:

I can use SDRAM on VGA chip instead of SRAM, but I will also need a better controller for the video output. This SDRAM will be compatibile with the one on MPU, and I will need to think about a special tactic for clock stealing, where I could access video memory from the video controller and main processing unit at once.
I can add another chip that will use time when video memory is not accessed (sync pulses, porches etc.) for copying blocks of data from the main memory to video memory.
I can use only one SDRAM memory, and request access to it from the MPU everytime VGA needs another pixel. That would slow down the whole system, but it would be simpler.

What do you think of this? What other ways (tricks, designs?) are here to have two units (main and video processing unit), from which one is being managed by another?

Thanks.


texts:
I'm looking for a sensor that can detect large magnetic fields.  Basically, I want a 1 when the field is greater than 75 Gauss, and a 0 when it's less than 75 Gauss.

I believed (EDIT: Wrongly!) Hall Effect sensors rely on moving through a magnetic field.  Unfortunately, my application does not permit me to move through the field, and the field is not changing.  It's since been pointed out that the Hall Effect does not rely on a change in the magnetic field.  However, I still do not have any control over the orientation of the field.

Does anyone have any suggestions on how to detect such a magnetic field?


texts: How thick a gold finish on a pcb for wire bonding?

texts:
As a partial reparation for my previous question today.
Please allow this rather esoteric/ but on topic question.
I was sending out a pcb that will have gold wire bonding pads.
It was a option at our board house.  I got a call when I was requesting a quote.

"How thick do you want the soft gold bonding layer?"
"I have no idea." I said, which is my normal response.
"What's your "standard" thickness.?", I asked.
I was shifted to engineering.
30-50 micro inches was the answer, after a nice discussion.
(It's always a pleasure to talk with the engineer's.)
So that's what I ordered.
I could order a thicker layer.
Has anyone done this?
I'll be wire bonding soon, so I can let you know if it works.

Edit:  Well I got the quote back and my jaw dropped.  The price is more than $2k for a few pcb's.  For that cost I could evaporate my own Ni and gold layers.

Edit 2: (Adding more to the question.)
So the reason for the high price is that the board house needed to send it outside for processing.  I asked for quotes on their other types of Gold finishes.

The first is called Deep Gold.  This is an electrolytic process and puts down 30 u inches of gold.  (I don't know if there is any underlying Nickel.)  This is also called hard gold and from limited reading I don't think it works for wire bonding.

The second is Immersion Gold.  or ENIG and puts down 3-10 u in (75-250 nm) of gold over a thicker nickel layer.  Again from limited reading it seems that one can not wire bond to this with gold.  But maybe with aluminum.  (Though there can problems with the Al/Au interface.)

And my final crazy idea is to make a mask for my pcb and evaporate my own Ni/Au layer.


texts: Darlingtons, MOSFETS, and bipolar junctions

texts:
I realize there are dozens upon dozens of kinds of transistors, each used for specific purposes. Sometimes there is great overlap; multiple kinds may work in a given circuit, but at times only a specific transistor is ideal.

Without reading all of the specifics of each kind, is there some kind of quick reference or guide that is useful when researching the type of transistor to use? For example, I'm familiar with some kinds of transistor, and often use them in my projects. Eventually someone will review the project and say "Why don't you use X instead of Y there?" It's at that point that I research X and learn something new.

If there was a "handy infographic of transistors" it might have helped me research all the types related to "X" so I'd have known to read up on them.

(For example, I was attempting to use a Zener diode in a circuit but wasn't aware that what I really wanted was a transient voltage suppressor. Something showing how Zeners and TVS's are related might have been useful.)

Searching the internet doesn't yield much other than a few transistor family trees and the like:

from Learning About Electronics

Does anyone know of (or wish to create!) a useful transistor selection guide that doesn't assume you are familiar with all the species of transistor?


texts: Wire peltier device and fan to power supply

texts:
I have 6 12v, 6 amp, 60 watt peltier devices and 3 12v, 0.08 amp fans that I want to connect to a 12v, 40 amp, 480 watt power supply. This guy over here:
https://www.banggood.com/AC-110V-220V-TO-DC-5V-12V-24V-2A10A15A20A40A60A-Switch-Power-Supply-Adapter-p-1191491.html?rmmds=cart_middle_products&cur_warehouse=CN

I'm an absolute newbie when it comes to electronics so I would first like to know whether that power supply is right for the job?

If it is right for the job, my next step is to wire the components to the power supply. This is where I'm having trouble moving forward. I assume I can't just jam all the wires into the 12v lines and turn it on, but I would rather need to find a way to split the output for the 6 peltiers and 3 fans and provide special connectors for them. What would this all entail? Are there products available for this or is this something I would need to build from scratch myself?

Thanks


texts:
So, I am to analyze this circuit.

So, this seems easy enough:
Node 3:
\$v_3=20 \space \mathrm{v}\$
Node 2:
\$\frac{1}{110}(v_1-v_2)+\frac{1}{100}v_1+2(\frac{1}{10})(v_3-v_2)=0\\\frac{28}{55}v_2-\frac{1}{110}v_1=6\$
Node 1:
\$\frac{1}{110}(v_1-v_2)+\frac{1}{100}v_1+2\frac{1}{10}(v_3-v_2)=-4\$

However, when I use, say, Cramer's rule (or wolframalpha) to solve for the equation, we get \$v_1=-67\$, which is unlikely. The other numbers don't look any better.  Would someone be so kind as to tell me what I am doing wrong here?


texts: Power source with buck converter, load and supercap

texts:
I have the following circuit created in MATLAB Simulink:

I have a power source (Vfc,Rfc) on the left. Its operating point is set by using a buck converter (mosfet,diode,L,C1), which controls the current of the source. At 33Amperes, the voltage of the power source is around 30V, which gives a power of 1000W. On the right side of the circuit I connected a load, and a supercapacitor. The load is specified through its active power consumption, which is set to 800W. The supercapacitor is set to an initial voltage of 20V. From what I understand, what should happen is that the load would draw the current it needs in order to consume its 800W, and the rest of the power (~200W) would be stored to the supercapacitor. However this doesn't happen; For some reason the supercap draws a significantly larger amount of current, and as a result, the load consumes a much smaller amount of power. Any ideas?

Edit: I tried to use a current source. Here is the model:

I used a time switch because the voltage was not initialized at start, and the divider gave an error. The concept of the current source is to force a current I = P(needed)/ V(t). I removed the supercapacitor (to simplify things) and added a simple resistor to consume the extra power provided by the main source. There is still a problem though. After switching to the measured voltage feedback, all the measurements in scope1 start oscillating, completely out of control (pick currents reach 10^5 A).


texts:
I'm creating this circuit (original circuit source here) and it requires a 7555 timer. A 7555 timer is like the next generation 555 since it is CMOS. Now there are no 7555s or CMOS 555 in my area and was wondering what will happen if I replace it with the NE555? Are there any consequences? Will it behave in the same manner? What would be the best thing to do?
Edit
Seems like in order to use NE555, adjustments must be made. What are they?


texts: How can I stablize an analog to digital reading?

texts:
I've built a clock out of a PIC16F877, some LEDs and other stuff...

To set the time in 5 minute intervals, I'm using a 22K ohm potentiometer connected between GND and +5V with the contact connected to analog input RA0 on my MCU.

It works, but it badly fluctuates between values. It's a 10bit ADC, and I'm looking at the most significant 8bits, and if I get my pot roughly in the center, I get an average reading of 128, but it flickers between 127, 128 and 129... even if I leave it alone and don't touch it.

How can I stablise the reading? I could probably write firmware to take an average reading, which may help a bit, but before I mess around with that wondered if there is something I could add (caps, resistors, etc) to my circuit to make it more stable? In this part of the circuit, I just have the pot connected to the MCU, nothing else.


texts: Jaycar short circuits Vol.1 bonus project 2: 3.5 minute timer

texts:
I have been trying to get this circuit working for sometime. Mechanically it works but when the potentiometer through which the capacitor charges is set to maximum the maximum timer period before the LED lights, or Buzzer goes off is roughly 12 seconds. As I don't have a smart phone to capture the schematic straight from the magazine I will show its reconstruction here. It is a fairly simple circuit so I can't understand what I must be doing wrong.

simulate this circuit – Schematic created using CircuitLab

The only difference in the schematic above and that from the magazine is that R1 is actually a POT which controls the timer interval before D3 goes off. I just substituted the maximum value of the POT (when rotated fully clockwise) so as to simulate it with its maximum timer interval.

The explanation the magazine gives for the circuit is such that when connected C1 charges up via current taken from R1, R2, D1, D2 and the base emitter junction of Q3. Because Q3 is providing current to the charging capacitor no current flows through Q2. When the capacitor is fully charged no further current can be drawn from the components connected to it and so Q3 swictches off turning on Q2 and hence the LED or buzzer. closing SW1 restarts this process. I have connected this circuit up on a spring board and it only runs for 12 seconds, not 3.5 minutes (with maximum POT value or R = 1MOhm).

If I had a smartphone I would photograph the spring board but I have constructed more complicated projects on the board than this and so can't see how my connections could be wrong. I have even gone through with a multimeter testing the components and noted that the capacitor did charge up causing Q3 to switch off and Q2 to switch on only this was much quicker than 3.5 minutes. Any tips or hints?

Thanks,

Simon.


texts:
I am designing a automatic sanitiser system with IR sensor. Below I have attached the circuit diagram.

But the reality is the DC Pump keeps on running and when IR detects anything the DC Pump stops. This is exactly the opposite way of behaviour. It would be helpful if I have did anything wrong, or how can I do the exact one.


texts:
Here is a technical drawing for a 3.5mm stereo audio plug, taken from a product datasheet (http://www.tensility.com/pdffiles/50-00396.pdf):

The right-hand end is a standard 3.5mm audio plug. The left-hand end also seems to be some sort of male plug. Into what is it designed to be plugged?


texts: Converting 8V AC to 8V DC - bridge rectifier gets very hot while idling

texts:
I am tinkering with an Arduino and recently had to convert 8V AC to 5V DC in order to run it.

The project is a custom doorbell, which gets the power from the doorbell transformer (transformer is located in the basement).

The doorbell transformer is a 220V AC to 8V AC transformer.

Since it is 8V AC, I needed to make it to 8V DC.
So I soldered a bridge rectifier and put a compensating capacitor to smooth the output (see supplying image).

This 8V DC output is an input of a DC-DC step-down module, which is based on a LM2596 power regulator. It delivers 5V DC and supplies the Arduino and a module, which is responsible for the bell sound. This module can drive up to 3W speaker.

The speaker connected to it is 2W 8 Ohm.

Unfortunately the bridge rectifier and e-cap are getting very hot even in the idle state (e.g. at night, no doorbell button pressed).

What am I missing in my circuit in order to get proper 8V DC for the step-down module and keep the bridge rectifier at the normal temperature?

29.07.2019 EDIT
Transformer is located in the basement and cannot heat up the bridge. It gets hot on it's own.

23.09.2019 EDIT
So I have found a probable root of that issue.
I have not checked, if there is any current on the doorbell button.
Both existing doorbell buttons are connected to the 8V AC line, causing lot of trouble when connected to the Ground and to a digital input on arduino (red arrow).

For the workaround see my answer below.


texts: Output resistance of emitter follower voltage regulator

texts: How to calculate an output resistance of such circuit?


texts:
How can I model a non-linear resistor whose current changes according to the equation shown below on Advanced Design System (ADS) or AWR Microwave Office?
$$i(t)=v-v^2-v^3$$
Where v is voltage difference between terminals of the resistor.
How can I create such a resistor?


texts: What is best options for simple but very low latency calculations?

texts: After reviewing my math, it turns out I had made a mistake in my calculations and was off by a couple factors. In an effort to make this question worthwhile, I am still interested in what type of device can perform very specific calculations at at high seeds and low latencies.


texts: Capacitor in series with voltage divider

texts:
I am trying to understand the dynamics in the following circuit:

I have a voltage source here.

Now, I measure current at C1 and voltage at C1/R2 and the result is this:

So, what I understand so far is that the capacitor "sucks in" all the voltage, so that the voltage that I measure is really low at the beginning. At the same time, the capacitor draws in a lot of current for loading until it is full and nothing more is drawn in.

But I do not get what happens when I change resistor values. According to voltage divider rule, the capacitor gets I_in * R2/(R2+R1) as voltage. So, I have 4/(4+1) = 0.8 in the circuit below. But when I change R2 to 1k, R2/(R2+R1) is 0.5, so the voltage provided to C1 should be lower. This means, it should load slower. But it doesn't the simulation will show the peak of the green curve earlier instead of later.

So, question is: What are the dynamics here? How can I calculate how fast the capacitor charges?

I tried to understand this circuit by using Ohm's law and the voltage divider rule but just nothing seems to work here...


texts: Power supply of LOGO 12/24RC PLC from SIEMENS

texts:
I bought LOGO 12/24RC PLC from SIEMENS, and I didn't try it yet because I am worry about the required voltage needed to switch it on. I tried to see the data sheet but I confused with lots of data. If any one has any idea I will be thankful.
Here is the data sheet for LOGO 12/24RC


texts: Which design to choose for highly stable LED or laser diode driver?

texts:
I'm looking at several design choices for driving a LED and/or laser diode in a very stable, low noise way.

The specs are as follows:

current: 1-100mA, adjustable (the adjustment can be either digital, analog or via a trim pot); current accuracy: a few percent of the set point over time, temperature etc.
voltage: different LEDs I may need to drive are between 1.4V and 3V forward
noise/ripple at the LED: as low as possible (10uV rms is a good target ** this is one of the tough parts of the spec)
turn on/off time: 0.1 ms or less

The options:

Use a LED driver chip. Pros: they are meant to drive LEDs :) Cons: most of them don't have anywhere near 100:1 adjustment range (eg LED1642GW, can be adjusted in software which is nice but the range is only 3mA to 40mA).  They also don't have any noise spec.  Many have a lot more than 1% current variation over temperature (sometimes deliberate, the current drops at higher temperatures). Also, multi-LED drivers tend to have a single resistor set the current for all channels, they are not independently controlled.
Use an adjustable LDO configured as a current source (and use enable pin to turn on/off). Pros: the noise is specified and can be very good.  Cons:  the current sense resistor is also the current adjusting resistor, it needs to be a low resistance (let's say 1 kohm adjustable down to 10 ohm) and has fairly high worst-case power dissipation (0.1W) for a potentiometer.  The enable pin turn on and turn off can be quite slow (sometimes adjustable turn on speed which is nice, but kHz operation is somewhat rare I think)

simulate this circuit – Schematic created using CircuitLab

Use an op amp, either directly or with a pass transistor: I breadboarded this.  Pros: complete control over the behavior; adjustable over a wide range of current, including setting the current using input voltage.  Cons: it seems pretty noisy and prone to oscillate; noise from the input can couple into the output; I haven't figured out how to make a version of this which is reasonably fast to turn on/off and also very low noise. If using just a positive supply, turning the LED off completely is not very straightforward.

simulate this circuit

Which of these sounds like the best design option for this spec?

(Btw: I will need to make a 100-channel version of this, with the current and on/off state of all channels controllable independently; this could be simply 100 copies of the same circuit.  Using some of the 16- or 24-channel LED driver ICs could be nice, but only if the current for each channel is independently controllable)


texts: What is the purpose of ferrite or inductor on the voltage input of FTDI chip?

texts:
I bumped into a couple of strange symbols that look like inductors or ferrite beads, I'm not sure what this is. Does anyone know what it is and what is the purpose of it? My guess is it has something to do with a general use of USB as a power supply. There are no parameters or anything to go by:

Here is a link to the document that has this schematic on page 28: https://www.ftdichip.com/Support/Documents/DataSheets/ICs/DS_FT4232H.pdf

My plan is to ignore it, but I am afraid it might be important for the stability of this chip

EDIT: it seems to be an LC filter, as mentioned on page 9 of the datasheet. I'm still not sure if that is what it is or how to make it.