texts: Rise time different from fall time; relationship differs between AND and XOR gates

texts:
I'm looking over the results from a lab I did in an introductory electronics class, and found something I'm unable to explain.

We measured the rise and fall times for two logic gates in this absolute value circuit:

The XOR gate in HA3 (U3,11)
The AND gate in HA2 (U2,10)

The results were as follows:

$$\begin{array}{|c|c|c|}
\hline
\ & \bf{Rise} & \bf{Fall} \\
\hline
\ \bf{XOR}& 44.8 & 64.0 \\
\ \bf{AND}& 51.2 & 19.2 \\
\hline
\end{array}$$

This raises the following issues:

According to the datasheets (XOR, AND), \$t_{TLH} \$ should equal \$ t_{THL} \$ (typical value: 100 ns), which is evidently not the case for either of the gates (and dramatically so for AND).
Following on from the first question, why is the difference in the transition time reversed between the two gates?
The load capacitance should be slightly lower for the AND gate, as the path taken is shorter (with one gate less). This seems to be the case for the rise time, but not for the fall time. Why?

At first I though that the explanation would lie in differences in the capacitive loads impacting each of the gates differently. However, the load capacitance-transition time relationship should be pretty much the same (figures 6 and 12 in the XOR and AND gate datasheets, respectively).


texts: Cannot communicate with serial device via an Arduino Nano serial communication

texts:
I am trying to communicate with an RFID reader via its serial port. The serial port has an RS232 connector on it. I also want to display the RFID tags ID on a 16x2 LCD screen using an Arduino.
I, therefore, purchased an RS-232 to TTL converter (shown below).

I connected an RS-232 cable from the reader to the converter (male to male RS-232 cable) and then to my Arduino Nano. I connected TX (RS-232 converter) to RX (Arduino) and RX (RS-232 converter) to TX (Arduino).
After uploaded a simply sketch:
#include <SoftwareSerial.h>

SoftwareSerial mySerial(5, 6); // RX, TX

void setup() {
 // Open serial communications and wait for port to open:
 Serial.begin(115200);
 while (!Serial) {
 ; // wait for serial port to connect. Needed for native USB port only
 }

 // set the data rate for the SoftwareSerial port
 mySerial.begin(115200);
}

void loop() { // run over and over
 if (mySerial.available()) {
 Serial.write(mySerial.read());
 }
 if (Serial.available()) {
 mySerial.write(Serial.read());
 }
}

The code is not mine, it is an example sketch from Arduino. I set the baud rate as per the RFID reader's settings, which was 115200.
After connecting everything, I then opened up the serial monitor and set the correct baud rate. However, no info was sent to the monitor. I also got a Serial to the USB connector. I connected this cable to the reader and then to my PC USB input (no Arduino). I tested the serial connection with this cable and opened up the serial monitor, set the COM port and baud rate. The serial monitor started to display the correct data.
After investigating the RS-232 cable (male to male RS-232 cable) I noticed the DCD (Data Carrier Detect) and the RX pin of the RS-232 was shorted (I tested with the continuity tester from my multimeter). Could this be the reason why no data is been displayed?
Update:


texts: DC Thump-like noise with Isolation Transformer

texts:
I put an isolation transformer inline with my audio (unbalanced 2 channel audio; with L, R, signal Ground).

It still makes noise when plugging the auxiliary cord in (kind of like 2 thumping noises) or when I tap the aux plug onto a piece of grounded metal. All other static like noises are gone though.

I thought the isolation transformer gets rid of the dc thump? What could this noise be from?
Could it be contact bounce?

Please tell me if anything needs clarification!

Have tried:

I have tried another isolation transformer that I made myself for fun, it got rid of ALL DC thump-like noises including when plugging the auxiliary cord in or when I tap the aux plug onto a piece of grounded metal. That transformer was not good at transmitting a big chunk of the lower frequencies of human hearing so it is not a viable choice.


texts: I'm looking at LM358 datasheet, This IC use VCC and GND as a source. Is that possible to use GND pin from LM358 as -VCC pin?


texts: Influence of I/O impedance in Butterworth passive filter design

texts:
I'm using a simple online simulator tool to build a passive Butterworth filter. An affirmation made in this page confused me:

  Enter the filter characteristic impedance. In all cases, unless you specify a matching network (see below), this is equal to the filter input (source) impedance. For Butterworth and odd-order Chebyshev filters, this is also the filter output (termination) impedance

Firstly, I'm trying to understand why they made the choice of input impedance = output impedance.

Secondly, I have found that source impedance is not even present in transfer function. For example:

simulate this circuit – Schematic created using CircuitLab

The transfer function of this circuit is given by

$$H(s)=\frac{R_{output}}{(L_1L_2C_1) \cdot s^3+(L_1C_1R_{output}) \cdot s^2+(L_1+L_2)\cdot s+R_{output}}$$

I see that the choices of \$R_{output}\$, \$L_1\$, \$L_2\$ and \$C_1\$ are not affected by \$R_{source}\$. So, why are there an "Optional Matching Network" where I can specify the source impedance if this will not make any difference?

I have already checked that this tool produces different circuit and component values for equal I/O (using "Characteristic impedance" field) in comparison with different I/O (using "Optional Matching Network" fields to enter impedances), but I can't figure out why my reasoning is wrong. The behavior I was expecting was, as mentioned above, no changes in components values and circuit topology when source/input impedance is changed.


texts: SPI MOSI line only hits 1.2V for speeds above 500kHz and below 4MHz (3.3V logic)

texts:
I'm trying to drive a ST7789 TFT display (datasheet) with an ATTiny-416, but for some reason SPI fails at speeds above 500kHz. So far I've had these results:

500kHz: pass
666kHz: fail
1MHz:   fail
2MHz:   fail
4MHz:   pass

The 4MHz is especially strange. Technically the AVR is operating out-of-spec there, since it runs 16MHz at 3.3V (max is 10MHz for 3.3V)
Here's my SPI routine:
void SPI_init(){
    //PORTMUX.CTRLB |= (PORTMUX_SPI0_ALTERNATE_gc);
    SPI0.CTRLB = SPI_SSD_bm | SPI_MODE_3_gc;
    SPI0.CTRLA =  SPI_MASTER_bm |
                  SPI_PRESC_DIV4_gc |
                  SPI_ENABLE_bm;

    //SPI0.INTCTRL |= (SPI_IE_bm) | (SPI_RXCIE_bm);
    PORTA.DIRSET = (1<<1) | (1<<3);
    PORTA.DIRCLR = (1<<2);

    //PORTA.OUTCLR = (1<<1) | (1<<3);

    PORTA.PIN1CTRL |= (PORT_ISC_INPUT_DISABLE_gc);
    PORTA.PIN3CTRL |= (PORT_ISC_INPUT_DISABLE_gc);
}

uint8_t SPI_write(uint8_t data){
    SPI0.DATA = data;   //write dummy byte

    while(!(SPI0.INTFLAGS & SPI_IF_bm));
    return SPI0.DATA;
}

And what the oscope sees:

And a schematic:

simulate this circuit – Schematic created using CircuitLab


texts: Addition of a Disturbance to a Microgrid system

texts:
I have a microgrid system which is represented in state space model by
\$\dot{\mathbf{x}}= Ax \$. The dimension of \$A\$  is \$32\times32\$ . I want to introduce a step disturbance in one of the states and plot the resulting response of some states  in MATLAB/SIMULINK. What will be the change in the state space representation when a disturbance in one of the state is introduced. How will I get the response of some states with time as the step input is introduced ?


texts: Interaction of AC and DC waveforms in motorcycle frame and their effect on AC & DC components

texts:
We are undertaking a LED lighting project and have figured out the way circuit in motorcycle works, the AC return is through frame and the DC return (negative) is through the frame to negative ground of battery,

When both AC neutral (return) and DC negative are connected (grounded) to frame of a motorcycle how do the AC and DC waveforms interact and how do AC & DC interact with DC/AC components respectively?  That is how does AC interact with DC components and how does DC interact with AC components and how is it possible to connect these circuits together through frame?

That is how circuit is connected but do not understand the laws/electronic properties that allow this to occur?

See wiring diagram below, the pertinent parts are AC generator to DC regulator rectifier and Brown (Br) wire to Ground (frame) shown.  Also AC supply to AC headlights and lighting which then returns to field coil on AC generator (shown connected to ground (frame)).


texts: what is this connector type (F200 realsense device)

texts:
I am looking for the type of connector this is.  I believe it to be a Micro IDT (molex) type connector or a version of the FPC type connection.  This is the one for the R200 or F200 intel realsense camera.

enter image description here


texts: Microchip MRF24WN0MB datasheet for use in STM32

texts:
We have designed a board where a Microchip MRF24WN0MB WiFi is connected to an STM32L082 ARM micro-controller through SPI.

I can generate code with STM32CubeMX (compiled with Eclipse SW4STM32) and run it on the board, and I wanted to start the Microchip WiFi but I can't seem to find any datasheet explaining basic things like initialization, configuration, registers, etc. The datasheet they provide gives the electrical configurations but nothing about programming it.

There are many references on their website to "MPLAB Harmony", which I downloaded. I found reference to MRF24WN drivers in the framework/driver/wifi/mrf24wn but no documentation on how to integrate it on my board.

Is there an official datasheet with those information? Or a somehow-documented standalone driver I could compile and use?


texts: how to find the active power supplied by an induction machine

texts:
3 phase, 8 pole, 400 volt, 50 hertz induction machine.
supply current 52.8A angle -72.5deg

How do I determine the Active Power supplied by the machine? Is it as simple as (400/root3)*52.8*cos(-72.5)??


texts: How to construct a low input voltage DC-DC converter if no suitable IC is available?

texts:
I need to convert a very low input voltage (around 0.5V) to a steady 3.3V output to deliver 50-80mA current with relatively high efficiency (>= 80%). After some research, it appears that some DC-DC boost converters from TI and Linear Technology are quite suitable for this application. However, they are somewhat expensive to purchase in small quantity. I'm wondering if it's possible to construct such a converter by myself, using components that are widely available. I don't have any prior experience in designing similar circuits, so I have no idea where to start. Any suggestions and/or pointers would be greatly appreciated.

PS. What I have in mind is a DC-DC boost converter with an inductor, but is it also possible to design an inductorless charge pump that meets the requirements that I mentioned above?


texts:
What would you consider to be a safe resistance for a speaker jack on a computer? I want to make a speaker unit for my laptop (which has awful built in speakers), but I'm afraid I'll end up drawing too much current. So I just need a safe estimate for how much resistance I should build into my system.

On a side note, I just want to be safe with my wiring. Audio jacks have two channel pins (L and R) and a common... "ground" I guess you would call it, right?

So if I wired like this... Left---Speaker---Ground---Speaker---Right would that work?


texts:
This is a fundamental theoretical question about power and efficiency of AC voltage source with very low output impedance, for example, a DC-AC converter; H-bridge converter or class E amplifier.

MY question is:

Does the source impedance of DC-AC converter always represent  losses?

To further elaborate the question,

Let's assume the converter to be a pure sinusoidal source with a source impedance of Rs follows. I understand that the source impedance can be a time varying quantity but for the time being, lets assume an equivalent source impedance to be Rs fro a given operating condition.

simulate this circuit – Schematic created using CircuitLab

With this representation, we know when Rs=RL, the maximum power is delivered to the load, and the efficiency become 50%.

My question here is that in actual implementations of such power electronic converter, when the load is optimized to deliver maximum power, is the efficiency always limited to 50%? If not, how it can be explained? Or in other words, Does the source impedance of DC-AC converter always corresponds to losses? I feel I am missing something here.

To elaborate this further,

If now we consider, for example,  a class E converter, we know the theoretical maximum efficiency is 100%, in practical implementations, it can easily be above 90%. But highest efficiency is achieved not at the impedance matched condition and I understand that it is not a usual practice to operate at matched condition for such scenario, however, this is for theoretical understanding of such operating condition.

For example, the following figure is from this IEEE paper, efficiency doesn't seem to be less than 50% when the maximum power is delivered to the load.

Additional explanation:

Even if we assume load resistance is not a fixed value (it can be a variable w.r.t with load, and also, it can be a time varying quantity depending on switching transients) we can consider an equivalent source impedance when the output power is maximum. For example, in the above paper, lets approximate power is maximized at 4.5ohm (say, power is maximized when the normalized resistance is around 0.5 in the above graph), then we can deduce that the source impedance seen by the load is close to 4.5ohm. If we consider only this particular operating point, what represents this source impedance (I stress, it can be an equivalent one, or, may  even be a time averaged one)?

In adiition, if we can agree that the source impedance is close to 4.5ohm then does the source incur losses corresponding to a 4.5ohm? Then, as the answer by @Neil_UK suggests, should the efficiency be always less then 50% at maximum power delivery condition?

I used this particular reference and numbers to clarify the question. My question is not necessarily limited to this particular converter or  class E topology. It is a general to DC-AC converters. I could not find any good reference which discusses this issue?

Or, in another way, is it completely incorrect trying to model a low impedance DC/AC converter (assuming high Q, and load current is fairly sinusoidal) with this model.


texts: Relay implementation of Muller C-element

texts:
This is a bit of a silly question, and I realize that. It's hard to imagine why one would use relays for this purpose, especially given relay bounce / etc. Nonetheless, it's an interesting exercise, if nothing else.

Any suggestions for how to go about implementing a Muller c-element in relay logic? Ideally, "pure" relay logic, as in no diodes / etc.

(For those who don't know, it's a latch variant. Output goes high when both inputs are high, low when both inputs are low, and stays the same as it was otherwise)

The best I've come up with thus far is this:

It has a few "amusements" though. Let's see:

R1 is required for the LL(L) -> HL(L) transition, as the first relay must switch before the second
C1 is required or else the second relay toggles off during the blip when relay one switches during the transition from HH(H) -> LH(H).
The output glitches slightly (to ~1/2 a volt, in this case, but the numbers are wildly wrong) during a LL(L) -> HL(L) transition if the circuit was previously in a state with output high due to C1 being connected to the output.
I have no idea how to size R1 and C1 beyond empirically "as small as possible".
It glitches if the output is too inductive. Rather interestingly, too.
It might glitch if the input is too inductive.
It has no snubbing across the coils. (Well, aside from C1)
It uses 1=high 0=low logic, whereas some things are easier with 1=high 0=floating.
It uses two relays, whereas there's only one bit of info being stored.


texts: Mosfet driverless mosfet Slayer exciter (adjustable power)

texts:
I'm new to electronics but I tried to make mosfet slayer exciter anyways. Most of the mosfet slayer exciter I've seen uses mosfet driver to turn on the gate of the mosfet, but since I don't have access to mosfet driver, I decided to use BJT to turn on and off the gate of the mosfet. I came up with the schematic my own but since I'm a noob, it didn't work :< Am I going the right direction with this schematic? Or is there any mistake in my schematic? Any help is appreciated.
The potentiometer is tuned so the voltage divider creates 4.2V for mosfet gate.
The resonant frequency of the secondary is 810kHz and primary is tuned at resonant frequency as well. (do I even need the primary tank capacitor? because its self oscillating)
When powered on, the circuit draws about 1 amp and mosfet heats up a bit (not much) which is kind of expected but no high voltage on the secondary.


texts: Wiring power banks in series for 25V output to power e-bike

texts:
So I have an old electric bike sitting around, no battery. Replacement 24V 10Ah batteries are $200+. However, I have/can get 10Ah power banks (to charge phones) for under $10. They all have standard 5V 2A outputs. Same brand and model. Bike is an ancient Ezip eco ride; 250W motor.

Can I wire 5 power packs in series to get a ~24-25V output? I can't do it via the USB ports, because I can't pass voltage back through the USB port - it overloads and shuts down.

I'm afraid of opening the power packs and wiring the batteries directly, because the PCBs are still connected and might get damaged.

Assume I disconnect the PCBs from the batteries before wiring them in series. Also assume I time the battery usage so they don't over-discharge. What's the chance this will go up in flames, Note 7 style?

If you're gonna call me an idiot for even suggesting this, please do so kindly. Thanks! ^_^


texts: Is there a standardized symbol/refdes for PCB mounting points?

texts:
I've seen a variety of different parts substituted in for mounting locations, including 1-pin header, test pad, and fiducial symbols. I've also seen a variety of reference designators for mounting locations, including M?, MT?, and MP?.

Is there a standard schematic symbol for mounting locations to remove this ambiguity?

Likewise, is there a standard reference prefix?


texts: Can I connect a DC motor directly to an Arduino?


texts: Changing Reference Voltage A/D on Microcontroller

texts:
I am using a microcontroller PIC18F4550. It has a reference voltage from 0 - 3.3 volts for the A/D converters.

I had two questions:

1) If the voltage drops below 0 (negative), will the A/D converter report the negative value?

2) Is there anyway to change the reference voltage, either by adding an additional circuit or by manipulating it by code?

Thank you!


texts: Confusions regarding swing up hybrid control?

texts:
I am trying to learn about swing up hybrid control and i came across a figure shown in attached snapshot. I have two confusions in this regard:
1)Both "swing up energy control"(u1) and "Balance control"(u2)will be active at same time??
2)The block in center,switching strategy block is logically OR block,And block or Summing Block or Mutliplexer


texts: Running brushed universal motor at different frequency than designed

texts:
First, the end goal is to run a power tool (namely a Dewalt DW734 thickness planer) designed for 110V at 60Hz at a country where the power is 220V at 50Hz. The motor is a brushed universal motor, constant speed (i.e. not variable speed, but also doesn't seem to be electronically controlled).

I've read a lot on the Internet about running motors (universal and induction) at different frequencies (50 and 60 Hz, which are the common frequencies around the world), but there are conflicting opinions.

Naturally I will use a step-down transformer to get the voltage to 110V. The question is how will the frequency change affect the motor?

Some sources claim that a universal motor doesn't care about the frequency at all (and can run on DC as well), while others claim that the motor will run at 50/60=83% speed (but this might be the case only for induction motors, not universal brushed motors).

Other places claim an issue not directly with frequency, but with the voltage-frequency ratio (110/60 vs. 110/50) causing the motor to draw more current and over-heat.

Another issue comes from electronic speed control and variable speed control (the DW734 doesn't have them, but other power tools do). Will these require the correct frequency, or do they operate on DC anyway and the line frequency is not important?

There are power supplies that convert the frequency as well (VFD invertrs), but they are more expensive than regular step-down transformers and not all of them produce a perfect sine wave (which is another question - how important is a perfect sine wave vs. a PWM signal?).


texts: Zener diode - Zener voltage vs reverse voltage specification

texts:
This may be a very simple question with a straight-forward answer, but I cannot get a clear answer on this.
Consider the following Zener diode. The table on page 2 lists a column for Zener voltage \$V_Z\$ and also a column for Reverse voltage \$V_R\$, with \$V_R\$ < \$V_Z\$ for all the device variants.
What is the difference between these two parameters? If I want to use the Zener diode to clamp the maximum input voltage to a circuit to 24 V (in case of a transient*), do I choose the device based on \$V_Z\$ = 24 V or \$V_R\$ = 24 V?
NOTE * - This will actually form part of a circuit where a TVS diode is used, but I cannot find a TVS diode that will clamp at a maximum of 24 V with a maximum working voltage of about 19 V (the actual operating voltage is 12-18 V). I am therefore resorting to choosing a TVS with a maximum clamping voltage higher than 24 V and want to use the Zener (placed in parallel, after the TVS) to clamp the input voltage to 24 V in case of a transient.


texts: VHDL unranged integer input ports bad practice?

texts:
I'm designing a customizeable interpolation filter and I'm looking for the best way to pass the coefficients (rather supporting points) to the filter. Below you see the current implementation.

package lin_interpol_filter_unsigned_pack is
        type supp_point_vector is array (integer range <>) of integer;
end package;

--! Use std libraries.
library ieee;
use ieee.std_logic_1164.all;
use ieee.numeric_std.all;
use work.lin_interpol_filter_unsigned_pack.all;
entity lin_interpol_filter_unsigned is

    generic (
        --! Determines number of interpolations steps by steps = 2 ^ <interpol_steps_exp_g>
        interpol_steps_exp_g    : integer := 6;
        input_width_g           : integer := 12;
        output_width_g          : integer := 12
    );

    port (
        clk_i               : in std_logic;
        supp_points_vect_i  : in supp_point_vector (0 to 2**interpol_steps_exp_g);
        input_stream_i      : in unsigned (input_width_g downto 0);

        output_stream_o     : out unsigned (output_width_g downto 0)
    );

end;

The user would then have to pass the supporting points to the module as a constant. Now I'm worried that Vivado can't optimize the input port to the minimum bit-width, but instead uses the full (32bit?) integer range. Can I expect Vivado to minimize the bit width?

I'm not entirely happy with this approach. I would rather like the user to pass the supporting points as a generic, but the generic declaration would then be dependent on another generic (the interpol_steps_exp_g generic) which isn't allowed. Is there maybe another way to pass the supporting points conveniently?

Thank you.


texts: Schematic help - Unknown capacitors for Raspberry Pi project

texts:
I'm recreating a Raspberry Pi project and ordered a custom Pi hat to follow their schematic. The only issue is that it doesn't have all of the information. I've emailed the creator but am yet to hear a response.

The actual schematic:

The PCB:

The project is here: Converting a Seeburg 3WA Wallbox into a Remote for a Modern Music Player.

I'm trying to figure out what the capacitances of C1, C2 and C7 are and where they go on the board as it's not very clear. Based on his photo of his final product, he didn't use one of those capacitors (I think it's C2). My guess is that C1 and C7 are the same.

Anyone out there to help?


texts: How to get a constant current from a DC power supply for high voltage/current

texts:
For a project we're working on we require 4 high power LEDs, we've been using these: http://www.digikey.ca/product-detail/en/bridgelux/BXRC-50C10K0-L-24/976-1277-ND/5180249.

We've purchased this power supply for running the lights: http://deltapsu.com/products/download/Datasheet/PMT-36V350W1AR

With our testing so far we've been using these lights using our bench power supply which allows us to set a current limit. We're quite unfamiliar with how current limiting works, so we're a bit concerned about just hooking our lights up to the power supply and letting it go nuts. Are there any off the shelf items that we would be able to put between the power supply and the lights to force a constant current, or are we being overly cautious?


texts: Need gate driver for MOSFET (IRF540) and microcontroller

texts:
I'm trying to use a STM32F100RBT6B microcontroller to turn on a n-channel MOSFET (IRF540) to switch on a voltage of 24V to an electrical magnet.

I understand I would need a gate driver between the microcontroller and the MOSFET. I know the NMOS Qgs is 10nC at max, so I figured I would need at least 10 mA from the driver to switch it on fast enough (1uS at 10 kHz).

I also know the VoH from the microcontroller for a TTL-port is 2.4V. Does anybody know of a gate driver that would work for this application, and how I would go about to find such a gate driver? (I'm a student still learning about this, so correct me if I'm wrong).


texts: Measuring if a transistor can work for SPI/UART when doing logic level conversion

texts:
I need to convert 3v3 to 5V and 5V to 3v3 for SPI/UART. I found many options. But I'm still confuse whats good for me. Because Transistors and few other components has rise and fall time. I want to know if a transistor is able to get to the speed that I want of SPI/UART.

My only concern here is about speed, not voltage threshold.

Lets say I want SPI clock speed of 1MHz, how do I know if specific transistor can able to work properly with it.

For example, SparkFun Logic Level Converter - Bi-Directional

The above product is using BSS138, according to its datasheet. It's total fall and rise time is (5 + 18 + 36 + 14) = 73ns

What I think is, convert 1 frequency to nano second and check if its higher than the total fall and rise time. I'm not sure about duty cycle of clock but I assume its 50%.

So if I need 1MHz clock speed, it would be 1us for each freq. Divide it by 2 as duty cycle is 50%. Making it 500ns.

Now reducing 500ns - 73ns = 427ns of actual duty cycle. But I do not know if 427ns is enough for SPI/UART ? or I'm completely wrong about whole thing ?


texts:
Below is the link for the famous smt module ESP8266-12E. In the link appears the module and another component which package is 8 SOIC. I am thinking that it should be the voltage regulator for the esp module. What are you thinking? It's written "SergMicro 25Q32ASSC6 1403" when searching with Google about any of those items I can not find any result. Does someone know what is this component?

Link : https://www.adafruit.com/products/2491


texts: Proving RC and RL circuits as integrator and differentiator using differential equations

texts:
I need to use first degree ordinary differantial equations to prove (solve) the Differentiator and Integrator Circuits of RL and RC (for example if RL is differeantiator or integaror or both i need to prove it with using first order ordinary differeantial equations).

Btw I know how to use differential equations but i dont know how to use them on circuits so i would be happy if you also show me the solution of some to solve others or maybe hint,tip etc. or some sources where i can learn this about and sorry for my english and this is my first question on this site. Waiting for your answers. :)


texts:
I have an assignment, where i'm supposed to (sort of accurately) measure the current drawn by a SIM-card, in the different phases it can operate in. The current is by no means DC, as the SIM-card operates at a clock-frequency of around 5 MHz. I am expecting current peaks in the range of 1mA-40mA. Therefore, my question is: How would you go about measuring such a relatively small HF current?

I have until now experimented with using a shunt resistor in a low-side current sensing configuration. The problem is that I am experiencing that with an increase in frequency, I see an increase in voltage amplitude across the shunt resistor, which I can't really explain. I suspect that some capacitive and/or inductive effects have a significant say at these frequencies and this messes up my measurements. So do any of you have alternative solutions to this measuring problem?

I am using a shunt resistor with a resistance of 0,22 Ohm.


texts: AVR GCC : Global / Static Array not getting initialized properly

texts:
Im having problem with global arrays in my C code. What i am trying to do is to use a display buffer (array of 8 uint8_t with each uint8_t representing a row) to light up the leds in 8x8 led matrix using column scanning.

the relevant part of code is:

#include <avr/io.h>
#include <util/delay.h>
#include <stdlib.h>
#include <avr/interrupt.h>

uint8_t string_size=3;               //DISPLAY STRING SIZE
uint8_t display_string[8][3];         //DISPLAY STRING
uint8_t display_buffer[8];            //CURRENT DISPLAY BUFFER

/*****************************************
CHARACTER MAPS
*****************************************/
uint8_t h[8]= {
0b11111111,
0b10000001,
0b10100101,
0b10100101,
0b10111101,
0b10100101,
0b10000001,
0b11111111
};

uint8_t o[8]= {
0b11111111,
0b10000001,
0b10111101,
0b10100101,
0b10100101,
0b10111101,
0b10000001,
0b11111111
};

uint8_t t[8]= {
0b11111111,
0b10000001,
0b10111101,
0b10011001,
0b10011001,
0b10011001,
0b10000001,
0b11111111
};

/*****************************************
FUNCTIONS
*****************************************/
void addCharToString(uint8_t pos, uint8_t chr[]);   //ADD PASSSED CHAR TO SPECIFIED POS IN STRING
void setupDisplayBuffer();                     //SETUP INITIAL DISPLAY BUFFER
void writeDisplayBuffer();                     //DRAW CURRENT DISPLAY BUFFER

int main()
{

   addCharToString(0,h);
   addCharToString(1,o);
   addCharToString(2,t);
   setupDisplayBuffer();

   for(;;)
   {
      writeDisplayBuffer();
   }
}

void addCharToString(uint8_t pos, uint8_t arr[])
{
   for(uint8_t i=0;i<8;i++)
   {
      //display_string[i][pos] = arr[i]; //PROBLEM HERE!
      display_string[i][pos] = 0b10000001;
   }

}
void setupDisplayBuffer()
{
    //COPY THE FIRST CHARACTER FROM DISPLAY STRING TO DISPLAY BUFFER
    for(uint8_t i=0;i<8;i++)
    {
        display_buffer[i] = display_string[i][0];
    }
}

void writeDisplayBuffer()
{
    for(uint8_t i=0;i<8;i++)
    {
        write595(display_buffer[i]);
        set2903Pin(i);
        _delay_loop_2(1986); // ACCURATE 1MS DELAY .. HIGHER THAN THIS = FLICKERING
    }
}

When I run it I see the whole column light up (whole 8x8 grid lid up with scanning) and it seems the problem is happening in the line

display_string[i][pos] = arr[i];

in addCharToString(). if i comment out this line and use a constant value (0b10000001) in the above code it gets displayed perfectly (first and the last column lighting up)

It seems that the array(s) h, o and t are not getting initialized properly. Any ideas what could be happening here

I am using ATMEGA8.

Update:

I am using -0s optimization with the following flags set

funsigned-chars
funsigned-bitfields
fpack-struct
fshort-enums


texts: why do rechargeable batteries fail so horribly in high drain environments?

texts: I've tried nicads and nimhs in flashlights and they always end up leaking.  I know how spikes and memory work in such batteries, but why do such high drain applications cause such catastrophic failures in these batteries while alkaline batteries perform quite well?


texts:
I want to design a digital circuit that transitions in the following sequence as follows:
(0,0,0,0) -> (0,1,0,1) -> (0,0,0,0) -> (1,0,1,0)

How would I go about making a k-map for this?  Should I add another variable, so that it looks like something I have below?

(0,0,0,0,0) -> (0,0,1,0,1) -> (1,0,0,0,0) -> (0,1,0,1,0)

I have tried making an ordinary k-map of 4 variables, but since there are two output values for (0,0,0,0), I have not had any luck.


texts: Is it possible to do "runtime" routing/switching of current paths?

texts:
I am designing a project involving 12 DC motors, only one of which
will run at any time. I will be using a high-current-capable H-bridge
driver (like this one), in
order to run them bidirectionally.

In view of cost minimization, I'd like to use only one driver for the
entire board, i.e., run the motors sequentially by driving one for N
seconds, then moving to the next one, and so on (switching speed/delays are not important at all).

Is it possible to design a low BOM-cost modification (< $5 ideally, for switching between 12 motors) to the circuit where I can runtime-switch
the driver outputs, i.e., programmatically have the driver jump from serving one motor to the next?

I understand that solutions like crossbar/crosspoint ICs as well as
FPGAs are traditionally used to facilitate on-the-fly routing of
digital signals, but what about high-current lines (in this case, 3-4
amps of current draw)?


texts:
I need help tracking down 2 replacement parts.
From what I know they are 1 Varistor and 1 Pico Fuse.
Could anyone confirm that and tell me what I should be looking for to replace them. Googling the writing on them doesn't really get me anywhere so can someone break down what the numbers mean and or where to order replacements.
Thanks very much
Nelson

This is the info I get off them
ZOV 07d471k cq01p (Varistor?)
STB3.15A (Pico Fuse?)


texts:
I am making bipolar voltage measurements in which the distance between my probes small enough that I think the geometry of the probe contact tips is non-trivial. As illustrated below, my voltage probes are cylindrical and situated on either side of a dipole. I want to know the effective distance between the probes and have heretofore been computing this on-center (Distance A).

I know that a complete-electrode-model of effective distance would have to account for contact impedance and non-infinite within-probe shunting, but this is beyond the scope of what I am trying to accomplish.

I believe that if I assume that the electrodes are perfectly conductive and have zero impedance, the effective distance between them is the distance between their nearest points (Distance B).

Is this reasoning correct? Am I making other (unstated) assumptions?

In my particular experiment, distance A is 5mm, distance B is 2.6 mm, and the probe contacts are 2.4 mm long and have a diameter of 1.28 mm. The probes are bathed in a conductive fluid.

Thank you.

EDIT: I added equipotential lines to the figure (the voltage values are for illustrative purposes only). I know the conductivity of the media and have solved the quasi-electrostatic forward and have a good estimate of the quasi-electrostatic inverse. I am now trying to use voltage measurements to assess the strength of my dipole but am unsure of what inter-contact distance to use in my equations. Assume that the dipole is centered between the probes.

EDIT: My fluid medium conductivity is on the order of 10^-1 and my contact conductivity is on the order of 10^7.


texts:
I'm actually trying to build a precise full wave rectifier. But after a first failed try, I though I would better be off break down things to analyse every part of the circuit.

So, I started building a half-wave rectifier...

and even at this point I'm seeing something I was not expected:

So, has you might guess, the yellow wave-form is my Vin and the blue is my Vout (both channels are AC coupled).

Here's the difference when I change my scope settings to have both channels to DC coupled:

I was sincerely expecting to get something more like this:

Currently I'm using 20k (1%) resistors, ahottky diodes (1N5818) and the TLC272ACP op-amp.

Any thoughts on what is going on? Why am I still getting a negative portion of the rectified wave form? I must have messed something up...

I've basically edited this post, because I realized that I've made a mistake on the circuit.
As I'm using this circuit to power up an A/C appliance, I wanted to use the same power supply to power up the circuit. So basically I've connected a AC/AC transformer to drop-down voltage from 230 to 6V (or 12V), and then got the AC converted to DC through a bridge rectifier and later regulated to 5V.

The thing is, I noticed I was using "different grounds" in different parts of my circuit. I was giving ground passed through the voltage regulator to the op-amp and giving ground directly out of the bridge rectifier to the bias the CT sensor.

For some reason that is not clear to me, between the "regulated ground" and the ground output directly from the bridge rectifier there's a difference of 2.3mV.

Well, know after having this corrected I get this on the scope:

Once again, I was expecting a closer match in terms of Max voltage...


texts: Can the capacitance of a proximity sensor be increase by adding layer to the capacitor?

texts: Would adding layers to the capacitor of a proximity sensor from lets say 1 (A) to 4 layers (B) help with increasing the capacitance and at the same time the distance that can be sensed with a proximity sensor?


texts: What type of silkscreen ink is used in PCB manufacturing?

texts:
Let's say I'm looking to start my own PCB manufacturing company* and I have everything figured out except how to silkscreen the boards.

Where do I get silkscreen ink from?
Is there a special type of ink specifically for PCBs?
What type of properties would I be looking for in a good silkscreen ink?
Can the inks be tinted to create any color I wish?

Of course, I've Googled, but many results deal with silkscreen printing for fabrics and I'm not sure how much of that info applies to PCB manufacturing. Thanks.  *I'm not. :D


texts: Over voltage and reverse voltage protection of analog input circuit with voltage follower

texts:
There will be 8 analog signals read by a microcontroller (STM32).I want to design a protection circuit for analog input.

The input can be 0-10V or 4-20mA controlled by the MCU using an inverter based on NPN transistor.
When the pin is high (v2=3.3 and v3=0V) the input is 4-20mA the op_amp sees the voltage across R2//R3.
When the pin is low (v2=0 and v3=3.3V) the input is 0-10V the output voltage is reduced to 0-3V with the voltage divider(R6,R8.)
R1 is used to limit the input current.
R2//R3 to reduce the wattage rating instead of one resistor.
I searched for a solution and I found this Over voltage and reverse voltage protection of multiplexed ADC with voltage follower.
I tried to use Matthew's suggestion but in the simulation I get 12.5V         with overvoltage input and -0.5V in the case of reverse voltage. The problem here is that my op amp allows only VSS-0.2V and VDD+0.2V.
I am looking for an explanation to how the back-to-back diodes work and any suggestion to fix this or any other solution to protect my circuit instead of using 32 diodes or 12 two diodes in series.


texts: VHDL - Cheapest-Fastest unsigned to signed binary number converter

texts: We know that to convert unsigned to signed (precisely, I want to convert a pure binary into CA2 number) we must negate the unsigned number adding, then, + 1. In VHDL I can implement an inverter and an adder that manages the carry in. I have two numbers of 32 bits. Is there another way to implement the sum + 1 using anything cheaper? Is there a solution to manage the carry in using only logic gates?


texts: Why is my negative peak detector behaving poorly?

texts:
Background

I have an amplitude detector circuit which consists of positive and negative peak detectors fed into an instrumentation amplifier.

The purpose of the circuit is to output the amplitude of an AC square wave. The reason I have both positive and negative peak detectors is because the square wave is not symmetrical about 0V. There may be up to a 200 mV offset for a 12V peak-to-peak square wave. If I had an input that was known to be symmetrical, I would just measure the positive peak and double it.

The circuit mostly works as expected.

Problem

For a 200 kHz, 7 Vpp square wave, the positive peak detector is only ~1% off from the peak positive wave voltage indicated on my oscilloscope. However, the negative peak detector output is ~10% less (in magnitude) than the peak on the negative side of the wave, and has large offsets when inputs are small.

Below is some data I measured from the actual circuit with square waves of various amplitudes and offsets at 200kHz. V+peak is the peak positive voltage of the square wave at the input to the circuit. V-peak is minimum negative voltage of the square wave. V+out is the output of the positive peak detector. V-out is the output of the negative peak detector.

V+peak | V-peak | V+out | V-out |
 0.22V   0.00V    0.22V   0.17V
 2.16V  -2.40V    2.15V  -2.08V
 3.66V   0.00V    3.63V   0.18V
 3.48V  -3.84V    3.48V  -3.49V

Notice there's also a pretty extreme offset voltage from the negative peak detector on DC square waves (the ones that don't go below 0V).

My negative peak detector has exactly the same circuit as the positive detector (shown), except that the polarity of the diodes is reversed.

Circuit explanation

Initially, the capacitor is discharged (0V) by R11 and U3 is in negative saturation. D3 blocks current. D4's bias current is provided by U1 through the 47K resistor. This configuration exists to prevent the diodes' reverse leakage from draining C12 and reduces droop of the output signal.

If U3's non-inverting input exceeds the voltage of the capacitor, the output of U3 races up to a positive value and current flows through D3 and D4. The voltage drop of the diodes is negated due to the feedback voltage being after the drop. The capacitor charges until it reaches VIN or when VIN drops below it's the capacitor's voltage, at the time of which U3 goes back into negative saturation. The capacitor slowly discharges through the R11. This is a major source of droop on fast or low duty cycle signals since it will discharge some before the next wave peak.

U1 is a unity-gain output buffer that prevents the next stage from draining the capacitor.

For the negative peak follower, the same explanation holds, except that the input op amp can't charge the capacitor unless its output is negative in excess of the capacitor's charge voltage.

Here's the data sheet for the AD843: http://www.analog.com/static/imported-files/data_sheets/AD843.pdf

It has a high slew rate (250V/us) and output current (50 mA) and low offset voltage (1 mV).

Question

Why is my negative peak detector performing so poorly (offset voltage, droop) compared to the positive detector?

Am I missing some essential element in converting the positive peak detector circuit to a negative peak detector?


texts: What is the difference between ADC single conversion mode and free running mode in ATmega32A?

texts:
Can someone explain this to me as I don't get what's written in this section of datasheet
A piece code written in C showing the difference would be great too .
thanks in advance.


texts:
I've got a bi-color LED in a push-button that is red when powered in one direction and green in the other direction. I would like to control it from a Raspberry Pi GPIO pin, e.g. High=Red, Low=Green.

I thought I could use some kind of H-Bridge to reverse the polarity, something like this perhaps?

The idea is that when input is High the BC547 is open and FET B and C are open providing polarity in one direction. When the input is Low the BC547 is closed and the FETs A and B are open providing polarity in the other direction.

I want to power it from Raspberry Pi's 5V pins however the GPIO is only 3.3V (that I can level shift up to 5V if needed).

The LED doesn't need a resistor, the button has an internal one.

I've put 4x 2N7000 (N-channel MOSFET) in the schematic as I've got a bag of them but happy to replace them with BC547 / BC558 or anything else.

Is the overall idea correct?
Will the gate levels be high enough to open the FETs?
Will the voltage drops on the FETs will still allow the LEDs to operate?

Thanks!


texts: Headset input crosstalk, or how to mitigate the effects of common ground resistance

texts:
I am building a cable to connect a guitar (or a piezo) and headphones to the TRRS connector of a smartphone through 4-wires cable splitting at ~1 mt from the connector.

I am experiencing a significant leak of the output signal back into the microphone output. After a few tests (also with a cheap headset affected by the same issue), I came to the conclusion that most of the crosstalk must be due to the shared ground wire resistance, which is not negligible.

I've reduced the circuit to the one in figure (there's only one output channel for simplicity) where Vo is the output signal from the phone, Ro is the headphone resistance, Vs is the input source (coil/piezo), Ri is the microphone input resistance.

Keeping aside all other aspects not considered by the simplification, I'd like to know if there is any way to counterbalance the effect of Rgnd, without having to run two separate ground wires. I was thinking about some op-amp based solution, or any other off-the-shelf chip (since it's a hobbyist project).

Edit: for further reference, here's how I wired the actual cable to the TRRS connector (image taken from https://source.android.com/accessories/headset-spec.html)

Edit 2: Ok, I performed additional tests with a resistance connected instead of the guitar. I'll try to sum up the results of the tests:

Nothing connected (no headphones, no input) -> very low crosstalk
No headphones, guitar only -> very low crosstalk
No headphones, resistance only -> very low crosstalk
Headphones only, no input -> very low crosstalk
Headphones + guitar -> sensible crosstalk
Headphones + resistance -> very sensible crosstalk

The crosstalk is almost the same for the first 4 cases, in case 5 it becomes very distinguishable and invalidating for any practical purpose, case 6 is even higher than 5.


texts: How can I measure distance travelled in cm without gps?

texts:
I was asked to build a circuit that will measure the distance travelled of a small vehicle, like a lawn mower.

There's a requirement that it would measure distance travelled in cm/sec. GPS is too inaccurate, and the starting point is unknown. I'm unable to put anything in the ground.

Any ideas? I can use whatever IC I want. I thought of using a camera pointing down, like a mouse, but it seems too complicated to process outside of home.


texts: Why Does Flyback Current Destroy Darlington Buffered Op-Amp?

texts:
I am working on a project where I'd like to deliver variable DC control voltages to a continuous solenoid motor in order to achieve different velocities of actuation.

To buffer my DC control voltage for high current to drive the solenoid I tried using a Darlington buffered LM358 op-amp like so:

For the Darlington I am using a TIP120 which is the following circuit in a TO-220 package. As you can see it includes a flyback diode:

I had thought the internal TIP120 diode between the collector and emitter would deal with flyback current. However I'm experiencing an issue where if I give the solenoid DC for too long I get massive flyback current when the op-amp input swings low again (I can see the flyback going crazy on my scope) and the op-amp ends up blowing itself up.

What is causing this to happen? Is there a way I can modify my circuit to protect again flyback current?


texts: I am trying to make an alarm system (audible and visual) using a siren and 3 strobe lights. I am using 12v battery like the one used in cars. Now I would like to detect when any of the alarms have failed. I think a strobe-light/siren would fail when it is open circuited or short circuited. So what came to my mind is that the current will increase dramatically when the strobe/siren had just failed. I need a comparator circuit (maybe Schmitt trigger? or an op-amp circuitry?) that will detect over-current in those alarms. Once that alarm failure is detected, I would like the user of the alarm system to be alarmed maybe by a piezo or LEDs.


texts: How to use functions from math library in Keil uVision MDK ARM?

texts:
I want to use log() function (natural logarithm) in one of my calculation of Temperature using the Stein Hart Equation. Microcontroller used is STM32L476 .

#define getTempKelvin(R) (1/(THERM_A + (THERM_B*log(R)) + (THERM_C*log(R)*log(R)*log(R))))
TempKelvin = (float)getTempKelvin(ThermResistance);

This is how I calculate the temperature where ThermResistance is the Resistance of the Thermistor that is measured. The problem is that, I'm getting 0 as value in variable TempKelvin ,I have included math.h library and checked CIMSIS DSP in Run Time Environment of Keil.
How to solve this issue?
 I'm able to open math.h in keil and C is the language used but shows log is undefined, when tried to go to the definition.


texts:
I'm trying to modify a small DC stepper motor from a single output to double output. Could a stepper with one output (front) be fairly easily modified to double output (front and back)? For instance, stepper motors like below seems to have a bit of the output shaft protruded from the back.

Could the shaft somehow be shifted to the back to make double output? Will the torque and other ratings be affected as a result?


texts: Is heating the nichrome wire with phone battery possible?

texts:
I want an nichrome wire to heat instantly red hot when connected with phone battery using 2 copper wires. Do I need any extra circuit to convert the volts into current for heating? (H=I^2Rt)
Would decreasing the wire diameter of nichrome wire to increase the resistance help that much to heat up?


texts: How can I connect wire to this push button switch

texts:
I've tried all the tricks to solder the pin for this push button, to no avail. Though I feel flux may help it stick (not sure), I just feel there has to be a better way. The pins are made of steel like slippery metal, and my solder never sticks.
Is there any jack connector for such pins that I am unable to explore yet?
Thanks for help, and hope this helps some newbie like myself.


texts: Supply voltage drops AFTER connecting to device

texts:
I have a 19V 2.1 amp (power mentioned is 45 watt) laptop adapter connected to a 19V 2 amp laptop (in description power mentioned 10.2 watt).

When I plug the adapter, the multimeter shows the rated voltage, 19V. But when I connect it to the laptop, it does not charge. Then when I remove it and check the voltage, it does not even show 1 V; somewhere around 200mV.

What and where is the cause?


texts: Does anyone have any idea what this device might be?

texts: I recently got a box of vintage stuffs. I came across this stuff. Its powered by a 9V battery. Does anyone has any idea what this is?


texts: Deriving NEC wire reactance table values

texts:
I'm verifying the NEC impedance table manually (how it gets the values in the table).

In the NEC list for AWG 1 above, the inductive reactance (Xl) for 1000 feet has value of 0.046 ohm for PVC conduit
See:
ftp://ftp.conagua.gob.mx/OCPBC/aps/Proyecto-PTAR-Las-Arenitas-Mxli,-B.C/MEMORIAS/6.-%20MEMORIA%20ELECTRICA/Tabla%209%20Resistencia%20y%20Reactancia%20de%20cables%20NEC%202008.pdf

1000 feet of awg 1 has calculated inductance of 687000 nH or 0.000687 H see: https://www.allaboutcircuits.com/tools/wire-self-inductance-calculator/

The inductive reactance is 2 pi f L... or 2 (3.141) (60) (0.000687) = 0.259 ohm see: www.66pacific.com/calculators/inductive-reactance-calculator.aspx

Why is the 0.259 ohm so far from the NEC listed value of 0.046 ohm?

How does NEC derive the 0.046ohm? Can you help derive 0.046 ohm? I've been trying it out for  hours already but couldn't match them. Thank you.


texts: MOSFET drain-source voltage in an H-bridge

texts:
I'm using an H-bridge to drive a DC motor.
The H-bridge is driven by sign-magnitude method (i.e. one of half bridges is not switching.)
I did the best I could but I couldn't figure out what's happening in the picture.
CH1 is the drain voltage, and CH3 is the gate voltage of the low side MOSFET with respect to source.
About 5 A is flowing through the motor.
Since I used typical 1 mΩ Rds(on) MOSFET (TPH1R405PL,L1Q), I expected negative 5 mV on drain-source, which is true on the other half bridge. But on the switching side my oscilloscope shows about 600mV drain-source voltage and it is not even negative.


texts:
The Signal Recovery Model 5184 is an ultra low noise preamplifier. The product description says

  ... and incorporates a special pseudodifferential input stage that can
  be floated to give the ground loop immunity normally associated with
  true differential inputs but without the associated noise penalty.

The question is

What is a pseudo differential input.
Why is there a noise penalty for real differential inputs.


texts: Book on memory from hardware perspective?

texts: Is there a good book that talks about memory (SDRAM, DDR, NVRAM, flash etc) from a hardware/system perspective? Most of what I've been able to find deal with memory at the transistor level. I am looking for overview of the different types of memories, power requirements and PCB guidelines.


texts: How to identify notebook motherboard parts that don't have meaningful description?

texts:
Recently I was trying to fix flooded laptop - Dell Inspiron 5370. After disassembling the motherboard (named ARMANI13) I noticed rust on one of the chips. Its location and surrounding elements suggest its somehow related to power management. However there aren't any meaningful part numbers on top of it. I tried looking for it in electronic suppliers catalog, googling all possible combinations of letters on top, but did not get any useful results.

I tried many combinations:
5X-4H, 5X=4H, M3Y etc.

In the first step I will try to remove it, clear and solder back. But I think it's possible the chip got damaged or its pins got eaten by rust. In such case I will have to buy a new one.

I also hadn't found any used / damaged motherboards with same chip and reasonable prices. New stock motherboard costs 80% of new laptop so the only sane way is to replace single broken part.

Not surprisingly I wasn't able to find any schematics of this or related motherboards.

Is there any way to identify such part? The only useful detail is the package.

Is it possible that a dedicated integrated circuit was manufactured for this specific kind of motherboard only and it's not accessible on market?


texts: Can anyone help me find a connector for this?

texts:
I'm having trouble identifying this connector

https://imgur.com/gallery/6M3bkJJ

I'm trying to find the connector to it so I can connect the 5 wires for video. This board is part of a arcade machine.


texts: If induced voltage (back-emf) is equal and opposite to applied voltage, what drives the current?

texts: Suppose we have a circuit with a voltage source, a switch open and an inductor all in series. If we close the switch, the potential difference of the voltage source is instantaneously applied to the inductor. As the current starts to build up, induced voltage from the inductance opposes it. If the induced voltage (back-emf) is equal and opposite to the applied voltage, and the net voltage is zero, what drives the current then?


texts: What is that component from the ADP5091 Schematic?

texts:
I am looking for an explanation what that component does inside of that circuit.
It can be found on page 3 of the Datasheet of ADP5091:
https://www.analog.com/media/en/technical-documentation/data-sheets/ADP5091-5092.pdf

It would help me out a lot. Thank you in advance!


texts: External 5V sensors separate 5V regulator , Poly fuse or both?

texts:
I'm producing an Arduino project that has two 5V inductive proximity sensors placed outside the project box.
The project is powered by a Meanwell 12V power supply then to a Murata 5V DC-DC converter which supplies the Arduino and other 5V components,  including the two proximity sensors.
The Arduino inputs have a series 1k resistor, TVS diode to ground, and a 10k pullup.
Question
As the project is water-based there is a small risk that the 5V supply for the external proximity sensors could be shorted to the ground and cause the Arduino to"brown out" or reset.
I have considered adding a separate 7805SR regulator, a couple of 0.1uf caps, and a 0.5A PTC fuse as a dedicated supply for the external components powered from the 12V Meanwell PSU. (common ground connections)
Is this a suitable suggestion?
EDIT: sensors are 5v 200ma, the system is powered from a 48V battery.


texts:
I have a device that is controlled by connecting a resistor between two of its connectors. The resistor can take any value between 0 and X, where X is an odd value. (E.G. X=1523ohm)

Does anybody have an idea how I can realise a circuit whose resistance can be varied manually between 0 and X? There must not be the possibility that due to user error the resistance is larger than X!

Many thanks.

Edit 1

To clarify: I do not have a variable resistor but am looking for a circuit that has a variable resistance with an odd upper limit. Variable resistors have standard upper limits, e.g. 100 ohm, 1kOhm, etc. but not 1523 ohm...


texts: First time PCB design - board dimensions question

texts:
I'm designing a PCB for the first time and I'm using NI's Ultiboard software to do so.

I tried uploading my Gerbers to a few cheap fabrication services, but I've noticed one discrepancy:  I don't understand how these services are determining the width and height of my board.  I designed my board to be 50.8mm by 52.6288mm - the size of the board outline in my design.  These services are all detecting my board as being sized 82mm by 66mm.  The height discrepancy is small, but why is the width discrepancy so large?

I suppose that the most general question is this:  what can I do to limit or estimate the actual size of a PCB before I upload it to a site to be fabricated?

This is my board as it is being interpreted by one such service:


texts: How do I stop signal looping with I/O port in this communication system

texts:
I am still a student. When I am designing communication system I am facing this problem: As shown in the figure I need to communicate with Master and Slave. But Master and Slave have single I/O port for receive and transmit signals. As shown in the figure, I am using a transceiver for this system to communicate with each other. But the problem is when the master transmits the signal, it loops and comes back to the master. How do I overcome this problem? I think problem is clear.

(In this figure I have shown I/O connection only.)


texts: Audio Capacitors - NP0/C0G or Film in Loud Enviornments

texts:
I hear a lot of "audio-foolery" going around about capacitors and I have always steered clear of multiplayer ceramic caps because I was under the impression that they are microphonic.

I am designing a circuit that will be used in a club environment, eg 100dB to 110dB (spl).

For this reason I want to be very careful of microphonic effects as that is some serious shaking! Not to mention the unit will be the same table as the sub-woofers.  I am reading a good bit online, but I wanted to ask some people with first hand experience and this is the place for it I feel.

-

The question :

Would NP0/C0G multi-layer ceramic caps be equivalent in this situation to using film capacitors? What realistic considerations should I be factoring into my decision as from a manufacturing point of view, this will bring cost down enormously as well as ease of procurement.

Thank you for your time.


texts:
I have found an old driver board (probably the mid 80's) for stepper motors (rated at 1.25V 3.8A) and I want to rebuild the H-Bridge using the parts on the board and a micro-controller as an input. I have the schematics but the ICs (mainly the transistors) are marked with proprietary numbers (not the typical TIP 120 for example). From the schematics and the board I know that I have PNP  darlington (called 3825) and NPN darlington (called 3805) transistors. Having no datasheet for the transistors I built a simple circuit to measure the gain:

Measuring the current between the emitter and the ground I get 0uA. Across the 1M resistor I get 8.89V and 0V across the 1K resistor. Measuring the voltage between the collector and emitter I get 9V.
I added a push button but pressing the button only changes the voltage between 8.99V and 9V (Although I'm not sure my multimeter is that precise).

So where did I miss something?
PS: My multimeter as an hFE function but cannot read gains higher than 999 and my guess is that those have higher gains than that.


texts: Will XORing the FIO0PIN register on an LPC175x6x give unexpected results?

texts:
Is this code guaranteed to only effect pin 22?

int* FIO0PIN = (int*)0x2009C014;
*FIO0PIN ^= (1<<22);

At first it seems like a dumb question but I remember working with a PIC18 microcontroller where you could corrupt the port output by doing this. Corruption happened when a previous write to the the output latch was not yet reflected by the output state (pin is driving a capacitive load), XORing an unrelated bit meant reading the port, doing the XOR and writing back to the output latch (with the old value of said unrelated pin).

int* FIO0PIN = (int*)0x2009C014;
*FIO0PIN &= (1<<4);  //set bit 4
*FIO0PIN ^= (1<<22); //if pin 4 has not yet transitioned to 1 because of capacitive load
                    //will this clear it again?

How does the Cortex avoid this problem? Or does it?

I am aware of the FIOxSET and FIOxCLR registers, bit toggeling through them is however much less efficent if one does not know the current value of the bit in question. I am writing a domain specific language using C++ meta programming which abstracts all basic IO functions and preforms optomizations on sets of them. With the LPC11xx parts implementing the bit toggeling is super easy, I just use the dedicated register, I would like to get the LPC17xx implementation as efficient as possible.

Here is the code in case anyone is interested: https://github.com/porkybrain/Kvasir the "register action" is created by the "makeToggle" factory here https://github.com/kvasir-io/Kvasir/blob/master/Lib/Io/Io.hpp using a template specialization here https://github.com/kvasir-io/Kvasir/blob/master/Lib/Chip/NXP/LPC17/M3/5x6x/Io.hpp I currently make a XorAction out of it for this chip, however I am not sure if it is correct.

I am aware that the FIOxPIN is in the bit band addressable reigion, however according to UM10360.pdf page 749 "Data accesses to this region are remapped to bit band
region. A write operation is performed as
read-modify-write. Instruction accesses are not permitted" which in my opinion would be just as suseptable to the above mentioned problem.


texts: analysis of BJT PNP type - why they can use voltage divider?

texts:
Hi everyone,
I try to understand why some books used in a voltage divider to find the Base Voltage?
or maybe the right question is HOW they can use voltage divider if there is base current? what I miss here?
what is the best way if I want to find what is the Base Voltage?
this is some example :
https://www.eeweb.com/quizzes/voltage-divider-biased-pnp-transistor
Thanks ahead.


texts: DC/DC boost converter voltage drop when connected to load

texts:
For my senior design project, I am trying to generate two voltage levels or rails from a battery powered circuit (12 V and 3.3 V.)

I am using an adjustable boost converter for the 12V rail and a fixed one for the 3.3 V.

The battery is a Li-ion 3.7 V_nom, 2200 mAh from Tenergy.

The boost converter is the ADP1613 and I also have a backup, the LM2735.

The 3.3 V is the LD3985M33R (buck.)

The loads I will be powering with the 12 V rail are:

An electromagnet that draws a max of 450 mA according to the manufacturer (but in testing measured 150 mA)
4 strings of of 4 LEDs, running at 20 mA each, which puts each string at around 80 mA (the forward voltage is around 2 V for each LED)
The bias voltage of an audio amplifier, the LM386N.

The 3.3 V is powering:

An MSP430,
A CC3200
An LED driver.

The issue:

When I connect any load to my boost converter, the voltage output drops significantly.

For the electromagnet, it drops to around 4 to 5 V.

With the LEDs, it drops to around 7 to 8 V.

For the audio amplifier, it drops to around 6 to 7 V.

Unloaded, the boost converter provides around 12 V.


texts:
A bit of background: We have a system currently in production, but the original programmer passed away, and the current hardware manufacturer cannot find hardware to run the (currently) DOS system, so I need to re-implement this in a more modern platform. I can only change the programming and the motherboard hardware.

I asked over in StackOverflow and was suggested I ask here.

I am new to the locating hardware side of embedded programming and so after being completely overwhelmed with all the choices out there (pc104, arduino, rabbit, custom boards, a zillion options for each board, beagle, volume discounts, devel kits, ahhh!!) I am asking here for some direction borrowing from your experience. (What would you do?)

Basically, I must find a new motherboard and (most likely) re-implement the program logic. Rewriting this in C/C++/Java/C#/Pascal/BASIC is not a problem for me. so my real problem is finding the hardware. This motherboard will have several other devices attached to it. Here is a summary of what I need to do:

Software requirements: Very minimal. No need for RTOS or multitasking, very low CPU requirements, I just need something I can program and something I can put a remote update mechanism into (updates to the code will be downloaded via modem maybe 1-4 times a year).

Required hardware:

2 RS232 serial ports (one used all the time for primary UI, the second one not continuous use [it's a serial printer])
1 modem (9600+ baud ok) [Modem will be in simultaneous use with only one of the serial port devices (UI), so interrupt sharing issues with one serial port is OK, but not both]
Minimum permanent/long term storage: Whatever O/S requires + 1 MB (executable) + 512 KB (Data files)
RAM: Minimal, whatever the O/S requires plus maybe 1MB for executable.

Nice to have:

USB port(s)
Ethernet network port
Wireless network

Implementation languages (any O/S I will adapt to):

First choice Java/C# (Mono ok)
Second choice is C/C++/Pascal
Third is BASIC

Ok, given all this, I am having a lot of trouble finding hardware that will support this that is low in cost. Every manufacturer site I visit has a lot of options, and it's difficult to see if their offering will even satisfy my must-have requirements (for example they sometimes list 3 "serial ports", but it appears that only one of the three is RS232, for example, and don't mention what the other two are, or how much it costs (or is even possible) to make it RS232). The #1 constraint is cost, #2 is size.

Can anyone help me with this? This little task has left me thinking I should have gone for EE and not CS :-).

Also, please let me know if I can phrase my question any better.


texts: I can't understand the function of this diode

texts:
On a past project, I've used the LM2576 buck converter with success. However, I've never understood how the catch diode works (D1 on the diagram).

The datasheet explains the importance of the diode, and why it has to be a Schottky. TI LM2576 Datasheet

My doubt is around the workings of this diode on the example circuit. Being a DC output, when the IC is shut down, the inductor will release charge flowing in all directions. IC output will prevent sinking that current, so it must take the load way. Is the voltage drop of the diode what is important here, maintaining the orientation of current? Does this means that current will flow to the load, after shutdown, and return via GND multiple times, using that voltage drop to slowly drop to zero? Does this solution prevent damage to the load, or the voltage source?

Thanks in advance for your time.


texts:
If I have a PCM-9361 Intel Atom board that says it uses 12V power supply and under max power consumption it uses 0.09A - does this mean the board uses 1.08 watts per hour?

Also, the board specs says if being powered by 5V, the max current is 2.38A... why does 5V use a lot more current than 12V?


texts: What is the setup/hold time of the RMII receive interface of the TI DP83630 phy chip?

texts:
I'm interfacing the TI DP83630 phy chip to FPGA over RMII interface and need to write the timing constraints. I'm having difficulties interpreting the receive interface setup and hold time from the image below. I suppose I should be able to deduce something from the T2.27.2 min/max timings but I'm stuck. Can anyone explain how are setup/hold times calculated from the image below?
Thanks a lot!


texts: Amplifying Millivolts with a Single Power Supply Op Amp in a Large Gain

texts:
I have a signal  around 1mV-10mV to be amplified. This signal should be fed into an ADC (ADS1115 ) which has minimum full scale range of 0.256V. So the gain should be at least around 300. I am thinking of doing this amplification with a single supply (5V) low power Op-amp. I went through some op amps (OPA, LM) and can't find if they are good enough as some don't have libraries to simulate and most are out of  stock in our area.
I would like to know if it is possible to achieve such a gain with an acceptable accuracy (error level 5~10%) and some suggestions of particular op amp models.
Couldn't find an ADC which has lower than 0.256V full scale range, seeking for suggestions if you have any, so I wouldn't have to amplify the signals in a large factor.


texts: Ultrasonic transducer response to harmonics?

texts: Does anyone know offhand whether an ultrasonic transducer will respond efficiently to harmonics of the fundamental? For example, will a 40kHz transmitter also transmit with reasonable efficiency at (say) 20kHz or 80kHz?


texts:
(source: electronics-tutorials.ws)

(source: electronics-tutorials.ws)

I want make this 3 input device 4 input legged. Any suggestions?


texts:
Is it possibly to use a Bluetooth receiver as an on/off switch in a circuit board?

Ideally, I would set the Bluetooth receiver into a low energy/sleep mode and use it simply as an on/off switch on a device. There is a small battery connected to the circuit board and an LED light at the other end, just to test if this will work.

Ideally it works like so:

Android/iPhone sends signal to Bluetooth receiver
Bluetooth receiver accepts the signal, then the LED light turns on/off
I know many people use bluetooth devices to maintain a constant connection with their phone and/or constantly feed information, however this isn't my intention.

I simply want to use it as an on/off switch that my phone can communicate with at all times.


texts: Best battery configuration: 1s1p vs 3s1p vs 1s3p?

texts:
I’m designing a product prototype using a single board computer (like a Raspberry Pi) that requires an 8-18V DC supply. It has to become battery powered, so I’m looking into the best possible configuration. Besides the SBC, another component in the device requires a 9V supply. The SBC currently consumes about 200mA when powered from 12.6V and we expect about 1000mA peaks from the 9V device.

The simplest battery configuration seems 3 LiPo’s in series. I’d need an additional buck converter for the 9V rail. What worries me more is balanced gauging and charging of the cells. Compared to single cell LiPo charging it seems rather complicated and I’m having a hard time finding a simple yet effective (pair of) ICs that do the job without having to spend too much time setting things up. For reference, I was quite overwhelmed by TI’s bq40z60 all in one solution. Very nice but too complicated for the time and budget I have.

I could also use a single cell pack with high C rating and boost it up to 9V. Add a simple charge IC and single cell gauge like I used before in other designs and done with it. Of course the run time would be significantly lower than with 3s1p but so much quicker to build!

And I guess 1s3p would increase the runtime again but also complicate the charging and gauging, so I don’t think that is really a good option.

What would you do in a case like this?


texts: I want to remote control the power going to a water heater on a boat - the water heater is 110v and the remote control voltage is 12v - can I use a 12v continuous use solenoid to pass the 120v - I am looking at using a continuous 200 amp solenoid the switching voltage is of course 12v, but can 120v be run throught it - have not been able to find a 12v solenoid that says rated for AC


texts:
I have been reading about communication theory and I was wondering if matched filters can be implemented with analog parts and what they would look like?

If they can't be it seems like the matched filter construct is of only theoretical interest without any practical implementations.


texts:
I have created a circuit using TINA and it has given me a "convergence error". TINA is telling me the issue is LED1 however I am unable to troubleshoot the problem.

The circuit is as below:


texts:
I am measuring a short between the D+ and D- lines between the USB micro connector and USB to UART chip (CP2102N). However by looking at the photos, there doesn't appear to be a short. Should I assume either a.) the chip is bad or b.) the pins are shorted underneath the chip?

The two pins of interest in the pictures are the ones connected by the two traces in the middle of the pictures.

This is a custom PCB for a project I'm working on. You can also see on the schematic, everything seems to be good.

I'm asking here before replacing the chip, because I currently do not have a hot air station, so removing will be a bit of effort.

Also, upon plugging in the board, I get the message: "Unknown USB Device (Device Descriptor Request Failed)" After discovering the short circuit, this message is hardly a surprise, but thought I would include that information.


texts: Does modern market has IC chips which can be fully reverse-engineered with optical microscope?

texts:
I'm planning a new course on digital electronics and semiconductors devices for my university. I think, it would be great to go to the lowest available level of abstraction, or, at least, slightly touch.

So, I naively think it would probably be a good lab assignment for students to grab microscopes and some acid, and try to completely reverse-engineer some simple chip. By “reverse-engineering” I mean not only looking at the picture of naked gates and conducting lines, but restoring the original model of the chip operation, without probing it electrically.

Back in history, it was quite common to have micrometer-scale integrated circuits which had only a dozen of isolated logic gates in a single package. Is it possible to buy something similar today?


texts:
I have read somewhere on a forum that there are two effective internal resistances of a capacitor in a DC circuit but can't seem to find any further information. From what I read 'parallel resistance' exists for a capacitor and is typically in the order of megaohms. Is this information correct, and if so can anyone point me to a more reliable source which contains some more background on the theory of this?

Thanks


texts:
I wanted to ask a few questions in the hoped that someone can advise me.

Basically I wish to use a sensor which will be attached to a large piece of fabric, I would then like to use the data from the sensor to inform me about the stress-strain relationship, create and predict models and compare with any existing models.

Any advise, links or research to read into would be incredibly helpful!


texts: Detecting signal / amplitude from 2 wire DC speaker

texts:
I want to create a circuit that replaces a 2 wire speaker in an existing electronic device. I want the device to be able to trigger an output when the amplitude of the signal that would regularly going to the speaker, exceeds a certain level. The device with the speaker is a small USB powered toy, so voltages shouldn't be very high.

If anyone could give me some pointers on how to achieve this with analog circuitry and or a microcontroller, that would be super helpful.


texts: What would be the best approach to align a photomask onto a PCB panel?

texts:
Issue: Alignment of photomask to reference holes drilled

When making PCB in panel form, the reference holes are usually drilled at 4 corners of panel to allow alignment of photomask to the PCB board. If the smallest trace width and gap are 70um, holes size of 0.15mm, what would be the best approach to align the photomask onto the PCB panel?


texts: how to enable and configure USB OTG for device mode on iMX31 Litekit?

texts:
I need to configure USB OTG on iMX31 for device mode. We need a raw channel between the host and target and usb seems to be the best suited. However I haven't been able to correctly configure the OTG controller. I dont know what I am missing. I have performed the steps mentioned in section 32.14.1 of iMX31 Reference Manual. I have also configured PORTSC1 register for ULPI.

Can any one help me out here? any poineters/code/any thing that can help me is welcome.


texts: Slowly supplying power to a very high load

texts:
Is it possible to supply power to a very high load within a huge time range?

This question particularly regards MOSFETs.
I know that a MOSFET must switch fast so that a little power would develop upon it's Drain-Source junction.

But what if I want a MOSFET to supply 5V, 10A to a load, while it's OFF to ON transition takes 10 seconds? (just an example, not a real scenario)
That case, what would I need to do in order to accomplish this?
Is it possible/realistic to accomplish with MOSFET or should I use other devices/components?

I've seen an "electronic switch" that it's OFF to ON time adjustment feature has been disabled, because that the MOSFET can't sustain high power while the slow transition occurs.

Edit #1 (27 Aug 2013, 20:00 UTC):
Would you say that HUF76629D3ST_F085 is good for the job?


texts: I need to receive signal from IR transmitter LED. I am not sure how to program the microcontroler. I am looking for some concept, how to do that. Whether I have to use A/D conversion? How to synchronize transmitter and receiver? What structure will be in coming data? Let's say that I assumed 600us for 0 (binary 0) and 1200 for 1 (binary 1) when I was programming a transmitter. What are the common steps to receive infrared transmission on PIC18F microcontroler?


texts:
I have a circuit with many LEDs, all the same,
VCC-220ohm-LED-GND. Using the Net/Label the schematic is very simple.
Is there a way to have multiple instances of this schematic on the board, and keep the schematic simple, with one net/label schematic?


texts: Widlar current source : get \$ I_{C1} \$?

texts:
from the Widlar schema

that you can see, from here, i don't know how to retrieve this formula :
$$ I_{C1} = {\beta_1 \over {\beta_1+1}} \left( I_{R1} - {I_{C2} \over \beta_2} \right) $$


texts: ESP32CAM not working when powering through battery

texts:
I am trying to power esp32cam (ESP32-S board) from battery and it is not working. I have used it powering it through FTDI programmer and it was working fine. Now I want to use it as a product and want to power it through the battery.
The things I have tried are (Input and output voltage has been measured by multimeter)

Power through 3.7V Lenovo Li-Ion battery(3000mAh) (used in Lenovo mobiles).
Power through 8V(8000mAh) battery and buck converter converting to 5v then to ESP32CAM.
Power through 8V(8000mAh) battery and l8705 voltage regulator(which gives an output of 5v when input is greater than 7) with some capacitors as suggested by some websites and then the output of 5.1V to ESP32CAM.

I tried all the above and no result. I think if someone has used microcontrollers with the battery will have a good knowledge and will be able to help.
Thanks.


texts: compute impedance from voltage and current measurements

texts: I want to compute the impedance of my system from measurements of the voltage and the current. Is it simply the ratio of the rms amplitudes of the voltage and current (Z = Vrms / Irms)?


texts: clarification on a particular 555 implementation for 4017 johnson counters

texts:
I'm trying to build a 13 count johnson ring counter (which flashes LEDs sequentially 1 thru 13 and then repeats), and I found this circuit which looks perfect:

I assembled it with an extra LED on the 555's output pin. Oddly, when I apply power, this LED stays solid on, while none of the outputs of the 4017 are lit. In trying to troubleshoot this, I noticed that the wiring of the 555 differs from all of the standard implementations described on wikipedia (astable, monostable & bistable).
QUESTIONS:

Does anyone know if this is a reasonable way to use a 555? The commenters on the aforementioned post seemed to think it was.
Otherwise, if you see it to be faulty, can you suggest an appropriate fix for this circuit? I tried a normal astable setup and got nothing, but I have to admit that my understanding of what the AND gates are doing is too foggy to know if this should work.

Thanks in advance for you help!

Edit: discovered a loose ground to the breadboard with the LEDs. Plugged this in, and now I see that a few of the LEDS are lit -- flickering & different brightnesses -- mostly on the second 4017. Totally stumped.


texts: Calculating grounded emitter amplifer distortion (Art of Electronics 3rd Ed.)

texts:
Referring to section 2.3.4 A1 (pages 94-95) of the Art of Electronics 3rd Ed., I'm having difficulty understanding how to calculate distortion of a grounded emitter amplifier. The book says:

  Because the gain is proportional to the drop across the collector resistor, the nonlinearity equals the ratio of instantaneous swing to average quiescent drop across the collector resistor:

$$\frac{\Delta G}{G} \approx \frac{\Delta V_{out}}{V_{drop}}$$

  where Vdrop is the average,  or quiescent, voltage drop across the collector resistor Rc.

Now in the example in the first paragraph of page 95, Vcc = +10V and the output is biased to half of Vcc hence  Vdrop = 5V. The authors were successful at comparing measured distortions to predicted values. The results were 0.7% distortion for 0.1V output sinewave amplitude and 6.6% for 1V amplitude. I tried to "predict" the distortion but either my math or general understanding is wrong. For the first instance, I said the ratio of instantaneous swing to be 0.2V and the average quiescent drop to be 5V:

$$ \frac{\Delta V_{out}}{V_{drop}} = \frac{0.2}{5} = 0.04 $$

Or 4%.What is the mistake I am making?


texts: MOSFET: Why the drain and source are different?

texts:
Why the drain the source terminal of the MOSFET function differently while their physical structure is similar/symmetrical ?

This is a MOSFET:

You can see that the drain and source are similar.
So why do I need to connect one of them to VCC and the other to GND ?


texts:
I am currently designing a pretty big 4-layer development board 350mm x 270mm. Keeping in mind I have multiple analog digital and AC mains voltage, what would the best practice be regarding routing my 12V + 5V + 3.3V rails?
My options:

Option 1
Route power rails on separate plane and stitch together the required polygon pours.

Option 2
Use each plane for GND, 12V, 5V, 3V3 and stitch as needed.

Option 3
Route power rails separately on multiple planes as needed.

With option 1 I will only use 1 plane (bot) for all my power rails, but have the analog and digital signals in-between. Could that cause EMI?
With option 2 I will have huge capacitance between planes?
With option 3 I have long fat traces running around my board.
What would the best option be (or the one with the least problems)?


texts: Using a P-channel mosfet instead of a PNP

texts:
With the LPC1343 microcontroller (Cortex M3), there is a USB_CONNECT line which goes low when the micro is ready to connect to the computer via USB. This "soft connect" feature is implemented on the LPC Baseboard with a PNP transistor circuit. Would I be able to use a p-channel mosfet instead? I have already built the p-channel mosfet equivalent, and it works, but wondering about its reliability and whether it is "good practice".

Possible issues that (I think) may arise could be due to the fact that mosfets are voltage controlled devices, and on power up of the device, the gate voltage may not rise as fast as the voltage supply (3V3) (although they are tied via a 33k resistor in my implementation), and the mosfet would erroneously "conduct".

Note: My p-channel mosfet circuit just consists of replacing Q1 with a p-channel, R69 remaining the same, eliminating R68, and changing R66 to a 33K (no particular choice, had one on hand)


texts: GDT in parallel with TVS diode. Should the clamping voltage of the TVS diode be equal to the DC breakover of GDT?

texts: I am putting a GDT in parallel with TVS diode, and I want to know if I need to have clamping voltage of TVS diode slightly higher than DC breakover voltage of the gas discharge tube OR have clamping voltage and DC breakover voltage the same.


texts:
I am trying to further my knowledge in discrete transistor design so I am  designing a CE power amplifier to drive a speaker.

What I have trouble with is determining where to bias my BJT at.

I can't really find characteristic curves for transistors on datasheets which makes it difficult. I also don't know how to determine the amount of current that will go to my load.

Say  I have biased such that VC = 5 V and IC = 10 mA.
If I then connect my load in parallel from the VC node how can I determine the current?

I would think my equation would look something like:

$$I_{total} = 10 mA = (5/R_{load})-I_{collector}$$

How would I determine this I_collector value?

Datasheet for transistor I am using:  onsemi.com/pub/Collateral/P2N2222A-D.PDF

Want to couple the speaker with a capacitor to the vout node.

Here is a picture (source image) for reference to the type of circuit I am talking about:


texts: Transfer function of loop-back bias circuit for RF amplifier

texts:
I am trying to implement a current mirror as part of a bias circuit for a RF amplifier. I want to do a transfer function of the bias circuit since it creates a loop from the amplifier fet drain to gate. In order to make sure that i dont get any instabilities i want to find the poles from the transfer function.

I have converted the fet amplifier and one of the pnp transistors from the current mirror into small signal models. I have a small signal rf circuit as shown in the drawing.

Any help is much appriciated.

Edit: Alright after being suggested to provide some more of my results i have uploaded some new pictures of what i have done. The above question remains the same, i have a hard time going all the way to a finished transfer function. I do not really know what to do.

I have uploaded the initial schematic of which i want to find the transfer function. I have uploaded a reworked schematic of the loop going from the drain of the Fet to the gate. I have made 4 current meshes, which gives me 4 current equations. I know current3 from the current source. I have made som voldtage division equations for v1 v2 and vg. Solving the system of equations gives me something very ugly and big, which leds me to think something is wrong.


texts:
Does grounding body to DC power source makes sense, to get rid of any electrostatic(?) charges from my skin/body ?
In my new house, when I'm standing on the floor, connect voltage meter (AC) and ground myself to ground pin in AC socket, then it shows ~40 Volts and when sitting on the chair and it goes down to 18 Volts. Current is below 1mA.
I'm simply scared to connect myself to 220V socket (ground) as someone else might put something into it, change wiring, so decided with some lower voltages.
I was wondering about buying "grounding matt", but they are not quickly reachable where I live, so I'm wondering about grounding my body to DC source, like USB port. This way, my voltmeter (when set to AC) goes down to 1 Volt. When I set it to DC, it shows ~0.6V.
So here come my two questions regarding this "grounding", like...
1. Does grounding body to DC (minus in USB socket) makes sense and current does really flow off me ? I may use some diode like 1N4148 if needed.
2. Any other/better solutions for grounding body ? There is too much "marketing" on the network, so I'd like to hear experts comments from you guys.


texts: Hardware Schematic For Connecting Vibration Sensor to MSP430

texts:
I have a MiniSense 100 Vibration Sensor with me, which I am trying to interface with my MSP430 Launchpad to track the vibrations of refrigerator compressor. However, I am not sure if connecting it directly to my Launchpad, can damage the MSP Board.
When I tried to research on my own, I came across there different suggestions, such as this one v/s this one v/s this one.
MSP430 has 3.3v operating voltage. In the third one, the guy has directly fed the pin to ADC pin of Arduino. Will doing this damage the MSP430 Dev Board? What schematic should I follow?
I had to ask this question because, I couldn't risk damaging the board. I'm completely newbie to designing schematics. Please guide.
Thanks


texts: Numerically Controlled Oscillator (NCO) Sample quantity

texts:
Ive been doing some research on NCOs and some initial information (or lack of information) is bugging me. Ive read a few articles on this topic:

FPGA based NCO

Blog on NCOs

But i still don't understand how such an oscillator can vary frequency without reducing the number of samples between different frequencies.

All of the articles on this topic mention the following arrangement:

Increment Word ---> Phase Accumulator (Clocked by the main clock) ----> Sine wave look up table ---> DAC and so on.

The above arrangement (as far as i can understand) varys the amount by which it iterates through the table thereby varying how long it takes to go through it and produce a complete sine wave. However lets say my Look-up table consists of 2^8 entries and i increment through the table by 1 each time, i will go through all 2^8 samples and get a frequency of Clock/256

Now if i were to instead increment by 4 each time, i would only go through 256/4 samples and would thus get a frequency 4 times the previous example.

So as even though the frequency is varied isn't the number of samples present at the different frequencies also different.

How can the frequency be varied without effecting the number of samples present in the wave?


texts: How to connect multiple of the same device to an Arduino using I2C?

texts:
I want to use two of the same magnetometer (HMC5883L) with my Arduino, but I cannot figure the code for calling each of them separately.

I have read online that connecting multiple devices is completely doable, as long as you call their respective addresses, the issue that I'm having is that because I'm using two of the same device they each have the same address.

So my questions are, can I change the address I2C address of one of my magnetometers and not have it break, how do I do this, is it a permanent change, and if so can I revert the HMC5883L back to default if need be?


texts:
What does a FET actually do?
I thought I knew the answer to this question, however upon researching further about the function of a FET I became unsure whether I had the right idea.
I thought that when the gate of an N-channel FET is positive and current flows towards the gate, another current flows from the drain to the source. And that a P-channel FET has current flowing from the source to the drain when the gate is negative.
What I really want to know is what happens when current is supplied to the gate of an N-channel FET and a P-channel FET?
If I were to connect an LED in the path, current follows from the drain to source or source to the drain...
a) Is the LED on or off when a current flows towards the gate of a P-channel?
b) Is the LED on or off when current flows towards the gate of an N-channel?
c) What would the difference be between PNP/NPN transistors and N/P-channel FETs?
If my initial ideas about what a FET does were right, then surely a FET is basically the same as a PNP/NPN transistor, apart from the way they toggle the ‘switch’, like how a FET uses an electric field to do this.
I don’t have a prototyping breadboard or any other components with me to test my ideas.
Sorry if my question sounds dumb, I’m a beginner in electronics.
Any help would be greatly appreciated.


texts: How to prevent DC motor from dropping voltage of supply when switching on

texts:
I have a circuit which uses an ATtiny85 output to a transistor (S9013), which will trigger a relay that controls a motor.

The reason for the transistor to relay is because I do not have a transistor that can take the current of the motor, so I am isolating it with a relay.

While I can purchase all these, it will take time to ship.

Here is the circuit:

SCHEMATIC NOT UPDATED, I HAVE A DIODE GOING ACROSS THE MOTOR, AND A 100uF CAPACITOR GOING ACROSS THE VCC AND GND TO SMOOTH OUT THE VOLTAGE (have also tried 100nF).

Everything works if I don't connect the motor OR if I isolate the motor with its own power source.

The issue now is that when the motor is switched on, there is a massive voltage drop and the ATtiny85 will reset. Here is a waveform of the motor trying to turn on three times:

Is there a way to prevent this drop or at least reduce it to a point where the ATtiny85 won't reset? I'm thinking wire up a simple voltage regulator but not sure if the added complexity will introduce other issues. I also know I can go out and buy a motor or voltage regulators but let's avoid that option.

EDIT: so as per the answer, a diode (cathode at +ve, anode at VCC) was added between +ve and VCC, assuming that there is a capacitor connected in parallel with the ATtiny85 (+ve end at VCC, -ve end at GND). Theory is that the cap gets charged while the motor is off to VCC. When the motor turns on, it's going to drop that voltage down to below VCC and the diode is going to be reverse-biased and prevent any conflict from the supply to going into the ATtiny85. The capacitor can now freely discharge into the ATtiny85 without the supply affecting it (without the diode, supply will average capacitor down faster than if it would just discharge alone). For reference, the bulk capacitance value I used was 100uF.


texts: I am looking to build a circuit that would control an output relay. This would be done in 12V and the sequence will be initiated by a manual switch. I will need an adjustable time delay (possibly displayed time) after the switch is released, then the output would be random before shutting off. The sequence would not restart until the button was pressed and released again. The time after the button release would be from 0 milliseconds to 3 seconds. The "on" time for the output to turn on the relay would be from 500 milliseconds to 1 seconds


texts: FPGA able to send data, but unable to receive data. (UART - RS232)

texts:
I have a DE0-nano FPGA board and I am trying to establish a serial connection with my PC.

I am using the RS232 implementation from here: http://www.fpga4fun.com/SerialInterface.html

I have tested sending from the FPGA, and it worked perfectly. However, when I try to send to the FPGA, it seems to not be working.

Here is my verilog code:

module Learning(
    input clk,
    input RxD,
     output LED
);

wire RxD_data_ready;
wire [7:0] RxD_data;
reg [7:0] data;

async_receiver RX(.clk(clk), .RxD(RxD), .RxD_data_ready(RxD_data_ready), .RxD_data(RxD_data));

always @(posedge clk) if(RxD_data_ready) data <= RxD_data;

assign LED = (data == 8'h24);

endmodule

Basically I have designed it such that a specific LED on my board turns on while I am sending the hexadecimal value 24. Since I am sending this value at a very high frequency I do expect the LED to remain on for the whole transmission. However, nothing is happening. It stays off.

I already tried the reverse bit option from my rs232 program. Also, using a symmetrical value like 0x55 didn't work.

What could be the issue?


texts: For a design project I am designing a plastic platform with a steel construction under it, which has a diameter of 4 meters which is able to support 15 persons. The platform should be able to rotate at slow speed (4 rotations per minute). Now I need to find out which electromotor is able to make this possible, does anyone have a suggestion?


texts: Function of characteristic curve of DC motors

texts:
I have found in the following graphic the characteristic curve of a locomotive with six DC series wound electric motors at 3000V.  As a translation: the y axis describes, on the left, the force in tf (metric tonne-force), and on the right speed in km/h. The x axis describes current in A. The first function from bottom describes the characteristic when the motors are connected between them in series.  In the second function there are two branches in parallel of three motors each.  In the third function there are three branches in parallel of two motors each.  These functions correlate speed and current. The straight line correlates traction force and current.  Note that in every case the current axis describes the current that flows through a single branch of motors in each combination.  The dashed lines describe each case with a shunt field.

I was trying to come up with a function that for a given voltage, speed and motor combination gives current and traction effort.  However I am not familiar with electric circuits and I have had no results.

Thank you in advance.


texts:
Now I'm trying to study about time borrow as refer to here:
"Time Borrowing": Static Timing Analysis (STA) basic (Part 2).

Especially, I'm looking at this:

How to get time and how to get this not setup violation?

In my understanding, L1 to L2 needed 8ns time but the period is 5ns. Then it needs 3ns more. But L2 capture the data of L1 at PH2 positive sensitive clock. At this time, the data have not arrived yet (it needed 3ns).

I can't understand how to say this is not setup violation L1 to L4?