texts: Equivalent impedance calculations from "both sides"

texts:
A circuit I have been working with lately consists of a binary counter being fed into an Op-Amp DAC, shown below. One of the major issues with this design is that the input impedance of the DAC will load the counter sufficiently and become problematic if one does not consider the equivalent circuit for each stage (i.e. the counter fed into the DAC). The equivalent source impedance of the counter is trivial, but the DAC is a bit harder to compute.

The most logical approach to this problem seems to be to find the equivalent impedance looking into the Op-Amp, but a textbook I have calculates the impedance looking out of the Op-Amp. Of what use to us is the impedance looking out of Op-Amp if we intend to interface with a previous stage?

Given the following circuit I repeatedly arrive at the following equivalent impedances:

Looking into Va : 2R
Looking into Vb : (8/3)R
Looking into Vc : (32/11)R

A slightly different rendition of this circuit is shown below with the book's approach to equivalent impedance (For LSB = 1 only, all others = 0).

Aside from being able to compute the transfer function and associated gain easier, of what use is this form of equivalent impedance and are they similar in nature? It seems to me that these two impedance calculations are entirely different and have no relationship to each other (aside from having the same physical circuit).

NOTE: The overall topology has the output of a binary counter (with TTL logic level output voltages) being fed into the DAC. The designer must either reduce the 5V output of the counter down to 1V logic levels or provide a second stage attenuation of the same amount. This second stage will be present to negate the (-1/4) scaling factor introduced by the first stage shown below anyway, so the designer then has to only adjusted the gain to compensate for the larger inputs; I went with the former design approach initially and ran into issues leading me to ask this question.


texts:
I was wondering why the 4N27 optocoupler has a pin for base of the phototransistor - and of course how to connect it.

I've usually dealt with PC817 optocouplers and connected them according to the schematic.

Now I want to do the same with 4N27 (pinout on the picture below,) so do I have to leave the base pin floating, or pull down it?


texts:
I'm a little confused about the Output Current block(s) in the TI LM2902/324A datasheet. Specifically regarding Section 6.5 (pages 5-6).

In this section, there are two Output Current blocks and, whereas the specs between the two blocks are quite different, I don't see how the parameters differ - except where one explicitly states that T=25C.

Could someone explain this?

Note: please ignore the Vo=200mV condition from the first block; I should have excluded that from my highlight below.


texts: Multimeter exploded during ACV measurment - What did I do wrong?

texts:
simulate this circuit – Schematic created using CircuitLab

A DT-830B meter.

I bought a new transformer, and I was trying to measure the output voltage. I plugged the probes on 'VΩmA' (not 10 A) and COM. and set it to 750(not 100% sure if i put it on 750 or 200) ACV.

Then I put my probe on the right side of the picture, which is the transformer output, and I got no numbers reading.

Then I wanted to check if the outlet was working right, and put the probe like the picture. My outlet has only two outputs, with no neutral/hot labeling, just two of them and they are 60 Hz 220 VAC.

Anyway, as I put the probes like the picture, the multimeter made zipping noises and it didn't display numbers. Maybe it was shorted inside? I put it like the picture again, and the fuse exploded.

Did I do anything wrong? I didn't think that I needed to swap to 10A because (I thought) it's only used when measuring currents. I just wanted to measure voltages.

Can you tell me what i did wrong?

oh, and I actually did put the probe on voltage measurement terminal.. It says VΩmA. I put my probe on VΩmA and COM.

Also I dont remember where I bought it, but the multimeter says DT-830B, and no make printed.

Plus, I think it was under 10 dollars.

Well, some of you wanted the inside of that meter. So I'm uploading some of the pictures. The inside looked simpler than I expected...


texts:
I'm trying to put together a simple superhet radio, receiving at 161.75MHz (this is for AIS reception.) I've been trying to design around NXP's SA605 chip (see SA605) but I'm having a hard time figuring out what values to use for some components. My IF is 10.7MHz & the LO is 161.75 - 10.7 = 151.05MHz. I'd like to avoid using a crystal. From the docs, it seems like a Colpitts oscillator should do the trick, with L = 82uH and C = 27pF (I know this is off a little bit, but I assume I can put a trimming cap in parallel with the capacitor across pins 3 & 4 to get it right.)

From one of the application notes, it looks like I can do this fairly simply:

...but the question becomes, what values do I use for the DC blocking cap, and the one on ground? I assume the value varies based on the oscillation frequency, but I don't know where to go to calculate that.

I've also tried to simulate this in the spice simulator now embedded in KiCAD:

...using the equivalent circuit from the application note:

...but I haven't had any luck getting it to actually oscillate. Do you have any hints on getting this going?


texts: Constant Current Regulator position in a series circuit

texts:
I'm designing a circuit with 3 LEDs, a CCR (NSI50350), and a power supply in series.

My question is:

Does it matter where I place the CCR?
Can I design my circuit this way: +V--LED1--LED2--CCR--LED3--GND?

Regards!


texts: Difference in BJT Incremental Resistance between DC circuit and AC circuit

texts:
I'm trying to write up a lab report, but no one seems to be able to give me an answer for what the incremental resistance of a BJT means, or why it's significant so I'm hoping someone here can tell me. In our lab, we first built a DC circuit, pictured below:

We measured the incremental resistance by calculating Delta(Vy)/Delta(Iy) at different Iy values (10 uA, 100 uA, and 1000 uA).

Then, we built a second circuit, this time with an AC component:

We measured the incremental resistance again, this time with a more complicated formula, and the incremental resistance changed - a good amount, but it was still on the same magnitude as measured before.

I hope I'm not being ignorant by asking, but I truly do not understand the purpose of this laboratory and no one seems to be able to tell me - even the TAs. I'm assuming there must be some theoretical difference in the incremental resistance between AC and DC circuits, but I don't know what the theoretical explanation is. Additionally, I don't know what the significance of the incremental resistance is and/or what the "theoretical" incremental resistance should be for these two circuits. I'm not sure if I provided enough detail, but I'm really just looking for a good explanation of incremental resistance.


texts: How do eradicate pad to pad clearance with-in the component in Eagle Tool?

texts: I tried clearing the error by defining Rules and net Class, but that does not happen. How to do this?


texts:
I've tuned plenty of RF devices using my VNA for impedance matching.  But I've never done an S21 measurement.

I have a shielded tent with some connectors and SMA cables that are going to introduce some kind of loss.

If I run an S21, will the results be across a frequency span like an S11?

Is there a way to calculate the average signal loss?

Am I thinking about this wrong?


texts: What is the correct term for this type of USB Input devices?

texts:
Hi, I'm working on something where I need to use a huge amout of these little guys (picture attached), probably around 32 or more for a start.. The problem is, I need to be able to connect all of them to my computer using 1 single USB (or COM port). To do so I need a device or a controller that have alot of inputs bi-pin attached to it, but I just can't figure out the name or the correct term to search for it on ebay. I'm starting to think it doesn't even exist..

All I keep getting when searching for this, is some USB AUDIO/MP3 input stuff that has nothing to do with what I need. Please help with anything you have. Thank you.


texts: How can I use arduino to control 4 motors speed and direction?

texts:
I consider this question different from others because of the variety of things I need this setup to be able to do.

Description:
I want to build a minimalistic motor controller capable of controlling the speed and direction of 2 servos and 2 brushed dc motors. That is to say that I have size and weight constraints that I do not think would be satisfied by off-the-shelf solutions.

The Problem:
I have an arduino board (all/any model) that can only output 40mA per pin which is not enough to power even the tiny dc motor I am using. If I power the dc motors directly from the 3.7v 150mA/h 25C LiPo battery it seems to spin at the top speed I need to be able to achieve from the arduino. I need to be able to controller the speed and direction of each of the motors from the arduino PWM output using power from 1 or more LiPo batteries. The battery I have came with the motors so I know it can power them.

Story:
I salvaged the motors and battery from a small rc heli and I want to rebuild it as a UAV replacing the onboard chip with my small arduino (pro mini or teensy).

Update 1:
Apparently I may have been overcomplicating the problem and a simple H-Bridge is all I need. I will post back if this turns out to be the case. Thanks for the helpful comments. I will upvote once I have enough rep.

Thank you!


texts: Compiler complaining about type declaration in function prototype

texts:
This is a library for motor control I am writing to use with the Sparkfun Monster Moto Shield.

I have stared at this code for hours, looking for a stray or missing semicolon, or whatever might be wrong, but I'm still getting the same compilation errors, and it makes no sense to me.

Specifically, the compiler says it is expecting a closing parentheses before the variable in the "go*()" functions below:

/**
 * motor_control.h
 */

#ifndef MonsterMotoShield_h
#define MonsterMotoShield_h

// Motor variables
#define LEFT_MOTOR                  0
#define RIGHT_MOTOR                 1
#define MOTOR_DDR                   DDRD
#define MOTOR_PORT                  PORTD
#define MOTOR_PWM_DDR               DDRB
#define MOTOR_PWM_PORT              PORTB
#define MOTOR_CURRENT_SENSE_DDR     DDRB
#define MOTOR_CURRENT_SENSE_PORT    PORTB
#define BRAKEVCC                    0
#define CW                          1
#define CCW                         2
#define BRAKEGND                    3
#define CS_THRESHOLD                17

/** Initialization functions **/
void initializePWM(void);
void initializeMotors(void);

/** High-level motor control **/
    void goForward(uint8_t speed);
    void goReverse(uint8_t speed);
    void goHardLeft(uint8_t speed);
    void goSoftLeft(uint8_t speed);
    void goHardRight(uint8_t speed);
    void goSoftRight(uint8_t speed);
    void goReverseHardLeft(uint8_t speed);
    void goReverseSoftLeft(uint8_t speed);
    void goReverseHardRight(uint8_t speed);
    void goReverseSoftRight(uint8_t speed);
    void pivotLeft(uint8_t speed);
    void pivotRight(uint8_t speed);

Can anyone see what I am doing wrong? Thanks! I am pretty new to C programming, so there may be other mistakes I am not aware of.


texts: Small signal analysis of MOSFET. Calculating Gain

texts:
I can do DC analysis and draw the small signal equivalent circuit just fine. I generally have trouble calculating gain. I'm having trouble understanding the answer to this question.

This is the question. Question 4.36:

This is my working. I hope it is clear:

According to the solution manual this is the wrong answer. The correct answer is $$A_v = \frac{V_o}{V_o + 1}$$:

I don't understand. \$V_i\$ is in parallel with \$V_{sg}\$ therefore \$V_i\$ must equal \$V_{sg}\$ right? Where did I make a mistake?


texts: I have been researching via stitching for the GND planes around the edges of the PCB for the past while. I have found alot of resources on the topic, such as the making the spacing distance equal to the smallest dominant wavelength divided by 20. However, I have also seen it said numerous times that if you place the vias too close together you can actually make the emissions worse than if you had no vias. I am wondering how this is possible, and if anyone has any half decent explanation for how too many vias can make the EMI worse.


texts: What is the true accuracy of a linear regulator or DC/DC converter design?

texts: Normally, vendors of LDOs and DC/DC converters specify the output voltage error in the range of 1.5% to 2.5%. However, the analysis often suggests that the error can range from 3% to 6%. Lately, I saw a demonstration on youtube, showing the significant difference between the actual min/max and the spec'd error of TI TPS784. The error is mainly due to the variations of Vref, Ib, and resistors' values. Why is the datasheet's value so low compared to the calculation results CircuitEXP provides? Do they emphasize different aspects?


texts: What is the best between a transistor and a pmos and which resistances

texts:
I need to create a switch to power on or off a moisture sensor.
PIN 10 is HIGH or LOW to trigger either the transistor or the PMOS

My sensor consume about 0.6mA
Moisture sensor information

My circuit work with 3.3V

I found the two exemples below

Keeping in mind my circuit work with 3.3V, powered by the 3.3V pin of my micro-controller

Now my question; I have pain to make a choose between the NPN and PNP transistor and the P NOSFET example. What would be the best as far as I know, the transistor work with Ampere and PMOS with voltage.

First, if I opt for the two transistors, how can I calculate the resistance values for a 3.3V circuit. The output of the PIO I/O has 3.3V, of course.

Lastely, if I choose the P MOSFET proposition, How can I calculate the value of R1 if I have a circuit of 3.3V.

Keep in mind that my sensor must have 3.3V at the VCC sensor pin.

I heard that PMOSFET is not suitable because it's work with higher voltage, but I know there is PMOFSET for 5 and 3.3V. What is your opinion?

What would be the best choose and best values for the resistances?

Many Thank a lot for you clarification, Cheers


texts: Series Damping Resistor for Low-Speed USB

texts:
The USB 1.1 spec gives well-defined \$V/I\$ characteristics for full-speed output drivers, which can be used to find the series damping resistance, \$R_S\$. The low-speed output schematics also reference \$R_S\$, but it's not entirely clear if it's the same (since low-speed characteristics are typically less strict than full-speed). And while the spec states:

  In the rest of the chapter, references to the buffer assume a buffer with the series impedance
  unless stated otherwise.

Does that mean it applies to both low-speed and full-speed, or just full-speed? If it's the latter case, then what's the valid range of \$R_S\$ for low-speed output drivers?


texts:
This is a quick and simple question but I was wondering if this was the right way to wire a NodeMCU to an RGB LED strip. I am using IRLZ44N MOSFET's and 470ohm 1/2 watt resistors.
I currently have it wired like this with the resistors connected to ground:

I have also seen it wired like this with the resistors connected directly to the controller:

I assume they both do the same thing but I might be wrong. Which way is better?


texts: Best way to implement a global FAULT input

texts: I've got several microcontrollers multiple feet away from each other in a network that must be able to be put into a shutdown state all at once, ideally before power loss. I want to trigger a shutdown from a button, like an e-stop. A pair of "FAULT" wires that gets shorted together to trigger the shutdown sounds logical, but if I use a pull up resistor on these boards, there may be current between the 3.3V rails of each microcontroller, which I don't prefer. What's the best way to implement this sort of thing?


texts:
I am trying to use the SoC CC2541 which is from Texas Instruments and is mounted with an 8051 mcu. I know that the firmware can be flashed through an Arduino board but as I want to avoid using an Arduino for flashing and uploading code to this mcu, I think that it is a waste of time and resources.

Is there any way to work with this mcu without using an Arduino? Maybe implementing an interface with a homemade pcb with an USB or something like that?

Here there are the datasheet of the CC2541


texts:
I try to implement MTPA (maximum torque per ampere) together with FOC, but I stuck in estimating the flux phi_f from the following document:
https://www.ti.com/lit/an/spracf3/spracf3.pdf?ts=1612451327724&ref_url=https%253A%252F%252Fwww.google.com%252F

How can I estimate phi_f from the other parameters and measurements?
Edit: Is it possible, that I only need to measure the back EMF and so
phi_f = sqrt(2/3) * (V_line)/(pp * omega_r), where pp = number of pole pairs, omega_r = speed in rad/s?


texts: Designing of an audio amplifier using LM386 and a preamplifier

texts:
This is the circuit . But i am still getting acoustic howling. What can I do to prevent it dynamically. Also I want to increase the sensitivity to the extent that when I rub my fingers in front of the electret mic the speaker should be able to play it . when I cover the speaker the howling stops . But the sensitivity is reduced and also I think that to eliminate the mains noise I need to eliminate the ground loops . How do I eliminate ground loop ?
Also Can i use a simple op amp like 741 c to eliminate the noise where the inputs are a scaled version of the output and the preamp input


texts: Opamp noise: When is a resistor in the signal path?

texts:
I am confused as to when a resistor is considered to be in the signal path and when its not when it comes to opamp noise calculations. For instance, take the following circuit:

simulate this circuit – Schematic created using CircuitLab

a very similar circuit is published in Douglas Self's book, he mentions that the only resistor in the signal path (on the non-inverting input) is the 100ohm resistor R3, so R1 and R2 do not contribute to the noise. It was my understanding that a resistor can be modeled like an ideal or noise-less resistor in series with a noise generator, so what I would think is that for instance, if I replace R1 with a noise generator given by \$\sqrt{4KTBR} \$ with R1 in series, then that noise generator should be amplified by the noise gain of the opamp. Why is R1 and R2 not in the signal path then?

The author also mentions the following circuit which is a simple inverting amplifier with a resistor on the non-inverting input to compensate for bias currents.

simulate this circuit

In this case the author mentions that resitor R3 causes noise, so I dont get it, in both circuits there is a resistor connected to the non-inverting input, yet in the first circuit it does not produce noise but it does produce noise in the second circuit, so how do I know when a resistor produces noise (in the signal path) and when not? it doesnt seem very intuitive.

Edit: I simulated the first circuit and ran a noise analysis, what I found is that if R3 is small valued, then varying the value of R1 or R2 does not affect the noise output and the noise depends only on R3 (plus the feedback resistors and opamp noise, etc.. Im just focusing on the non-inverting input), however if R3 is not small, then the value of R1 or R2 does affect the noise output, however, I believe this is because of the voltage divider effect is attenuating the noise of the first resistor R3, not because R1 or R2 are contributing to the total noise output, so yeah, to add to the confusion, it would seem that only R3 is in the signal path of the non-inverting input and R1 and R2 contribute no thermal noise to the output, I dont understand this. Doing a simpler simulation, just connecting a resistor to the non-inverting input in parallel with a voltage source shows that the EIN of the resistor is 0, effectively contributing no noise to the output.

I also simulated the second circuit and in fact R3 (of the 2nd circuit) does affect the noise output if I vary its value. So my observations are: shunt resistors in the non-inverting input when using as non inverting amplifier do not contribute to noise, whilst a resistor in the non-inverting input when using as an inverting amplifier does contribute to noise.


texts: Wheatstone bridge sensitivity and accuracy

texts:
From my earlier question I was able to wire up 2 SEN-10245 weight sensors (each forming one half of a wheatstone bridge) with an AD620 InAmp & 47 Ohm resistor (to set the gain to ~1000). I then ran the signal through the MCP3008 Analog to Digital Converter and finally to my Raspberry Pi.

Now that I have everything wired up, I am seeing some strange behavior when applying pressure to the weight sensors.

When applying small amounts of pressure (a soda can, for example) the sensor reading rises ~15%. However, if I really push on the sensor it drops anywhere from 30-60%. Why is this?

The end goal is to detect individual soda cans on a shelf; is there anything I can do to my circuit to modify the sensitivity or increase accuracy?

Please note that Vref on the InAmp currently has no voltage source

AD620 Data Sheet

MCP3008 Data Sheet

The pictures below illustrate my current setup:

Python script for reading values from the ADC:

import spidev
import time

spi = spidev.SpiDev()
spi.open(0,0)

# read SPI data from MCP3008 chip, 8 possible adc's (0 - 7)

def readadc(adcnum):
    if ((adcnum > 7) or (adcnum < 0)):
        return -1
    r = spi.xfer2([1,(8+adcnum)<<4,0])
    adcout = ((r[1]&3) << 8) + r[2]
    return adcout

# weight sensor connected to adc#0
weight_adc = 0

while True:
    weight = readadc(weight_adc)
    print "weight:", weight

    time.sleep(1)


texts: How to connect 4MHZ crystal oscillator to get 16MHZ

texts: I've 10 4 MHZ crystal oscillators. I need a 16MHZ clock signal. Can I connect multiple 4MHZ oscillators somehow (serial, parallel) to  get 16MHZ?


texts: Which frequency measurement method is more suitable for RF signals from 200MHz to 915MHz?

texts:
I need to build embedded circuit, an RF frequency meter (also known as RF frequency counter) to measure frequencies of remote key fobs. The frequency range I need to measure is 200MHz to approximately 1GHz
I found a good reference, the following book:
George Kamas, Time and frequency user’s manual, May 1977.
In this reference, are described the following methods:

Direct Measurement
Prescaling
Heterodyne Converters
Transfer Oscillators

I would like to know which of these methods would be more suitable? Is there another method that might be better for the case?
EDITED:
A tolerance of +/- 1MHz would be acceptable. These key fobs operates at different frequencies, for example: 290MHz, 315MHz, 433MHz, 915MHz. I dont need a very accurate measure, but it needs to be sufficient accurate to distingish between the different frequencies. So, a good cost-accuracy relation would be enough.
The user need know the frequency. So, He or she, will press a button on the key fob, point it to the device and the device will inform the frequency of that key fob


texts: Can anyone confirm that this is a reliable method to charge multiple SLA batteries in parallel?

texts:
Found this diagram at this link

Can anyone confirm that this is reliable?

Also, anyone know the circuitry for charging 2,3 and 5 battery system?

Thanks in advance.


texts:
With mosfets there are two resistances called DC resistance Vds/Ids and AC resistance dVds/dIds at the operating point.
I am wondering about the purpose of giving the DC resistance here?
Where the concept is used?
Why do we need it?


texts: Calculating current and voltage using superposition

texts:
I'm trying to calculate Vo and Io from the following circuit:

I was using node analysis but I don't really know how that worked. A friend of me told me that I could better us superposition. I understand that I have to calculate the current for each generator with the others excluded (open for current, short-circuit for voltage) so i would have 3 different problems to solve in this case. Now I looked up some examples online but they don't include capacitors or imaginary numbers (the j in the circuit is considered the imaginary number i, to avoid conflicts with the current I). Can anyone explain me how I would solve this?


texts: Help with simple Arduino/Transistor/Solenoid circuit

texts:
I'm trying to use an Arduino+transistor to control a shutter (which I believe is a solenoid) at work. The shutter is normally connected to a power supply by two small wires (positive and negative) and from what I've gathered with my DMM an 11.3 V 3.8 mA current is applied to the shutter to keep it closed, and when it is opened the voltage and current drop to 0 before reapplying the current to close it again.

Right now I have the following circuit configured so that the transistor base is connected to the PMW 9 pin on the arduino, which cycles between 5 seconds of output = HIGH (5V) and output = LOW (0V). What confuses me the most is that when I take measurements with my DMM I get roughly the same results (12V and 4mA) on the solenoid but the shutter doesn't close.

Any thoughts? Is there something I'm missing in my circuit? The only thing I can think of is that maybe the current isn't ramping up fast enough to induce a noticeable magnetic force (I think that's how it works, don't judge me I haven't taken emag in a while), but I don't know how I'd be able to combat this. Thanks.

My circuit http://www.docircuits.com/circuit-simulation-public/12041

If my circuit isn't clear enough (mostly in the arduino area) leave a comment and I'll try to clear things up.

EDIT: I realize now that the arduino is actually sending a pulse-width modulated signal with duty cycle of 100%. Could this be causing problems?

EDIT2: Updated the schematic.


texts:
I have a current sensor (sensitivity is 22mV/A) which is being used to measure AC current with its time stamp data.
I have connected this sensor to an ADC (12 Bits resolution
Can somebody please let me know whether we can measure an AC sinusoidal current as low as 0.3A with its time stamp data (like input side of a mobile charger from 2-Pin socket), I would be very much appreciative.


texts: Altium clearance between different layers to control crosstalk /capacitance

texts: I want to set a clearance rule between different layers in a multi-layer board.  In particular, I have a signal class on one internal layer that a polygon pour in another layer needs to avoid.  I would also want to make sure that traces of certain net classes don't pass too close to each other on adjacent planes.  I tried to create a clearance rule with custom queries and layer specifiers, but that doesn't seem to work unless the objects are on the same layer.  Is there any way to do this?


texts:
I am being told that the circuit below will regulate current, I am wondering how true that is and how exactly does it do it if so. As far as I can tell: two NPN transistor with their bases biased by the two resistors. This looks to be a negative feedback loop that holds current steady, but I don't quite understand the loop and if it really does regulate current.

A Google search shows me that a current regulator of which I think is the same as a current mirror normally has the bases of both transistors on one node of which doesn't seem to be the case in this circuit.

Here is the circuit:

simulate this circuit – Schematic created using CircuitLab


texts: Should I step-up or step-down the voltage if I have the option?

texts:
I'm building a series of gadgets for my kids that mostly (microchip, sensors) run off 3.3 but there are some switches and possible servos that run off 12v.

My original idea was just to have two wires, one for 12v and one for 3.3v but I don't like that since most of the items won't need the 12v and it adds clutter in the wiring. The other option is to only have one wire and either step down or up the voltage in the components that need it. The heat from stepping down 12v to 3 worries me and since most will be running of 3v it seems more logical and economical to use step ups when I need the 12v. Is this the best approach or is there another approach that I'm overlooking?

Most of the 12v components are buttons with built in leds so power consumption is pretty low, I guess they are mostly used in auto applications so most of the leds require 9-12v to light up well.


texts: Powering TTGO T-Call (ESP32 + SIM800L board) with only battery

texts:
I have recently bought a TTGO T-Call board. This nice board assembled together the ESP32 and SIM800L (GPRS module).
The board is working well if I am powering it up with it's USB type c input.
One of its' feature is to power up by lithium battery (3.7V) by the IP5306 power manager and pressing reset button for more than 1 second.
Of course the IP5306 also responsible to charge the battery in case there is another external DC source.
The IP5306 has a boost converter that close in case the button is pressed. The output of the IP5306 is regulated 5V which supply the whole board components.
When I connect battery (charged battery with Voc=4V) to the board and pressing the reset button I see that the 5v signal is rising fast to 4V and then dropping to ~2.2V. After that the signal is stable at ~2.2V and if I press again it jump to 4V and then drop down again...
The scheme can be found here:
https://github.com/Xinyuan-LilyGO/LilyGo-T-Call-SIM800/blob/master/schematic/LilyGo-SIM800L-IP5306-20200811.pdf
Can anyone help to solve the problem to start up the board with battery?
Thanks


texts: Does potentiometer accuracy change with degree of movement?

texts:
I want to use a conductive plastic potentiometer for my actuator application where movement is +/- 40 degrees.

As in datasheet, the potentiometer linearity is given as +/-0.2 % which I think is for full rotation. My rotation would be approx 80 degrees only.

Can I say that (80 * 0.2) /100 = 0.16 will be my accuracy for the potentiometer or in every case it will be always (360 *0.2)/100 = 0.7. or what I'm doing is wrong?

Actually, I need a sensor which can give me an accuracy of less than +/-0.2.


texts:
I am currently taking MIT 6.002 course to get a head start prior to starting EE next fall. Right now, I am really struggling with this first lab.

Problem:

You have a 6-volt battery (assumed ideal) and a 1.5-volt flashlight bulb, which is known to draw 0.5A when the bulb voltage is 1.5V (see figure below). Design a network of resistors to go between the battery and the bulb to give \$v_s=1.5\text{V}\$ when the bulb is connected, yet ensures that \$v_s\$ does not rise above 2V when the bulb is disconnected.

Hint: use a two-resistor voltage divider to create the voltage for node A. You'll have two unknowns (\$R_1\$ and \$R_2\$) which can be determined by solving the two equations for \$v_s\$ derived from the constraints above: one involving \$R_1\$, \$R_2\$ and \$R_{\text{bulb}}\$ where \$v_s=1.5\$, and one involving \$R_1\$ and \$R_2\$ where \$v_s=2\$.

What I was able to figure out:

It is obvious that we would need to have one resistor in series and one parallel to the light bulb. Furthermore if the light bulb is removed we would have the resistors in series.

Without the light bulb we would have $$(R_1+R_2) \times I = 6\text{V}$$
With the light bulb $$(R_1+(R_2 \parallel R_b)) = 6\text{V}$$

Other than that I am stuck.


texts:
I've been going through Design of Analog CMOS integrated circuits 2nd Edition by Razavi. I'm currently at the Cascode amplifier section. The author does an example for calculating the gain for the circuit below, but I don't understand how he got his end result.

He first starts by obtaining Id2, noting the the current generated from M1 is split between Rp and the impedance seen looking into the source of M2, which is
$$1/(gm2+gmb2)$$

$$Id2 = gm1Vin\frac{(gm2+gmb2)Rp}{1+(gm2+gmb2)Rp}$$

I don't understand how he comes to that conclusion for the current of Id2.

Next, he just states the voltage gain is given by:

$$Av = -gm1\frac{(gm2+gmb2)RdRp}{1+(gm2+gmb2)Rp}$$

I attempted to use the Lemma technique to solve it (Av = -GmRout) but I can't seem to get anywhere. I think I'm missing an important step he's doing to obtain that gain.

Could anyone provide some insight into the process he is doing to obtain those results (Id2, and Av)? Thank you.


texts:
I have a very simple central locking system in my car that I installed last weekend. It came with no remote at the moment it only works if I use the key in the drivers do where the master actuator is or if I touch the lock/unlock wire to ground. It has a small control box.

Now to lock and unlock the car via remote(Arduino). I need to pull the lock or unlock wire of the control box to GND. How do I do this? The wire only needs to be connected to ground for a second as the control box controls the timing on the actuators.

Can I do this with the Arduino only or need something like a transistor?

I have a sketch that uses a RFID module to check if the correct tag is presented and toggles the lock. It also locks the car in the setup method in case of a power issue.


texts: I'm looking for a connector for PCIe 4.0 testing (not a standard PCIe connector), but I'm not seeing frequency range values for PCIe, so I'm not sure what connector specs I need. Is there a good rule of thumb to use (twice the unidirectional bandwidth?)?


texts: RC Circuit Analysis Direction Changes Formula

texts:
In my Circuit Theory lesson, we were studying RC circuits and there was a question which I tried to make before our senior but I accidentally came up with a different answer due to choosing current direction opposite to our senior;

simulate this circuit – Schematic created using CircuitLab
It's the basic RC structure, the switch was closed for enough time and opens at \$t=0\$;

simulate this circuit
Notice the red arrow at the right, because of its direction my calculations went this way:
$$KCL\; at \; Node\; 1:$$
$$-i_R+i_C=0$$
$$-\frac{V_C}{6}+10\mu\frac{dV_C}{dt}=0$$
$$\frac{dV_C}{dt}+(-\frac{1}{60\mu}V_C)=0$$
If we solve the diferential equation according to \$\frac{dx(t)}{dt}+\alpha x(t)=0\ \Rightarrow\ x(t)=x_0e^{-\alpha t}\$ :
$$V_C(t)=V_C(0)e^{-(-\frac{1}{60\mu}t)}$$
Since \$V_C(0)=9\$ :
$$V_C(t)=9e^{\frac{1}{60\mu}t}$$
And here it is, according to this result, the voltage at C1 is increasing over time which is impossible. My senior's result was \$V_C(t)=9e^{-\frac{1}{60\mu}t}\$ because he took the direction of the \$i_C\$ opposite to mine, therefore at KCL, signs of currents were the same so the final equation had a negative sign, unlike my result.
I've been told that I can choose the current and polarization directions as I want at Node or Mesh analysis and it will not affect the final results(maybe voltage and current signs can be wrong) but in this case, it changed the whole equation to something meaningless.
I would like to know what I am missing here.


texts: Allegro: plotted artwork only has hatched pads

texts:
I am trying to find my way around Cadence Allegro. My aim is to make a PDF file with the copper mask.

I made a schematic with capture, created a PCB layout with Allegro PCB Designer and created artwork using Manufacture->Artwork.

I then imported this artwork into Allegro and selected File->Plot and printed via a PDF printer. My problem is that the copper for the pads is not filled solidly but with thin lines. Why is this so and how can I get solid filling?

See the attached example:

even very thick lines are solid
pads are hatched only


texts: Loading and displaying on VGA monitor a Background image in DE2-115's SDRAM

texts:
I would like to load a background image which I currently have saved as a .bmp into the DE2-115's SDRAM. I would then like to display this background image on a VGA-monitor (640x480). I will then be drawing additional images overlaid to this background image.

I am using NIOS II by the way.

I have implemented games using a VGA controller such as brick breaker but they simply had solid colors which I would draw in .sv code quite easily.

If I want to draw this  .bmp to the monitor what steps should I take? Should I draw it from software in C or from hardware using a vga controller and reading from memory? Lastly how should I upload the .bmp to the SDRAM?

Thank you.

UPDATE!!:
I should probably explain more of the project. So I'm trying to develop a texas hold em game. The fixed background image is a poker table and in fixed locations on the table I want to overlay the card's of 2 players, as well as the 5 common cards. The poker table will be a .bmp as well as each card. Based on the current game we will be displaying different cards. We will have to display several cards at once.

So effectively what I wanted to know is how I should deal with displaying all of the above for a given game. I have the game all setup, I know just have to determine how I will store all these .bmp's in memory and read them and display them during a game. I have a VGA controller setup and a color mapper but they were used for a brick breaker game which didn't require reading from memory for drawing.


texts: Does mutual inductance change individual inductances?

texts:
If I have two inductors, with inductances \$L_1\$ and \$L_2\$.  I put them really close to each other to make a transformer.

Are their individual inductances still \$L_1\$ and \$L_2\$?

Or has the mutual inductance changed their individual inductance?


texts: Scattering matrix in microwave amplifier

texts: What exactly is the scattering matrix in a microwave amplifier. I tried to deduce from lectures what it is used for in a microwave amplifier, but all I found were the formulas corresponding to the calculation of such matrices. Does anyone have any specific information on what this matrix is and why we need it for the topic of microwave amplifiers?


texts: I have a lot of AVR Atmega128P boards, and I would like to use it as timers WITHOUT PROGRAMMING, as example, just like 555 timers. Is it possible? If yes, how can I do that?


texts: How does this modified H-bridge circuit work?

texts:
I am trying to design a circuit which will have as an input a single microcontroller pulse which will cause a circuit with two 555 timers to output two consecutive pulses which are able to have their pulsewidths adjusted through potentiometers. I want to create a circuit which will take these two square waves and produce alternate positive and negative pulses of a much higher adjustable voltage (between 10v and 48v).
I have found this circuit on the internet which I've modified slightly to use 48V instead of 110V and simulating it shows that it does what I want it to do however I would like to understand how it is actually working. I recognise that the four central transistors (2 NPN and 2 PNP) form an H-bridge configuration however I don't understand exactly what the other transistors in the circuit are doing. My question is what is the purpose of Q5/Q6 together with the capacitor and zener diode combination on the base and the capacitor and 1k resistor between the emitter of Q5 and base of Q1 (or emitter of Q6 and base of Q2)? How were the values in the circuit selected to perform this functionality?
I'm trying to understand the circuit from a design perspective.
edit:
The Zener/Capacitor combination seems to be the simplest kind of voltage regulator that there is and I think it's purpose is to keep Q5 or Q6 always on by dropping any excess current from the V1 supply across itself to ground.


texts: how to use a network analyzer for multititle synchronization for RFSoC

texts:
I have configured my rfsoc dacs ZYNC to produce a signal from two DAC's
then we put them into network analizer at single frequency and measure S11 as amplitude dB
and S21 as phase, then we divide the two ,s21/s11.
i cant see how this trick is supposed to show if the two signals have the same phase(sinchronised)
Thanks.


texts:
I am providing a 5 V power supply to play with 3 Relays, they are 2 channel 5 V relays, when I turn on one bulb other relays do not get the sufficient voltage to operate. How would I prevent or overcome on such voltage drop?

If I do not get the sufficient voltage then other relays will not work, so I just want to keep the voltage above 4.5 V at all ends.

Here is the circuit,

and the tabulated voltage readings:

Note :

I am taking readings from multi-meter at the ends shown in the image (bottom left corner).
To turn on any bulb we need to turn on the switch , in other words the IN pin of the relay needs LOW signal to make the bulb ON.

ADDENDA:


texts:
this is a power circuit I'm trying to complete:

the button at top turns the curcuit on, supplying VCC to mcu, and the MCU will output a high signal to a pin (marked in pink) which turns the N-MOSFET on, and the P-MOSFET on as well. (right?)
when the button is released, the mcu signal still keeps the VCC supply on, through the IO pin.
MCU is able to turn itself off (by turning the N-MOSFET off, which turns the P-MOSFET off, thus cutting the VCC supply)

should I place the filters (the caps and choke in the yellow rectangular) before or after the mosfets?
(I placed them before mosfets, so that the load isn't capacitive. so that I can get rid of C1 and R1. is it good practice ?)

Do i need to limit the inrush current? (Vout is going into a switching regulator, and from that to an LDO, then to MCU. do these component qualify for being "capacitive load" ?)

if so, how values of C1 and R1 are calculated ? (which are supposed to limit inrush current)


texts: How to properly turn off a Raspberry Pi when instant plug-out is a criteria

texts:
I want to create a stand-alone internet radio device. Therefore I want to use an existing subwoofer box with connected speakers. Inside the subwoofer box there is the electronics for the sound system. There is also a 5V supply wire where I can connect my Raspberry to.

But what if my radio is running and I don't want to listen to it anymore? I can't just plug out the subwoofer box from the socket. This will cause the Raspberry Pi to lose its supply. The filesystem on the SD card will be harmed if such a plug-out is performed when OS is running. I'd like to properly shut it down by recognizing the plug-out and executing sudo halt after that.

What is the best solution for my intention? I have thought of a backup battery for the Raspberry Pi. Just like the battery which is used on motherboards. But will 3.3V be enough? Is there a battery which can provide that much current to run the Raspberry Pi (Note: a HD44780 display and a WLAN dongle is also connected to the Raspberry Pi)? How can I assure the battery is not used when the regular 5V supply is available (to not use battery AND 5V supply at same time).

Any help is appreciated.


texts: the parameters changing of w element interconnect model for various technologies in hspice?

texts: how can I change the parameters of w element interconnect for various technologies, for example, 90, 64, and 180nm technologies in hspice? I attach one code in the attached picture from hspice tutorial pdf.


texts: Offset an input voltage of -2.5V - 2.5V to 0V - 5V?

texts:
I have a circuit input which provides a voltage range of negative 2.5 volts to positive 2.5 volts. How do I change this so the output voltage is 0 - 5 volts?

simulate this circuit – Schematic created using CircuitLab


texts: Add external antenna to router with only internal antennas?

texts: Does anyone know if its possible to add an external antenna to a router with only internal antennas? I'm trying to improve the signal of my Linksys e4200v2. I'd like to add a high gain antenna if possible. Hopefully this would apply to a few of my Linksys WRT160N's that I'm using as client bridges. I saw some kits on eBay to add an antenna but I'm not sure how legit it was.


texts: How do I control the brightness of an LED street light

texts: I am currently using a DC-AC ERI Solid state relay (Model number 001J) with a PIC16F microcontroller to control the operation of an LED street light. I have dumped a PWM code onto the microcontroller. I'm able to see a variation in the voltage on the input of the Solid state relay (Corresponding to the code). However, the intensity of the LED street light head (which runs on 220V AC mains) connected to the output of the Solid State relay remains the same. Am I doing something wrong, or is there a device I can replace the Solid State Relay with, to ensure smooth operation?


texts:
I'm currently designing a PCB in Eagle to build my own Nixie Clock. I know kits exist but I'm trying to do this from the ground up to get the experience. Nixie Tubes require 180V and I'm trying to mimic and existing  SMPS Circuit (the bottom of the page has a parts list) but this was designed years ago and a lot of the parts it used are no longer available.

For Example C1: TPSD107M035 it is 100uF with a voltage rating of 35V with a comment saying to use the lowest ESR available. I'm trying to use SMD packages and I'm having trouble finding the part in Eagle. Only a handful of parts have 100uF and 35V voltage rating but they don't list the package type so I don't know what to set it as. This capacitor seems like it would work as a replacement but I cannot find its package information and I don't know if just matching 100uF and the voltage rating is all I need to do.

Would a higher voltage rating work as well? I know there is also polarized vs non-polarized capacitors exist but does that make a difference in most application?

Appreciate the help!


texts: Bulk capacitance equation derivation from appnote

texts:
I am looking at SLTA055 by Texas Instruments. It discusses, among other items, how to determine the bulk capacitance required for a buck regulator if a LC filter is used. Since the "L" will not allow the high frequency current draw to come from the PSU, it needs to come on the buck side of the L.
Two things on this appnote that are vague:

There is zero mention about where this equation comes from, or how it is derived. I have searched everywhere online, and can't find this anywhere else. Any idea where they got it from? Itr is the max transient current draw, L is the series inductor value, and delta V is the max voltage sag.

Immediately above equation 9, they also say

The next step is to decide if a series filter inductor is going to be
used. If using an inductor, pick a value no greater than 560 nH.

That also confuses me, as using equation 9, you could in theory use as large of an "L" as you want. You will just need to use large capacitors that wouldn't be practical. Maybe this is just a rule of thumb, that they don't mention as such?


texts:
Can someone please help me to understand what type of connector is the below :

How do we classify this 99S12D-40MA5-y connector which is on page 33 in the Catalog document?

Do we call it as a contact type, male or female connector header or something else? I understand that it is not contact type since I have seen images of contact type connectors (connectors which don't have a locking mechanism). Can someone tell me what type of connector is that?

Can someone tell me also what type of connector is this? What do they mean when they call the Gender of this connector as PLUG and what does the 40M signify? Please help to understand.


texts: How to protect against a short circuit fail in 12VDC X capacitor?

texts:
When adding an X capacitor for simple line filtering in a 12V DC electronics project, how would you add protection against an unlikely short circuit failure in that capacitor?
Is it as simple as a fuse or something more interesting?


texts: Can a switching power supply be built on a breadboard?

texts:
I'm toying with the idea of putting together a switching power supply (my first), using something like the LT1076-5 or the LM2576 controller ICs. These ICs have low external parts counts, and a relatively low switching frequency (56kHz-100kHz). Having spent some time reading datasheets for controller ICs, it's clear to me that some component placements are critical to the design. I'm wondering, then, if it's advisable or even possible to create and test the power supply on a breadboard, and later move it to a breadboard-layout protoboard.

If I'm not requiring ultra-high efficiency (any switcher's gotta be better than a linear when dropping ~35V, right?), does that make a difference? Or is it more likely to simply not work at all?


texts: TimerBlox LTC6992 PWM variable clock generator at 2.3MHz... out of tolerance or used incorrectly?

texts:
The TimerBlox LTC6992 (https://www.analog.com/media/en/technical-documentation/data-sheets/LTC6992-1-6992-2-6992-3-6992-4.pdf) is a PWM chip specified to have a master output frequency maximum of 1MHz, and provides a set of pins (MOD, SET, and DIV) to control the output square wave. I built a circuit that fixes the duty cycle near 50%, and allows for the divider and master frequency to be adjusted by potentiometers. What's baffling me is I'm getting over 2.3MHz out of this chip. I'm not sure whether I've misunderstood the technical limitations of the LTC6992, or if my chip is damaged and somehow out of tolerance.
For some context, this circuit will be used to generate a variable clock speed on a Z80 microcomputer, and there is an engraved label plate involved that I would like to rely on being engraved accurately.
My circuit consists of three main parts, each of which I will explain.
The MOD Signal
This is a simple voltage divider producing around 0.5V. While the chip states the MOD signal can be effected by the SET signal, it is not significant in my circuit and a static 0.5V holds the duty cycle very near 50% at all times.
The SET Signal
The 6992 holds this pin at 1V and looks for current sink via a resistor RSET between 50K and 800K (see top of page 4). A parallel 4M resistor and 1M variable resistor generate 0-800K resistance, which is in series with a 24K resistor producing the range 24K to 824K, just over the maximum range specified on either end.
The DIV Signal
The DIV signal drives a set of discrete values detected by an internal ADC with preset ranges. From 0v to VCC/2, the available denominators are 20, 22, 24, 26, 28, 210, 212, and 214. If VCC/2 is exceeded, the scale reverses and the polarity of the duty cycle is inverted. My circuit uses a small variable resistor to prevent the larger potentiometer from ever passing the VCC/2 boundary. It is a simple variable voltage divider between 0V and 2.5V.
Here is the relevant portion of my circuit as I planned it in a simulator. Please note that some components are represented by a pin header showing they would plug into the board rather than being soldered to it.

And here is a photograph of a breadboard prototype of that circuit:

Running with both dials turned left (no division and highest base frequency) I see over 2.3MHz, 230% the specified maximum for this chip.

Running with both dials turned right (highest division and lowest base frequency) I see a reasonable 3.68Hz, which is very close to the specified 3.81Hz minimum.

Context notes:

All VCC is at 5V
The 6992 is a surface mount component, and I've soldered it to a 2.54mm adapter. The board has been cleaned aggressively with alcohol and an antistat brush.
The 6992 is further nested in a socket because the pins weren't long enough for a breadboard

Have any other details you want me to add? I'll add them to this list.
TL;DR Why is this LTC6992 running faster than 1MHz, and am I able to prevent this behavior?
Adjustments made per the posted solution:
The RSET value must be clamped to the range 50K to 800K. I formerly assumed it would clamp internally based on the wording of the data sheet. To achieve this, I've replaced the 24K resistor with a 100K variable resistor, tunable to exactly 50K. I've also replaced the 4M balance resistance with 2M plus a 2M variable resistor. This resistor can be tuned to produce a total resulting resistance of 50K (set by first pot) to 800K. This circuit is confirmed to produce a near-perfect 3.81Hz to 1MHz, exactly as specified in the datasheet.


texts: Generating a 10 volt rail from a High Voltage Supply with unknown Ground Potential

texts:
I have a sticky situation where my power supply is coming from a charged capacitor with 200 volts across it. Because of the way it was charged, I can't guarantee that the negative side of the cap is at "ground" potential.  All I can depend on is that there is a 200 volt difference.  It could be that one side of the cap is 10 volts and the other side is -190volts.  As a result of this, I'm nervous about trying to mix other control circuitry that uses a different ground potential, so what I want to do is simply use the 200 volt circuit to run the control circuitry.

From what I know all I have to do is use a voltage divider to generate a third voltage leg that has the 10 volt difference I want for my control circuitry.  Then I should be able to run IC chips (like NE555) and mosfet gates off the 10 volt difference without any problems.  It also shouldn't matter whether I make the 10 volt difference relative to the low side or the high side.

Is all my understanding correct?  Are there any problem areas I could run into when trying to divide high voltages to much lower voltages?  What if I had an even higher voltage supply such as 1000 volt?  Can I still divide it like this to run ICs and mosfets?

Here's a pic to help illustrate:


texts: STM32F091 Jump to Bootloader from application

texts:
I'm trying to implement a jump to the STM32F091 USART1 bootloader from my application.

I'm using the following function(based on https://community.st.com/thread/40238-stm32l476rg-jump-to-bootloader-from-software):

void SB_SystemBootloaderJump()
{
    typedef void (*pFunction)(void);
    pFunction JumpToApplication;

    HAL_RCC_DeInit();

    SysTick->CTRL = 0;
    SysTick->LOAD = 0;
    SysTick->VAL = 0;

    /**
     * Step: Disable all interrupts
     */
    __disable_irq();

    /* ARM Cortex-M Programming Guide to Memory Barrier Instructions.*/
    __DSB();

//  __HAL_SYSCFG_REMAPMEMORY_SYSTEMFLASH()
//  ;

//  /* Remap is bot visible at once. Execute some unrelated command! */
//  __DSB();
//  __ISB();

    JumpToApplication = (void (*)(void)) (*((uint32_t *) ((0x1FFFD800 + 4))));

    /* Initialize user application's Stack Pointer */
    __set_MSP(*(__IO uint32_t*) 0x1FFFD800);

    JumpToApplication();
}

From APP Note AN2606: System Memory address as in picture: https://i.imgur.com/nVcgoBg.png

From SWD Utility, memory contents at System Memory: https://i.imgur.com/PeepkrX.png

From Debugger, SP and Reset handler as picture: https://i.imgur.com/PagQng0.png

Program execution up to breakpoint at Bootloader address : https://i.imgur.com/koKfObe.png

Considering:
A - Using a jumper to VCC on BOOT0 pin, I can successfully access the system bootloader via STM32 Flash Loader Demo. The same is not true if I jump to the bootloader from my app.
B - I'm using a FTDI FT230x USBxSerial Bridge.

Questions:

1 - Since I'm using the absolute system memory address, there is no need to use __HAL_SYSCFG_REMAPMEMORY_SYSTEMFLASH(). Correct?

2 - Am I missing something on this function?

3 - Is there a timeout between the bootloader starting and receiving the "0x7F" byte on USART1?

4 - Will opening/closing the serial port affect the bootloader? Do I have to reset the MCU if I close the serial port and open it again?


texts: Solar high voltage regulator & power logger circuit - design review

texts:
I was wondering whether someone could give me some feedback on a circuit I have been throwing together. The circuit is supposed to act as an voltage regulator and power logger for my high voltage solar array (400 V max). Since the desired output voltage is never supposed to be higher than the array voltage, I chose a buck converter topology. Up until this point, I have not built such high voltage circuits and I'm therefore not that confident in my design.
My major concerns are:

Are the isolation distances big enough?
Do I need to add additional protection to the buck converter (e.g. Zener diodes on GS)? (answered)
Is it OK to have the ground planes "split" like that or should they be connected?
Do I need complete isolation of HV/LV?
Are the bootstrap caps big enough?

PS: Please excuse my English, I'm not a native speaker.
Note: fixed freewheel diodes (replaced by low side mosfet), half-bridge, added gate zeners, increased resistor count im voltage divider


texts: Avastar SP88W8782 wifi module Pinout 12 pin usb

texts:
I just opened a HP wifi driven printer and found an Marvell Avastar 88W8782 Wifi Module with 12 Pin connector to the main board. From googling I found that this is a USB interface driven module but I cannot find a datasheet with any pinout info. This module is suppose to have a Uart and also a spi bus. Does anyone has any idea on how to use this module?
Only datasheet I am end up with is enter link description here


texts:
I'm trying to wire a simple inverting op amp circuit just to test it. I have been unable to make it work. This is the circuit I have:

I have simulated this circuit and it gives 1.92V (it should be -1.92, but I guess that is because the simulator doesn't like negative voltages).
And this is how I wire it:

In the board, the + rail is 3.3V and the - rail is 0V
The op amp I'm using is this: OPA23344PA
The 3.3V rail voltage come from a voltage regulator, which is powered by a 9V battery.
I have double checked that the rail voltage is 3.3V.
I have tested this same op amp in non-inverting mode and it works fine.

What I'm missing here?


texts:
I have designed a 50 Ohm microstrip line. Following is an image of it.

This is drawn in Eagle. Two layer PCB. Blue plane is the ground plane. The dimensions are:

Width: 1250 micrometers
Thickness: 1 oz
Height (between ground plane and microstrip): 700 micrometers

Dielectric is FR-4. Frequency is 1575MHz. These parameters yield 50 Ohm impedance.

You see, the problem is that the end of the microstrip is too wide that it almost contacts the pins of the IC. Is it possible the narrow down the width around that area while maintaining the 50 Ohm impedance of the microstrip?

Here is the updated layout, based on the suggestions.


texts: Implementing HID input device with an Atmel AVR32

texts:
I want to implement a small HID input device using one of the Atmel AVR32 chips (Atmel AT32UC3B1256). The chip has an on-board USB transceiver, with D+ and D- pins etc.

I've been looking at tutorials from Patrick Hood-Daniel on Youtube. Also referring to neat little devices like the USnooBie, where the USB interface is done using software, and only supports USB 1.1.

I want to achieve something like USnooBie, but instead, us an AVR32 chip utilizing the built in USB 2.0 transceiver on the chip.

Are there any instructions available online to aid in this process, getting the basics done?

I've Googled around and finding it a bit difficult to find something in relation to the AVR32 USB transceiver.


texts:
Let's assume we have three-phase diode (not SCR, ignore those in the picture) rectifier like in the picture:

Assuming we have no source inductance and other ideal conditions, diodes from 1 to 6 are conducting at following angles (of course we need to add some load):

Diode 1: 30º < X < 150º
Diode 4: 210º < X < 330º

Diode 3: 150º < X < 270º
Diode 6: 330º < X < 450º (= -90º)

Diode 5: 270º < X < 390º (= -30º)
Diode 2: 90º < X < 210º

As we can see, each of the diodes conduct exactly 120º per cycle. Also, conduction of diodes 1,3,5 and 4,6,2 does not overlap.

However, as soon as we look at some more realistic scenario and add source inductance, diodes start conducting more than 120º per cycle because of the commutation process. Subsequently, the conduction angles start overlapping. For example, diode 1 conducts from 20º to 160º and diode 3 conducts from 140º to 280º. Diodes 1 and 3 are overlapping for 20º.

My question is - how is the angle of conduction and overlapping angle affected? I know that it changes with source inductance and also current load on DC side, but I would like to know exactly how. There are lots of pages discussing firing angle of the SCRs in this case, but this is not what I am interested in (I only have plain diodes).


texts:
Why does the IPC standard allow for smaller clearance on inner layers than external layers?

In this thread it is alleged that external layers are susceptible contamination. That makes sense with home-etched boards. But I thought no contaminants could get to the copper layers through the solder-mask.

For example, the IPC: IPC2221A (mentioned in that same thread) recommends for 100V traces a minimum clearance of only 0.2mm for inner layers, but 0.4mm for external coated layers.

Does it have to do with the conductivity of the PCB itself or the solder-mask?


texts:
If I have a P-channel mosfet and I want it to operate  with Vgs much more than absolute maximum ratings what's the best solution which can I do?
I thought that a zener between gate and source might be a good solution but, if I go through this what would be happened if the zener does not start to conduct immediately and the mosfet receive the whole amount of voltage even for a few micro seconds until the zener starts to conduct?

The mosfet is intended for reverse polarity protection.


texts: What's the name of this small connector?

texts: I would like to know what's the name of the connector on the side of the PCB? It's really small. Width: ~ 5 mm. Height: ~ 1.2 mm.


texts: Filtering power to stepper motor drivers for EMI

texts:
I have been using Allegro A5977 stepper drivers for a while now (a few years) and I had not too bad of a result meeting the EMI compliance targets even for CLASS B.

However I went by the seat of my pants when filtering the VBB (the Motor power voltage). I use a filter consisting of an electrolytic cap to the GND, 68uF SMT can right at the chip's VBB, then I put a BLM18KG221SN1D ferrite bead in series (220 Ohm at 100MHz, 50mOhm DC resistance 2A rated) and finish it off with another cap, this time a X7R 22uF chip capacitor to the GND.

This filter is at every driver. Then it runs to my 12V input where it meets the board's input filter which could vary depending on a board and POL DCDCs I use. But no matter what, there will be a 100uF electrolytic and 1uF film cap there.

I have my doubts as to the ferrite bead efficiency as the currents that could go into 1A peak will render the bead not very... resistive to the noise which is quite low in frequency in the first place and is certainly not in multi-MHz region.

How can a I design a board with stepper drivers and ensure that CLASS B FCC standards are met for EMI?


texts: Arduino-to-Arduino SPI unexpected characters

texts:
I've been trying to follow the posts on Nick Gammon's page which are admittedly a bit old, but seem to be everyone's recommendation for trying out Arduino to Arduino SPI. I'm able to get communications working, but there's a small issue I can't seem to pinpoint. Every once in a while there are three characters that show up in my output that are completely unexpected. Where are these characters coming from?

Here is what they are:

Hello, world!
Hello, wo&⸮BHello, world!
Hello, world!
Hello, world!
Hello, world!

In the second row, you'll see &⸮B in place of what should be rld!\n.

I have two Name-brand Arduino UNOs both being powered via USB to my computer, and they each have pins 13,12,11, and 10 directly wired to each other. Here's the code I'm using:

EDIT: The unexpected characters are the same every time, and seemingly show up as UTF-8...the decimal values for those characters amounts to 38, 226, 66, 10. I'm not sure if that has any significance.

Master:

#include <SPI.h>

void setup (void)
{
  Serial.begin(115200);
  digitalWrite(SS, HIGH);
  SPI.begin ();
  SPI.setClockDivider(SPI_CLOCK_DIV8);
}

void loop (void)
{
  char c;

  // enable Slave Select
  digitalWrite(SS, LOW);    // SS is pin 10

  // send test string

  const char p [14] = "Hello, world!\n";
  for (int i = 0; i < 14; i++) {
    SPI.transfer(p[i]);
    Serial.print(p[i]);
  }

  // disable Slave Select
  digitalWrite(SS, HIGH);

  delay (2000);
}

Slave:

#include <SPI.h>

volatile char buf [100];
volatile byte pos;
volatile boolean process_it;

void setup (void)
{
  Serial.begin (115200);

  // have to send on master in, *slave out*
  pinMode(MISO, OUTPUT);

  // turn on SPI in slave mode
  SPCR |= _BV(SPE);

  // turn on interrupts
  SPCR |= _BV(SPIE);

  // get ready for an interrupt
  pos = 0;   // buffer empty
  process_it = false;

  // now turn on interrupts
  //SPI.attachInterrupt();
}

// SPI interrupt routine
ISR (SPI_STC_vect)
{
  byte c = SPDR;  // grab byte from SPI Data Register
  if (pos < sizeof buf)
  {
    if (c == '\n') {
      buf [pos++] = '\0';
      process_it = true;
    }
    else{
      buf [pos++] = c;

    }

  }
}

void loop (void)
{
  if (process_it){
    char * bufp  = buf;
    Serial.println (bufp);
    pos = 0;
    process_it = false;
  }
}


texts: What do you do to help you grasp a concept or understand something you're seeing for the very first time?

texts:
Often in industry you come across a lot of different devices or even concepts you're seeing/hearing for the very first time. Things like encoders, resolvers, PID, pressure transmitters etc.

I would like to know what some of you guys do in order to quickly get a clear understanding of it and become a master at the subject matter.
Are there certain steps you follow or is it just random?
It would also help if you gave an example of a time you saw something for the first time and the steps to you took, and how long it took you to master it.

I'm not sure if this is the right platform for this but I'll take my chances anyway. I'd appreciate any positive feedback.

Thanks!


texts: 555 PWM motor driver controlled by external analog signal

texts:
I used the below 555 timer PWM circuit to control the speed of a dc motor, and it works like a charm :)

now i have a requirement to change the PWM speed externally from another module, that module consists from a simple potentiometer, as shown below

both VCC and GND is common between the 2 modules.
so basically what i need is to find a way to make the output signal from the POT, change the speed of the PWM output, alternative to change the R100k value in the first picture, i could not make it works at all :(

i also tried the VCO mode, but the result of motor speed was not reliable,
Thanks all in advance


texts: Why multiple bias voltages are required to drive LCD?

texts:
I have read this document:
AN658 - LCD Fundamentals and the LCD Driver Module of 8-Bit PIC® Microcontrollers

I understand that the main concern is to maintain 0 Vdc bias on every pixel when driving LCD display.

But I do not understand why there are multiple bias voltages required to drive backplanes (= common nodes).

Why are required such crazy unintuitive waveforms?

Why I can't use just static biasing?
For example when I want to make 1 pixel on:
1st frame would be BP0=1 (common), SEG0=0, the 2nd frame would be BP0=0 (common), SEG0=1. This would make 0 Vdc bias and the pixel would have the maximal contrast.


texts:
I have a football field to wire up. It measures 900m x 450m. I need to connect multiple light weight devices that use a 100-220vAc adapter that convert the voltage to 24v for the daughter device.

What i was thinking was to use a Single Phase 220v to 480v Step up transformer at the starting point and to have step down treansformers at the nodal points. A 10AWG copper cable laid on the border of the field to connect the main transformer to all the following ones in a parallel setup. I have around 15 of those adapters to plug. The devices use 24v 0.5A load.

Am i planning something wrong here? Is there a better approach for this solution?

I dont want to plug in 15 UPSs at the nodal points, it would be best to have one on/off to power all of them 15devices on/off.


texts: Transfer files from mass storage device to other machine via wifi

texts:
How can one build a device that presents itself as a mass storage device to a machine via usb, then whatever files are transfered to it, get sent to a remote location via wifi (can be ad hoc). Something like the eye-fi but that can send any files.

Something similar to these devices :

http://www.infinitec.com/ (Why can't use : Will be released first of july which is too late for me )

http://www.hsti.com/ (Why can't use : Remote file system is mounted read only)

Thank you


texts: The nameplate or nominal impedance of most modern speakers is 4 or 8 ohms .It has been known for generations that the Actual impedance varies somewhat with frequency and is not pure resistance .Amplifiers are designed with this in mind .The DC resistance  measured with a DVM is about 6 ohm for an 8 ohm speaker and about 3 ohm for a 4 ohm speaker .This observed ratio of DCR to speaker impedance appears to be relatively constant and has not changed for many decades .Surely this means that 75% of the audio power is wasted before the mechanical and acoustic matching losses   occur .Loudspeaker efficiency is important when considering low power equipment .So my questions are :Are modern speakers more efficient ? And  Why dont they make a speaker with lower DCR with a thicker lower DCR voice coil with the better permanent magnet materials available ?


texts:
I need your help to find the answer for 2 questions:

What is exact name of the golden trace in the red area?
What is its purpose, and how to draw it in the PCB

Thanks for your help


texts: Connect two batteries in parallel with transistors?

texts:
I am trying to figure out how I can connect two small 12V lead acid batteries in parallel using transistors, but when testing this circuit on the breadboard, the voltages didn't equalize so that tells me the two batteries weren't connected to each other.

How could I make what I am wanting to accomplish?

The bases in the schematic will be pulled low by another transistor when a certain condition is met in the microcontroller, thus isolating the batteries.

The goal is for the microcontroller and other circuitry to be running off of the BT2 battery when a motor causes a voltage drop from BT1, and when the motor is turned off, the batteries are normally connected together increasing the capacity of the system.

Thank you.


texts:
I have a relay SRM-1C-SL-5VDC. I am trying to switch the load On/Off using this relay. I am not sure how to connect it correctly as there its not mentioned clearly in the datasheet. Which pin on the relay am I supposed to connect the Load? I have uploaded my schematic below. Pin 1 on the two pin connectors is the 'Live' rail and pin 2 is the 'Neutral' rail.

The footprint for the relay is shown below:


texts:
Is the following circuit electrically sound? My recollection is that the right way to do it is to use a PNP transistor on the high side and an NPN transistor on the low side. Will it work if they are both NPNs? What differences in performance are there?

simulate this circuit – Schematic created using CircuitLab

A, B, C, and D are 0 - 5V logic signals from a microcontroller. Obviously the truth table of the two circuits is a little different:

A B D1      C D D2
0 0 OFF     0 0 OFF
0 1 ON      0 1 OFF
1 0 OFF     1 0 OFF
1 1 OFF     1 1 ON

Something feels inappropriate to me about Circuit Topology #2 though, do you agree? Can you explain why? or why not? When is it absolutely necessary to use a PNP transistor rather than an NPN transistor?


texts: Simple Motor driver circuit diagram help

texts:
I am trying to create a small motor driver for a DC motor, 9 V - 12 V. Max current and stall current I do not know, but I am using the stock motor of a Blade CP Helicopter. I just want to know if I am using parts that will work and what parts I should replace.
The FET i am using is a 22N50 N-channel FET. Any advice or things I should look out for?

Motor will be only going one direction and will be controlled from a 3 V - 5 V PWM

Yes, I know about the diode across the motor which is a 1N4000.

The schematic:


texts: How to find cause of reset in PIC16F microcontroller?

texts:
I've worked with other microcontrollers that have a register that I can check on powerup to check a register that contains debugging information on the cause of the reset.

Initial searching revealed an RCON register that may not be available in my current PIC.  Haven't found much in the initial search of the datasheet either:

http://www.microchip.com/wwwproducts/Devices.aspx?product=PIC16F1704


texts:
First of all I’d like to state I’m fairly new to this and ask for grace if my explanations are hard to grasp.

I’d like to know if it is possible to wire a scroll wheel encoder (the one with three points) so that when scrolling up, every increment or time it makes contact it will act as a button press and same goes for scrolling down wired to another button. I’ve read that you will need some sort of microcontroller to add logic and translate the signal from the encoder into pulses. (such as CD4013 D-type flip-flop?)

I am wondering whether I’d be able to get a simple schematic circuit for wiring the encoder to pulse to  2 separate LEDs one for scrolling up and one for scrolling down. It doesn’t necessarily have to count the amount of increments, but it does need to spam the button rather than hold it in.

The actual project is to modify a game controller to spam a button scrolling up and spam a button scrolling down. I have already bought a mod pack to tap into the buttons I will imitate with the encoder, but I know it isn't as simple as wiring the encoder straight to the mod pack.

I’ve seen a very similar question asked, but none of the answers have quite been what I need to know.

I highly appreciate any help with this.


texts: Can a 555 output be made to pull to ground?

texts:
I have design in Multisim with a  555 timer that I want to pull to ground when the signal changes. It's a missing pulse detector for resetting an mcu.

Is there anyway I can achieve this with say a transistor or mosfet?

I need it to pull to ground so i can reset a MCU.


texts: Diagram shows four wires coming from my two wire power supply, what am I missing?

texts:
Completely new to electronics and I’m trying to follow a blog post to wire up a linear actuator to a dpdt relay and photocell.

I’m stuck, because the diagram I’m following is showing a total of 4 wires coming from the DC power supply. However the DC power supply only has two wires. Am I missing something? Am I supposed to split them somehow?

The diagram is below but here is the post I’m following if that helps.


texts: CMOS NAND VS an Alternative NAND Structure

texts: The CMOS version of a NAND gate has two NMOSes series on the bottom and two PMOSes in parallel on the top. We can replace the PMOSes with a resistor and the circuit works (alternative NAND). What are the differences between these two NANDS? Which one is better? Which one is practical? Why we use either of them?


texts: Cannot Find the Syntax Error Near Process

texts:
I'm very new to VHDL and this one must be a really easy question. The code gives me the error that there is a syntax error near the last process, please take a look:

library IEEE;
use IEEE.STD_LOGIC_1164.ALL;

entity fsm is
    Port ( D : in STD_LOGIC_vector(1 downto 0);
           CLK : in STD_LOGIC;
           outLed : out STD_LOGIC);
end fsm;

architecture Behavioral of fsm is
    type state_type is (s1,s2,s3,s4);
    signal next_state, state: state_type;
begin
    process(CLK)
    begin
        if rising_edge(CLK) then
        state <= next_state;
        end if;
    end process;
    outLed <= '1' when state = S1 and D = "01" else
              '1' when state = S2 and (D = "01" or D = "10") else
              '1' when state = S3 and (D="01" or D= "10") else
              '1' when state = S4 and D="10" else
              '0';
     process(state, clk) begin
        case state is
            when S1 =>
                if D= "01" then next_state <= S2;
                else next_state <= S1; end if;
            when S2 =>
                if D="10" then next_state <= S1;
                elsif D = "01" then next_state <= S3;
                else next_state <= S2; end if;
            when S3 =>
                if D = "10" then next_state <= S2;
                elsif D = "01" then next_state <= S4;
                else next_state <= S3; end if;
            when S4 =>
                if D = "10" then next_state <= S3;
                else next_State <= S4; end if;
            when others =>
                next_state <= S1;
      end process;
end Behavioral;

Thank you.


texts:
I have a cable like this with 4 wires inside.  Each wire is 20 AWG.

I've been told that I can twist the ends together (i.e. green and red, white and black) on both ends of the cable and this will effectively increase the wire gauge.

This would make perfect sense to me if the wires were naked (no green/red/white/black plastic coat around it) so it would be copper twisted the full length instead of just the ends...  does the coat affect the current? I'm not an electrician or EE so I'm not too sure about this.

I want to use this for sprinkler valves.


texts: Plessey Epic Sensors For Non Contact ECG

texts:
This may not be the right place to ask this question. If this is the case, please suggest an alternative and I will gladly move this question to a suitable forum. I am trying to wirelessly capture an ECG signal using the EPIC sensor from Plessey Semiconductors. As marketed on their website, it seems that their sensors can pick up the signal at a distance.

I have read all the datasheets on their websites but they are more confusing than helpful. On the website, some the sensors (especially the PS25203) are said to allow capturing an ECG signal at a distance. However, there is no specification of the distance between the sensor and the person. If anyone on this forum has ever used the sensor, would you please elaborate on:

Practical distance between the person and sensor to capture an ECG signal
Analog circuit interface to the sensor
Which EPIC sensor (PS25201, PS25251,PS25203, etc), is appropriate for this? It seems PS25102 used in their EPIC demo kit is expensive ($504.00) and, according to the datasheet, does not differ much with other sensors.

Again, if there is a better forum to post this type of questions to please let me know and I will move the question.


texts: DC 3-12V Water pump connected to power source doesn't work

texts:
I'm trying to make a simple connection of 3-12V Water Pump to a power supply(https://www.amazon.co.uk/dp/B07D3XS91J?ref_=pe_1365641_54848841).

I'm using power supply which is 5V (https://www.amazon.co.uk/dp/B01ELGR26I?ref_=pe_1365641_54848841).

I have made simple connection, whith positive on power supply to positive on pump, and same with negative.

When I turn on the power supply, it's LED turns green for fraction on second and water pump starts, but then it goes off and repeats.

As Im absolute beginner, please point me in any direction. Thank You.


texts:
I have faulty power supply in my digital reverb unit and after replacing all capacitors the problem is still there - fast on/off switching with clicking sound. It does turn on sometimes though but rarely. So I have decided to buy whole new power supply board instead, since it is not expensive.

"Mean Well RT-50C" is what I am going to buy. And my question is about line filter, because in my reverb unit (Dynacord DRP-15) has dedicated line filter board which is connected to power supply and I am not sure if RT-50C does contain some line filter circuit already or not. I want to know if I should remove the stock line filter also or keep it there.

Thanks in advance.


texts: Can I use a Zener diode in place of a 3.3V voltage regulator to power an nRF24L01?

texts:
The nRF24L01 operates at a voltage range of 1.9 – 3.6V.
I have a power supply of 6V. I need to regulate to 3.3V. I used an LD33V (3.3V regulator), but I need other solution, so I decided to use a 3.3V Zener (half watt.)
I got  garbage values on the serial monitor.
I believe that is due to low power at the Zener output.
Can someone suggest a good power supply method to power nRF24LO1 to regulate 6V to 3.3V?


texts: Transmitting from omni to directional antenna

texts: If an omni-directional antenna (transmitting antenna) transmits to a directional antenna (receiving antenna), how will the SNR be affected compared to when both antennas are omni?


texts:
I have a circuit like below in which the photodiode is connected to opamp via a capacitor and resistor

The purpose of the opamp is to convert photocurrent of photodiode to voltage (Vo) than this Vo , will be amplied using another op-amp

1.The problem here is that i dont know which Op-AMP is suitable to use for the conversion and amplification ? .  Initially i used 741 , but it seems to be stucked as it requires V+ and V- as 15V and -15V while arduino only supply voltage arround 0-5V.

2.I want to read the Vo values , than transfer it to arduino for processing . Vo is expected to be much larger than 5V (which is the maximum analog reading of arduino) . So how can i do this ?


texts: Where is the positive and negative on an antenna?

texts: What I am wondering is how to build an antenna. Upon unscrewing my telescopic antenna from it's base, I see only a metal screw base, nothing more. The F Connector has a positive and negative (or ground) connector, the outside is negative and the pin in the center is positive, but I don't see how to make an antenna like this. Where do the positive and negative connectors lead to if the antenna is basically a metal stick?


texts:
I want to have a go at building a Tesla Coil.

Has anybody here tried to build one before? How much do all the parts cost? Is it possible to make a small scale one? When can I get the plans, and what equipment/tools do I need?

UPDATE To make this question a little more specific...

There are a few parts of the general design of a Telsa coil that I'm unsure about.

The HV transformer - I've seen that some plans say you can use a microwave oven transformer for this, and other plans say that you need to stack them by wiring the primarys in parallel and secondarys in series, but then you can get insulation breakdown. Is a MOT a good choice? If it's not good to use an MOT, then what?
The tank cap - the general idea is to get a load of lower voltage caps and solder strings of them in series to get the voltage rating you need, then parallel the strings together to get the capacitance you need... but how do you stop it arcing across the leads?
Whats an RF ground? Does it mean drive a stake into the ground and attach one side of the secondary to that?
Finally, nearly every circuit I build fails to work the first time for one reason or another, and I use my meter and scope to work out whats wrong... How can I safely test parts of the circuit without being zapped with 20KV?


texts:
I am working with a B-L072Z-LRWAN1 board and a 8pya00-simcom-evb v1.02 board with SIM7000E. This SIM module operates through AT commands and I need to send these commands through an UART connected between mentioned boards.

I have already set up the UART in the B-L072Z-LRWAN1 and I am able to transmit bytes of information, but I am not sure how to send AT commands.

Which is the format I have to use to send the commands? Do I use char variables? Do I use uint8_t variables and add '0' at the end to make them chars? Do I need to add \n\r at the end of the command?

I am a little bit confused so I need your help.
Thank you!


texts: Recommendations on any working circuit that has at least 20 components

texts:
I am currently a computer engineering student taking up basic electronics course. Right now we are learning how to etch a circuit on a PCB and our required output is to design a PCB layout for a working circuit using at least 20 components.
Currently, I am having a hard time looking for circuit designs that are easy to analyze and implement that meets the 20 components requirement. I'm looking for designs easy to analyze or understand since I am just quite a beginner in this type of area.
I'm not that knowledgeable on complex circuit designs, hence, I was hoping to look for circuits that are easy to analyze and implement. At the same time, circuits the can be easily implemented on a single sided PCB and can be auto-routed easily (since many components make it hard to manually route and auto routing usually end up with double sided designs which isn't optimal in most cases).


texts: Is it possible to use a lead-acid battery as a power bank?

texts: I have an Oxygen 6v 4.5Ah lead-acid battery. Can i use it somehow as a power bank to recharge my cellphone? Your response and help will be greatly appreciated.


texts: "Beep" when testing VCC and GND with the multimeter

texts: Sometimes I use my multimeter solely for testing if there is a contact between two points. However, sometimes, when I measure between VCC and GND on some of my PCBs, I hear a short "Beep" and then it stops. Therefore I assume that there should be a short-timed connection between these two points (but it should not). But where?


texts: High value resistors go higher in value; high voltage resistors go higher in value

texts:
During repairs of vintage hifi I occasionally observe two failure modes with resistors:

High-value resistors, say hundreds of K-ohms, go 30-100% higher in value.
Resistors connected to relatively high voltages go much higher in value, e.g. recently 47K became 1.9M, and I have seen 15K become 1.5G while definitely still conducting. In both cases there was about 300V at one end.

These are only two recent examples out of dozens or hundreds over ten or more years.

Vacuum tube anode load resistors are a familiar case of both. It is a commonplace among hifi restorers that you will have to replace the anode loads but usually not the cathode loads, and I don't remember ever having to replace a grid leak resistor, which are typically 330K-1M but have zero voltage across them statically.

The phenomenon happens even if the currents concerned are tiny or non-existent: for example, the 47k above was the anode load of a tube whose heater wasn't heating, so it wasn't conducting at all (in theory). Maybe especially in these cases.

I am wondering what the underlying failure mode is, and what high voltage has to do with it.

These are typically carbon composition or carbon film resistors, given the age of the equipment.


texts:
I have an relay in an old device (a heated display case), that seems to be failing.

The relay is a Midtex 157-32U200, and the few distributors that I could find that carry this relay refuse to sell it to me as it's supposed to be a "restricted item" (I guess only machine resellers are allowed to buy it).

I've found something similar at my local electronics place - it's a generic relay named JQX-53F 32. The ratings seem to be similar, and while this relay has an additional bank of connectors in the middle row, the original one only used the outer rows, so I don't know if that would be of any relevance.
Obviously, I'm not an electrical engineer, so I don't know the first thing about relays, but perhaps somebody can help me find a suitable replacement for my dying old one.

I've attached the wiring diagram of the machine, and pictures of the old and new relay, so perhaps that'll help more than my amateurish explanations...


texts: Deriving PU / PD given a sketch of a PMOS

texts:
For the PMOS given below I can derive the function f, such that f inverted in its variables corresponds to the expression of PMOS(f) and f inverted equals NMOS(f).

For this specific problem I have however two contradicting solutions and thus would be happy, to have a 2nd opinion.

My solution:

\$ f(a,b,c) = (\bar{a} + \bar{b})(\bar{a}\bar{b} + \bar{c}) \$

\$ PMOS(f(a,b,c)) = (a + b)(a b + c) \$

\$ NMOS(f(a,b,c)) = a b + c(a + b) \$

Suggested solution:

\$ f(a,b,c) = \dots \$, not available

\$ PMOS(f(a,b,c)) = (\bar{a} + \bar{b})(\bar{a}\bar{b} + \bar{c}) \$

\$ NMOS(f(a,b,c)) = \overline{a b + c(a + b)} \$

The differences between the expresseions are not much, nonetheless I would like to know, what is correct, what is wrong.

In the image below, Erdung can be translated to ground or earthing.


texts:
I recently hooked up a cheap laser module to a mircrocontroller (via a MOSFET), mounted on top of a couple servos.

simulate this circuit – Schematic created using CircuitLab

This worked fine until I invited my coworkers to access the controls for my laser turret.  One wrote a script that moved the servos from 0° to 180° and back repeatedly as quickly as possible.

Now my laser is dead.  It is very dim and gets hot when power is applied, and both my cat and I are very sad.

Unfortunately, I don't have much information about the laser module itself other than what you see on the linked page.  The inside looks like this:

So what killed the laser?  My suspicion is reverse voltage from a servo motor.  If that's likely the culprit, what can I do to guard against it?

Edit: As requested, a photo of the whole rig – although I'm not too sure it's very useful given the rat's nest of wires.


texts: Are Civilian GPS signals cryptographically signed?

texts:
As far as I understand, receiving enough GPS signals at the same time enables to deduce the position and the time.

So I guess it is possible to use an offline receiver as a very precise clock?

If so, is it possible to flood this offline receiver with fake signals to make it believe it's 12:00:01 when it's actually 12:00:00?
Or more specifically, is it possible to design a receiver who can't be attacked this way?

If GPS signals (or Galileo's, ...) are cryptographically signed, it's easy to reject non-signed signals by saving the public key of the satellites beforehand. But are the GPS signals cryptographically signed?

Edit: My question is not about the civilian signal being encrypted or not (meaning unreadable for people not having a secret key), but signed or not (meaning the authenticity of the signal being verifiable thanks to a public information: the public key of this satellite).


texts: How to find Vo in a circuit with two voltage sources

texts:
I do not know how to find Vo in this circuit. According to my notes about how to take node voltage, I get

0 = Va + 6.857 V + 0V

Vo = Va

But that doesn't sound right. And I get a different answer using mesh, then using

Vo = V Across the 4k resistor

I would really appreciate the help! Thank you!


texts: I need help identifying these two IC's. They were in my father's electronics shop and I found them in a box. There are many of them. I searched the net and could not find any info at all so was hoping someone here would know.


texts:
I am trying to understand about the Mosfet operation.
It would be great if someone could help me get answers to these questions -

What happens to an AC signal (DC+ small AC signal) if it is applied to the gate of a MOS which is biased in Linear mode.
In the saturation mode, the output at the drain/source can be found using the small signal analysis mos model.
In the Linear mode, how do we analyse this? As the mos behaves as resistor here the output automatically should be DC+ AC component? What happens to the gain here?
From the transfer characteristics of, say CS amplifier, it is seen that the output at drain is small and dvo/dvi is small.
What would happen to the gain and other parameters for a circuit which is biased in saturation with an Ideal current source as seen in the image, for small signal analysis.

vo (node) DC value would be Vdd-I.Rd
Also with an assumption that device is huge (KW/L = huge), vs (node) DC component can be taken as -Vth.
What would be the AC component of voltages at these nodes? Will there be any gain here?
Also, If we have a big bypass cap at vs node, then the analysis would be the same as that for a CS amplifier. Is that right?


texts:
For a project, I have to determine the RPM of a turning resolver. I can correctly read the angular position of the resolver as as a hex number via an RDC. This number is then converted into a 14-bit decimal number and then sent to a 7-segment display. To give an idea how this works, when the resolver is at 180 degrees, the RDC will return 0x8000, when it is at 359 degrees, the RDC will return 0xFFFF, and at 0 degrees, the RDC will return 0x0000. The separate module then converts the 16-bit values to a 14-bit value.

I am calculating the RPM in its own Verilog module called RPM_calc. The angular position of the resolver is being read at 1000Hz. Inside RPM_calc, I have clock that samples the position 4 times a second every posedge. Every time this posedge hits, it reads the position data being fed in and moves the previous position into a different register. These two registers are subtracted, and the position difference over time (0.25s) is then used to calculate the RPM. The RPM direction is not displayed, and if the direction results in a negative number, it is converted from 2s complement to a regular number. The res input just determines whether I want a 10 or 12-bit resolution from the RDC. My verilog code is shown below.

module RPM_calc(
input clk_i,                //1000Hz sample clock
input res,
input [13:0] position_i,
output [13:0] RPM_o,
output sample_o
);

reg [8:0] clk_4hz_counter = 0;
reg clk_4hz = 0;

reg [13:0] position_reg;
reg [13:0] prev_position_reg = 0;

always@(posedge clk_i) begin  //4Hz clock generator
    clk_4hz_counter <= clk_4hz_counter + 1;
    if(clk_4hz_counter == 125) begin
        clk_4hz_counter <= 0;
        clk_4hz = ~clk_4hz;
    end
end

always@(posedge clk_4hz) begin
    position_reg <= position_i;
    prev_position_reg <= position_reg;
end
//2s complement wires
wire [13:0] deltaP;
wire [13:0] abs_deltaP;

assign deltaP = position_reg-prev_position_reg;
assign abs_deltaP = (deltaP[13])?(~deltaP+1):(deltaP);

//if res is 0, divide by 2^12, else divide by 2^10. 240 = 60*(4Hz)
assign RPM_o = res? 240*(abs_deltaP)/1024: 240*(abs_deltaP)/4096;
assign sample_o = clk_i;

endmodule

The problem I ran into is when the RDC rolls over at 360 degrees. For example, if I sample at 350 degrees, and 0.25s later, I sample at 10 degrees when travelling clockwise, my module thinks I traveled 340 degrees in 0.25s, which is incorrect. I need a way of determining what the correct RPM is when two samples happen with a rollover in between. Does anyone have an idea of how to do this?

Thanks


texts:
How can we find the RPM of DC motor using the given voltage?.
To be clear, I need to find out rpm of a motor using the pwm signal sent from Arduino Uno.
In my case i'm using a BO motor, the link is here:
http://www.coretechnologies.co.in/index.php?route=product/product&path=64_83&product_id=753

I'm doing this for my tachometer project, for proving theoretical values and practical values are correct. For getting practical values i'm using this:
http://playground.arduino.cc/Learning/Tachometer


texts: Output Compare Interrupt does not work avr atmega

texts:
Hey I'm trying to do blinking led using interrupts on 16 bit timer.
My atmega model is Atmega168A.
Chip clock rate is 12Mhz.

Here is my code:

#include <avr/io.h>
#include <avr/interrupt.h>

ISR(TIMER1_COMPA_vect)
{
    PORTC ^= (1 << PC5);
}

int main()
{

    DDRC |= (1 << PC5);

    PORTC |= (1 << PC5); //led on

    sei();

    TIMSK1 |= (1 <<  OCIE1A); // cmp interruupt enable
    TCCR1B |= (1 << CS12) | (1 << CS10); //prescalser 64
    OCR1A = 11718; // value to compare
    TCCR1A |= (1 << WGM12); // set ctc mode

    while(1)
    {

    }

    return 0;
}

When the program startup led turn on.
After compare match it should turn off. And it works, but with one strange problem.

If I change OCR1A, only the first peroid of time before led on and off changes.

When I set OCR1A e.g 0x100 the led turns off very quickly.

When I set OCR1A e.g 0xfffa the led turns off slowly.

But only the first state change.

Another led blinks do not take over about changes of OCR1A.

Whats wrong?

Do I need reset some flags or something like this?


texts:
So, I know (conventional) current goes from the + pole of the battery into the anode of the LED, leaving through the cathode and into the - pole of the battery.

However, I read the cathode is the negative end. I figured it should be exiting through the positive end, and be "conventionally repelled" away.

So you end up with a circuit like this:

(battery) --->  + (LED) --->  - (LED) --->  - (Battery)

Is this right? How does it make sense?


texts: Replacement for a P-Channel Depletion MOSFET

texts:
I've read some of the questions about P-Channel Depletion MOSFETS and I understand their availability is very limited and often expensive. So what I'm hoping to discover with those that view and respond to my question, is an appropriate replacement for a P-Channel Depletion MOSFET for my circuit design.

A bit of background:
P-Channel DMOSFET was perfect for me because I need to have two wires shorted together a majority of the time. A P-channel DMOSFET will connect these two nodes with minimal voltage between drain and source when the gate is grounded; which is exactly what I want because the two wires I'm connecting is actually shorting a wire to GROUND in the absence of an external signal.
Once this external signal is connected, I also route it appropriately to the gate of the DMOSFET so it opens the switch, no longer grounding the drain.

EDIT1:
This is a basic depiction of the part of the circuit in question (omitting basic resistors and capacitors):

simulate this circuit – Schematic created using CircuitLab

M2 is a low forward voltage diode so VCC from the battery doesn't open the M1 switch.
M1 connects the 'Signal' to ground, until a charger is connected in which case the Signal is disconnected from the part of the circuit I have illustrated.
The device on V_out is drawing less than 1mA which is highly beneficial for the battery life.
/EDIT1

An obvious alternative to this design is using an N-Channel Enhancement MOSFET and an inverter to the Gate, but I'm trying to make this design as minimal (physically) as possible so I can enclose it in a 3D printed design as small as possible for portable purposes.
The design without an inverter is also preferable because there would be less current draw from the battery a majority of the time, without the constant current drain and power consumption that would be occuring in the inverter.

The switching speed need not be fast, and there is not significant current connected to the MOSFET (milli-amps in my design)

Is there any other ideas?

Thanks :)

Edit1: Included basic schematic and brief explanation.


texts: Why is bulk always known to be associated with source and not the drain? What would be the result or outcome if I connect the bulk to the drain instead of the source?