texts: Interfacing Atmega 2560 with 74ls240 inverting buffer

texts:
I am trying to light up the 7 segment display using inputs to the Port B pins, causing output on the Port k pins, which are inverted using the 74LS240 chip.

The Arduino is correctly outputting the correct high or low voltage on the Port K pins. However, the problem I have encountered arises when trying to interface the outputs from the Port K pins to the 74ls240 chip. Regardless of whatever the voltage on the Port K pins is, the output from the 74LS240 is always low. However, if I feed the ground voltage from the arduino board, the inverter outputs a high voltage, so I know that the chip is working fine. Below is the pinout and the logic table for the 74LS240.

I have VCC connected to Arduino's 5v pin, and G1, G2, and GND are tied to Arduino's ground pin.

Here is my code for Arduino:

// Define Port B Register Pointers
volatile unsigned char* port_b = (unsigned char*) 0x25;
volatile unsigned char* ddr_b  = (unsigned char*) 0x24;
volatile unsigned char* pin_b  = (unsigned char*) 0x23;

//Define Port K Register Pointers
volatile unsigned char* port_k = (unsigned char*) 0x108;
volatile unsigned char* ddr_k  = (unsigned char*) 0x107;
volatile unsigned char* pin_k  = (unsigned char*) 0x106;

int A;
int B;
int C;
int D;

void setup() {
  // put your setup code here, to run once:

Serial.begin(9600);

 *ddr_b &= 0x00; //set all pins to input
 *port_b |= 0xFF;// enable poullup resistors

 *ddr_k &= 0xFF;

}

void loop() {
  // put your main code here, to run repeatedly:

if( *pin_b & 0x01 ){A = 1;}
  else{A = 0;}

if( *pin_b & 0x02 ){B = 1;}
  else{B = 0;}

if( *pin_b & 0x04 ){C = 1;}
  else{C = 0;}

if( *pin_b & 0x08 ){D = 1;}
  else{D = 0;}

if((B==1 || D == 1)&&(A == 1 || C == 0)&&(B == 0 || C == 0)&&(A == 0 || D == 1)&&(A == 1 || B == 0 || D == 0)&&(A == 0 || B == 1 || C == 1)) // Boolean equation if a is 1 FIXED
{*port_k = *port_k & 0xFE;}
else
{*port_k = *port_k | 0x01;}

if((A==1 || B == 1)&&(B==1 || D == 1)&&(A == 1 || C == 1 || D == 1)&&(A == 1 || C == 0 || D == 0)&&(A == 0 || C == 1 || D == 0)) // Boolean equation if b = 1 FIXED
{ *port_k = *port_k | 0x02;}
else
{*port_k = *port_k & 0xFD;}

if((A == 1 || C == 1)&&(A == 1 || D == 0)&&(C == 1 || D == 0)&&(A == 1 || B == 0)&&(A == 0 || B == 1)) // Boolean equation if c = 1 FIXED
{*port_k = *port_k | 0x04;}
else
{*port_k = *port_k & 0xFB;}

if ((A == 0 || C == 1)&&(A == 1 || B == 1 || D == 1)&&(B == 1 || C == 0 || D == 0)&&(B == 0 || C == 1 || D == 0)&&(B == 0 || C == 0 || D == 1)) //Boolean equation if d = 1 FIXED
{*port_k = *port_k | 0x08;}
else
{*port_k = *port_k & 0xF7;}

if((B == 1 || D == 1)&&(C == 0 || D == 1)&&(A == 0 || C == 0)&&(A == 0 || B == 0))// Boolean equation if e = 1 FIXED
{*port_k = *port_k | 0x10;}
else
{*port_k = *port_k & 0xEF;}

if((C == 1 || D == 1)&&(B == 0 || D == 1)&&(A == 0 || B == 1)&&(A == 0 || C == 0)&&(A == 1 || B == 0 || C== 1))// Boolean equation if f = 1 FIXED
{*port_k = *port_k | 0x20;}
else
{*port_k = *port_k & 0xDF;}

if((B == 1 || C == 0)&&(C == 0 || D == 1)&&(A == 0 || B == 1)&&(A == 0 || D == 0)&&(A == 1 || B == 0 || C == 1))// Boolean equation if g = 1 FIXED
{*port_k = *port_k | 0x40;}
else
{*port_k = *port_k & 0xBF;}

Serial.print(A);
Serial.print(B);
Serial.print(C);
Serial.print(D);
Serial.write("\n");

delay(250);

}

Essentially, my question is why will the inverter chip not invert an input of a low voltage from the Arduino, yet it will invert a low voltage if I test an input to the chip with Arduino's ground pin?

Edit: here's a partial schematic

simulate this circuit – Schematic created using CircuitLab

This is an example of one of the outputs of the controller being fed into the 74ls240 chip.


texts: Altium 18 - "Override library primitive" option missing?

texts:
I'm busy setting up my new install of Altium 18 to match my preferred settings, namely making the default schematic font Consolas (for the purposes of mono spacing and slashed zeroes).

Normally this involves going into Tools -> Preferences -> Schematic -> Defaults screen, and changing all the fonts to the desired one for each primitive. However, since Altium 18 I notice the "override library primitive" checkbox for parameters/designators/values is missing, meaning while I get Consolas as the default font for any new schematic symbols I make, any existing library symbol I use still hangs on to Times New Roman.

Old Altium:

Altium 18:

Any ideas where this checkbox went, or how to emulate the same functionality?


texts: When current flows, Is there any potential difference?

texts: there are electrons that can move, and protons that can’t move. Then when current flow exists, does electrons that can move move? How can I explain this phenomenon? If it is true, how can I explain this picture? (Sorry, I'm not good at English, )


texts:
I was reading about the self-biased common-source stage and I understand that it has an inherent 'feedback' mechanism against variations in threshold voltage. For example, if Vth decreases, current would like to increase, but the voltage at the drain and hence the gate will also decrease, so current falls back down, correcting itself.

My question is, what's the point of the feedback Rf resistor? Current to the gate will always be zero, why do we need a Rf resistor?


texts: Why does a Darlington pair have a higher input impedance compared to a regular normal BJT transistor?

texts:
Freshman here, and I've been searching for an answer to this question, but I could not find any actual justifications yet. Basically, I am studying the concepts of a Darlington circuit, and saw that its current gain was really huge. My notion (and I hope I am correct) is that because the input current is passing through a transistor twice, that means that it gets amplified twice.
But what I also realized is that a Darlington circuit has a high input impedance! Now for that, I can't seem to find an answer to. Is it also because there are two resistors, so the total input impedance is the summation of transistor 1 and 2's input impedance?
Hope I can get some clarification. Thanks!


texts: In conductive grid pad charging applications, how does the charging base distinguish between human and metal contact to avoid electrocution?

texts:
I've been following a few products that were announced recently that use conducting grid charging and they're all advertised as being safe for users, even though some of these operate at high voltages and currents. These are a few examples of what I'm talking about:

http://www.skysense.co/charging-pad-indoor/specs

http://www.edronic.com/

https://www.flicharge.com/

I'm curious as to how are these charging bases designed to distinguish between human contact and metal contact, what would happen if I were to touch the charging base while the a device is being charged on it?


texts: Where can I find data sheets for a Sanyo Denki 103H5208-1241 Stepper Motor

texts:
I've acquired some Sanyo Denki 103H5208-1241 stepper motors and I can't find the data sheet for it for the life of me. I've spelunked their catalogs and such looking for them.

Where can I find them or can I safely use another stepper data sheet interchangeably?


texts: PC start button effect from electrical point of view

texts:
What I basically want to do is to connect one of the digital pins of a network-attached Raspberry PI to (one of) the connectors of the PC Power On button, so that when I issue a command coming on the network, the Raspberry will receive it and send an power on signal to the PC.

Can someone tell me more about the power on/off signaling procedure on a PC (hardware enabled)?

I assume it is something like the button allows or disallows the connection to sink or source for some amount of time (at least for power-off the amount of time seems to be relevant). I need to know also the source voltage, of course.

I think the button in its regular position will allow the flow of 5V (high) and disrupt it when the button is pressed, 0V (low).

My multimeter is currently broken.


texts: How to get right voltage output with Bts7960b H-Bridge?

texts:
I am using a NodeMCU to control a BTS7960b motor driver. (datasheet of the BTS7960)
This driver controls a 12v dc motor. This image shows my wiring (without the display and the buttons and with a NodeMCU instead of the Arduino nano).

My problem is, when the driver is set to maximum speed (the pins L_EN and R_EN set to high, as well as either LPWM or RPWN to 255 [pin naming visible on this page]) the output voltage to the motor is consistently only 3v instead of 12v. Because of that my 180 RPM high torque motor just runs with about ~42 RPM.
Decreasing the speed also decreases the output voltage. E.g. setting the speed to 150 decreases the voltage to ~1.8v.
It doesn't matter in which direction the motor is turning.

The motor, NodeMCU and driver are powered by the same power supply with a buck converter. I get the same behavior with 3.3v and 5v on the NodeMCU and the driver.
What am I doing wrong?

Thanks for the help! :)


texts:
I while ago I asked this question about interfacing static ram to an fpga for the purposes of a vga frame buffer I wanted to make as a little hobby project. It became clear to me at the time that the project was too difficult for my level of knowledge (as I'm basically a c++ programmer and knew little about electronics) but since then I've built a few smaller cpld based projects so now feel I know enough to look at the project I want to build again :)

I'm thinking of using this memory chip as it seems to fit my requirements. The data sheet indicates that I can read a data byte every 10ns and that I have to set up the address a minimum 10ns before I want to read the data. It has a "Data Hold from Address Change" time of 3ns.

This implies to me that assuming a 10ns clock I can simply set the address lines each clock cycle, and read back the data from the previous address.  That the data output will be valid at or before the next 10ns clock, and will remain valid for at least 3ns after I change the address , so it's safe to read it.

Is this a reasonable thing to so (setting the address at the same time as I read back the data from the previous address). From looking at the data sheet it seems so.

This is the fastest it would work, I could also use a slower clock if pushing the timing to the limit like this was a problem, I just wanted to understand if I'd understood the data sheet correctly.


texts: Protecting a wireless router from voltage fluctuation

texts:
Background:
I have a wireless router ASUS DSL_N12U. Input voltage and current is 12V , 1.5A respectively.
I also have an Inverter (works on three modes: Solar, Battery, Mains) at my home.

Problem:
What happens is whenever my Inverter switches its power source (From Battery to Mains or Main to Battery), electricity of my home turns off and on for a very short time (although this switching is visible as lights goes off and on).
Earlier when the router was directly connected to the inverter, it used to hang up because of this switching and I had to restart in order to connect to it again.
So in order to save my router from this voltage switching, I connected the router to a standby UPS (with transfer time approx: 4ms). But the problem is still there as router still hangs up when power switching happens and I have to restart it.

I searched this problem on internet and found that the wireless router's circuit may be very sensitive and connecting it to an Online UPS can work.

My requirement is to have a small online UPS that can power to the router. However I am not able to find such a small online UPS for this purpose.

So Is there any small online UPS available in the market for this purpose?
or can I make one?
or Is there any device which can be placed in between the router and current standby UPS in order to solve the problem? Any other suggestions/comments are welcome.


texts: Implementing power on/off through gpio pins for mcu while asserting for few seconds

texts:
I'd like to know how can a power-on/power-off system for a battery operated device with GPIO inputs can be designed that has the following features:

When MCU is off, pressing and holding down a switch for 4 seconds should only turn it on
This switch must be usable as a GPIO input pin to the mcu after it turns on
Pressing and holding again the same switch for 4 seconds should turn the system off by either cutting off the power supply or controlling a Shutdown signal to the regulator.

The last part can be easily done by having a timer run in the mcu and check the duration of press everytime there is an interrupt generated, and then asserting the shutdown signal of the voltage regulator when ready. But I'm not getting ideas for 4 second turn on, and at the same time be usable as a GPIO after power on. Subsequent short press on this switch should not turn off the system. Any thoughts ?


texts: How two or more consecutive zeros(off) or one (on) in digital circuits are recognized?

texts: So in digital circuits work by using two states either on or off and i was wandering how two bits of zero(or one) be identified? is there like a timing circuit or anything like that?


texts: How to synchronize random resets in two Ethernet Controllers (DP83816)?

texts: I use two Ethernet Controllers (DP83816) in a design which also has a CPLD. When the power is supplied, Ethernet chip undergoes a random reset and it resets the CPLD (XC95144XL) internally. Since I have two Ethernet chips the reset of these can be possibly at two different times which will screw up my design. Is there any way to synchronize these resets?


texts: What is "Configurable clipping rectangles"?

texts: I was going through the features of one Graphics accelerator-IP core. And one important feature of this graphics accelerator is "configurable clipping rectangle". Can any one help me to under stand what is this ?


texts: Touch IC TTP223 hangs at 5V after working

texts:
I used a TTP223 IC operating on 5V. I use the touch IC output (when high) to turn on the LED and (when low) to dim the LED. The LED is operated by the external 5V.  It uses only the touch IC output as a signal. I used a blue LED.  What is the problem?
It works fine when turned on, but after several days the touch output hangs.


texts: Need component/device to power a light from two seperate inputs

texts:
First question here, and don't work on electronics often, so tips are welcome.  This might have a very simple solution.

I tried to use the schematic editor to the best of my knowledge to recreate an aftermarket headlight on my car that has stopped working (U1 and Lamp 3 are inside the headlight).  The contents of the U1 box is my question.  The 100 ohms on the lights were the default of the editor and is not accurate.

The ground wire might go into U1, and Lamp 3 might pick up the ground from U1, but I drew it outside for simplicity.

Lamp 3 is a LED strip.  When the headlight switch is in the "OFF" position, SW2 is open, SW1 is closed, and Lamp 1 (the daytime running lights) is on, and Lamp 3 should be on.  Right now the LED is not on because of a failed part in U1.  When the headlight switch is "ON", SW1 is open, SW2 is closed and Lamp 2 is on (the actual headlight).  Lamp 3 is currently on and working as it should.

I need to replace U1, which is enshrouded in heat-shrink (1/2" x 3/4" rectangle) and located in an unreachable area of the housing.  I have access to all the input and output wires, so I can fit a replacement once it is built without damaging the light.

Main question:  What parts are in U1 that will allow two power sources to feed Lamp 3 without the two power sources touching each other and back-feeding?  For instance, if U1 was just a wire-nut, Lamp 1 and 2 would both be on if either SW1 and SW2 were on.  To my knowledge, SW1 and SW2 are never on at the same time.  Lamp 3 is an LED strip, and I would expect it to draw < 5A.  The entire system is 12-14VDC (automotive system).  Temperature range is extreme - probably from 0-200 deg F because of the proximity to a high-wattage halogen bulb, car engine, sun, etc.

simulate this circuit – Schematic created using CircuitLab


texts: Uploading Program to Arduino Using FTDI Cable or Programmer

texts:
I would like detailed instructions on how to go about uploading a program onto an Arduino using an FTDI cable/programmer.  I'm just not quite sure what parts to order and how to go about doing it.

Do I require both the FTDI cable as well as a breakout board?  Or just one or the other?  How exactly does it physically connect to the Arduino/computer?  Links would be appreciated.  Thanks!


texts: Mesh current analysis voltage and current source

texts:
Can somebody please point me in the right direction here

Im trying to create two equations to solve for IA(left hand loop) and IB(right hand loop)

I need two equations consisting of IA and IB to then solve again using matrices.

What effect does the current source have on the circuit?

simulate this circuit – Schematic created using CircuitLab


texts:
I am trying to create a power-on delay with a 555 timer IC. I have never used one of these before and I am finding it a bit tricky to make applications with it - a lot going on.

I found this circuit online

I also saw this from GreatScott showing the internals

My question is in relation to the power-on delay circuit (first picture) above. Initially the 100uF capacitor is fully discharged (0V) , so doesn't that mean that the trigger pin will be low (less than 1/3 Vcc) and thus the flip flop will get set high and thus cause the output to go high -> defeating the entire purpose?

Secondly, how is it possible to measure the 100uF capacitor voltage from the negative terminal, wouldn't that always be 0V?

Is it just me or are these circuits hard to understand at first?


texts:
I am trying to implement edge triggered flip-flop using CMOS logic. Google search provides following diagram on wikipedia:

Upon simulating this using tanner, I find out that output resembles positive edge triggered flip-flop.
I want to know the logic behind this circuit. How one can proceed to implement clocked flip-flops using cmos? Right now, the only thing clear to me here is the use of inverter to convert ~Q to Q


texts: Tips for designing a permanent magnet synchronous generator?

texts: I'm currently working on designing a permanent magnet synchronous generator for one of my personal projects and I'm having trouble getting a voltage I am satisfied with. My goal is to get around 4-6 V atleast. I have 3d printed a protoype and I do understand once I get a metallic core and such that my flux with increase however I'm just wondering if any of you have any tips for designing this. I want it to be 3 phase and my magnets right now are very weak I have n52 magnets that I ordered coming in soon. In the photos below, those are my two prototypes, the one on the left has 300 turns each and the one on the right has 200 but manages to get more voltage, must be due to airgap.


texts:
I'm really confused on how to implement this circuit diagram on a breadboard. The short wire indicated with v1 is the confusing part. I tried to make it on a breadboard but I can't seem to get it. Any hints?

EDIT: This is my attempt at building the circuit. But I'm not sure if it's right and I can't test it because I do not have a multimeter. Any comments/tips? I don't have any 100k resistors, so I just used two random ones, but everything is labelled.


texts: Modifying an op amp filter to use single supply

texts:
I'm having much difficulty modifying a "state variable" bandpass filter from being dual supply to single supply. (https://www.electronics-tutorials.ws/filter/state-variable-filter.html)
Here is what the circuit and frequency response should look like, screenshot from the website. I am only concerned about the bandpass filter response.

The following LTSpice simulation is done with dual supply rails and matches the expected graph:

But when I try changing the supply rails to what I think would work, I don't get much of anything at the output. I've tried variations on this but all them end up being down in the -50dB to -60dB range.
What I've done is simply change all the negative rails over to ground, then changed the (+) terminals of the op amps to a bias voltage at half-rail (2.5V).

I'm not quite sure what's going wrong, and have been stuck for some time.
Any help appreciated.
Edit:
In response to the comment below, here is what you get when you change the AC source ground to vbias. Adding or removing the cap between V2 and R1 doesn't change much, adding or removing the 1M resistor also doesn't change much.

Update with answer:
I picked an op amp at "random" in LTSpice's menu. Changing the type and adding the cap between the source and R1 fixed the simulation. I breadboarded the circuit below, but am still getting the response above - more debug necessary. But that is a separate issue and this question here is resolved. Here is what I ended up with.

Thanks everyone!


texts: Is sytem level testcase different from block level testcase? And what is a test vector?

texts:
I usually see these terms. In the field of Digital IC Design or in Design Verification, is system level testcase different from a block level testcase? I mean I know they differ from the level of abstraction but what I want to know is the difficulty of doing it. From what I understand, if you can create a block level testcase then you can also create a system level testcase. Is this correct? Do they differ in difficulty? Are there some things that are in system level but are not in block level testcase?

Another question is, what is a test vector? I usually see this term on verifying an SOC. Usually they refer to a testcase that will be done on actual silicon. What is this?


texts: How are speakers matched with audio amplifiers? (avoiding overloading either)

texts:
I know a similar question title has been asked, but I believe that does not answer my question (and I couldn't think of a better way to phrase the question).

I'm a bit confused by how exactly an amp can overload a speaker, and vice versa.

Many guitar amplifier speakers are 8Ω impedance.

If I understand correctly, the output amplifier (should) outputs a fixed voltage signal output regardless of what load is placed on it.  If this step is wrong, please correct me.

So if there is a fixed voltage signal, (say, +-15V, i.e. 30V of swing) and if the speakers' impedance is ~8Ω (I understand it will vary with frequency but say it is around this figure), then how is the wattage varying with different amp combos even though the impedance is roughly the same? Is it that the voltage increases with higher wattage amplifier/speaker combinations.

For example a 10W combo with an 8Ω speaker vs a 100W amplifier connected to a 4 speaker cabinet wired for 8Ω impedance (parallel connect 2 series pairs of 8Ω speakers), the 100W is obviously louder. Is it that the output voltages of the 100W amplifier is more? Else how can you get the wattage to increase if you are keeping voltage and impedance constant?

What would happen if you connected the 10W amplifier directly to a 4 speaker cabinet? Would it overload the amplifier? Or just play it quieter? Theoretically, if the voltage is the same and the impedance is still 8ohms, the wattage should be the same, i.e. 10W through the 100W rated speakers.

If so, is this true then: when we say 10W 8ohm speaker, we mean its able to handle maximum peak voltages of (P=V^2/R, V=sqrt(PR)) ~9V. Whereas for a 100W 8ohm speaker, it is able to handle peak voltages of ~28V?

In what situation can you harm a speaker? By connecting a too powerful an amplifier to it? But then isn't that something that is recommended by many people? (Amplifier output of atleast 2x the speaker rating). If so then the voltage output of an amplifier is not fixed? It varies according to which speaker is connected to it? (even though the impedance is the same?)

In what situation can you harm an amplifier? By connecting too high a wattage speaker to it? Then why do I see so many people posting videos on youtube of 1/2W guitar amplifier builds connected to big wattage rating 4 speaker stack speakers or atleast even 2 speaker combinations?


texts:
We are making a production product using the MSP430G2231 and want to keep the code a secret.

I have searched online and found out that blowing the security fuse disables access to the MCU.

Could somebody please clarify that by giving 6 and 7 V (100mA) for at least 1ms to the TEST pin we can blow the JTAG security fuse? Is this the right way to do it?


texts:
This is a beginner level question on understanding modulation and channel coding. The confusion arises when I am trying to implement the concepts. Let's say I have the information bits as x = rand(1,N);

Then,

information_bits = x>=0;

Q1. Why cannot we use the information as numerical data? Why do we need symbols 0/1 or M-symbols in communication?

Q2. Modulation - I have seen in many places where BPSK modulation is invoked by this statement: transmitted_data = 2*(x>=0)-1;

This generates +1/-1 symbols. Where is the coding at the transmitter? If we are not doing any coding, then how come a hard decision decoder is applied in this example link where in the paragraph for Simulation model and in the code is written : perform hard-decision decoding. Without channel coding, why should we do this step?Or maybe I cannot understand the way coding has been done.

Q4. How can we demodulate the data at the receiver for example for BPSK? Is hard decision a way of demodulating?

Q5. What is the correct way of doing QAM modulation, coding and then decoding and demodulation


texts: Recently I read in the basic EM theory course , that the Ohmic power dissipated in a conductor is directly proportional to the conductivity and the square of the electric field intensity , but we know perfect conductors (conductivity=inf) dissipate zero power , isn't this contradictory , also formula is given on Page 391 , Alexander Sadiku ,EM Theory , thanks.


texts: What are the rules that function should pass in order to be used in RTOS

texts:
I use ATSAM4LC2A ARM microcontroller that drives 3xUSART, GPIOs, DMA. timers with the use of interrupts and all the remaining logic of my application..
The project is functional but with out a RTOS yet.
This is my first attempt and I want to port my code logic with the help of FreeRTOS but I am afraid to use because theadsafety is all new to me.

Is there a software checker that evaluates my code as thread-safe?
Or is there a set of written rules that I can use as a ckecklist for every single function I use?

The only rules I can think of are:

No use of global variables inside functions.
Use mutex if global variables are used..

Also is it better to check for thead-safe or reentrant for my embedded application?


texts: How are 200 GBit/s over twin-axial copper cable achieved?

texts:
The 200GBASE-CR4 standard [1] defines ethernet communication with 200 GBit/s using four lanes and PAM4 modulation over a maximum distance of 3 m.

A single PAM4 symbol encodes two bits, therefore, I expect that a single lane is modulated at approx 25 GHz.

According to [3], 40GBASE-T is the Ethernet standard with the highest bandwidth using twin-axial copper cables. It uses four lanes, therefore, we have 10 GBit/s per lane and PAM16 encoding. Thus, there should be four bits per symbol and I expect that a lane is modulated at around 2.5 GHz.

From my understanding, such high frequencies are very difficult to handle as the wavelength becomes comparable to the dimensions of the cable and one has to use coaxial cables or other waveguides.

Particular problems I would expect at these high frequencies are high attenuation because of the skin effect [2] and an impedance mismatch due to thermal and mechanical effects on the cable.

Questions:

Is the 200GBASE-CR4 standard, communication of 200 GBit/s through twin-axial copper cable achievable?
What effects make it difficult to transmit such high-frequency signals in practice? Are there any books which cover this particular topic?


texts:
I would like to have a circuit with 8 LED outputs and one input - clk.

On each clk edge output should be like this:

0000 0001

0000 0010

0000 0100

0000 1000

0001 0000

0010 0000

0100 0000

1000 0000

How to move by one is clear for me. But how to start with value 1 in the register? Or there is other solution without shift register?


texts:
I am trying to build a communications system for a car, for turning gadgets on or off. One idea was to parasite on power lines, but what kind of components and signaling could be used for this?  I am thinking pretty low communication speed is acceptable, such as below a megabit, but more than 10 kilobits per second.

Is there some suitable standard for a hostile environment such as a car?


texts:
Is it there any differences between a thermal relief in a 'X' shape for a '+' shape?
I am using Altium and the software has boths styles for selection.


texts: Using TIVA's onboard JTAG to connect to a 3rd party arm controller

texts: I have a mikrochip's CEC1702 based board and a TIVA tm4c123 launchpad with onboard debugger. I wish go program the CEC board but datasheet suggests it can only be programmed via JTAG. Can I use the TIVA's onboard debugger for this purpose? I do not have a segger jlink.


texts: Arduino serial communication produces noise on electret microphone

texts:
I am currently working on a circuit which uses an electret mic and am LM386 op amp to feed an audio signal into the arduino. During testing, I've used my scope as well as headphones to analyze the sound coming out of the op amp. I've found the headphones to work well for qualitative analysis.

When I simply listen to the signal coming out of the op-amp with my headphones, I hear the generic ambient sound I would expect to hear from any recording device. But, when I open the serial monitor in the Arduino IDE, I get a horrible sounding hiss in my headphones. The scope shows a crazy amount of noise between the power and ground lines when the serial communication line is opened. I have concluded (I think rightly) that the serial communication is being picked up by the microphone and making my signal extremely noisy. I also hear minor noise when sending digital signals from the arduino to the potentiometer I have within the circuit, but they are quiet 'clicks' that don't affect the sound dramatically.

Needless to say, I'd like to eliminate this digital noise from my microphone circuit. I have read about the need to separate analog and digital power planes in circuits for proper circuit board design. So, I attached two diodes in parallel coming from the input +5V from the USB to prevent the resulting two power lines from 'talking' to each other. One power line fed directly to the mic, while the other fed everything else on the board. This solution did not rectify the issue.

Any suggestions would be appreciated. I am sort of a noob when it comes to circuit design, so I am not entirely sure I've isolated the two power lines from one another. Thanks.

--- Edit ---

I'm using a solderless breadboard with an ATMega328. I am also using Sparkfun's FTDI breakout board for computer-board communication.

The schematic and scope screenshots are at the link below. I can't post photos without 10 reputation and can't post more than 2 hyperlinks. The cap between pins 1 and 8 on the op amp is for feedback (giving it a gain of 200). Pin 7 is a bypass pin. 2 and 3 are the inputs, and 5 is the signal out, feeding into the analog input on the arduino.

Schematic and scope readings link

Scope Shots:

Still scratching my head. I've got decoupling caps (not shown in schematic) near all the power inputs for my ICs on the board, as well as decoupling caps periodically up and down the power-ground strips. I have also tried putting a decoupling cap between mic power and ground to no avail. I'll try to respond to most comments as they come in. Big thanks for the feedback so far.

--- 2nd Edit ---

I have tried the same circuit using an arduino Uno board connecting to the mic and op amp on a separate breadboard. Same results as previously mentioned.

--- 3rd Edit ---

I realized that the noise is not being picked up by the mic necessarily, but by the op amp. I can remove the mic from the circuit and identical noise at the same volume level (when listened through headphones) still persists.


texts: Looking for AVR MCU with internal PLL clock source with more than 8 pins?

texts:
The 8-pin AtTiny x5 MCU (ie. AtTiny25, AtTiny45 and AtTiny85)
can be set to use it's internal clock source
to something as high as 16Mhz without any external components
by setting PLLCLK which would enable the internal PLL for high frequency clock generation (no crystal or capacitor or what ever is needed).

This feature can be used to implement a simple and cheap USB device
as in V-USB with ATtiny45 / ATtiny85 without a crystal

Is there any AVR (AtMega or AtTiny) with more than 8 pins having this feature (referring to PLL)?


texts:
What is the plain English explanation of the Doppler Spread?

Looking at different sources I come across complicated definitions which I struggle to understand.

Example for such one:

  Doppler spread is a measure of the spectral broadening caused by
  the time rate of change of the mobile radio channel, and is defined as the range of
  frequencies over which the received Doppler spectrum is essentially non-zero.

What does the spectral broadening mean?

the reference link

useful link: http://www.einstein-online.info/spotlights/doppler


texts: Altium connection lines do not show the shortest connection

texts: The connections are between a processor and a DDR chip. The problem is that Altium only shows pad to pad connection line not the shortest (eg not via to via or via to pad). The strange thing is when I start routing, still do not show actively the closest track segment. I checked the topology rules and "From to editor" property. Everything is normal. I couldn't figure it out. I can route those tracks anyway. But this is really annoying.


texts:
I'm watching LTT's new video with Electroboom where they shock RAM with an ESD gun. In some occasions, they do it without grounding the RAM stick. Doesn't the current have to go back to the source? I see 2 explanations (there could be another one).

Does the current actually flow through the things that the RAM is resting on, for example table, and not into the RAM?
I heard Linus say something about equilibrium, which seems to debunk the 1st question. If question 2 is false, then how does a 12kV potential develop between the ESD gun and the RAM stick? Or any potential in electrostatic phenomenon, like lightning or rubbing your feet on a carpet and touching a doorknob.  Does it happen due to capacitance?

Water analogies welcome.


texts: Removing switching artifacts from a commercial audio amplifier

texts:
I got an audio amplifier but I have problems with it.
How can I remove switching noise (artifact)  from the  output of  a Behringer iNUKE NU1000 Power Amplifier  audio amplifier?

I got from oscilloscope. Ch1 is sine wave and ch2 is output of the oscilloscope.


texts: Can I decrease voltage to get higher amperage?

texts:
If I have for example a battery that outputs 10 V but with a maximum of 0.5 A. If I took the output of the battery and entered it in a buck converter to get 5 V will I get the same 0.5 A at 5 V or I will get 1 A?

In my small knowledge what I know that the watts should be the same so 10V * 0.5A = 5W, so 5V * 1A = 5W. Is this true or it's only theoritical?


texts: Op-amp bias issue to to charging of DC blocking capacitor

texts:
We're using the above circuit to drive a sinusoid with constant current into a custom sensor which is best modeled as a series capacitance & resistance (~100ohm, 1uF). The op-amp is single supply, and biased to 2.5V. A 1kHz signal with fixed 500mV DC offset is driven into the circuit. We measure the voltage over the sensor in order to determine changes in its resistance. An additional sense resistor (precision 100ohm) is included in the feedback loop to better estimate the current through the sensor (voltage measurement circuitry omitted). A 5Mohm resistor is placed in parallel with the sensor to provide a DC path.

The problem we have is that a DC potential is developed across the sensor each time the circuit is powered up to take a measurement. This happens because the sensor sources the charge required to bias up the DC blocking capacitor. This potential eventually decays through the DC resistor in parallel with the sensor, but not quickly enough to avoid long term damage to the sensor (which is very sensitive to DC voltages).

We do not wish to reduce the size of the DC resistor because it will affect the accuracy of the measurements. At the moment we implement a clumsy solution whereby we temporarily short out the sensor with a digital multiplexer whilst the op-amp is powered on, and the circuit stabilizes to 2.5V. Does there exist a neater solution to quickly bias up the circuit to 2.5V whilst not developing any DC voltage across the sensor?


texts: What happens if the output of a 74LS05 IC is connected to the input of a 74LS04 IC?

texts: Explain what would happen if I connected the two ICs?


texts: Mass Production Ultra-Low Current Calibration Methods

texts:
I'm attempting to design calibration for mass production on a newly designed product. The product is designed to use sub 1mA, so any digital calibration is unlikely.

An example of this would be in the following scenario (note: this is not the actual design):

simulate this circuit – Schematic created using CircuitLab

What methods are available to calibrate each of the input resistors ranges on this circuit that are cost and power sensitive?

My own research/input:
The only thing I can see as a feasible option is trimmer potentiometers and perhaps using automation to do the calibration. But this seems like a time-consuming process and the fact that the potentiometers can move over time and have significant temperature drift. I have seen some people put adhesive on the trimmer but then in future, the device can be calibrated which is required.

I don't know if there are any methods for digital potentiometer setting which can be powered off and remember its position?


texts: Why do they add a TRIAC after an MCP3020 optocoupler?

texts:
I have a relay circuit (I use it instead of a relay) that uses a MCP3020, which I think does the physical separation of the two circuits (it's a LED and a photo cell inside a chip) and a BTA08 TRIAC.

Then connected to PIN 6 ("mains term") of the MCP3020 there is a resistor going to the middle pin (gate) of a BTA08 TRIAC. The other mains pin of the MCP3020 goes to the other mains pin of the TRIAC. It's like the MCP is switching (on/off) the voltage coming from mains to gate (plus the resistor). So, when the MCP3020 is on, then the TRIAC gate goes on and so the TRIAC allows AC through it's external pins. Isn't this redundant? What does the TRIAC do that the optocoupler does not do or vice-versa?


texts: How to power servos externally in Arduino

texts:
I tried to control 2 servos with my arduino. It worked fine but if I try to control 5 servos with my Arduino, it doesn't work. I want to power up the servos externally but I don't know how to do it. I'm using 5 push buttons and a pot knob to control the servos. And what battery should I use? And how to connect it with servo and Arduino?

The servo specs is:

Operating Voltage: 4.8-6.0V
PWM Input Range: Pulse Cycle 20±2ms, Positive Pulse 1~2ms
STD Direction: Counter Clockwise / Pulse Traveling 1500 to 1900µsec
Stall Torque: 3 Kgf.cm (41.3 oz/in) at 4.8V, 3.2 Kgf.cm (44 oz/in) at 6V
Operating Speed: 0.2 sec/ 60° at 4.8V, 0.18 sec/ 60° at 6V at no load
Weight: 38g (1.27 oz)
Size: 41.3*20.3*38.7*48.5*10
Plug Available: FUT, JR
Special Feature: Heavy Duty Plastic Gears, Economy Servo

What battery should I use to control 5 servos of above spec?

What should be spec of the battery?


texts: Adder tree with 4:2 compressors. What to do with Cout?

texts:
I'm trying to build an adder tree using 4:2 compressors. I want to add together 16 bytes at total, so I figured that a possible architecture for that tree is the following:

Each 4-Byte adder has 3 outputs, the 2 of them are the sum and the carry (which we send to the next adder) and the third one is the Cout from the last 4:2 compressor of the adder.

My question is, what to do with the Cout? How should I add it to the rest of the sum?


texts: Interfacing a four wire resistive touch screen with STM32F429DISCOVERY

texts:
I'm trying to interface a 4-wire resistive touchscreen to a STM32F429 Discovery board but I can't figure out how it works. I want the MCU to detect a touch so I configured the 4 pins like this:

X+ --> input w/pullup connected to EXTI external interrupt
X- --> input floating (tristated)
Y+ --> input floating (tristated)
Y- --> output to GND

in this configuration I should be able to detect a touch and trigger an interrupt on the EXTI line so I can enter a ISR and sample the x and y values with the ADC. But when I connect the X- pin the X+ pin goes to near GND. It seems like current flows between X+ and X- (so the X- is not tristated?).
Here's the code I use to configure the GPIO pins:

GPIO_InitTypeDef gpio;
gpio.Pin = GPIO_PIN_2 | GPIO_PIN_1;
gpio.Mode = GPIO_MODE_INPUT;
gpio.Pull = GPIO_NOPULL;
HAL_GPIO_Init(GPIOA, &gpio);

gpio.Pin = GPIO_PIN_0;
gpio.Mode = GPIO_MODE_INPUT;
gpio.Pull = GPIO_PULLUP;
HAL_GPIO_Init(GPIOA, &gpio);

gpio.Pin = GPIO_PIN_5;
gpio.Mode = GPIO_MODE_OUTPUT_PP;
HAL_GPIO_Init(GPIOA, &gpio);

HAL_GPIO_WritePin(GPIOA, GPIO_PIN_5, GPIO_PIN_RESET);

/* initialization using registers, works the same as above */

//  /* Xr and Yu open (input floating) */
//  GPIOA->MODER &= ~(GPIO_MODER_MODE2 | GPIO_MODER_MODE1);
//  GPIOA->PUPDR &= ~(GPIO_PUPDR_PUPD2 | GPIO_PUPDR_PUPD1);
//
//  /* Xl input with pull-up */
//  GPIOA->MODER &= ~GPIO_MODER_MODE0;
//  GPIOA->PUPDR |= GPIO_PUPDR_PUPD0_0;
//
//  /* Yd to GND (output set to 0) */
//  GPIOA->MODER |= GPIO_MODER_MODE5_0;
//  GPIOA->ODR &= ~GPIO_ODR_OD5;

I can't understand what I am doing wrong or how to configure the tristated pins correctly so they don't pull down the X+ pin.


texts:
Why do we need an external ADC when there are microcontrollers available with internal ADC?

I think it makes it economically expensive to add to 2 chips separately on the PCB, adding peripherals, using board space.

Are there any other advantages of using an external ADC?


texts: How do you account for receiver sensitivity in tranceiver half wave dipoles?

texts:
if you are to design 2 halfwave dipoles, both can transmit to each other using 3 watts and have receiver sensitivity of -80dbm (a picowatt). Suppose they are 800m and have same height from ground. How do you design such a system, assuming all impedance matchings and efficiencies are perfect?

traditional equations are P = 1/2*Resistance(73-ohm)I and E = (ηI)/(2*pi*r). I could put P = 3 watts in the first equation to solve for I, then put I in the 2nd equation to get the field at that radius offset. But then I wouldn't have used the -80dbm, the equations don't account for both powers. How do designers account for sensitivity?


texts: Identifying the right motherboard for a project

texts:
Let's say you're trying to find a motherboard that has exactly this many of type x interface, and that many of type y interface, and you don't want any more interfaces that are usually on a motherboard but you know you won't use them.

Is there a source that an engineer can use to find a specific motherboard for a project?
If I can't find this specific motherboard, is there any framework that would allow me to customize a standard motherboard design easily. I don't think it's an easy undertaking to design one from scratch, but perhaps it's possible to start with a generic motherboard and use pcb to customize it?


texts: Would oversampling reduce in-band signal noise floor?

texts:
I understand that oversampling will reduce quantization noise floor.

Would oversampling also reduce the noise floor of the noises in band of interest?

*******EDIT 20150320*********

The correct answer is from the comment of  Brian Drummond.

Oversampling combined with proper DSP will help reducing quantization noises and thereby increase ADC resolution, under given conditions. Details can be found at:  http://www.silabs.com/Support%20Documents/TechnicalDocs/an118.pdf

However, it cannot reduce in-band noises.


texts:
In the lab I measured the Vgs x Id and Vds x Id curves of a MOSFET transistor (actually, the CD4007 IC that has 3 PMOS and 3 NMOS transistors within).

How would I go into turning this data into a SPICE model? I don't need high accuracy.

I tried writing a VDMOS model for LTspice but it looks like it is more suitable for power MOSFETs.


texts: Soldering wires directly to male AC prongs

texts:
I am making a project that will fit into a 3D printed enclosure.  I want to keep the project neat so I will have just one extension cord running from the wall (120VAC) into the enclosure to power all of my electronics.  One of my devices requires 12VDC so in order to save space inside my constrained enclosure, I thought that I could solder wires directly to the AC input prongs of the power supply and heat shrink & electrical tape over that.  The reason for not directly plugging it into the female end of the single extension cord entering the enclosure is that I need two additional items to be plugged into the cord that I was going to use wire nuts for.  This 12VDC adapter will be powering 1A for only a few minutes at a time, maybe once per day.

Is it safe to solder the wires to the AC input prongs of the 12VDC supply?


texts:
I have an enclosure which consists of a power entry module and a 24V DC power supply. So inside the enclosure, the 24V DC power supply is powered by the 230V AC through the power entry module. And this 24V DC power supply will be used to supply/source 3A current to a 8 Ohm load which is a heater.

The power entry module for the AC mains side needs fuses to be installed across both line and the neutral.

As far as I know I need to install slow blow type AC fuses.

But how should I estimate the current rating for the AC power entry module's fuses?


texts: High frequency switching node in DCDC converter

texts:
There are some nodes with high frequency switching contributing to EMI in Flyback and Forward converters, which should have minimal copper area to minimize the EMI. Here we see the Forward high frequency nodes:

What are the nodes that should have minimal copper area if I move the upper diode on the secondary side to the output negative rail (and also replace it with a FET but that doesn't matter this time I think)?
Here is an image of a Flyback, with the mentioned change with the diode:

So the question is: which are the EMI contributing nodes in case of Flyback and Forward converter secondary sides assuming the diode (or synchronous FET) on the negative input rail?


texts: Are rise/fall times typically affected by the clock speed.  That is if I have a AVR at 16 MHz will it have a different rise/fall time than the same AVR at 32kHz?


texts: Precision of estimating power consumption with a current sensor

texts:
When estimating power consumption with a current sensor, what is the usual precision that can be achieved for home appliances? I'd like to make a simple circuit using such a sensor and a microcontroller to collect the measurements and estimate consumed power.

For an ideal resistor, we can compute power as I²R. But for an ideal capacitor or inductor, this would be very different. For example, an ideal inductor/capacitor connected to an AC would have 0 average power regardless of current, so I²R over-estimates the actual value.

How much can the above ideal resistor estimate be off for devices that contain inductors, such as motors? And can it ever under-estimate?


texts: Class-D amplifier of present vs Class-A of the past

texts:
Quite a sensitive question, and perhaps on the edge of the off-topic.

But I'm interested in a balanced view on the technology evolution over recent decades. The semiconductor industry made a huge leap, clock frequency has increased enormously, and intuitively one would expect that the PWM amplification (i.e. Class-D) should have improved over the time. Does it still lagging in terms of characteristics behind the direct amplification of Class-A? Could compare it with the transistor Class-A technology of 80-s? or 90-s?


texts: sawtooth wave form generator using Hspice

texts:
Hello
I tried to simulate this circuit in Pspice or Hspice to generate sawtooth wave but I didn't get any result
my Hspice code is shown below

[


texts: Narrow bandpass filter using maximally flat LPF prototype design

texts:
I'm doing a project involving wireless power transfer, where an LED will be turned on via 2 induction coils (tx and rx). The interfacing power circuitry for this has already been figured out (an arduino, transistor, caps, and resistors). What I want to do is transmit the wireless power at a specific frequency though (13.56kHz), so I'm trying to design a narrow band-pass filter that will allow for transmitting at this frequency. My understanding is that the transmitting coil already transmits at it's own frequency, dependent on the capacitors, and its own inductance value, but I'd like to 'fine tune' this to only transmit at 13.56kHz. This is where I think I'd need a bandpass filter, right before the transmitter coil, right?

The problem I'm having involves the filter design itself:

I'm doing my design by calculating component values for a 3rd order filter, using the "maximally flat LPF prototype design" method, then using impedance and frequency scaling to transform to a BPF. My bandwidth is 5%, so 678Hz. The element values I'm using are for "maximally flat time delay LPF prototypes"; so for N = 3, I obtain g1= 1.2550 g2 = 0.5528 g3 = 0.1922 g4 = 1. I'm simulating all this in LT Spice.

My dilemma is that I'm not getting as narrow a pass-band as what I think I need? It seems to be centered around 13.56kHz, but with a wide pass-band. What else can I do to make the bandwidth narrow? Secondly, is this the right method to use in order to have a filter that will allow for a specific transmission frequency?

Lastly, is it better to go for an active filter design method, where you use op-amps in the filter circuit? Or is this mostly for audio applications?

Below is my circuit in LT Spice, and the frequency response.

I also tried the g1 to g4 element values from "maximally flat LPF prototypes", where g1 = 1, g2 = 2, g3 = 1, g4 = 1 and get the following response:

The element values I'm talking about (g1 to g4) are taken from my lecture notes, which I assume are a standard in theoretical filter design.


texts: Current controller: how to dampen resonance to increase bandwidth?

texts:
I need to design a +/-1.5A, 3kHz small-signal-bandwidth (absolute min, for 3° max phase and 1% max error on amplitude) current controller for a 20 Ohm 0.1H load with a +/-100V supply rail (the current setpoint profile I'm planning to request should make the load swing +/-80V).

I want to make that controller based on a high power op-amp (because I need very good smoothness so no H-bridge) from PowerAmp Design, the PAD129. It has in particular a GBW of 1MHz and a correct SOA for this application. The opamp controls the voltage across a sense resistor capable of dissipating the heat.

Here is the best of my many attempts using the manufacturer's SPICE model of the opamp, and yet it still does not work. I've also tried placing the RC between the output of the opamp and the negative input, with similar results.

I have calculated the transfer function and plotted it considering the opamp to have a finite gain equal to a first order with DC gain of 1 million and rolloff frequency of 5Hz, and I have noticed that the feedback network has very little impact on this resonance:

So it seems the inductor is resonating with something, but I don't see how to damp it enough to increase the gain-limited bandwidth (the phase-limited bandwidth is more or less what I need).

And finally, I thought the wobble on the waveform above was due to that resonance, but how can a pure sine input result in an output waveform with a different frequency, since the opamp is supposed to be linear (the output voltage is not clipped)?

Do you have an idea of how to modify the circuit to make it work? I'm out of ideas.

Edit: Suggestion of peufeu (and one of my previous attempts). This is the furthest I can push the resonance, and it still isn't enough.


texts: Thick line with square brackets on schematic

texts:
I was trying to read a schematic and i came across thick lines with square brackets... What do these things mean?

I attach a picture of the aforementioned sight.


texts: RS-232 signals on Bluetooth modules like HC-06, HM-10, etc

texts:
I would like to access any I/O pins of a bluetooth module of the likes of HC-06, HM-10 or their clones from both a Windows PC and/or Android system connected wirelessly to the module. I need Windows for one project and Android for another; they wouldn't use the same bluetooth module at the same time (that would be impossible, of course).
The 6 (or 4) pin header on the HC-06 and similar modules have nothing like a RS232 signal except for Tx and Rx, so I'd need to take those directly from the castellation in the smaller module soldered on it.
Since Windows and Android "see" the device as a serial port, I'd think the RS-232 signals like DTR, CTS, DCD, RTS, etc, should be available on the module and accessible to the remote end, but so far I've got no luck with programs like RealTerm to monitor or change any of the module's pins. I want to pass low throughput signals (e.g. low battery, turn LED on, etc.) remotely. Both the Android cell phone and the Windows PC have their own standard internal bluetooth adapters.
Something along these lines:

Can this be done? How?


texts: TRIAC Dimming Modules - 60Hz Module on 50Hz Supply

texts:
I live in Ireland, on a 240V/50Hz supply. I run a Wink Hub, and therefore am bound to using US based Z-Wave frequencies, which usually operate on a 120V/60Hz supply.

I have an Aeon Labs Dimming Module, and have checked the components for suitability for 240V. The TRIAC is rated 600V. I have tested this on an incandescent lamp, and it operates fine; however, I am yet to test this on a LED luminaire to see if it flickers. I have been told a dimming device created for one regional frequency could flicker on another frequency (a 60Hz dimmer on a 50Hz supply).

My question is concerning the technical operation of the dimming feature. I can see it uses a TRIAC. The Z-Wave ZW0301 chip has a ZEROX pin (zero-crossing).

Once it has synchronised with a zero-crossing, it is my understanding that it waits a period of time before switching on the TRIAC until the next zero-crossing (known as leading-edge dimming). The amount of delay would be a function of the period/frequency, and the amount of dimming required. If the device was programmed for 60Hz, and was operating on a 50Hz supply - all I can fathom happening is that it would not have the same 'range' of dimming.

Why wouldn't a manufacturer simply use the zero-crossing to synchronise/determine the exact frequency of the line it is operating on; instead of hard-coding the device to either a 60Hz or 50Hz value?

So - the only issue I can see with flickering on LED luminaires would be due to the LED driver itself not drawing enough via its bleeder circuit to latch the TRIAC once it has fired. Which has nothing to do with 50/60Hz.

So when a manufacturer says 'compatible with most leading and trailing edge dimmers', I can only assume it is to do with the choice of L and C used on the dimmer - and whether or not the LED driver has an appropriately sized bleeder. Adding a few more LED drivers on the same line would probably resolve any of those issues though.

Any thoughts on my ramblings?


texts: Bridge Rectifier's Output Became Near-Zero Value After The Implementation of a Voltage Divider

texts:
Weird. I have both simulated (shown in picture) and practical circuit built. Simulation works as expected.
On the practical circuit, the output of the full-wave bridge rectifier gives the result similar to simulation. But after implementing a voltage divider (in order to scale-down the rectifier's output voltage of 7.3V to 4V for microcontroller to read) at the rectifier's output, the output of the voltage divider (as well as the output of the rectifier) gives a value near-zero (millivolts range). Any idea what happen to my practical circuit?
(As you can see, the simulated circuit is working as expected, 7.3V can be scaled-down to 4V. But not sure what's the reason of the practical circuit being brought down to approx. 0V after implementing the voltage divider...)
(Transformer: Scales down 230Vrms to 6Vrms;
FW Bridge Rectifier: Convert sine AC to pulsating DC;
Voltage Divider: Further scale-down voltage to 4V)


texts: Op-amp unexpected behaviour; amplification regime breakdown

texts:
I'm still trying to understand real-life op-amps. I've built this circuit:

simulate this circuit – Schematic created using CircuitLab

Op-amp is an MCP6141 (datasheet) I've chosen for its low-power consumption.

\$V_{\text{in}}\$ is sourced by a waveform generator, and has the following equation:

$$V_{\text{in}} = 1.5\text{ V} + 5\text{ mV} \times \sin(2\pi \times 3.8\text{ kHz} \times t)$$

When \$R_1\$ is between 0 and \$5.9\text{ k}\Omega\$, I have a normal behaviour, signal is amplified, and gain increases. By the way, I obtain a gain of 40 dB for \$R_2 = 5.9\text{ k}\Omega\$, which is strange twice, because

\$20\log(5900/100) = 35\text{ dB}\$ which is lower than 40 dB
datasheet says op-amp gain at 3.8kHz is around 30 dB.

As we can see output signal (yellow) is slightly distorted but everything happens as expected (except the gain as explained above).

FTT shows the main frequency is amplified by 40 dB for \$R_1 = 5.9\text{ k}\Omega\$:

But suddenly for \$R_1>5.9\text{ k}\Omega\$, things change and output signal becomes strange:

Does somebody has any idea why there is this strong discontinuity in the regime of the op-amp when \$R_2\$ crosses \$5.9\text{ k}\Omega\$?


texts:
I have a project which is of very low costs. The management has at least agreed for a cheap Mobile set and a solenoid valves. They have also agreed for a few extra project budget.

The solenoid valves requires 12v to open. It would be connected to a liquid dispenser unit. I am planning to use http://fonetwish.com/ USSD Mobile App to identify users and send data to web server.

But how can I control the solenoid valves via a normal mobile handset?


texts: What is the purpose of RC in series on FPGA output pin?

texts: Does the RC branch connected to the output as shown serve as a low pass filter? Shouldn't the output be tapped after the 50 Ohm resistor if it were to be used as a filter?


texts: What are the origins of the window functions in DSP? Why not just use a rectangular window?

texts:
As far as I know, in DSP we wish to remove or reduce the effect of some undesired signals by separating its frequency spectrum from the spectrum of the whole signal (our main signal and the noise). This process is done by using a window of rectangular shape, right?
I thought that the window function is something in the frequency domain that is multiplied by the frequency spectrum of our main signal that is being filtered. I thought we took an FFT of the main signal, multiply it with the filter rectangle window which looks like a rectangle in the frequency domain (each sample of window multiplies with corresponding sample of the FFT of the main signal) and then did an inverse FFT to get the filtered main signal back. I think this will not work very well since our main signal is not periodic (like speech) and we do not have ALL samples of it when we do the FFT, so perhaps the filtered main signal would not be good.

My confusion is arising from coming to know that the window function has its origins in the time domain and not the frequency domain and the window function is convolved in time with our main signal to filter it! (For the window function in the frequency domain we get all this mess with lobes that look weird, which is another thing I do not understand). Why don't we filter in the frequency domain by taking FFT and multiplying it with a window and than doing an inverse FFT?

Apparently a rectangular window is bad since its side lobes are not small enough and there is something called "power leakage" in the spectrum so we do not use a rectangular window. It's all confusing me.


texts: What will happen if we don't bypass capacitor at pin 5 of 555 ic as an astable multivibrator.Will voltage/current changes in line affect on pulse width?will capacitor at pin 1 discharge late?


texts: How to modify winding of 3 kW 4 pole motor to run at 200 hz

texts:
Please guide me how a 3 kW 4 pole induction motor can be modified to run at higher frequency in the range of 0 to 200 hz.
If the rotor motor is die cast copper. What should be done with present winding to suit 200 hz.

I want to use this motor for a utility vehicle running on battery.

Can I get a ready vfd to run this motor ?

With warm regards

C. B. Patil


texts:
I'm drawing a schematic diagram using Orcad. In order to put a power source, I'd like to use one of the vcc, vcc_arrw, vcc_bar and so on. But I have no idea when people use each of them. Could anyone please explain the difference between them?

Thanks in advance


texts:
I'm reading the Spartan 6 user guides, specifically the Memory Controller Block guide. I quote the introduction:

  The Memory Controller Block (MCB) is a dedicated embedded block
  multi-port memory controller that greatly simplifies the task of
  interfacing Spartan-6 devices to the most popular memory standards.
  The MCB provides significantly higher performance, reduced power
  consumption, and faster development times than equivalent IP
  implementations.

I don't know what 'IP' stands for in "IP implementation". Both "intellectual property implementations" and "internet protocol implementations" don't make sense in this context.


texts:
I have been experimenting with the BiPolar Transistor transmitter circuits. They worked well on the 88 - 100 MHZ Range. I am now looking to increase the frequency to about 1-2 GHZ. I cant find a capacitor small enough for this freq but the coil could be winded smaller though.

I would like to know if this can be done by the use of transistors or if other Techniques are available for creating the carrier wave of 1-2 GHZ. Lastly, is there any IC's that are capable of generating this 2ghz oscillation? I have not come across any or maybe my searching was bad. Hope to hear from you guys. Thanks.
![BJT Transmitter] http://www.talkingelectronics.com/projects/Spy%20Circuits/images/KolibriCct.gif


texts:
Looking for a low cost implementation to post ambient temperature readings from a sensor to servers via a COTS router.

1) Have a temperature sensor connected to a micro controller which sends data via a Wifi Module with a TCP/IP Stack to servers
2) Have a temperature sensor communicated via Zigbee to a coordinator that is plugged into a router and communicates with the servers.

Would like to keep the cost of the solution below $20. Another constraint is the battery life. Wifi modules with TCP/IP consume more power and cost more.

What particular devices/chips/microcontrollers would you recommend to solve my data communication problem and fit within my budget?


texts: Can oscillators be made from a single supply?

texts: Oscillators such as a Wein-bridge sinusoid or a square wave Schmitt trigger oscillator. Is it possible to bias these so they oscillate above 0V?


texts: BJT 'Hard Saturation' Equivalent for MOSFET?

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For a BJT, we usually want to hard saturate it by assuming Beta value is very low. This way we can maximize the current at the collector. However, I am not sure what is the equivalent for a MOSFET transistor.

Is there anything similar to Hard Saturation for a MOSFET transistor? If so, how can it be achieved?


texts: ST10F269Z2T3 abnormal Input Logic Levels

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We are using a ST10F269Z2T3 Microcontroller (Datasheet) in one of our old Designs. Among other things, the ST10 monitors the functionality of external devices using Standard logic Inputs. Eg.: Input is high --> device connected and working, Input is low --> device is defective or not connected.

While doing some tests i discovered that the ST10 has abnormal input voltage levels for detecting high and low. The datasheet states (see Table 44 on page 161) that a low input ranges from -0.5V to 0.9V and a high input is detected from 1.9V to 5.5V (when supplied with 5V). The ST10 also has the functionality of activating so called "special thresholds" for Inputs (see Table 44 on lage 161 again). If special thresholds are activated a low input would range from -0.5V to 2V and a high input would range from 3V to 5.5V (again when supplied with 5V). While testing i discovered though, that the Controller detects a low from 1.38V downwards and a high from 1.53V upwards which is definitely neither near the standard TTL input levels nor the "special threshold" input levels.

The measurements where conducted with multiple boards to rule out a defective IC, showing the same results. Also there was no external circuitry connected to the corresponding inputs while the measurements where conducted (besides a DC source to simulate the input). The measurements where conducted on P3.12 and P3.13.

Thanks in Advance


texts: How can I make an attractive enclosure for my circuit?

texts:
I have finished working on the circuit and firmware for my design of a MIDI controller. I'd now like to take it off the breadboard and put it inside some sort of enclosure. I can handle making the PCB, but I really have no idea about how to go about making an attractive enclosure?

The circuit has a 16 button grid and 2 potentiometers on it and a USB connection. I saw the design of the Midi fighter and really liked it. I looked at Radioshack and saw they had some cheap looking boxes, but that's not really what I was looking for.

Is there some sort of resource or pointers to how to do attractive enclosure design?


texts: Voltage drop problem with my solid state relay

texts: My solid state relay seems to be dropping the potential by 35 volts.  I read about 80 volts from one end of a modified plug and the other end is plugged into a 120 volt wall socket.   I have the hot wire cut and the ends connected to the leads of the relay.  The neutral wire is not cut anywhere.  I knew there would be a small internal resistance but not by this much.  Is there something I am missing?  I would simply like to control a 120 volt lamp with my arduino.


texts:
Can someone explain how this really works?

I don't understand those bubbles, and how you get different colors on this type of screen, or it is only black&white, does it works similar to capacitive and resistive cellphone touch displays? How they display shades of gray?


texts: LM7805C alternative to produce less heat

texts: I'm currently using LM7805 for circuit which requires 5V for MCU/misc ICs and draws 100-300mA current. Input voltage is 12V from car socket. I don't use heat sink due to space constraints(neither I want to lay down on PCB). Voltage regulator is producing too much heat I understand it's due to power dissipation of 12V to 5V. The question is how can I get this 5V with minimal overheating? Maybe some other common voltage regulator or other technique?


texts: Why does my LM317 give lesser output than with LM337?


texts: Viability of Voltage Controlled Amplifier circuit

texts:
As part of the synthesizer project I have been working to design a simple voltage controlled amplifier. Due to the complexity of other parts of the circuit and the amount of time I've spent on this project overall I am seriously considering opting for a variable amplifier chip; an OTA perhaps. Still, working with what I have now, I have drawn up what I think might function as a voltage controlled amplifier from discrete components and an op amp.

As I understand it the circuit should behave as follows: T1 acts as a low impedance emitter follower, biasing the incoming signal at VCC/2 so as to allow for continuous operation of T2. This second transistor functions as a current source with the right end of R4 effectively at GND. The amount of current flowing through this resistor is determined by voltage across the base and emitter junctions of that transistor (Vbe/R4). Because of op amp rules the current flowing through T2's collector/emitter must be mirrored across R5. This produces a voltage at the output proportional to the voltage at the collector of Tr2.

During testing, however, the circuit didn't exactly behave as above. To account for possible errors in the values I chose for that test I have ignored assigning values to this particular circuit. Does this circuit make sense? Is my analysis correct.

P.S. Perhaps this is a different topic but please feel free to critique my EAGLE labelling conventions and circuit syntax as well. It's still new to me.

EDIT: Fixed an error in my drawing in which the non-inverting pin of the op amp was erroneously tied to GND and not 1/2 Vcc.


texts: What is the purpose of the 7805 input capacitor?

texts:
Most 7805 datasheets specify an input capacitor of 0.33uF or so. This one (the LM340 http://www.ti.com/lit/ds/symlink/lm340-n.pdf) at least specifies that the cap is only required if the regulator is "far" from the power supply filter, without further qualifying what "far" means. 0.33uF is nowhere near low impedance at power line ripple frequencies so we can rule that out.

Edit: the differences are self evident in the title of the question.


texts:
I plan to buy a low flow switch for my heater protection from Mcmaster (2371K4, 0.1GPM set point). The catalogue says that the switch operates on 120/240VAC supply. Would this switch be able to operate on 14V DC supply and a max 40mA current?

Regards,
DPK


texts: I am purchasing a 3 ampere USB A power supply (5V.)  What would be the easiest way to apply a known load from 0-3 amperes (in 0.5 ampere increments, for example) so that I could connect a multimeter and see how close the supply is to 5V at each of those loads?


texts:
I have an IR2104 MOSFET half-bridge driver connected exactly as shown in an example circuit in its datasheet:

I'm using two IRGPS4067DPBF IGBTs and a 100nF bootstrap capacitor.
The whole circuit including the high-side IGBT collector are running on 5VDC.
SD and IN are pulled to Vcc.
Yet for some reason both the high-side and low-side outputs of the driver are pulled to ground at all occasions (measured with an oscilloscope) and neither of them ever goes high no matter if IN is high or low.

I tried using a different driver yesterday (L6384) with exactly the same results, so I thought that maybe it's broken and bought a different driver today, but without any success as I explained.

What am I doing wrong?


texts: I am using 10 AWG wire to power a BLDC motor, and these wires can get quite hot. When an IC is intended for high power uses, it is common practice to put a heat sink on it, but what about for wires? Should I simply use a thicker gauge wire?


texts: Current modulator for laser driver and analog audio signal modulation

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I would like to build a proper laser driver and use an audio output to modulate the laser output.

At the moment, I connected the audio output instead of the battery in a laser pointer. It works, but the laser signal is very weak and I would like to use laser diodes instead of laser pointers. The ready-built laser drivers often use TTL signals, MHz modulation or not enough current. The laser can handle currents up to 26mA. A circuit plan would be great!

Final Project: I would like to use the audio line output to modulate the laser and use the audio line input to read the photodiode signal, laser audio communication setup.

This previous question (link) is amazing, but I have an analogue signal and not a TTL signal.

Thanks a lot in advance.


texts: How to preserve signal power in a splitter?

texts:
I have a double Yagi antenna setup that I used successfully in the past, with both antenna connected directly to a 4G mobile broadband WiFi router, achieving 50-80 Mbps. The antenna have different polarities, one vertical and one horizontal. This was the recommended setup for max performance and stability.
Now I have moved this setup to a remote cabin in the mountains, but with a new addition: a GSM remote starter for my kerosene furnace. This requires a splitter, ref picture. My question is how do I minimize loss of signal?
There are three parts to this: the splitter itself/the splitting of power between two devices and the unused terminals.
Will splitting the signal half the power hitting each device, as in "input signal power"/"number of devices"? I suspect the math/physics to be slightly more complex than this ...
I understand that every additional thing will decrease the power of the signal passing through, but I seem to recollect someone saying that it is wise to terminate the unused terminals, for some reason. How and how much (relatively or absolutely) will an unused and unterminated output affect the signal?


texts:
simulate this circuit – Schematic created using CircuitLab

I have a system where i need to have a clock enable for two 74LS374 D Flips that do not already have a clock enable. I have decided to use a single 2n3904 NPN BJT, with the collector connected to the clock pin, the base (through a resistor of course) connected to my enable signal, and the emitter connected to the system clock, so that when I assert enable, the clock pin will be seeing either ground or 5V. I have read online that this configuration is the wrong way to do it. Why is this?

Keep in mind that I am here because I am by no means an expert, and up until now i assumed that high base voltage means collector = emitter in an NPN. Am I on the right track or completely wrong?

Is there a better way to accomplish what I would like to do?

Thanks

EDIT: Thanks to some users for their suggestions, a simple schematic is now included. Values and part numbers are exact.


texts: Why ground plane is placed in helical antenna and how to calculate size of this ground plane?

texts: In most of the helical antenna, I have seen a ground plane, what is the role of this plane and is there any size restriction for this plane? I am trying to design a helical antenna with minimum ground plane size.


texts: Transient solution of current in circuit with two coupled inductors, with resistances

texts:
Circuit in question is given below. I want to find why I can not get the
same current waveform as PSpice gives me.

Basically I want to calculate formula for i1(t) by hand and get something as close as possible to what PSpice gives me. Either my math is wrong or PSpice is using some model that I am not familiar with.
Assume: No accumulated energy in the inductors and perfect coupling between inductors.
(Note: My PSpice works well for k=1, if someone tries to simulate below circuit and gets error(s) because of k=1,then just put 0.99 for coupling coefficient)
Switch closes at t=1us,and TTRAN=0.1us.
My transient calculation for i1(t) gives me
$$i1(t)=\frac{E}{R1}*(1-e^{-\frac{R1*R2}{L1*R2+L2*R1}*t})$$
What I did is, I used KVL for two loops, with coupled inductors in them. Then I solved the system of two ODEs and found the i1(t). This is the system I use to find i1(t):
$$E-i1*R1-L1*\frac{di1}{dt}-M*\frac{di2}{dt}=0$$
$$i2*R2+L2*\frac{di2}{dt}+M*\frac{di1}{dt}=0$$
$$M=-1*\sqrt{L1*L2}\text{ (see dots and currents assumed in the picture above)}$$
Simulations done in PSpice for various L1 values, do not agree with what I get when I use my derived expression for i1(t). Simulated curves for i1(t) are not so exponential in nature, as my formula above suggests. For i.e. when L1 is small, like in uH, i1 peaks very fast, according to PSPice.
That actually happens when ratio L2/L1 is big.
See image(s) below.
From looking at the wave forms I would say that i1(t) function is composed of linear part(with steep slope) which then continues as exponential curve.
So,

Is my math wrong or I am using circuit model which is limited in same way so that I can not get
the same result as PSpice.
As far as I know K_linear works like linear transformer without core losses.
I did try to use this model:
https://resources.pcb.cadence.com/blog/2019-creating-a-linear-transformer-model-for-circuit-simulations.It is T-mesh plus ideal transformer and my math gives me the same result again.

If my math is OK, then why I am not getting what PSpice gives me? My suspect is that there is
something with K_linear part and the way it works.

What i1(t) is/should be? Looks like it is not just exponential function.

For i1(t) and i2(t), what would be the inital conditions?
For i1, I use the fact that current is zero,at t=0 (iL1(0)=0).
For finding i2(t), I would use voltage accross L1 at t=0 to be equal to E (uL1(0)=E). Is this right?

Images of i1(t) current I get for different L1 values in PSpice are below.
(Sorry for not overlaying those curves.It was easier for me to do them separately.)


texts: Measuring currents between 100pA to 100uA

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I want to measure absortion/resorbtion currents of dielectric when applying 1000V, 1500V, 2000V.

I have made a small currents measuring device using a LOG114:

I use : LOG114 with 1uA reference current on input I1.
The power supply for the LOG114 is made using an 78L05SMD (12V -> 5V) and after, the ICL7660 to get the -5V.
The logarithmic output of the LOG114 is scaled to 0V..2.5V and feeded to the 24bit ADC LTC2400.
I use an microcontroller to get the readings and send to computer for further processing.

The problem is how do I connect this device to measure capacitor charging/discharging?

If I use for example a simple current source made of a 1.5V battery and a 91Mohm 5% resistor, I get correct readings of current 16nA.

I need help me adapt this to measure charging and discharging of a capacitor.

I have found this board used by someone to measure this currents but no explanations, it is using the LOG104 :

I made the schematics:

The connection of current input is like this on the board that person uses:

The question is what is this:

Why the 50Mohm resistor is not connected to ground, are those voltage dividers of 10K/1K from the 5V reference used to offset both input current and reference current that goes to LOG104?


texts:
I want to calculate power supply THD (Total Harmonics Distrotion) using microcontroller.

My current sampling rate is 5000 samples per second to measure other parameters.

I have followed some formulas like using FFT but it is not showing results near by to industrial meters.

If anyone have some methodology or way to find please suggest.

Thanks in advance

-Abhishek


texts: How do I use VHDL generic parameters when I place a sheet symbol in Altium?

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I'm using Altium Designer Winter 09 to synthesise a design for an FPGA. This includes a VHDL-defined entity MyShifter that includes generic parameters so I can have it be reuseable:

library IEEE;
use IEEE.Std_Logic_1164.all;

entity MyShifter is

generic
(
       data_width : positive;
       pad_width : positive
);

port
(
    -- ...other ports...
    DataIn        : in std_logic_vector(data_width-1 downto 0)
);

-- architecture follows...

With any other VHDL entity I could just right click on a schematic and use Place » Sheet Symbol, and then synchronise the sheet entries with the ports defined in VHDL. Altium will, later on, automatically generate the higher-level VHDL that maps ports to other ports and I don't have to worry about it.

When I try this with my entity-with-generics, I end up with sheet entry labelled DataIn[-1..0]. This is unsurprising, since I haven't "told" Altium what data_width actually is.

My question is: how do I tell Altium what the generic parameters data_width and pad_width are for a particular instance of MyShifter?


texts: How to tell the difference between a voltage regulator in an SOT89 sized SMD and a transistor same package

texts:
Newbie here with just enough knowledge to be dangerous.  I have a Mazak Laser, vintage 1990 with Panasonic servo drivers, 3 axis. One of the power transistors went out which tripped two breakers and when I turned them back on an SMD, size SOT89, blew up and I'm trying to determine whether it is a voltage regulator or a transistor so that I can replace it.

There are 11 other miniature boards identical to the blown one on the main driver board and I was barely able to determine the part numbers on the chips as being XL31, which I could not find in any database or web search.

Since I have so many other examples for comparison I was wondering how to measure the good components to see what they are and then find (hopefully!) something local (Radio Shack?) to replace the bad component. Of course an identical part is near impossible to find but there must be other components that perform the same function, just not as small and neatly as the SMD.


texts: Can you harvest electrical energy from the air?

texts:
I found a website recently about harvesting energy from the air, and I am wondering if someone could tell me why the following wouldn't work?

Their "generator" is supposed to make electricity from the ionosphere (not UV, X-Ray, etc). Some claim it can knock out your electric bill totally (a bigger version, not this example). From what I understand, this is possible (it was discovered by Nikola Tesla), however this diagram doesn't look like it would work. Any help would be appreciated.

An example from the website:

You need:

(4) 1N34 germanium diodes
(2) 100 µF 50 V electrolytic capacitors
0.2 µF 50 V ceramic capacitors

Here is the electrical diagram they provide:

And they claimed to power a cell phone with it. I am not sure what kind of antenna to use.

While this seems like a sham, I just found this website recently and am looking for more info on the physics behind it.

Perhaps Teslo's patent explains things better, so here it is: Patent 685958.pdf

Found something: Here is a page that explains it.
Nikola Tesla free energy: unraveling Greatest Secret


texts: What to do about very hot planar inductor?

texts:
What I'm doing:

I am designing a DCDC converter to generate ±24v from an incoming supply of 18v - 36v. For this I am using the TI TPS54160, and following the document Create a Split Rail Power Supply with a Wide Input Voltage.

To save space, I designed a planar transformer, using a split transformer core. I put 12 turns on each side of the transformer, which according to the datasheet of the core should give 244uH (12x12x1700nH).

Added:

I have been using an Excel based calculator provided by TI to calculate the correct component values. The calculator is specifically for designing this circuit topology with this IC.

The Problem:

The problem is that at 500kHz switching frequency, the transformer is getting very hot. If I reduce the switching frequency, I can get it a little cooler, but if I reduce too far, the circuit no longer has enough drive current.

My Question:

What should I try in version 2? Would a physically larger transformer core help? Should I try reducing the number of turns on the transformer? At 500kHz, I calculate that I only need 65uH, so I could certainly go down to 8 turns.


texts: NMOS - Bulk Voltage going from 0 to -Inf

texts:
The question is

Consider an NMOS device where all terminals are at constant voltage except the Bulk terminal. A voltage is applied to the bulk terminal (w.r.t. GND) that varies from from 0V to -Inf. What is the effect on the threshold voltage of the NMOS device?

My understanding is that

The bulk terminal connects directly to the p-type substrate of the NMOS device.
By driving the bulk voltage lower and lower, you attract more free holes to the bulk terminal.
This makes it easier for electrons to accumulate near the gate and form a conduction channel.
Thus, since it's easier for a channel to form, threshold voltage should decrease.

Is that correct?


texts: How to identify the value of an unmarked SMD capacitor on a PCB?

texts:
I have an unmarked SMD capacitor on a PCB and I want to identify the value of this SMD capacitor. I have an LCR meter (BK880) and I want to use it to measure directly the capacitance of this SMD capacitor.

Do I need to discharge the SMD capacitor before measuring it?


texts:
I can easily understand these simple circuits:

or

but I can't wrap my head around this:

Not (A AND B) is all I get, but there is still a logical sum at the end (OR) and I have no idea where to put it

but for this, I can understand:

Not (A AND B)


texts: Dual power supply by chaining two lm317 voltage regulators in series: will it work?

texts:
I am short an adjustable negative voltage regulator, so I am trying to link two lm317 regulated power supplies to form a dual power supply. Is this possible? They are both connected to a center tap transformer. One is using the center tap as ground, the other is using the center tap as the positive supply. Will a dual power supply set up like this work and hold the regulated voltages? Also, is there another way to make a dual power supply with only lm317s?

The schematic is something like this. Sorry for the fast patch together with paint, but I think this will get the gist across. The component values are not set in stone, so don't worry about the values. I am worried about the general layout and the order of things.


texts: Convention for describing larger or smaller wire awg

texts: With wire awg, a larger number means a smaller wire.  What is the proper convention for making comparisons between wire awg?  For example if you you say it a wire needs to be larger than 12awg, is that more or less copper?  Should the word larger/smaller be avoided and lower/higher used and clarification be asked when they are used?


texts: Simplest shift register test circuit - clock

texts:
I'm looking for the simplest way to test the operation of a 74HC595 shift register without complex circuitry.

Currently (on a breadboard) I have a 47K SIP resistor in a pull-up fashion connected to pins 9 through 14 to make all inputs a default high. Yes I'm aware pin 9 is meant as n output and I'd be wasting some current if output of that pin is high but that particular output is useless to me anyway.

I then select random Qx output pins to connect directly to LEDs through current limiting resistors.

So I begin my tests and determined that the data line (pin 14) works, and enable (pin 13) also works, and the store clock (pin 12) also works along with the reset (pin 10) works.

But the clock (pin 11) is hard to tell if it is working because I need to pulse it faster than the fastest typist which I can't do. Every time I pulse it (make clock line low then make clock line high about 1/2 second later) after inverting the input data line, it seems all data output changes to the new input value instead of just one data output line.

So then I added a 10uF capacitor between clock (pin 11) which is the capacitor across the "wire" button in an effort to eliminate "bouncing", but that method isn't working.

So is there a simple way to test this clock line so that the IC sees that only one clock pulse occurred rather than hundreds of pulses?

The only answer I can come up with so far is to make an oscillator and connect it's output to the clock but I want to avoid too many extra chips if possible. Heck, if I can rewire my capacitor or resistor or even change their values, then I'd rather do that just to make the clock respond correctly.

Any ideas?


texts:
BACKGROUND:

For sometime now I've been in need of a pulsed power supply that can put out 200 V pulses with a minimum pulse width of 400 nS. After researching effective switching devices, I decided upon using a Mosfet.

Unfortunately, my research has not yielded any schematics or techniques for how I can wire a Mosfet to provide a select number of pulses per second at a pulse width that I can determine (not like a controller, but just something that I can figure out).

QUESTION:

I was curious if anyone knew how I should wire a mosfet to get a select number of pulses per second and a minimum pulse width.

EDIT: I don't need the supply to be adjustable, I only need to be able to know what the number of pulses per second will be (through equations and the likes) and how long each pulse will last (pulse width).


texts: How to use an array type as parameter of a Procedure

texts:
I want to read input values from a file and store them in an array

I have defined a custom array type in a package as :

TYPE qit IS ('0', '1', 'Z', 'X');
...
Type qitArray IS Array(Natural Range <>) OF qit;

and I have a procedure defined as :

Procedure ReadFromFile(Signal Output : OUT qitArray; File_Name : IN String; Delay : Time);

In Test Bench, I have declared a qitArray signal and I have passed it to procedure as parameter like this :

 Constant Input_FName : String := "input_file.txt";
 ...
 Signal Output : qitArray;
Begin
  ReadFromFile(Output, Input_FName, 20 ns);
  ...
End;

there is no compile error on the package file, but when I want to compile Test Bench, an error says :

  Array type of "Output" does not have an index constraint

The array length is unknown

How can I use an unknown-length array type ( or dynamic array ) as parameter in a procedure ?


texts:
I was doing some work on a blown circuit board and I cam across two identical components I had never seen before. One looks burnt so I think that might be the problem. The whole board is designed to operate at up to 1200 watts so I think it might just be a large ceramic resistor. I'm not sure though. Attached are pictures of the blown one and the normal one.
Thanks


texts: What is the aim of 100ohm resistor between the micro-controller pin and the gate of the N-channel MOSFET?


texts: 74HC595 Rows/Columns to drive LED matrix

texts:
Let's say we have one 74HC595 and we want to light 16 leds (common anode) connected as a 4x4 matrix exactly as in the following picture :

So, 4 first outputs to controls 4 rows.
The remaining 4 output to controls 4 columns.

From what I understand at this moment:

In the picture, there is a NPN transistor on the 4 columns to allow more current than what the 595 can sink.

Let's say only ROW1 is active, and all columns are active (LED1,LED2,LED3,LED4). Column 1, Column 2, Column 3 and Column 4 on the 595 will indicates a very low current, just the current set at the base of each transistor by the base current limiting resistor.

However, at ROW1, would it indicates at the 595 the sum of each led current of this row? So 80mA, if we assume each led at 20mA ?

If it's the case, in my case, there is much more 595 and much more leds and I don't want to operate near/over the 595 maximum current (75mA), would I simply add appropriate PNP transistors + base resistors to each ROW to reduce the current of each 595 rows pins ?

I want to keep the 74HC595 IC and low-cost single transistors. I know there are shift registers with higher current capacity and transistors-arrays IC that saves wires and resistors. Also that I can reduce the current of each led with higher resistors to keep it under 75mA, but I would like to understand how to properly work with a matrix arrangement that needs more than what the 595 can work with, using these simple components only.

In other words, is 4 PNP for rows and 4 NPN for columns, the best way to
handle >= 75mA on a single row ?


texts: Push-pull driver level shifting driving laser diode module

texts:
I am driving / modulating a small laser LED module LC-LMD-650-01-03-A (3.3V @ 25mA). My job is to PWM modulate it at 10kHz for 50msec, driving it with DSPIC33CK256MP503 (3.3V) dsPIC processor.
First I was just switching it using an NPN transistor, which acted as a simple open collector switch. PIC was pulsating its base, the emitter was on ground and the laser diode module was in its collector as load. My problem was the laser turned on strong and fine, but when the transistor closed, the laser was turning of slowly due to its internal circuitry. I needed to come up with some way to quickly turn it off.
So I used a standard NPN/PNP push-pull circuit, which I attached directly to my 5V battery source, before the 3.3V LDO regulator.
Now the laser modulation worked. Receiver recognized it, but the laser was too dim. Reason was clear, the push-pull circuit output is always about 0.6V less than its base input, which is driven by my 3.3V processor I/O output pin. Laser diode was only getting about 2.5V instead of desired 3.3V, regardless what was the voltage powering the push-pull circuit.
My selected I/O pin happens to be 5V input tolerant.
My question is, can I just switch my I/O pin to be open drain, and attach it to increased voltage by using a Zener diode, as on attached picture? The goal is to have 3.9V on the push-pull base, giving it the desired output of 3.3V.

UPDATE: After @AndyAka suggested to go back to open collector NPN, just to modify it, I am adding here my original first schematics section in order to continue the discussions.


texts: How VDB JFET circuit reverse-biases the gate-to-source voltage?

texts:
I already know how Gate-bias, Self-bias, and Current-source bias works in a JFET configuration. However, I am still stuck in voltage-divider-bias JFET circuit. (circuit below)

In a JFET circuit, the gate-source voltage must be reverse-biased. However, in a VDB JFET circuit, the gate voltage is always positive.

Posted below is also the transconductance curve, it shows that the Q point in this VDB circuit will have a negative voltage at either Q1 or Q2, how is that suppose to happen if VDB produce positive voltage at the gate?


texts:
I am making a LED wall clock with an ATmega328P Xplained Mini board, 64 LEDs (4 is for the "main ticks" 15,30,45,60) around the PCB to show the seconds, and a 7 segment 4 digits display to show the hours and the minutes.

My (beginner) question is:

Will this idea work? I tried to put in enough decoupling capacitors (not sure if needed), but I don't know if something is missing or wrong (the multiplexing maybe)?

Is this the way to wire the buttons and the shift registers?


texts:
This my first time to deal with RTC. I forget to add the crystal oscillator to the OSCI of the PCF8563 chip (I thought it has an internal oscillator). Therefore, I had to insert a 32.768kHz (sine wave) clock source from an external function generator to my PCB. I am using a 1 meter coaxial cable between OSCI pin and the function generator output.
The problem is when I read from the RTC it keeps giving me false and random readings. if I try to read the year for example, the reading is faulty and it changes randomly.
I checked the I2C signal and it is correct. I also has an EEPROM connected to the same I2C bus and it works properly.

What could be the cause of this false reading?
is it the connection of the OSCI from external clock source?


texts: How would I wire this tapped transformer welder?

texts:
I was gifted this old arc welder, w/o switches and the leads floating.
I asked this question on a welding forum also, but no response as of yet.
Dual 12 gage copper primaries
Dual 6 gage copper secondaries in series.
Originally there must have been 3 pushbutton selectors. No facility for on/off switch
3 pics of the x-former, the coil arrangement as given, and some inductance/resistance measurements.

These with a Fluke, but I will try an old very low ohms meter as ohming out 12 gauge copper has it's own issues.
I see that
coils 1&2 have logical value for inductance....
Coil 3 high value of resistance....
I saw a similar video where "pairs", 1&2, 3&4, 4&5 of coils get terminated/bridged on the switch lugs?
I've attached a pic of the welder and some sketches of tracing the primary coils
I would appreciate it, as this is a bit puzzling...
regards, and tia,
Nick


texts: generating a custom half duplex 1 wire serial protocal

texts: I want to use a microcontroller from NXP to generate a SWD (Serial wire debug) serial signal. A SWD signal is a clock and a host to target header, a single cycle wait period, followed by either a host to target or a target to host reply. It looks ALMOST exactly like a I2C signal, but I need to be able to transfer more than 14 or 28 bits (I forget exactly) after the header is transfered. The docs for the NXP uC I looked at had a hard limit on the number of bits that could be transfered after the header data. A simple RS-232 could do it by connecting the data wire to both Rx and Tx, but I also need a clock line.


texts: What is the best way to implement spi using 8085?

texts: I have to make a compass using 8085. I have to take serial data from magnetometer of mpu9250. Should i prefer bit banging to implement spi or make parallel out and parallel in hardware using shift registers, since 8085 can easily process parallel data.  I want to implement the least complex method.