texts:
New to electrical in general, so be gentle...

Looking to drive a TEC1-12706 as a cooler/heater, using 24V, 500 Hz PWM as input. To avoid thermal cycling caused by PWM, incorporating LC filter.

In the question/answer here (How to drive a Peltier element?), Olin states that ripple should be <10%. Based on this requirement, this document (http://www.onsemi.com/pub/Collateral/AND9135-D.PDF) gives a method for choosing LC components in a buck converter (Does this apply?)

Using equation 20 with a 50% duty cycle gives the highest value for L_min of 10mH.

Based on this, I’ll need a 10 mH inductor rated for 6A and 12V. Looking through Mouser I found P/N FIS111NL rated for 15 A w/ 22 mH (cheapest for >10mH and >6A).

(1) Is there a better solution here?
(2) Should I be looking at multiple smaller inductors?

Solving for EQ’s 31 and 34, get 250 uF and 0.06 F respectively, with some assumptions. Plugging these into Falstad it appears that the 0.06 F create a low frequency high amplitude ripple, and then takes its sweet time to discharge, both of which are undesirable. 250 uF provides some decent filtering, but does not seem altogether necessary.

In a previous thread, I was pointed to (Low side N-Mosfet buck converter) which seems like a good circuit design to use. But some issues were pointed out:
 - Load not referenced to ground (ignored)
 - Radiated emissions (solved?)

So based on all that I’ve got the following circuit

simulate this circuit – Schematic created using CircuitLab

24V PLC drives 500 Hz PWM via PID. PLC controlled relay determines cooling/heating mode of Peltier. Assumed 10V gate voltage on N-MOSFET.

…and some more questions…

(5) Is it fine to have the load not ground referenced or should I figure out how to do this with high side switching? (If so, can you point me in the right direction for this sort of power level? Maybe some components to start with?)
(6) Is the radiated emissions issue solved? I am assuming that plopping the inductor after the load fixes the common mode voltage issue as well as reducing the length of a potential EMI source, per Olin’s comment on the original circuit.
(7) What Schottky diode should I use? Searched in Mouser for Schottky, through hole, Forward surge > 6A, cheapest, came up with the MBR160RLG. Is there something better or more common? Am I doing this right?
(8) What transistor should I be using? MOSFET? Darlington? Ideally I want to be able to get a full 12V to the Peltier. Can someone provide a suggestion for the component to use here?
(9) Should I bump up the power supply voltage to account for lost power from the transistor and relay? (It appears that is what Francesco did, but it seems like not the right method.)
(10) Since I’m running 24V to this thing anyway, does it make sense to change the circuit to accept 24V instead and step it down to 12V?

I numbered all my questions to make it easy for folks to help.

Thanks!

Also, here are the numbers I used for my calculations above.

Inductor Size

Voltage In (V_IN = 12V)
Voltage Out (V_OUT = 6V)
Duty Cycle (D = 0.5%)
Ripple (LIR = 0.1%)
Current (I_OUT,MAX = 6A)
Switching Frequency (f_SW = 500hz)
Inductor Size (L_MIN = 0.01H)

Cap Size 1

Ripple (LIR = 0.1%)
Current (I_OUT,Max = 6A)
Switching Frequency (f_SW = 500Hz)
Capacitor Voltage Ratio (CVR = 0.1%)
Voltage Out (V_OUT = 6V)
Capacitor Size (C_MIN = 0.25F)

Cap Size 2

Inductance (L = 0.01H)
Peak Current (I_PK = 6.6I)
Overvoltage (V_OV = 0.6V)
Voltage Out (V_OUT = 6V)
Capacitor Size (C_MIN = 0.058F)


texts: How to detect a magnetic field going over a coil?

texts:
I have a coil with solid core, there is an small magnet that pass over it (like on the image) but not touching the coil (there is an small plastic between them, no more than 0.5mm thick). I need to detect when the magnet pass over the coil, i've investigated the hall effect devices but i'm not sure if they will work here as the magnet pass over the coil and not over the sensor.

I've connected an oscilloscope to the coil and watched while the magnet pass but i didn't recognize anything over all the noise (I connected the probe to one side of the coil and ground to the other side).

Any help or ideas will be highly appreciated.

Edit: The coil is not made from 4 turns, it has way more than that (around 50) but i was too lazy to draw 50 turns on the image. Also on the best escenario the coil should remain there, but i'm open to other devices like the reed switch (that i'm going to try soon).


texts: Low voltage drop transistor/mosfet switch - 3.3V 200mA

texts:
I need to make a switch. However p-n junction drop seems to be a problem for my use. Hence I am unable to use something like this:

In this case, my load won't be getting exact 3.3V across it. Straight forward method will be to use a mechanical relay, but I want to avoid through hole and bulky components. In fact, I want to make it as cheap and small as possible - probably a few resistors, transistors or a small mosfet is what I am planning to use. Is there any good solution to such a requirement?

Edit:

Load requirement:

3.2V i.e. a drop of 0.1V will work fine. Current will be approximately 200 mA.

As answered by Olin and highlighted out by JRE, a FET definitely solves my problem.


texts: Why does the base-emitter voltage of a BJT decrease with temperature?

texts:
According to Sedra/Smith Microelectronic Circuits, \$v_{BE}\$ changes by \$-2\text{mV}/\text{°C}\$. I cannot understand how this could possibly be the case given the equations I am familiar with.

With all currents kept constant, we have:

\$\large{i_E = \frac{I_s}{\alpha}e^{v_{BE}/V_T}}\$

To keep \$i_E\$ constant, any change in \$V_T\$ would have to be accompanied by a change of the same factor in \$v_{BE}\$, otherwise \$\alpha\$ or \$I_s\$ would have to change, which as far as I understand is not possible.

So, how can \$v_{BE}\$ be inversely proportional to \$V_T\$?


texts:
I have this code and i use in my device.

PIC18F252 PCH compiler CCS 5.007
//t_time_stamp=3776590560;            // 2019/09/04  12:56:00
utc_sec = t_time_stamp % 60;          //int32

min_temp = t_time_stamp / 60;         //float32
min_temp_int = t_time_stamp / 60;     //int32
utc_min = min_temp_int % 60;          //int32

hour_temp = min_temp / 60;            //float32
hour_temp_int = min_temp / 60;        //int32
utc_hour = hour_temp_int % 24;        //int32

day_temp1 = hour_temp / 24;           //float32
day_temp1_int = hour_temp / 24;       //int32
day_temp2_int = day_temp1_int % 1461; //int32
utc_day_cnt = (day_temp2_int % 365) + 1;

utc_year_cnt = day_temp1 / 365.25;    //int32 code here

It work correctly until 5 last month,
but hour_temp_int is not correctly now; hour_temp_int is 11 at 10:26 to 10:30 but it should be 10!
Only this parameter and at this time is not correct!
What is my mistake?

I change types float32 to unsigned float32  or float48 but i have Error


texts:
Hello i m writng a program for UART receive interrupt for PIC24FJ64GA306

i m receiving a data which is in format of 0xAAXXXXXXXX, where data after AA can be anything... the data transmityted through host and received by pic doesnt match

Also i observed a strange issue: when i transmit for ist time the data is not fully received, only 2 bytes of data is received, where in when i transmit 2nd time i get a OVER run error.

The code is as follows:

static void uart1_DebugSerial_init(void)
{
  /*Setting the RPINRbits to map the peripheral port pins*/
   RPINR18bits.U1RXR = 26;   /*Selects RP26 as UART1 RX pin*/
   /*Setting the RPORbits to map the peripheral port pins to UART TX pin*/
   RPOR10bits.RP21R = 3;   /*Assign U1TX to RP21*/

   U1MODEbits.STSEL = 0; // 1-Stop bit
   U1MODEbits.PDSEL = 0; // No Parity, 8-Data bits
   U1MODEbits.ABAUD = 0; // Auto-Baud disabled
   U1MODEbits.BRGH = 0; // Standard-Speed mode
   U1BRG = BRGVAL; // Baud Rate setting for 9600

   //   U1STAbits.UTXISEL0 = 0;        // Interrupt after one TX character     is transmitted
  //    U1STAbits.UTXISEL1 = 0;
  IEC0bits.U1TXIE = 0;           // Disable UART TX interrupt
    IEC0bits.U1RXIE = 1;            // Enable the UART RX interrupt
  U1STAbits.URXISEL = 0;         // Interrupt after one RX character is   received

  U1MODEbits.UARTEN = 1; // Enable UART
  U1STAbits.UTXEN = 1; // Enable UART TX

  /* Wait at least 105 microseconds (1/9600) before sending first char */
  DELAY_105uS
  //U1TXREG = 'a'; // Transmit one character
  }

Uart transmitt code:

int uart1_DebugSerial_send(char *buf)
 {
    int len, buf_length;

   buf_length = strlen(buf);
   len = buf_length;

   while(buf_length--)
   {
       while(!(U1STAbits.TRMT));   //stay here until the UXTSR register is empty
       U1TXREG = *buf++;
    }

   return len;

}

UART Receive ISR

void __attribute__((__interrupt__, no_auto_psv)) _U1RXInterrupt(void)
 {
   static char str[50];
  unsigned char RxChar;
  static uint8_t uart_header_rcvd_flag = false;
  static uint8_t i = 0;

  IFS0bits.U1RXIF = 0;    /*Clear the Rx interrupt flag*/
  /* Check for receive errors */
  if(U1STAbits.FERR == 1)
   {

//          continue;
  }
  /* Must clear the overrun error to keep UART receiving */
  if(U1STAbits.OERR == 1)
  {

    U1STAbits.OERR = 0;
  //        continue;
}
/* Get the data */
if(U1STAbits.URXDA == 1)
{

    RxChar = U1RXREG;

}
/*If the Received char is 0xAA and Header received flag is false, then
 start receiving the packet*/

if (RxChar == 0xAA && uart_header_rcvd_flag == false)
{

    uart_header_rcvd_flag = true;
    i = 0;
}
/*If the Packet reception is already commenced, then check for the PKT_SIZE
 to stop populating the host_rx_buf
 */
if (uart_header_rcvd_flag == true)
{

    host_rx_buf[i++] = RxChar;

    if (i == HOST_PKT_SIZE)
    {

        host_pkt_rcvd_flag = true;
        uart_header_rcvd_flag = false;
    }
}
 }

Please help me, where i m going wrong

Thanks in advance


texts:
How many bits does a pH or conductivity sensor have? I need a Analog-to-Digital-Converter for these sensors. Thus I need to know how many bits are required in order to purchase the right ADC.
I am not sure if 8, 12 or 16 Bit. Can anyone help me out here?

EDIT: For now we have HACH sensors connected to the SC100 controller, but I am searching other sensor which do not require a controller. Yes 4-20 mA is the output of the sensors I am looking for as well as the controller from HACH SC100.

I don't know the voltage ouput yet.

I want to connect the ADC to a Simatic S7-1200.


texts: Help understanding 1986 schematic for Rohde & Schwarz cryptographic key generator

texts:
From https://www.cryptomuseum.com/crypto/rs/pu104/index.htm :-

  PU-104 was a key generator for perforated paper tape, made around 1986 by Rohde & Schwarz (R&S) in München (Munich, Germany). The device was able to create long sequences of truly random numbers and send them to external paper tape puncher via its built-in V.24 interface.

I'm trying to understand how random noise was sampled by the CPU.  I don't think that they used an dedicated analogue to digital converter, but rather went directly from analogue to digital logic. I can't follow what happens after the  noise enters the purple square in the following schematic extract:-

The extract is from the complete user manual at https://www.cryptomuseum.com/crypto/rs/pu104/files/pu104s2_manual.pdf.  See pages 24-27 of the PDF file. The 'bottom' board photograph clearly shows two PM156 op-amps which I cannot locate on the schematics. They're not of a style I'm accustomed to.

It don't know why there are two schematics.


texts:
I'm designing my first PCB layout at 2.4GHz, I have done a couple of designs at 868MHz, but never 2.4GHz.

I have due to limited space routed some components in 90 degree, but know that the guys on the review team will complain about this, because they thinks it is bad practice.

I have read numerous of articles that says it should be ok, but the articles never mention a frequency limit, so because this is my first 2.4GHz design, I just wanted to ask here, if my layout is not optimal.

Shown below is the PCB TOP layer, below this layer is a solid GND plane.


texts: How to export gerber with milling layer in EAGLE 9?

texts:
I've got a pcb design with some high voltage traces that are separated with a line drawn on milling layer (46).

How to generate a valid gerber file for manufacturer (JLCPCB) with informations about this milling.

Using default 2-Layer, CAM Processor template milling isn't included into any gerber file.

Is adding milling layer into Profile file a valid way to do it?

Using: Eagle 9.3.2


texts: average calculation vs rms calculation in rectifiers

texts: In rectifier \$R_{load}\$ we calculate \$P_{load}=V_{avg}\cdot I_{avg}\$ why cant we take \$V_{rms}\$ and \$I_{rms}\$ as we are taking like in electrical calculations and also what is the use of calculating rms value in rectifier \$R_{load}\$?


texts: Detect Infrared beam projected onto X-Y plane. Save and display coordinates. CMOS sensor?

texts:
I'm working on a project in which an IR laser is pointed perpendicular to the surface of an X-Y plane (Think like the old game "Duck Hunt"). I don't know where the IR beam will land on the plane but would like to detect the location, distance from plane(based on area of beam in comparison to beam aperture or its intensity compared to its initial intensity) and save it for display in an app.

From my research I think an array (or multiple arrays) of receiving ir/photovoltaic sensors would work but I want to avoid that method (if plausible) because I'm trying to use the minimal amount of components and I want to keep the programming "relatively" simple (if possible). [I've got mechanical engineering background not electrical. Apologies, friends]

I did more research and I think a CMOS sensor (commonly found in almost all digital cameras these days) could potentially be used (or perhaps a kinect?)

This is where my question comes in: IF I were to pursue the cmos sensor method, how could I best go about finding the location? IF the cmos method would be overly complicated (there has to be a better way) to display this information. I'm open to any microcontroller suggestions as well. Any help or guidance in the direction to research would be appreciated.

Thanks for your help

**Edits: Want it to detect on a physical plane can be opaque or clear. The surface area I'd like to detect is about the size of a sheet of paper (8.5"x11")

Let's assume we dont have control of the ir laser and that it can hit anywhere on the plane. The only thing we can alter is the plate and the sensor.


texts: Stiff, shape-retaining insulated wires vs "floppy" ones which "bounce back" - are there actual technical terms for those two types?

texts:
Pretty much what the questions says. I find myself in need of some wires and I want to get the "floppy" ones, but I realised I don't know what the actual technical term for it is and so I don't know what to search for.

Also, while we are at it - is there much difference between the two types in terms of durability?


texts: What are different types of computer architectures?

texts:
I am going through the book "Elements of computing systems". This book teaches how to build a whole computer from scratch. While I was just browsing the chapters on computer architecture, I noticed that it all focused on the Von Neumann architecture. I was just curious as to what are the other architectures and when & where they are used.

I know about only two, one is Von Neumann and the second is Harvard. Also I know about RISC which is used in uC of AVR.


texts: Traces in connector's solder keep out area

texts:
I'm designing with a Molex 87438-0443 connector whose PCB footprint includes a 'solder keep out area' between each pair of copper pads for each connector lead.

It appears that the manufacturer wanted a discontinuity between the connector's signal side (i.e. the part of the pins jutting out) and its mechanical side (i.e. the bottom-side part of the pins) though I don't have a solid guess as to why.

Is there any harm in running a ~10 mil, solder-masked trace connecting these two pads?


texts: Frequency range of interest in PCB decoupling network

texts:
All the material I found about decoupling write "[...] low impedance in the frequency range of interest [...]" but it's never discussed how this is defined. Does it come from

The external noise on the supply network that should be filtered
in going into the chip?
The frequency range of the current drawn by the chip such that this current faces a low-impedance?

If it's the first (1): That does not usually depend on a particular chip since the noise is external. And how would I know the frequency range of the noise? For example, if I use my cellphone close by (or even have RF parts closeby) this may couple into my supplies. So ideally I would like to filter up to multi-GHz no matter what. But I find it is extremely hard to get a PCB decoupling network (using 0402) that's not inductive for more than some hundred MHz.

If it is the second (2): Suppose I have a (mixed signal) chip with a) some digital logic, operating at 100 MHz, b) some analog amplifier, operating at up to 1 GHz. The 2 blocks have different supplies.

For a) the fundamental of the current draw will be 100 MHz. However, the current drawn are current spikes, so the frequency content is very high (as opposed to just 100 MHz). For that reason, again, I would like to cover multi-GHz, which is not possible.

For b) there is essentially no (significant) ac current drawn. This would imply no decap is necessary at all. Clearly this is not true, since analog chips also have decaps. Then, if (1) is correct (and I assume the noise has infinite bandwidth), it means that my decoupling network would need to work up to 1 GHz. But again, this is not reasonable.

So how exactly is this frequency range of interest defined and what do I do if the interesting frequency exceeds 1 GHz - far more than PCB coupling can cover?


texts:
Why does a processor overclock faster when cooled with liquid nitrogen? Also, is the inverse the reason why the processor slows down when it get's hot?

I'm specifically interested in Intel processors.


texts:
I'm planning on making a small desk toy involving LEDs and a motor to turn a reflective element, and I just want to know if what I'm planning is safe or not.
I want to use a series resistor to limit current to the motor. I only need the motor to turn slowly (no exact RPM defined), and I don't need variable motor speed either.
I know that it's better to use a real motor controller (or at the very least PWM control), however everything else in the design is completely passive/dumb and I'd rather not introduce an Arduino just to run a motor at a slow speed.


texts: Consider the circuit diagram below. What will happen if at some instant the inverter input is zero?


texts: What facilities/methods exist to debug and simulate programs for PIC microcontrollers

texts:
In the university, even though I did do some PIC programming and project, the project was quite simple. We could always put in a blinking LED as a sign of life into our program or have the code write to the serial port every now and then to let the programmer know that the code is executing ok. However, I am sure that there are some real proper standard ways to (1) debug and (2) simulate the PIC code. This becomes important when we have really huge and complex programs.

I think there is some sort of simulator for PIC but I can't find a link which says "The simulator does ABC and this is how you use it...". So what do the experts here say?


texts: what are the possibilities for Op amp's power supplies?

texts:
I am looking for a way to remap a voltage between 0..24 volts to 0..5 volts in order to read this voltage in a microcontroller ADC.For that ,I am intending to use an operational amplifier as an attenuator.Assuming that i have read several posts that couldn't solve my problem i have to ask:

Are they any IC that can convert 24 volts to -24 volts to provide  negative supply to the Op amp?if so can you suggest an op amp reference that could stand to a 48 volts?
Is it possible to provide a non symetric voltage to an Op amp in the positive  and negative
supply like for example 24 volt and -5 volts


texts:
I have a signal which can have a different offset voltage based on the requirements. However, I need the voltage to start at zero.

Since the offset is variable, I was hoping if there are any techniques/ideas how to design a analog circuit which makes a variable offset in such a way that is  ensured that the voltage is always positive. So starting at zero.

I am aware that I might be asking something which is impossible.
But hope someone designed something similar


texts: Bluetooth SPP (Serial Port Protocol) and Cobra Tag

texts:
I have been trying to build something similar to the Cobra Tag (Check out the video). I have written a prototype android app which uses SPP to connect to a bluetooth module and exchange commands, which is working great. But, i have a few queries

From what appears, does Cobra Tag also use SPP or any proprietary custom profile ?
I am able to connect to a single device over SPP and do the data exchange, how do i go about connecting to multiple devices simultaneously. Does Bluetooth/SPP support that ?
Should i be using any other bluetooth profile/protocol which would be more efficient for this purpose ?


texts: Strange leak problem in simple tone control circuit

texts:
I built the following circuit (physically):

V1 is my audio signal and the circuit is a simple tone and volume control. When both the volume and the tone pot are turned all the way down (so each wiper is closest to ground), some small amount of the signal can be heard on the output. It decreases as I turn the volume pot up again.

With higher values for C1, this gets worse. With lower values, say <1 µF, this behaviour disappears, however, the cutoff frequency of the low-pass filter will be too high for my purposes.

I'm at a loss as to why this happens. One reason that surely contributes to it is that I can measure a residual resistance between the Rvol wiper and ground even when it is fully closed (around 5 Ohms). I believe this is common though. I've tried to increase the value for Rvol, thinking that the output voltage between those 5 Ohms will then be lower, but this didn't help.

Any help would be greatly appreciated.


texts: Difference between PCS and PMA loopback in transceivers

texts: Can someone let me know the difference between PCS and PMA loopback used in XILINX transceiver IBERT testing.


texts: How to explain the logic of designing a linear voltage source from a current source by using transistors?

texts:
I know this is not an easy question but at least I thought someone may relieve my pain by explaining the big picture.

How is a voltage source made from current mirror or a constant current source by using BJT or MOS transistors? Can you give an example with a big picture explanation. Is that how linear voltage regulators built?


texts:
I'm working on upgrading an ancient oven that we bought second hand, which came with almost zero documentation.
I have identified two fans one is exhaust fan and the other is a circulation fan.
Is it common practice for the circulation fan and the exhaust fan both run continuously, or should I treat the exhaust as a "cooling" loop when designing the control system?


texts:
simulate this circuit – Schematic created using CircuitLab

When designing combinational circuits using MOSFETs, it is right to say that if two of them(identical) are in series then their channel length gets doubled but their width remains unchanged?

Edit 1 : Inserted the schematic


texts:
I was trying to understand the SG3525A (from ST-Micro) working. So I built a circuit as shown below. I read various articles on this chip, it mentions that to know whether its working or not, it can be checked using the Ct pin which would show the Sawtooth wave.

In this circuit, I have the following questions.

The Vref pin is supposed to provide a 5V precision reference. Its not detectable in the oscilloscope. Is it normal?
What is the maximum input voltage that can be given to each pin.
In many reference circuits I found that the compensation pin is connected with a series capacitor and a resistor and it is fed to the inverting input. Why is it done and how is the values of capacitor and resistor is selected?
What is the work of the oscillator pin? Am I supposed to see square wave in the scope with the set frequency using RC?

Please help me out in finding the answers. Thank you!!


texts: Why isn't it dangerous to put finger in light socket?

texts:
This is in reference to "Why three prongs?".

Why does this hold true: "Curious kids might still stick their finger in a light socket and receive a shock, but the unwanted current was directed through the length of their finger and caused no danger of heart-stoppage."


texts:
Here is the schematic for LFSR (Linear Feedback Shift Register) polynomial division by \$w(x) = n_3x^3 + n_2x^2 + n_1x + n_0\$

\$\oplus\$ denotes adder without carry logic, (nx) denotes multiplicator by \$n_x\$ coefficient and boxes are flip-flops.

The drawback of this solution is that polynomial \$w(x)\$ has to be of constant degree, otherwise the circuit won't work.

Are there are any solutions to build LFSR division unit which is able to divide by polynomial of non-constant-degree (there is specified maximally allowed degree)? Or maybe some not-LFSR units?


texts: I saw this sensors in an YouTube video where these things were glued to Glenn Maxwell's dress and his whole movement was monitored for the making of a cricket game.


texts:
Long story short, I want to have a relay turn OFF when the output of a 4017 goes high.

So I installed an opto-isolator, connecting the LED to the output of the 4017, ie "on" until the ouput goes high. That's when I discovered the 4017 will output a voltage to light an LED ... but the off does not connect to ground !

Thus, I installed a p-channel FET wired to ground via a 1.2meg resistor. IN THEORY, (I've yet to reach that stage) the high output of the 4017 into the gate should make the voltage flow low enough to de-energise the relay.

But I still can't get the relay to turn on. I measured the voltage from +ve (12v) to collector of opto, and only got 7.5v. So what to change? The LED resistor? The gate resistor? Add another transitor to the opto emitter with a pair of resistor on opto output?

simulate this circuit – Schematic created using CircuitLab

When switch is closed, it connects 9v to circuit. This switches on LED via FET, and opto transistor turns on relay. The contacts close, supplying AC to the LED driver, which then powers circuit as SW1 is released. (D2 and D4 simply stop 9v reaching LED output drivers, and stops said driver from trying to 'charge' the 9v battery which is at a lower potential. IN THEORY, when the 4017 goes high, it 'affects' the gate, and the output drops to about 2v, so relay loses holding current

(Whilst typing this, have realised the opto may now be 'redundant', and I can wire the relay directly to the 2N3820! But still be interesting to discover what's wrong with current design)


texts: 4 wires from from power brick to 2 wire fixture

texts:
I am attempting to hook up a 12-volt water pump to an 110 outlet.

I bought an AC/DC switching adapter to make the conversion. Intended on wiring a black and red wire to a black and red wire. But my power brick also has a blue and white wire. I'm assuming these are some sort of feedback wires for the protection of PSU's but I don't know what to do with them.

When I ignore them and just hook up the red and black wires the power supply decides to stop sending power through, it shoots small test bursts of electricity through and never powers the pump. is there an easy way to override the protection mechanism if that is what is happening? If that is not the issue what are the white and blue wires?

Power brick specs:

brand: MeanWell

model#: GS220A12

Input: 100-240VAC, 50/60Hz, 4.0A

Output:  12v 15A, 180w MAX


texts:
I have come across the following problem a few times in the past:

You have a break-out board where some pins have already been pulled up or down for convenience, e.g. RESET pulled high to keep the board running even when you don't connect the input pin to your MCU. Now you want the opposite standard behaviour when the pin is not set (e.g. in sleep mode or when no power is applied to the MCU). How can you achieve this? The only answer I can think of is to (physically) remove the pull-up and hook a pull-down between the MCU and the break-out board. I would rather not mess with the SMDs on the break-out board, so is there another solution?

A concrete example is an audio amplifier that is by default on and needs to be pulled down by a pin to switch off. Now when I remove power from the MCU, it automatically turns on again and pops audibly.

Yours gratefully
Jerome


texts: Is it typical for power adapters to vary by such a margin? I just purchased this PS and my multimeter is showing 25V ±0.001 V. Is this typical or is the device defective?


texts: Should I Remove the Power When Unplugging Components From an Arduino?

texts: When I am done with a circuit and want to build another, should I remove power from the Arduino or can I just remove the unnecessary parts and start plugging in the necessary parts?


texts: Powering up an ESP32 with IO extender (MCP23017) and two of 8 channel relays from an external 5 V, 10 A power supply

texts:
I'm working on a project that needs an ESP32 board, IO extender (MCP23017), two of 8 channel relays and some sensors, I've powered up all of the parts from a stable 5 V, 10 A power supply as shown in this block diagram:

Added: More detailed wiring diagram:

After connecting all the parts to the external power supply, the ESP32 gets too hot and then it burns after 10 seconds.

Could you please correct my connections, if there are any mistakes?

The sensors are:

2 DHT22
2 MQ135
2 Magnetic switches
Ultrasonic

Thanks for your time.

Update: The connections were correct. I've just added voltage dividers and it worked correctly.


texts: How to interpret MAX7219 timing diagram?

texts:
I'm trying to connect this module to atmega32u4 (16 MHz):

Everything seems mostly working, but I have a question:
how much time is needed for the latch to take effect?
I.e., is a delay needed between SLAVE_DESELECT and SLAVE_SELECT in the following example?

#define SLAVE_SELECT    PORTB &= ~(1 << PB0)
#define SLAVE_DESELECT  PORTB |= 1 << PB0
...
DDRB |= 1 << PB0;
PORTB |= 1 << PB0;      // begin high (unselected)
....
  SLAVE_SELECT;
  for (int i = 0; i < NUM_DEVICES; i++)
    writeWord(0x0A, 0x0F); // brightness
  SLAVE_DESELECT;

  SLAVE_SELECT;
  for (int i = 0; i < NUM_DEVICES; i++)
    writeWord(0x0C, 0x01);
  SLAVE_DESELECT;

(SCK frequency is 4MHz in my configuration.)

Also, I do not understand how to interpret the timing diagram from datasheet:


texts: Does the addresses of an arbitrary peripheral register can be used to store data randomly during code execution?

texts: I need to make sure of the concept of volatile qualifier in C-language. so volatile is used when we don't want the compiler to optimize the variable being identified as a volatile or in other words volatile tells the compiler not to care when or where the variable may change and just change it. So when we define a peripheral address we use define for example #define PORTA_DATA_R (*((volatile unsigned long *)(0x4000.000))) if I initialized it to a certain value in my code and made some operations then completed with my code can the compiler randomly uses this address for example to store other data in it if it was needed or this address is only specific for the data register of the port and can't be used except for this purpose.


texts: Two voltage sources - selecting with digital signal

texts:
I'm trying to build a fan controller based on Arduino.
It will be (at least I hope so) possible to either control with pure PWM or voltage regulator based on buck converter.
Now what I'm trying to do is:

build a circuit that will allow me to choose, if I want to power the fan with full 12V (for PWM fans) or buck converter output (for 3-pin fans).

Selection should be possible with Arduino digital output (either LOW or HIGH).
I to google some solutions and tried to simulate some circuits based on diodes or transistors, but it wouldn't work as I envisioned. I lack knowledge to fully design what I want.
I would like to get i either:

sample circuit (if possible simple and cheap)
phrases to google (I'm    not native english speaker and maybe I'm
not looking for the right thing)
some insight if my "vision" is achievable and makes sense
(alternatives?)

Thank you!

EDIT.
According to "pure PWM" or "12 V".

4-pin fans use 12V supply all the time with additional cable to control via PWM.
3-pin fans on the other hands should be controlled by varying input voltage.

This is conceptual image of what I'm trying to do:

Input voltage to buck converter is 12V.

Thank you for tag suggest!


texts:
I've come across this circuit diagram in Biomedical Digital Signal Processing by Willis J Tompkins and in the description it says it is to do with ECG amplification. The input to the non-inverting terminal comes from the output of an instrumentation amplifier. But I am not exactly sure what is happening in this part of the circuit. Would anyone be able to give a brief overview of what is happening or point me in a general direction of where to look further?

Thanks


texts: How to find a number a such that an input 10e^-at to a transfer function does not have a Ke^-(at) term in the output

texts:
I have a transfer function, \$H(s) = \frac{-16(s+4)(s-1) }{ (s^2+16)(s+2)}\$.
The impulse response is \$-16*(-3/10 * e^{-2t} + \frac{13}{10} cos(4t) + \frac{1}{10}sin(4t))u(t)\$.
I am supposed to find an input of the form \$10e^{-at}\$, where \$a\$ is a positive number, so that the response does not have a term of the form \$Ke^{-at}\$. I believe \$a\$ is not necessarily the same number in the input and response.
I am sure it is not a trick question. So far I have written out the transfer function \$\frac{(s+4)(s-1)}{(s^2+16)(s+2)(s+a)}\$. I don't think the constants are important for determining the value of \$a\$. My strategy is either the \$s+2\$ term would have to be eliminated or a conjugate \$-Ke^{-at}\$ would have to be added to the response to cancel them out. I have no ideas for eliminating the \$s+2\$ term. I tried to find a number that would make \$(s+2)(s+a)\$ into \$\frac{s}{(s+y)^2+w^2}+ X\frac{w}{(s+y)^2+w^2}\$ in the partial fraction expansion. I tried to use the Heaviside coverup but I didn't have any success. Any ideas on how to proceed would be appreciated.


texts: LM317 to create constant current of 2mA?

texts:
I have a circuit where I want to have a constant current of 2mA through a variable resistor.  I've been told that I could probably use a LM317 as a current regulator, with one resistor on the ouput.  But I've read some places that the LM317 takes minimum 5-10mA load to function correctly.

How can I achieve a constant current output of 2mA when I don't know the resistance of the variable resistor?

The input voltage is about 2.755V. Output voltage doesn't matter, just the current.

Here's an image to my feeble attempt at a schematic:


texts: How come the value in my RAM of DS1307 RTC become zero?

texts:
I'm using the 56 bytes of RAM in the DS1307 to store some data. My DS1307 is connected to the PIC18F46K22. But after running a few days, all the data inside the RAM will suddenly become zeros. The time in the RTC is still accurate but it's just that all the data in the RAM has become zero.

I have check my coding but cannot pin point what's the problem. Do you guys have any idea? I did not reset it to zero from my coding.


texts: JK flip-flop timing diagram positive edge triggering

texts:
Welcome I would like to ask you for explain this timing diagrams. I got some assignments for reading timing diagrams and solved it but I am not sure if it is good.

I have JK flip-flop which is positive edge triggering (from low to high). Here is task

If I am not wrong the input is only J and K = 0 right?

Here is my solution

Guys, what do you think about it? Is it good?


texts: I have a remote controlled airplane that I am putting LED lights on. The power supply is a lithium polymer battery that is rated at 22.2 volts and 4000 miliamps. I have an LED that is rated between 12-19 volts. How do I figure what size (wattage) and what value resistor to use. I have heard about Ohm's law and am familiar with the equation but obviously don't know how to apply it.


texts:
I'm relative new to this, I have a question about designing the power for a circuit.
What does efficiency mean for a voltage regulator?
Here's an example
Let's say I have an LDO that create 5V at 2A with an input of 10V at 1A with an efficiency of 50%
Does that mean that the LDO can only output a maximum of 5V at 1A and the other 1 A is lost as heat?
Similarly, if the efficiency is at 60%, does the LDO can output a maximum of 5V at 1.2A?
Thank you for the help


texts:
I am very confused as to why current changes as resistance is added. Where does rest of the current go?

Let's say I have 100V voltage source. Which by chance produce 10A . But the light bulb can only handle 10mA. So I add resistance in between thus decreasing the voltage via V=iR. Because voltage is lowered, current decreases. But 10A produced by 100V does not match the incoming current of lowered current. Where does rest of the 9.990A go?

Correction: If voltage source is current source that produces 10A constantly


texts:
I bought this board a while back:

(source: seeedstudio.com)
http://www.seeedstudio.com/wiki/GPRS_Shield_V1.0
I mistakenly connected positive and negative instead of each other and the yellowish thing near the power select on the board (477 j / 110 m 3) fired literally and fell off. When I correct it, it works fine.
My questions are:

What is that part name and use on the board? Is it some kind of fuse?

Can I just replace it? Is it necessary? The board works fine without it.

The firing keeps me thinking, is it safe to put it in the car? Is it possible that fires up again?


texts: Undervoltage protection strategy for Li-ion batteries

texts:
We are using a Li-ion battery with built-in safety PCM (Enix MGL9070), a gas gauge to monitor the battery voltage (STC3115A from ST) and a battery charger (bq24133 from TI).

To protect the battery, the current strategy is:

when the gas gauge detects that the battery voltage is below 3.2 V, a warning is shown to the user (low battery) when the board is powered up. The system will go to sleep and the power consumption will then be quite low (100 to 500 uA).
the board then relies on the battery's built-in safety PCM to cut-off the power if the voltage goes below 2.75 V.

We initially had also a voltage supervisor at 3.2 V which could pull down the enable pin of the main regulator, so the board power consumption could drop down to almost nothing. This voltage supervisor gave us troubles (bad filtering, high voltage drop when powering other peripherals which triggers it, etc.)

The problem that we would like to solve is this: A user empties the battery down to the low battery warning and then leaves the system unattended. A year or two later, the user tries to charge the system again to use it.

Questions:

is it safe to rely on the built-in safety PCM of a Li-ion battery?
does it damage the battery to actually reach the built-in safety PCM and can it be then safely charged again?
would it be good design to do everything possible (using a voltage supervisor, for example) not to reach the built-in safety PCM of the battery?
does a better strategy exist?

EDIT 1:
It is a general consumer product.


texts: Determine an 8-SOIC MOSFET for boosting current capability

texts:
I am a complete electronics newbie.
I recently designed a set of PCBs for LED tail lights. I have a sequence controller for them that can can control 28 channels at 260 mA. What I want to do is boost the current on only a single channel. I know I can boost a single channel with a single P-channel MOSFET and some resistors. What I really want to do is redesign my board to use something in a 8-SOIC package and maybe a bit more efficient. I know it can be done I just don’t know how to calculate what 8-SOIC package I would need to accomplish my goal. The image below the schematic shows a board with the ICs I’m looking for but I can’t make out the numbers. There are 28 channels (inputs) and 14 ICs that convert each input to 3 A max output. There are also resistors on the bottom of that board but I can’t make those out either.
To recap:

I want to boost a (or multiple) 12 V 260 mA ground switched control channel(s) to a max of 3 A.
I want to use an 8-SOIC package to accomplish integration into my board design to keep components and form factor smaller.

28 260 mA ground switched inputs boosted to 28 3 A outputs. This is not my board. I would like to integrate these ICs into my board design.


texts: Can smartphones connect to bluetooth mesh networks as nodes?

texts: In an existing Bluetooth Mesh network where there are a few nodes that communicate with each other. Can an android smartphone connect to that network (where necessary) and be a part of such network as a node broadcasting some data to the other nodes?


texts: What is In-circuit debugger and In system programmer

texts: On many boards I have found that there is a circuitry called In-circuit debugger and In system programmer. What are these and how they are related to JTAG? I understand JTAG is also a kind of hardware debugger. Shall appreciate if someone can enlighten me.


texts: Why is RS-422 interface interference insensitive?

texts: I am trying to understand differences between RS-232 & RS-485. I just don't grasp what is the core principle behind RS-422 inteference resistance? Is it number of wires (4 instead of 3)? Is it because these wires are twisted?


texts: Which NXP ARM processsors have LIN capability?

texts:
I am looking for potential alternatives for my current STM32F091 uC (they currently can provide a very lousy stock).

Searching through datasheets and reference manuals, I can't pinpoint where to look when I want to find NXP uC-s that have LIN protocol capability. DigiKey suggests that only MK22FN 1M0 AV LK 12 has LIN but I couldn't confirm that in the Datasheet.

I am more interested in low pin count and/or small footprint uC, 64...80 WLCSP, QFN...

So any ARM uC family will do. ARM and KEIL support is more crucial.

Thanks a bunch!


texts: Getting the right configuration of an HC component with an LED

texts:
I am using an 74HC299 shift register and would like an LED on each of the 8 outputs.  The LED I chose is the SML-LX1206YC-TR.  I have a 100ohm resistor in series with each of the LEDs and each are tied to one of the 8 outputs. The LEDs seem to light initially but eventually fade away, I'm guessing as the chip warms up.

The LED has a forward current 30mA with a peak current of 60mA and a forward voltage of 2V. I'm guessing this is way to much for an output of the 74HC299 to drive.  Now that I am looking at the data sheet on HC components I'm thinking they can only drive around 4mA in the high state.

So, what is the correct chip to add between my 74HC299 and the LED to drive it properly?

Note my entire design is based on using the HC(T) family of chips.


texts:
I am budding engineer working on RE testing. I know about series termination. We are using 50 ohm as trace impedance. We are getting large reflection and emission in SD clock. I used series resistor values upto 33 ohm as suggested in datasheet. But If I put 100 ohm emission is reducing. Why????

Trace impedance value is 50 ohm. If we match the output impedance of input driver to that value, then I will get minimum reflection.
But If I increase the value higher (approx. 100 ohm), then I am getting less reflection. Why????


texts: How can I check if two outlets are connected to the same electrical circuit?

texts:
I have some internet problems, and I was thinking to buy a PowerLine, that will help me extend the WiFi range. The thing is, to get this PowerLine working, both need to be conected to the same electrical circuit. So, one of my outlets is in A room, near the router, and the other outlet is in the B room. How can I check if the outlets are connected to the same circuit?

I live in an apartment, and I have a circuit breaker. Here is a photo:


texts: Is the Garmin GPS 12 on board 16.368 MHz oscillator GPS controlled?

texts: My plan is to use my old Garmin GPS 12 as a frequency standard. As it has no pps (pulse per second) output I am thinking about using the on board oscillator as the clock source. So my question: Is the 16.368 MHz oscillator that is controlled by the big crystal on the circuit board (see image below) "GPS disciplined" and thus has a high accuracy and stability?


texts: Why are Marx Generators built like that?

texts:
Short introduction:

A Marx Generator is a capacitor arrangement that transforms a DC input voltage of let's say 1 to 20 kV to a multiple of that. Capacitors get charged in parallel and when they reach the break down voltage, they discharge themselves over spark gaps and essentially get connected in series leading to a much higher output voltage (theoretically input voltage times capacitor amount).

I built such an arrangement, but the sparks it produces are kind of small. The easiest thing would be to measure the output, but I don't have a multimeter for voltages that high. Additionally I also want to understand the theory behind it, which is why I wrote this question.

This image is a circuit diagram of a Marx generator. During my research I found several diagrams for Marx generators. They differed a bit, but all of them had the problem described further down. The image will help me describing my problem:

Let us assume that the DC input is 8 kV and the resistors (Rb and the 10 resistors without text) have a value of 1 Mohm. According to my knowledge, that would mean that the first capacitor is charged with 8 kV and a resistance of 1 Mohm which would be perfectly alright. However as far as I know, the 2nd capacitor isn't charged with the same resistance; it is charged with 8 kV and a resistance of 3 Mohm (Rb + 2 times resistor without text). The third would get charged with 8 kV and 5 Mohms and so on.

My question is the following:

Is my assumption about the charging behaviour correct?
If yes, why would someone do that? Why would you connect the resistors in series instead of in parallel, just like the caps? Why would you want the caps to not get charged with the same current, so they achieve break down voltage at the same time?
If no, what is my mistake?

Thank you for reading this far.

I am pretty new to the field of electrics, so please be patient with me.

Edit: As I don't know how to post an image in a comment, I will put in here.
Some of you mentioned that the resistors would be exposed to the full voltage if placed in parallel too. Have a look at the picture. Wouldn't that fix the problem?

Edit again: New circuit diagram


texts:
I have a task where I want to measure a 24Vdc motor's rotational speed using an AC tacho attached to the same shaft of the motor. When running the motor at full speed, the tacho generates around 9Vac at a max frequency of around 1kHz. So I was going to feed this through a precision rectifier and ADC to sample the digital value with MCU but this got me thinking:
If I am only interested in measuring the speed of the motor, do I only need to measure the frequency of the tacho signal? I don't think I need a rectifier and could use a zero crossing detector and counter to calculate RPM?
Or is it more complex and does the voltage magnitude have to be considered too as this changes with frequency?
How is this achieved in current technology?
EDIT
I have measured the AC tacho signal. At full speed it generates around 8.6Vac at a max frequency of 900Hz. When turned slowly by hand it produces approx 150mV at around 25Hz although I won't be running the motor this slowly so I suspect the low end voltage to be at least 0.5V to 1V.
EDIT 2
I am thinking of using an op amp comparator to convert the positive half of the AC tacho waveform to a square wave signal. So the square wave is high during positive cycle, and low during negative cycle.
I am thinking of measuring the time between the pulses to calculate the motor's rpm. I want to use a 16 bit counter that starts counting on the rising edge of the square wave pulse and capture the counter value during the next rising edge. How can I convert this counter value from 0 to 32768 to an rpm range from 0 to 4000?
Thanks for your help everyone!


texts: Looking for a transparent conductive spray/paint/ink

texts:
I know there are conductive sprays available, but these are strongly coloured due to the metals inside them. I am trying to make a (dry) wooden surface capacitive, but would like to have the feel and look of the wood remain intact. Therefore I would like a spray/paint/ink that is transparent and conductive and preferably also water-resistant.

Does anyone have any ideas or suggestions?

P.S. I'm using it to measure capacitance all across the wood (which is 1.5m in length) so the resistance per cm^3 doesn't matter. It could have a nice effect if the capacitance differential is significantly different at various distances from the point I measure.


texts: Convert Eagle v6 BRD file for autorouting?

texts:
I've just finished designing a PCB in Eagle. Now I want to use the freerouting.net autorouter to route my board (because Eagle's default auto is crap, sadly).

The one problem: converting my Eagle PCB in BRD format into the DSN format used by the freerouting.net router. There seems to be no way to export a BRD as a DSN.
I've tried using the brd_to_dsn.ulp script on the freerouting website, but it's broken.

How can I convert my BRD to DSN? Alternatively, is there any good autorouter that can accept Eagle files?

Any help is greatly appriciated!


texts: Alternative to lead-acid battery on power wheel toy

texts:
This might be a silly question, but here I go. My son’s power wheels car battery (12v 9.5Ah lead acid) is gone and, here in Venezuela, they are pretty difficult to find, not to mention the high prices. So looking for an alternative I found that a local computer store have those laptop battery packs on sale (10.8Vdc 2600mAh/28.08Wh Li-Ion) they also sell external chargers for this battery pack, and I started to wonder if I can build a battery pack that works properly on the power wheels. I been reading about, it takes more than basic knowledge on batteries to do that, so I decided to post this question.

Is it possible to make an arrangement of these batteries to power this type of car?

I know that these type of batteries needs circuitry to prevent overcharge (over 4,2v), prevent over discharge (below 2,5v), charge balancing, and prevent over current (more amps than they support during discharge).
What my limited knowledge (mixed craziness) tell me to do is, buy 4 battery packs, 4 chargers (that will solve over charge and charge balancing problems), and use them in parallel to power the car (10.8Vdc 10400mAh 112.32Wh), I suppose I’ll need some circuitry to prevent over discharge, and I don’t know if I need something to limit current since 10.4Ah are over original battery 9.5Ah.

And yes, crazy as it sounds, I can buy 4 laptop batteries plus chargers by half the price of original power wheels battery.

Thanks in advance for your help, and sorry for my English.


texts: Why does the 741 op-amp saturate to the top rail when inputs both grounded?

texts:
I created the following circuit in MultiSim:

It shows a typical 741 op-amp with voltage rails connected to +/-5V and both inputs grounded. With (for all intents and purposes) equal voltages at the inputs, I would expect the output voltage either to be 0V, or very close to it (perhaps ~800mV or less).

Instead the op-amp saturates at the positive rail (or at least maximum Vout). Why not the negative rail? Why not 0V?

Would connecting pins 1 or 5 have an effect?

Regards


texts: Creating the proper Vref for a thermistor

texts:
I have a 10kΩ @ 25°C NTC thermistor for temperature measurement. Problem is, I only have 3.3 V on the board and the ADC inside my micro-controller has a Vref of 1.6 V.

I tried to make a voltage divider circuit (with two 10 kΩ resistors), then have the 2nd divider circuit with the thermistor and another 10 kΩ resistor to ground:

3.3 -------R1--+--(Therm)--+---ADC pin
               |           |
              R2           R3
               |           |
              GND         GND

R1 = R2 + R3 = 10 kΩ

This didn't work. Is there a way to do what I need with resistors alone? Seems like there should be.

edit
Thanks to Steven, I was able to get the solution. I'm editing my original question so others can see the complete solution.

So I actually wanted the limit to be 122°F/50°C, and that (via lookup table for my thermistor) = 3500 Ω. Solving for R3 in the traditional voltage divider equation shows 3300 Ω. Now the issue is how to measure the resistance of the thermistor so the
Steinhart Hart equation can be used to calculate the temperature. Here is my code (excuse the python)

Vcc = 3.3
Rdiv = 3300
To = 298.15     # K = 25C
beta = 3950
r25 = 10000
adc = readADC()

V = float(adc) / 1024 * 1.6
R = (Rdiv*Vcc)/V - Rdiv
r_inf = r25 * math.exp(-beta / To)
tempK= beta / math.log(R / r_inf)


texts: Why choose a PMOS over an NMOS or vice versa?

texts: I know it sounds dum and that I sound dum but theres such a large amount of MOSFETs out there, there are N-channel and P channel devices that have extremely similar functionalities, capabilities, rating's etc. why choose a PMOS or NMOS over the other when all the ratings are practically the same?


texts: Why does a current mirror have low input resistance?

texts: I know that the output resistance needs to be high otherwise the output current will vary depending on the load.  However,  I don't understand why the input resistance needs to be low?


texts: How can I use a 2N2222 transistor as a temperature sensor?

texts: I'm supposed to use a TMP36 transistor for a class to read the temperature of the environment, but I only have a 2N2222 transistor; the Arduino will have an analog read of it, but the numbers won't change even if I heat it up. Am I screwed or can I fix this?


texts: PICAXE very short interval timer (for playing sound)

texts: I have a PICAXE (08M2) that I'm using to play sound, using the Roman Black algorithm mentioned in the answer to this question. My question, then, is this: How do I get the PICAXE to wait for the appropriate time interval (1/bit rate = 1/44100 = 22.6 μS) (I think) between each bit? As far as I know, the WAIT command only goes down to one millisecond, much longer than I need. Furthermore, I'm loading the sound bits in from an I2C EEPROM chip (with a 440kHz bus), so how do I factor in the time it takes to load each byte in from there, perhaps into a 4-byte (32 bit) buffer? It seems to me that any slight variation in the timing of the code would result in the sound getting pretty distorted, so how does one compensate for this? I'm (obviously) pretty new at this, so thanks for any insights!


texts:
I recently replaced a motor run capacitor in an old AC Fan. The replacement capacitor was of wrong value having previously been 2uf I replaced it with 6.3, It worked for about 2 weeks but then it started to run very slowly (barely even spinning) and hum. My first instinct was to replace the capacitor again with the right value this time as the symptoms where of capacitor failure however after replacing the capacitor again the fan still shows the same symptoms. I suspect that the motor has gone bad due to the incorrect capacitor value, any ideas on how I can fix it? If possible I would like to repair the motor and not completely replace it as its an antique fan and I would like to keep the parts as stock as possible.
Thank you.


texts: What 7400-series logic variants include input clamp diodes?

texts:
When prototyping, I often use spare 7400-series chips I have lying around. I have a good variety of chips, including many 74HC and 74AHC parts, as well as older varieties like 74LS.

From time to time I like to implement "quick and dirty" 5V to 3V3 level conversion, and one easy way to do this is with by interfacing a 5V signal to a 3V3-powered chip with a current-limiting resistor. The idea here is that the "input protection" clamp diodes present on the inputs of a logic chip will conduct any excess current on the input to VDD, limiting the input voltage to the supply voltage (3V3), accomplishing 5V-to-3V3 conversion on the input with only a single resistor.

I've looked around the web, and I haven't been able to find any resource indicating what 7400-series variants include these diodes on their inputs. Of course I can look at individual datasheets, but I have a suspicion that certain variants (e.g. 74HC) usually include them, while other variants (e.g. 74AHC) may not. (these just are made-up examples)

Does anyone know what the general situation is, or if there is any definitive answer for this? And does it depend on the manufacturer?


texts: Relationship between voltage and current of a power transformer

texts:
I'm currently analyzing data from a power transformer and I stumble over the circumstance that voltage and current is almost not related to each other. Since I'm not an engineer I wonder why is this?

From my knowledge, the voltage must drop when current flows but I know it is possible to build voltage-stable circuits. This is probably also valid for transformers because I think nobody would like to have a different voltage when (hundreds) ones neighbours need power as well.
Is this (simple) explanation correct or is there another reason?


texts:
Can anyone identify the SMD Code and manufacturer part number of the following device?

Code t9GRID

Review photo


texts: How to correctly calculate the Rfb value in AD5933

texts:
I was reading the datasheet of AD5933, and I did not understand a few things about the calculation for the Rfb value and other things.

This is the Rfb equation:

How do I find the value of Zmin?

I intend to power the AD5933 with 5V, use the 1st Output Range (3Vpp in this case) and PGA gain = 1.
With a frequency sweep of 1K Hz up to 100K Hz:
Internal oscillator: MCLK = 16.776 MHz
fSTART = 1000 Hz
∆f = 1000 Hz
Increments = 99

In addition, I will use a high pass filter with a cutoff frequency of 100Hz, a circuit with a current source controlled by voltage (1mA), and an instrumentation amplifier INA118 (Gain = 2). This circuit will use 4 Electrodes. Similar to this:

In AN-1252 APPLICATION NOTE, page 3 of 12, it is said that for range 1 (Adding external op amp) Zout is equal to "> 100 Ohms". And on page 5, The maximum ratio, ZMAX / ZMIN, for my case is x45. Right? If it is correct. How to calculate Zmax and Zmin for "> 100"?

Furthermore. What is "RCal" for? If I do not use it in any equation.

In the example on page 7, the Zmin value is 4.7K and the Zmax value is 47K. Why? I dont understand.


texts: How does the magnetic field of an inductor affect the operation of a DC circuit?

texts:
I was reading about the operation of inductors in DC circuits on the website All About Circuits, and I'm a bit confused on how an inductor operates in a DC circuit.

So far, I understood that any current flowing through a conductor will produce a magnetic field force and, consequently, a magnetic field flux, which is perpendicular to the conductor. And by making the conductor coil-shaped, the magnetic field flux will increase because it gets concentrated.

So far this is kinda clear.

But then two sentences confused me:

  Whereas an electric field flux between two conductors allows for an accumulation of free electron charge within those conductors, a magnetic field flux allows for a certain “inertia” to accumulate in the flow of electrons through the conductor producing the field.

What do they mean by inertia accumulating in the flow of electrons?

What I understood from this sentence is that eventually the magnetic field force will become so high that it will prevent any more current from flowing. However, I know that magnetic field flux is perpendicular to the conductor, so I don't see how it can prevent the current from flowing. This is why I'm confused and why I think they mean something else by inertia.

  As the electric current produces a concentrated magnetic field around the coil, this field flux equates to a storage of energy representing the kinetic motion of the electrons through the coil.

From this sentence I understood that magnetic field flux is the equivalent of energy in the inductor. And of course this energy was taken from the circuit's voltage source, so if this energy becomes equal to the energy supplied by the voltage source, shouldn't it, eventually, prevent any more current from flowing through the circuit?

I'm really confused in here...


texts: Is a pullup resistor needed on an Inverter output?

texts:
So I assume the answer is no but want to be 100% sure.

I will already have a pulldown resistor on the inverter input,
the output is connected to 555 timer trigger input (it triggers on falling edge), typically when a transistor or switch is used to pull the trigger input to ground a pullup resistor is needed.

Will the inverter hold the input high at Vcc?


texts: Parameters needed to identify the correct capacitor

texts:
In a traditional power switching supply PCB like this one,

(source of the image)

ceramic capacitors are sometimes present as discrete components. They appear as:

(source of the image)

I would like to correctly identify them, when no schematics is available, to replace them if/when they get damaged. In the case of the above image, these parameters can be obtained:

the capacitance 822, which, according to this answer, is: 82*10^2 pF = 8.2 nF;
the tolerance Z, which, according to this table, is -20 %, +80%;
the voltage rating 1KV, which is 1000 V.

(A letter can occasionally appear above these parameters, and I do not know its significance).

Is any ceramic capacitor, which has these same values, suitable to replace the above one, or other features must be taken into account when replacing such a component?

This question is related to a previous one.


texts: USB C or other compact connector for 19 identical, general purpose lines?

texts:
I'm building an LED lighting system that requires around 16 connections to an Arduino (15 LED power supplies plus a common ground line), and I want to clean up the cabling. It's important for my application that the connector at the ends of any cabling be small and neat.

Essentially I would love to use a USB C cable – without any of the internal chips/resistors – simply to carry 19 identical general purpose wires. Then I could use standard USB C breakout boards at each end of the cable, and use the USB C cable as a simple wire conduit with nice connectors.

For all my searching, I can't find anything like this...

Does something like this exist? Is there an obvious solution to this problem that I am failing to see? Perhaps a different type of common connector that I'm not thinking of?


texts: How can I add (kHz to MHz) high voltage signal to a high voltage DC offset?

texts:
I am working with MEMS structures and need to move a device (switch) in a operating point with quite high offset. (150V DC offset and a voltage swing of 60V) To generate the high HF Voltage (up to 5MHz) we use a System WMA-300 from Falco Systems.

Do get this DC offset on this system I was inspired by this answer to use a transformer (e.g. WB1010) to offset the input voltage.

In the end I want to record a response function of the device depending on the frequency (between 1Hz ideally (but 5kHz is fine) and 5 MHz) of the driving signal (between 120V and 180V). The signal that needs to arrive at the MEMS device should look as follows (Sorry for the badly drawn chirped sine).

When thinking about the solution, I was mainly afraid that somebody would operate the system wrongly applying a low frequency signal to the input coil thereby burning the primary coil. (50 Ohm source impedance, and 0.3Ohm coil resistance)
Do I need to prevent this by adding a High-Pass filter in front of the primary coil?

Is there a better idea how to create this signal?

There is a better way to do it (see the accepted answer), seems the transformer is overkill.


texts: ATtiny2313 refuses to be programmed after setting CPU clock to 500kHz

texts:
The other day I was writing a program for an ATtiny2313. Once it worked I decided to test it at the various clock speeds that are available and programmed through setting the LFUSE as described on page 159.

The default clock speed is 1MHz;
so I tried 8MHz next and all worked fine;
Then I set the clock speed for 4MHz with the /8-prescaler resulting in 500kHz clock.

Although the controller runs the program at the expected speed, my programmer refuses to reprogram the controller since. avrdude (5.11.1) just throws the well known: 'Yikes!':

avrdude: Device signature = 0x000000
avrdude: Yikes!  Invalid device signature.
         Double check connections and try again, or use -F to override
         this check.

I tried adding the -F flag, but of course that didn't either.

Here are some code sniplets I used and changed the clock speed as expected:

// 0.5MHz
FUSES = { .low = 0x62   , .high = HFUSE_DEFAULT , .extended = EFUSE_DEFAULT , };

// 1MHz (default)
FUSES = { .low = 0x64   , .high = HFUSE_DEFAULT , .extended = EFUSE_DEFAULT , };

// 8MHz
FUSES = { .low = 0xe4   , .high = HFUSE_DEFAULT , .extended = EFUSE_DEFAULT , };

For programming, I use an Arduino with the ArduinoISP (version 04m3) sketch that came with Arduino IDE 1.0.1.

This is the command to program flash:

avrType=attiny2313
avrFreq=1000000
programmerDev=/dev/ttyUSB003
programmerType=arduino
avrdude -p$(avrType) -c$(programmerType) -P$(programmerDev) -b$(baud) -v -U flash:w:$(src).flash.hex

This is the command to program the fuses:

avrdude -p$(avrType) -c$(programmerType) -P$(programmerDev) -b$(baud) -v -U lfuse:w:$(src).lfuse.hex

My question is twofold:

What is the reason I cannot program the controller after setting it to 500kHz clock (while the program in the controller seems to run just fine);
What are my options for reprogramming the fuses without using a HV-programmer? Did I perhaps miss any useful flags to avrdude?

BTW: Had the same issue once with an ATtiny45 @ 128kHz. HV-programming solves it, but I want to prevent the HV situation.


texts: How would I monitor I/O on multiple circuits at the same time?

texts:
I've got a device that communicates over a 8 wire cable. I'd like to examine the signals going into and out of the device without having to test each line individually with my multimeter. Is there a device better suited for this task?

I was imagining some kind of multi-channel multimeter that could monitor more than one circuit at a time, but even then I'm not sure I need that much detail (though if an affordable one existed < $150 I might consider it). Even a simple array of LEDs that lit when a given wire was active would almost be enough. Ideally something in between these two examples would be best.

Short of building something myself, is there some off-the-shelf tool/device that could serve this purpose?


texts: how to flash CC2530 without cc debugger?

texts: I was working on TI CC2530 and wanted to flash the chip with using USB mini cable without using CC debugger. would this be possible? and if yes, then what steps do I need to follow.


texts:
I lately built a 10W amplifier using a TDA2003. I used this circuit (though I removed R4 since I didn't have it, C4 is 50n (two 100n's in series) and R1 is 50Ohm (two 100Ohm's parallel)):

Everything worked fine and there was no noise as far as I could hear.

Now, I wanted to be able to switch between two inputs, like this:

This works, but I get a lot of noise now. All wires are shielded, so I concluded the noise arises in the switch and is amplified after that. Is this correct or am I jumping to conclusions?

How can I decrease the noise? I do not want to switch later,  after the amplification, that would produce too much heat and consume too much energy since I'd have to amplify two signals of which I'd only use one.


texts:
For a project I have to design a led beacon that will consist of +400 LEDs. These LEDs will be driven only a short amount of time maximum of 3% duty cycle (frequency: 100Hz, pulse: 300us). The LEDs have an individual Vf of 5V and an If of 5A for this short surge. I wonder if there are smarter ways to make a led driver because the way I'm thinking about now is to create a led driver from a current shunt, MOSFET, and opamp so that the current is adjustable and the surge duration is adjustable.
When I look into LED drivers the downside is normally that they have a fixed frequency and only PWM dimming. Is there a better way to do this since I'm now looking into combining 16 LEDS in series and 25 (or more) of these strings parallel? The flash frequency and duration must be adjustable by microcontroller.
Summary specs per led:

If: 5A
Vf: 5V
Frequency: 20-100 Hz
Pulse: 102-300 us

Powered by mains power and there will be a capacitor bank.
Lifetime and durability is more important then cost and space.


texts: Power Circuit to Subtract a Voltage by a Known Amount

texts:
Using a charge-pump it's possible to add voltages together (i.e. source 10V + PWM 5V = 15V, ignoring diode drops)

simulate this circuit – Schematic created using CircuitLab

Surely there must be a way to subtract voltages using a similar technique (i.e. 10V - 5V = 5V)?

I know subtracting voltages can be done with OpAmps, but I'm specifically looking to do this and draw a measurable amount of power from the output (> 50mA).  The best solution I could conjure to date involves a transformer.


texts: How do I find the equivalent resistance using symmetry?

texts:
I know this could be solved using delta-to-y transformation, but I want to solve this using symmetry.

Considering the middle line the symmetry axis this becomes:

simulate this circuit – Schematic created using CircuitLab

Then, you see the we have the equivalent resistance: (1 + 0.5 + 0.5) + (0.5) = 2.5 ohms.

What's the problem?


texts:
I have constructed a half-wave dipole antenna for the 433MHz frequency.

I'm using the antenna to receive in a simple setup, where I measure the output power of a transmitter.

Everywhere I read about the antenna is stated that the impedance is about 75 ohms, so if the antenna was used to transmit, I can be seen as a 75 ohms load, and therefore is simple to match. Ok, I got this...

But I cannot find how to match the antenna, when using it as a receiver?

Is it just a source with 75 ohms output impedance, or is a dipole not good for receiving?


texts:
I want to instruct an LVDT with a range of 250mm, But I do not know the calculations for the winding.
How to calculate the length of the winding and the number of turns?
I think for modulate and demodulate of signal from the winding, AD698 is a suitable choice, is it true?
If there are any points in construction and design, please tell me.
Thanks,


texts:
Let's say I have a signal where 1v is digital 0, and 4v is digital 1.

I am a little lost how can I use PNP+NPN transistor to have +11..12(for 1) or -11..12V(for 0) output, provided that I have +12/-12 PSU?

UPDATE: This is for low-power MOSFET driver, which has to be done in discreet transistors.


texts:
I have built a half-wave rectifier with a 5V peak sine input, 1kHz. In theory the RMS of the output should be 5V/2 = 2.5V, but the oscilloscope only measures 2.01 V. What could be the reasons for such a difference? 0.5 V seems like a pretty significant difference given the scale.

simulate this circuit – Schematic created using CircuitLab


texts: Bootstrapped charge pump design for phase frequency detector

texts:
I'm trying design a charge pump as it's showed in the following link:

https://ibb.co/DDc6DsF (for some reason I couldn't upload it, I don't know why).

what I don't understand is what is \$I_{ref}\$ (the current on the left circuit) and how I can calculate it by the equation of Mosfet transistor equation?


texts:
What I'm basically trying to do is to modify a stacking device to skip stops normally dictated by a mechanical switch that stops on a cogwheel tooth. I want to put a circuit between the switch and logic that would skip specified stops so the stacking device would leave either 1 gap, 2 gaps, 3 gaps or no gaps at all.

Obviously a binary counter will provide the 2n divisions, but what about the division by 3? Isn't there any other way than putting a binary counter and a separate counter that counts to 3?


texts: Why the output voltage of a transfer function is not equal to zero when the exciting signal is at the frequency of the zero

texts:
I was reading this document and I found something that I did not understand ...
https://cbasso.pagesperso-orange.fr/Downloads/PPTs/Chris%20Basso%20APEC%20seminar%202016.pdf
Suppose the following transfer function :
$$\frac{Vout(s)}{Vin(s)} = \frac{1+\frac{s}{w_z}}{1+\frac{s}{w_p}}$$
When :
$$s = -w_z <=> Vout(-w_z) = 0 $$
The question is what is s ? In the Laplace domain s is defined as :
$$s = \sigma + jw$$
In the Fourier domaine sigma is equal to 0. So Fourier domaine is included in the Laplace domaine. Suppose s is equal to :
$$s = jw$$
Then
$$-w_z = jw$$
or
$$w = jw_z$$
And now how I can apply a signal at a frequency :
$$f = 2\pi \cdot jw_z$$ ?
Thank you very much and have a nice day !


texts: Building a powerbank into a record player

texts:
My "portable" record player has a 5VDC 2A input via a barrel power jack and I want to use a normal powerbank to make it truely portable.

Can I just solder the 5V output of my powerbank to the 5V input of the barrel power jack via an on-off switch? The switch is so I can disconnect the powerbank when using the record player over the normal power cable.

I sketched something out in Fritzing with the MAX15 PCB representing the internals of the powerbank/record player.

I have never before worked with liion batteries and I am a bit scared of blowing something up.


texts: What is the required bandwidth for QAM modulation?

texts: Why is the allocated bandwith smaller with QAM-16 or 64 compared to e.g. QAM-4? I am not a professional so I'm looking for an intuitive explanation.


texts: FPGA Configuration Flash as General Purpose Memory After Boot

texts:
I am currently working on a system with a Spartan-6 FPGA and have a need for some low volumes of non-volatile memory to be used during system operation.

My question is, since I have a relatively large (25Mbit) flash memory already on board storing configuration data, can I effectively partition a block to be used for general purpose memory during operation? It would seem silly to add duplicate hardware for such small amounts of memory.

Memory size is not an issue as I know the configuration data does not fill the flash (leaving more than enough memory that would be required during operation < 3Mbit).

Has anyone ever done something similar to this?

Thanks!


texts: DC biasing arrangement in this audio phase shifter circuit

texts:
The circuit is composed of four phase shift opamp stages each with a JFET used as a variable resistor. Part of the circuit I do not understand is the DC biasing arrangement. I can see that it uses a 4.5V Zener diode to provide the 1/2 VCC supply as this circuit runs off single 9VDC supply. I do not understand how the 4.5VDC gets to the stages. Do R6/R9/R12/R15 provide the DC component to the stages? Or does R2/R3 simply bring the DC to the first stage and it gets passed through each stage?

Finally, I can't figure out the purpose of R18, the 1k resistor at the output of the last stage.


texts: A Funny-Looking Sign Off on Television (Test Pattern Generator Image)

texts:
I came across this display on television while I visited the island of Mindanao in the Philippines in November 3, 2017. I thought this might be a sign-off display from a TV network, but I noticed that it shows the same display all day.

It looks like this:

Getting closer:

I thought that sign-off display for many TV networks in the Philippines look like this: A vertical strips of color with some identification of TV network

Example would be

My question is:

In the first two photos....what are those display?


texts: Why do some computer power cables not have ferrite beads? What type is usually used?

texts: Admittedly I'm clueless when it comes to electrical engineering. I felt compelled to add a ferrite bead/choke/clamp to my computer's power cord since it was missing one. Would it be helpful? What kind should I get, or are most sold generally the same? Does the wire need to wrap around the ferrite bead, or can I just clamp on the bead and call it a day? Thanks a bunch!


texts:
I have 13 \$\pm 15V \$ DC/DC  converters and 1 \$\pm 5V\$ DC/DC converters which I am connecting in series to generate a \$\pm 200V\$ output giving a total output range of 400V. The problem is what would be the best arrangement in the PCB/layout so that I get the analog GND centered at 0V (200V for single output)? As per my arrangement, I am getting a shifted GNDA at 210V.

I also have 1 extra \$\pm 5V \$ dc/dc converter which could be used for this purpose.

Any ideas/suggestions?

Thanks!


texts: Advice/Help choosing a proper (switching) voltage regulator

texts:
I am trying to wet my feet with switching regulators. Please note I am not an expert on electronics.

Currently, I wish to have an adjustable supply of about 3 - 25 Volts, 5A available across the voltage range. The input to this is 30VDC from a transformer/rectifier at max 7A.
The original decision was to use an LM1084 adjustable regulator, and even though it won't be able to supply sufficient power at the lower levels (at Vi-Vo=25V less than 1A), I would know how to use this device. I don't want to switch multiple in parallel.

Now I have looks at the more efficient switching regulators and datasheets on Mouser, but the have a lot of circuitry around them to get right (example circuits for different types of converters), and I'm not sure I understand all the ratings or which circuit I need in the datasheets.

For example, LT's LT1070 datasheet lists the following:

  Negative Buck Converter

  Positive Buck Converter

  Negative Current Boosted Buck Converter

  Positive Current Boosted Buck Converter

  Negative to Positive Buck/Boost Converter

  Positive to Negative Buck/Boost Converter

  Voltage Boosted Boost Converter

  Current Boosted Boost Converter

  Negative Boost Regulator

  Negative Input/Negative Output Flyback Converter

  Flyback Converter

  Totally Isolated Converter

  Forward Converter

What would be an "common" adjustable switching regulator that I can control with a potentiometer that would be appropriate for this application, and the appropriate circuit type?

Thank you in advance.

EDIT

After suggestions of a Prosivite Buck Regulator, I came up with an LM2678.
On page 22 of the reference design, there is a reference circuit:

There are also long lists of inductors for L and Schottky diodes for D1 to choose from. I think they recommend 47uH for L.
What is the use for D1? Is it a flywheel diode??


texts:
I put a square wave of relatively low rise and fall time (of about 10ns), and wanted to see the response from an emitter follower output.

I put together the circuit and here's what I see on scope.

I could not explain why the fall times differ so much, and the fall time of the wave at the output increases with the emitter register.

In spice the waveforms look entirely different. The spice model is quite simply showing the discharging of the \$C_{BE}\$ capacitor, with the downward spike across R1 as the direction of current flows reverses while discharging.

So what is actually going on?

The \$C_{BE}\$ capacitor should have discharged the way shown in the spice, but it does not in reality.

PS: I have done the circuit in Veroboard.

PS: Here are some Ft values with different resisters.

R1      Rise time     Fall Time
220       ~10ns          ~20ns
1k        ~10ns          ~57ns
10k       ~10ns          ~522ns


texts: This diode's datasheet seems to contradict itself; what is it really saying?

texts:
I'm looking for a diode with a forward voltage (VF) of 0.6 V at 10 mA IF.
While searching for it, I came across many diodes' datasheets where they seem to contradict themselves.
For example: BAV99

As in the table, it says VF is 0.855 V at 10 mA IF at 25 °C, while in Fig 1 it is around 0.75 V.
For this one, it is just 100 mV difference, but I've seen other diodes with a higher difference.
Which part of the datasheet should I use?


texts:
simulate this circuit – Schematic created using CircuitLab

I recently began in electronics and I was wondering why a Programmable Uni-junction Transistor needs two resistors "connected" to the base; one from the positive wire of the power supply to the base, and one from the base to the negative wire of the power supply?

Why does the gate have to be connected to the negative end of the power supply?

Does a PUT have to be oriented in this way?

Disregard the purpose of the actual diagram, I'm only wondering about PUT's. I substituted a diode for the actual PUT because they don't seem to have one for schematics.


texts: Why are this monopole and dipole antenna so similar?

texts:
I opened two different GSM antenna housings as shown on the images.

The first image shows the RF SOLUTIONS  ANT-GHEL2R-SMA antenna, which is an helical 1/4 wave monopole antenna.

The second image is the SIRETTA  DELTA2C/X/SMAM/S/RA/25, which is, according to its datasheet, a dipole antenna.

My question is why do they look so similar except for the shape of the copper? I would expect a dipole antenna to actually show two poles. Does the connector housing act as the other pole? If so then why is the monopole not a dipole as well?


texts: Is it okay to put a solar cell and battery into resin?

texts:
I was thinking about making a simple circuit with LED, solar cell and battery and put it in resin mold to make it weather proof.

I wonder is there anything wrong (chemically) with putting a battery into resin?

I know battery will die at some point and I wont be able to replace it, but it's ok since the cost of the whole thing will be low.


texts: Transients in series RL circuit with AC source

texts:
Why the transient current will die off in series RL circuit with AC source ?
Every time the ac voltage source reverses direction so does the current and the current has to pass through the same resistance and inductance every time. Voltage source, current, resistance and inductance all are same for every reversed direction and energy that electrons get in each reversed direction is also the same. Then why will the transient current die off with the passage of time ? I need intuition. Can anyone explain this to me please ?


texts: I have a solar borehole pump: 24 volts - 270 watts panels (two x 135W). I want to move my panels 300 to 350 meters away from the borehole, reducing the risk of theft. What size of cable should I use given the distance? The wire will run in PVC conduit pipe underground. Ambient temperature during the summer: 30 - 40 degrees celsius.


texts:
I was looking for some instrumentation amplifier, and I've been catched by this one:

The part number is LT1002.
In the caption it's written:

Gain = R4/R3 * [1 + 1/2*(R2/R1 + R3/R4) + (R2+R3)/R5].

I can't figure out why.
I've tried doing superposition, and using the LKC on the V- node of the first opamp, but I'm stucked for the presence of R5.
Do you have any advice on how to find the correct result?
Thanks a lot!


texts:
I want to understand the following statement that describes a flyback converter when the switch is turned off :
"
When the PWM controller instructs the power switch to turn off, the voltage across the primary
inductor suddenly reverses, in an attempt to keep the ampere-turns constant. The voltage
developed across Lp now appears in series with the input voltage, forcing the upper switch terminal
voltage (the drain for a MOSFET) to quickly jump to
Vdsoff=Vin+VLp ..........(1) "
Vdsoff: is the voltage of the drain to source of the MOSFET when the switch is off
Vin: is the input voltage.
VLp: is the primary inductor voltage
Question:
How does the primary inductor voltage reverses in attempt to keep ampere turns constant and at the same time it keeps its polarity positive in the equation (1)?


texts: Counteracting Sound Card AC Coupling for Reading Digital Data

texts:
Disclaimer: I am new to EE. Everything I have learned so far I have taught myself from reading online and posting questions like this while working on this project. I apologize if I do a poor job of explaining my problem as I probably lack to the technical knowledge to do so properly.

I am attempting to read two flow meters through the mic port of a phone/tablet. The flow meters' pulse pins toggle between +0V and +5V as their pinwheels rotate.

I am using the following schematic to mix the signals from the two flow meters and send them through a mic port:

I mix the two pulse pins together using an R-2R. This allows me to watch for voltage changes and know which one of the two flow meters changed state based on the magnitude of the voltage change. For example, if I see a voltage change 2.5V, I know that flow meter 1 has turned on. If I see a voltage change of -1.25V, I know that flow meter 2 has turned off. I then use a voltage divider to drop the voltage within the sound card's voltage range.

The sound card is AC coupled and converts the voltage changes into an amplitude change with a formula something like amplitude change = (voltage change)/(voltage range). The AC coupling slowly pulls the amplitude back down to 0 as well. So if my PC sound card has a voltage range of 2V, and the flow meters cause a voltage change of -1.5V, I read through the mic port an amplitude change of -1.5V/2V = -0.75. My algorithm sees this amplitude change and, based on some thresholds, determines if it was caused by flow meter 1 or 2. This can be seen in these screenshots of my Java program running on my PC:

Raw signal read from PC mic port:

(source: awesomebox.net)

Program highlighting detected flow meter state changes:

As you can see, the program is successfully identifying flow meter state changes; smaller amplitude changes are caused by flow meter 1 and larger amplitude changes are caused by flow meter 2.

The problems start when sending the same signal to my Galaxy Note 8 Android tablet. Here is what the signal looks like when read through the tablet's mic port:

(source: awesomebox.net)

Note that all amplitude changes seen above are caused by the same voltage change (all state changes are from the same flow meter). Solo or infrequent voltage changes appear as very small amplitude changes while closely grouped voltage changes (of the same magnitude) appear as larger amplitude changes and closer to what I would expect. It seems the closer a voltage change is to other voltage changes, the larger the amplitude change it creates.

Here is what I read from my PC's mic port and what I expect. Notice that all the amplitude changes are about the same magnitude:

(source: awesomebox.net)

Expected: A voltage change of 1.5V or -1.5V should always cause an amplitude change of 0.75 or -0.75.
Actual: A single voltage change of 1.5V or -1.5V causes an amplitude change of 0.1 or -0.1. A series of 10 voltage changes of 1.5V and -1.5V in short secession causes amplitude changes of 0.75 and -0.75.

This inconsistency makes it impossible for my algorithm to identify which flow meter an amplitude change was caused by. Why do these single voltage changes cause such small amplitude changes? Is there any way to make the amplitude changes always consistent with the voltage changes?

Also, instead of the signal slowly falling back to 0 like I would expect from AC coupling (and seen in the signal read through my PC's audio port), it seems to drop back towards 0 immediately and oscillates a few times before finally settling back to 0. The oscillation adds a lot of noise to the signal and makes it difficult to determine if an amplitude change was caused by a voltage change or is simply an oscillation from settling back to 0. Is there a way to eliminate these oscillations?

Sorry for the short novel and thanks for any advice,
 - Mike


texts:
I need to choose a Transistor to cope with the power requirements of a pair of 12V 710mA 8W LED cluster lamps. The circuit I plan to build is the classic PWM LED dimmer circuit from the EEVBlog. Can anyone point me to a table from which to pick one for the job as the BD136 is not rated for the current needed. This could be a job for a MOSFET but I wouldn't know where to start in identify the parameters to make a choice.
Any help and pointers would be greatly appreciated.


texts:
I have heard it from multiple people over the last 5 years that Optoisolators are failure prone and should be avoided when able. I'm working on a project (for personal use) that I was going to put an optoisolator on to isolate a logic system from a 170V rail.
I do plan to use this device for teaching and would hate for it to stop working because an isolator failed. I know there are magnetic coupling ones now that may be better?

The real question is that I have not been able to find any real data on the internet that confirms optoisolators fail easily or with respect to other solutions.

The only thing I found was a report by Sharp Found Here.

I'll also add all I need to do is move a square wave pulse of 100-500kHz from a logic supply that is floating to a -170V rail. So it can tolerate slow edges and such that a digital com system could not.


texts: Can somebody identify this 12" silicon wafer?

texts:
I just bought a silicon wafer off of eBay to decorate my office. The seller didn't tell/know, but I'm dead curious as to what this wafer is. Could anyone help me identify which chips should have been built out of it?
Full picture
Here's a picture of the entire 12" wafer.

Poor man's macro
Here's a zoomed-in picture of the lighter rectangles that are scattered over this wafer. I took it using a super cheap magnifying glass.

Another poor man's macro
Here's another angle trying to show both the light and dark rectangles. Unfortunately I only have a smallish magnifying glass so I can't see any better.

Extra info

This is a 300 mm wafer
I couldn't find any marking on the front side
The backside has a serial number (K444R215WFB3) and a QR code that's so small I couldn't decipher it.
The dark rectangles probably have something drawn in them, but it's impossible to see it even with a magnifying glass.


texts: Calculating inductance and resistance of a coil from current and voltage

texts:
I have the following question:

What I've done so far:

drew a vector diagram with the known voltages:

used the vector diagram to come up with 2 equations using pythagoras and used them to solve for BC and CD
calculated coil impedance from 180 V and 2.4 A and used that as the "resistance" part
calculated XL using the value I calculated for CD
calculated the phase difference using sin (VL/180), where VL is CD

My final answers are BC = 38.3 V; CD = 175.88 V; "R" = 75 ohm; XL = 73.28 ohm; phase difference = 77.72 deg.
My 2 equations for BC and CD:

I'm pretty sure I went wrong somewhere but I can't figure out exactly where I went wrong. I THINK its in the calculation of CD, I can't remember where I got the 125 from. Any help would be appreciated!


texts: Feedback topology of a common emitter circuit

texts:
I was studying the topology of this particular circuit.

I do not understand how the topology of this circuit is considered series-series. I can see it in input , but at the output it would make more sense to me that it was a shunt topology, because Vo is equal to the voltage drop in the resistance RE.


texts:
We are building a device based on a low-power CPU and we need to choose between a color back-lit LCD with a touchscreen and an "old-school" black and white LCD for the device. Obviously the user experience would be much better with the former, however, power consumption is a priority for us and in principle we can sacrifice user experience in case the black-white LCD saves us battery life considerably, i.e. for example 2 days vs. 5 days.

I'd appreciate if you could give me an insight into this. Am a software engineer myself.


texts: Output resistance of BJT common emitter circuit

texts:
I have found this circuit on a video, he talks about output resistance of the BJT of common emitter amplifier circuit not being infinite but very large so that it must be included in the re model.
In some other websites they do not include Ro for the common emitter re model, should it be included and why?


texts: BCD adder not seeing output of 9's complementer in verilog

texts:
I am attempting to construct a BCD adder-subtractor circuit in verilog using a BCD adder circuit and BCD-to-9's complement circuit.

The modules operate correctly individually. However, when instantiated as part of BCD adder-subtractor circuit, I do not get the correct output sum from the BCD adder when simulated.

Instead, I get only the LSB of the complementer going to the BCD Adder and  the following warning, which somewhat implies this is what is happening:
"[PCDPC]- Port size (4) does not match connection size (1) for port 'N'" and "PCDPC] - Port size (4) does not match connection size (1) for port 'B'".
N being the output of the 9's complementer and B being the Addend of the BCD adder.

This is somewhat frustrating, as the port size for N and B are correctly defined in their relevant modules.

The module declaration are as follows:

module BCDto9Compl(A, N);
input   [3:0] A;
output  [3:0] N;

module BCD_Adder(A, B, Cin, S, Cout);
input [3:0] A;
input [3:0] B;

BCD_AdderSub(A, B, Cin, S, Cout);
input    [3:0] A;
input    [3:0] B;

and module instantiation is as follows:

instantiate modules

BCDto9Compl  B9C(B, F);
BCD_Adder    BcA(A, F, Cin, S, Cout);

I would very much appreciate any insight that you may be able to give.

Thanks


texts:
I have a quick sanity check question because it seems too good to be true.
If I have a LvPECL signal that I want to receive, I can just use a LVDS receiver (422/485 specifically) right? From reading the specs, LvPECL has a swing of 800 mV while 485 is 200 mV (while 422 is just the swing). Since my receiver is more sensitive, I should be fine?
Thanks!


texts: Are traditional vacuum tubes still used anywhere?

texts: Apart from very specialist audio amplifiers?


texts:
I am doing a traffic light design control circuit, so the light will change from red to yellow (for 3s) to green(for 12s) then to yellow(3s) , my question is how do when the light is green, how do I make it green for 12 s before turning yellow again. I was given a clock with 3s cycle.

Do I have to use J-K flip flop or counter ? Is there a way not to use it ? Because we wont be taught them until next week .


texts:
For an assignment I have to create a sinusoidal oscillator with 5 Vpp (centered around 0 V) oscillating at 10.0 kHz. The oscillator works as expected, at the right frequency, but the voltage needs to be regulated between 0 to 5 Vpp.

The following picture shows my design so far;

As you can see the circuits consists of the Wien-bridge oscillator with a low-pass filter to attenuate the higher harmonics. I have tried using a voltage divider but that method does not hold for 0 to 5 Vpp. I am only allowed to use basic components, like the 741 opamp and 1N149 diodes, besides capacitors and resistors.

Does anyone know a method on how to achieve 0 to 5 Vpp regulation using these simple components?


texts:
Why resolutions when we recording video or taking a picture with our cellphone camera are different? Video recording resolution is always so smaller compared to our photo resolution.
Is it hardware limited or? Can that limit be removed?


texts: Using a relay switch to switch power to solenoid

texts:
I'm fairly new to electronics, so I'm hoping I'm not so misguided that I am wasting all of your time. Basically I need to power a solenoid which in turn controls a gate valve, and the solenoid requires 24V DC. The manual for the whole thing describes very little, and I don't have any info like inrush current, which I'm worried about since any searching so far has had people providing that. The solenoid just has 2 black wires coming out of it, and is marked 24V DC.

To power the thing, I am going to use a 24V AC/DC power supply (here). I want to be able to control the whole setup remotely using a computer, so I immediately thought to use a relay controlled by USB. However, any time I've used this sort of stuff in the past, I've just been going off of Arduino tutorials or something, so I just bought what was recommended there.

I want to make sure I have a proper understanding of how to use these. What exactly is the difference between requiring 5V vs say 12V to power the relay? Can 12V handle more current passing through them, and that's the main reason to use a stronger one? If I were to say purchase this relay board, would that work? Under relay parameters it states 5V/72mA, 15A/24VDC, 10A/250VAC. The 5V I would understand as the potential I need for the relay, but does 15A/24VDC mean it can pass up to 15A/24VDC, meaning this would work for my application here? Or am I really misunderstanding this? Is there an entirely easier solution that I have no idea about? I currently envision connecting the power source to COM, then the solenoid to NO and switching it when the solenoid needs to be powered.

Additionally, bonus question, the relay will be very far away from my pc (guessing 60-70? feet of wire), should I worry about power loss by powering from USB? I just grabbed a USB powered one from a search, powering at the location and controlling via usb is perfectly fine, but usb powered would be convenient.

Thanks for your time and any help you can provide!