texts: Understanding the negative feedback and stablizing of a current limiter

texts:
Here's a current limiter circuit that uses the negative feedback to limit the current to a certain point.

simulate this circuit – Schematic created using CircuitLab
I have not studied feedback systems before as I'm not an EE student just do it for fun. But here's what I know about this circuit:
When the current through R2 increases the voltage on the base-emitter would also increase.  When the voltage reaches about 600mV Q1 will start to conduct. The  collector current in Q1   will pull the gate voltage down due to R1     turning   the mosfet off, hence reducing the current through the LED. Probably this will continue until Vbe and Vgs reach a certain set point.
Using the equation for a negative feedback loop, assuming the open loop voltage gain is G, we get for the closed-looped voltage gain
$$GV=\frac{G}{1+\beta G}$$
where the denominator takes account for the feedback fraction. Knowing all of this I want to calculate the Vbe and from that measure the current through the LED.
I know the open loop gain of the CE stage but don't know how to start off. I also don't know how to calculate the feedback fraction. I have not seen a practical example of such a circuit before. I want to go through each feedback loop and calculate everything, and finally get a good estimation for all circuit parameters. So any hint would be appreciated.
Here are some observations(out of breadboard):
For Vcc=5V and LED's FWD equal to 2V, I got the following readings:
Vbe=0.47V
Vgs=3.8V
I(led)=40-50mA

UPDATE 1:
I have written a simple code in matlab that runs through a loop for 5000 times, each time calculating a Vbe based on a new Ic.
I used the fact that for a silicon NPN BJT the collector current is 4mA at Vbe=0.7V. For Is I took 8.11*10^-15A. I got a wide range of results as you see below. To save space I've kept some interesting ones. Here's the code and the output:
function clcm()

I=4E-3;
Vbe=0.7;
Ic=40E-6;
Is=8.11E-15;
Vt=26E-3;

R=zeros(10,3);

for i=1:5000
    Vbe=Vbe-Vt*log(I/Ic);
    I=Ic;
    Ic=Is*exp(Vbe/Vt);
    R(i,1)=i;R(i,2)=Vbe;R(i,3)=Ic;
end

disp(num2str(R))

end

Here's the output with the 2nd column indicating the Vbe and the 3rd showing corresponding Ic:
1     0.58026558  3.9954399e-05
2     0.58023592  3.9908849e-05
3     0.58020626  3.9863352e-05
4      0.5801766  3.9817906e-05
5     0.58014694  3.9772512e-05
6     0.58011729   3.972717e-05
7     0.58008763   3.968188e-05
8     0.58005797  3.9636641e-05
9     0.58002831  3.9591454e-05
10     0.57999865  3.9546318e-05

3630      0.4726373  6.3647499e-07
3631     0.47260765  6.3574938e-07
3632     0.47257799  6.3502461e-07
3633     0.47254833  6.3430065e-07
3634     0.47251867  6.3357753e-07
3635     0.47248901  6.3285523e-07
3636     0.47245936  6.3213375e-07
3637      0.4724297   6.314131e-07
3638     0.47240004  6.3069326e-07
3639     0.47237038  6.2997425e-07

4991     0.43227299   1.347568e-07
4992     0.43224334  1.3460317e-07
4993     0.43221368  1.3444972e-07
4994     0.43218402  1.3429644e-07
4995     0.43215436  1.3414334e-07
4996      0.4321247  1.3399041e-07
4997     0.43209505  1.3383766e-07
4998     0.43206539  1.3368508e-07
4999     0.43203573  1.3353267e-07
5000     0.43200607  1.3338044e-07

The Vbe=0.46V is what I exactly measured. I also measured collector current at about 6.8uA so it doesn't agree with what I got above. There should be some constraint that forces me to stop running the code up to a specific iteration, because it's giving me a broad range of currents and voltages. We know the system in a negative feedback should reach equilibrium somewhere.
UPDATE 2:
Here I have plotted the I-V characteristic of the BJT using the data I found above:

Here's the actual behavior of the circuit simulated in LTspice:

where V(n004) is the base-emitter voltage. As you see it doesn't agree with the above schematic. I'm actually trying to understand how I should modify the code to achieve the predicted result.


texts: What's wrong with my interpretation of what should happen in the circuit and what's happening?

texts:
Here is what I expected to happen:

A B C D
0 0 0 0
1 0 0 0
1 1 0 0
1 1 1 0
1 1 1 1
0 0 0 0
...

Initially, suppose all flip flops have output 0. Then, Q' of the last flip flop is 1, so all flip flops are in a stable configuration.
On the next clock pulse, first flip one flips to 1 (because of Q' of last flip flop), and so on.

After the 3rd pulse of the clock, the flip flops are in the state 1 1 1 0.

On the next pulse, here's what I think should happen:
Last flip flop takes in a 1, forcing it's Q' to become zero. That resets all the previous flip flops to 0. After resetting to 0, the output of first flip flop resets the last flip flop, effectively cycling back to the initial state with all flip flops being 0.

I reckon I have made some mistake in reasoning over here because it appears to not behave like that when I simulated it with QUCS. (I didn't have access to digital simulation in it but worked with transient simulation, so I might be wrong here too)

Any input is very much appreciated.


texts:
I have a arduino running with bitlash running on it connected to a shiftbrite.

I can use a terminal program to send it commands such as rgb(1023,0,1023) and it will work but when I do it with python it doesn't.

Here is my python code. I don't know why it doesn't work. I can even print the string on an LCD connected to it and it comes out correctly

#Python Menu
#File: PythonMenu.py
#Basic menu system for use with Arduino and Shiftbrites
#over a wireless xbee link

import os #For clear
import time #For delay
import serial #For serial comms to the device

def printMenu():
    """Prints the menu ready with all options"""
    print "/--------------------------------------------\\"
    print "|      |  | |  | /--- |  |  __  ---|         |"
    print "|      |--| |  | |  - |--| |__ |___          |"
    print "|      |  | |__| |__| |  | |__  ___|         |"
    print "|--------------------------------------------|"
    print "| Please select from the following options   |"
    print "|                                            |"
    print "| (1) White                                  |"
    print "| (2) Red                                    |"
    print "| (3) Green                                  |"
    print "| (4) Blue                                   |"
    print "| (5) Fade                                   |"
    print "| (6) Off                                    |"
    print "|--------------------------------------------|"
    print "| (0) Exit                                   |"
    print "\\--------------------------------------------/"

def clear():
    """Clears the console screen"""
    os.system('clear')

def sendColour( r, g, b ):
    """Sends a RGB value to the shiftbrite"""
    #build up string
    tmpData = "rgb("
    tmpData += str(r)
    tmpData += ","
    tmpData += str(g)
    tmpData += ","
    tmpData += str(b)
    tmpData += ")"
    ser.write(tmpData)
    print(tmpData)

    return

###
#
###

#Setup serial
ser = serial.Serial('/dev/tty.usbserial-A600dJm8',9600)
#Start main code LOOP
while True:
    clear()
    printMenu()
    userInput = raw_input('Selection:')
    if userInput == '1':
        sendColour(1023,1023,1023)
    elif userInput == '2':
        sendColour(1023,0,0)
    elif userInput == '3':
        sendColour(0,1023,0)
    elif userInput == '4':
        sendColour(0,0,1023)
    elif userInput == '5':
        sendColour(0,0,0) #To be implemented
    elif userInput == '6':
        sendColour(0,0,0)
    elif userInput == '0':
        print "Quitting"
        ser.close()
        exit()
    time.sleep(2)

Anyone got any ideas?


texts:
That is my circuit:

Input: 400V DC

U2_1: LTC1285 (ADC) http://www.farnell.com/datasheets/1575635.pdf

U2_2: IL261 (digital isolator) http://www.nve.com/Downloads/il260-1.pdf

The circuit behavior is:

1: resistive partitor with high precision resistor to decrease the input voltage.

2: zener diode protect from eventually overvoltage.

Now the question:

In point 3 is useful to use a low pass filter for clean the DC on ADC input from eventually high frequency noise? If yes, how can I connect it for a proper functioning?

Is the first time I use an ADC.. thanks in advance!


texts: The current I=-10e^-2t,Find the voltage of the source Vs?

texts:
This is the Question

Attempt:
I Solved this circuit with two different method like this

Now In the laplace transformation method I am getting an extra term that is first derivation of impulse(doublet).
Now why is there discrepancy in this two method? What is the mistake i am doing?

Thanks


texts: Harmonic resonance calculation in power-factor correction

texts:
Eaton's Power factor correction:
a guide for the plant engineer states,

  Capacitors and transformers can create dangerous resonance
  conditions when capacitor banks are installed at the service
  entrance. Under these conditions, harmonics produced by
  nonlinear devices can be amplified manyfold.
  Problematic amplification of harmonics becomes more likely as
  more kVAR is added to a system that contains a significant amount
  of nonlinear load.
  You can estimate the resonant harmonic by using this formula:

\$ h = \sqrt {\frac {kVA_{sys}}{kVAR}} \$

kVAsys = short-circuit capacity of the system
kVAR = amount of capacitor kVAR on the line
h = the harmonic number referred to a 60 Hz base

  If h is near the values of the major harmonics generated by a
  nonlinear device—for example, 3, 5, 7, 11—then the resonance
  circuit will greatly increase harmonic distortion.

Two questions:

Why would resonance depend on the short-circuit capacity of the system? (Can you explain the formula?)
I can't find a similar equation for 50 Hz. Any suggestions?

For reference, this is for a 1 MVA transformer (short-circuit capacity not known at this time) and 350 kVAr PF bank).


texts: How to simulate simple on/off, Single-Pole-Single-Throw switch?

texts:
I am trying to simulate ON, OFF switch in this simple circuit:

V1 0 1 1.5v
Rfan1 3 4 1
S1 1 4 SW ON
Rwire1 6 5 0.00001
VV1 0 2 dc 0
VRfan1 3 5 dc 0
VRwire1 2 6 dc 0
.dc V1 1.5 1.5 1
.print dc i(VV1) i(VRfan1) i(VRwire1)
.end

but I got this error:

ngspice stopped due to error, no simulation run!

the circuit I am trying to simulate is like this one:

if I replace the switch with a resistor, the circuit will work normally.

any idea?
EDIT

I have fixed my switch as the following:

S1 1 4 98 99 mySwitch ON
.model mySwitch SW vt=0 vh=1 ron=1n roff=10k


texts:
If I connect a digital multimeter directly to a DC power supply, the voltage shown on DMM is higher on the power supply.

For example, if the source is 3.29 V then DMM shows 3.31 V. What is the reason for this?


texts:
(ACTUAL QUESTION IS AT THE BOTTOM)

I am a beginner in electronics and am learning more day-by-day to my best. I first got interested in Nixie tubes a few years back, so those are what I play around with, as they sparkef my curiosity.

I have been using this circuit I came up with:

And it has been working fine; all five 74141's I have had been working until late.

But I have found that, for some reason, when I had started using some new breadboard I had bought, that, suddenly, the circuit did not work. I removed it all and put it back together on my old breadboard and found that it did the same; all of the digits would be lit up at the same time save for one or two and would barely flicker. I did not think to swap out the 74141 for some of the other ones I havhavbut instead I decided to swap the tube for some LED's as I have before done using the same layout; all of the anodes connected together, sharing one common resistor:

It was at this point I saw that a handful of the LED's barely lit, others cycled through my test program, but LED #6, on pin 10 of the 74141 stayed on no matter what. Frustrated, I undid the entire circuit and redid it still the same thing. I have no idea why, but I decided to swap out the 74141 for another; it works perfectly; testing both multiplexing and just normal half-second cycle through, as should be expected.

QUESTION:

Exposition out of the way, IS THERE ANY WAY I COULD HAVE DAMAGED IT WITH MY CIRCUIT? Or perhaps just something random with the IC itself; it's not old (it's datecode is 1540--fortieth week of the 2015.) Some are still producing the K155ID1 in Russia for some reason. Perhaps dropping it? Or accidentally swapping the VCC and GND for it?


texts: how to find the DC motor turning angle using encoder?

texts: I have a DC motor (MTR11_200) encoder rotating at 100 RPM with and encoder(EH_30_M) which sending 200 PPR how to fix the DC motor to turn at specific angle using this information?


texts:
Its a little thought experiment. Below you see a transmission line consisting of 2 parallel wires. With an LCR meter, I am measuring the inductance of the cable.

On the left side, the LCR meter measures one cable.
On the right side, the transmission line is shorted out at its far end. The LCR meter measures the inductance of two cables.
Will the inductance measured on the left side be half of the inductance measured on the right side?
In the cables datasheet, we often find inductance per unit length. Is the inductance per unit length measured like on the right side?


texts:
Maybe sharing this idea after building a prototype would be much better.

As many of you know, there is a technique to make a PCB with laser CNC. You spray a matte black paint onto PCB, and burn that paint at some points to create tracks.

The problem is that me, and I am sure, many other people doesn't have laser engraver. Either too expensive to buy one, or building a quality one at home is not that easy. This entry is about easing this process, and making it very cheap. My proposed method is as follows:

Cut a PCB at the size of a DVD. Inner hole should be cut as well.
Spray the PCB with black matter paint.
Put the PCB into DVD writer.
Start the DVD writer program that reads what to be written onto DVD (PCB) from gerber file.
Laser of DVD burns each bit on DVD that removes paint from there.
Take out the DVD (PCB). Etch it with chemicals.

Actually, to be able to understand this procedure, one needs to use his imagination. Above idea came to me 5 minutes ago. So, it is not perfect maybe.

Please check this picture first: http://en.wikipedia.org/wiki/DVD#mediaviewer/File:Comparison_CD_DVD_HDDVD_BD.svg

In this procedure, problems are as follows:
1. Minimum diameter of a point a DVD writer can focus is 400nm.
2. There is 420nm distance between top and bottom points.
3. Fume of burning paint cannot escape from DVD writer while it is already being burned.
4. Inner circles of DVD has less sectors than outer ones. Conversion from gerber file (e.g. black-white image) to bits on sectors can be hard.

I know this as less like a question, but a blog post, though has anyone experienced doing anything like this? I don't have enough big PCB and spray paint right now unfortunately.

Question is that is there anyway to modify DVD writer's head moving mechanism to remove that 420nm space, so that it can draw a seamless track?


texts:
In case of switch mode power supplies, we uselly use "Error Amplifiers" (Type 1,2 & 3), my question is:
The output voltage of this amplifier (Verr), is it the DC error of the Vref and Vout (i.e: Verr=A(Vout-Vref), A is the DC gain of the error amplifier)? if is not, please explain to me what is it and what is the role of DC gain in that case??

simulate this circuit – Schematic created using CircuitLab


texts: If a MOSFET has infinite inner resistance (ro), how does current flow through it?

texts:
Ideally the MOSFET is a current source in saturation mode, but I don't understand why is it modeled with an (ideal) infinite inner resistance.
How would the current flow?


texts: What is the difference between a BIOS chip and a PCH

texts:
From what I can gather, the BIOS chip is a loadable memory space that handles initial I/O, system checks and CAN configure certain things like power states and clock rates, before handing operation over to the chipset/CPU. The chipset then orchestrates connection and throughput between CPU and peripheral devices i.e. RAM, PCI lanes etc.

Is that the main difference? If so, why don't we just let the chipset handle all the initial boot stages?

Please close if off-topic and I will ask in superuser.


texts:
I have built an active band-pass filter on a breadboard with the use of an MC33078p op amp. Gain is 32 on paper.

When I apply the AC signal to the circuit, 18.1mV P-P and 660kHz, the oscilloscope measures a voltage of 1.22V at the output but with zero frequency. When the earth probe is not connected, I measure a frequency of between 30 and 60 Hz.

Is there any obvious reason for this?

As well as the frequency problem, the output voltage doesn’t seem to be inverted, it’s a fairly basic circuit and don’t believe I’ve connected anything wrong.

Any ideas?


texts: Does the voltage affect the AWG wire size choice?

texts:
I read a lot of website and articles about how to choose the right wire size, this one for example, and all of them have a table with AWG size and a corresponding maximum amperage. However, they never talk about voltage.
Let's say I need a wire for 60 000 V @ 1 A, by looking at the table, I could go with a 29 AWG. If I now need a wire for 1 V @ 75 A, the same table tells me to go with a 7 AWG. This would imply that the smaller wire will withstand 60 kW and the larger cable only 75 W.
I found all of this a bit strange, why should I use a smaller wire for a higher power?


texts: A 4 bit counter d flip flop with + 1 logic Verilog

texts:
I'm trying to implement this D flip-flop counter with + 1 logic through verilog. But I'm getting a lot of error codes about multiple contant drivers for net. Can anyone give me a hand im very new to this programming language. Here is also the code soo far

module LAB (clk, clear, Enable, Q);
  input clk, clear, Enable;
  output[3:0] Q;
  reg[3:0] Q;
  wire D;

  assign D = Q;

  always @ (posedge clk) begin
    if (!clear)
      Q <= 1'b0;
    else
      Q <= D;
  end

  always @ (Enable) begin
    if (Enable == 1)
      Q <= D + 1;
    else
      Q <= D;
  end
endmodule

here are the error codes i am getting

Error (10028): Can't resolve multiple constant drivers for net "Q[3]" at
LAB.v(17) Error (10029): Constant driver at LAB.v(9)
Error (10028): Can't resolve multiple constant drivers for net "Q[2]" at LAB.v(17)
Error (10028): Can't resolve multiple constant drivers for net "Q1" at LAB.v(22)
Error (10028): Can't resolve multiple constant drivers for net "Q[0]" at LAB.v(22)
Error (12153): Can't elaborate top-level user hierarchy
Error: Quartus II 64-Bit Analysis & Synthesis was unsuccessful. 6 errors, 4 warnings
Error: Peak virtual memory: 4613 megabytes
Error: Processing ended: Sun Apr 19 18:39:09 2020
Error: Elapsed time: 00:00:01
Error: Total CPU time (on all processors): 00:00:00


texts: Are my calculations for this LED boost driver circuit correct? (TPS61169)

texts:
I have a display with the backlight LEDs arranged 6S4P (so 4 parallel strings of 6 LEDs joined internally, so must be driven as single string) and have been trying to find a suitable driver for it - I thought the TPS61169 looked promising but now I've run the numbers I think I'm busting the 1.2A switch current limit.

Using TI's reference circuit & calculations from the datasheet (plus measured voltage on an example screen):

Vin = 5v
Total LED voltage (converter Vout) = ~26V
Total LED current (Iout) = 240mA
Assuming ~80% efficiency
Inductor = 10uH
Switch frequency = 1.2MHz (fixed)
VFB = 204mV
Diode Vf = 0.5v

I calculate:

Sense resistor (RLED) = 0R85
Input current (ILDC) = 1560mA
Inductor ripple current (ILP-P) = 337mA
Peak inductor current (ILP) = 1728mA

So assuming ILP will flow through the switch that's going to let the magic smoke out of the IC.
So, are my calculations correct? If so, without wanting to violate the "no shopping questions" rule, pointers to a more suitable device (ideally in the same footprint) would be most appreciated.


texts: What is the purpose of an AND gate with the same signal on both inputs?

texts: If this is a buffer, why use an AND gate, aside from better availability of that gate in a single package? This is on an Analog Devices SHARC eval board.


texts: How to analyze/decode a Manchester encoding?

texts:
I have a barcode scanner working on 433Mhz (FSK). Since this is a relatively old product and the PC software is not working with Windows 10's and I can't use the SDK anymore. I, therefore, have decided to make my own receiver hardware and a PC software accordingly.

I have disassembled the scanner and directly wired to a simple logic analyzer from the device's transceiver module. There is not much information about this module. But, I know pin-outs, their functions and "receives and transmit data packets at 36864 baud Manchester encoded".

So, I have opened the old program with an old Windows OS version and start scanning right after I clicked the start button on the Logic analyzer.
Normally, the receiver has continuous reception regardless if I am using the scanner or not. We can consider this as other emissions in the environment.

As far as I discovered, there is a carrier detect signal leading the scan data and around this (beginning of the carrier detector after carrier detect signal) there are serial of bits looking like preamble with 0's (if I am not mistaken, because shouldn't that preamble always right after the carrier signal as part of the data?)

Logic analyzer Manchester setup:

And some output from the analyzer (you can ask more detailed look if you like):

There are two consecutive barcode scannings here.

I have tried several version of the settings. I tried to place some random numbers in the Preamble bits field or different bit rates, positive or negative edge, LSB or MSB but I couldn't get the analyzer decoded my signal. At least I would like to see the barcode I scanned somewhere in the data part.

I am not an expert on this encoding and RF communication but learning and I am reasonably enthusiast.

Any pointers would be greatly appreciated.

EDIT:

In order to be certain what's being really sent by the scanner, I have also recorded the transmit data from the source directly. I believe that it is giving more clue than the captured receive data.
(There are two different barcode scannings included and placed one after each vertically in order to analyze/compare better)

EDIT:

Here is the transceiver module sitting on the main board as daughter board:

It is Telital RT14.
Pins are marked in a red square where I hook-up them to the logic analyzer.

EDIT:

A diagram of how the RF device is connected to the barcode reading system.


texts:
I have this circuit:

This circuit is working for a long time like this, with the switch open. So, the circuit is stabilized and the voltage across the capacitor is 40V.

At t=0, the switch is closed.

What is the voltage across the capacitor 3ms after the switch is closed.

MY SOLUTION

After the switch is closed, the capacitor will change its voltage to match the one imposed by the voltage divider composed of R1 and R4.

At the left side of R1 there is 40V and at the right side of R4 there is 30V.

If we remove the capacitor, we can calculate the current in the circuit to be

\$V = RI\$

\$(40-30) = (100 + 22)I\$

\$I = 81.96mA\$

So, the voltage drop across R1 is equal to

\$V_{R1} = 100 x 81.96mA = 8.1967V\$

So the voltage between the resistors is

\$V_{div} = 40 - 8.1967 = 31.80V\$

This will be the voltage across the capacitor after stabilization.

So far, so good. This matches the value I get from the simulator I am using.

Now I want to know the voltage across the capacitor 3ms after it starts discharging.

If I substitute both voltage sources with wires, I see that the capacitor is in parallel with R1 and R4, what gives me an equivalent resistance of 18.0327.

Now I use

\$V_c(t) = V_s e^{-\frac{t}{RC}}\$

\$V_c(3ms) = 40 e^{-\frac{3e-3}{18.0327 x (1000 e-6)}}\$

\$V_c(3ms) = 33.8695V\$

The problem is that when I simulate that using software simulators I get the voltage across the capacitor after 3ms to be 38.7438V.

What is wrong?


texts: The difference in lengths of the differential pairs are tremendous, which is quite evident in the screenshot. I just don't see how I am supposed to length-match this. Tips will be appreciated!


texts: MicroSD with STM32 and SPI mode - pull-ups and EMI filters

texts:
In the context of using the STM32F103C8T6 microcontroller I wonder I am thinking about the most practical and relevant method of the microsd application in the device from the point of device security.

PLAN:

There are three modes:
a) SPI
b) SD card 1 bit mode
c) SD 4 bit mode (4 bits at a time)
I would like to use SPI mode, so DAT1 and DAT2, as a rule says, will not be connected to a microcontroller.

Question

Among the information and example applications on the Internet, I realized that despite the existence of internal pull-up resistors in STM32, it is worth using external pull-ups and placing them as close to the Microsd socket as possible due to the potential interference with long paths between the microsd card and the microcontroller. However, if this is true, should the unused pins DATA1 and DATA2 also be connected to 3.3V in the SPI mode of the Microsd card control, or only these four resistors, as in my diagram? Or maybe additional capacitors are required
EMI Filter - Is it worth using an EMI filter between the MicroSD and the microcontroller? I've seen a complex CM1624 IC here:

https://www.acmesystems.it/pcb_microsd
but in very small size. I wonder if are there any simpler protection systems that you have tested?


texts: Why do programs stop watchdog timer on MSP430?

texts:
Many sample programs for the MSP430 have their first line as:

WDTCTL = WDTPW | WDTHOLD; // Stop watchdog timer

Why do they do this?


texts: For a simple logic implementation of clock gating I used BUFGCE. When went through the schematics I noticed logic is implemented using FDCEs. But CE of FDCE are not used. My question is why BUFGCE didn't got optimized using CE in FDCE. Am I missing something here ? Please help.


texts: Advice for this P-Channel MOSFET Power Source Selector

texts:
I know there are already questions and answers about P-Channel MOSFETs and power source selection, but I still find myself pretty confused, as many of those are more complex than my circuit or simply connected differently. I'll lay out my design and then list a few questions. Any thoughts would be greatly appreciated!

I'm powering an ATMEGA328P using approximately 5V (so it can run at 16MHz). Normally, it will run on 3 AAAs in series (4.5V total). When I connect a 5V FTDI USB-to-serial board to program it, I'd like power from the battery to be cut to keep from damaging the battery (I don't want to have to put a diode there). I'm planning to use a logic-level P-Channel MOSFET. I expect to draw about 50mA max, but may plan for 100mA just to be safe.

simulate this circuit – Schematic created using CircuitLab

Analysis:

Vusb range: [4.75V, 5.25V] (per USB standards)
Vbat range: [3.8V, 4.8V] (min needed for 16MHz and max from 1.6V AAA estimated max voltage)

USB Connected:

Vusb    Vbat    Vgs    Expected MOSFET State
--------------------------------------------
4.75V   3.8V    0.95V  OFF
4.75V   4.8V   -0.05V  OFF
5.25V   3.8V    1.45V  OFF
5.25V   4.8V    0.45V  OFF

USB Disconnected:

Vusb    Vbat    Vgs    Expected MOSFET State
--------------------------------------------
0V      3.8V   -3.8V   ON
0V      4.8V   -4.8V   ON

Questions:

Are there any glaring mistakes with this design?
What's the best way to keep the MOSFET from accidentally opening? I've tied the gate to ground through R1, which seems correct.
I've connected Vusb (gate) to VCC (drain), then added a diode to keep the MOSFET from always being open. Is this a correct assumption?
Do I need any other diodes on the two power lines? I'd rather not have their voltage drop (otherwise I'd just use a simple ORing diode circuit to get what I want). What circumstances would produce backfeed current into either the battery or USB?
I've often seen P-Channel MOSFETs connected the other way around, with the load connected to the source rather than the drain. What's the deal with that? Can current flow both directions? Which is most conventional?
I'm planning to maybe use FQP27P06, though it seems most logic-level ones have a compatible Vgs(th) range. Have any better/cheaper suggestions?

Thanks again! I've asked multiple questions on this forum and y'all are always so helpful.


texts:
I would like to charge a 20,000mAh power bank with a 18V 20W solar panel. The power bank has 8*18650 batteries in parallel. I came out with 3 options.

The first one is to use a buck DC-DC converter with a BMS 1S in order to charge the battery pack directly.
The second one is a Q.C. module directly connected to the solar panel, since the power bank is compatible with Q.C.
The last one is an MPPT charge controller based on a CN3791. (This one comes in two versions, 9V and 12V. I don't know if it will support my solar panel.)

Which configuration will be more suitable and get the maximum amount of power? Or can you give another solution?


texts: Opamp operation with "unbalanced" power supplies

texts:
Usually the way to operate an opamp is to feed a +V and a -V of the same magnitude but opposed polarity. Or, just +V and GND.

But now, I need an opamp's output to be In a different range. About -1.25V to +28V. The opamp i have is an MC4558, which has a supply voltage (max) of ±22V.

Can I supply this with, say, -3V and +33V? The configuration I'm using is drawing "B" in this answer: Setting LMC6001 offset voltage

Some opamps, like the LM324, say supply can be 0-36 or ±18V. This one only mentions ±22V. It doesn't say 0-44V.


texts: Photodiode non-inverting amplifier circuit

texts:
I am a Masters student currently working on a project of a two-axis moving structure that will scan the sky for diffuse irradiation. The sensor I am using is a silicon photodiode SP1110 from skye instruments - it outputs 10uV/W/m2. I plan do measure various irradiance points at different azimuth and zenith angles in order to create an irradiance distribution map of the sky, hence, speed of measurement is important.

I have been trying to build a circuit to amplify these small voltages up to the mV level so it is then read by an 16-bit ADC (adafruit ADS 1115) which will be connected to an arduino. The current circuit that I have is the following (using an LTC1050 op amp):

Note: ignore the two bottom 6 Pin Sets as these are supposed to represent an RTC circuit and an SD card reader. The 10 Pin set on the right hand side of the circuit is the ADC (adafruit). Using an LTC1050 Op Amp.

I have also experimented with the transimpedance photodiode circuits but without any success for any of them - the output voltage simply remains the same no matter the input. Could this be because the output expected is negative and due to the fact that I am using single supply it doesn't work? (Vout = -Iph * Rf). One of the circuit that I experemented was the one that comes in the LTC1050 datasheet (photodiode amplifier).

The main problem I am experiencing is the lack of amplification at very low voltages, more precisely, in the 1-40 uV input range and even after those, the amplification still doesn't satisfy the selected GAIN (=1000, also tried with 100). Here is the input-output graph that I get using a Keithley SMU :

Note: the orange curve is the theoretical curve i.e. what i should be getting with 100 gain in this case.

Furthermore, I also experience problems once i connect the output of the circuit to the analogue input of the ADC. Once I do that, the voltage remains stable at a few mV without changing in relation to the input, is this due to its impedance? How would I go about correcting that?

I also tried doing this in a two-stage amplification but that also didn't work and the output remained at a single value of a few mV's no matter the input. Could someone help me with this and potentially explain where I am going wrong and why any of these circuit isn't working?

PS: Tips in designing this circuit in a PCB would also be appreciated.

Thank you in advance.

------EDIT-----

The Forum doesn't allow me to post any more links than the ones I already have, therefore I'm not able to post my circuit layout on my experimental board.

I have tried increasing the values of the resistors as recommended by @peufeu from 3.3k to 330k and the results don't seem to ameliorate. The circuit only starts amplifying at 30 uV (output 5mV) and at 100uV(highest expected input for this application) it outputs 80 mV. The gain (=1000) is only satisfied once i try to feed 1mV in the circuit, at this point the output is 1 V as expected. Additionally, i found out that the capacitors in my circuit don't really do much, i attempted to remove them and the results didn't change much. Should i remove them completely? And does anyone have a clue why this circuit doesn't amplify correctly at low voltages?

In regards to the transimpedance amplifier, I attempted this circuit which again didn't work, the output went to saturation even when i was feeding in only 50nA. Unfortunately I can't upload anything to demonstrate this but it seems that taking the current output configuration is proving to be more difficult.

Thank you again for your time to respond and to help me in any way.


texts: How do I receive an entire string as opposed to 1 character at a time on the arduino?

texts:
I followed the instructions on this website successfully:

http://www.doctormonk.com/2012/04/raspberry-pi-and-arduino.html

and I was able to get communication between the pi and my arudino mega exactly as the website specifies.

However, instead of sending an integer representing the number of times the LED blinks, I want to sent ASCII text like:

"MOVE 5 METERS FORWARD",  "TURN LEFT",  "MOVE 10 METERS BACKWARD" to the arduino from the pi.

I wrote the following code:

char inData[64];
char inChar=-1;

void setup(){
   Serial.begin(9600);
   Serial.begin("Waiting for Raspberry Pi to send a signal...\n");
}

void loop(){
    byte numBytesAvailable= Serial.available();

    // if there is something to read
    if (numBytesAvailable > 0){
        // store everything into "inData"
        int i;
        for (i=0;i<numBytesAvailable;i++){
            inChar= Serial.read();
            inData[i] = inChar;
        }

        inData[i] = '\0';

        Serial.print("Arduino Received: ");
        Serial.println(inData);
    }
}

I flashed  above code succesfully to my Arduino Mega 2560.

I switched to my python terminal on the Raspberry Pi and in the console I typed:

import serial
ser = serial.Serial('/dev/ttyACM1',9600)
ser.write("MOVE")

What gets displayed on my Arduino's Serial Monitor is as follows:

Arduino Received: M
Arduino Received: O
Arduino Received: V
Arduino Received: E

But what I want is:

Arduino Received: MOVE

How do I change the code above to get all characters into the inData buffer?


texts:
The mither in-law asked me if I could fix the OLD electric moulinex beater...
Once open I saw that both CDC's connecting the brushes are broken. I am having trouble identifying them, could you help? I'm not in anyway an electronics specialist.
She'd be better off buying a new one but I like a challenge...

Reference numbers:

1n5m 250v
GA 565-1
HSF

Can I replace this with a modern equivalent?

Any help greatly appreciated.


texts: Diode (LED) forward voltage in series and parallel

texts:
As a preface I am just a hobby electronics enthusiast and not an electrical engineering student, and I am just starting out at that, so these may be obvious answers for even a first year student.

As I understand it a basic LED has a forward voltage that it will "consume" from the voltage across a circuit (I am not sure for the correct term for this), so when you calculate the current-limiting resistor value required to protect the LED, only consider the voltage across the resistor, which in a battery-resistor-LED series circuit is the voltage in minus the forward voltage of the LED.

So an LED with a forward voltage of 2V connected in series to a 9V battery will require a current-limiting resistor to drop 7V.

If multiple resistor-LEDs are connected to the battery in parallel, the voltage is the same across each "junction."

So the voltage at points A, B, C, D and E should all be 9V? Therefore again each resistor is dropping 7V and each LED 2V.

My question is, what would happen if 5 LEDs were connected in series? I think we can use one resistor as the current in a series circuit should be the same at all points, but if we used a 9V battery and each LED had a forward voltage of 2V, what happens with 5 in series?

As the voltage drops in total are more than the voltage provided by the battery, would each LED drop one fifth of the 9 volts in (all else being equal)? As the voltage in minus the voltage out must equal zero, this is my guess as to what would happen, and that if that voltage was below the "operating forward voltage" of each LED then they just wouldn't light?

I know that if they were resistors then each one would have a voltage drop proportional to its resistance to the total resistance in the series circuit, but as LEDs aren't resistors presumably they wouldn't necessarily behave as such? The textbooks I have read don't tell you you need to "calculate" the forward voltage of the LEDs, you just go by the component datasheet.

Apologies if my questions are a bit all over the place, I am just trying to understand what is going on here.


texts: Phase margin for a system (design of PD controller)

texts:
I have a system with the following transfer function:

\$G(s)=\cfrac{20}{s^2+s+20K_f}\$

where \$K_f=1.75\$

I want to use a PD controller and I want obtain a phase margin of 35 degrees. I need to determine the parameters (\$K_p \text{ and } K_D\$) for the PD controller.

I made a Bode plot in Scilab for G(s):

As I want a phase margin of -10º, I would have to see the \$f_0\$ for which I have a phase of \$\phi=-10-180=-190º\$, but with -190º the system is unstable.

I can not determine \$f_0\$ from the Bode Plot, because the graph only reaches -180º. How can I design the PD controller for this system?


texts: serial vs parallel for electromagnets: power consumption

texts:
I am designing a project that will require about two dozen smallish electromagnets (larger than in a relay but much smaller than used to activate car door locks). They will be powered by a battery bank in an RV, so 12 vdc and the equivalent of about 4-8 car batteries in parallel. I have not chosen the electromagnets yet, so part of what I am deciding is what voltage rating to look for.

I used to be an electronics technician in the USMC, but all my work was in low-voltage signal shaping, where power use played almost no part in the way the circuits worked. I assume the serial vs parallel math is different when powering electromagnets is involved.

Here's the question: Would I be better off arranging these electromagnets in series or parallel? Would the actual current coming out of the batteries change much at all when the electromagnets are doing the same amount of total work either way?

By the way: These will only be in operation for about a second, every day or so. They are to release catches that hold things closed.

Naturally, parallel will be better for later troubleshooting. Should I just get 24 12vdc electromagnets, arrange them in parallel, calculate the total current, size my wire accordingly, and consider it done? Are there any other concerns I need to consider?


texts:
I'm currently using 74HC595 shift register to light leds. Recently I decided to start using RGB leds instead of simple 1-color leds. Which means that I now have to use 3 output pins for each individual led. So far so good.

The problem however, is that I cannot fully enjoy the power of the RGB leds. I would like to use the full color-depth by mixing the 3 color components (Red,Green,Blue) at different individual distinct brightnesses.

There is an Output-Enable pin on the 74HC595 which can be used to control the brightness, but as far as I know, its value applies to all output pins, and cannot be used to set the brightness of individual outputs.

Can it be done with the 74HC595 shift-register, or is there a more appropriate component ?


texts: Checking my understanding of this datasheet of a TFT LCD display?

texts:
I'm trying to modify an HDMI decoder board by Adafruit(https://learn.adafruit.com/adafruit-tfp401-hdmi-slash-dvi-decoder-to-40-pin-ttl-display/downloads) to work with an IPS screen that has a 51 pin connector. The adafruit board supports only 40 pins.

I've got the datasheet for the screen and while I have been able to decipher most of it, there are a few pins which I'm unsure about. I was hoping I could clarify some of it before going out and producing the PCB.

Here's the relevant part of the datasheet:

My questions:

1) Pin 39 - Does the reset pin need to be connected to ground? If it is active low, would connecting it to ground cause the device to keep resetting?

2) Pin 40 - Does low enable mean it is enabled by pulling to ground. I read if a CS pin is off it ignores the outside world for both inputs and outputs. Does this mean it should be connected to GND for the device to receive RGB data?

3) Pin 47-48 - The screen supports different interfaces but I need to use the RGB interface. Does this mean I should connect pin 47 & 48 to 3.3V so it reads as 1 for both and activates the RGB interface?

Also for reference here is the entire datasheet: https://www.scribd.com/document/383775532/4in-IPS-display


texts:
I have two solar panels in series giving ~106 volts when open circuit and around 4 Amps when loaded.

My mppt controller could accept 150v on the input, but it blew up when the battery was disconnected while the panels were active :(
My spare controller can only accept 100v on a good day and only 92v in certain conditions.

I tried putting a 1N5377B zener across the input to prevent the controller being overwhelmed, but it only worked for a while before it went dead short and started smoking.

I found a circuit using a mosfet and a zener that when fitted in series with the -ve lead from the panels, eats a few volts and stops the controller getting overvoltage, the problem is that it always eats those few volts, even on a cloudy day when the panels are only at ~75v.

How can I prevent the controller getting too much voltage without permanently losing 10-15v? It doesn't need to disipate the entirety of the 450W, just the first 40W or so, so that the controller is never presented with more voltage than it is designed to deal with.

Except under no-load conditions, the full OC panel voltage would never be present, so the device would spend most of the time doing nothing.


texts: I am looking for a small device/system that I can pre record a one or two word message on and play it back with the push of a remote button. Ideally, the remote would have 3-5 buttons for different messages and it would be wireless. If it had to be wired, the wires would need to be about 4 feet long. Does a product like this exist? Any thoughts? I work with special needs students and am looking for a discrete device as opposed to a phone or tablet app. I'm thinking something similar to what goes into stuffed toys may be applicable.


texts: What kind of sensor could this be? (Also recommended sensor for detecting the entry of vehicles)

texts:
Any idea which sensor this might be? It is being used to detect the presence of a cold and ferrous vehicle, in this case a truck passing by, with minimum speed 1km/h and max speed 5 km/h.
Also would like recommendations on sensing the presence of large vehicles. Reading distance can be as low as 0.5m and maximum 10m. I've narrowed it down to photoelectric or PIR. Is there a better way for this? I'd prefer to have a method with both the emitter and receiver in the same casing. (Rules out photoelectric thru beam)


texts:
How do reflections work, physically to the charge carriers level?

Considering a square wave generator connected to a long, open cable, I've made a quick chronological diagram of the propagation of the generator voltage, but I can't explain how electrons and holes bounce off the open end. For light (so... coax cables?) and sound it sort of makes sense to reflect when there is a sudden change in impedance, but here...

Based on those diagrams, the generator should start producing a higher voltage when the line is "full" (can't push any more electrons in), therefore after a single delay; however it does that after a return delay right? Does it "push" electrons in until there is an open voltage across it? How should that diagram be modified so that it is accurate?

The diagram is helping me to understand the "how" of this video.


texts:
I have an n20 DC motor which has a gearbox with a 55mm m4 threaded shaft (see image below for visualization of the motor). I'm compressing a spring with this motor, so the motor needs to work relatively hard to compress the spring.
I am noticing that the spring compresses significantly less (3/4 the expected compression) after the 2nd or 3rd subsequent time that I try to compress the spring (I take about a 1 minute break between runs). I am noticing that the motor is slightly warm after 1 or 2 of these spring compression runs.
Is it expected to see such a large difference in spring compression?
Also, does the motor wear out over long time of use? I have been using this motor for about a month and am wondering if all of this use is causing degradation?
I've attached an image of the specs of the dc motor. The gearbox has a reduction ratio of 1/52 and I am using the 6V motor. You can see our motor's specs highlighted in red.
Could it be that the m4 motor shaft is wearing out over time and causing friction as a result? What about the m4 insert I am using (could that be causing friction over time)?
Here is the spring we are using: https://www.mcmaster.com/9657K371/
Thank you very much for the help.


texts: are 100K resistors too weak for connecting HC to cmos?

texts:
I have created two identical circuits. The only difference between them apart from the number of lines on the LCD is that the old circuit uses 10K pull-up resistors instead of 100K pull-up resistors. I'll explain further...

I created a circuit in which data gets fed serially into shift registers (74HC164) via a serial port. The output of the registers are connected to a AT28C256 EEPROM which then loads the data to an LCD. This saves the micro controller from using up its space to store lengthy LCD messages.

When I tested things, both circuits turned on the LCD as expected, however in the newer circuit, the LCD didn't respond to anything where as in the older circuit, the LCD did respond and produced correct text on the screen.

I tested the LCD in the older circuit (even though it didn't fit), and the LCD does work.

I also tested the new circuit and fixed all the short circuits and open circuits I could find.

In both circuits, the pull-ups I described above are connected to the outputs of the shift registers (74HC164) because I was told that a solution was to use the 74HCT164 instead of 74HC164, but they might create EMI, and its harder to find 74HCT.

The reason why I jumped to 100K is because I wanted to save power on my circuit but the question is is 100K too high of a pull-up resistor value between an 74HC output and a cmos input? If so, what is the maximum value I should use?

EDIT: Just to clarify, old circuit uses 10K resistor pull-ups and new circuit uses 100K resistor pull-ups. Other than that, the schematic below was used for both circuits. Items marked J were staples that conduct electricity.

The LCDCLKB and LCDCLK connect together to prevent the 74HC164 inputs from floating.


texts:
I am using the en=g5la relay to activate the charge of a capacitor. Does it make sense to use a relay when you have a capacitive load? The general layout is that I have a diode brigde ( 4 diodes rectifier) on one side of the relay side which feed power and I got a 2.5 F capacitor on the other side which serve as energy pool. I switch on/off by using an arduino ouput the relay with a BJT who drive the inductor.

simulate this circuit – Schematic created using CircuitLab

[EDIT] This circuit worked perfectly in the end.


texts: What will happen to TLV1117 (5V / 3.3V) from reverse voltage?

texts:
There is a step-down DC / DC converter that receives 5V input and 3.3V output
It powers the Atmega328P microcontroller.

TLV1117 TI

For the firmware of the controller, I will use the USBASP programmer. It connects to the ISP connector (MISO / MOSI / SCK / RST / 3.3V / GND).

During programming, the 3.3V line will be powered from the programmer.

What will happen in this case with the down converter turned off? Power will be supplied from the bottom of the inverter. Is it necessary to put a diode on the 3.3V output?


texts: FTDI's GND pin removes noise from thermistor Arduino + ESP8266

texts:
I have connected an Arduino Pro-Mini 3.3V 8MHz to an ESP8266 via I2C.

The Arduino is in charge of collecting data from a thermistor (analog temperature) (T2) and a SI7021 (digital temperature) (T1).

The ESP8266 is in charge of sending the data received from the Arduino to an endpoint.

Here is my repo: https://github.com/ClemRz/Solar-Water-Heater-Monitor. In the res folder you will find a picture of the circuit.

The issue I am having is that as long as I leave the FTDI RS232 programmer connected to either the Arduino or the ESP I'm having a smooth response from the thermistor but as soon as I disconnect it, the response get some noise. What is happening?

Here is a graph where we can see 3 phases:

Programmer disconnected: some noise can be seen
Programmer connected: smooth noiseless curve
Programmer disconnected again: noisy

If I remove Rx and Tx and I leave GND connected to the FTDI I also observe that the reading is smooth and noiseless.

EDIT: I switched the wall adapter with a better quality one and it fixed the noise issue.


texts:
I think I am right in saying that 8k UHD is the highest a screen can go, so is there a limit to the number of pixels on a screen, limit to what the eye can recognise or what is physically possible?

WOuld there be any point in going up to 1M one day for example?


texts: Lower corner frequency in an emitter follower (Common collector)

texts:
I have a doubt about the lower corner frequency of an emitter follower.

I don't rember where, but I have read that it is given by:
\$\omega_L=\frac{1}{R_BC_1}\$ where \$R_B\$ is given by the parallel of the two biasing resistances R1 and R2, and \$C_1\$ is the capacitance before the base of the BJT. This expression should be derivated considering that the input part of the circuit is similar to a high pass filter.

Could you tell me if I correctly rember this thing?


texts:
I need exactly 6 PWM pins and PWM pin 11 is MOSI on Arduino nano. I use SD card to read configuration when program starts and to log few things later.

I would like to use CS pin for SD card module and when it is 1 to turn on MOSI transistor, or turn on PWM transistor when it is 0.

Is there any IC that has two inputs, one output and switch to select them?
What would you use to make this if space is limited?


texts: Can I isolate a onewire device using a bidirectional serial isolator?

texts:
I'm designing a board which has five onewire channels. One non-isolated, four isolated (spanning one isolation barrier rather than four separate barriers).

Can I simply run the onewire bus through a bidirectional serial isolator like an ISO1541, assuming it has pull-ups both sides? This would theoretically give me one device per isolation channel.

While I could use a DS2428-800 on the isolated side of the barrier, I'd prefer not to due to software complexity - each onewire bus has a single unique ID chip attached, and rather than implement all the required DS2428 features I'd rather just bit bang the unique ID devices once at device startup using the arduino onewire library.

Thanks!


texts: How do you determine which ethernet standard I am using?

texts:
I am new to the field and learning as a gateway via Ethernet cabling.  I was curious as to how exactly these standards were implemented.

Are these standards implemented as per the data transfer rates your ISP sets for you (i.e. the ISP itself is conforming to said standards)?

Is this dependent on something on the user end?

As an additional part to this question, though kind of unrelated..I was wondering if there were any cheap copper whole sources that are already gauged for home applications?  Sources for insulation, etc?

I want to try to do this project hands-on rather than crimping pre-existing lengths of CAT-x cables.  Though, I may do a small project on some extra CAT-5 cable I have laying around as to practice.

EDIT:  If this is the wrong forum for the first question, my apologies.  That said, I forgot about determining my NIC, which I have done..fairly standard issue, but there is nothing I have seen indicating as to which standard it implements.


texts: Lab Power Supply based of LM317 (Project)

texts:
I'm pretty new into electronics, But  I do this mostly for educational purposes. Even if there are cheaper/more effective ways to build  a  power supply, I want it to be based of the LM317.

This project isn't finished yet, I just wanted to ask for any insights or tips that might make this better/safer. This is my circuit atm:

(Copy Image link for a higher resolution)

I was also thinking of using two extra pots for fine tuning the current + voltage.

My main goal is to have a simple power supply based of LM317 with both Current and Voltage adjustment. Thank you!

EDIT: If i use this design and what to add a transistor for increased load like this: https://embed.gyazo.com/e8ff3fd621ad4c0f7444903f880a4804.png

Where does the collector go?

EDIT2:
One guy here suggested that i might use a wire-wound potmeter to control the current. Is there any other solution? Maybe controlling the current using an op-amp/transistor? If so can anyone show me an example circuit? I have checked out most of the datasheets but i don't think that they explain it that well. Cheers!


texts: Differences between 2nd order low pass filters

texts: I don’t know how to design filters, but I need a second order low pass filter. I searched them on the internet and found two schemes. One is Sallen-Key, and the other I don’t know what is called. Question: what is the difference and which is better to use? How is the filter calculated in Figure 42?


texts:
We know that SNR is defined as "power" of the transmitted signal to the "power" of the noise. In practice we transmit time limited signals (for simplicity consider the case that there is only one transmission), hence its power is zero, since $$P=\lim_{T\rightarrow\infty} \frac{\int_{-T}^{T}|x(\tau)|^2d\tau}{2T}$$
and as energy of a time limited signal is limited, as $$T\rightarrow\infty$$
the power will be zero, hence in real case, the SNR is always zero. Where is my fault?


texts: Program ATtiny45 with Atmel Studio and Arduino ISP

texts:
Is it possible for me to somehow upload the application I have written with C++ in Atmel Studio with the Arduino ISP that I can use in the Arduino IDE?

I have no idea how to do this, and I also have no idea where to set the fuses and what to set them to (I want to use the 8 MHz internal clock).


texts:
schematic_1

schematic_2

schematic_3

If I wired like schematic_1, L1 and L2 are lighting.
But, in schematic_2, L1 is not lighting even though L2 is lighting.
When I wired in series as schematic_3, L1 is lighting.

Why L1 is not lighting in schematic_2 but L1 in schematic_1 is lighting?


texts: How to avoid voltage drop when using full bridge rectifier as reverse polarity protection

texts:
I found a couple of old bridge rectifiers. After reading some docs and tutorials about reverse polarity protection decided to give them a try. The problem is nobody offered a solution against the voltage drop (and the power loss) after the rectifier, which is usually mounted at the load side not at the supply side.

What is the way to avoid this drop - using higher voltage as input or additional circuit to overcome this at the load side?

Note that I chose this way of protection so the protected device will continue to work


texts:
I am confused regarding the working of a Line Impedance Stabilizer Network. To analyze the conducted EMI of my DC-DC converter (simulation only at this point of time) I know we need to connect in series a LISN device. The filter portion will come after the LISN module, before the converter. My question is, isn't the LISN itself acting like a filter? Because when I was simulating the converter I had first chosen the LISN inductor = 50 uH, and this caused trouble since it is a 12 V to 5 V buck converter. When I changed it to 5 or 10 uH, all the waveforms were as expected.
Also, how is the correct LISN chosen in the real world for a switching converter?


texts: Why are twisted pair cables used in electric power distribution systems?

texts:
I'm an Electrical Engineer, and understand how a twisted pair of wires can be used to reduce noise in the presence of magnetic fields.

However, I recently noticed the power company replacing the cables on a high voltage transmission system with a twisted pair of cables. The top most ground cable is still a single cable, but they now use two cables twisted in a pair for each of the 3 power cables as shown here.

Why do they use these types of cables?

EDIT: After reading the answers by WhatRoughBeast and Waqar, it would seem that the most plausible explanation for using 2 cables would be current capacity versus weight, but there must be more to it than that.

The engineers that designed these transmission systems 30 years ago weren't stupid. They certainly knew about skin depth, and could easily calculate the optimal cable size and number of cables to use.

As far as I can tell, this idea of using multiple cables for each phase is relatively new. I recently noticed that in some cases, they use multiple sets of two cables for each phase.


texts:
I have a particular powerup sequence from a datasheet that require this:

  At power-up, VDDIO needs to reach 0.6 V before VDDIN reaches 1.0 V.
  VDDIO voltage needs to be equal to or below (VDDIN voltage + 0.5 V).

This MCU has 5 VDDIO and 1 VDDIN ports.

Each VDDIO and VDDIN port has a 0.1 µF decoupling capacitor plus one 10 µF on VDDIO wire from the voltage regulator and one 10 µF on VDDIN wire from the voltage regulator.

Only one voltage regulator of 3.3 V is used to supply VDDIO and VDDIN.

If I power on the voltage regulator with this configuration, will I meet the requirements? If not or I can't be sure of this, how can I respect this power up sequence?

I've problem to solve this statement "VDDIO voltage needs to be equal to or below (VDDIN voltage + 0.5 V)", this mean I can't simply use a load switch that power up first VDDIO and after some time VDDIN?


texts: 100W LED going dim/bright/dim/bright every second after 10-15 seconds of power

texts:
I have a 100W LED chip which I have plugged into a 400W ATX PC power supply.  I am using a DC step-up converter (10-32v to 12-35v at 150W, 16A max in, 10A max out) to bring the 12V->30V to power the LED (30-34 volts are recommended.)
At 26V or less, I get stable light from the LED.  When I start to go higher, after 10-15 seconds of power it starts going dim for a second, then back to full brightness, then dim and so on.
What I'm trying to figure out is whether this would be a problem with the LED, the step-up converter, or the power supply. Can anyone give any suggestions on either what it might be, or on what tests I could run to figure out the problem?


texts: Does there exist an internet-like peer-to-peer packet radio system?

texts:
Has anyone designed a peer-to-peer communications networks system, which works almost like the internet, but wirelessly? I mean a system, which:

you can connect the transmitter to an usb port and operate it with a laptop
can be used to transmit data (for example, text messages)
units will connect automatically to nearest units of same system, and generate a routing table, and therefore you can send your message anywhere in the network, so that other units will relay your message forward until it reaches its destination.
The transmit power should be couple of watts (to get a range of couple of kilometers/miles per station) and the frequency band should be some legal band for free use (27 MHz, for example).

A purpose for this kind of device would be estabilishing a communications system in an area facing a natural disaster or to help people communicate in countries where government censorship prohibits using the internet.

As an electrical engineer, I know that this kind of system:

is possible to build
and the most hard part is to develop the protocol (communicating between two units is trivial, but how to get the message through multiple stations to its destination).

But has anyone done it yet?


texts: Can a "distributed gap" powdered-iron or ferrite toroidal core be used for a flyback converter's coupled inductor?

texts:
As just about all of us who deal with switching power supplies know, flyback converter designs use an air-gapped coupled inductor instead of a transformer.  Typically, this gap is an explicit gap in an E-I type core.

Nick Alexeev points out in a comment, though, that:

  Transformer cores are usually not gapped. Inductor cores tend to be gapped. Toroid cores of power inductors have what's called "distributed gap", which you can't see.

Can a "distributed gap" toroid core yield satisfactory results when used for a flyback converter's coupled inductor, or will it cause undesirable effects when used instead of an E-I core with an explicit gap?


texts:
There is a corelation between IIP3 (third-order intercept point) and P1dB (1dB compression point) as shown below.
$$P1dB = IIP_3 - 9.6dB$$
Is there a corelation between P0.1dB (0.1dB compression point) and IIP3?


texts:
this is the circuit I am considering everything ideal. according to me it will clip the AC voltage from both cycles but the battery polarity of 15V with D2 is confusing me.

According to me the output will be like this
Please help me in understanding if I am write and correct  me if you think its wrong and please guide.

Thanks


texts: FatFs: Why am I not able to properly read sector 0?

texts:
Background: I am using an nRF52832 Development Kit with this microSD card in this breakout board. The card is powered at 3 V (I've tested running off the dev kit regulator and an external power supply). I am using 22 ohm series resistors on the SCLK, SDO, SDI, CS lines and a 10k ohm pullup resistor on SDO.

I am using FatFs to mount the SD card and write to a file. I am able to initialize the card, but my call to f_open returns error code 13 (FR_NO_FILESYSTEM).

After some digging, I was able to determine that FR_NO_FILESYSTEM is being returned from a call to find_volume, which tries to find a FAT partition on the drive. I understand that this means reading sector 0 of the card and reading bytes 510 and 511. For a valid FAT volume, those bytes should be 0x55 0xAA. However, looking at the SPI transactions, my card seems to be returning 0x00 0x00.

I've tried formatting my SD card as FAT32 using the official SD Card Formatter, the Windows format tool, OS X's Disk Utility, Ubuntu gparted, and dd, but to be sure, I used Hex Workshop to read the boot sector of the SD card on my laptop and did see 0x55 0xAA at the appropriate position:

I'm using a Saleae Logic Pro to capture the SPI sequence. I am not sure the best way to share the whole capture, but here is a table showing all the decoded values: http://pastebin.com/gQh07QfE

You can see that the initialization works alright (it responds to CMD0, CMD8, etc), and towards the end returns 0xFE (which I understand indicates a valid data token?), but then 0x00 0x00 instead of 0x55 0xAA.

My ffconf.h is here: http://pastebin.com/1XRa7c94 -- My sdmm.c is slightly modified to use the Nordic SPI API (nrf_drv_spi_transfer) and delay function (nrf_delay_us). I am using a separate GPIO pin as my CS (nrf_gpio_pin_set and nrf_gpio_pin_clear).

Does anyone have any ideas about why this read isn't working?


texts: Cleaning up GND/PWR-plane air wire errors in EAGLE + bonus questions

texts:
So I've just finished up my first complete PCB board. The layout is 4-layer based, set up as ((1*2)*(15*16)) ---not sure if it should be ((1+2)*(15+16)) or ((1*2)+(15*16)) instead, please advise--- and uses a power- and ground-plane as layers 15 and 2, respectively. This was a layout that was recommended in a blog post from Autodesk EAGLE, so I figured that'd be the way to go --- however, it failed to mention the aforementioned syntactic setup --- on that note; should I specify the depths, or is this determined by the manufacturer? Furthermore it has all components atop, and only out of necessity I route signals through via's, as recommended.

I need help with the remaining problems; the ground and power planes do indeed show up and I've verified the connections where appropriate, so the polygons have poured copper in the correct places. Although, EAGLE still complains about air wires on every single power and ground connection --- these show up as direct errors, so how do I fix this?

With the respect to the wiring I'd also like to ask if my clearance is good enough. I had to lower the clearance distance to get signals out to pin headers among other things (see attached image). The default (and only used) net class has been set to a width of 10mil, drill of 20mil and clearance of 6mil.

Are there other things I need to consider or check? Please advise. I hope you have a lot of great feedback on this matter so I can patch this thing up and order my very first PCB :D

Hope to hear from you guys soon, and thanks in advance --- have a good one! :D


texts: Gearmotor : Principles and usefulness compared to a regular motor

texts:
I'm a student in an engineering school and I have a question for professionnals : What is exactly the usefulness of a geared motor that uses a gear to reduce the rotation speed compared to a regular motor which can, I assume, already modify its own speed without a gear ?

PS: What are the disadvantages, or problems that could occur while using a gearmotor, compared to other alternative systems that you may know of ?

And what are the different types of gear motors ?

Thank you so much for your answers !


texts:
Good afternoon fellow students of life,

I have a particular question that relates to the use of a Duracell USB switching power supply as the main supply for a high sensitivity sensor board. Most of the noise is below 3.58MHz going down to 300 kHz.

and has this waveform.

The schematic uses this configuration to try and eliminate the noise by blocking it in the first place. The chip inductors are separate.

A variation on this that I found on the web was to use a decade of capacitors (100uF, 10uF) in front of a ferrite bead with an electrolytic, taltanium, and ceramic (10uF, 47uF, 0.1uF) after.

http://www.ti.com/lit/an/scaa048/scaa048.pdf and http://www.ftdichip.com/Support/Documents/AppNotes/AN_146_USB_Hardware_Design_Guidelines_for_FTDI_ICs.pdf

I know that there is no perfect solution to this problem

Is this a better way of accomplishing noise suppression?

As you can see there is an extra inductor (L3) to decouple the AGND and the DGND.

Thanks ahead of time.


texts: In jfet, how can VGS(off) be found with just IDSS and gm0?

texts:
Transconductance curve of jfet is a parabola.

Given a point (0, IDSS) and
gm0, which is the slope at VGS=0,

how is it possible to find the VGSOFF ? One point and slope give a straight line, not a parabola right? My textbook says it can be found:


texts:
I am trying to create a schematic for driving two WP154A4SUREQBFZGC RGB LED diodes using ON Semiconductor's CAT3626 and here is my schematic:
 and here is proposed circuit from CAT3626's datasheet:

Kingbright's RGB LED Altium's part library was downloaded from SamacSys webpage. Now, I am confused since I've connected anodes to PWM outputs of CAT3626 because I want to control every color of each diode indepedently, but in datasheet there is a connection as we can see from 2nd image Common Anode Configuration. How do I transform my schematic so it will comply with CAT3626 "rules"?


texts: What is the difference between Rectification Efficiency and Transformer Utilization Factor?

texts:
As I was studying half-wave rectifiers and why they are less efficient than center-tapped and bridge type full wave rectifiers, I came across these two terms that both try and describe how well the rectifier... well, rectifies.
Rectification Efficiency = DC power delivered at load ÷ AC input power from transformer secondary
(=40.6% for half wave rectifier)
&
Transformer Utilization Factor = DC power delivered at load ÷ AC power rating of the secondary transformer
(=0.287 for half wave rectifier)
Naturally, I tried to find the difference between AC rated power and AC input power but found that my textbook uses them interchangeably.
I've understood the formulae and expressions but would like

A qualitative differentiation between the two.

My book cites: "In any power supply design, TUF is necessary to determine the rating of
the transformer"

So shouldn't different rectifier circuits(half wave, full wave, etc) differ in rectification efficiency alone?
If transformer utilization depends on the characteristics of the primary and secondary windings, why does it depend on the subsequent diode arrangement at all? Why are their values different from model to model? Why is it studied under rectification?


texts: Is the frequency response of a circuit only valid for steady state (phasors)?

texts:
This is my first post. I just finished a course about advanced circuit analysis techniques (the content was taken from textbooks by Sadiku, Hayt and Irwin.) As you know, phasors are used to solve sinusoidal AC circuits (and also non-sinusoidal AC circuits, with the help of Fourier series), however, the answer you get from analyzing a circuit with that technique is only the steady state response, not the complete response (which also includes the transient response). When we're introduced to the frequency response analysis, the only difference is that now frequency is an independent variable just like time, and we still solve the circuits with phasors.

So my question is this: is the answer obtained by a frequency analysis (output voltage, ratio of output to input voltage, transfer function, etc.) only valid for steady state? I'm assuming this because in freq. anal. we still use phasors, which give only the s.s. response.


texts:
I have development board with LDO used for reducing input voltage to 3.3V.

I want to bypass that LDO. Can I simply interconnect input and output of LDO? What happen if I brings the same voltage to both input and output of LDO?

In my case LDO is LP5907MFX (datasheet) but i prefer generic answer rather.


texts:
Good afternoon, I am a high school student and in my scientific fair project, I would like to do an experiment about wireless energy.

I want to implement the resonant inductive coupling.

According to what I have read and researched:

The advantage of the resonant inductive coupling, compared to the inductive coupling, is that, when the receiver and transmitter coils are on the same frequency, the loss of energy is much less.

In addition, the diagram is: (the image is from wikipedia post about resonant inductive coupling)

And this, is other diagram: ( the image is from this pdf)

You will understand, that I do not have much knowledge of this, for which I want to know if what I understand of the diagram, is correct. If not, I need to know how it works.

According to what I have read and researched:

The resonant circuits are the coils, which are made of insulated copper.

The coil on the left has a "resonant antenna" or "resonant coil" on its left, which is a circle of isolated copper wire, i think that  is the D in the second diagram, because is connected to to what is providing the energy, a battery or something like that. This "resonant coil" is connected to an electronic oscillator, what I do not understand for what it serves in this. And this electronic oscillator is connected to what provides power (battery or something like that).

And on the right side, it is the same, but instead of an electronic oscillator, there is a rectifier, which, as I have been investigating, I must use it to transform the alternating current into direct current (since this current is the one used by electronic objects).

So, my doubts arise and they are:

What is the oscillator for in this experiment?
Why are two copper circles used, instead of directly the resonant coils?
Is my understanding of the diagram correct?

In addition, there are some symbols that escape me, I think one is the resistance and this is to control the voltage, but the other 2 do not know what they are, I have been looking for, but no symbols appear like those.

I would greatly appreciate your help, I do not have anyone else to ask, my teachers are not too good.


texts:
I want to know the difference between surface mount device and through hole components other than the mounting style.
Differences such as if the through hole counterpart of the surface mount device has has considerably more resistance or consumes more power etc.
Finally, I want to know if the SMD components can be totally replaced by through-hole in a circuit.
Thanks.


texts: Does it matter how I cross a 2 MHz SPI clock signal on a two layer board?

texts:
Background

Currently I am working on a breakout board which allows me to connect a number of external boards (analog and mixed signal) to an Arduino Micro, using a variety of connectors.
The breakout board is limited to two layers, and has to deal with nine analog sensor signals, as well as seven digital (SPI) signals, viz. clock (SCK), MISO, MOSI, and four chip-select signals (CS).
The Arduino is configured for a 2 MHz SPI clock frequency, but I could not find any information about typical rise times.

The problem is that I am not sure what is the best approach to routing the digital signals on my breakout board.
Since my question is pretty basic, I boiled it down to the minimal example described below.

Simplified problem

In this simplified example, I have a ground plane, an SPI clock signal (SCK), a chip select signal (CS), and a relatively large "keepout area," as illustrated in the figure below. Please note the example is not to scale: the actual trace length would be over 10 cm.

The pin assignment on the connectors cannot be modified, nor can I move/rotate the connectors or keepout area.

The basic problem is that the CS signal needs to cross over to the other side of SCK (2 MHz).

Assuming it is best to keep the SCK trace on one plane, intact, there are several options for CS, as illustrated in the figure below:

use vias to route CS under SCK (orthogonal, with minimal gap in ground plane)
use a jumper, or zero-ohm resistor, to jump CS over SCK (keeps ground plane intact, but adds extra components)
use a detour around the keepout area (keeps ground plane intact, without extra components, but increases length of the trace considerably)

EDIT: Unfortunately, routing the entire CS signal around the SCK signal on the bottom plane is not an option. The actual board size would be around 10x10cm. Trace lengths will be around 10 cm, with an increase to 15 cm using option 3.

Question

What would be the best choice, assuming the traces will be around 10 cm (with an increase to 15 cm for option 3), in terms of both signal integrity and electromagnetic emissions (EMI)?

I suppose I won't need to be overly concerned with high-speed design topics such as impedance matching and signal termination?

On the actual board, I have two CS signals which both need to cross SCK, MISO, and MOSI. Would that change things?

What I think

Given that the SPI clock frequency is 2 MHz, and based on what I've read so far, e.g. here and here, I suspect it might not make such a big difference, in my particular case.
However, I don't have any experience to speak of, and I am unsure about the high frequency content of the clock edges.

I am inclined to keep the ground plane intact as much as possible, so that would imply the use of either option 2 or 3.
Using option 3 on the actual board, I can route nearly all signals on the top plane, without actually crossing or breaking the ground plane, but the detours add some 5 cm to the trace lengths.
Moreover, the result hurts the eye...


texts: How can I make my ILI9486 Display not show my frame until I'm done? (Flickering!)

texts:
I have a ILI9486 TFT display and I am using an LPC1768 with it.

The issue I am having is in the following:

        if(!(LPC_GPIO1->FIOPIN & (1 << 27))) {
        TFT_Clear(Black);
        TFT_DrawButton(80,80, "First Message", White, Purple);
        TFT_Show();
    } else if ((LPC_GPIO1->FIOPIN & (1 << 28))) {
        TFT_Clear(Black);
        TFT_DrawButton(80,80, "Second Message", White, Blue);
        TFT_Show();
    }

What happens is that the screen flashes and flickers black and then show the other box. If I don't use TFT_Clear(Black); it writes this over the old box and there's little bits of it left. what I want is for the screen to not show what I'm writing to it's memory until I decide it's time basically, Or at least for it to not show the TFT_Clear() function until I am done writing the rest.

This is my TFT_Clear() function for reference:

void TFT_Clear (int16_t color)
{
    unsigned int   i;

    LCD_WindowMax();

    TFT_StartWrite();
    for(i = 0; i < (WIDTH*HEIGHT); i++) {
        TFT_SendData(color);
    }
    TFT_Show();
}

TFT_StartWrite() sets the pins (CS RD etc) according to the datasheet and the TFT_Show() turns the CS back on after the Writing is on.

This is the Display's datasheet for reference.

I also had this issue when showing a circle move up and down. It'd just get dim and have a very strange flickering, Even when I didn't use the clear function and just redrew a black circle in the previous position before drawing the new one


texts: Balancing a stick using two different designs and comparing both

texts:
I want to understand which feedback systems are in general preferred over another model (that I'm going to show in image),so first we take a example of a particular system (here stick at 90degree from horizontal at initial condition)and then try to understand same concept for a general system as well
Here is our system (image )
And I want that it remains at 90 degree irrespective of whatever disturbance force is so basically I can say it's output reference would be v=0 or x=0(where v and x are velocity and displacement of centre of mass of stick)
Now I'm thinking about two different approach of modelling to achieve desired result
1st approach-
Going with basics of feedback which is based on reducing effect of disturbance (basically output) using feedback gain (k) to achieve output  approximately close to reference (desired output) .here(in image) is a block diagram of that feedback system

But to design this model we need to know about  one variable only and i.e k ,but for desired value of 'k' we need to know about state model of open system G .
Now 2nd approach-
So here I'm trying to reduce or even cancel the disturbance (D(s)) rather than it's effect because if disturbance becomes zero it's effect will also becomes zero so here I modelled a feedback system like this (image)
Where k1 and k2 are proportionality constants and we have to design only a electrical system H(s) (which is inverse of mechanical system G) .And again for designing H(s) we need to know about state model of mechanical  system G and here we get v=0 mathematically and that is what we wanted to achieve.
So my question is

Is both models are good to achieve desired result for  this particular system

2.is second model can be considered as feedback model or not?
3.why feedback concept based on reducing effect of disturbance rather than reducing disturbance itself
4.which model(in above two)is in general preferred and why?
5.Or my assumption is wrong that for value of 'k' we need state model of G?


texts:
On many boards I've seen, there are little copper dots used for the purpose of "Copper Thieving". They're small round copper dots connected to nothing and arranged in an array. Supposedly they're for balancing the copper on the boards to improve manufacturability, but no explanation I've heard has convinced me that they're needed or useful. What are they for and do they actually work?

Below is an example with squares.


texts: How to remove an inductor after getting signal from it?

texts:
In the circuit that I've designed, I get 3 different signals and I process them via a microcontroller. 2 of them are from different inductors and 1 of them is from kind of a button. So, my question is can I make an open circuit the inductor after getting a signal from it. And, make short circuit again when I get no signal.
Please forgive me for my bad English. And ask anything that not clear. Thank you for your time.


texts: Options for getting 4.5-6V out of (mismatched) AA alkaline batteries?

texts:
I have a huge stack (400+ or so) of used AA Alkaline batteries (Duracell Industrial).
Remaining capacity left varies anywhere between 0% and about 30%.
I have no way of knowing which ones are really empty and which ones are at 30%.

I've got a couple of small gizmo's (containing a few LED's and a tiny DC-motor) that can be driven by any DC power-supply in the 4.5V-10V range and which draw only 10-20 mA current each.
I currently run these gizmo's from a USB charger wall-wart with a DIY Frankencable.

I would like to find a way to use those AA batteries in stead. Seems a waste to just send them in for recycling.

Putting 4 AA's in series would do the trick, but I'm well aware that putting mismatched batteries in series is potentially dangerous and certainly not efficient due to the weaker batteries having higher internal resistance.

Any ideas how to do it? Or is the 4 mismatched AA's in series not problematic enough to cause issues (besides draining the batteries quicker than normal)?
A way to identify the really empty ones would be nice too. (I'm using a 1.4V LED to test if a AA cell can light it up. But that only tells me which batteries are really dead.)


texts: What is the foam pad on the bottom of a large, through-hole capacitor for?

texts:
Large, through-hole capacitors (typically electrolytic) sometimes have a foam pad on the bottom like the one in this picture:

What is the pad for?


texts: Advice needed for replacing old ER3055 transistor

texts:
I have a transistor in a guitar amp with the label ER3055 that needs to be replaced.  I asked about another transistor that I needed to replace in a post a few days ago here and I tried using NTE to find a replacement.  What I found was that, while nobody seems to have a replacement for "ER3055", there are replacements for "3055" or "2N3055".  Is the "ER" prefix something like a manufacturer code (for an extinct brand) or is this something that is crucial to the transistor specs?  The specs I found for 2N3055 here seem to match up with with the other transistors in the amp so I think that the "ER" is not necessary but I wanted to check with other people first.

Thanks


texts: What are the options to properly wire an MFRC522 sensor to an Arduino board?

texts:
I have 3 MFRC522 RFID sensors that are hidden in a drawer. Those sensors are connected to an Arduino which is at a distance of 3 meters. Those cards communicate via the SPI protocol.

The wiring is not very clean, I would like to redo it.

However, I think there must be a way to cleanly wire those sensors. Could you advise me on the possible types of connectors?

Regards,


texts: How does electrical signature devices work when there is more than one load connected?

texts:
Now more than ever I see energy monitoring devices like this one that uses "AI" to detect the loads connected to your home electrical network, like the washer or a hairdryer.

These devices use electrical signature measurements and compare them with a large database in the cloud to predict the type of load. Electrical signature measurements is not a new tech, we engineers had been using it to detect anomalies for example in motors and other loads as a nonintrusive means to explore the load.

You create a signature by collecting information about the frequencies with a fast Fourier transform, the phase, and power. And that's not rocket science. What really puzzles me is how can you identify a signature when there are several loads connected? I mean, I can create an individual electrical signature for my dishwasher, my 2 TVs, my Xbox and my fridge, but if several of those are running together the signature properties add so I will need to try every possible combination of signatures to predict what devices are powered on? Is it that brute forced the way these devices work? or there is an elegant solution to the problem?


texts: DC-DC Boost Converter Only Works with a Second Supply

texts:
I'm trying to build a 5V to 8V boost converter to use at another mosfet's gate voltage. I'm using a PIC mcu to create a 50kHz square wave signal to switch the BUZ101L. For test purposes i also added a potentiometer connected to an ADC channel which controls the duty cycle of square wave output.
When the PIC and potentiometer are connected to 5V supply from USB and DC-DC boost circuit is connected to seperate DC supply, it works like a charm. But when i try to connect them to the same DC supply, somehow it draws above 1.5A and doesnt work at all. What am i missing in here?
I thought the reason may be that DC-DC boost circuit saturates before PIC initializes when i supply them from same line. I tried connecting dc-dc boost part a while later then turning DC supply on. Didn't work.
here are the pictures


texts:
This is not homework.

Imagine an infinite resistor grid which the picture shows a part of. The question is what's the resistance measured across any of the 1k\$\Omega\$ resistors. I don't want you to tell me the answer, I already know. I want to know how to find the solution. I wish I could show where I got so far, but I'm afraid I don't even get started.

To anyone who wants to try for himself, and doesn't want to know the solution: don't click the link to the solution.


texts:
Got a question about the Sparkfun radio modem  WRL-08495.

A pair of these replace an RS-232 cable, right? simple as that?

What if my neighbor also has a pair of these?  Is there mutual interference
or is there encryption?


texts:
I've built a "Bass Enhanced Crossfeed" from a kit, which I believe is based on Meier's Crossfeed design.

I prototyped it first on a breadboard, forgot to ground the output jack because it wasn't explicitly in the diagram.  It sounded terrible.  After I grounded, it seemed to sound pretty good!  So I built the 'hi' version.

Now that I've built it, the low range just seems very subdued compared to my previous test.  I suspect I didn't solder it correctly, though I've looked over it with a magnifying glass.

So, how can I verify the build without an oscilloscope and just a multimeter?

I've done some checking, like checking for shorts between left and right ... where are the useful points to check for the right value of resistance?  Between R/Lin and R/Lout?  Should that be R9/7?  Should I check the resistance between each leg of each capacitor?

Probably overkill, but could I put this into a simulator and see what the simulated values would be vs. actual?

Apologies.. I'm a software guy.  I'd write unit tests if I could!


texts: How to Synchronise phases of main and ups?

texts: I need help to synchronise main AC phase with UPS phase so my ups change over time less than 8 ms and hence no restart occur in computer with pic pic micro controller?


texts:
I just learned today that, when you're routing the board you can delete the pad of through hole connectors on the internal layout. Some company even ask to delete all the internal pad that are not used.

I was wondering, what is the purpose of deleting all the unused internal pad? Is that for the isolation? Is there any possibilities to have problems with non used internal pads?


texts: Protecting circuit boards against shock?

texts:
Our company have been designing and manufacturing custom circuit boards for some 10 years now, and up till now by far the most common reason for board failure has been a mechanical shock - heavier SMD components (like inductors and such) has a tendency to simply break off the boards even with the slightest shock (like device being dropped even a mere feet from the ground).
How is this problem being handled in the mass manufactured equipment (especially devices used in vibration prone environments and vehicles)? I believe that hot-glueing every component in place is not a proper way to do this, right? Is there any epoxy coatings or something like that being done after board is soldered?


texts: Power Factor Correction Controller IC limits

texts: I've been considering throwing in an active PFC circuit into a high power PSU (about 5kW max surge at 240Vrms, 1400W typical), and while looking for an easy to use, low passive count controller, I found my way to TI's website, looking at datasheets for their controllers in which some state in their description (not the maximum ratings) as being "Suitable for 100-a few kW"..... I recall at least one saying "3kW", while most just don't state anything of the sort at all. In comparison, OnSemi has a line of IPM PFC's with integrated IGBT's, and to my understanding, the maximum power they can handle is limited only by the integrated switch and the passives/inductors, ie- 50A. Ignoring all of the passives, inductors, and the external FETs/IGBTs, what exactly is the limiting factor for TI's controllers, such as the UCC28070A or the UCC28180, and really any PFC controller in general? At no point do they ever specify where they got "a few kW" from, nor what "a few kW" means empirically. Not being all too familiar with PFC controllers, is it just a generalization, or is there actually some unspoken quantum-mechanics level reason behind it?


texts: Using a lower voltage for a replacement fuse

texts:
I need to replace a blown fuse in my Tacklife DM02A multimeter.

It says on the back of the multimeter that the blown fuse is F1 250mA 600VAC. Its size is 5mm x 20mm and it has to fit into a clip inside the multimeter. I think it is ceramic because it is not see through.

I have looked for an exact replacement for this fuse and have been unable to find any. Most 250mA fuses seem to be 250VAC and most 600VAC fuses seem to be 500mA minimum.

I know it would be a bad idea to use a higher current rating for the replacement fuse, but would it be okay to use a lower voltage? If I used a 250VAC fuse, say, would that just mean that I can't connect the multimeter to more than 250V? I've only been using my multimeter for simple battery powered circuits so can't think of a reason I would need to test that many volts.

Also, would it be okay to use a glass fuse instead of ceramic if I can't find a suitable ceramic one?


texts: LED as light sensor not properly working in circuit

texts:
I read some articles about using an LED as a light sensor. I chose an IR LED and checked the voltage levels produced in different light situations resulting in about 200-300mV in full artificial light and around 30 mV in the dark, which seemed to be fine enough for an analog Arduino/AtTiny pin. The IR sensor LED also worked sufficient on the breadboard, but unfortunately the values seem to get messed up in my soldered setting which is an AtTiny dimming a 10W LED when a PIR gets activated and the light sensor value is low. In this setting I get much less sensitive analog readings from the sensor LED. The main difference are longer connecting cables as I want to place the sensor LED in some distance from the rest of the circuit.

Can it be that the current of the LED is too low and therefore the reading gets disturbed by the circuit in some way?
May I need a very high pull-down resistor for the sensor because without it the sensor pin floats in the dark?
IR is supposed to be the most sensitive but actually I want to measure daylight which has a lower IR part than warm electric light. So maybe another LED would make more sense?

I know there should also be a resistor between the PWM and the MOSFET, but it seemed to work fine on the breadboard without it.

simulate this circuit – Schematic created using CircuitLab


texts: How is it possible to get faint green and disappearing tracks when stripping photoresist?

texts:
I begin to wonder now what is going on.

When I make circuits, I use a presensitized PCB board from MG chemicals along with their positive developer (sodium hydroxide?)

This is my 2nd attempt of a circuit I attempted to develop (I'm reusing the mask that was printed with toner on vellum paper rated at 105gsm).

On the first attempt, the circuit background turned pure copper which is good but some tracks faded away.

Now the second attempt got worse even though I taken advice.

One advice I took (I believe from kinsten, a chinese PCB supplier) was to move the UV light for exposure to 4 to 6 cm away from the board and expose for a shorter time. For both tests I used roughly a 20 minute exposure time.

For my developer mix, I used about 12 parts of water to 1 part of developer which is weaker than what MG chemicals suggested, and I deliberately did weaker to see the action.

I then shut my room light off and the brightness in my room was at about 10% since outside was dusk. It was still hard to see fine print without light shining on it.

Once I shut my light off, I go and use an ultra-bright red LED as my safelight when handling and developing the PCB since the presensitized PCB is sensitive to light.

I then sandwiched the circuit board and the artwork together (toner side to the circuit board)

After exposure, I briefly examined the board and noticed the pattern. Then I put my board in developer for about two minutes. Once I'm done, I rinsed it and thought my circuit is perfect, but once I turn the normal light back on, I was dismayed to see that part of the circuit board background was faint green, but what's worse is that one track was fading away into the background, yet my original artwork didn't call for this.

What could I be doing wrong? Could the vellum be the culprit? am I forced to just use transparencies? I've wasted at least $20 to unintentionally make failing boards and I don't want to make anymore.

Someone suggested using sodium silicate instead of sodium hydroxide but I think there's more to it.

Any ideas?

UPDATE

As requested by someone, I needed to mention in my question that I don't have a good quality camera to take the pictures with.

The track size thats problematic is 0.3mm wide.

The UV source is this cfl-like light: spencers.scene7.com/is/image/Spencers/00912691-a?$Thumbnail$


texts: Extracting and Using Sensor in Camera Assembly of Nokia Lumia 1020

texts:
I am trying to use the awesome camera sensor in the Nokia Lumia 1020 for research purposes. Unfortunately, my screen is broken so the screen is completely black. I intend to disassemble the phone, extract the camera assembly out of the phone, and use the camera sensor severed from the phone itself.

Are there means to connect the camera assembly/sensor to my computer? If not, what would be the next easiest alternative in using the camera sensor remotely?

Here are the specifications:
https://www.microsoft.com/en-gb/mobile/phone/lumia1020/specifications/#head_camera

And some pictures of the sensor/assembly itself:

(source: allaboutwindowsphone.com)

(From left: Complete camera sensor, the barrel shift OIS 'mechanism' around the lenses, the side view cutaway, and the sensor plane)

(Bottom most sensor is the Lumia 1020 sensor I'm looking at)


texts:
I have a very cheap crimping tool and am trying to confirm where to crimp to ensure a good connection is made.
I’m using red 18awg wire but the dot doesn’t really align with a spot like most crimpers. I’ve already done a few on the spot where it says “insul and” as my connector has insulated heat shrink over it. Is this the right spot to do it? I can’t find any similar crimpers that confirm this is correct.


texts: Fast to Speed of Three Nand Architecture, Need Help?

texts:
The following transistor architectures shows three implementation of two-input Dynamic NAND.

  Figures a-b-c shows these architectures from fast to slow (speed).

I think this example is wrong and b-a-c is correct. anyone can help me why the example mentioned the speed of these structure in another way?


texts: Calculate voltage, current, and power for each element

texts:
My attempt at the problem starts with,

-I assumed that the value of the independent current source which is \$10 mA\$ is the same throughout all the elements since it is a series circuit (Please tell me if this is right, because I based all my #s on this)

-Knowing this, I calculated \$V2\$ using \$V=I R\$

\$V2=(10 mA)(1 k\Omega)= 100 V\$

-I calculated P2 & P3 using \$P=V I\$,

\$P2=(100v)(10mA)=1 W\$

\$P3=(10v)(10mA)=0.1 W\$

Now I'm only left to find \$V1\$ & \$P1\$

By using passive convention, in the end, the sum of power is going to equal zero

-so I assumed that,

\$(-P1)=P2 + P3\$

\$P1= -1.1 W\$

So what's left is \$V1\$, and knowing that \$P1\$ is a negative value, I thought that somehow, the direction or polarity of the \$I1\$ or \$V1\$ needs to be in the negative direction... but I wasn't sure how to draw in a way that would satisfy passive convention.
I got stuck from here.

Somebody please help me, and correct me if I made false assumptions. Thank you in advance.