texts: MUX Notation A vs B vs Cin vs S notation

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Original video:
https://www.youtube.com/watch?time_continue=76&v=AS17X2rcRKM

http://i.stack.imgur.com/cByOK.png

If A, B, and C_in are all select inputs, then why is C_in labeled differently? What is the distinction? See pic at very top
Later, in a separate problem, I get confused by this notation in another example
http://i.imgur.com/CtlWbTI.png

Is S or Cout the "top decoder"? What "top decoder mean" ? Why do we still have this C notation and is Cout somehow related to Cin? Why distinguish S and Cout with different letters? Shouldn't I just have 2^n Cout outputs?

There's mention of "other outputs" in this pic
http://i.imgur.com/CtlWbTI.png

I only see two total outputs- S and Cout. But there should be 2^n outputs I thought

Later in a totally different example problem in the link below that has answers but no solutions, I get more confused by the C and C bar as two inputs instead of a C_i and it looks we input S1, S0 twice in a row except the bottom time there is an A and a B associated with it. What does this notation mean? See below

http://i.imgur.com/to9WUHR.png


texts: What's the need for a temperature controlled soldering iron?

texts:
I have very little soldering experience - nothing harder than resoldering audio wires in headphones or replacing a mechanical switch on a computer mouse circuit board. I used a plain old unregulated 40 watt soldering iron at all times.

Now turns out there're temperature controlled soldering irons - reading that answer was the first time I heard about them. Which makes me suspect that maybe my prior soldering experience might have been better should I have one of those.

How do I know if I need a temperature controlled iron? What are specific scenarios in which a temperature controlled iron will be advantageous?


texts:
It's been a long time since x86 was introduced (80386 for example was manufactured 27 years ago... Oh god I am old), so I wonder, what is stopping 3rd party companies from manufacturing x86-compatible processors?

Also, I've heard that one cannot patent instruction set architecture, what is patented then which prevents from manufacturing compatible processors?

I can understand that one cannot use Intel or x86 trademarks, but what else?

Update: Does anyone have a link to oldest 'blocking patent' on any x86 tech (486, Pentium) which is still in effect?


texts: What does the 8086 CPU do with the data returned from an address in RAM?

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I understand how a CPU works fairly well, but there is this one thing which I've never really gotten the hang of.
Say we have an Intel 8086 CPU (16 bits wide registers) which is about to fetch its next instruction from RAM (also with a 16 bit data width). As the CPU fetches the instruction, say at 0x44AB, what exactly does RAM return? Is it an 8 bit op-code and an 8-bit operand? Does it return a 16 bit op-code, and then the operand is stored in 0x44AC?
In the first case, operands cannot have a value greater than 0xFF (255), but then why would you have 16-bit registers? In the second case, the program counter must be incremented by two between each instruction, and you use twice as much memory.
So how does this work? The question might seem a bit vague, but all I'm asking is really what the CPU does with the data returned from an address in RAM.
EDIT: Made the question more specific so that it's easier to give a good answer.


texts: what is the current limit through a trace?

texts:
Similar questions and topics have been asked before such as

Standard PCB trace widths?
Formula for voltage drop vs PCB trace width, temperature, current, and trace length

I've used PCB Toolkit in the past and I haven't had practical issues, but I also didn't have more than 1A running through signal traces before. What I'm noticing is that there is a difference between some of the calculators. I'd like to know which set of tools is more trusted.

I understand that there are alot of pictures with information all over the pictures, you can skip to the bottom of this question for a summary of the pictures show if that is easier.

PCB Toolkit

With IPC-2152 modifiers enabled

The general window looks like this

I've played around with the conductor width until I was able to ~2A. My input settings are the following

I believe my fab house starts with 0.5oz base and then plates up.

Here are the results for external layer

Internal layer (I've updated my conductor width to 22 mils)

If I were to change the option from plane present to no plane present, I get a different set of values.

Keeping the settings for the external layer the same, and changing only plane present: no

With IPC-2152 without modifiers enabled

From a question I had asked earlier, Will forced air on PCB improve current capacity of trace? , which seems to indicate that heat dissipation improves current limits, then the presence of the plane helps with cooling and therefore can handle higher currents than without.

CircuitCalculator.com : PCB Trace Width Calculatr

I would have expected that the values to have been similar between the two, but they really are not.

If I were to enter the same values I had entered for the PCB Toolkit (with the exception of the plane present status and base copper and plating copper. I get the following

**Summary**
The following all has a target current of ~2A with a 20C temp rise.
PCB Toolkit with IPC-2152 modifiers           Internal Trace       22 mils
PCB Toolkit with IPC-2152 without modifiers   Internal Trace       55 mils
Circuit Calculator                            Internal Trace       52.6 mils

PCB Toolkit with IPC-2152 modifiers           External Trace       12 mils
PCB Toolkit with IPC-2152 without modifiers   External Trace       36 mils
Circuit Calculator                            External Trace       20.2 mils

So my question is, which is correct because I am also trying to maintain a 50 ohm line if possible ? I'm leaning towards that PCB Toolkit is more accurate, since the online calculator is using IPC-2221A and the website does not appear to have been updated since March 2008 (last blog entry).

In the end, what I am looking for is a smallest external/trace, that can handle 2A without being excessive on copper thickness. Smaller traces make it easier to get 50 ohm line without having to increasing my board thickness.


texts: Shematics: optocoupler controls a transistor and doesn't work as expected

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I'm applying optocoupler TLP521 to decouple microcontroller Atmega88 (on the left of the schematics) from the power circuit.

I have a problem understanding why the schematics below doesn't work in Multisim. The real board also doesn't work. Desirable behavior: if Key A = open then XMM5 and XMM6 = 0, if Key A = closed then XMM5 and XMM6 = 10-12V. Observed behavior: no matter what the I do with key A the output is always the same XMM5 and XMM6 = ~9V

After playing around in Multisim a bit, the following schematics work as expected:

Questions:

Can you explain why the first schematics doesn't work?

What schematics should I use for such application and how to calculate resistors and other parameters?

Do I need some pull-up or pull-down input resistors?

UPDATE:

Based on all the recommendations I tried the schematics below with a real board and it seems to work as expected:

However, I don't understand why on the real board I have 0.8-0.9V on the input side if the input isn't connected to anywhere (check the schematics below). What may be the reason?


texts: How to convert USB 2 device with USB A connector to flippable USB C

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This question has been asked a couple of times, with some interresting answers but I need to go further in depth. My device is a Corsair Void Pro USB. I want to change its USB A connector to a USB C connector, and it must work on all my devices (PC and mobile). The reason for this conversion is that USB A is bulky, so is the USB A to USB C adaptor, and most of my devices have USB C receptacles. Those that don't, I'll just use a minuscule converter (shown below).
I used this specific connector:

I followed this popular Youtube video (and adapted it for my specific connector) and it worked on my Google Pixel Slate. But when using an adapter to convert USB C back to USB A (for my PC), the device worked when the USB C connector was inserted in one way but not the other (i.e. it's not reversible). Here's the adapor:

So I figured I had to wire both the A and the B side of the USB C connector (that required some micro-soldering directly on the connector leads). Now the connector works when inserted both ways in the adaptor. Here's the schematic:

The device works fine on my Pixel Slate, on a Chromebook and on my PC. But not on my phone (Google Pixel 3), no matter the way it's connected! It kind of starts for 2 or 3 seconds on a Google Pixel 1 but then it stops. However, here's a silly cascade of adaptors that just works:
USB C connector -> USB C female to USB A male -> USB A female to USB C male -> Phone

The white adaptor is the one that came with a Google Titan security key set.
Now the question: what's missing from my connector so my device works on my phone? (Or what's so special about Google's USB A to USB C adaptor?)


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I'm trying to design a ground impedance monitor. The idea is that the equipment in question needs to disallow operation if the ground wiring is disconnected or the connection is poor quality.

This is what I have now:

simulate this circuit – Schematic created using CircuitLab

The LED is actually the emitter of an LTV-844S opto-isolator. The blocking diodes are actually S1M (but I figured 1N4004 were similar enough for the purpose).

In testing right now, it takes a ground impedance of ~120 k-ohms to trip the system. That seems like it's way, way too high. My first instinct is to crank up the series resistance, but I'm hard pressed to see how I'm going to wind up with something that's suitably sensitive AND accurate (the spec calls for a trip level of around 12k - 100 ohms per volt), because the impedance level to trip is a tiny fraction of the series resistance, meaning that the series resistors' own tolerances will swamp the desired measurement.

Adding a huge amount of active circuitry is something I would not be happy about doing. At the moment, there is an isolated power supply powering the logic systems, but that power is on the "safe" side of the dividing line - where the detector of the opto-isolator lives. It's not really reasonable to bring that power across the line, because then the two sides won't be galvanically isolated.

EDIT: I've tried to work some more on this circuit, but I'm still not sure I have a good answer yet. There are competing goals at work that frustrate an easy solution. On the one hand, nominal AC voltage may vary anywhere from 100 to 130 VAC (this may need to operate internationally or on poorly regulated power) and the resistors have a 5% tolerance.

My latest attempt changes the series resistance to 240k and adds a 10 volt zener diode reverse biased in series with the opto-isolator. The hope there is that the zener tolerance of 3% being 3% of 10 volts will allow it to possibly "discipline" the relatively sloppy tolerance of the resistors. The idea is that until the voltage across the zener exceeds 10 volts, it won't conduct at all, and the higher the impedance to ground, the lower the voltage across the zener will be.

On the bench, this design appears to work well, but I'd like to hear from folks about this. My worry is that this design works with one set of components but will not be sufficiently reliable when copied.

Note that in the intervening time since I posted this question the actual supply voltage for this test circuit has been moved on the load side of a contactor. If the test fails, the contactor will open, meaning that there will be minimal exposure to dangerous voltages on the chassis when the ground is open.

Anybody have any ideas?


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[
*Violet is the bias voltage. Yellow is the CT output. You can see it drifting from bias volt a little. *

I want to build a power measurement circuit using STM32F407. I am using LM324N opamp for the current transformer. The circuit is working fine. But the issue is when there is no load at the current transformer, it’s drifting form the bias voltage a little around 1.68 to 1.63. And my STM32 detecting that as a load current.

The picture is when there is around 40 A load at current transformer.
BLUE- BIAS VOLT 1.65V YELLOW - CT OUTPUT  RED- 230 VOLT WAVEFORM(Ignore that)

And please tell if there any improvement I can do with the circuit.

simulate this circuit – Schematic created using CircuitLab


texts: I have a color sensor from the original lego mindstorms set. I have had a hard time finding any reliable specs on the thing, but I did find somebody who has reverse engineered it quite a bit here. The thing only has two connectors though. I am not very good at circuits, but I would like to hook this up to my arduino and read values from it. Does this appear possible? If so, do you have any idea which pins to use, or what kind of code I need?


texts: What is used to detect light from fiber optic signals in high speed Internet?

texts: I'm curious, do they use photodiodes or something? As far as I know, that would be the cheapest way to do high speed communications over fiber (fibre? I'm 'murican) but I'm not sure.


texts:
Suppose I power a Peltier device to heat up/cool down some water. Then I later use the same Peltier device, in reverse, to convert the separated heat energy back into electricity.

I have read somewhere that a Peltier device can realistically achieve about 10% efficiency. Since the device is used twice, will I only recover about 1% of my input energy?

I am building a machine and considering the operation mentioned above. If only 1% would be recovered, I should explore other means; If so, then what heat-pumping/electricity-generating options should I consider if I am concerned about efficiency?


texts: Lithium battery consuming more power on Sleep Mode

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I am trying to reduce the power consumption for PIC18F87J11 on sleep mode. The PIC is drawing about .01 mA (6 uA) on sleep mode with Alkaline AAA batteries and other power source, but when I use Lithium batteries the power consumption is higher. It starts low then ramps up all the way to 1.06 mA and remains at that level. I am not quite sure what's different about Lithium batteries that's causing higher current consumption durning sleep mode, maybe someone can shed some lights.

Thanks!

Lithium Battery Specification


texts: LED driver on 74HC164 - need explanation

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I'm building thermometer with long led bargraph (is that correct word?). It will be 60x 0805 LEDs. I want to use low-cost PIC16F1503 microcontroller with just 12 I/O pins.

I have few spare 74HC164 shift registers, so I decided to use them in this project. I was looking for some ideas and I found this 7-segment LED driver:

Original image link

Unfortunately page with description is in chinese or japanese.

Can someone explain how it works in general?

I don't understand why next shift register is connected to last output of previous register.


texts: Significance of bias when driving an LCD

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I've got hold of several bare-glass T218010 LCDs and would like to drive them with a bare MCU (or, rather, an MCU plus a couple latched-output SIPO shift registers such as 74HC595). However, the only useful information I've found on the topic of driving glass-only LCDs is Atmel app-note AVR340, which describes a way of driving a 1/2-bias 4-backplane LCD with logic-level output. The problem with this is that the particular LCDs I happen to have are stated in the datasheet to be 1/3-bias, and I haven't found any useful information on direct-driving those (besides the obvious "buy a driver IC"). Which led me to wonder how big of a problem it really is.

My question, thus, is how significant sticking to the datasheet-specified driving method is and what might happen if one were to violate the specs in that respect. On top of that, any additional knowledge on LCDs, methods of driving them, pointers to useful materials, etc. would be greatly appreciated.


texts:
I would like to know does anyone know how to model the frequency dependent IQ imbalance. The frequency independent model is when gain and phase imbalance are just constant now assume that gain and phase are linearly changing.

The independent case is modeled as

$$\alpha  x(k)+\beta x^*(-k) $$  where \$x^*\$ is the x complex conjugate and \$\alpha\$ and \$\beta\$ are related by cosine and sine relationship.

How can I make the FD IQ imbalance to add it to simulation as a distortion. I know this will happen when the filter in I and Q are different but is there any set of equations like the above case that models the frequency dependent case.


texts: Comparing two hardware accelerators with different number of MAC units

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I am a software engineer but am admittedly a bit of a noob on the device side of things.
I am wondering how to compare two chips. Let's say both chips have hardware accelerator components. Only thing differing between the two chips are # of MAC (multiply-accumulate) units of hardware accelerator components. How would the chip compare, when data flows through the hardware accelerator units, in terms of (1) power consumption (2) memory consumption/bandwidth if need to write data to DRAM (3) latency of computations. This is for the use case of running inferences of a convolutional neural network.
My thought process is following: I am guessing that the one with more MACs will have higher throughput and therefore have lower latency. But power consumption / memory bandwidth may increase since more data flows through in the same amount of time. Overall memory consumption does not change though (since overall data is the same)
Is this a correct analysis or am I going the complete wrong direction?
Any input would greatly help. Thank you so much :)


texts: Output to ground rail on single-supply op-amp with grounded load

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I'm having some problem comprehending the internal functions of op-amps and I'd appreciate any insight in to why my circuit behaves the following way:

I'm working with TI's OPA548 op-amp (PDF datasheet link) in a single-supply non-inverting voltage-follower configuration as shown here:

simulate this circuit – Schematic created using CircuitLab

The datasheet claims "In single-supply operation, the input common-mode range extends below ground." and the table in section 7.5 shows input voltage common mode range to be at least (V-)-0.1V.

For Vin > 0.45V the circuit works fine and the output tracks the input as expected. However, the Vout node never goes below 0.45V, even though I bring Vin to ground. It does not seem to matter whether I have R1 installed or not.

I do get that the op-amp datasheet does not claim rail-to-rail output but figure 13 on page 10 seems to indicate that for miniscule current the negative output should swing all the way to the rail.

My thought is that since the other side of R1 is grounded I'm not really asking the op-amp to pull anything down to the ground rail, I'm just asking it to stop supplying current through the top-portion of the output stage. Since the input range extends below ground I feel the op-amp should be able to "see" that its inverting input is at a higher voltage than its non-inverting input (when it's at ground) and cut off the top transistor.

What is it that I'm missing here? Is there any good way for me to remedy this?

The circuit above I've built on a breadboard but I have the exact same problem with TI's OPA548EVM evaluation module.

Edit: I even tried swapping R1 for a 1Ω resistor, but the output was still 0.27V above the op-amp's negative power suppply rail (ground). This presumably means that the top output transistor is supplying 270mA even though I'm asking the op-amp to lower the output voltage.

I also tried raising V1 to 60V to match the datasheet's Vs = +/-30V condition (should look identical to the op-amp). The result is the same (the voltage difference actually increased to 0.47V).


texts: ESP32 and P-MOSFET controlled voltage divider

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I have a stupid Nubie question that I am hoping someone might be able to answer.  I am wiring an ESP32 with a P-MOSFET for a high level switch to get the voltage of the battery that is powering the board.  I have the following circuit.

I have both the 5V (6.6V max) and ground attached to the ESP32 from the solar battery, and it appears to be running fine. I have attached the GPIO pins from the ESP32 at 2 points, one to control the gate and the other to read the voltage from the divider. When I toggle the Gate GPIO Pin High and LOW, the P-MOSFET never turns on and off, it is always reporting the V3.5 on the analog GPIO like it is stuck grounded.  Everything I have found on the web says this should work, but the IRF954 never closes the gate.  I would really appreciate anyone's advice on this.


texts: How to design a Lithium-Ion battery pack?

texts:
I have a project that I am working on that requires the use of a rechargeable battery pack. The major issue I have is that the battery pack needs to be as slim as possible. So far all I could find are 3.7V single cell lithium-ion batteries. The project draws around 1A MAX or 500mA nominal current at an input voltage of 9 to 12V (anything in that range works).

My design thoughts so far is that I could use three of these batteries wired in series. Additionally, I would like to use this charging IC.

According to the datasheet, it looks like this IC can handle more that one cell, which is exactly what I need. My plan is to use 3 of the cells I listed to achieve the required (minimum) 9V.

My question is, what precautions do I need to take in designing this circuit so that I do not have any explosions. Is this design feasible and are there any options for a slimmer battery pack?

Also, I have read about using boost, buck converters.... How would the use of such converters effect the battery life ext?...

I simply want to explore my best option for this project.


texts: diode and resistor in parallel connected to voltage source

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Can anyone explain the meaning of this circuit?
Why is the resistor connected in parallel to the diode? (obviously they have the same voltage drop), why the diode connected to the voltage source in that way? I guess it's a basic question so bare with me...
Edit: The 3 wire module on the right side is a connector to an external fan. Pin 2 of this connector is connected to 12V (which is not shown).


texts:
I am using a timer interrupt for multiplexing however my question relates more closely to interrupt service routines.

If I set the prescaler and turn on a timer, using the below code I can run code asynchronous to the main loop at a certain interval depending on the prescaler. Or at least this is my understanding of it.

ISR(TIMER1_OVF_vect) {
    //code to run asynchronously at a certain interval
}

Now if for example I set my timer to interrupt every millisecond (16000 cycles on at 16Mhz AVR) and the code I run takes for example 2 milliseconds to execute; is the code completely executed by the second timer interrupt.
That is, does the next timer interrupt depend on the previous one completing and could having slow code slow down an interrupt?

I am using an Atmega328P-PU with an external 16Mhz crystal as clock.


texts: Digital or analog transmission for transmitting data off-board?

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I have some digital sensors with ADC build in and the problem is this type of sensor have lots of control pin. It is hard to separate this sensors from  my mcu board. Analog sensors are much simple but susceptible to noise.

If I want to transmit few channels of analog signal with bandwidth of 3200Hz over a short distance, am I going to face any problem? How to overcome them?

Edit:  Good accuracy is one of my biggest concern. The data is used for scientific research purpose they want to minimize any error. Short distance means about 1 to 2 Meters.


texts: Measuring the resistance of USB car chargers

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I have a few USB chargers that are powered through a 12 V car receptacle. I measured their resistance with a multimeter, applying the probes to the contacts of the 12 V input.

One of the chargers had a resistance of 1 MΩ, another one had on the order of hundreds of kΩ, and one only 1 Ω. Presumably, there is a switching DC-DC converter inside the charger, and on the average, the charger has to consume a bit more power than the power given through the USB ports.

Is measuring the resistance of the circuit in this way useful?
What are typical resistances of step-down converters when measured from the input side?


texts: How would you go about connecting a 555 timer to a circuit with a 16x2 LCD display, which is already connected, to create a digital clock that counts the time? Do you have a sample of how this code would work? I have researched online and found nothing tangible.


texts: I have a 12v 6ah Peltier Mini Fridge will using a 12v 10ah power supply harm the Peltier?

texts: Hi all I have a commercially made mini fridge which displays it power requirements of 12v DC 6ah power supply. I have a 12v DC 10ah smp power supply. Can I use it with the Peltier fridge without harming anything or do I need to put resistor in line to limit the Ah output.


texts: How to design a circuit that the input signal type(positive or negative) can be selected via software configuration

texts:
Firstly, Hello to  all,
I am trying to design a circuit  for automotive application that circuit  will read positive and  negative input signals in the same pin via selecting the type of input in the software. I designed a  prototype circuit to do it.You can see  it in this picture.

I refered a digikey article. Link of the article is here Protecting Inputs in Digital Electronics. When I want to  read positive signal (9 V - 32 V). I will set internal pull-down resistor and input will be active high. When I want to read negative signal (0 V) I will set internal pull-up resistor and  input will be active low. Internal pull-up and pull-down resistor value of the STM32F042C6  vary between 25k to 55k but typical value is 40k. Do you have any recommendation to improve design of the circuit ?

Edited:
If I don't use pull down resistor.While reading positive signal.The capacitor(C1) will not be discharged after I switch(SW1)  from positive signal to floating(not connected) and I will still read it as  a high input.In this picture you can see that the input of the mcu is hanging arround 2.96V when the input not connected and the pull down resistor not selected.Is there any way to solve this problem without using pull down resistor?


texts: Is it possible to power a solar MPPT charge controller from a backup DC power supply?

texts:
I have a solar setup for some computing equipment that is working pretty well for me (most of the time), however it doesn't have quite enough juice to make it through the night on very overcast winter days.

While I could throw more panels and batteries at the problem it would not be economical as I would not be able to utilise that energy >90% of the time.

I have a large unused UPS transformer from a UPS that used to power this equipment and I was wondering if there is anything preventing the possibility of stepping down the 240V AC wall power to around 40V-60V DC using it, and then feeding the charger controller from this.
I would of course connect this in such a way that it cannot operate at the same time as the solar input or back feed into it.

I was also wondering then if a rectification step would still be required for the DC conversion, or would the charge controller be able to handle that step? I would think a charge controller anyway rectifies so probably it is unnecessary but perhaps I am missing something?


texts: SMPS Input Circuit - Formulas resolving diodes, capacitors, voltage, etc

texts:
For fun, I made a project from an old PSU and the parts inside it, and ended up with my new HVDC power supply. Consider this diagram:

Whenever I plug this in to 120 VAC, I measure 350 VDC on the output. I already know that the capacitors and the rectifier, in their setup, double the output voltage well above the input voltage.

Would somebody please take the time to explain the math and formulas involved in this particular circuit, which considers the voltage, capacitance, frequency, etc., so that I can calculate how the measurements influence each other?

Thank you in advance!


texts:
I've recently started to use my laptop more and more on my lap and I'm worried about exposire to radiation emmited by the laptop.
I keep it at a distance of about 10cm but still...

I was wondering if there are any effective ways to build an EMF radiation protection without spending lots of money.

There are commercial solutions like this but nobody sells anything like that in my country and if I order it, with transport fees, customs taxes, etc can get quite expensive.

So what materials can you use (wire mesh, led foil, mylar foil, etc) and how you can arrange them in order to build an effective EMF radiation protection or any harmful radiation coming from a laptop?


texts: Cannot jump-start car directly when I disconnect the dead battery

texts:
So I have a car B with a dead battery and a good functioning car A.
I remove the dead battery from B and connect the terminal directly to car A's battery terminals.

I cannot start car B.  I tried to start car A, and then start car B but to no avail.

Is it because the jump cables I use introduces such a significant resistance that insufficient power reaches the bad car?

I measured the voltage drop across the good battery and the voltage drop across the jumper cables that are connected to the good battery, and they were identical.


texts: Want to convert 14.8v to 5v at Max 30 Amp current draw

texts: I want to convert 14.8v to 5v at Max 30 Amp current draw. IS this possible using resistors?? I don't know that how much current a resistors can draw without any circuit issue. Readymate solution for very small current.


texts: Implementing a voltage sensor with voltage dividing resistors

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I am implementing a power storage system. The voltage of the storage device must be sensed in order to direct current to and from the storage device.

The storage device voltage will vary between 0 and 60 volts, and the system's current will be up to 60 A. The micro-controller operates at 3.3 V.

To map 0 to 60 volts onto 0 to 3.3 volts:
60 V x  10 kΩ / (10 kΩ + 170 kΩ) =   3.33 volts

The current through the resistors is 0.333 mA. (Corrected from original 3.33)

Would this work as expected. Is there something I am neglecting?


texts:
I need a and b value.

a=2;
b=a+=++a;
a+=-b;

  Solution is:
  a=0
  b=6

Why is this the right answer? I know it's simple but I am sure  I'm doing something wrong. Tried so many times to do it that I can't even think.


texts:
I am a beginner hobbyist form Brasil, posting here for the first time.

I am trying to understand the schematic of an old Transglobe radio that my late grandfather gave me. It motivates me to learn more of analog electronics.
After searching the internet for oscillators, it appears to be something like a Colpitts Oscillator, but not quite.

If any of you could tell me what oscillator it is, it would be of great help.

The Signal comes from  T101 and goes to T103, which is the mixer.

From what I understand T102 gives the gain to maintain the oscillation, but where is the Tank circuit?

Where is the feedback? C112 maybe? But from where does it come?

Why is t102's base a constant voltage?

Really appreciate any help! Sorry if it was too much of a beginner's question.


texts: How to model and understand the asymmetry of a parallel RLC circuit spectrum

texts:
I'm working with some parallel RCL circuits and I have noted that when I record a power spectrum (so \$\rm{dB}\$ vs \$\rm{Hz}\$) that the spectrum is asymmetric:

As I'm sure you all know if we calculate the impedance of a parallel RCL circuit

simulate this circuit – Schematic created using CircuitLab

we get
$$ z_{\rm{RCL}} = \frac{i L R \omega}{R + i L \omega - C L R \omega^{2}} $$

and if we take the real-part of this then we get
$$ {\rm{Re}}\left(z_{\rm{RCL}} \right) = \frac{1}{R \left(\frac{1}{R^{2}} + \left( \frac{1}{L \omega} - C\omega \right)^{2} \right)}$$
which just by looking at we can tell is symmetric. But if we plot it:

So my first question is: Where does this asymmetry come from?

My first guess is that this is parasitic inductances and capacitances.

So my first question is: how can I adjust my equation to consider these asymmetries so I can do better fits?

My end goal is to extract the \$Q\$-factor and resonance frequency.

Further research and comments

Some additional comments since having an answer. The circuit proposed in the answer below is indeed a better fit,
$${\rm{Re}}(Z) = \frac{R}{1 + C \omega^{2} (C R^{2} + L (C L \omega^{2} - 2))}$$
and is asymmetrical in the direction that is shown by my data. However there seems to be other components at work as the tilt in my data seems to be more extreme than is represented by the lineshape as described above.

In the graph above we can see the data, which I have linearised, add the lineshape as shown above. While the asymmetry is present (if I plot to large frequency spans) it seems to have a quite small sensitivity to frequency scaling, which makes me wonder if parasitic inductances and capacitances would adjust this.

Just for clarity here is the new lineshape showing the asymmetry better in logarithmic units:


texts: Constraint relative arrival time for a group of signals

texts:
Imagine a situation where the absolut delay of a group of signals doesn't matter, but it must be ensured each signal of the group has roughly the same delay until it reaches a certain point, say a FF. How does the constraint for this look like?
E.g. there are 4 signals (A-D) arriving from outside the FPGA. I don't care how long these signals are delayed inside the FPGA, as long as they arrive at the FFs within a time window of +/- X ns, i.e. A arrives at a FF at time T, D arrives at a FF at time T+X ns, and B and C arrive at FFs some time in between.
Is it possible to formulate a fitting constraint in Xilinx' UCF or XCF syntax? Or do all these timings have to be handled within the IOBs and there is no way to handle this inside the FPGA?
The desired constraint seems to be similar to an OFFSET constraint, but is not the same, since there is no maximum value for the total delay.


texts: Question about ETL and UL Certifications for battery powered tools

texts:
A friend is considering importing a 15 volt Lithium-Ion Battery (2600mAh) operated tool from China to sell to consumers in the USA.

The battery charger that comes with the sprayer has a stamp that says that it is certified and it plugs into the wall socket.  (see attached image below)

But the battery itself does not have any certification stamps, or any markings on it at all.

So what I am trying to find out is do they need to get the battery, or the tool itself certified by UL or some other safety certification before it can be legally sold in the USA, or is the charger the only component that is required to be tested and certified?

If the answer is yes, what kind of testing and certification is required to import it from China and to sell it here in the USA?


texts: Decoupling capacitor with resistor in series

texts:
I am looking over a datasheet, and I saw something that puzzled me. Why is there a 1 ohm resistor (R2) in series with the capacitor?

This is a power rail, so I'll assume it is a decoupling capacitor.

Pin 15 is VREG_OUT - Power Regulator output (1.8 V while awake, 0 V during deep sleep).

After a few Google search attempts I was not satisfied with the responses or lack thereof. What is a plausible purpose of "R2"?


texts:
I am trying to build a 555-timer that delays the switch of an input signal, both ways. When input goes high there should be a delay before output goes high, when input goes low there should be a delay before output goes low. If the input switches for a too short amount of time it should not switch the output at all.

I hope I am making myself clear here. I guess I need to use two 555 timers, I have been fiddling around but have made no progress.


texts: Hobby Project - Signal Frequency detector

texts:
Context: I have taken on a little side hobby project to learn by making a circuit which should be able to only go high when it sense an acoustic signal with a frequency around 40kHz. To do this I will be connecting a microphone to a band pass filter and then hook it into an arduino which I am somehow going to programme to indicate when this happens:

Main Idea

Microphone > Band pass filter > High voltage when 40k+ goes to Arduino to log this information.

For this whole project I will be using a battery so I will have 0 to +5 volts and so I cannot use -5v in any op amps.

For my band pass filter I have 2 options I can go really simple with something like a passive band pass filter:

Or I can go further and make an active bandpass filter: [ Although I do not understand how it works fully, I know that it is a higher order and is more precise and accurate :

The issue with this is the fact that the ADA4062-2 Op amp is extremely small. I would not be able to solder it or use it in a breadboard. Is there a way to find an op amp that could do this to avoid this issue?

For the Microphone/ultrasonic sensor I will be using this:

https://uk.farnell.com/camdenboss/ctd40k1007t/ultrasonic-transmitter-110db/dp/2610513

My questions:

1) Will using the simple passive band pass filter be enough.
2) Is there a way to find DIL integrated circuits to replace small surface mount ones?
3) In regards to the ultrasonic sensor can I just connect this to the band pass filter directly?

I am sorry for my lack of experience. I would appreciate any help.

Higher order circuit designed using:
https://www.analog.com/designtools/en/filterwizard/


texts: Of what real, practical use is electronics certification?

texts:
I am brand new to EE/ECE and am aware that companies such as UL offer a gammit of services such as:

Circuit verification (they verify your schematic does what its supposed to do and doesn't have any design smell to it)
Circuit testing (they verify the functional correctness of your circuit/electronic system)
Circuit certification (not sure how this really differs from testing, but the end result is that you get to put their fancy "certified" logo on your product)

I completely understand the value of the first two: verification gives you confidence from a 2nd set of eyes that your design is valid. Testing gives you confidence that you are in fact ready for production (or at least prototyping). But the certification service is what has me baffled. As a consumer, it would never naturally occur to me to check some new stereo, MP3 player, or remote control helicopter for a "UL" logo prior to using it. You guys might, but then again, you're EE/ECE peoples :-)

So is the certification just for establishing trust/confidence in the product? Does it have implications with regulatory bodies or insurance carriers? If so, what bodies/carriers/policies? Are there "electronics insurance carriers" that specialize in selling "Electronics Liability" policies to electronics suppliers, and perhaps they only sell the policies for "certified" products? Of what real-world, practical use is the certification?


texts:
First of all, I would like to say that I'm a noob at electronics, so please be merciful :)

I'm trying to convert AC'97 audio front panel dongle on my PC to IntelHD one. The difference is that IntelHD is able to detect the fact someone plugged in headphones or microphone.

Here are some schematics, showing the difference:

So, when the mic is plugged in, SENSE_SEND(7) and SENSE1_RETURN(6) should get interconnected. Similarly, for headphones its SENSE_SEND(7) and SENSE2_RETURN(10). Seems simple.

Unfortunately, I can't find proper audio jacks anywhere. As you can see, IntelHD requires jacks with normally open switch, while I can only find AC97 jacks, having normally closed switch. So, I need to 'invert' the switch somehow...

I've been thinking about this and came up with the following: SENSE_SEND is probably just a logical '1', so motherboard just detects voltage level on SENSE_RETURN pins. So I came up with this simple NOT-gate:

When the headphones jack is in, and therefore switch is opened (for AC97 jacks), SENSE_SEND gets locked to SENSE2_RETURN via 50k, therefore having logical '1'. When the jack is out, the SENSE2_RETURN is short-circuted to the ground pin (2), therefore having logical '0'.

This is where strange things begin. First of all, SENSE_SEND surprisingly has 2.5V instead of 5V as I expected. So I'm not sure now if the motherboard really measures logical levels on SENSE_RETURN pins. And secondly, whether SENSE2_RETURN is short-circuited to the ground or not doesn't seem to matter! PC detects that headphones are present no matter if I open or close the switch.

I suspect my initial assumption about logical levels is wrong. But then... how it might work inside? Any ideas where I am wrong or how else can I invert the switch?


texts:
I designed a board to mux 16 inputs into a 4 channel scope using relays. I also included circuitry to replicate a 10x probe on the board. That is, I placed a 9M ohm resistor in parallel with a 1.4pF variable cap. These values came from a 9:1 ratio with the oscilloscopes internal 1M ohm resistor and a 13pF cap. From there, a BNC cable connects the board and the scope.

Here is a schematic:

PV1, PG1, PI1, PV2, PG2, PI2 are all attached to 4 separate normally open relay contacts.

When I went to tune the capacitors for a 1kHz square wave, the wave was completely scewed and no cap value from .9pF to 9pF would fix it. To my surprise I realized that the wave looked the best at the upper value (around 10pF) instead of near 1.4pF like I had expected. I replaced it with a 22pF cap out of curiosity and the square wave looked quite a bit better - not perfect - but also has a slight DC offset.

Any ideas what is going on here? Is the problem with the BNC cable, or possibly inductance / capacitance of the circuit. How should I have designed this in the first place?

FYI: There is no ground plane because each have slightly different grounds. Also, I injected the square wave directly on the cap, with ground connected to the BNC ground. I get the same result when injecting from anywhere else.

Here is some waveforms on the scope. From top to bottom: No cap installed, around 10pF, and the bottom is 22pF.

Also, comparing the signal with the original square wave.

Update: Thanks for the answers. Someone suggested I use a circuit such as below to create a 100x probe. Would this work better?


texts: Which serial protocol or encoding scheme does this scoreboard use?

texts:
I am trying to decode a signal stream coming from a Nevco scoreboard controller:

Packets like this are sent every ~2.7 ms.

I suspect it is some sort of UART signal because it is on the RX line of a ATMEGA48, but I cannot identify the finer protocol details like parity and stop bits. All the combinations I have tried returns junk data, so it may be another encoding scheme.

What's unusual is that the same signal is also sent to the MOSI pin of the microcontroller, but there is no clock signal anywhere.

A .vcd file is here.

The shortest pulses (both high and low) are always 8us in length.

This is what two packets look like. Anyone got ideas?


texts: How to have custom keyboard scancode set

texts:
I'm new to the hardware field in general. For one project I'm trying to create a custom keyboard that will have some extra keys, say 20-25 more than a standard keyboard. I've read about scan codes and scan code sets. I've also read about keyboard encoders, controllers etc. at pages like these:

http://retired.beyondlogic.org/keyboard/keybrd.htm

http://www.computer-engineering.org/ps2keyboard

But still I'm not clear which encoder will allow me to generate a custom scan code that is not defined in any standard scan code sets. Also will the standard keyboard controller (8042 compatible) in a PC process these non-standard scan codes?


texts: Instrumentation amplifier noise amplified

texts:
I built a simple circuit with an instrumentation amplifier (PGA204AP) in order to clean a differential signal from noise. The signal is generated few meters away from the acquiring point and the cable (twisted pairs shielded) pass through a very noisy environment.

The circuit is the following :

The shield of the cable is grounded in the Op.Amp side, and in the other side it is not connected. As you can see, the input of the Op amp is filtered through a differential mode filter (R1 R4 and C2) with the cut-off frequency set to  ~60kHz, and a common mode filter (R1-C1 and R4-C3) with the cut-off frequency set to ~1MHz.

At the output of the PGA204 I put a 2nd order low pass filter with the cut-off frequency set to ~500kHz.
I tested the circuit with no input, just to see if the noise from the environment would have been attenuated: the noise present in the environment was the following (measured with the scope directly from the cable) :

250ns/div

5us/div

So clearly there was a very strong noise a 2MHz, but once I connected the instrumentation amplifier, the noise was amplified (more than doubled). So I decided to put this 2nd order filter just to see if this 2MHz noise would have been eliminated. But the result was the same, and this seems very strange to me because two completely independent devices have the same issue.
In addition, I tested the device with some noise produced with the signal generator at the input (noise applied at one input, and the other input had it as well thanks to the twisted pairs cable) and the result was the following:

Upper ones are the two inputs, lower one is output. It seems pretty good.

What I'm not sure about this 10k resistor (R5) between V- input and ground. I've been told to put it for the bias current but doesn't it interfere with the LP filters at the input?
Is there something else I should pay attention to with these filters? Suggestion for the next tests I should do in order to solve the problem?


texts: Equivalent DC circuit of 3 phase induction motor

texts:
I'm currently trying to model a simplified circuit of an inverter + 3 phase induction motor. For now, I want to represent the DC link as an ideal independent voltage source. To keep this example simple, I also want to keep frequency and input voltage the same, though I expect to be changing these to simulate a VFD

I'm using https://myelectrical.com/notes/entryid/251/induction-motor-equivalent-circuit as reference

The output I want is motor torque and resulting current on the DC link.

So, given \$V_{DC}\$, what would \$I_{DC}\$ be in terms of inverter equations and induction motor equations?

I think I'm most of the way there, but I can't find a full set of equations for this, only separate equations for motors and inverters.

simulate this circuit – Schematic created using CircuitLab

For input voltage to the motor, I think this is correct
$$V_{L} = \frac{3}{\sqrt{2}\pi}V_{DC}\\
V_{P} = \frac{V_{L}}{\sqrt{3}}$$
It's my understanding that torque is per phase
$$T = \frac{1}{2\pi n_s}\frac{R_{2}}{s}\frac{E_{2}^2}{\frac{R_{2}}{s}^2+X_{2}^2}$$
So total motor torque
$$T_{3\phi} = 3T = \frac{3}{2\pi n_s}\frac{R_{2}}{s}\frac{E_{2}^2}{\frac{R_{2}}{s}^2+X_{2}^2}$$
To calculate back emf \$E_2\$:
$$E_{2} = V_{P}-\frac{I_{1}}{Z_{1}}$$
Impedance per phase:
$$Z_1=R_{1} + jX_{1}\\
Z_m=jX_{m}\\
Z_2=\frac{R_{2}}{s} + jX_{2}\\
Z=Z_{1}+\frac{Z_{m}Z_{2}}{Z_{m}+Z_{2}}$$
Would the calculation back to \$I_{DC}\$ be as follows?
$$I_{1} = \frac{V_{P}}{Z}$$
$$I_{L} = \frac{I_{1}}{\sqrt{3}}$$
$$I_{DC} = \frac{3}{\sqrt{2}\pi}I_{L}$$

EDIT:
Specifically, I want to know if the equations I have above are correct for determining the average current on the DC link (neglecting most losses for now)


texts:
We are working on DALI LED control gear type product. We are using TPS92515 as LED driver and its controlled through Iadj pin (analog dimming). Our issue is even if we give input zero (GND) to control pin (Iadj), there is 3mA current through LED and it is ON, but at low brightness. This means we cannot turn OFF the led by issuing DALI command DAPC 0 (OFF command), but DALI spec says LED shall switch off upon OFF command (Refer. Sec. 11.3.2, page 54, IEC62386-207:2016). Will this be an issue with DALI compliance certification? Any help would be appreciated.

Thanks


texts: Determine the Base Current Amplification factor using Ltspice

texts:
I'm trying to calculate the resistances of my circuit but I'm stuck because I'm missing the B value and don't know how to find it out .
I want to calculate the resistors with which I can determine the current amplification factors B of the transistor 2N3055 (in common emitter circuit) at IC = 200 mA and at IC = 1 A (UCE ≈ 15 V)
This is my circuit :

To calculate the resistances R1 :
I would need to calculate either B or IB and the problem here I don't have both values
$$ RV1 = B(V1-UBE)/IC $$ or $$RV1 =  (V1-UBE) / IB $$
R2 here is easy to calculate since I have the value of UCE = 15 V which make UR2 = 15 V for both IC_1 = 200 ma and IC_2 = 1 A
Which makes
R2_1 = 15 ohm
and
R2_2 = 75 ohm
The problem here stays with R1 because I'm missing B/IB values . Is there somehow a way with the use of LTSPICE that can get me the B value of 2N3055 transistor or should I just guess it ?
I checked the Data sheet shown in Ltspice but it was unclear there .
This is what I found


texts:
How is a general 16x2 LCD display contrast defined?
Is it with voltage on pin V0 or with total resistance of potentiometer?


texts:
I have a Meanwell GST120A24-P1M +24V power supply (picture below).

I want it to power a circuit of mine. Say the circuit is as shown below: one power supply and one resistor. How do I connect the side connected to ground when I only have one DC positive output from my power supply?
Even if I would connect 2 split wires to the DC output they would still both have +24V wouldn't they?


texts: How to connect sensors to an Android device?

texts:
I need to build a device, which measures several parameters (body temperature, conductivity and pulse) and transmits them to an Android mobile device.

The system has following parts:

The sensors
Sensors -> logic unit connection
Main logic unit
Main logic unit -> Android device connection

I intend to use IOIO Mint as the main logic unit and Bluetooth as "Main logic unit -> Android device connection".

Now comes the problem - I need to place the sensors close to the human body such that they are easy to wear. Probably, the sensors will be located at a different part than the main logic unit (the former - attached to the skin, the latter in a pocket).

Ideally, the sensors would have a wireless connection to the main logic unit or to the Android device.

My first idea was to connect the sensors to FLORA, add a BlueTooth module to FLORA such that FLORA communicates with the Android device directly. But AFAIR there is no good-enough support for BlueTooth on FLORA.

Are there any other ways to transfer data from sensors to main logic unit or to an Android device (except BlueTooth, wires and conductive textiles) ?


texts:
At no load my boost converter will be the same as in the photo. I'm thinking without a load at the end of the boost circuit the output impedance will be very high which will make the potential difference after connecting the output to a (Semikron an-8005) which has an input impedance of 30k will make the boost output decrease to around 70V and if I take the output of the Semikron inverter to a filter and then 1K load after that the voltage will decrease even more to around 6V only.

How can I avoid this drop?

Will putting a very high resistor in parallel with the output capacitor of the boost solve this drop?


texts: Necessary Bandwidth of Current Shunt Amplifier in FOC + SVPWM motor control

texts:
I am designing a BLDC motor controller using sensorless FOC + SVPWM, planning to use a shunt to measure current, and using an observer to determine the rotor angle. I was wondering, what bandwidth do i need for the op amp for the shunt amplifier.
I read somewhere that the bandwidth needs to be at least 30~50 kHz. Is that true?
My Current PID loop will run at 30~50 kHz and thus the ADC will sample at 30~50 kSamples/s.
The gain for the amplifier circuit is 16, would a LM324DT be sufficient? (it has Gain Bandwidth product of 1.3MHz).
LM324DT datasheet


texts: I know it isn't best practice to put a via or a component in between LVDS traces. But my routing requires the LVDS traces to go in between of vias. How bad is this for the signal integrity?


texts: Why do European motorized appliances draw less inrush current than their American counterparts?

texts:
I have been trying to tease apart the history and evolution of arc fault circuit interrupter requirements, and in the process, came across a curious historical sidenote early in its genesis, namely that the use of a 5x-or-so (IEC "B" curve) magnetic trip on general branch circuit breakers is said to serve as a highly effective fire prevention means.  This was followed up on by EIA with a proposal in the 1996 NEC, but according to a UL whitepaper, the proposal was rejected due to concerns about inrush from tungsten and motor loads.  However, according to this article, said IEC "B" curve breakers are considered "generally suitable for domestic applications" in at least some countries utilizing IEC-derived wiring standards, with "C" curve breakers (8x-10x magnetic trip) reserved for dedicated motor loads or other high-inrush situations (such as magnetic LV lighting transformers) in the domestic context.
This raises a question, though: why is it that the North American market seems unable to utilize magnetic trip thresholds below 7x-10x (roughly "C" curve, and generally equivalent to a QO's magnetic trip, at least on 15/20A single pole breakers)?  Is it simply a matter of "half the voltage = twice the motor inrush," or is there some deeper reason that domestic motorized appliances made for the rest of the planet have a lower inrush current than their North American counterparts?


texts: Show that the power dissipated in a resistor over infinite time is equal to the energy stored in a discharging capacitor

texts:
I am learning about RC transient responses and if a charged capacitor is connected to a single resistor, its voltage will decrease exponentially. I understand this and how its equation is derived. I also understand how the energy stored in a capacitor is obtained.

So, given an infinite amount of time, all of the energy will be dissipated in the resistor. I would like to prove that the integral of p(t)dt between 0 and infinity is equal to 0.5CV₀². I've tried substituting in i²(t)R for p(t) and then equating i to -Cdv(t)/dt but I end up with something that isn't even an integral anymore, namely of the form RC²∫dv(t)/dt between 0 and infinity.

What sort of substitution should I make to allow this to be integrated? Thank you for reading.


texts: Soft errors from SEUs/SETs in early 8-bit microprocessors?

texts:
Why is it that soft errors due to single-event upsets/transients never seemed to be a problem in early 8-bit microprocessors, like the MOS 6502 or the Zilog Z80?  The microprocessors themselves were widely assumed to be deterministic, like TTL logic gates, and didn't have any any sort of error detection/correction, and seemed to work with little issue (from soft errors, there were plenty of worse problems) for a wide variety of applications.
When I say "never," I only mean microprocessors in consumer level applications, not including niche aerospace or other mission-critical uses, which I know have always included fault-tolerant and rad-hardened electronics.  Also, I am not asking about the issues with memory, like those radioactive DRAM chips in the 1970s which led to parity becoming more widely used, but only soft errors that may occur in the microprocessor chip itself, which seem to be becoming an increasingly common problem today as feature size scales down and transistor density scales up.  This is especially true for those mission-critical applications, including servers and financial computers.
Was it because the transistors in those early microprocessors were microscopic instead of nanoscale?  Was it because of the transistor density and processor complexity?  Was it something else entirely?
It just seems that the soft errors were only a worry in RAM with these computers in the majority of applications, like in consoles or personal computers, and rarely in the microprocessor itself.  There seems to be an elegance in the simplicity, determinism, and functionality of the early microprocessors.


texts: Wiring a membrane potentiometer to give two outputs

texts:
I'm using a softpot membrane potentiometer in a project and I have found that pressing two fingers on the strip gives strange results. I was expecting it to short to the lower resistance value but in reality it gives some resistance in between.

In researching this, I found someone who managed to wire it acting as two voltage dividers giving both finger positions simultaneously - the video to this can be found here: https://vimeo.com/38404771

Could anyone explain what's happening in these two scenarios?


texts: How to test and rate a home-built low dropout regulator?

texts:
I built a low dropout regulator following experiences building a discrete linear regulator. The circuit is simple like this:

simulate this circuit – Schematic created using CircuitLab

I would like to know how to test the maximum voltage inout and output, current carrying and heat dissipation ratings of this circuit with parts as specified in circuit, as well as its minimum voltage dropout.

By supplying a regulated 5.5V into this circuit I can get the maximum of 5.4V at the output under 30mA load. Does this spell a minimum 0.1V dropout at 30mA?

I also got a minimum of 2.5V voltage output without load. How to modify this regulator so that it can shut the load down by turning the pot one way all to the end?

Also is the op-amp getting power from the unregulated input a problem?

--- EDIT ---

Since this circuit is not protected, how to add overcurrent protectection? I am considering using LM358 instead of LM741 as the op-amp chip, and how to construct the current sensing and overcurrent protection circuit using the extra op-amp from LM358, a shunt resistor and a few more MOSFETs? (I have 2N7000, BS250, IRF4905 and IRF540 spare parts lying around in bulk)

--- EDIT 2 ---

Rounding up suggestions, does this seem like a better circuit?

simulate this circuit

The reference is modified per @SpehroPefhany's suggestion to use a TL431 powered through a 680Ω resistor. The old 741 is swapped out with OPA2134 dual rail-to-rail op-amp (expensive!) per @andyaka's suggestion. Some frequency compensation is attempted using capacitor C3 at the gate of pass transistor M1.

My intention of the overcurrent protection is like this:

  The second op amp in the OPA2134 package is wired into a differential amplifier, monitoring the voltage difference between current shunt resistor R4. When the current approaches 4A the voltage drop across R4 increases to the point that the voltage output of the differential amplifier OA1b approaches the threshold voltage of 2N7000 and start to push it on, pulling the voltage at the inverting input of error amplifier OA1a lower, pushing the gate voltage of M1 higher and start to shut M1 down.

--- EDIT 3 ---

Rounding up suggestions again, would this be better?

simulate this circuit

The op amp is no longer driving the pass MOSFET directly, and current shunt voltage is directly matched against the threshold voltage of a MOSFET PNP BJT. This should be able to eliminate the need for a RRIO op amp. I am still using a relatively modern LM358 but is 741 suitable here now?


texts: Is it possible to disable a TP4056 lithium battery charge IC when no battery is present?

texts:
I have a circuit that's setup to use either USB or a 3.7V lithium battery. When both are plugged in at the same time, the battery is charged through a TP4056 IC. The charger also has two LEDs attached to it. One that's red which is on whenever it has power. And one that's green which lights when it's fully charged.
However, these stay on and flicker if you plug in the device without a battery. Is it possible to somehow detect that no battery is present and if so, disable the charger?
My biggest issue is that when there's no battery attached, the charger will output a voltage to the battery positive.
This is my current design, USB power enters from the top left. But I'm willing to redo the design. I also have access to multiple free pins on a microcontroller, if that could be used.


texts: How can I add a logo to PCB with Altium Designer?

texts: I am trying to add a logo to my PCB using Altium Designer 16.1 via "PCB Logo Creator" software. However it was not so neat. Do you have an idea to prepare better logo which would be taken from a photo or picture?


texts: I'm analyzing a board for some device (game handheld console). I've found a simple SPI flash on it (W25Q) but there are 2 pads exposed for what I assume is factory testing (there are no other pads exposed on the whole board). The thing is, those pads are the ones for /CS and DO. However, as far as I know you cannot get anything out of the chip without driving both CLK and sending a command through DI, so I just wanted to know if this makes sense from an engineering perspective, or it might be just something that will probably be driven by the main CPU or something.


texts:
Recently, I use the Tl431 to be a regulator, and I want to change the output of TL431.
I read the TI datasheet if I want to change the output I need to change the divider resistor, and I also use PSIM to simulate it, it can works.
but I don't know how to analyze it, I want to know why the output voltage can be written as Vref*(1+R1/R2)+Iref*R1
can someone give me some advice?


texts: How to estimate green or yellow based on the output of RCCC CMOS image sensor

texts:
RCCC is a kind of color filter array with one Red filter and three Clear filters, which means it only outputs red color or monochrome signal (Interfacing Red/Clear Sensors )

I know that some RCCC cameras can output coloured images. This must be down be via color mixture technology. Unluckily, I am totally new to this area. Are there any suggestions for me to start to mix the output of RCCC sensors? To be specific, I want to estimate the yellow or green color.


texts: TL431 / TLV431 supercapacitor voltage clamping circuit

texts:
I have a question regarding a circuit I've been working on for some time.  The circuit is based around existing supercapacitor protection modules and uses a TL431 (actually a TLV431 lower power version) precision Zener device.  Basically, the circuit works, but I wanted to get some feedback about resistor values, and whether or not my NPN or PNP transistors are doomed to fail.

In summary, the circuit uses the TLV431 and it's reference and sensing resistor divider to set a trip point (somewhere around 2.65 V as I have it at the moment) the TLV431 then starts conducting, pulling current (this is where I get foggy) from the base of the PNP transistor (BC557) turning it on (hopefully in saturation).  When it turns on the NPN gets (an unknown amount of?) base current, and turns on sinking the charge current (with a maximum of?) through a resistor and 'around' the capacitor cell.

Eventually I'd like to have this circuit in series with my series capacitor strings so that any stage in the stack never sees more than it's 2.7 V (2.65) so long as I stay under the dissipation capabilities of this circuit on the input.  The current modules that I bought from eBay only seem to limit on supplies up to about 500 mA.  I'd like to get this up to 2 - 3 or 4 amps.  Let me know what you think - the specific question is about R3 value, R4 value, R5 value, and if a resistor is required between the PNP and NPN base.  Thanks!

I've seen versions of this circuit that omit the PNP base resistor, but I've added one because without it I think the TLV431 would burn and fail - perhaps someone could also clarify this aspect of the circuit?  If anyone else is building protection circuitry around the TLV431/TL431 for 2.7V supercapacitors I'd really appreciate you chiming in!


texts: Convert Output Voltage from Delsys Trigno to Acceleration in Matlab

texts:
I have the Delsys Trigno Wireless EMG Sensors connected to NI DAQExpress and am reading the signals into MATLAB. I am reading the EMG data from one sensor (Ch 1.1) into AI1 port and the acceleration in z direction from another sensor (Ch 2.4) into AI2. The DAQExpress only reads voltage measurement types, so I need to know how to convert the output voltage from the second sensor to acceleration. Here is my code:
d = daqlist("ni")
deviceInfo = d{1, "DeviceInfo"}
dq = daq("ni");
ch0 = addinput(dq, "Dev1", "ai0", "Voltage");
ch1 = addinput(dq, "Dev1", "ai1", "Voltage");
ch2 = addinput(dq, "Dev1", "ai2", "Voltage");
ch1.TerminalConfig = 'SingleEnded';
data = read(dq, seconds(30));
figure
plot(data.Time, data.Dev1_ai0);
title("Accelerometer Reading");
ylabel("Voltage (V)"); %Differential Voltage
xlabel("Time (sec)");
figure
plot(data.Time, data.Dev1_ai1);
title("EMG for Biceps Brachii");
ylabel("Voltage (V)"); %Single Ended Voltage
xlabel("Time (sec)");
figure
plot(data.Time, data.Dev1_ai2);
title("Acceleration of Vibrator");
ylabel("Acceleration (g)");
xlabel("Time (sec)");


texts:
it's a long time that I'm looking for a 220V - 5V 200mAh switching power supply and I haven't found my solution...

My board uses 140 mAh and it needs a small power supply whit no heatsink assembled on my board.
I would be really happy if any one can suggest me a schematic of a small power supply that suit my board.

(The cost doesn't matter!!!)

---THANK YOU---


texts: Why aren't DC motors getting enough power?

texts:
UPDATE: I really appreciate your help! I´ve found the error, and it was a very basic one. I´m posting it here in case it helps someone
  out there in the future. I didn´t realised (I´m still learning), that
  you have to power up your arduino AND your motors separately! So
  Connecting the arduino to power supply (in my case a 9v adaptor, and
  then a 12v adaptor) didn´t help at all, because the motors have to get
  ANOTHER power source, in this case using the Vin pin connected to a
  positive row of the breadboard. Yes, I realise its a silly newbie
  mistake, but I wanted to go and write this down anyway. I didn´t
  undertand at first when people answering and commenting asked about
  what powered my motors... now I get it! THANKS!!!

  About the squematics... I´m trying to get acquainted with circuitlab, because it is more complicated to understand -to me al least- than fritzing.

  I´m not posting this as an answer because it is more than a clarification, and there are several comments already to post yet another one :)

I'm trying my first Arduino project, a Bluetooth controlled car. I've divided the project into two parts, one that connects the Arduino to Bluetooth and one that makes the DC motors work. I've found lots of tutorials, but I stuck with following one:

Controlling speed of DC Motors using Arduino

I've been reading a lot about Arduino and DC motors the last couple of weeks and I've tried some smaller things first (LEDs, buttons, light sensors etc). The problem here is that the motors are quite slow (the wheels won't even move when on the floor). I have an Arduino Mega and an Adafruit motor controller.

As I don't have a voltmeter right now I started to test without the motor sensor, because I thought that maybe it was consuming too much power. These are the tests results so far:

If I connect three AA batteries to both motors directely, they spin vividly, so I think there's no problem with them. The motors are two DC 4.5/6 V.
If I connect a 9V/1A DC adaptor, it's even worse: the motors won't move at all. I thought that maybe the adapter was faulty, but I've tried with another one. The second one is a DC adaptor 12V/1.5A center pin positive and the result is the same. No movement. The LED that I've added to the board for test purposes does light though.
I've attached those three AA batteries to the Arduino like the diagram below and it moves but oh so slowly!
I've added a simple alkaline 9V battery instead of the three AA (and I've put it together with the three AA too!) and the result is the same, no movement or very, very slow movement.

As the motors do spin I don't think that I've set the pins incorrectly or that the code isn't working but I fail to understand why this is happening?

UPDATE: Sorry about the diagram (I havent posted it, but I did provide the link though). Im new to the arduino and thought that was the kind of diagram that it should be posted. What should I attach instead?


texts:
I want to learn USB and its hardware interface and start with a trivial design. I found some VHDL in github for the ISP1362 and I wonder if that is a good starting point. I have already used Quartus to design other hardware for FPGA that I can download to the Altera FPGA:s.

Now I want to look and learn how USB and its hardware interface are designed and preferably starting with something basic and general and a specific design from a specific manufacturer (Qualcomm, Motorola, Philips...)

I found a design for ISP1362, would that be a good starting point or could you suggest something better for me to learn the USB design and specification?

My goal is to be able to formally verify the model, design and specification for real hardware, but I need to start with something basic and easy.


texts: How can I access more than 15 addresses of data from my 8 bit incomplete computer?

texts:
Last year I started researching upon how computers work, so I started making one, at least on paper last month, but I ran into a serious problem that isn't getting a satisfying answer from any article or past question.
If I have an 8 bit memory, and according to some good reliable sources like Ben Eater and crash course computer science, half of the byte in memory is the opcode and the other half is the address which means 4 bit or 15 opcodes which is enough, but just 15 addresses which I think is not sufficient to cover a 32 kB EEPROM, so I wonder how am I supposed to get more than 15 addresses accessed from the computer or the instructions itself? Let's say I have an opcode 0101, and I want to refer that to the address 16, I can't because the highest I can go is 01011111, which is just doing something to highest of 15 addresses but if this is the reality, a 64 bit device should only be able to use 4 GB of RAM,  but there are 16 GB also, so how can I fix this problem?
If I have a look at a MOS6502 Microprocessor, it has 16 address pins, so does it mean that it is a 16bit address register and that it is designed for working with a 64kb memory and is that why Ben Eater in his EEPROM  video turned the EEPROM off using the Chip enable whenever the processor fetches beyond the 32kb range of the EEPROM.


texts: Does AM Broadcast Use Sideband Modulation

texts: Does AM broadcast radio in the United States use a sideband modulation, or are both sidebands and the carrier present in the signal? Please provide a reference.


texts: Ideas for driving an electromagnet with high voltage AC current from a PCB

texts:
I have an aquarium pump that is no longer being used and I want to integrate it into a design of mine. I am inexperienced designing for stuff with high voltage AC or AC current in general. i've done many <12V DC electronics designs, even complex ones involving BGA FPGAs, I've never NEVER touched high-voltage or AC current on my PCBs before.
Here are some photos of the pump:
https://imgur.com/a/iZFpGGL]https://imgur.com/a/iZFpGGL[/url
The pump plugs into mains voltage and seems to have a potentiometer and some passives to control the amplitude, and what i believe is a flyback diode for the inductive load. I'm not really sure the circuit for it but i'd be happy to dissect if further if someone wants to help explain what each passive does. I assume the diode is for sinking the induced negative voltage from the massive inductor when the AC voltage switches polarity, but i'm not sure what the capacitor is doing there. I only plan to use "half" of it since it's essentially two electromagnets each of them pushing two dual-diaphragms. So I only intend to use one electromagnet pushing two diaphragms.
The product page for the pump shows that the entire unit only uses 6 watts at 120VAC, i only need half the unit so the section I would need would use 3W@120VAC; quick calculation means one half only uses 25mA of AC current.
At first I was thinking of plugging mains power directly into my PCB using something like an IEC connector and then using a PCB mounted AC-DC converter to step down to 5 volts for the rest of my design (raspberry pi zero, stepper motors, LCD display, etc) and have the AC side of the PCB feed into a relay that connects to the inductor and have the relay switched with the raspberry pi's logic level output. This seemed like an okay approach but it also has me nervous since i've never used high voltage and in addition the PCB mount switching power supply i'd need to go from 120VAC to 5VDC would be huge and unwieldy to design around. That part alone would take up half of my planned PCB board space.
I need at least ~7Amps supplied on the 5VDC side because that side of the design uses 12 MG996R servos which have a running current of 500mA; truth be told I will only ever be actuating one servo at a time but when the board comes online I don't want the inrush current from all the servos to burn anything out. The other components (rapsberry pi, LCD display, addressable LEDs, etc) all use a relatively small amount of current, the Pi being the largest at no more than 300mA (but probably no more than half that to be honest).
I was wondering if a better idea was to use a commercially available power brick to provide 12VDC 10-15A to the board and then make a smaller section of the PCB somehow drive the AC electromagnet. Is believe DC-AC converters are called inverters? Does it seem reasonable to be able to convert 12VDC to AC for something this low power (roughly 25mA by my calculation)? I've also found these but the output frequency is too high to drive the electromagnet correctly.
What do you all think? Should I use the huge PCB mount AC-DC converter with a relay thrown from the 5V side? Or is there another circuit I could build if instead I supplied 12VDC 15A and used a section of PCB to convert to higher voltage AC?
Would an H-Bridge driver work for this? Maybe I could use a DC-DC converter to generate 120DC and use an H-Bridge to alternate the current flow? It would be a square wave so maybe I could use a low pass filter to get a sinusoid. I would need another circuit to do the switching unless I manually controlled the switching in software (non-ideal as it's one more thing to deal with).


texts: How does one increase Vds in Transistors technically speaking?

texts: I tried to google my question but I found no answer. Obviously the voltage at the drain is increased. But I'm actually interested how this solution is technically implemented.


texts: Limitation of baud due to propagation of voltage over distance

texts:
I need to make sure I have my facts straight here; the math works but I may be missing something:

In a 100BaseTX network over Cat-5 copper, each party has a circuit (one twisted pair) on which they send and one on which they receive. Let's consider one circuit, and thus the parties can be labelled sender and receiver.

To send data, the sender first turns each 4-bit nibble into a 5-bit word, which ensures that five straight zeroes is never valid and indicates signal loss. That bitstream is then encoded into voltages using a combination of NRZI and MLT-3 encoding schemes, the end result of which is that a "1" is represented by a transition of voltage between three states (call then -1, 0, and 1) in a cyclical fashion; a stream of all 1s would be represented by 0,1,0,-1,0,1,0,-1 etc. This reduces the maximum speed at which the sender must cycle voltages in order to maintain the maximum bitrate in the worst case; the required "fundamental frequency" for the desired 125MHz baud rate is 31.25MHz.

Now, a change in voltage must propagate through the wire; first the recipient will see it, and then the sender themselves will see it on the "undriven" side of the circuit. The sender must see this feedback in order to ensure continuity (doesn't it?). So, the limit to the total circuit length, assuming the ideal that voltage propagates at c, is how far light can travel in 31.25 microseconds. That distance, given a simplistic c = 3*108 m/s, is 9.6m ~= 31.5 ft. Since that's total circuit length from sender to receiver and back, the actual total cable span is half that, or 4.8m ~= 15.75ft. Beyond this length of Cat5, it is simply impossible for the sender to toggle the voltage fast enough to maintain the fundamental frequency, so the two parties negotiate a lower frequency, resulting in a lower maximum bitrate over the longer cable.

By the time we get out to 182m, the Cat-5 specification's maximum cable length at which simple resistance of the spec'ed cable will have reduced signal voltage below the threshold of the receiver's distinction between the three states, I calculate that this speed-of-light limitation will also have reduced the maximum sustainable fundamental frequency to approximately 1.65MHz, for a baud rate of 6.6Mb/s and a true data rate of only 5.28Mb/s.

Compounding this is the fact that propagation of voltage over distance is not at the speed of light; depending on the cable, voltage typically propagates along wire no faster than .9c and as slow as .4c, so we could see data rates as slow as 2.1Mb/s at this extreme (though I'm betting that cable this poor wouldn't meet Cat-5 spec in other significant ways).

Is this line of thinking on track? Is there anything I'm missing that changes any of this significantly? What I'm not sure of is whether the sender actually does need to register the voltage differential on the other side of the circuit (the circuit may be differentially-balanced with both sides being "driven" in opposite directions). If they do, the above holds. If not, all my results get doubled. if I have any unk-unks in this, it could be completely off.


texts: Need a transistor to drive 12v 400mA Solenoid

texts:
I need a transistor whose base will be driven by a controller (3mA max base current).
the Vce(sat) should be less than 0.5 or max 0.7. And collector current required by solenoid is 400mA. I am unable to find a transistor with such specification.
can you suggest any? single or darlington is also ok


texts: How to turn on module like ESP8266 only when switch is activated?

texts:
I'm looking for a way that the ESP8266 (or alternative, like an Attiny85 with an RF module) is only turned on once a reed switch (or similar sensor) has been triggered.

The problem is that the ESP8266 should have just enough time to power on and send a message over the Wi-fi network. The reed switch could close too fast for the device to send a signal.

Are there any components I can use to add a minimum power time before the reed switch (or power, somehow) is closed again?

The purpose is to keep the batteries for a long time while also notifying when the reed switch is activated.


texts: Why my non-inverted amplifier does not work?

texts:
I'm trying to use a TL081, for which I used a DC power supply regulated by MPL1303, to feed the TL081 and a Vin from a DAQ assistant giving an analog signal of 0 to 5 V. I tested the signal from the DAQ and the supply from the MPL and it is working well, but I'm not being able to read anything from the output of the opamp.

My questions are:

1) Should I set the power supply on the TL081 with +12 V on Vcc+ and -12 V on Vcc-, or can I set 0 V on Vcc-?

2) Can I use any value for the two resistors, because I want gain of 2, so R1/R2 = 1?

3) When measuring the output with a voltimeter, can I use any ground, or should it be the virtual ground?

Thanks,

![Thanks for the explanations,
new circuit that I'll test]4


texts: Power supply for multiple parallel LED strings?

texts:
My sister is building a display sign, and wants to have several "marquee letters" lit up on it. Like this one:

She bought 9 letters like this, and they all run off two AA batteries, and internally they're just a string of 7 to 9 LEDs hooked up in parallel with no resistors, just direct to the battery compartment running 3 volts.

So, she wants me to remove the battery compartments and wire them all together (74 LEDs in total) so they can all be powered off one power supply, and I feel like this is a little outside of my electronics knowledge. It would basically be 74 LEDs in parallel, and I don't have any concrete specs except they light with 3 volts across them.

In my past dealings with LEDs, it was always understood that there should be some current limiting resistor at play to protect them. There's none there now, should there be?

Also, if I try to recreate their current setup would I get a 3 volt power supply? Would it be wiser to use something larger and if so how should it be wired? Much of what I find on google on the subject is a bunch of info about choosing power supplies for 12-volt LED strips, but this is a bit different.

Could one of you be so kind as to help me understand? I hope I'm overthinking a simple circuit, I just need a little help sorting it out.

Would it make more sense to pull out the existing LEDs and insert a string of LEDs that's designed to plug into an outlet?

Thanks.


texts: Should I avoid placing a SMPS inductor close to a magnetometer?

texts: I am designing a board, which has a high current (~2A) buck-topology switch mode power supply on it, which uses an unshielded SDR0805 inductor. About 4cm from it, there is a magnetometer (combined mag/acc LSM303DLH.) Would problems be encountered with this setup? Would I need to shield the inductor?


texts:
I am currently learning about FET transistors, and there is some things that I do not understand about an n-type JFET.

I have two question about this transistor.

Why is Vgs important and how do we calculate it?
How can we calculate the pinch-off voltage without the datasheet?

Thanks in advance!


texts:
I'm building a boost converter and want to implement a shutdown feature. The particular chip I'm using, LM3478, has a shutdown feature which is activated by a high level on the frequency adjust pin. In this case, I'm assuming a high level would be 12V since the chip is powered by 12V. The control signal I will be using will be from an MCU which has an output level of 3.3V.

I cannot simply use a P-channel MOSFET since 3.3V at the gate is not enough to turn the MOSFET off if the source voltage is 12V. I could use a PNP transistor since it is current controlled but that would require the control signal to be open-collector (tri-stated to turn off, low to pull up).

I'm thinking I could maybe combine a PNP transistor and a small MOSFET to do this. The PNP emitter is connected to 12V and the collector is connected to the pin on the chip. The MOSFET drain is connected to the transistor base through a resistor and the MOSFET source is connected to ground. I would then control the whole thing by a signal on the MOSFET gate.

Is there a better way to do this?


texts:
I am thinking of creating a ternary computer from scratch, mostly as a hobby project, are there any parts out there that I could use? Or would I have to create them from scratch?  If so, what would be a good method?

I was thinking of a balanced Ternary system, much like Nikolay Brusentsov's Setun.  I am familiar with VHDL and I am quite familiar with Binary logic.  I was hoping to avoid using digital components, such as FPGAs and make a purely ternary computer, so I was thinking more of what to use a logic units, in lieu of transistors.


texts: What does the radiation from an antenna look like?

texts:
Just out of curiosity, I searched for antenna on Google Images, and what usually shows is something like this. So I really thought that an antenna radiates in a circular and equal pattern. But as I read the specs of an antenna and understand terms like DBI and Polarization I got more confused. So my question is, what does the signal radiating from an antenna really look like?

Update

For example, how can we draw this linear polarization inside this?


texts: Wheatstone bridge why not use a voltmeter?

texts: I have been reading up on the limitations of a Wheatstone bridge, one of which is that for high bridge resistances any imbalances are hard to detect because of the small current that flows through the galvanometer. Why can't we just use a voltmeter instead? Is it because a voltmeter is less accurate or something??


texts: Using a FQP30N06L MOSFET on a 3.3v microcontroller

texts:
I'm trying to drive a 2.5A/12V load controlled by a 3.3v micro-controller.

In the past I've used a TIP120. In this case I'm trying to drive a solenoid and the voltage drop I'm getting across the TIP120 is too high.

I was looking at other options and people recommend using a MOSFET. The problem I'm having is I need to drive it from 3.3v. Many people and tutorials suggest devices that -may- work at 3.3v but in reality may require up to 4.5v to fully switch. And this minimum voltage can vary from transistor to transistor.

I'm not an expert and this is confusing. I'm not very good at reading data sheets but keep finding recommendations for devices that upon looking, seem as if they need at minimum 4.5v to guarantee saturation.

So to clear it up I thought I would ask here: can I use a FQP30N06L (which is cheap for me to obtain and in the package (TO-220) that I require) to power my load if I drive it's base from a 2N2222 transistor?

The datasheet for the FQP30N06L states: 32A, 60V, RDS(on) = 0.035Ω @VGS = 10V.

So I guess I need 10V to fully saturate it?

If so that is fine. I was wondering if I could use a 2N2222 like this:

Very rough drawing I made up at the time in mspaint. Would this work and be acceptable?

Thanks!


texts:
I use auto routing with Altium and I search a way to force routing a connector on Bottom layer (as I do PCB prototype myself, it easier to solder connector on Bottom side).
To do this, I create a room and place it on this component.
Then I create a rule on this room.
But, it doesn't work.
Can someone help me to achieve this?
Thanks


texts: A generator would need to produce 'x' Volts in order to provide 'y' Amps? Am I understanding this correctly?

texts:
Let's say I have a device that requires 190A to work.
My generator has an internal resistance of 2 Ω.  The device has a resistance of 0.3 Ω.  This would mean that the load on the generator is now 2.3 Ω.  Using Ohm's Law IxR=E, the generator would need to produce 437V (not accounting for the voltage drop).  I this correct?
And if I add another identical device, then the load is now 2.6 Ω which would mean the generator would now need to produce 494V.
The voltage drop would be 190A x 2 Ω = 380V, so the actual voltage output of the generator would be 57V with just one device or 114V with two devices.
Is any of this correct or am I just way off?  Thanks!


texts: Why aren't CPUs cooled from below as well as above?

texts:
The transistory bits of an integrated circuit are approximately in the centre of the (plastic or ceramic) package.  They sometimes get hot, and we cool them by affixing a heat sink to one side.  Sometimes we just blow air over them with a fan.  Some of this heat propagates upwards, but some must also go downwards towards the PCB.  I don't know the ratio.  The following is the underside of a Intel Core i7-7700K CPU dissipating 91W of heat:-

There are many   connection pads. Clearly they act as lots of micro heat sinks that transfer some significant proportion of the heat to the socket /PCB.  Indeed many surface mounted components dissipate heat through (via stitched) copper layers.

So if cooling is important (as for the CPU overclocking community), why aren't CPUs cooled from beneath the PCB as well, with say a fan?

EDIT:

Whilst the below comments are on the whole negative, there are two new items.  One, there is a long thread on Overclock suggesting that a  significant number of degrees could be taken off the CPU temperature with a fan on the backplate. And two, I tried it (admittedly with only a Raspberry Pi). I covered the top side with cloth to isolate the Broadcom CPU, whilst cooling the underside only with a 60mm fan.  The fan reduced the maxed out CPU temperature from 82 deg. to 49.  Not bad, so I think that this idea has legs...


texts: Electric power of the light bulbs in a circuit with diodes

texts:
Let \$R_1 = 1 \: \Omega, R_2 = 2 \: \Omega, R_3 = 3 \: \Omega, ...R_{10} = 10 \: \Omega\$ be the resistances of the light bulbs depicted in the circuit below and let \$U = 2 \: V\$ be the voltage of the source in the middle.

  Problem:

  Compute the eletrical power \$P\$ of the light bulbs when the
  diodes' resistances and voltages are neglected. Then do the same when
  the polarity of the source is inverted.

I just need to know how to attack this problem. My strategy is trying to close the circuit through the light bulb which I'm currently solving.

My thoughts:

Let's look at

\$R_3\$:

The current is flowing through \$R_6\$, \$R_4\$ and \$R_4\$, so
$$P_3  = U \cdot I_3 = U \cdot \frac{U}{R_3 + R_4 + R_6} = \frac{4}{13} \: W.$$
Now we can see that the same goes for \$R_6\$ and \$R_4\$, so
$$P_6 = P_4 = P_3 = \frac{4}{13} \: W.$$

\$R_1:\$

Now I think that if you rearrange \$R_2\$ and \$R_3\$, you can claim that the current goes through \$R_1\$, \$R_2\$ and \$R_3\$, so
$$P_1 = U \cdot I_1 = U \cdot \frac{U}{R_1 + R_2 + R_3} = \frac{2}{3} \: W.$$
The same goes for \$R_2\$, so:

\$R_2:\$
$$P_2 = P_1 = \frac{2}{3} \: W.$$

\$R_5:\$

The current goes through \$R_6\$, \$R_4\$ and \$R_5\$, but it needs to get to the opposite side, so it goes through \$R_3\$ as well, giving
$$P_5 = U \cdot I_5 = U \cdot \frac{U}{R_3 + R_4 + R_5 + R_6} = \frac{2}{9} \: W.$$

\$R_7 - R_{10}\$:

is just mess for me. I think that the problem is:

How do I get the voltage when I'm not on the same parallel?
Should I just continue in the same fashion and try to close the circuit through the light bulb?

In that way, I'll try to guess \$R_{10}\$:

The current goes through \$R_6\$, \$R_8\$, \$R_{10}\$, \$R_1\$, \$R_2\$ and finally \$R_3\$, so:
$$P_{10} = U \cdot I_{10} = U \cdot \frac{U}{R_1 + R_2 + R_6 + R_8 + R_{10}} = \frac{4}{27} \: W.$$

Kirchhoff's law diagram as suggested in the comments:

simulate this circuit – Schematic created using CircuitLab

The equations are:

$$I_2 \cdot R_2 + I_3 \cdot R_3 + U = 0$$
$$I_1 \cdot R_1 - I_2 \cdot R_2 = 0$$
$$U + I_3 \cdot R_3 + I_6 \cdot R_6 + I_4 \cdot R_4 = 0$$

and so on...


texts: How to read AC power dissipation in LTSpice components?

texts: I'm interested in determining the dissipated power in an audio speaker using LTSpice.  Clearly the speaker is simply modelled as a resistance, say 8 Ohms.  LTSpice can directly display the DC power dissipation in a component, but how do I see the AC power dissipation?  Is some sort of manual calculation required or can the software provide it?


texts: Mosfet Protection Diode Part Number 3S4L VH10  I can not find it or anything like it. It has 2 leads like a diode, but uses a Mosfet. Very low voltage drop. I am using it for reverse voltage protection as it hooks up to a battery and sometime it can get reversed by accident. It was a fairly new device but does not show up in any search. I would use a substitude if I could find one.


texts: [UPDATED, not solved]Simulating a Buck converter

texts:
Im trying to simulate a buck converter done in class to see if this fits what the theory says it would be, It must receive 110 V and send to the load around 60V and 20 A,  the circuit is:

And with the next pspice circuit code

VS  1   0   DC  110V
VY  1   2   DC  0V
Vg  7   3   PULSE (0V 20V 0 0.1NS 0.1NS 27.28US 50US)
RB  7   6   250
LE  3   4   681.82UH
CE  4   0   8.33UF  IC=60V
L   4   8   40.91UH
R   8   5   3
VX  5   0   DC  0V
DM  0   3   DMOD
.MODEL DMOD D(IS=2.2E-15 BV=1800V TT=0)
Q1  2   6   3   QMOD
.MODEL QMOD NPN (IS=6.734F BF=416.4 BR=.7371 CJC=3.638P CJE=4.493P TR=239.5N TF=301.2P)
.TRAN 1US 1.6MS 1.5MS 1US   UIC
.PROBE
.options abstol = 1.00n reltol = 0.01 vntol = 0.1 ITL5=50000
.FOUR  20KHZ  I(VY)
.END

It was expected to see something like this

But Im getting this outputs

this are too much different between the expected graphs, the I(VX) would be ok except for the fA values instead of A. V4 means the load voltage so its supposed to be around the 60 V. The component values were calculated in class so Im assuming these are ok.
Why does not match the two graphs? (discarding print errors, and wrong components values)

UPDATE
The logic of the netlist is fine, I play with the values of the trans operator changing from

  .TRAN 1US 1.6MS 1.5MS 1US UIC

to

  .TRAN 1US 1.6MS 1.5MS 1US

Giving the next output

That is more or less the idea except for the fA values- and the fact it seems to be showing only one pulse of the source.
So its some sort of options error, what other values could be adjusted?


texts: Does the Si4731 / Si47xx provide the necessary info to fetch left/right demodulated audio levels?

texts:
I'm working on a project which uses an Si4731 broadcast radio receiver IC (Si47xx family) and which calls for left & right demodulated audio level meters based on a source FM broadcast signal.  I expect this to be available via I2C from the IC.  However, I've read through the manufacturer's programming guide (linked above) like five times now and I'm still not sure.

The closest thing that I've found to this in the above-linked guide is the TX_ASQ_STATUS (Audio Signal Quality) property, but I don't see exactly how it would apply here.  I'm already reading the FM_RSQ_STATUS (Radio Signal Quality) property and using that to get the Radio Signal Strength (for RSSI), Signal-to-Noise Ratio (SNR), and FM "Pilot" indicator via I2C.  Perhaps it's in there somewhere and I'm overlooking it?

Can someone with more experience with radio receiver ICs please help me understand this better?


texts: Circuit to prevent spark from plugging Li-po batteries into motor driver with filtering capacitors

texts:
I have a motor driver that handles 2 150watt motors powered by 2 Li-po 12V batteries (connected in series). Obviously, I need filtering caps on my driver so I used 2 1200uF caps connected in parallel.

My issue is that every time I connect the batteries there is a spark because of the caps. How do I prevent this spark from happening? I am pretty sure that there has to be a nice solution for this. Also, the motors never have to run right after connecting the batteries.


texts: What circuit will output a short latch pulse when the clock input pauses?

texts:
I'm transmitting serial data across a cable to a shift register. I transmit data in discrete packets, where different packets have different bit lengths. The clock frequency is about 20 MHz while transmitting.

When each packet ends, I need to generate a short pulse to latch the shift register. I know a packet has ended when the clock stays low for a few cycles.

What circuit will output this latch signal?

Commenters asked some good questions about timing, so I'll clarify:

The shortest packet is 800 bits, for a duration of 40 μs minimum.
Idle time between packets is 10 μs minimum.
The latch pulse duration must be 10 nanoseconds minimum.


texts: Sensing human touch or proximity to large metal pipe

texts:
Suppose one has a large metal pipe made of mild steel approximately 6-feet tall and 8-inches in diameter.  Suppose this pipe has an regular pattern of perforations on its surface.  Imagine the pipe is standing upright on the ground, mounted on a platform.

(Spoiler alert: I have such a pipe!)

I'd like to create a sensor or sensor network of some kind to sense when a human touches or nearly touches the pipe.

My initial inquiry went towards capacitive touch sensors and I've tried breakout boards using the MPR121 and AT42QT1010 chips, and have also tried a simple circuit like the one depicted here using the Arduino Capacitive Sensor library.

Nothing has worked.

I've connected the boards via wire directly to the pipe, and I've tried using electrodes (aluminum - about 6" square and another 2" square) insulated in a ziploc bag mounted to the inside surface of the pipe.  What I've learned (I think) is that the massive amount of metal itself is such a large capacitance source (if that's the right terminology) that the differential when a human touches it is too minimal.  The relative capacitance increase is too little.

Questions:

Is that right?
Are there techniques to improve this approach?
If this approach is futile, what are some other approaches I could use?

Bonus:  If there's a way to get any level of resolution of where a person is touching the pipe, that's actually my perfect application, but I'm starting to think that's a pipe dream.   (...sorry.)


texts: Is it possible and safe to charge a NiMH battery with this circuit?

texts:
I am trying to design a circuit to charge NiMH battery packs from 2.4V to 9.6V and also single cells. From what I have read about charging NiMH batteries, it seems that all that needs to be done is to supply them with a constant current and monitor the voltage and possibly temperature to know when they are done charging.

My first thought was to use an op-amp current source to supply a constant current. I have started out with the schematic below from an instructable on building a constant current source by GreatScott:

Here is my schematic:

simulate this circuit – Schematic created using CircuitLab

I kept most of the circuit intact except for changing the op-amp to one that can handle a 12 volt power supply. The potentiometer will be replaced by a voltage divider of precision resistors once I have determined the values needed for the correct charging current. The only issue I have is choosing the value of the sense resistor. I am planning to charge the cell or battery pack at a current of 1A, which should be OK for 2300mAH AA-size cells. How should I choose the value of the sense resistor for this?