texts: A peculiar issue in an atomic force microscope

texts:
I'm not sure where else to turn for this issue. Hopefully you all can offer some insight. Sorry the title is so vague, I don't know how to explain this concisely.

I am a teaching assistant for an introductory engineering lab which teaches the fundamentals of nanoscience. As one of the labs, the students synthesize and image carbon nanotubes. The imaging is done using an atomic force microscope.

Monday's class went fine. But yesterday (Tuesday), an interesting problem developed. Tuesday section's sample of nanotubes appeared to give inverted images. Essentially, the microscope reports the tubes as being deeper than the sample surface, rather than raised above the surface, as would be expected.

On some investigation I strongly suspected that what we were seeing were not CNTs, but rather scratches on the surface of the silicon substrate. My supervisor doubted this, saying that he's had this issue before and has no idea what causes it. Apparently this issue develops sporadically, and disappears just as randomly. He strongly suspects the issue is electrical in nature, which is why I am turning here.

I seriously doubted the electrical explanation, because there is some seriously bizarre behavior involved here. The sample also has small specks of catalyst used to grow the CNTs, and these particle are quite large and raised compared to the CNTs. These particles appear perfectly normal in the images. Only the CNTs appear inverted, which I can't come up with an explanation for. In an attempt to show my supervisor that what we were seeing were in fact scratches, I loaded in Monday's sample. I went to the same region that I had previously imaged, and took new scans. Lo and behold, the exact same problem. CNTs which I had previously scanned were still there... just inverted.

Is there anyone who has any idea at all as to what could be causing this behavior? I just find it utterly bizarre and can't reason to myself what could possibly be the cause. For your reference I've attached some scan images below (please excuse the camera pictures of the monitor, the computer is running Windows 98).

This is an example of expected behavior. You can see the raised catalyst particles, as well as the raised tubes.

This is a scan of the same region, but at a different time (hence the differing scale and orientation etc). Notice the catalyst is raised as expected, but the tubes are clearly inverted.

Here is a 3D view of the same scan. The "trench" effect I'm talking about is clearly visible. Also, do notice that even the catalyst splotches appear to be surrounded in trenches as well before finally raising up as expected. The trenches surround the catalyst particles are aphysical, and I actually didn't even notice them until now. It seems that whenever the probe tip encounters a bump, it first lowers before raising?

Thanks for any help. I'm really at a loss here.


texts:
From s-parameter lossless network definition , The sum of the incident powers at all ports is equal to the sum of the reflected powers at all ports.

But how do we derive the above unitary property expression involving S22 and S21 ?


texts: Altera Quartus - structural architecture

texts: I am relatively new to VHDL and I am supposed to use structural architecture and Altera Quartus on my assignments. But, I have noticed that the Unisim library is not compatible with Altera Quartus, so when I try to use components such as INV, AND2, OR2, they are not recognized. So, is there an equivalent library on Altera Quartus which has the same functionalities?


texts: L293E, voltage difference exists between output 1 and output 4, yet it can't drive a small motor

texts:
I'm using L293E to drive one motor in two direction.

Output 1 and output 4 are connected to the motor and I alternate Input 1 (1A) and Input 4 (4A) between VCC and GND. (never input1 == input4).

Vs and Vss of the L293E are both connected to VCC = 12V.

Here's my schematic :

The problem is when I connect Input 1 to VCC = 12 and Input 4 to GND.
I measure 10.8V between output1 (1Y) and output4 (4Y), yet when I connect the motor it doesn't turn.

The motor is a small motor. For instance, when I connect it directly to the power supply (12V), it only sucks about 400mA.

Here's the datasheet of L293E


texts:
How do you decide the value of your stack layer ? Dielectric constant, thickness, material for prepreg, core, thickness of conductor in oz...

What is your methodology to do so ? Do you only relyon your pcb manufacturer to impose their requirement and then you adapt to them or do you do the opposite (set value and constraint manufacturer to follow them )?

I know it sounds a general question


texts: How do I set up a circuit in order to help me measure the resistance of a 1-meter length copper wire with changes in temperature?

texts: I am a high school student and I am taking Physics at school. I have been given the task of measuring the resistance of a copper wire with changes in temperature, however, I have no prior knowledge of electricity and how circuits work. At school, I only have access to a few multimeters, a power supply, some crocodile clips, copper wire, and an IR camera. My teacher has suggested that I change the temperature of the copper wire by using the power supply, and to measure the temperature of the wire using the IR camera, however, I have no idea how to change the temperature, or by how much to change it, or what real effect it will have on the wire if I change the numbers on the power supply. I carried out a preliminary experiment, however, as I turned on the power supply which was on +100 VDC (which I don't even know what that means), I saw a decrease in the number on the multimeter when measuring resistance, and I have no idea what happened there. I'm not sure if there is anything else that I could do, or how I could do it. If there is a better way to carry out the experiment that I have been asked to carry out in a high-school environment, I am just not aware of it. I would truly appreciate it if anybody could help me understand and identify what I could do for my experiment, and how I could carry it out.


texts: A question about protected extra-low voltage system

texts:
I don't understand what is meant by the following about PELV:

On wiki it says the AC RMS range must be smaller than 50V and DC must be smaller than 120V. Is AC limit here for the output of the power supply?

It also mentions:

  IEC 61140 defines a PELV system as "an electrical system in which the
  voltage cannot exceed ELV under normal conditions, and under
  single-fault conditions, except earth faults in other circuits".

  A PELV circuit only requires protective-separation from all circuits
  other than SELV and PELV (i.e., all circuits that might carry higher
  voltages), but it may have connections to other PELV systems and earth
  (ground).

  In contrast to a SELV circuit, a PELV circuit can have a protective
  earth (ground) connection. A PELV circuit, just as with SELV, requires
  a design that guarantees a low risk of accidental contact with a
  higher voltage. For a transformer, this can mean that the primary and
  secondary windings must be separated by an extra insulation barrier,
  or by a conductive shield with a protective earth connection

Since these are confusing to me I wanted to ask this on a practical example.

My question is:

Is this SMPS PELV? And how can I understand whether it is or not? And in what circumstance PELV would be safe?


texts:
I don't know a lot about linear actuation, but I need a precise device that I can control easily (using some kind of hobby board) that is able to perform linear positioning with a resolution of at least 1 micron. I've seen piezo actuators, stepping actuators, ultrasonic actuators but I'm not sure which is the simplest. Is this possible? What would such a device be called?

Thanks.


texts:
TL;DR: How can I "splice" two different cords for different barrel jack sizes?

I'm rather new to this sort of stuff, so bear with me here.

I am attempting a project where I need to create a port on the outside of a case for a barrel jack. I am getting power from a USB hub for a Raspberry Pi, and this is my basic setup:

|             |
|PI---HUB[<---[<---...
|             |

Where | = Case Wall, - = Wires, < = male barrel port jack and [ = female barrel port jack.

I ordered a USB hub online, and the company assured me that the barrel jack size would be 5.5mm by 2.1mm. I went ahead and ordered a 5.5mm x 2.1mm extension cord, so the male end would plug into the hub and the female end would go through the outer case, creating a port.

Sadly, the USB hub company was woefully incorrect. I received the hub to find that they used some weird barrel port size -- none of the wires I tested at RadioShack would fit. RadioShack recommended I go to this other store, but first I had an idea.

What if I could change the barrel port size?

I am thinking that I would wire my now useless 5.5mm x 2.1mm extension cord's female end to the male end of the power supply that came with the USB hub. Then I would order a 5.5mm x 2.1mm power supply with the same voltage, and use that size for the outer port instead.

In essence, I would be combining two extension cords.

Would this work? Can I just connect the wires on the two cords and both will work?

Here's the diagram of what I'm thinking, if it doesn't quite make sense:

|              |
|PI---HUB[<~~=={/---
|              |

Where | = Case Wall, - = Generic Wires, < = Weird proprietary male barrel jack, [ = Weird proprietary female barrel port, / = standard male barrel jack, { = standard female barrel port, and the different squiggly lines are two spliced wires.

Would it be possible to solder these two power jacks together and have them work?


texts: I am making a small, mobile device with the Raspberry Pi that depends on batteries, so power consumption is an issue. I have scaled the "arm_freq_min" (unsure if clock or instruction cycle frequency) to much lower than the default frequency by about a factor of 10. I have heard that \$\textrm{Power} \propto fV^2 + P_{base}\$, but when does this linearity between power and frequency break down?


texts: How to calculate the number of pages of a process, and the size of the page table(in bytes)?

texts:
I just need a second opinion on the result that I got for a question to see if it is right.

I am dealing with a computer system using paging, where the address space space of every process has a size of C = 2c bytes and the page size is S = 2s bytes. Each entry in the page uses E bytes.
I am trying to calculate the number of pages of a process, and the size of the page table (in bytes)?

My solution:

Number of pages of process = 2c/2s = 2c-s

Size of page table = 2c-s × E bytes

I will be grateful for a second opinion in case I made a mistake.


texts:
thanks for the many great questions and answers over the  years.  This is my first question.

I use Altium Designer for capturing designs.
I had an idea to make my processor components a little more flexible/readable.  With all the functions that can be held by processor pins these days, having all the functions in one name is unwieldy.  Perhaps I could put into the pin, as parameters f1 f2 ..., all the different pin functions and make them visible when needed and hide the original Display Name of the pin.  I like the idea so far but I always have to ask what dangerous beast is waiting for me down the road.  Can anyone see a drawback to this method?

I believe in the schematic a pin could be modified to show a different name/function parameter by editing the pin if needed and hide the ones not needed.
Maybe someone has done this before if you have I would appreciate knowing any drawbacks to this approach.

Thanks in advance


texts: Quad 2-input NAND-gate Not seems to work

texts:
I have recently bought this IC:

It's a NAND gate. So just to be clear, we agree that if both inputs are 1, the output will be 0. (The IC is a Quad 2-input NAND-gate 74HCT03, the datasheet can be found here )

This chip just won't  work for me. I'm using a breadboard as you can see beolow, and no matter what I do, it wont work.

As you can see in the picture, I have connected the right side of the chip to +, and the left side to negative. This should mean that the IC is ON. I then connect the wires to pin 1 and 2. And a LED to pin 3. I have connected the pins to 10k resistors to ground, so they can be 0 if no power is on. I have tried to remove the switches and just create a wire that goes directly from + to pin 1 and 2 but nothing happens. The funny thing is that whenever I disconnect the wire that goes from pin 7 to ground, the LED starts to light. I migth be stupid, but I can't really figure this out..


texts:
In the non-inverting amplifier shown below, when the DAC output (TP1) is held constant at 2.5V (same input code), the OP213 opamp output (TP2) fluctuates between 8.750 and 8.775V i.e., roughly 25mV. Any idea why it fluctuates?

The 12V supply is derived from a transformer after full-wave rectification and sufficient filter caps. It is free from ripple and noise.

Thanks in advance!


texts: Raspberry PI powering a peripheral device while accessing it via USB causing PI brownout/short-circuit

texts:
My current project utilises a Raspberry PI (3B+ or 4B) to communicate and control an external peripheral device.

The Raspberry PI also has a UPS (PiJuice) attached, including a Li-Ion battery (and therefore ~3.7v).

Background

This peripheral device, was not designed or made by me, and is current limited in the device's circuitry preventing the device to be wholly powered via the USB cable.  It was never designed to be used the way I am using it.  It is instead, meant to be powered via a stand alone power source (AA batteries). USB was only meant to program the device, then be disconnected.

The device which requires ~4.2v-5v and pulling around 40mA to correctly operate within tolerances, contains a microcontroller (3.3V) and microSD card.  When the voltage drops (AA batteries), other components on the device stop working, due to their own (less forgiving) tolerances.  As mentioned above, when the device is connected solely via USB, the same component circuitry also stops working, as it doesn't receive sufficient power.

The device has my custom firmware, enabling access to the microSD filesystem via a MSD protocol.
The PI gpio is used to control the device's CLK, RST and another interrupt pin, externally signalled via jumpers, which switch the device between its normal mode, to MSD mode.

So in summary, the PI is connected to the device via both GPIO pins and a USB cable to access the USB MSD and interact with the USB HID, when the mode permits.

Side Note 1: Until I've come up with a working solution, I added a simple arduino style 5v relay, to disconnect the AA battery when not in use and conserve power, but this needs to go also.
Side Note 2 The device is highly sensitive to noise, as it records ultrasonic audio.  The PI USB has been found to introduce noise in the ultrasonic recordings, so I added python code on the PI to control the USB hub power, which disconnects the USB power when the device is recording (not in MSD mode).  This removes much of the the noise in recordings.

So far all this works, but it isn't nearly pretty or a long term workable solution.

Problem

I'm trying to remove the need for the additional power source for the peripheral device, as it causes big headaches when the AA batteries go flat.  I have a battery right there, already in the PiJuice.

Connecting the 5V pin on the Pi to the VCC of the peripheral device causes the PI to turn off every time, whenever the USB port is also connected.

I can successfully power the device (no AA batteries), via the 5V pin on the PI whenever the USB is not connected.

Any suggestions how to power my peripheral device, and get rid of those pesky AA batteries?

tl-dr

Generally, when a peripheral device needs supplementary power and a USB connection as well, how should a PI connect to it?


texts: I/O initialisation. Curious for the reason PIC16F18877

texts:
For the initialisation of an I/O in the pic the datasheet indicates to clear set the TRIS correctly and clear both PORT and LAT bits. I thought I understood why and the program works. When looking at the disassembly however the PORT clearing and LAT clearing generate the same instructions. I did not look further but I think that the PORT bits are cleared as a result of the LAT bits clearing.

Is there a specific reason that the datasheet (asm) indicated to clear both PORT and LAT and in C it boils down to one action only on LAT.

C code example lead both to identical asm after compilation:

PORTAbits.RA0 = 0;
LATAbits.LATA0 = 0;


texts: How does a transistor sweep generator work?

texts:
In particular I'm wondering about oscilloscope sweep generators, but the concept I don't understand remains the same for any type, which is, what does the triggering? I know a transistor can be switched on and off incredibly fast, but I've got a sweep generator in front of me that consists of 2 transistors and some resistors and capacitors. No matter how many components you have in a sweep generation circuit, that command to turn on and off that gets sent to the transistors, it's got to come from somewhere. To my knowledge, a transistor can only switch as fast ast it's being told to switch by an on and off base current. What kind of component originates this?

I was under the impression that Q14 and Q15 were the sweep generator. But I don't understand what is actually generating the fast signal responsible for the creation of this sweep.


texts: Powering a stepper motor (on Arduino), what's too much and too little?

texts:
I'm an electronics noobie, just learning on an Arduino.
I'm following some tuts online, and bought myself an arduino and a 28byj stepper motor.
It's 5v DC.
I power the arduino via a 9v battery or via USB.
I was warned not to try to run the  motor via the arduino, I have to provide a separate 5v to the motor, I thought if I put 3AA batteries together I get 4.5v or 4 for 6v - but not 5v. :(
So which is better?
A little over or a little under voltage?
If over, how much over can I go, for example can I use a 9v battery?
Thanks in advance! (Feel free to leave any advice, am totally new to this and all suggestions and comments are welcome!)


texts:
Not too long back I did some reading on the Alpha CPU architecture and (probably out of a burst of nostalgic stupidity) procured a couple; there's only an issue - the ones I have are the 21264 C variant, that features an LGA pad-out rather than a PGA setup due to the increased clock speed.

The initial Alpha 21264 datasheet I've tracked down, but I can't seem to find any references anywhere as to the 21264C variant's datasheets, which would contain the prerequisite pinouts and mechanical specs for me to do anything with these devices. Because Compaq offed the whole Alpha architecture, there doesn't appear to be a reliable manufacturer source anywhere on these devices.

Not that I have any game-changing ideas for these things, but it'd be kinda neat to do something with them other than have them gather dust or buy a complete OEM system for them. Or, if nothing else, learn about them for learning's sake.

Anyone have any clues as to where I could find the particular datasheet?


texts: Circuit to randomly light one LED or another

texts:
I am attempting to make a cheap and simple "quantum-ish" coin flip circuit.  My idea is to use something like an SR latch driving two LEDs, and have the initialization be driven by some random event.

I will be cross-posting in the physics stack exchange as for what could qualify as a quantum trigger, but my initial thought was to compare the resistance of two LDRs in the dark as a "quantum" event. So essentially the SR latch would be powered up and whichever LDR had a slightly lower/higher resistance would drive the latch to initialize in that state and stay there until power is removed.

What would a circuit like that look like?  Is there any way I can tune it so that the probability is approximately 50-50 for each LED.


texts: How to specify a "standard", not CR, servo

texts:
What do you name a servo that rotates to a specific angle and stops there, to differentiate it from a continuous rotation servo, a linear servo, or any of the other varieties?

I've seen them specified as "positional rotation" servos, but this doesn't seem to be an industry standard. Is there an accepted term to explicitly specify the most common kind of servo, that rotates to a specified position and stops there?


texts:
In the circuit below, how is Q1 turned on? When there's voltage in the bias winding, it turns Q2 On and subsequently turns Q1 off. Also, does the end of R4+R7 keep floating when Q1 is off? It should go to ground. I'd appreciate any help to better understand the startup circuit in the yellow square.

EDIT: Idea with an Enhancement MOSFET

EDIT: Another approach with Enhancement MOSFET


texts:
Does anybody know how to light up a vacuum tube? I have about 9 of them and only 1 I can see the name. It is a 12DT8. Is it possible to find the heater without the datasheet by using a multimeter etc... And if so, is it possible to power it with a DC battery?

I am not trying to operate it for complex electronics, I just want to light them up for decorational purposes. I got these from a 1950's radio, if that's any helpful info.


texts:
A wall climbing robot's controller board distributes power to a 150W brushless suction motor, 2x 30W brushless wheel motors and precious digital electronics (Intel NUC + STM32), the latter is connected through dc-dc converters.
Would you recommend placing an LC filter at least on the input of the 150W motor controller and why?
Schematic below shows the precautions of the suction motor's esc power connection.

I have seen people attach LC filters to their drone's ESCs to improve analog video transmission. I have a digital link and I am more worried about motors puking current and voltage onto the robot's brain (aka digital electronics).


texts:
Can you please help me with this exercise?

In each circuit, calculate the current flowing through the 10kΩ resistor and calculate the voltage drop across the germanium diode. Please assume that a germanium diode has a forward-biased junction potential of 0.3V.

Circuit (a)

Supply Voltage = 5V,  R= 10kΩ,  Junction potential = 0.3V, I =? VDrop=?

VD = (5V – 0.3V) = 4.7V
I = VD/R = 4.7V / 10kΩ = 0.47mA

Circuit (b)

Supply Voltage = 10V, R= 10kΩ, Junction potential = 0.3V, I =? VDrop =?

VD = (10V – 0.3V) = 9.7V
I = VD/R = 9.7V / 10kΩ = 0.97mA

Can you please review my solution?

I am not sure about the voltage drop, which in my calculation is indicated as VD. Also the second circuit, which is reverse biased, I'm not sure about the calculation I made.

Thanks in advance.


texts: In 2020, what are the most common approaches to power-line-communications for hobbyists? (updated)

texts:
I'm looking for modern control protocols, designs and/or components to simplify controlling (and running) a very low power system on a chip safely from mains power.  I'm in the USA, and on a hobby budget. Consumer trends here are of interest, but so is the National Electric Code.   Surely the world has come a long way since X10.

Has Bluetooth LE (BLE) made the older power-line communications standards old-hat?  Are there ways of coupling BLE into the power-line that are considered good practices?

==Research Update==

I found the datasheet on the Cypress Semiconductor CY8CPLC10 I was referring to earlier (below).   Cypress labels it a Integrated Power-line Modem PHY using 2400 bps FSK.   That part number suggests its based on the PSOC-1 (8-bit) 5 generations behind their current 32-bit models.   I don't think I care about the 8-bit part if I can treat it as a re-programmed modem.

However, the Digikey listing however has some sort of end-of-life notice link, dated July 2019.  But that EOL notice seems to be for a CCS7331P-CAZR from Cirrus Logic.   Seems like a different device, can anyone clarify what that means?

Also featured in the datasheet is:  "Reference Designs Comply with CENELEC EN50065-1:2001 and FCC Part 15".   I know what Part 15 is, but I'm not familiar with CENELEC.  Seems to have something to do with the 131.5 KHz to 133.5 KHz band.

==What I've tried == (earlier)

A web power-supply-only web search like AC DC Isolated Power 3.3V uA turns up the sort of component I might use for PS alone.   Some quite quite inexpensive while still claiming up to 3kV isolation.   It even seems like there are some defacto standard pin-outs for these board mounted power supplies.  E.g. ebay "1PC NEW AC DC Isolated Power Board Precision 12V300mA 3W 3.5W"  at $1.99 quantity one.

But if I add the PLC part AC DC Isolated Power 3.3V uA with power line communications, the results disappoint me.

==Background==

The Cypress Semiconductor PSOC 5LP illustrates the class of SOC i'm looking to use as a building block.  Its got a pretty wide DC input range, so I'm not even sure if I need a regulated supply.

I'm not tied the PSOC family, but I've found it to be very low-cost prototyping friendly.   This sort of device has some impressive programmable analog and digital blocks that might make sense to leverage to keep chip count to a minimum.    As I remember, Cypress had a PLC product line some years back, but it seems they are out-of-the-game.   None of Cypress's current applications notes seem to make recommendations.


texts: I have a non functional PC power supply unit, and I would like to keep its heat sinks, but they have no model or part number in them. Is there a way to estimate, calculate or measure their thermal resitance? The PSU is a Sentey BCP 450-OC, here is a picture of the heat sinks


texts: Cooling a CCD cam need help with power source

texts:
Lately my brothers love for astrophotography left me to embark on this endeavor.
He has a metal CCD camera and in the sport a major way to reduce image noise is to cool the camera.
So I ordered some artic silver 5 some peltiers and found and old heat sink.
I would like use and old power pack I have which is giving out 12.27V and 12A.
From everything I can find on the peltier it is 12V 6A and 60W .
Edit:
Also I need it bringing down more for the fan as follows
0.8A for the fan.
Now I have read up on many components on limiting the current and I tried using a Zener diode which worked successfully but the diode created a lot of heat not good for the job in hand I could really do with keeping it down to minimal as I am really desperate on not using a PCB and hopefully something that can be concealed in heat shrink.


texts:
Should your motor have less Amp draw than your ESC or more, and should your ESC have more or less Amp draw than your battery can supply?

Thanks!


texts:
I have a USB barcode scanner and I have difficulty getting the data out of it. What I did was to get one of these adapters, and followed this tutorial with no luck. When I connect the ports as shown, it does not even power up the scanner to make a BEEP. With computer it works as a PS2 keyboard I guess without problem.

Any recommendation on how I can go forward?


texts: Will (LiPo) batteries draw current/voltage between packs if main lead is disconnected?

texts:
Never learned this stuff in school (electrician study) oddly enough.
But if you serial up 4 batteries (3S LiPo's x4 to be specific), and you switch off the main leads to the power bank..

Will the batteries still draw/distribute load in between each other?
I know the loop is broken but for some reason the one thing that got stuck in my head is that batteries - lead will always try to balance out it's internal overcapacity of electrons vs protons, and if one pack has more protons and still have a negative lead connected to it's positive, will those two packs balance each other out?

I apologize for the noobish question, but it's out of concern for battery safety!


texts: Select between two sources with transistors

texts:
I'm sorry if this has been asked before but I can't find useful data on this matter.

I have two sources of data and I want to select one of them using transistors.

If I had to guess I'd make the circuit below.
Sadly I never had any electronics courses so maybe I'm missing something obvious here but as I can't find anything about my goal on internet I'd rather ask here.

I just heard about SSRs and they seem to be the best solution for my needs, but I still want to know about how to do this with transistors if this is possible.

Thanks

Vout is bottom-right

Edit:
The sources are composite video signals


texts: How to properly wind coils for a solenoid?

texts:
I need to wind a small electromagnet "solenoid?". About 3cm high and 2~5cm wide running at 5V/0.5A.  This magnet will be put into a desk bell so it pulls the clapper down and rings the bell. I have found ready made solenoids that push out but not pull.

So I am attempting to make my own magnet and I have wound several different types of screws, nails and bolts with different types of wire. And now I have noticed a problem with precision :) I can wind a massive coil and it will work but how do I wind a small yet powerful coil?

I can't really find a laymans explanation on what diameter core cable to use and how many windings. In general the more windings the stronger the field which is common across all articles I read.

I found an article where somebody says that the windings should be wound in the same direction (clockwise layer, clockwise layer...etc) to create a truly stronger solenoid but all articles say just wind them back and forth (magnet?)

Can somebody in general suggest what kind of core material and diameter would be the best and if winding the coils in the same direction will actually help. Also is there any difference which way the ends are pointing or do both sides emit the same field?

At the moment I have PCB with 3 1000uf caps in parallel to the coil that is triggered by a transistor. I will be using aTiny that triggers the transistor maybe 0.2seconds and I need a jolt of magnetic power to pull the clapper down and release instantly.

simulate this circuit – Schematic created using CircuitLab

-EDIT

This is a project that somebody got working using USB power and winding his own coil. He uses a darlington transistor? Does that influence the coil somehow? I only have a normal transistor.  The gap there has to be about 1.5~2cm so the clapper can smack the bell. I have the same bell. He reckons he used 2m of cable to wind the coil... I used 3.5metres and wound it much much neater than his..

BDX53B Darlington transistor
1 x 2200uf 10v cap

YouTube

-EDIT2

I ended up using a 5v solenoid. Removed 2 capacitors and used the pushing end of the solenoid to kick the clapper out. And DING! It works like a charm. I have no idea how the guy made that electromagnet pull down the clapper?!


texts: Replacing a DC barrel connector with a molex connector?

texts:
I'm considering removing the DC barrel jack connectors on my Raspberry Pi 2 and another component (this one) and replacing them with molex connectors. The boards are mounted on standoffs in an enclosure. And I'd like to have everything wired neatly inside the enclosure.

My question is simply, wouldn't it be more appropriate to use something like a molex and wire it directly to my 5V DC power supply.


texts: I know how to program, how do I learn how to wire things up?

texts:
I'm computer science student, I know:

some basic VHDL
program in C or assembler
basic electrical laws (ohm law, kirchhoff, ..)
basic electronic parts (diode, tranistor, ..)

What I don't know are those practical things like:

where to put pull up resistor and why? What resistance do i choose?
it seems like there are randomly putted capacitors all round circuits and i have no idea why
i dont know what to do in order to not blow up processor
that crystal trick that generates clock .. how do i compute the numbers?

I have theoretical background, but that doesn't tell me anything about how to handle interference and those "practical" guidlines. Do you know any good youtube videos or books?

I know i could just use arduino, but that's so expensive! And it's quite overkill for some basic projects like: light up led if cat passes laser latch for 1 minute.


texts:
I wish to use some extra power supply filtering for my DAC, ADC, CPLD and OpAmp devices. In this question I got the point about the global locations for ferrite beads. If I understood correctly, the ferrite bead should be placed close to the device regardless whether it is a noise-generating, or noise-susceptible device. Please, correct me if it's not a general case. I saw some example schematics where the beads are placed before or within the bypass cap circuitry:

Note to the pic: Power source is Vin, Chip is Vout

Is there a significant difference between the two approaches above?


texts: Charge density (σ) and distance between plates of capacitor given just the relationship between potential difference (V) and width of a metal slab?

texts:
I’m trying to become an electrical engineer and I was given a problem in school (calculus-based physics) to work on. Basically, a parallel plate capacitor is charged to the same potential difference as the battery that is connected to it. Then, a metal slab was inserted between the two plates (after the battery is removed) and the new potential difference (V) across the capacitor was measured. Next, various metal slabs with different thicknesses (cm) replace the original, again measuring the new potential difference across the capacitor. I was instructed to graph potential difference (V) as a function of slab thickness and got a linear relationship with a slope of about -2.5 V/cm.

Now, I’m tasked with finding charge density (σ), which is charge/area, and the distance between the two plates. My professor insisted I must use the slope to do so. How do I do this?

To be quite honest, I’m quite lost. I’m not too familiar with the capacitance equations but I know that Charge = Capacitance * V and Capacitance = KEoArea/distance, even though I’m unsure if these relate. I derived V without the metal slab to be σd/2Eo but I don’t think I can use this with a metal slab now inserted. Any help is appreciated! Hopefully someone will be able to find the answer!


texts:
What tools and techniques can I use to identify an unknown IC with no markings?

Today I encountered a microcontroller under an epoxy blob. The blob had 11 pads on each of four sides, perhaps 44tqfp. From the board, I know which pin is the reset line and I probably know which pins make up an SPI interface.

Is there such a thing as an expert system for answering these puzzles with the information I have?

Are there any searchable databases of pinouts online?

Would X-raying/Decapping the package be worthwhile?


texts:
How do I create a combinational circuit that encrypts a message using Caesar's cipher?

And another circuit that decrypts this message?

I thought about using modular arithmetic, but I did not find a simple way to do that either.


texts:
I would like to perform a simulation on LTspice about a switching MOSFETs.

In particular on how the parasitic inductance and capacitance affect the switching transient.

In order to perform this analysis I need a MOSFET model of SCT3022AL from Rhom semiconductor.

Following the link:
https://www.rohm.com/datasheet/SCT3022AL

Unfortunately it is not avaiable the LTspice model of this MOSFET.

I could create my own model but I saw that the information needed are:

L (channel    length)
W (channel    width)
VT0   (zero-bias  threshold   voltage)
KP    (transconductance,  μn/pCox)
LAMBDA     (channel-length    modulation  coefficient,    λ)

These information are not avaiable in the datasheet.

How can I do to create my own model? Alternatively, do you know if this model is avaiable?

Thank You.


texts: Arduino powering an external circuit with higher voltage

texts:
First of all, I'm sorry for the newbie question. I'm a software engineer and only a hobbyist in electronics.

I'm trying to power up an external circuit using an Arduino digital pin.

The external circuit uses a 12V power source and drains about 4mA.
I have successfully done this using a transistor.

According to the specs, the Arduino digital pins can supply up to 20mA with no problem.

Therefore, I was wondering if it is possible to power up this circuit directly from the pin, without using the transistor, nor the 12V external source.

The questions are:

1) Is it possible? How can I accomplish this?

2) What about the higher voltage? I think the circuit is designed to work with 12V and if I supply a lower voltage it should drain less current (according to Ohm's law) and the current wouldn't be enough. Does it makes sense?

3) If (2) makes sense. Is there any trick to do to achieve this needed higher voltage from the pin?


texts: Problem managing voltage for sensors and LCD

texts:
I have this 5V voltage regulator circuit that is supposed to power these 2 circuits:

NodeMCU (will automatically turn on if plugged in)
Turn on/turn off the LCD and sensor when the pushbutton (BTN1) is pressed. (The circuit on the right blue box.)

The problem is, when I read Q3's collector using a multimeter, it shows 5V,  but when the LCD and sensors are plugged in, the voltage drops. Am I missing something?


texts: Will LD33V voltage regulator overheat with 12V 2.4A dc input?

texts: The circuit works and it provides a stable 3.3V output, but it heats up and I'm afraid it can overheat and cause problems.


texts: Replacing zener diode with a resistor in current limiter circuit

texts: Can we use a resistor to replace the zener diode in this current limiting circuit ? Why do you think using a simple resistance is not enough to trigger the base ?


texts:
I am trying to make a 600v RC filter with a cutoff frequency of 1hz or less.
The problem is the capacitor prices for these voltages are too high.

I want to use series capacitors to up the voltage rating and lower the cost but I have a few questions.

For starters how do I determine resistor value for the leak resistors?
Does leak resistor balancing mean I can use differently rated capacitors?
Also, how does this configuration affect the filter itself?


texts: How to make input filtering capacitance circuit (capacitor bank) if values of one capacitor are not enough to handle with voltage and capacitance? For example, calculated input capacitor value for AC-to-DC converter 1.4 millifarad 640 V.


texts: Resistor dissipating 0.1W in heatshrink tubing

texts:
I have made a LED lamp by soldering together a 3mm red LED and a 1K resistor form ebay. I then wrapped it in heatshrink, to insulate it and make it look nice. But now I've done some maths and I realized that the resistor will have to dissipate 0.1W (12V power supply -> 10V/1KOhm=10mA -> 10V*10mA=0.1W) and I am worried that it might run a bit too hot and malfunction (cause a fire).

Am I right to worry or will it be fine? It has been on for about an hour now and it is only a little warm on the outside (probably not even 30°C), but I don't know what thermal resistance it has.


texts: How to connect two FPGA boards achieving speed in tens of Gbps?

texts:
I want to connect two FPGA boards e.g. B1 to B2 such that the link could transfer enough data per second from B1 to B2. What i mean is that the link between the two boards should NOT be the bottleneck. So that i could test the throughput of the FPGA on B2.

The data transferred is Layer 2, Layer 3 packets. The FPGA is of the Xilinx.
Probably I need more speed provided by PCIe 2.0 i.e 5 Gbps. Can I use Ethernet cable Cat 6a, Cat 7 or above for this purpose? Or Can I use Very High Density Cable Interconnect (VHDCI) connector between two FPGA boards as it can provide 80 Gbps speed? Or any other link that could provide higher Gbps speed between Xilinx FPGA boards?


texts:
I have very little knowledge of PCBs and electronics, so bear with me.

I have a requirement where I have to read the temperature of an object. The thermocouple part has been figured out and currently we have a very simple setup with an Arduino Uno using a MAX6675 (thermocouple ADC) and displaying the temperature on a LCD.

Next step of the project is to to eliminate the LCD, try to design a custom PCB which contains the microcontroller, ADC (it doesn't have to be MAX6675) and accessories to send the data to a host PC or save the data in an SD card,
whichever is feasible and the program for all of this.

The reason for a custom PCB is because the PCB has to be around 18mm in diameter as it will be mounted on the object whose temperature has to be measured. It needs only one input and output as we will be measuring just one temperature point with one PCB.

Is this all possible in a custom PCB and can it be made that small?

I am trying to educate myself and look for possible problems before I talk to PCB manufacturers.


texts: Noisy output on voltage reference and correct probing

texts:
I'm building a circuit that has a 2.5V Voltage reference for use on the internal ADC of a STM32F7 in 12 bit mode. As each bit corresponds to 610uV I'd like to have as little noise in the signal as possible. The voltage reference is also adding 1.25V DC offset to the incoming signal, as the signal is partially a negative voltage, so I have a 1kohm by 1kohm voltage divider on the output.
The voltage reference is TIs REF5025 datasheet here: http://www.ti.com/lit/ds/symlink/ref5025.pdf
I'm using the voltage reference in its simplest configuration, 10uF Cbypass and 1uF CL; from the datasheet:

My issue is that I can't measure how much noise is genuinely on the output of the voltage reference. It is outputting 2.5V as expected but I also wanted to see how "clean" the DC out is compared to my bench power supply that is currently being used for these tests (the final circuit is using an LM7805 as the 5V supply)
Channel 1 is the power supply (yellow) and channel 2 is the voltage ref (blue). as you can see, the power supply actually has LESS noise than the voltage reference (approx. 10mV compared to 20mV).

The power supply is cleaner because my ground connection is as short as possible so I'm picking up less measurement errors/ background noise I'm guessing.

So I believe that this is just measurement error and the noise is from my probe acting as an antenna and picking up background noise.
If I wanted to measure the genuine noise coming from the voltage reference how can I do this?
The datasheet states 3.5uVpp/V, how can I ensure that I am getting this accuracy (or more realistically, < 1mV noise?
How can I ensure that I am at least getting a reference accurate enough for an ADC resolution of 610uV per bit?


texts: What is the difference between a multiplexed bus and a multi-master bus

texts: The jargon of terms in bus architecture literature is half the difficulty in understanding it. At some places the term 'multiplexed' bus is used while at some other places 'multi-master' bus is used. They both look same to me but maybe they are different in some sense also. How to know what exactly is the meaning of these two terms?


texts: Identify a 320V DC Brushless IC Power MOSFET(?) Driver

texts:
I need some help identifying this IC. It comes from a bladeless fan.

It is presumably a 230V Power MOSFET(?) element connected to the FCM8201 Three-Phase Sine-Wave BLDC Motor Controller.

The thick top traces come from a capacitor connected to the rectified 230V AC.

More photos on the EEVBlog Forum.


texts: How to use solenoid valve with vacuum pump

texts:
I am a software developer working on small pick and place machine. I have bought mini vacuum pump and one solenoid valve. I want to control vacuum pump suction through solenoid so that when from Arduino I turn ON and OFF solenoid I can control vacuum and this way I will be able to pick and place component. But am not sure how to connect vacuum pump with solenoid  so can any one guide me on it, how to connect them.

My solenoid pic operated by 24 V.

Vacuum pump pic operated by 12 V.


texts:
Are there any single chip solutions combining two Wi-Fi interfaces into a single chip?

I want to build a device which creates two Wi-Fi networks: the first is for the communication with a PC, and the second, as a client to the network router.


texts: multistage amplifier design steps/process

texts:
I have a project for one of my classes and it is to design a bjt multistage amplifier. I can use any combination of npn or pnp and any type bias that I choose but I do have a few constraints which are given by the professor which are to use a set input voltage, audio frequency, and power output. I know how to perform the dc/ac analysis, gain, and etcetera of a circuit that is already constructed but I am unsure of how to design a circuit myself to give me the desired output freqency to power the 8ohm speaker for the project. I am looking for guidance on the proper steps of design such as (First do/calculate X), (Second do/calculate Y), (Third do/calculate Z) and so on. I will post the guidlines for the circuit just in case anyone is interested, but I DO NOT want anyone to work the circuit out for me just guidance on how to do it myself.

Audio Amplifier Power Output selection: 3.2 W, 5.6 W, 7.1 W, 8.4 W, 11.5 W, and 16.3 W

Audio Amplifier Input Voltage (peak) selection: 150mVpeak, 200mVpeak, 250mVpeak

Audio Frequency: 20 Hz – 20 KHz


texts:
I have been working mostly with 5V rated MCU but I am venturing into the world of 3.3V rated MCU's.

That should not effect PWM,right?

(PWM is bound to time, not voltage as I understand it)

Any info would be appreciated. Thanks.


texts: DALI : How commissioning process takes place in DALI system?

texts:
I have gone through various documents regarding the Commissioning in the DALI interface. But I finding it difficult to understand some of the points. So if anyone with DALI Commissioning can help me understand the commissioning procedure. I already know this part.

first initialization command is sent.
Then randomize command is sent which will generate 24-bit random address at ballast side.

After this how it assigns the short address to each ballast is out of my knowledge and this is where I am stuck right now. Any help would be much appreciated.


texts:
I'm working on a project where I want to have christmas lights (or LED strips if needed) react to music. In this case, the end goal is to have them pulse to the beats/bass of the music. There's a lot of LED strips that come in kits where there's a microphone that listens to the music but this doesnt work for me for a few reasons- 1) seems cheesy 2) doesnt give me just the bass and 3) I'd prefer a hard-wired solution.

There's a lot of solutions on youtube where people hack in to their speakers and simply power the lights from the signal being sent to the subwoofer in the speaker. This works, but I can only drive a small number of lights this way AND this is also highly dependent on the volume of the music. Another approach is to build a SSR (solid state relay) based circuit like this but the problem here is that i'm not looking to do any high voltage wiring myself (Just an EE student here) due to the fact im not comfortable with it and I don't know anyone who really is.

I thought of the idea to purchase an audio amplifier (Or I guess I could make one with a transistor and POTs) that would normally drive a set of speakers and instead have it drive my lights. I know it would put out a lot of power I wouldnt need, but I can adjust this using the gain controllers on the amp (power efficiency isnt the goal here- overkill is acceptable). Would this even work? Fundamentally I think this would work, but am I missing something? -perhaps resistive load issues


texts: Do I need to place any additional component(s) getween isolated grounds?

texts:
Initially I bothered with this question regarding isolated flyback switch mode power supplies. However I'd be happy to investigate this question dipper.

So as the output of the power supply is isolated from its output - grounds can have widely different potentials which is OK until voltages become dangerous for the isolation strength. Besides the parasitic capacitance can lead to false signals transfer from part to part. If I'd have no additional information for the subject - I'd place a big (1M for example) resistor to let the extra charge flow slowly from the one end to another.

But I realise that this approach can have some drawbacks. I tried to Google for some reading but I did not use correct request nor there are no such articles in the first 10-20 results.

Thank you in advance!


texts: The math and the physics behind POTS phone lines

texts:
Since high school you learn something about Fourier Analysis and you can easily grasp the idea that a given signal that is variable over a given timeframe, is composed of multiple sub-signals with different frequencies.

Lately I learned that POTS lines work, at the same time, with both AC and DC power, the DC signal is used to feed the device, the phone, and the AC signals are the "inputs" from/to the user or the ISP ( dialing, ringtone, dtmf tones ).

This is kinda of a black magic to me, at this point, I really can't grasp how the so called multiplexing of the signal is happening.

It's true that POTS signals typically travel over RJ plugs and separate copper cables, usually there are 4 cables, so things are much simpler in practice since the 2 AC and DC are probably always separated from each other.

In modern times a phone cable also carries a DSL signal, but I'm just going to assume that this is just an "addon" to the several AC signals that a POTS line already delivers.

Anyone can explain the math/physics principles behind the multiplexing of POTS lines or phones and ADSL lines in general ?


texts: Help identifying connectors from an art project

texts:
I am working on getting an art project with poor documentation back into working shape, and as part of that I'd like to identify some of its electrical connectors so I can purchase some interoperable parts. I've looked through image-based catalogs in Digi-Key and tried browsing Molex's catalog without success.

There are two that are giving me trouble at the moment:

5-pin connector

(I recognize that this connector is being used as a 4-pin device…I don't know the original design intent but they likely didn't want this one to be interoperable with the other connector listed.)

5-pin connector side view:

5-pin connector front view:

4-pin connector

4-pin connector side view:

4-pin connector front view:

Any leads (including useful search services) much appreciated!


texts: Does this linear current source driver deliver constant current?

texts:
I was reading on LED driver designs, and I have a question about the linear current source driver. In the circuit below, will D1 ever turn off when there is too much current through R2? In other words, will D1 turn off when Q1 turn on?

Because the base and the drain are driven by the same voltage Vcc, I am assuming Q2 is an N-Channel MOSFET (and not a transistor). And I can see when Q1 is activated, Q2 turning off because the voltage at the node between R1, Q1 and Q2 would be ~0V (GND).

However, there is no mention of this side effect. Ideally, the circuit regulates current in itself without switching off the LED.

Is my assumption false and does this circuit works like a constant current source?


texts: long current return path in star topology of grounding?

texts:
I'm designing a system with a MCU board and multiple peripheral boards.  I chose a star topology for grounding, in other words, the GND pins in each board is connected to the power source.

However, I'm not sure if this is good regarding the signal current return path. For example, in the following figure I have a board that contains a high power LED and a sensor(I2C slave device). Here the signal current should go back to the MCU board through the power source. Is it better to connect the GND pin in the MCU board to the LED&sensor board, which means there is no direct GND wire between the power source and the sensor board. To me it's not clear how to avoid making ground loop and achieve a short current return path at the same time.


texts: MOSFET driver circuit configuration for half bridge MOSFETs for power amplifier

texts:
I am making a class D audio amplifier and I am using a MOSFET driver to control two MOSFETs in a half bridge configuration as shown in the circuit below

When I connected the circuit without the MOSFET half-bridge, I grounded Vs and I got a neat output according to my needs 15 V peak at HO & LO, The problems started when I connected the MOSFETs, The HO & LO terminals started sending out the same signal but with a max voltage of 3 V or  probably less, then the circuit drew around 1 AMP from my voltage source and burned the MOSFET driver chip, I knew for sure that it was burned because the resistance between the VDD terminal and the COM terminal was 26 Ohms instead of the high resistance a new chip had. An engineer in my uni suggested that the problem might be caused because I was providing the 15 volts to the MOSFETs from the same node that supplies the same voltage 15 V to my entire circuit, although my circuit was drawing only 40 milliamps from the power supply before connecting the MOSFETs.

I would like to note that the chip is FAN7390. I have fried two so far. I would guess that the common power supply might be the problem?, or it might be that the switching frequency of 125kHz the problem? The Hin and Lin signals are PWM signals with 15 V peak.


texts: Which comparator type to use as an On/Off switch for a DC motor via FSR (force sensing resistor)

texts:
I want to use an FSR (force sensing resistor) to turn on a 300-350mA (steady state) 4 volt DC motor while one press into the FSR. As the image shows my plan is to have a voltage divider between the FSR and some other resistor such that, once you press into the FSR the voltage in the (-) input terminal increases and it turns the output  of comparator high which in turn turns the mosfet ON driving the DC motor. I have found those comparators(NCS225x) that will work at low voltages (3-5v) and output enough current (about 40mA) do you guys think this setup will work properly? Also, what mosfets would you recommend using for a low side driver of a 3-4v motor?

Data sheet for the comparators: https://www.onsemi.com/pub/Collateral/NCS2250-D.PDF

The difference between NCS2250 and NCS2252 is that the NCS2250 has a "complementary push pull output" while the NCS2252 has an open drain out put. What does that mean in terms of my application? Thanks!


texts:
I am looking at getting a 3 port USB wall charger, to save having so many individual ones plugged in. A lot that I've seen offer Qualcomm FastCharge, and other similar things, which are around 2.4A, or higher.

The chargers that I currently have (which are cheap ones) are alll 1A or less (with the exception of my Lenovo tablet charger, which is 2A). I'm slightly concerned that using such a charger will overload my devices (eg phone), and cause damage to the battery. I have a fairly large powerpack, I think 10Ah, and it says that it should be charged with a 1A current.

Am I right to be concerned?

A very related question is "Choosing power supply, how to get the voltage and current ratings?". It's not a duplicate question, but the answers there provide an answer for this question. The answers to this question given confirm that the answers to the linked question do indeed apply here.


texts:
EDIT: Thanks everyone, I got it to work:

Now if only I could accept multiple answers...

.
.
.

Is the output of this op-amp circuit linear in input voltage? The last equation \$A = \frac{R_f}{R_1}\$ seems to imply the output is linear but when I simulated it in multisim with a sine wave input, the output was either a sine with an amplitude of 0.1V or a square wave with amplitude of 4V for small changes in input amplitude. How can I keep the output linear?

I am trying to amplify a 10µV to 100 µV differential signal to at least 1V using an analog amplifier so that I can measure it using an ADC such as the one on an arduino. Is there an easier way to do this with only a few parts?

Frequency range: 8Hz to 50Hz

The opamp I used in multisim is OP497 (this was the first one I found in the multisim catalog that had a DIP package)

edit: I flipped the op amp and now the output seems linear but the peak to peak output voltage is only 45mV. Shouldn't it be much higher than the input?

Input in simulator: 20Hz sine at 500mV peak, 500mV offset

Screenshot:


texts: Ideal Voltage and Current Sources in series

texts:
For the circuit below determine
  a) the current I,
  b) the voltage \$ V_R \$ and
  c) the voltage \$ V_o \$ across the current source

Note: VR should be V subscript R and the case is the same with Vo.

The diagram above is from a set of lecture notes and the accompanying questions were never covered in class.
I'm been sitting with problem for a while and getting nowhere.

KVL gives
$$
V_o - V_R -24V = o
$$
but from here I'm lost.

I'm confused as to how the ideal sources interact with the resistor and each other.
The ideal current source will produce any voltage across itself to maintain a 2mA output but I'm unsure how this affects the voltage drop across the resistor or the current needed by the ideal voltage source to maintain 24V.


texts: Why is this comparator loading down a voltage divider?

texts:
I just built up a circuit with a LM311P comparator with open collector and emitter (I don't think that's relevant). The negative input is a voltage I create with a voltage divider and the positive input is the signal I want compared.

simulate this circuit – Schematic created using CircuitLab

However it seems like the comparator is heavily loading the voltage divider because the voltage at the negative input looks like this (yellow trace), blue trace is the output signal.

It's fluctuating by almost 2V. And this is after I already made the voltage divider smaller. The fluctuation was even worse with a combined resistance of about 20kOhms. I know I can stabilize it with a big capacitor but I first want to understand where this is coming from. Here is a screenshot from the datasheet of LM311P (http://www.produktinfo.conrad.com/datenblaetter/175000-199999/175994-da-01-en-IC_LM_311P_DIP8_TID.pdf):

The current through the voltage divider is 2.1 mA which is 7000 times as big as the worst case bias current of 300nA.

Am I missing something here? Any help understanding why this is happening would be very appreciated.


texts: C/C++/C# programming for interfacing USB to PIC microcontroller

texts: I am a computer sciences student looking to do some PIC microcontroller programming for some small home projects . I am fluent in C/C++/C#/Java and i also have an understanding of programming microprocessors(ALP - the 8086 ) . I plan on building a USB interface to control some lighting and a motor in one of my projects . I have the circuit components and the layout planned out .  I have the PIC 18f4550 in  mind and I have already downloaded the libraries from the microchip website . The only problem is I don't know what code to write for this .  The libraries are huge and I don't really need to go into all the details(that's what I think) . I tried finding other resources but it appears that the PIC is old and most of the links off of Google have only been dead ends . Does anyone know of a blog , a video , or anything that could help me get started ? I'm hoping it's possible to do this using one of the languages I mentioned above .


texts: Is there a portable alternative to LTspice?

texts:
I am constantly on the move and come across many computers to which I have access and which have some version of Windows installed. I was wondering if there's a portable alternative to LTspice (or if there's a way (a wrapper or something equivalent) by which I can install it on my USB stick and use it anywhere)?

A quick Google search revealed no obvious alternative. There are a few online spice simulators  like circuitlab.com, partsim.com and ngspice.com. But none are too keen to explain their limitations for free use. For instance, I tried reading the terms of service for partsim.com, but that too wasn't very enlightening. I wanted some advice before signing up.


texts:
i'm doing a project with esp32 (3.3v), dht11(3v-5v), soil sensor (3.3v-5v the cheapest Chinese), nrf24l01 (2.6 - 3.6v). I'm using lifepo4 right now (3.32v) but when the battery drop about 3v, soil sensor won't work.

So I'm gonna use lipo 18650 4.2 max, then use step down LM2596 to regulate at 3.3v.
My question is, when i connect battery to 4.2v,2.6Ah --> LM2596 --> 3.3v. do I receive 2.6A at output too? I mean is it always drain 2.6A? or it just drains Operating quiescent current: 5mA.

Sorry if this is a noob question


texts:
There's been a lot of soft-latched power switch circuits discussed here and elsewhere on the internet. However, I can't wrap my head around how to implement the following requirements:

Battery powered (Lipo voltage range, LDO is used for noise reasons, device will measure in the millivolt range)
Push to turn on (short hold to turn on would be acceptable too)
While on, register button presses from MCU to handle soft power off
Way for MCU to power system off
Hold to force system off in case micro hangs

That last point is rather important as this circuit will go into a device where it would be very inconvenient/impossible for the user to disconnect the battery.


texts:
Suppose I have 512 leds in a 16 by 32 grid.  I want to control what is displayed on the grid.

To do this suppose I have a timer counter that is constantly counting between 0 and 31 in binary.  This timer is hooked up to 2 things.  The first is a decoder so that one column of the LEDs is "activated".

The second is a kind or RAM (I don't know what to call it), which has 16 bit words and 64 addresses.  The timer is hooked up to the bottom 5 bits of the addressing system of the ram, and the LED grid is hooked up to the outputs.

The Micro controller is then hooked up to the top address bit so that this system can have two separate memories to grab data.  One is active while the micro writes to the other memory locations.

Here is a simplified schematic (obviously I will have transistors and what not where needed):

My question is: What can I use for the RAM memory? And what is it called?

Some requirements:

Can be read at 32kHz
Has at least 64 words with a word size of at least 16 bits
Can be writable while still reading other memory addresses


texts: I am trying to understand the Vgs threshold on this datasheet. it says that the maximum is 1.45v but I have switched with 3.3 from a microcontroller. am i damaging the mosfet using this voltage?


texts:
I have prototyped a connected object with arduino and I would like to go for mass production, actually just a few hundreds to start.

I'm going to design a customed PCB with everything integrated: this is for the hardware part.

My question here is about the software part.

Ideally, I would like to keep the same code for my final product as in my current prototype.

It looks like it is something that is not advised. Why ? Can I ask a manufacturer to put a pre-programmed atmega providing my arduino code ?

Thanks.


texts: Relationship between input and output voltage on a complex inverting integrator circuit

texts:
I am on my first semester of electrical engineering and I came upon an exercise where in the given circuit I have to calculate the relationship between the input and output voltages of the op-amp.

After some searching I found that the given circuit is an inverting integrator. In wikipedia it states that the relationship between the input and output voltage is:$${\displaystyle V_{\text{out}}(t_{1})=V_{\text{out}}(t_{0})-{\frac {1}{R_{\text{i}}C_{\text{f}}}}\int _{t_{0}}^{t_{1}}V_{\text{in}}(t)\,dt.}$$

So I tried to solve it myself.
I started with a 1st Kirchoff's law equation which came out as:
$$I=I_1+I_2$$
then I substituted using Ohm's law:
$$\frac{V_{in}}{R_1}=\frac{V_{out}}{R_2}+I_2 \space \space (1)$$
For the last current I used:
$$Q=C_2V \rightarrow Q'=C_2 V'$$
and because $$Q'=I_2 \space and \space V'=V_{out}'$$ it resulted in
$$I_2 = C_2 V_{out}$$
Then through substitution in the first equation I found:
$$V_{out}'= -\frac{V_{out}}{R_2C_2}+\frac{V_{in}}{R_1C_2}$$
At this point I thought I would integrate and find the result given by wikipedia but I can't seem to work it out and I think I've made a mistake in my calculations.The last equation seems to me like a differential one which unfortunately I don't know how to solve. I also have my doubts about this circuit being an inverting integrator because of the existence of capacitor C1, that I did not take into consideration. Any help on what's wrong would be greatly appreciated. Please excuse my ignorance and/or any mistakes.


texts: How did the Motorola 68000 handle instructions on 32-bit data?

texts:
The Motorola 68k, despite its 16-bit external bus, had 32-bit data and address registers, with support for .L-width instructions over four bytes -- which is 32 bits in this case.

I figure that this would be done in the space of two cycles, but I'd like to know some details about how this is executed; specifically, things like:

Data load order
Whether externally-loaded data is staged in some intermediate storage before the instruction that requested it is executed
Whether there's even a general execution model for 32-bit data on the 68k, or whether the execution model differs between instructions


texts: How does this heavily oxidized copper-to-steel joint work in earthing?

texts:
Wikipedia article on grounding features this photo:

Here's a close-up of the joint:

Clearly the steel rod is heavily oxidized and the copper wire is oxidized. The clamp is coated with something like zinc and is not oxidized.

How does a joint of an oxidized copper wire to the clamp and from the clamp to the oxidized steel rod provide conductivity that is good enough for grounding?


texts: Operational Amplifier Single Supply Negative Output

texts:
I've built a comparator circuit that I want to use to drive a PMOS transistor. I only need negative output, but I'm on a single 12V/24V battery supply. I know I can create a virtual ground and split the supply, but since I only need negative output or 0 output is there a way to accomplish this without splitting the supply?

What would happen if I were to ground the V+ terminal and apply the battery positive to the V- terminal? In simulation this seems to work, but I haven't seen any information about it so I'm not sure what to do. I'm using an OPA454 TI operational amplifier (I know it's overkill for a PMOS, but the comparator I ordered (LM211QD) isn't in yet.


texts: Why does my current in parallel circuit not add up when I check using a multimeter?

texts:
I have a simple circuit 9v connected to 3K resistor coneected to a wire. On this wire, I have two LED's connected in parallel, both leading straight to ground.

When I check insert my multimeter between the positive and resistor I get around 2.54 mA.

When I insert my multimeter between LED 1 and Ground, I get around 1.12

When I insert my multimeter between LED 2 and Ground, I get around 1.06

I'm off by around 30-40mA.

Is this acceptable and/or normal OR is multimeter broken?

I already checked the fuses, and they're not broken, as far as continuity checking is concerned.

I also replaced the batteries.

Update:

The discrepancy seems to be less when I use resistors in place of LEDs. Does the multimeter change shunt resistor when using an LED?

when using LEDs in parallel, my current is off by 20-40% if I will base it on the source current and divide that by number of branches.

but when I use resistors in place of LED, my current is off by less than 5%

Is it simply the shunt resistor or is my LED doing something I'm not aware of?


texts: Using a PIC12F675 to generate a PWM signal using Timer0 and Timer1 interrupts

texts:
I would like to generate a PWM signal using Timer0 and Timer1 interrupts.
The reason for using Timer0 interrupt is adjusting the frequency and the reason for using Timer1 interrupt is a adjusting stop (off time).
I wrote the ISR for that in mikroC.
Can you help me?

void interrupt(){
  if(INTCON.T0IF){
    tmr0=122;
    tmr1l=122;
    tmr1h=0; //NOT USING TİMER1 H BİT
    INTCON.T0IF=0;
  }
  if(PIR1.TMR1IF){
  GPIO.B0=0;
  PIR1.TMR1IF=0;
  }
}


texts: Problems with voltage supply in Altium IBIS simulation

texts:
I have a question regarding my project. I am designing high speed output from my microcontroller.

Switching times should be around 450 MHz, so I found IBIS model for my microcontroller and line driver, but when I have simulated reflections, the voltage level is wrong. It is 5V but should be 3.3V instead.

I changed all voltage range of the pins to 3.3V, but it still doesn't work.

Can someone tell me what am I doing wrong?


texts: Discrepancy in output of post PAR simulation and bit file output

texts:
I am using Xilinx ISE to generate a bit file. I verified the functionality by post synthesis as well as post Place and route simulation . But when same bit file was loaded in FPGA there was a zero stuck output ie no output at all . The FPGA outputwas verified on desktop PC screen using Chip scope pro. Kindly suggest me some ideas about how to deal with this problem.

Shalini


texts: How to determine the right trip point of thermal cutoff for 1/4 hp 3A 115V single phase ac motor

texts:
The Thermal fuse blew in my Ryobi DP102L drill press motor, while I was drum sanding. There were no markings on the fuse. The single phase induction motor is 1/4hp 3A (no load) 1750rpm on 115V AC, according to the manual. There's no name plate or information available from Ryobi. Comparing it to similar drill press motors online, it's probably Class A insulation, but that's a guess.

I want to replace the fuse with a thermostat type cutoff which will reset so I don't have to tear the motor down again. The temperature rating for Class A is 105degC. The device I'm considering is a CanTherm T22, which comes in a variety of trip points which match the different NEMA classes.

Research online yielded only two results for this specific question. One suggested 25% above the rated temperature. Another, which was an article about thermistors, suggested 10%. The trick of course is to have the thermostat remain closed under normal operating conditions, but trip if I push things too hard (like drum sanding at too slow a speed) then reset when things cool off.

If I understand correctly, I don't want the thermostat to trip right at the rated temperature like this one : T22A10505DFFBG0E. But slightly above like this one: T22A12005DFFBG0E. See full list here: CanTherm T22

Does the device I'm choosing makes sense? Are there other considerations? Are there any issues with the current capability of the T22 which is much higher than the required 3A of the motor?

Thanks.


texts: Regulations (if any) for using electronic devices built by myself in my house

texts:
Are there any rules and regulations for using electronic devices built by a user in his own house in the UK?

Like for example, if I build a DMX control system (from scratch - i.e. PCB and enclosures etc) to control my lights in my home, do I have to comply to any regulations like the big companies do?


texts: Flexible flat cable AWM 20798 female connector? (16 pin/1mm pitch)

texts: Where can I buy a female connector for a AWM ribbon flex cable 1.00 mm pitch 16 pin. Its about 17.00 mm wide. I need this for connecting this cable to a patch panel with 2.54 mm spacing.


texts:
I am trying to build a small battery powered device containing a servo. I would like to be able to turn off the servo to save battery life. I have read previously that MOSFETs can be used to do this, but I am having trouble finding example circuits that are detailed enough (missing resistor values with no way to calculate them) and to be honest I am not too sure what sort of circuit I am looking for (I have never used any FETs before). Can someone please give me a nudge in the right direction?

potentially relevant info:

code running on a mega88 @ 3.3V
4.8-6V servo connected straight into the 6V battery pack (I would like to change this)


texts: AXI SPI of MicroBlaze connected to SD card

texts:
I would like to connect SPI IP core of microblaze on custom board but I have some problem.
I need 100-400 KHZ clock but the system clk is 100MHz and SPI Clock is 6.25 MHz.
Is it necessary to reduce clk frequency for initialization?

I just send CMD0 to reset,I would like to check the write and read buffer to see tranfering of command is correct,but I couldn't get a correct result.

IS anybody can help me ?


texts:
I'm designing the power circuit for the \$V_{BAT}\$ portion of an STM32 microcontroller, using a supercap to hold the charge when the main is off.

I was calculating which resistor I should charge the supercap through, but I stumbled on the  specifications:

What is the meaning of the MAX current at 30 min. column ? It does not seem to be the absolute maximum rating.

The capacitor charging current will drop exponentially, but I don't know from these specifications if it can withstand 150mA for 10-20 seconds when charging the capacitor from 0V.

The capacitor case is can-like with a diameter of ~17mm, and the specs does not specify power ratings for the case.


texts: Trouble shooting stand up florescent lamp with a 4 pin connector

texts:
I have a florscent stand up light and it stopped working.  My assumption was the bulb burned out.  I replaced the bulb and it still isn't working.
I tested the bulb (F552D/830) with the ohms meter and get 1.9 on both sides.
It appears the new bulb is working.
Then I tested the wall outlet and that appears to be working - I did move the lamp to the kitchen to a known working outlet.  My multi meter set to 20 in the V~ section I get .37 when the lamp is turned on and .27 when the lamp is turned off.  Looking at the plastic base it says amps 8.5 and wattage 58.   the lamp has a dimmer switch and the .37 number doesn't change as I rotate the dimmer switch.
The fixture is a single molded piece of plastic so without breaking it, i can't get to the insides to test any other pieces.  Any ideas what else I can test or try?
I tired posting pictures but they are to big for the website.
Thank you


texts:
I am having an issue trying to get Input capture to work on one of the stm32f373 pins (PB0, TIM3 CH2 ). The reason why i'm stuck with this pin is because m doing this on my own personalized board with stm32f373rbt6. The rest of the pins are either taken or dont have corresponding functionality attached to them. I'm certain that the pcb is fine and traces are fine (did a continuity check from the source to the pin). On stm32f373rbt6, PB0 could also be configured as an analog input for the built in sigma-delta ADC module. But since my project does not require any adc i havent even touched or configured it anywhere in my code. Below is the code and the corresponding IRQ Handler.

Please do let me know if you find any configuration errors.

RCC_AHBPeriphClockCmd(RCC_AHBPeriph_GPIOA,ENABLE);
RCC_AHBPeriphClockCmd(RCC_AHBPeriph_GPIOB,ENABLE);
RCC_APB1PeriphClockCmd(RCC_APB1Periph_TIM2,ENABLE);
RCC_APB1PeriphClockCmd(RCC_APB1Periph_TIM3,ENABLE);

GPIO_InitTypeDef GPIO_InitStructure;
GPIO_InitStructure.GPIO_Pin=GPIO_Pin_5;
GPIO_InitStructure.GPIO_Mode=GPIO_Mode_AF;
GPIO_InitStructure.GPIO_Speed=GPIO_Speed_50MHz;
GPIO_PinAFConfig(GPIOA,GPIO_PinSource5,GPIO_AF_1);
GPIO_Init(GPIOA,&GPIO_InitStructure);

GPIO_InitStructure.GPIO_Pin=GPIO_Pin_0;
GPIO_PinAFConfig(GPIOB,GPIO_PinSource0,GPIO_AF_2);
GPIO_Init(GPIOB,&GPIO_InitStructure);

TIM_ICInitTypeDef TIM_ICInitStruct;
TIM_ICInitStruct.TIM_Channel=TIM_Channel_1;
TIM_ICInitStruct.TIM_ICPolarity=TIM_ICPolarity_Rising;
TIM_ICInitStruct.TIM_ICPrescaler=TIM_ICPSC_DIV1;
TIM_ICInitStruct.TIM_ICFilter=0x0;
TIM_ICInitStruct.TIM_ICSelection=TIM_ICSelection_DirectTI;

TIM_ICInit(TIM2,&TIM_ICInitStruct);
TIM2->CCER |= TIM_CCER_CC1E;

TIM_ICInitStruct.TIM_Channel=TIM_Channel_2;
TIM_ICInitStruct.TIM_ICPolarity=TIM_ICPolarity_Rising;
TIM_ICInitStruct.TIM_ICSelection=TIM_ICSelection_DirectTI;
TIM_ICInit(TIM3,&TIM_ICInitStruct);
TIM3->CCER |= TIM_CCER_CC2E;

TIM_Cmd(TIM3,ENABLE);
TIM_Cmd(TIM2,ENABLE);

NVIC_InitTypeDef NVIC_InitStructure;
NVIC_InitStructure.NVIC_IRQChannel = TIM2_IRQn;
NVIC_InitStructure.NVIC_IRQChannelPreemptionPriority = 0;
NVIC_InitStructure.NVIC_IRQChannelSubPriority = 1;
NVIC_InitStructure.NVIC_IRQChannelCmd = ENABLE;
NVIC_Init(&NVIC_InitStructure);

NVIC_InitStructure.NVIC_IRQChannel = TIM3_IRQn;
NVIC_Init(&NVIC_InitStructure);

TIM_ITConfig(TIM2,TIM_IT_CC1,ENABLE);
TIM_ITConfig(TIM3,TIM_IT_CC2 ,ENABLE);

void TIM3_IRQHandler(void){
__disable_irq();
++capture;
GPIOE->ODR ^=GPIO_Pin_9;
if((TIM3->SR & TIM_SR_CC2IF))
{
    GPIOE->ODR ^=GPIO_Pin_9;
    TIM3->SR=(uint16_t)~TIM_SR_CC2IF;
}
EncoderFreqQuery(TIM3,&RightFreq);
__enable_irq();
}


texts: STM32f103 NRF24L01 Communication Problem

texts:
I am trying to apply communication between two stm32f103c8t6 with NRF24L01 modules. And using uart with usb to ttl module to reach putty terminal. I am using KEIL and for generating code CUBEMX. Here my while loop:

 uint8_t CTR_RXBUFF[32];
 while (1)
 {

    if (CTR_nrfGetPacket(CTR_RXBUFF)==1){
        HAL_GPIO_WritePin(GPIOC,GPIO_PIN_13,GPIO_PIN_SET);
        printf("Received package: ");
        HAL_UART_Transmit(&huart1, CTR_RXBUFF, 32,1000);
        memset(CTR_RXBUFF,0x00,32);
        CTR_nrfSetRX();

    } else {

        printf("Cannot get any package \r\n");
        HAL_GPIO_WritePin(GPIOC,GPIO_PIN_13,GPIO_PIN_RESET);
        HAL_Delay(1000);
    }
    HAL_Delay(1000);
   }

Now here I tried to connect stm32 without nrf24 and putty terminal says:

"Received package: (some nonsense symbols)"

And if I try it with NRF24 connected then putty terminal says:

"Cannot get any package"

I took the code from here
Any suggestions please. Thanks a lot for reading.


texts: Timer interrupt priority over TCPSocket Callbacks

texts:
I have a Timer Interrupt Routine which runs periodically (1000/sec). I plan on using mbed's TCPSocket  to receive incoming messages. For obvious reasons, this should not block.

It is essential that Timer Interrupt Routine takes priority over the TCPSocket Callback. How can I ensure this?

I suspect that this won't be a problem if the time taken to receive + time taken to run timer interrupt routine is less than 1/1000th sec. Is this correct?

I realise it's hard to estimate, but considering each "message" contains only 12 bytes, approximately how long would recv() take to transfer the data into a buffer? Microseconds?


texts: Can I create a multiplexed array of IR photodiodes?

texts:
I'd like to use an Arduino to read from a large number of IR photodiodes. I have seen this question: How to Use SFH235 IR Photodiode Correctly? and would like to use a similar technique to the circuit on the left:

However, I'm not just trying to read from one photodiode. I have a large number of photodiodes arranged in a grid. I would like to be able to read from this grid with the simplest possible wiring scheme. I thought that it might be possible to use a scheme similar to what is often used for grids of LEDs:

D1,2,3 represent digital pins. I would operate this by setting e.g. D1 to output LOW, and the other two to high impedance. My hope is that this essentially "disables" the second and third column of photodiodes (since their anodes are effectively disconnected), and I could use the ADCs to read only the first column. Then I would toggle the digital pins to activate the second column, then the third, etc.

Will this work? I was originally concerned that the high-impedance state of the Arduino would be too leaky, but this link suggests that it's equivalent to a 100 Mohm resistor.

Aside: I'm an amateur, I don't really have a good grasp on the behaviour of photodiodes, so I find it difficult to reason about situations like this. I also had trouble finding SPICE models for photodiodes, so I couldn't really simulate this setup. Does anyone have pointers to approachable introductory resources for photodiodes, or SPICE models?


texts: Why should we set input source equal zero for calculating output resistance of common source amplifier?

texts:
This lecture (page 10) gave derivation of common source output resistance.

What I don't quite get here is why we should set the input source equal 0 for calculating output resistance.

Could anyone explain that?


texts: Issue with SD Card Initialization via SPI: No CMD0 Response

texts:
I am working on a project to read files off of SD cards with an xmega128a4u via SPI.
I noticed that some cards initialize without an issue. However, I have two cards that just wont.

As far as I can tell, I am using the prescribed method of initialization for SPI communication:

Assert the CS line
Send at least 74 clock pulses (I's sending 80) at 100kHz to 400kHz (I'm at roughly 250kHz).
Deassert the CS line
Send CMD0 with 0x00000000 as the arg and 0x95 as the CRC
Wait for a 0x01 response (or something other than 0xFF).

I have 5 Micro SD cards: 2 x 2GB, 1 x 4GB, 1 x 16GB, and 1 x64GB. I am having issues with only the 2GB cards (they are the same brand). Both never return anything but 0xFF. Even if I retry multiple times or poll indefinitely for something other than 0xFF.

I have ensured that they are FAT formatted and do work in multiple other devices.
I have also verified, via a scope and a logic analyzer, that the expected signals are being sent with the right timing.

So the question is why? Is there a possibility that these cards just will not work with SPI? Or maybe there's another slightly different process to try with some cards?

Any info would help.
P.S., I'm not using FatFs (or Petit) because I need something event further stripped down a purposefully made, and I'm also trying to learn.


texts:
In the Whetstone bridge circuit:

If the circuit is balanced (and all resistances known), and we measure Vg as a function of time, then the fluctuations correspond to $$4K_bTR$$ the well-known thermal fluctuations. My question: what should be used for R here?


texts: how can i understand when a stepper motor get a complete round?

texts:
i have just get out from an old printer a stepper motor and i'm experimenting with it and arduino and easydriver board.
the motors has 4 pin and 8 magnets. i can drive it correctly: i run it and change direction.
but now i just wondering the best solution to understand when it makes a complete round.

i've done a simple circuit: with a button i get it moving, when i press the button i reset a counter, when the button is pressed the counter is incrementing and then i realease the button the counter is saved. then i print the counter: more or less it is near 1600. this is empiric and for now it works. but: how to find out a precise value?


texts: How do i measure -50 v to 50 v using At-mega micro-controller

texts:
I am working on a project where i require to measure -50 v to 50 v using At-mega micro controller(10 Bit ADC). I have tried voltage divider circuit for the positive side of the voltage range which works fine. ADC doesn't measure input voltage below 0 volts. i have done some research online and lot of people suggesting to use OP-AMP for it. can anyone suggest the best way to solve this problem.

Thanks


texts: How To Add Or Create 2 Pole 6 Position Rotary Switch In Proteus Or Any SPICE

texts: For my design I need a 2x6 rotary switch. I would really love to use the auto PCB design feature of PROTEUS since I ran my simulation there but there is'nt a 2x6 rotary switch in PROTEUS library. Should I create one on my own? That would leave me with no PCB print which would be useless. I tried to find an external library but I could'nt.


texts:
I am trying to integrate with Raspberry Pi (RPI) and VC707 (FPGA board from Xilinx).

VC707 has two GPIO SMA ports but it's input voltage is 1.8V according to manual.

As output voltage of RPI is 3.3V, I need to shift the voltage from 3.3V to 1.8V.

Or can I use FMC Cards for FPGA to communicate with other devices?

Any idea will be helpful.

Thank you.


texts: Project containing different components with audio problems

texts:
I am creating a project where I have a speaker that starts playing music as soon as movement is detected. When movement is detected a ledstrip also turns on to illuminate the room.
The project consists of the following main parts:

12 volt power supply
The power supply powers the arduino led controller and the amp board with speaker
Arduino led controller
Consists of a prototype board with an arduino nano that drives the ledstrip through mosfets. It also contains an IR sensor and radar sensor for detecting movement.
The arduino has a serial connection (only transmitting currently done with voltage divider) with the rpi so it can send a message when movement is detected so the rpi can play or pause the music.
The arduino and RPI are grounded.
Raspberry Pi Zero
Volumio image is installed on the SD card. I switched gpio pin mapping so I have audio an arduino signal coming out of gpio pins.
The pins are connected with a twisted wire to the amp.
The rpi and amp are grounded to each other because both are connected with a ground wire to the prototype board.
Amp board with speaker
The amp board is connected to the prototype board of the arduino led controller that is powered by the power supply.

Currently my setups works but I come across a couple of problems.

Problem 1:
When led strip is turned on I hear some weird sine wave like noise (depends on the color) when no music is playing

My thought: I think the ledstrip is generating noise on the ground line.
    I have seen some component like a dc/dc isolator on other projects on youtube regarding amplifiers in combination with other components from the same power supply.
    Could this resolve the problem and where to place this in the circuit?

Problem 2:
The rpi and the arduino should always be on, but I am not sure if I want that to be the case for the amplifier. I was thinking turning it on or off with a relay when the rpi receives signal to start playing or pausing audio.
The problem is everytime I turn on the power to the circuit I hear a pop from the speaker. This would be annoying to hear the pop everytime when movement is detected and music starts playing.
Is there a way to solve this issue or doesn't it matter that the amp and speaker are always powered?
Problem 3:
When no music is playing I still have some quiet buzzing sound coming from the speaker. Currently there is only 2 twisted wires without ground going from the RPI to the amp as audio input.
This was because I thought the RPI is already ground through the ground wire for the serial connection with the arduino, in which the arduino prototype board has a ground connection to the amp.
Is it better to make 3 twister wires (with ground) from rpi to the arduino and will that reduce the noise further?

I don't have a overview circuit diagram for the wiring but if it helps I can create one. Improvements are always welcome!

Here are pictures:


texts: Standard PCB input / output connectors/technique?

texts:
I'm designing my first PCB but I'm a bit stuck on how I'm going to use it.

At the moment my design is on breadboard with a single input and output.

I want to use my PCB as like a little module where I can just put a input wire into it. Also how I would connect up power and found etc.

I thought of using a row of female jumper connectors just like the black strips on an arduino and then I can just insert the wire inputs into the headers. However it seems like its not such a standard component and farnell and rs don't stock the jumper.

So it got me thinking what is the commonly used connector or method just for simple input and output.


texts: How to find an MCU with specific characteristics?

texts: I am trying to find an MCU in which there are some specific requirements for I/O peripherals (such as UARTs, SPI, I2C, etc). I also want to be able to search by the footprint size. Should I go to each popular MCU website and search from their selection list or is there any other possible way to do that?


texts: How to use 555 timers to control 2 relays

texts:
I'm looking for a way to do the following:

Once triggered, the circuit will

close the first relay (R1) for 10 seconds, then open
then close the second relay (R2) for 10 seconds, then open
have a pause of 60 seconds until it can be retriggered.


texts:
In this image on Wikipedia
https://en.m.wikipedia.org/wiki/File:SPI_three_slaves.svg
The connections are called 'lines'.
In a book I'm reading right now, these are called 'nets' in a similar context.
Are there any differences or are they just two terms for the same thing?


texts:
I formed a startup business six months ago. The first product has been designed consisting of a PCB, some firmware, verification tests, and some supporting PC-based application software. The first prototype is ready for commercialism. Therefore I am looking to add a team to help bring this to market and to further build this venture.

To do this I am looking for ways to collaborate with these new team members, some of which are located all around the country in different time zones. The team will be expanding from just embedded design to include: mechanical designs for enclosures, website design, and business and marketing development. I have looked at a dozen or so web-based tools. Many charge a monthly or annual fee and start you off with a crippled free starter site.

I am not looking for recommendations here in this post. These are easy to find via Google. What I am looking for is useful comments from engineers who have used collaboration tools in the past. I'm looking for something more extensive than just GitHub. This startup is based on embedded products so comments from working hardware and software engineers are very important.

What features did you like?
Did the team welcome it's use, or did interest wane as the project moved on?
What features were missing and you wish were included?
Which features were too complicated or could be simplified?
How were files shared and stored? Or did you just use something like Dropbox?
What would you use in your next project?

I welcome any comments on your experiences with collaboration tools? Maybe this post will start a dialog useful to other embedded engineers. Thanks to readers of this posting.


texts: Filter high-frequency PWM but keep low-frequency modulation

texts:
I have a simple circuit that drive a LED:

simulate this circuit – Schematic created using CircuitLab

The input PWM is created as follow:

base frequency: 200 kHz
PWM duty-cycle: 0..100% (to change light intensity)
low freq modulation: 10 Hz..10 kHz

I mean, the low frequency modulation turn on and off the PWM signal.
I'm looking for a way to filter out the 200 kHz base frequency, leaving the low frequency modulation there.

In other works, the PWM duty-cycle should be "levelled" ( = filtered) to obtain a constant DC voltage to drive the LED when it's active. I tried to put a capacitor in parallel to the led but I don't know if it's the best place to put it.

Increasing the capacity will filter a bit the 200 kHz but also "levels-out" the low-frequency modulation.

Is that position the best one?
Is the x20 PWM base frequency enough to easily filter that and only that?


texts: How can a device like the ETP BD-10A pass electrical safety testing?

texts:
http://www.electrotechnicproducts.com/vacuum-leak-and-holiday-detectors/?sort=bestselling

The device produces output exceeding 55kV in short pulses. The current while claimed to be low by the manufacturer, measures three to four amps in pulses of about 100nS every time the device fires.  I measured this with a Tektronix current probe and oscilloscope.  They may be intending to say that the AVERAGE output current is low.

The electrode tips that they sell have an air gap insulator section which insulates the low voltages (110 or 220V) from the tip but passes the high voltage sparks with little loss.

The high voltage output is required for it to function in its intended application.

The manufacturer does not seem to have UL or CE claimed anywhere.

Also, how would you test the safety of this device, and what standards would apply?


texts:
I'm trying to make a logic circuit simulation in Python. Currently i'm implementing a full adder. What bothers me is logic gates truth tables. I found out a full adder logic circuit schema:

and comparing it with truth tables found on wikipedia article:

http://en.wikipedia.org/wiki/Adder_%28electronics%29

Let's say this full adder gate have inputs: A = 1, B = 0 and Cin = 0. According to wikipedia article truth tables, the first HA (Half Adder) will output S = 1 and C = 0 (A and B are inputs). The second HA would have inputs Cin = 0 and the first's HA S = 1 which will again output S = 1 and C = 0. The OR gate will have two C = 0 inputs, which will of course output 0. So, the final answer should be Cout = 1, S = 0.

But wikipedia truth table for full adder says if A = 1, B = 0, Cin = 0, outputs are Cout = 0, S = 1.

Where am I making mistake?

Thanks.


texts: How do phototransistor and photodiode work in multisim ? How can one cause the photodiode to trigger the phototransistor?

texts: I would like to design this circuit shown in the picture. I have simulated it in Multisim. It functions as follows: When the switch is open, the phototransistor is high impedance, when the switch is closed it is low impedance. I wonder how to input this into Multisim. I would like to adjust current on phototransistor according to distance between photodiode and phototransistor. For example: if the distance is 1 metre, current on phototransistor is 10 mA; if distance is 2 m current on phototransistor is 4 mA. I have not found out how to do this in Multisim. Do you know how to do it in Multisim or do you know other software where this is possible?


texts: N MOSFET bi-directional level shifter draining Vcc possible?

texts:
I'm not a specialist in analogue electronics, so my question can be a very simple for someone to answer.

I have a  bi-directional level shifter built with N-channel MOSFET as on picture below. It will pull down HV1 when LV1 pulled down, as HV1 is pulled up via R4 resistor.

My question is: what will happen if HV1 is connected to Vcc, for example +5V? If I pull down LV1, will it result in shortcut with my MOSFET blowing up? If it will result in shortcut what I can do to protect against it? Shall I use a resistor to pull down LV1, so it will limit current flow in case HV1 can't be drained?

Just to clarify, from schematic perspective it will be unknown if HV1 is connected to Vcc, or just pulled up.


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We have an 8-bit register called CL on x86 CPU architecture.

Does it mean that physically it contain 32 bits, but we have access only to lower 8 bits?
Or does this register physically have only 8 bits?

So in general my question is: Are all the registers physically have the same size (say 32 bits) or not?


texts: Find transfer function from state space representation

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The following system is given : $$\dot{\bar x}=\begin{bmatrix}0&1&0&0\\-1&-2&0&0\\0&0&0&1\\0&0&0&-3 \end{bmatrix}\bar x+\begin{bmatrix}0&0\\-1&0\\0&0\\0&3\end{bmatrix}\begin{bmatrix}u_1\\u_2\end{bmatrix}=A\bar x+B\bar u\\$$

$$y=\begin{bmatrix}1&1&0&1\end{bmatrix}\bar x$$

After calculations I found $$Y(s)=\frac{-U_1(s)}{(s+1)}+\frac{3U_2(s)}{s+3}$$

The problem follows: Let $$\bar u=\begin{bmatrix}1&1\end{bmatrix}\begin{bmatrix}u_1\\u_2\end{bmatrix}+\bar r$$

Now how do I find $$\frac{Y(s)}{R(s)}$$ How does my transfer function change? Will it still depend on U1 and U2?


texts: USB ground wire -- Where does the voltage go?

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I am trying to figure out where exactly the current of the ground wire of a USB 2.0 cable goes?

I am referring to the pin number 4.

I know that normally, the current flowing on the ground wire should be redirected to earth, towards the earth plug on the switch, but this is not always possible. For instance, my phone charger does not have a earth pin. It has only - and + pins. Hence, that makes it impossible to the ground current of the USB cable to go back to earth.

As we can see the USB adapter has no earth pipe. Only - and + .
This leads to me to the question, where the hell does the ground wire voltage go?


texts: How to charge two 18650s in series without a middle connection?

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I have a battery pack of 2 18650 cells in series, so it is possible for me to charge it without connecting anything to the central 3.7v potential point as many answers mention? The battery in question is https://uk.rs-online.com/web/p/lithium-rechargeable-batteries/1449410/, which is sealed and has only 2 wires coming out. This means that I cannot access the central part. I understand that a 7.4v charging circuit is most appropriate, but is it possible for me to implement 2 TP4056 boards in series somehow? I wouldn't be able to do a setup like

simulate this circuit – Schematic created using CircuitLab

given that the grounds would be shorted, and thus so would the second cell. So, does this mean I have to resort to a specialised 7.4v circuit, or could I manage with a 3.7V circuit (that I have 3 spares of with me currently, which is why i want to use it).

Furthermore, the datasheet on Rapid Electronics for that battery pack lists that it has over-charge and over-discharge protection - does this mean I can hook it up to a 8.4V (safe current limit of, say 500mA once near full) bench power supply? This would be even more convenient to charge, but I do not want to damage the battery if this is dangerous.

Many thanks.


texts: Is this internal rearrangement of charges in a circuit a current and is this current different from the “normal” current of the circuit?

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In the figure, the circuit is physically isolated from Earth (The black line at the bottom). The red capacitors are parasitic capacitors.

Under switching conditions the node voltages relative to the zero reference swing in such a way that the internal charge in the circuit stays the same. This is understandable because the circuit is isolated from ground and cannot get more charge or lose any charge. So the charges internally rearrange themselves in a way that leads to the node voltages being what they are.

How is this possible. Is this internal rearrangement of the charges a current? Is this current different from the “normal” current of the circuit (The 1mA)?

I think that Electric fields that change and exist between charged bodies will cause something like current flow, called displacement current, such that a change in the electric field on one body affects the electric field on a nearby body. But how does this affect the 1mA current that appears in the circuit?