texts:
About the following circuit:

*source: https://youtu.be/niZizzHBanA?t=1779

It is described as a negative power supply, where R1, R2, Q1 and Q2 form a current sink and Q3 "amplifies" the zener voltage, keeping a stable voltage between its drain (GND) and source (out).

So I have a few questions. I'll start just with the current sink. I've reduced it and isolated it as below:

1) Can I call the current sink configuration a series feedback pair?

I know it has the benefits of the high output impedance of the JFET, and the high gain of the BJT which allows a proper negative feedback. So the way I see it works like this. In initial conditions, Q2 gate is assumed at 0V, since there is still no current flowing through Q1. So Q2 will allow a \$I_{DSS}\$.

At the next moment, R2 will have a \$V_{BE}\$ across it from Q1 as long as \$I_{Q2}*R2>0.7V\$.
That should be enough to keep Q1 saturated and R1 will set Q1 collector current. The voltage drop at R1 will set the voltage at Q2 gate.

2) Should Q1 be really saturated? I can't see other way, since there is really no restriction for its base current.

It is also clear how negative feedback works. If \$I_D\$ in Q2 tends to increase, \$V_{BE}\$ in Q1 tends to increase, also increasing Q1 collector current, that makes \$V_{GS}\$ more negative and regulates the disturbance.

R3 is the load and operating current in the example is \$\frac{V_{BE}}{R2}\$ , calculated for a 2.5mA renders \$R = 269\Omega\$.

J2 at left of the circuit is there just to check the actual \$I_{DSS}\$ for this part in LTspice, and that is equal to 5.19mA.

Simulations showed excellent results, ranging from R3 short circuited (green) up to 4.48k (pink). Last step was to 5.6k (not displayed below), that started to reach the compliance voltage.

3) How is it possible that \$V_{GS,Q2}\$ goes down to -14.5V and there is still current flowing through its drain and source?

According to this part datasheet: LSK489A, its pinch off voltage should be about -1.7V for a \$V_{DS}\$ of 10V at 25C. In my example, \$V_{DS}\$ ranges from -470mV for the 5.6k load to -14.3V for the short circuit. But any \$V_{GS}\$ more negative than ~ -1.7V should not allow the calculated current of 2.5mA in R2.

How is this possible and suggestions for fixing it, if needed. Changing R1? That still seems weird to me, because \$V_{GS}\$ and \$I_{DS}\$ are related by the

JFET basic equation: \$ I_{DSS}(1-\frac{V_{GS}}{V_p})^2 \$

Where \$V_p\$ is the pinch-off voltage.

So how is \$V_{DS}\$ of Q2 supposed to accomodate variations in voltage in order to keep the \$I_{DS}\$ when its \$V_{GS}\$ is being held by the voltage drop in R1?

I will elaborate further questions on the actual "zener amplified regulator".

EDIT1: fixed equations.


texts: PIC18F4550 - Display 16X4 and menu with more than 4 items

texts:
I need to print a list of items of a menu in a 16x4 LCD using a PIC18F4550. I already did it using MPLABX and XC8 compiler and it worked fine, however, I need to migrate it to mikroC environment. But, It is not working. The characters are messy in the display. Although the indicator of line works fine, the text on the lines is unreadable characters, pieces of words in the wrong place and without meaning.

I put here a slice of code because the code is big to put it here. But, can someone find a mistake in this code that I wrote here? Sorry for the lack of comments in the code, but it was in the other language and the variables too, I translated the variables to make the code more readable here.

EDITED:

The code works in the following way: I have a stack to store the menus, the menu structure has a field that points to a list of items that has the line text.

I guess the problem is in the pointer of the menu to list Of Items. This way as below

stackMenus->stack[stackMenus->top]->itens[0]->text

It is in the function of menu_draw(Tstack *stackMenus). If I put a string directly, the line will be written correctly. But, if I use the code above, it doesn't. I didn't put the entire code because it is too big. I used a lot of pointers in this passage, so I'm afraid that this is causing the problem, so I put the code related to this passage here. Sorry for the incomplete information.

Here is the code:

(...)

Tstack stackMenus;
stackMenus.top = 0;
error = menu_stack(&stackMenus, &mainMenu);
changeMenu = TRUE;
typeActualMenu = eSubmenu;
menu_handleMenus(&stackMenus);

(...)

Terro menu_stack( Tstack *s, PTmenu iten ){
Terro error = SUCCESS;
if(s->top == SIZE_MAX_STACK_MENUS - 1){
return ERROR_STACK_MENUS_FULL;
}
s->stack[++s->top] = iten;
return error;
}

(...)

Terro menu_handleMenus(Tstack *stackMenus){
(...)
menu_draw(stackMenus);
(...)
}

(...)

void menu_draw(Tpilha * pilhaMenus){
(...)

Lcd_16x4_Out(1,1, stackMenus->stack[stackMenus->top]->title);
Lcd_16x4_Out(2,2, stackMenus->stack[stackMenus->top]->itens[0]->text);
Lcd_16x4_Out(3,2, stackMenus->stack[stackMenus->top]->itens[1]->text);
Lcd_16x4_Out(4,2, stackMenus->stack[stackMenus->top]->itens[2]->text);
(...)
}

//This is a 16X4 LCD adequacy code of the original library of MicroC

void Lcd_16x4_Out(char row, char column, char *text){
switch(row){
case 0x01:
LCD_CMD(128 + column - 1);
break;
case 0x02:
LCD_CMD(192 + column - 1);
break;
case 0x03:
LCD_CMD(144 + column - 1);
break;
case 0x04:
LCD_CMD(208 + column - 1);
break;
}
Lcd_Out_Cp(text);

}

These are the List of Items:

const TitenMenu listaItensMenuPrincipal[] = {
{0, eSubmenu, "Iten1", NULL},
{1, eSubmenu, "Iten2", NULL},
{2, eSubmenu, "Iten3", NULL},
{3, eSubmenu, "Iten4", NULL},
};

Tmenu mainMenu = {
menu_numberOfItens(mainMenuItensList),
"Main Menu",
(PTitenMenu)mainMenuItensList,
NULL
};

These are the structures and types:

struct Sstack {
PTmenu stack[SIZE_MAX_STACK_MENUS];
Tint8 top;
};

typedef struct Sstack Tstack;

typedef Tuint8 TidMenu;
typedef TidMenu *PTidMenu;
typedef unsigned char TmodoItenMenu;

struct SitenMenu {
TidMenu id;
TmodoItenMenu type;
char *text;
void *submenu;
};

typedef struct SitenMenu TitenMenu;
typedef TitenMenu *PTitenMenu;

struct Shandlers{

Terror (* create)(void);
Terror (* selection)(TidMenu);
void (* destroy)(void);
};

typedef struct Shandlers Thandlers;
typedef Thandlers * PThandlers;

struct Smenu {
unsigned char numberOfItens;
// Title
char *title;
PTitenMenu itens;
PThandlers handlers;
};

typedef struct Smenu Tmenu;
typedef Tmenu *PTmenu;[/code]

I solve the problem !! At least until now... When I did

const TitenMenu listaItensMenuPrincipal[]

Is was not working , So, I did:

TitenMenu listaItensMenuPrincipal[]

And it works fine. I don't know why it happened, but, I will keep it this way. Does someone have any idea of why it happens ?


texts: JSN SR04 not giving correct readings when connected to ESP32?

texts:
When I connect a JSNSR04 to ESP32 and power it with USB of my computer, I am able to get correct readings.

But when I power it with buckconverter for short distances ( <150) JSN gives correct readings but for long distances JSN gives error readings.


texts:
i need help from you. I want to use 220V DC input to microcontroller. For this purpose i have to use optocoupler, so how can i choose optocoupler with input for 220V DC?
Thanks!


texts:
Consider we have a nonlinear opamp circuit like this.

According to theory this op amp should take log of input.

I wonder whether it is possible to get a response like this :

I tried to plot vOut versus vIn but I didn't get meaningful results.

First try

I replaced diode with a 1N5817 schottky diode and changed resistor value to 200k. This time I got quite interesting result.

To plot transfer function on the horizontal axis I select V(n001). On the vertical axis I select v(vO) trace to plot.

Second try

After reading @Mattman944 's answer I exported Circuit's Lab simulation results as CSV. Since my primary OS is Ubuntu and Excel or LibreOffice Calc skills are quite bad I exported data to MatPlotLib.

import matplotlib.pyplot as plt
import numpy as np
import csv

time=[]
vIn=[]
vOut=[]

with open('devre.csv', 'r') as csvfile:
    plots= csv.reader(csvfile, delimiter=',')
    for row in plots:
        time.append(float(row[0]))
        vIn.append(float(row[1]))
        vOut.append(float(row[2]))

plt.plot(vIn,vOut, marker='o')

plt.title('Log amplifier')

plt.xlabel('vIn')
plt.ylabel('vOut')

plt.show()

The result looks like this. May be there might be some way to plot data in logarithmic scale.

To be more precise I got these example from the textbook which I study.

In the example they ask \$v_O\$ in terms of \$v_I\$ and \$R\$ and they want us to quick sketch of answer. Also \$ \large i = I_S(e^{\frac{qv}{nkT}} - 1)\$, \$\large \frac{kT}{q} = 26mV\$ and \$ \large n\$ is between 1 and 2. These circuit parameters are given.

I solved the example on paper and sketched the output. Which looks like this.

I wondered whether theory matches practice so I tried to simulate the circuit in LTSpice.


texts:
I have a CRT monitor which I was looking to open to acquire CRT for a project I am working on. I know its probably not the best idea but I have taken some safety measures.   They are as follows:

1) Switched off and unplugged the monitor and made it sit for 3 months.

2) Read about high voltage circuits and the dangers they pose.

3) Ordered a good pair of Rubber Gloves

4) Watched some videos on Dismantling.

I wanted to know is 3 months enough time and How can I make sure if I have discharged everything that needs to be discharged? Is there any specific components which is considered dangerous?


texts: Problem Powering 13.3 inch LCD Screen with 3.7v Battery

texts:
I have been working on a project that involves running a 13.3 inch lcd screen off of a rechargeable battery. I bought the lcd screen and controller board listed below and verified that it was working by plugging it into a working 12v 3a power supply. The specs of the screen specify that the screen requires 5-12v and more than 2a to function.

After verifying that the screen worked I tried hooking it up to my 3.7v lipo battery that you can also find listed below. I put the current through a voltage booster to get the voltage to 12v as required by the lcd screen. When I try the power the screen from the battery with the voltage booster it does not work correctly. The controller board powers on, then the screen flashes on, and then it shuts off and that process repeats. At first, I believed that this was because I was not supplying enough amperage to the lcd screen. I measured the amperage the screen was using when hooked up the the correct 12v 3a power supply and running. It was only using about 0.6a. The 4000mAh battery I have should easily be able to supply this amperage, therefore I do not believe a lack of amperage is the problem.

At this point I have no idea why I am unable to power the screen from my battery. After putting the current through the voltage booster it is giving 12v power and should be able to supply enough amperage for the screen. Is there anything else that I am missing? Or is there something else that could cause me not to be able to power the screen?

I am willing to go into futher detail or answer any questions to clarify. I apologize for being unclear, for I am new to electrical engineering and have little experience.

Thank you for your help!

Links:
LCD Screen: https://www.amazon.com/gp/product/B06XWVLNMT/ref=ppx_yo_dt_b_asin_title_o08_s00?ie=UTF8&psc=1

LiPo Battery: https://www.amazon.com/gp/product/B07BTTQDJQ/ref=ppx_yo_dt_b_asin_title_o01_s00?ie=UTF8&psc=1

Voltage Booster: https://www.amazon.com/gp/product/B06XWSV89D/ref=ppx_yo_dt_b_asin_title_o01_s00?ie=UTF8&psc=1


texts:
Are there switches realizing these 3 states, or at least the 1st and 2nd?:

They could be switching DC or single-phase AC. I am trying to find out if they exist, how they are called and if there are any available on the market. Looking at 230V/20A at least.


texts: Which family of ARM processors should I learn: ARM7TDMI or Cortex M3?

texts: I am looking forward to learn the ARM7 family of microcontrollers. When I searched on the internet, I found there are two versions: slightly older ARM7TDMI (LPC21xx etc) and newer Cortex M3 (LPC 17xx etc). I am a bit confused between these two. I want to choose one which can help me to get placed in a firm in future. Please help me to choose one and also please tell me the major difference between the both versions.


texts: Voltage between ground and positive / negative terminals, is this correct?

texts:
I recently acquired a used BK Precision 1660 triple output power supply.

Upon powering it up, I did some basic voltage checks.  On both the master and slave outputs, voltage between positive and negative terminals were correct.

However, on the slave output, I actually measured 0.25V between the positive terminal and ground, and also -0.25V between the negative terminal and ground.  This doesn't happen on the master output.

Is this normal?

I'm somewhat new to these things but something tells me this isn't right


texts: Terminal Block Strip Electrical Block Connector 3A 5A 10 Amp /36 Wire Connectors min and max current limit?

texts:
With reference to the picture below:

The first block connector have a 3A shown beside, the second one with 5A and the third one have 10A.

What do the 3A, 5A and 10A mean?

Does it mean that the 3A can support a maximum of 3A current? Does the 5A support maximum of 5A current and a minimum of 3A current?


texts: I am just getting into coils - I need 110VDC for some loud ringing apparatus. You'll have to forgive my inexperience. I'm very curious about best practices for making a long-lived transformer (possibly heatsinked if that's an issue). So two coils are needed, and what else? Google abounds with info, but I want to get the right parts and formulas and components off the bat, and also not die. The apparatus I need to drive is of the old PSTN type, which got its jolts from the landline. Thanks in advance, cluebats at the ready.


texts: What receiver is appropriate for studying compromising emanations in 2019?

texts:
I'm currently reading the Cambridge Technical Report Number 577, Compromising emanations: eavesdropping risks of computer displays, by Markus G. Kuhn and published in Dec 2003. In the paper, Kuhn uses the R-1250 wide range receiver to conduct his emissions experiments on CRT monitors. My intuition is that receivers suitable for this purpose have continued to evolve in the past decade and a half since the original report was published.

So which receivers are appropriate for use in emissions security in 2019?


texts: 555 Timer Monostable Circuit Triggered When Circuit is Powerd

texts:
My monostable 555 timer circuit (like the one seen below from Electronic Tutorials) behaves as it should in a steady a steady-state environment.

However, the 555 timer is also undesirably triggered when the circuit is initially powered.

How can I prevent this unwanted startup activation?


texts:
We're using the PIC32MX795F512L on a number of custom boards. I'm responsible for one design, for which we currently have two prototypes. The first board appears to work perfectly.

On the second, the PIC is mostly unresponsive. Pressing the Reset button doesn't help. Occasionally it will report a Device ID to the PICkit but for the most part it appears dead... until I briefly short the 3.3V supply to ground (don't ask how I discovered this). After that it seems to work just fine - every time, without fail. If I power it down for more than a split second, it begins to fail again.

I think the successful functioning of the first board rules out most design issues, but there's gotta be something wrong somewhere. These were hand-assembled; I've checked all of the connections but I'm wondering if a particular component might be suspect. Any ideas on where to look?

EDIT: thanks for all the replies so far. As requested, a schematic of what's currently connected to the MCLR' line:

To clarify, this is our first time designing boards for these chips so there are bound to be some less-than-ideal conditions present (rules we forgot, or thought we were implementing but didn't, etc.); it's clearly serviceable somehow, though, since my first board works.


texts: Is there a cheap and accurate electromechanical method to provide a configurable counter-torque?

texts:
Given a continuously rotating motor shaft, is there a cheap and accurate electromechanical method that would provide a configurable counter-torque?

Rotation is in one direction only, RPM range is 0 - 12000, torque range from 0.001 to 1 Nm.

edit: Before the edit I was asking for a constant counter-torque regardless of the motor's RPM. I have removed this as it just adds complexity, increases cost and is not strictly necessary IF the magnitude of the counter-torque is precisely known at whatever RPM the motor's shaft is currently spinning at.


texts: How to specify the correct phase shift of special transfer functions ?

texts:
I know how to construct the Bode diagrams of first order and seconde order(Complexe conjugate) transfer functions. But here in the two examples below i confront some difficulties. I hope someone can explain it to me how can i overcome the problem.

As a first example consider the transfer function: $$T_1(s) = \frac{1}{900+s^2\tau^2}$$

hier is: $$s=j\omega$$

with j the imaginary unit. The Bode diagram of phase is:

I begin to construct the phase diagram with low frequencies, so the transfer function is a real number nl.: $$\frac{1}{900}$$ so it lies on the right hand side of complex coordinate system so the phase should be zero. My interpretation is consistent with the transfer function here. As the frequencies grows the transfer function gets negative and more negative so it's still a real number but it lies in the left hand side of the complexe coordinate system. so i guess its phase should be: $$\pi$$ My interpretation is not consistent with the diagram anymore.

As the second example consider the transfer function: $$T_2(s) =  1600 + s^2\tau^2$$ with Bode diagram of phase:

I follow exactly the same principal, so with low frequencies i get only a real positive real number so its phase is zero again, it is consistent with my interpretation and as the frequency increases it gets negative so it's is still a real number but negative so its phase should be 180°. You see my interpretation is totally consistent with with de diagram.

I'm pretty much sure that i make a mistake somewhere but i don't see it. I hope someone can explain why i'm wrong or where i make a naive mistake.


texts: How to calculate a capacitance of a probe in a equivalent circuit of oscilloscope?

texts:
I want to caculate the value of capacitance of probe which makes the transfer function H(s) from V_in to V_out become equal to 1/10 at all frequencies.

How can I calculate it?

Thanks in advance :)


texts: Are there any commercially available crystals in the sub 32 kHz range?

texts:
I'm looking for a low power clocking solution and it looks like crystals bottom out at 32 kHz.  Are there any low power (nA) solutions (crystals/ceramic resonators/custom transistor oscillator circuitry) that operate on nanoAmps of power in the single digit kHz range or lower?

EDIT

I wanted to summarize the facts from the answers below as well as my own research:

Crystals do not commercially exist lower than the standard 32 kHz flavor, due to size/resonance constraints of the quartz used internally (thanks to Olin Lathrop)
For a 32 kHz clock solution in the 100s of nA range, this oscillator IC could be used (thanks to stevenvh)
For lower frequencies (but not necessarily nA current consumption) many silicon oscillators, frequency synthesizers, PLLs, or real time clocks include internal clock divider circuitry and can be used to generate clocks as "slow" as 1 Hz.

So there is no solution which satisfies both of the constraints of sub-32 kHz & sub-\$\mu\$A operation, but individual solutions that will satisfy one or the other.


texts: Regulated power for radio module HM-TRP. Is config correct?

texts:
I'm trying to figure out how to make a nice power supply to the radio module HM-TRP.

I heard that running certain voltage regulators with capacitors having high ESR values is a bad idea and will cause instability.

For this reason I made the voltage supply setup to my circuit as follows:

The 7.2V battery powers everything and gives power to the 5V regulator LM2940.

Due to specs in the datasheet, I placed a 22uF electrolytic cap as close to the input and output of the LM2940 as possible.

then on the 5V side, I sprinkled a few 47nF ceramic capacitors throughout the board to reduce ESR and to give each section of the board better chances of a solid voltage. I have about a total of maybe 10 ceramics on-board (Its a large project).

Next, I have an LM1117 which the 5V feeds into in order to get a clean 3V output. It's ok if the output is between 2 and 3.9V. The output of that regulator currently has a 220uF electrolytic capacitor attached to it along with another 220uF (not shown) capacitor in parallel.

I then test my entire circuit out. Every single thing works beautifully, except for the radio module. I try running the thing with a speed of 38400bps and with the two wireless devices no farther apart than a meter.

When I run the test, for continuous wireless data communication, the data flow works nicely for about a few minutes, then the radio on my board stops working for roughly a minute, then it starts working again. and the process repeats. I did not create code in my microcontroller on-board that makes these delays happen. In fact, when the remote unit sends data to the on-board radio, the light must blink green. This light doesn't go on when the on-board radio stops working for the short time.

So I thought maybe its an issue with the ESR of the capacitors? So I tried replacing the second 220uF electrolytic capacitor with a 100nF ceramic capacitor. The results were maybe 1% improved but I still get that hiccup where the on-board radio module stops working for a period of time then works again.

Question is, is my voltage regulator setup? or could I use a better model number for either regulator?

And what about my capacitors? is my ESR out of valid range? or should I just go with a new kind of capacitors?


texts: How important is td(on), (off) and tr rise/fall. How close do they need to be for a primary side mosfet

texts:
I have a power supply with a mosfet on the primary side that has failed. I am attempting to repair it, however, I am having difficulty finding a replacement. The part number svd4n65f and has a td(on) of 20 and a td(off) of 128. The trise is 19.3 and the tfall is 20. The other specs have been easier but not with the above specs.
They are VDSS = 650V,
         Id = 4A,
         Rds(on) = 3 ohm,
         Idm = 16A,
         Vgs(th) = 3V.

I have a couple of mosfets I was thinking of trying but I wanted to ask about the td and trise/tfall first.

The closest one has a td(on) of 6 and a td(off) of 58.5 The trise is 2.5 and the tfall is 9.5.

If you can advise on this I would appreciate it greatly.


texts:
I'm trying to send data to an SD card from a PIC18f4580, but the PIC is not sending what it should be.

related global variables:

unsigned char TXBuffer[128]; //tx buffer
unsigned char TXCurrentPos = 0x00; //tracks the next byte to be sent
unsigned char TXEndPos = 0x00; //tracks where new data should be put into the array

I am adding data to a buffer using the following function:

void addToBuffer(char data){

    TXBuffer[TXEndPos] = data;
    TXEndPos++;
}

And putting the data from the TXBuffer into TXREG with the following interrupt:

else if (PIR1bits.TXIF == 1){

    if((TXEndPos - TXCurrentPos) > 0){         // if there is data in the buffer
        TXREG = TXBuffer[TXCurrentPos];           // send next byte
        TXCurrentPos++;               // update to the new position
    }

Using an oscilloscope I am able to see that the PIC is sending 0x98, regardless of what I put into the buffer. In fact I never put 0x98 into the buffer.

However, if I replace

TXREG = TXBuffer[TXCurrentPos];

with

TXREG = 0x55;

or

TXREG = TXCurrentPos;

then I get the expected results, that is the PIC will send 0x55 repeatedly, or count up from 0 respectively.

So why does the PIC have trouble sending data from the array, but any other time it is fine? I'll emphasize that transferring is handled in an interrupt, because I feel like that's the root of my issue.

EDIT: It is a circular buffer in the sense that TXEndPos and TXCurrentPos return to 0 when they reach 127.
I also disable the transmit interrupt when TXEndPos - TXCurrentPos == 0, and re-enable it when adding data to the buffer. Really, my code works completely as expected in that if I add 13 characters to TXBuffer in main, my PIC will transmit 13 characters and then stop. The problem is that they are always the same (wrong) character - 0x98.

EDIT2: more complete functions are here: http://pastebin.com/MyYz1Qzq

EDIT3: By changing our linker script and appropriately using pragmas we're able to get some of our data into our buffer. We statically placed variables related to the buffer into the same memory bank, and that has certainly helped but not all of our data is getting into our buffer. Strangest of all, running the program multiple times yields different data in the buffer, even though all of the data to be placed in the buffer is defined in our code. Also, we get drastically different results when the pic automatically runs after programming it, when we cut the power and restart power with the pickit3 still plugged in, and when we reset the power with the pickit3 disconnected. Also, simulating in MPLAB results in the buffer being filled perfectly, however when actually running the code on the PIC and viewing it's memory, it is not.

Our code as of 5:38 9/22/10 is here.

Our modified linker file is here.


texts:
The following timer code running on a 8Mhz ATMega32u4 should toggle the onboard LED every second, and calling the ISR code manually does so. Yet, the ISR does not seem to get called.
Could anyone please help me getting the timer to work?
#define LED_BUILTIN 13

void setup()
{
  cli();

  // set output pin
  DDRC |= (1 << PC7);

  // Don't toggle any pins
  TCCR1A = 0;

  // Clear timer once matched, pre-scaler of 8
  TCCR1B |= ((1 << WGM12) | (1 << CS10) | (1 << CS12));

  TCCR1C = 0;

  // (Clock / (pre-scaler * rate)) - 1
  // (8MHz / (8 * 100)) - 1
  OCR1A = 7800;

  // Enable channel A interrupts
  TIMSK1 |= (1 << OCIE1A);

  // reset interrupt flag
  TIFR1 |= (1 << OCF1A);

  // set counter to 0
  TCNT1 = 0;

  // Enable interrupts globally
  sei();
}

bool on = true;
ISR(TIMER1_COMPA_vect)
{
  // toggle pin
  PORTC ^= (1 << PC7);
}

void loop()
{
  delay(1000);
}
```


texts: Can a SMPS be turned off to increase overall efficiency for low power applications?

texts:
I am designing a wearable low power application. Most of the time (>99%) the application uses less than 50µA. With such a low current all switch mode power supplies I could find get really inefficient. At this rate most energy is used just to keep the oscillator running.  My idea was to place a big 330µF cap after the power supply. Now I can turn off the power supply until it drops 1V in approximately 1,0s. After which I can turn it on again and charge the capacitor with a higher efficiency (higher current). Could this be a valid method to increase the efficiency of a digital circuit?

My thought is that the dU/dT  would still be low, and won’t cause any problems as long as the components  have a corresponding  VCC range.


texts: Heat means stored kinetic energy in matter. Microwave owens and induction heaters works on increasing kinetic energy on matter. Is it possible to make inverse of this  heaters like cooler. We can decrese kinetic energy by using like electromagnetic slower device. It will change many things in engineering.


texts:
I took out a little board from a radio clock that looks a lot like this one. I believe this is used for automatic clock setting - the coil is probably used as an antenna.

It looks like this:

The contacts on the far sides I believe are ground and 3V power supply (since the device uses 2 AA batteries). The two in the middle, labelled T and P2, I have no idea what they do.

There is a crystal resonator on the back of the board, and the label "JS-D65" (which yielded no useful search results)

I tried bringing up one of the middle contacts and listening on the other, but it stayed on the voltage. Because of the chip under the epoxy, I assume the communication is digital.

Any help would be appreciated.


texts: Why isn't the frequency dependency of an Operational Amplifier not considered

texts:
When deriving the transfer functions of common OPAMP circuits, like an inverting amplifier we begin with:

VOUT=A×(V+ − V-)

A two stage operational amplifier for example, could be considered as a second order system. The equation above only signifies the DC gain of the amplifier.This equation does not account for the dependency of gain of opamp on frequency.

Shouldn't the transfer function of OPAMP's internal circuitry be considered for accurate analysis?


texts:
I've always been too embarrassed to ask, but the notion of "ground" has always puzzled me.
The way I understand it, in theory, is that the earth acts as a giant sink/pool of electron and thus will maintain its potential. Thus, if I connect one electrode of a battery to the ground, the other to a lamp and the other end of the lamp to the ground, the lamp should turn on.

However, if I try this with a 5V battery and a small incandescent light bulb, planting a small wire into the dirt, it doesn't work. And hum, why should it, it's not like the dirt is particularly conductive...

So is this something that only works for high potentials? When you have a lot of contact area between the electrode and the "ground"? What exactly constitutes a valid ground?


texts: Can we declare output as "inout" to design a flip flop in VHDL?

texts:
I want to design a JK flip flop in VHDL. In this output depends on previous state. One method to implement this condition is by declaring a state as a signal inside the architecture.

Another method is by declaring outputs as "inout". I simulated JK flip flop using "inout" and it worked without any error.
In real hardware Q and Q_bar are outputs, so I doubt declaring that as "inout" is a technical mistake.

Which method is correct one .?


texts: How does one match irradiance to Luminous Intensity in Candela of source?

texts:
A light source has an Irradiance of about 1.6 W/m²/nm at wavelenght 385nm and an LED:

Peak Wavelength     385nm
Viewing Angle   30 °
Luminous Intensity  80 mcd

If this light source shines on a circular area of 0.01m² how many LED's would be required to shine on the same area to provide an equivalent Irradiance at 385nm?

I have tried to illustrate the matter below.


texts:
I'm trying to read the voltage of the battery so I can simply calculate the battery status.
I'm using a 8.4V battery (recharcable PP3) that I've meassured now to 5.57V. The circuit will die long before but of the max 8.4V its now at 66%.
My MPU is a is the ESP32, that is a 3.3V device. In order to lower the voltage I've put two resistors in series; 4.7k Ohm and 1k Ohm. I should get a Vout of 0.977V @ 5.57V from the battery. But I'm getting 0.476V.
Now, in order to not drain the battery I have a 2n2222 NPN transistor between the battery og the first resistor. 0.476V is about halv of the expected 0.977V. Is that whats expected? Or am I using the wrong NPN here? Can I just double the Vout so I get the expected value?


texts: It is common to find these cheap Backup Battery Switching on the internet. But the issue I have with these ones is the load gets reset when switching from the main source to the battery. It seems like there is a delay during switching of the relay. Could this be improved by designing a transistor-based switch?


texts: Negative resistance, impact on voltage source?

texts:
According to this, if \$R_1=R_2=R\$ then input resistance is \$R_{in}=-R_3\$, and if we assume that op amp is ideal. So negative resistance is in parallel with voltage source \$V_s\$.

Am I understand this well, in this case ideal voltage source is acting as load and input resistance \$R_{in}=-R_3\$ is acting as generator?
So how is it possible that ideal voltage source \$V_s\$ which internal resistance is 0, acting as load?
If \$V_s\$ is a real voltage source with finite internal resistance, what impact on the voltage source, i.e. battery, will be in this case? Can we somehow destroy that battery with excessive current?


texts: I have a PIC24F based device that normally connects to a PC via USB. The device can be controlled through PC software this way. I want to add an optional hand control box that can also be plugged into a separate connector on the main device and can be used to control the device and read/display data from the main device. This hand control box will also be PIC based. I am trying to decide which communication technique to use between the main device and the optional hand control box. I like the idea of SPI but I know that is not intended to be used over long distances. Do you think my best option would just be to use the UART modules with RS-232 line tranceievers to boost the signal to +/-12 volts? Are there really any other options?


texts:
def analogInput(channel):
   spi.max_speed_hz = 3571
   adc=spi.xfer2([1,(8+channel)<<4,0])
   data = ((adc[1]&3)<<8) + adc[2]
   return data
def Volts(data):
   volts=(data*3.3)/float(1024)
   volts=round(volts,2)
   return volts

I'm using the mcp3008 for raspberrypi. I built DC/DC converter, and in the output I put divider voltage and the maximum value that ADC can get is 3V in CH0. I want to display this voltage in my LCD, so my problem that I have a deviation. I think that the problem in the define of spi.max_speed_hz = ?, how I define that due to what?


texts:
i'm doing some researches about how to close/open RS485 data line in my RS485 multi device bus.
I'm following this nice research-document: Link Here.
Basically i'm thinking how to solve this problem in a real-world environment, as you can see in page 43, the strategy is very simple: every slave, using a microcontroller and a relay, will have A-B data lines normally closed, and when the master want to set/reset/reconfigure the slaves address it will manage the relay coil and sends to the respective slave the "configuration" messages.

I wish to receive some advices in how i can manage the RS485 data lines using a low cost and effective solution without using a relay: my goal is to develop the same system using smd components.
EDIT: WHY?
I have 10 contact sensors that are placed around my home, they monitor the door open/close status and using RS485 trancievers the slaves (that are equipped with an ATMEGA328P) will expose those information to the master of the bus.
Now, i want to be free to position those devices in my home without worrying to set a slave address hardcoded in my firmware or using hardware dip-switches.
They are connected using a CAT5e cable and the total length is around 20 meters, the cable will transport: A-B-VCC-GND.
Every device is wired in daisy chain mode and the preceding device will control the power up of the following sensor, using a mosfet on GND controlled by the MCU (as reported in the image below):

I don't know if that can really work: the RS485 data lines are connected anyway, also if the circuit is not powered on...
Basically, this "sequential power up" is intended to solve the issue to know "where (for example) is located the device with id 3?"
Any suggestions?


texts:
How do you represent a forbidden state of an S-R Latch (Active High) in a timing diagram?

Where S is 1 and R 1 is and C is 1.


texts: Hello I have an old Intel Motherboard DP35DP, I was using this board as a file server using RAID (Its crucial to get that RAID array working again). It seems like the culprit is a transistor, its resistance is now almost 0 not enough to beep but well below the others in circuit of the same model and smd capacitors around it are all in short. The transistor / mosfet reads 823 T23 N03G but I can't find its datasheet anywhere, therefore I do not know how to pick a replacement.


texts:
I'm into a preliminary design of a eletrical vehicle that uses BLDC permanent magnet motors for motion (3 phases 36V 300W hub motors in wheel). For safety compliance this vehicle needs to provide a breaking mechanism that stops the vechicle when there's a power failure. My first choiche will be using reverse-action brakes/clutches that will triggers in case of power-loss unfortunately I have no room around motor and wheels.

I'm thinking about another solution that uses relays.

My idea is to place an SPDT relay (with coil bound to the primary power source) between motor driver phase output (relay NO) and BLDC motor phase (relay COMMON)
all relays NC will then be connected togheter (trough a resistor?).

In normal operations relays will be forced into NO position allowing drivers to handle motors.
In case of power loss all relays will return to their NC position and thus all phases will be shorted togheter. If the vehicle is then forced to move (because a slope or something pushing at it) BEMF will react in opposition to the motion.

I don't think this idea is something new I will only know if someone sucessfully used this or if there are hidden dangers/pitfall into my approach.


texts: Can current still be (alternatively) measured with a blown multimeter fuse?

texts:
With a blown fuse in a multimeter, is it still possible to measure current of a device by somehow measuring voltage and resistance?

If so, how would this work? Do specific probing/measuring points matter?


texts: How to detect IR pulse using phototransistor and voltage comparator (subtracting constant light)

texts:
I want to detect an IR pulse with a phototransistor. I did the following schematic, using the voltage comparator LM339:

The problem is that this will work if in the dark, but if there is some light, the OUT LED will be ON anyway. What I want is a way to automatically subtract the "constant" ambient light, and have the OUT LED ON just during a pulse of light to the phototransistor.

Thanks a lot in advance for your help.


texts:
I'm trying to read capacitor output values as the cap discharges for a physics project, and am getting a high voltage while charging, but dropping to 0V 3000 \$\mu\$s after stopping the charging signal, which doesn't seem right.

Schematic:

The cap is 1mF, resistor 1k\$\Omega\$.

I'm trying to charge the cap by sending +5V out through the digital line for 2 seconds, and then trying to discharge by either switching the digital output line to high-impedance (by switching it into input mode, pinMode(DIGITAL_OUTPUT, INPUT);) or by writing a low signal (digitalWrite(DIGITAL_OUTPUT, LOW);).

I've tried both methods of triggering discharge, but the analog signal that I've read (analogRead(ANALOG_INPUT);) has gone from +5V while charging down to 0V 3000\$\mu\$s after.  I was under the impression that the cap should take at least 2 seconds to fully discharge.

I assume I've messed up the circuitry somehow, and the code is actually working after enough debugging, so I haven't wasted space with 97 lines of code, but the code is in a pastebin if the circuit looks like it should work.


texts: How to make radio reception better with antenna 133 cm long

texts:
My low cost FM radio receiver Philips MCM129 is not receiveing some radio stations well. It has antenna made of about 133 cm long thin insulated wire which I suspect is the rason of the problem.

Can I make the reception better by making the wire longer/shorter?


texts: Various definition of return ratio in a feedback circuit

texts:
I am reading about return ratio to analyse stability of a circuit.
However, some of the definitions are confusing.

The first one from the page is defined as below. I understood this and it is not too hard.

The second definition from the page is as below.

I really have no idea about that.

Could anyone explain that?

Does it have anything relate to the first definition above.


texts: I scraped some battery cells off two old pc battery packs. In both packs there were a sensor but I can't figure out what kind of sensor it is. Can someone explain what kind of sensor these are? I have of course tried googling the number on the sensors, but nothing shows up. If possible do you know what the number indicates? Is it a serial number or does it indicate an operating voltage or other info on the sensor?


texts: I make neon lights and have been for 10years on my own and just recently found out that I could get in alot of trouble for not having my signs UL certification done. I want to make it right and want to know how to go about getting my certifications done so I can correct this so how would I go about getting it me certified in UL lighting.


texts: Is there an example of a Mealy state machine that can not be converted to a Moore?

texts: I understand that they are generally interchangeable, and also that all Moore machines can be converted to Mealy, hence the doubt if there is one where the reverse is not possible?


texts:
I'm having trouble understanding the biasing of the common-emitter amplifier as depicted below:

(Image source: Electronics Tutorials - Common Emitter Amplifier)

I keep reading that we should bias the collector voltage to be around half of Vcc, but I thought we should be biasing the base voltage to half of Vcc? In other words, I don't understand why we enforce Vc-Ve = (1/2)Vcc; I thought we should enforce Vb - Vin = (1/2)Vcc.

My reasoning is that the whole point of biasing was to prevent clipping and so biasing the input to half of Vcc would give us maximum swing. I am very lost on understanding this circuit so any step-by-step assistance would be appreciated.


texts:
Read many time about Channel-Loss and Channel-Insertion-Loss, but confused that, is that same thing or opposite?

Which has +ve or -ve values in dB?

In reference to equalization of USB3.1.


texts:
I’m trying to design programmable UART controller. Its features are as below.

Microcontroller (MCU) has UART port with TTL level output.
Now based on requirement MCU should be able to select appropriate level shifter (RS232/RS422/TTL) to get the required output interface at the end connector.
Output connector pin connections according to the selected interface are shown in fig.
Is there a method to get the above feature?
I’m thinking that black box-1 functionality can be obtained using a digital I/O buffer. Is this correct way of doing?
For black box-2 I ‘could not imagine anything of sort. Could anyone have any idea about this.

I would like to elaborate my actual concept. What I'm actually looking for is,

In many of my projects, I'm getting a requirement like sometimes I need to connect to a device which is Having TTL interface for communication and say some 5V as power input.
In other project, requirement is similar but the device is at RS-232 level, with 8V power input.
At present we are designing new PCB for each requirement or doing some Hardware changes like changing resistors for the voltage regulator to get the new voltage (5V or 8V) and soldering the RS-232 level IC manually to get the RS-232 interface.

Now what I'm thinking is, with out designing new PCB for each requirement or with out making any hardware changes, just by changing software I should be able to make the board ready for the new requirement.

Our major changes are only either input voltage to the device or device communication interface standard (TTL/233/422)

We will not be switching between interface standard on the fly. It's one time factory settings.

And for the voltage regulator part does anyone came across digital programmable regulators (with out changing feedback resistors manually) above 8V output with a current rating of 1A.

Connector signalling was thought in a such a way that we use the optimum number of pins and the wire harness remain same even if we change the interface standard


texts: Toggle Flip-Flop for Voltage Higher than Logic Levels

texts:
I need a T flip-flop for 24V. The purpose is to take a 24V 50% duty cycle 0.5Hz pulse wave and halve its frequency to 0.25Hz, so that the output wave toggles between 0 and 24V at the input's rising edge.
I know one solution is to use an impulse latch relay, but those are quite large and expensive.
Since logic circuits for 24V are uncommon, relays or transistors would be most suitable.
There is one solution demonstrated by CreativE EngineerinG (link) which I have replicated in falstad simulator (link), but the simulation does not work properly. I'm unsure about this solution because the simulation does not work and because I need to purchase the components before constructing the circuit, so I must be sure that it works. Plus, this solution is for 5V and not 24V, so the components values must be different, and higher power BJTs will have different internal characteristics.
What is the best solution (preferably one that can be simulated)?


texts: What happens if a 240V appliance is connected in a 120V AC power supply?

texts:
I know that putting 240V through an appliance rated at only 120V would almost certainly damage it.

But what if I connect an appliance rated for 240V into a 120V AC socket? Apart from degradation in performance, would there be any damage to the appliance itself?


texts:
I have a device which needs to be manually restarted (switched off and back on) after every 4 hours or so. I was wondering if there is some device which I can buy or make which does this work for me.

Sorry if this question does not belong here, I am new to this. If it is inappropriate just tell me and I will remove the question


texts: N channel MOSFET not turning on under inductive load

texts:
I am trying to build a simple motor controller circuit. I have a lithium ion battery (7.4 volts, 20C discharge, 800mAH capacity) that powers the motor and I am using an adjustable voltage supply on the MOSFET gate.

I have the circuit set up according to the image below:

The motor pulls about 3 Amps at 7.4 volts and the MOSFET is a logic level enhancement mode n channel MOSFET. The gate threshold is about 2.5v and it can handle a continuous current up to 20 amps.

MOSFET Datasheet:
https://www.vishay.com/docs/91021/91021.pdf

The MOSFET should start to turn on at 2.5V but when I probe the drain of the MOSFET with 3.3v at the gate I still see 7.4V.

This exact same setup works perfectly if I just replace the motor with an LED. I know the motor is working too. The MOSFET just does not seem to pull its drain low if the motor is connected, even with a gate voltage present.

Why doesn't my circuit work with the motor?


texts:
From the ATMega328 datasheet, section 24.9.1:

  The internal voltage reference options may not be used if an external
  reference voltage is being applied to the AREF pin.

From the Arduino reference pages:

  Alternatively, you can connect the external reference voltage to the
  AREF pin through a 5K resistor, allowing you to switch between
  external and internal reference voltages. Note that the resistor will
  alter the voltage that gets used as the reference because there is an
  internal 32K resistor on the AREF pin. The two act as a voltage
  divider, so, for example, 2.5V applied through the resistor will yield
  2.5 * 32 / (32 + 5) = ~2.2V at the AREF pin.

The ATMega328 datasheet confirms the "internal 32k resistor" reference in table 29.16 ADC Characteristics with: Reference Input Resistance = 32 kOhm.

That being said, the above two statements seem to be somewhat in opposition to one another. I've got an application with some sensors outputting 0-5V full scale and others outputting 0-1.8V full scale. The application would benefit from the increased resolution of switching to 1.8V AREF when sampling the 1.8V sensors and switching to the internal AVCC reference for the 5V sensors.

The Arduino reference pages suggest that's an OK thing to do given you've coupled to the 1.8V AREF through a 5kOhm series resistor and accounted for the implied voltage divider with the internal 32kOhm resistance. Is this just bad advice from the Arduino reference, or is it in fact a common practice to do this sort of thing? Is Atmel's statement restricted to external voltages applied to AREF without an external current limiting resistor (and if so why, given the internal 32k resistance)?

As an aside, obviously, one could achieve a similar result with a properly constructed op-amp to scale the 1.8V signals up to 5V, but the added complexity and parts seems wasteful if it can be handled by the on board ADC just as well by taking advantage of the change-able voltage reference. Likewise if you could convince yourself that the sensed signal would not exceed 1.1V you could take advantage of the internal voltage reference. Again, it just seems more elegant to me to use the 1.8V regulator I'm powering my low voltage sensors with to set the reference.


texts:
I wired one up. It's the low side assembly for:

I'm using a small cheap coil for my breadboard. I have been told already about the resistor 470K Ohm between the gate and source. I made sure that its there. It's color codes I looked up. When I apply 6V of power it's very nearly a short circuit. I actually saw 0.25A for a short time however it didn't last long and my mosfet is allowing about 1.87A through it. It doesn't take long for it to become burning hot to the touch with that flow and I really don't want anything to happen to my mosfet so I turned it off right now.

I've had a very difficult time getting power to stop in the drain source direction on these mosfets however the source drain direction can be stopped very easily by toggling its gate with 0V 12V.

So if that is my schematic and I tried to shut down this mosfet but it doesn't. I'm not sure what to do because if the mosfet ignites (It hasn't yet) then my schematic is not really where it's supposed to be or I am doing something wrong. (I posted a version of this question but I wasn't sure exactly if I worded everything or it was really complete. Hopefully I feel good enough about this one that it stays for a while.)

Thanks for any replies.

P.S. I did find out that the 12200Ohm resistor assembly really helps keep power down in the drain source direction on M3. The 470K resistor seems to do basically nothing in this type of configuration I have shown in my breadboard screenshot. I think my question actually has turned out to be that there is 0.44A's that flow between M3's drain and source @ 12V. So it seems that may possibly be intended to happen or perhaps not.


texts: JFET Different Output Characteristics for different Vgs,off

texts:
Hi guys, I've been trying to design a simple amplifier with some gain. My first question is, why are there multiple output characteristic graphs (2 shown) for a single JFET? My first step in designing an amplifier/switch is to usually get some Quiescent (Q-pt) point based from the datasheet graphs. However, with this case, I don't know which graph should I use. Is Vgs,off device specific or is it also affected by the Quiescent point? The datasheet shows that Vgs,off is between -3v(typical) to -8v (maximum).

I also want to know if I am doing the right steps in my design. In my case, I want to make two single stage each with around 10x gain to get an amplifier with around 100 gain. I am not as good in designing using FET's compared to using BJT's honestly. In fact, this is my first time using a JFET, but from what I understand, they are very similar to MOSFETs, only that this time, -Vgs (instead of +Vgs) is applied, and controls the width of the channel (ie controlling Id). So here are my steps roughly for designing just the single stage. I am using the graph for Vgs,off = -3v.

1.) Choose some Q-pt on the output characteristic.

2.) Let's say I choose some biasing pt. Since my Vcc = 12, I would roughly want my Vds to be around 4 to 10v to make sure that my JFET is in saturation region, while having some room for swing. My input AC is 20mVpp, so with my target gain of 10 for one stage, I am expecting an output of around 200mVpp.
Say I get this Quiescent point: Vds = 6v and Vgs = -0.3v.
From my little research, I came across this formula: Id = Idss(1-(Vgs/Vgs,off) which is applicable for JFET in saturation. Idss in this case is around 10.5v (midway of 12 and 9v) since Idss is the max current that can flow when Vgs = 0. However, I didn't used this formula and instead, just used datasheet with some visual estimation since I believe the equation above is just a rough estimation that doesn't take into account the effect of Vds(which is less compared to Vgs, when JFET is in saturation). Going back to my calculation, visual estimation would tell me that for Vds = 6v, Vgs = -0.3v, then Id ~ 8mA. So now, I can get the restriction on Rs + Rd. Via KVL, Vcc = IdRd + Vds + IdRs. Since Ig ~ 0, then Is = Id. So 12v = (8mA)(Rd+Rs) + 6v -> Rd+Rs = 750ohms.

3.) Now, I got to take into account the gain that I want, the small signal gain that is. Approximately, Av = -gm(Rd//ro) assuming ro >> Rd. I also came across this assumption very often from what I read. So Av = -gmRd. I came across a formula, gm = (-2Idss/Vgs,off)(1-(Vgs/Vs,off)). For other case, I used visual estimation using the Vgs vs Id curve (3rd figure) by trying to draw a tangent line at my quiescent point and getting Id/Vgs = gm. But since the only Vds vs Id curve on the datasheet is for Vds = 10v, I decided to use the formula whenever my chosen Vds /= 10v like in this case. In this case, gm = 6.3x10^-3 S using the formula above. I can now compute for Rd. Rd = (Av)/(-gm) = (10)/(-6.3x10^-3) = 1587ohms. This is in contradiction with what I got above since Rd + Rs = 750ohms and my computed Rd is greater than this.
I try to choose another Q pt then. Note that most of my calculations led to this case, so I was thinking that I am missing something here. Any help would really be appreciated but my priority is knowing how to get the Vgs,off exactly, so I can at least know which graph to use. (which is a problem if Vgs,off is actually -8v for example, since the datasheet only shows output characteristics for -2 and -3v).

Additional: Assuming I didn't get the problem above, here are my next steps
4.) Assuming I got Rd < Rd + Rs, I could get the value of Rs then.

5.) I now have to decide the values of R1 and R2 to get the Vgs I need. Vgs = Vg - Vs. Vg = Vcc(R1/(R1+R2) = 12(R1/(R1+R2)). Vs = IdRs.
So Vgs = Chosen Vgs = -0.3v = (12R1/(R1+R2)) - (8mA)(Rs). I will then set some value for R1 then solve for R2.

This should finish my calculation for the components (well resistors at least).


texts: How would you go about getting the small signal transfer function for this inverting circuit?

texts:
I am trying to get the small signal transfer function for a circuit that looks like this:

It is an inverting amplifier connected to an output branch and a branch with a capacitor in series with an inductor. I have not been able to figure out how the small signal transfer function would look for something like this so any help would be greatly appreciated.


texts: I'm reading over a manual for a RF generator and I've come across the terms leveled and unleveled RF power. I'm curious what the difference is between leveled RF power and unleveled RF power.


texts: Do soldering glasses protect eyes from capacitor explosion

texts:
I am concerned about safety while working with electrolytic capacitors.

Can I use soldering safety glasses to protect my eyes while working with electrolytic capacitors?


texts: Best way to charge 750mAh in portable device

texts:
I know there are many posts on voltage regulators in battery powered applications but I hope to gain a better understanding of my specific problem.
The portable device I'm working on charges a li-ion device at 750mAh 500 mA (charging current) using disposable batteries. The solution needs to use consumer available batteries and the device will be used in a remote area without outlets so needing to charge is inconvenient. Also a small form factor is desirable. I only want to use a separate li-ion and rechargeable batteries if there's no other option to reduce complexity.
My first solution was using 4 aa batteries in series and a switching buck regulator to charge and power the components at VCC = 3.3V. I am aiming for 8 hours of use time. I know more measurements would help but I have none right now.
My plan is to have confidence in the approach and then take measurements and optimize. If anyone experienced could help me out that would be greatly appreciated.


texts: Capacitors selections for proper bandwidh

texts:
I need to design an amplifier in orcad with

Vin  = 10mVac

Vout = 2,5Vac

RLoad = 50 ohm

The low frequency fLow = 50Hz

fHigh = 20kHz

I came up with this schematic

I need to select the right value for the capacitors in order to get the right amoplification and cutoff frequencies.

Here I have the time simulation

And the frequency simulation

Can you help me?


texts: Using an L298 to drive 2 unidirectional and 1 birectional motor simultaniously

texts:
First up I am not an EE and am fairly new to this, so please forgive my ignorance.

I have a project that requires me to control 2 unidirectional and 1 bidirectional brushless DC motor at the same time with independent speed control on each motor. From what I can tell the L298 is advertised as being capable of driving 2 bidirectional or 4 unidirectional motors. Hence logic dictates I can hook up one side to my bidirectional and one side to my two unidirectional motors.

Am I correct in my assumption or am I going to burn things out? Also I cannot find a clear answer as to whether I can drive two motors on one side simultaneously (since as far as I understand you digitally toggle a pin to set the direction on one side, and driving two motors on a side seems to just take advantage of the reversing polarity).

If this is not the case, what alternatives could I look at? I do not want to use two bridges because 4 I/O pins is already too much (I have 6 to work with and I still want some sensors). I have considered using an I2C expander, but I cannot seem to find one that supports PWM output. As a last resort I could use an AVR like an  ATTiny2313 and use that as an I2C slave, but I'm not really comfortable programming this raw.

One more thing, both size and power are a factor. So I cannot just take one of the few motor shields and be done with it.

Thanks in advance!


texts: Open Circuit Voltage with Open FET and Zener?

texts:
D2 is a 18V Zener, LM3Z18VT1, diode. M1 is a NCE01P30K. Node DO is 8V by default and 0V when the circuit activates.

If M2 in the circuit below opens, what is the voltage at the gate of M1? Now because there is no current flow through M2 I would assume that M1's gate would 18V due to the Zener. But something doesn't seem right here. Any help is greatly appreciated.

Thank you for your time.

simulate this circuit – Schematic created using CircuitLab


texts: How to interpret s parameters including S21 on Smith chart on VNA display

texts:
I'm trying to become re-acquainted with S parameters, VNA, and transmission lines for some projects at work.  I'm using Agilent, Advanced Design Simulator, to practice on the computer and to get the basic theory down and try to really get the feeling of it.  I'm simulating some basic circuits and using the built in VNA to look at the results.  Below are the results of a simple band stop filter, resonant at 5Ghz.  There the Smtih chart represtation of S11 and S21 next to a magnitude and phase plot of each.
My question is, how do I interpret S21 on the Smith chart?
S11 makes sense to me.  At 5Ghz on the Smith chart, the impedance, Z is at about infinity, so the reflection coefficient, Γ = 1.  So all energy from 1 goes back to 1, which the magnitude plot agrees with.
For S21, the magnitude plot makes sence, because it goes to 0, meaning no energy from port 1 is appearing at port 2.  However, I don't understand why the Smith chart would show 1 + j0 at the 5 Ghz point.
It looks like for S11, the chart plots the impedance, from which the reflection coefficient is calculated, that represents S11.  It seems to me that the impedance looking back from port 2 would be the same.
Unless it is meant to mean the impedance from port 2 to port 1, which in that case it seems to indicate that the ports are matched, in which case I would expect maximum port transfer, which of course is not the case.


texts: How to get my internal Harddrive to spin externally?

texts:
I have a Seagate ST3500620AS Harddrive that's just laying around and not being used. I want to power the motor at full speed (rated to run at 7200rpm) and do some hobby projects with it.

Problem is, I can't seem to get the harddrive to spin up. I have connected a SATA power cord to the harddrive and have connected yellow to 12V, red to 5V, the two blacks to ground. Yet I'm not getting any movement.

I've read various sources and found that it could be a variety of things
1)The motor is an AC motor, therefore needs AC voltage(some sources say it's a DC brushless motor)
2)The circuitry for the motor is fried, thus need to drive the motor sans the circuitry

What route should I take to get this motor spinning? Does anyone have experience in running newer internal harddrives externally? All I need it to do is spin at full speed.


texts:
My department of the company I am working at is in charge of developing a circuit for production, and security in the embedded system is a crucial requirement. The current prototype of our embedded system runs Linux on a micro SD card (with a MPU, Am335x). My job right now is to change the design into something more secure -- something that can't be easily modified by the user. However, I haven't done this in the past so I am not really sure what are the guidelines.

My thoughts so far:

Look for an EMCC chip on a BGA package with an internal layer on the PCB for the traces. That way it would be impossible to reprogram unless the user destroys the PCB. However, I am having difficulties finding an emmc chip on Digikey, apparently they are not very common and they are all sold out.

Other thing I was thinking was not using an EMMC at all but a secure NOR flash. However, I am not really sure if that would increase the development time in my department because I suppose that would require modifying the device trees on our AM335x so that it works with a secure NOR instead of an EMMC or a micro SD card.

Edit:
The security requirement I am referring to on this post is related to hardware only. We are using a TPM for secure boot and a remote attestation protocol to assert the state of the PCRs remotely. All software (new firmware) must be code signed to run. Also, all sensitive data in flash is encrypted. Thus I am not worried about someone desoldering and reading the EMMC. I am concerned however, about all the communication that goes from the EMMC to the AM335x, so I need to make sure it would be hard for someone to connect a test probe to the PCB traces. And of course, reflashing the chip and/or resoldering a new one. Those are the two basic requirements I am in need of.

Any guidance on this would be greatly appreciated.

Thanks in advance.


texts:
I'm trying to solder a new headphone plug - 3 pole, i.e. stereo with no mic.
There are 4 wires: copper, red, blue green. I was expecting 3.
Copper and red I understand to commonly be ground and right respectively. Blue and green are confusing me however - what could they be? Blue or green is usually left... but there are both.

They're Etymolic HF5 headphones.


texts:
I have this code to blink an array (8-led) of led one after one:

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

#define dela 500

int main (void)
{
    DDRC = 0xFF;
    for(int i=0; ; i++,i%=8)
    {
        PORTC |=(1<<i);
        delay_ms(dela);
        PORTC &= ~(1 << i);
        delay_ms(dela);
    }
}

I want to light up those led partially, like dimmed version of this, something like PWM

Now my question is how can I do that, how can I write analog output ?

Micro-controller : ATmega8A - PDIP


texts: What's the relationship between volts and amperes in batteries?

texts:
I recently bought a bag of 100 5mw 4.5V laser diodes (the spec said they have "driver: out"). My idea was to connect two and two of these in series to get something that needs 9V, and then connect about 70 of these diodes in parallel and run it off a 9V battery.

This didn't work as expected.

Just using 6-8 diodes, the light was already getting visibly dimmer. I figured there could be a short somewhere, but it seemed everything was in order. The 9V battery was used, but only for driving a few LEDs for a few hours.

So I decided to try something else. By using a battery pack of 6 1.5V batteries, the laser diodes were shining at full force again. I tried using about 20 of the diodes in the same setup as above, and still everything seemed fine.

Thus it seems I'm stuck with AA batteries for my setup.

Anyway, my questions are:

Why is this happening?
Are there not enough amperes to drive the lasers?
Why is the battery pack able to drive the lasers when the 9V battery isn't?
Is there any way I can calculate the approximate number of lasers the batteries can drive?
Will an amplifier or extra driver be able to fix this so I can still use the 9V battery?

Bonus question: If the answer to 5 is "yes", can I find such an item on eBay? I just need an example of what to look for since I'm just a hobby electrician.

EDIT:

Since you good folks asked for it, here's all the data I have regarding the laser diodes:

http://www.ebay.com/itm/110887381932

EDIT 2:

A brand new 9V battery was able to drive the diode arrangement after all. There appears to be a small resistor on the diode board, so I took my chances that the diodes would not blow just using them as described above (and I had spent way too much time on this Halloween cannon already to bother soldering 40 or so more things into the setup). Last night I used the cannon for a full entire night, and the lasers were still jolly good by the end of the evening.

Plus the cannon looked damn good in a dark nightclub with some artificial fog :)


texts: I have three light sensors which outputs appropriate AC currents with respect to light intensities. I only have one pin left for my ADC IC that I have on my board so I can't sample three sensors using my ADC. What I want is that I want to average those three light sensor's current by sampling their sum feeding that number into one of my ADC and dividing it by 3 using micro controller and so on. I need help with adding three AC signals. I can't find out appropriate circuit for it.


texts: What are the resource requirements (RAM, flash) of the latest Nordic Bluetooth Low Energy (BLE) stack?

texts:
I want to understand how much RAM and flash I have available for my own program memory and program space after I incorporate the overhead of Bluetooth communication when using an nRF51822.
https://infocenter.nordicsemi.com/index.jsp?topic=/struct_nrf51/struct/s110.html


texts: Circuit protection incorporating a Transient Voltage Supressor and Polyfuse

texts:
I want to protect some microprocessor equipment ( 5.0v, max 700mA ) which is powered by usb cell phone type chargers from damage due to such things as polarity reversal, over-voltage, power surges etc. I don't want a voltage drop (such as from a series diode) and it should sustain, without damage, a prolonged fault condition.

Is it simply enough to have a polyfuse in series with power input and afterwards a unidirectional transient voltage supressor (with 5.0v standoff voltage) reversed across power input ?

Eg

1PMT5.0AT1G 5.0v unidirectional TVS diode
http://www.mouser.com/ds/2/308/1PMT5.0AT3-D-32851.pdf

LITTELFUSE  60R050XPR Polyfuse 1A tripping current.
http://uk.farnell.com/littelfuse/60r050xpr/resettable-fuse-60vdc-40a-radial/dp/2383313

Follow up question: Under what circumstances would a bi-directional TVS be used in this scenario ?


texts:
Currently I am studying about short circuit detection on long lines and I can't solve one task:

I have line between two substations, and there is short circuit some where on this line. I know current and voltage which are measured at one of substations:

Voltage in phases is in complex form (\$V_a = 72\angle 0^\circ \$, \$V_b = 19\angle-137^\circ\$, \$V_c = 18\angle121^\circ\$)
Second sequence voltage is \$V_2 = 19\angle177^\circ\$
Zero sequence voltage is \$V_0 = 16.8\angle1^\circ\$
Current in phases is in complex form (\$I_a = 0.1\angle140^\circ\$, \$I_b = 1.4\angle-1^\circ\$, \$I_c = 1.4\angle-139^\circ\$)
Second sequence current is \$I_2 = 0.6\angle-70^\circ\$
Zero sequence current is \$3*I_0 = 1\angle-70^\circ\$

So I know that if there is zero sequence current it means, that it is one phase fault, but I cant understand which phase is connected to ground.


texts: What solder for low temp removal and resoldering to pcb

texts:
Have an issue with some legacy system - need to replace throughhole parts on PCB in situ while PCB is sandwiched between two sheets of acrylic with only small holes to access the leads on one side (i.e the back access is through a 3mm wide hole through a 10mm sheet of acrylic) and the front access is also tight (but just able to get a fine soldering tip in).

What we've been doing so far is prewarm the PCB to about 80C while trying to shield as much acrylic as possible.  Then warm the leads  (these have been soldered w leaded solder, (Sn60/Pb40) and remove but it is extremely difficult to get enough heat in due to the tight access and large ground planes and is causing issues with pad removal etc.

So I was considering using a low temp solder alloy but I am not experienced with them and from what I have seen, most are used mostly for when you want to reuse the IC not the PCB.

I'm sure it will work well for removal but its when we add the replacement part I am concerned that leftover low temp solder will produce a weak joint?  I have read that many low temp solders alloy with leaded solder to produce brittle alloys - are there any that don't?  Cost is not a major issue.

Thanks


texts:
I have come across about active all pass filters which provides phase shift with unity gain.

I dont know this is the common practice in part of circuit design. For a fixed or variable unity gain phase shifting application is this the common way?  Is it the only way?

Is the above topology common way to go or is there a more ad hoc IC for the purpose of phase shifting? I know it could be a very large topic but any big picture would make things clear.


texts: Can you have a compensating wave in steady state?

texts:
In a circuit in steady state is it possible to have a compensating wave? My understanding of a compensating wave is that it is there when a switch is switched. It provides a voltage and current that is the negative of what is so that KCL is obeyed whilst the current flows into the negative of the source.

simulate this circuit – Schematic created using CircuitLab

For example, if this switch had just been opened, I would say that there is a compensating wave to make the voltage and current to the right of SW1 equal to zero otherwise current would be leaving the junction but not entering.

So my question is can there be a compensating wave in steady state? My intuition says no since there is no change to compensate like in the circuit with the switch.


texts: What is the best starter adjustable power supply for pretty cheap (preferably ac/dc)

texts: Please I am just a kid no $8953739857239875 power supplies. Btw I am an inspiring electrical engineer and I'm 10 so I need a bit of help so I don't  how do I put this nicely, ahem trip the breaker if you know what I mean


texts: Understanding how TFT driver operates (ILI9486)

texts:
I'm trying to understand how to interface TFT driver ILI9486. I'm doing this because I want to control TFT display with PIC microcontroller and not AVR (for which libraries already exist). I own the following display. It looks like that only 8-bit parallel bus can be used for communication between uC and driver + some control lines for reading, writing, etc.

So far I managed to understand what needs to be done in order to read from or write to the driver and whether the currently latched data on the parallel bus is either command or parameter to command. However, I do not understand the following graph under "Display Data Format" section of driver datasheet.

I understand everything (and it is well explained in early sections of the datasheet) from RESX to RDX control line. However, I have no idea what could those colored bits of data on data lines of parallel bus (D0 to D7) mean.
Only part that seems logical is that each dashed line window represent 2x 8-bits or 16-bits total; and this is then somewhat "mapped" as 18-bit data. Does first (yellow colored) sequence of bits represent some command and then following (RGB colored) bits have to do something with addressing the pixel location/formation? What is "Frame Memory"? Why are bits colored as RGB? Does this sequence of byte transmission represent command, following by command parameter data?
Assuming from n-bit/pixel means that such data must be transmitted in explained manner to achieve illuminating single pixel on the display? Is the color of shown pixel then determined by state of individual bits in each window of 16-bits? For example, if all 16-bits are HIGH state, then pixel is white, and if they are LOW, pixel is of black color?
Then there is also graph for 18-bit/pixel order, where D6 and D7 are blank in dashed line window and each window includes 3x 6-bit data transfer (where first row being only Red, second Green, third Blue). One can have a look at the following datasheet.
P.S.: I would really appreciate any advice or explanation on this topic, since I could find very little information about this stuff on web.


texts:
I bought a relay that has a 7 segment display on it.
It's placed "incorrectly" according to what I need so I want to move it off the board as simple as possible. (Because I'm not that good at this).

So lifting off the 7 segment I see this two rows of connections that I figure there might be a extension for.
Dream scenario would be a male part for this with a few inches of cable and then a female part again.
I understand that is probably not the case.

What are my options?
Do I have to unsolder the pins off the board and solder cables to each end of this row of pins?
It looks pretty hard to be honest.


texts:
Here's the fan I want to use: http://www.nmbtc.com/pdf/acfans/4715ms.pdf

The 220VAC model costs $70 while the 230VAC model costs $17. Can I safely use the 230VAC model in China, where the mains voltage is 220? What are the consequences of using the 230 part in a 220 environment?


texts:
I have an AC signal and want to give it a new DC offset.  There are some questions about my experiment results.

(The original signal bias and terminal output bias are the same because I want to know if there is the attenuation or phase shift or not.)

(yellow-TP,blue-V2)

Can I apply these two circuits to provide DC bias? Why are the waveforms changed in each circuit with different capacitors?

Similar question, but this time is with different resistor.


texts: Is it possible to use ST Link USB for UART Communication?

texts:
I am using STM32L1 Series Discovery board and want to do uART communication via same UART port that is Used for Embedded ST Link V2

 .

Embedded ST Link uses USART1 of STM32L100CT6 and Mini USB is connected to my PC. Refer following fig.

PA9 Pin  as USART1_Tx of STM31L100CT6
PA10 Pin as USART1_Rx of STM31L100CT6

I also connected JP1 that is provided on the board so now main problem with this is that I didn't find COM port !!!

Is it possible to use ST Link USB for UART Communication ?


texts:
I am working with a twisted cable model.
Therefore I have:

2 input pins
2 output pins

But I also have a fifth input/output call "reference conductor". Based on the notation, it seems to be an input. But what is it?

Here is the model code VHDL-AMS of the compenent that I want to use.

Entity PVC Is
  Generic (Constant length : Real;           -- line length in meters
           Constant temp   : Integer := 0);  -- temperature parameter
  Port (Terminal A1, A2 : Electrical;        -- input ports
        Terminal B1, B2 : Electrical;        -- output ports
        Terminal A0     : Electrical);       -- reference conductor
End Entity PVC;

The rest in encripted.


texts: Best method/circuit for converting 240VAC to 5VDC (Low power)

texts:
In short, I'd like to power Arduino-like devices (small PIC devices as well) run off of a mains socket at 240VAC - which obviously can't be done with a simple wire. I assume I'd need an output anywhere between 3 and 5 volts DC.

I don't want to use a generic plug power supply as they're usually designed for higher current outputs (I'd probably need 500mA at most - the processor and a couple of LED indicators), can cost a reasonable amount and I'd like to up my electronics knowledge/DIY skills by creating something myself (even if it is just a couple of soldering joints).

Also, when I say "best", I mean either the simplest to build or most efficient (or a combination of both).

My apologies for the generic question, I've just never done this sort of thing and I'm not sure how to word it properly.


texts: Should I add protection on an internal USB circuit?

texts:
I'm designing a pcb that includes a SOM and a GSM/GPRS chip. Both have USB capabilities and I'm going to communicate with the GPRS chip via USB. As I'm not exposing the SOMs USB to an external port is it neccesary to add protection? Also does D+ on the SOM go to D+ on the GPRS chip? Or is it like serial, where TX => RX and RX => TX.
Cheers legends.


texts:
I have a STM32WB55 custom board where I put the Read out Protection to level 1. I would like to change it back to level 0 as in this level, I am unable to program the PCB. I have tried using the ST LINK utility and the STM32Prog to change it back to level 0 but to no avail
STLINK Utility:
 Could not set Option bytes!
    Please reset the target and retry.
    Can not read memory!
    Disable Read Out Protection and retry.

STM32 Prog :
Error: Expected value for Option Byte "RDP": 0xAA, found: 0xFF
Error: Option Byte Programming failed

From what I read online if my version of STLINK utility is higher than 4.0 it will work but it is not the case. Boot0 is at high and I have try reseting it but to no avail as well. Any ideas on how I can change it back?


texts:
I am by no mean an expert in electronics. But I am an active hobbyist in RC equipment for last 15 years.

I am on a project that has always been on my mind but never got to do it. But here is the day ! So long story short.. I am modifying a gamer's steering and pedals set to work with RC cars.

It is already done and working beautifully but on my throttle side of the project I am using only the throttle pedal to control (throttle up, brake and reverse). What I want to achieve is to effectively use the brake pedal to brake and reverse.

I know I have got to use 2 potentiometers to act as only one. Like 50% of the range on the throttle and the other 50% on the range on the brake pedal. Now i am utterly confused with it.

If you don't know how an RC transmitter works for throttle and brakes I am more than willing to give my best explanation for it.

Throttle channel work as

50% = neutral
50% to 100% = throttle up
0% to 50% = brake

Now to reverse you have got to fully brake, let the brake off to neutral and brake again.

Is there a wizard here that can point me how to do so?


texts: Having trouble with an aviation-band receiver

texts:
I finished assembling an aviation band receiver that I bought online. I thought it would be good project for my resume, as I am an electrical engineer major at a University in California. I read the schematic properly and soldered everything on to the PCB board.
Unfortunately, I cannot hear any sound. I can't figure out if it is maybe the components or the circuit board it self. Or maybe I need a different antenna.
I am very confused and really wish I could get this to work.
What kind of formulas or theories do I need to use in order to start from scratch in making my own schematic? Do I need to incorporate a high-pass filter?
Here is the schematic of what they sent:

Here is the completed PCB:


texts: boost converter circuit simulation in LTSpice

texts:
Could you please explain why the V(R1) is not 2V?

I'm studying boost converter using LTSpice. According to theory the output voltage of this circuit should be determined by the duty cycle of the square wave which is generated by the switch. Here I used 50% and expected that the Vout would be 2*Vin. But the simulation results in this.

From this simulation I found that the Vout is dependent of L, C and R. Is that true? I don't understand what is wrong.


texts: Jumper wire for thin connector pin / holes

texts:
I have a board with a Samtec SFM-115-L2-S-D-LC connector. This connector has 30 (15*2) pin holes, with a 0.050" / 1.27mm pitch, and accepts pins that are smaller than those used in breadboard / prototyping jumper wires. Therefore, I can't directly connect my prototyping jumper wires to the connector holes.

In the datasheet for the male version of my connector (TFM-something) I can see that the pins have a width of 0.018" / 0.46mm, while my jumper wires have the standard thickness (0.0254" / 0.65mm).

How can I connect individual pins/holes of my Samtec connector to, say, a breadboard? Are there jumper wires or headers with the appropriate thickness?


texts:
How do these 2-wire analog buffers work? The one on the left is driving a current sink and the negative supply is hooked up to the output. The one on the right is a current source driver and the positive supply is hooked up to the output.

I'm trying to wrap my head around why the rails are able to be hooked up to the output and still work...I can't figure out how to factor in the current source/sink into the circuit.


texts: ADS Simulation of IV Diode Characteristics

texts:
I’m still quite new to ADS, and I’m trying to get a simple simulation of the IV diode characteristics.
I want to plot the diode current against a DC sweep from -0.2V to +0.2V
Here’s what I’ve got so far, not so sure as to why the current is negative.
Is the circuit OK?

Would appreciate some help and guidance.


texts: AVR Pin Dual Use: Input and Output at (seemingly) the same time

texts:
I have been working on a few different versions of a bicycle light control circuit which reads in various buttons and sets various outputs accordingly such as headlight, taillight, blinkers, etc.

My current design is based around an ATtiny24 (Datasheet) using the internal oscillator (8MHz), programmed in C using AVR-GCC. I would like to keep external components such as shift registers to a minimum. Resistors are OK since they are cheap and small, and I am using MOSFETs (NTD4960N: Datasheet) to drive the LED banks.

Essentially, what I am looking to do is drive the MOSFETs with a 200Hz PWM signal to control the LED brightness, but limit the duty cycle to 90%. With that in mind, I would only need a pin to be an output for a maximum of 90% of the time. In the remaining 10% of the time, I want to switch the pin to an input to read the state of a button.

I tried a lot of various configurations to allow the MOSFET to stay OFF when it is supposed to be OFF, regardless of input from the button, and this is the best I could come up with:

The supply voltage (VCC) is 5V, so when the button is pressed, about 0.9V is seen at the transistor gate. This is not enough for the transistor to start conducting, but it can be read by the MCU ADC which has been enabled using the internal 1.1V reference.

So the code drives the MOSFET with a 200Hz PWM signal. The duty cycle will vary with the desired LED brightness, but will not be greater than 90%. During the last 10% of the PWM cycle, the I/O pins are set as inputs (internal pullups disabled, digital input buffers disabled) and the ADC is used to read the state of the pin. The 10k resistor keeps the MOSFET off, and if a button is pressed, 0.9V is read by the ADC. This value is still not high enough to turn the MOSFET on, so the LEDs stay off, regardless of the button press.

Since the ADC is turned off and on, I discard the first reading and keep the second. This is done in plenty of time before the pin needs to be reset as an output to start the next PWM cycle. Since I am reading multiple buttons, I only read one each duty cycle, then update the ADC multiplxer to read the next button at the end of the next duty cycle - hence, each button is read once every [(# of buttons) * (200Hz)^-1]. The PWM and button reads are handled entirely by interrupts while MAIN determines what to do with the state of any particular button.

I have built and tested this circuit, and it seems to work perfectly, but I wanted to present the description here with the following questions:

First, is this a bad idea? If so, then why?
Is there an obviously better way to do this besides GPIO expanders/shift registers?

I can post some (or all) of the code if you want. I just thought the description might be enough, and I didn't want to make this any longer than it already was.

UPDATE

I should have said this the first time, but the MCU supply voltage (VCC) is 5V, the battery voltage (V_bat) is 12V (could be more like 14 on a fully charged battery), and the total LED current (as in the amount going through the FET) will be close to 2A. The LED bank will consist of numerous parallel strings of 3 series LEDs (white, V_LED = 3.3V) and a series resistor in each string. The pulsed current is around 50mA per string. With 40 or so strings equaling about 2A total.

I have tested and verified my ADC version of the circuit as well as the "digital" version presented by DrFriedParts below with a small current (50mA total), but have not yet tested either circuit with the larger current load.

This is the original project that I am redesigning. When I first built this bike light controller, I was new to microconctollers, so it was more of a learning experience than anything else.


texts: When using a Laptop, is it desirable to keep it charged from the Mains all the time?

texts:
While using laptop I usually plug in my Laptop charger (i.e., from Mains power).

What is more effective - to keep Laptop plugged in at all times when possible, or some other approach (e.g., running on battery till it fully discharges, then plugging in the charger, and so on)?

"Effectiveness" here could relate to battery lifetime as well as what is good for the laptop internals' life.


texts: How to identify the communication protocol?

texts:
I have this card to control my pool heatpump.

This card allow the display of several information:

input temperature
output temperature

and allow at least one command:

heat the water.

What I do not understand is how this system communicate with the heatpump as I only see three wire.

I would like to gather and command this heatpump from another device.

Any idea how I could, based on the picture, determinate or at least shortlist the protocol used to communicate with the heatpump ?


texts:
I have seen people using ferrite beads to suppress EMI from switching power supplies.
Recently, I came across the following blog post where the author successfully re-models a switching power supply to reduce EMI noise. At one point, he makes the following comment.

It is common to attempt the use of ferrite beads to suppress RF Interference of this sort, but it's very unlikely that it will help much - particularly at lower frequencies (e.g. lower HF bands such as 160 and 80 meters, not to mention the AM broadcast band) because these devices simply cannot add enough inductance to add a significant amount of impedance:  At these frequencies (say, below 10 MHz) it takes multiple turns on a chunk of ferrite to add enough reactance to make even a small dent in the amount of conducted interference!

My question is that whether the author is right or not? I have read that ferrite beads in EMI filtering, acts as a lossy element and turn the RF energy into heat. Did the author forgot to consider this and only considered the high impedance of an inductor at RF? I'm confused as his strategy worked nevertheless
EDIT: But, I have seen another ham successfully build and test an SMPS using  ferrite beads.Here is the link and here is the circuit Of course he used quite a handful of ferrite beads.


texts: Blending between exponential and linear control voltages

texts:
I have two control voltages(CV1,CV2).
Both represent the same data, but one in linear and the second one is exponential response.
I would like to have a potentiometer to blend from CV1 to CV2 so I can smoothly transfer from exponential to linear mode before feeding it further to IC. I'm pretty sure I could do it with a dual potentiometer wired up so that R increases for CV1 while decreasing for CV2, before summing them in op-amp. I hope to find a solution that would work with a single potentiometer. Is there a term that describes this kind of function that I could read upon? I'm not even sure what Tags to use in this question.
Thank you!
Control voltages are audio rated so 20kHz would be the maximum frequency they would operate. And Voltage range is 0 to ~+2V. Ideally it will be -30mV to +2V, but I guess the negative can be removed if it complicates the solution.


texts:
I have a precision burden box, whose burdens are switched by a rotary switch, and there are 21 positions. I want to make it "digital controllable", that is, using MCU to switch between these burdens. The current flow through the burden may be 10A max. Now I list the possible methods I know. In all method, I need to consider the current capacity and on resistance, and
for some methods, I need take more into consideration.

Using solid state relays. (The on resistance and current capacity maybe a problem.)
Using MOSFETs. (I need work more on the driving circuit and heat-sink design, as well as the space maybe a problem.)
Using electro-mechanical relays. (The on resistance maybe a problem. Is there a relay with Ron comparable with a rotary switch, that is, <10 mOhms? )
Using a stepper motor to drive the rotary switch. (If using open-loop, I can't know exactly the position of the 'wiper', so it may not be reliable.)

That's what I know for now. Can someone give me some suggestions on the possible methods, or some recommendations on parts selection.


texts:
I am building a homebrew CPU and have now reached the point of designing the SRAM part. I plan of using a simple 32K x 8bit static RAM (such as the Cyprus CY62256N). My concern is that the part is asynchronous but I want it to act like a synchronous part.

In the the rest of my design, registers are written to on the rising edge of the clock with the required new value already on the data lines. During the rest of the clock period the new instruction is processed and a new value might be placed on the data lines. This is fine because the register only updates on the rising edge and not later on, even though the clock happens to still be high.

I presume this approach will not work with asynchronous SRAM. I am concerned that the rising edge of the clock will update the SRAM, but if the clock happens to still be high when the value of the data lines is updated for the next instruction it will cause another update that is not wanted.

Is there some common technique to achieve what I need?


texts: Why isn't \$I_s\$ (resultant current phasor) zero in FOC of PMSM?

texts:
Suppose I have 3 phase (A,B,C) star connected PMSM.

For running this motor with FOC the \$I_s\$ (resultant current phasor or \$I_a+I_b+I_c\$, where \$I_i\$ is current in the phases) is keep at 90 degree with the rotor flux.

So, I can't understand why \$I_s\$ is not zero as \$I_a+I_b+I_c = 0 \$ according to Kirchhoff's current law.

How there is a non-zero \$I_s\$ which people are able to keep at 90 degrees?


texts: what is the Outer casing of alkaline battery made of?

texts: what is the outer casing of a typical small 9v alkaline battery made of? Is it conductive?


texts: Why are capacitors needed in dimmer circuits?

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In a circuit like the one below, why is capacitor C1 needed? I mean I can make do with just a resistor and pot to attenuate the voltage to some level suitable for switching.
What does using capacitors add to the circuit, and what is it's advantages and disadvantages over just using simple resistors voltage dividers instead?
Also in the circuit in the 2nd graph I am not so sure what the purpose of adding C2 and R3.


texts: Using 3-Axis Digital Accelerometer to Measure Rotational Acceleration in a Helmet?

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I'm very new to using sensor components and I have a 3-axis digital accelerometer I can use, but I don't know if I can use one to measure rotational acceleration in a football helmet? Is the sensor even suitable for that purpose, and if it is, can I do it with just one or do I need multiple?

I looked at a few posts discussing how someone could use an accelerometer to measure rotation but they were limited to one axis or involved some kind of bearing to measure two. Will a 3-axis accelerometer be able to measure rotation in every direction?

Thank you very much in advance!
Here's a datasheet for the accelerometer, just in case: http://www.nxp.com/assets/documents/data/en/data-sheets/MMA8451Q.pdf


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I am just trying to build a small fan to keep my Mac a little cooler from outside.
So I have this little Box Design I made. Now, I'm a total noob at this thing so I need beginner level help here. I've made this circuit, which works great.

What I'm doing is that I'm using the USB outlet to power this motor which is connected to a Fan blade.
There's no resistor in the circuit. The motor is heating up in a use of just 1 minute so I need assistance on what I should do. I've read that Small DC motors can also catch fire if overheated too much.

Also, there's no readings on the motor related to its current and voltage input so I don't know what to do. Is there too much current or too much volt? I believe the USB port delivers 5V and 0.5A


texts: How to Send Video from a Raspberry Pi (HDMI) to 20 pin LVDS

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Through shenanigans, I have come to possess 4 small LCD screens. I've found the pin-out for video data on page 12 of this datasheet. I think it's LVDS. I'd like to know what I need to learn to be able to connect this screen to my Raspberry Pi. From what I've read about people attempting similar things, I believe I need to make or find a controller board(?) I know I'm probably way out of my depth, since most of my electronics experience is Arduino's and breadboards. Still, I'm at the point where I'm trying to make mistakes and learn.

If this is far beyond a novice, I'd also appreciate any suggestions on other projects I could use these screens for, and hopefully learn something in the process.


texts: Does anyone knows where I can find SPICE model for PMBFJ309 or similar? I searched a lot and could not find. If anyone knows, could you please share the link.


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I'm trying to amplify an AC wave (from an audio input) with a maximum amplitude of about 1.8v to a DC oscillation between 0V and 5V with the centre (what would be the zero-crossing on the input) at the midpoint of 2.5V.

I've attempted to use a differential amplifier design to achieve this but my output is inverted from the input.

Here's my current schematic from CircuitLab:

And the simulation output:

I'd really like it if I could produce a non-inverted output without any additional active components, how could this be done?

Thanks in advance!


texts: Calculate Current Used: Diode vs. LDO for lowering voltages?

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Could anyone lay out the math for how you would calculate how much current is being wasted if you used a standard silicone diode to drop a 3.7V source to 3.1V?

I'm trying to evaluate if an LDO is more efficient, than just dropping a voltage using a diode.

Say the base case is the device is sleeping and pulling 1mA of current.

Where do you start on that kind of calculation?

(The real case base case is a module that expects a 3.7V LiPo and is fine from 4.2V to 3.3v, but another IC that wants a 3.6V - 3.3V source. This board is VERY space constrained, so in one sense the diode probably is the smallest way to drop the voltage for the IC in question).


texts: How can I get this circuit to "make noise"

texts: I designed this noise generator circuit that uses a 1N514 Schottky diode with a VDB transistor amplifier(note: the upper VDB resistor is actually 15kOhm). Looking at the oscilloscope trace it seems to work fine in generating continuous white noise with a fairly flat FFT spectrum and maximum peaks between 4 and 5 volts. But when I try to connect the output to a small speaker I don't hear anything. I haven't done much frequency analysis but perhaps should I add a frequency shifter or low-pass filter so the output is in the audible range?


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Are there any differencies in functionality between those two or any advantages of one over the other?
The only thing that comes to mind why someone would use diode-connected transistors over diodes is if, for example, the whole integrated circuit technology is based on transistors and it's easier and more cost-friendly to just configure some of them as diodes when it's needed, other than integrating a diode in the circuit. Or, if transistors are more temperature resistant than diodes?
Are there any other differencies?


texts: How to determine radiation at a certain distance from a sunlamp

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I have a sunlamp, with four UV bulbs, emitting UVA and UVB. These are parallel-mounted tube bulbs and the total area of the light emitting area is 20 cm × 25 cm = 0.05 m2. Each bulb is 15 W and so this is 60 W / 0.05 m2 = 1200 W/m2 = 1.2 kW/m2.
I'd like to be able to calculate W/m2 of radiation at different distances from the lamp, to ensure that I don't exceed the amount that I would typically get on a sunny day. I understand the 1/R2 rule, which indicates that as you if you double your distance from a source, you quarter the power. However, I don't know the radiation at a distance from the source, I only know it at source, where my distance from it is zero. Because zero times anything is zero, doubling my distance isn't something I can do.
So, two questions:

How do I determine the power from the lamp at different distances?
How much UVA and UVB radiation typically hits the earth on a sunny day? I can only find figures for total radiation, which is about 1.35 kW/m2?