texts: Scaling down the sensitivity of an MEMS mic

texts: I'm using an MEMS mic ADMP401, and the datasheet said, that the sensitivity form the chip is -46dbV, my question, how to can the scale it down, mean that I hear only really loud sounds?


texts: Signal conditioning of the acceleration data from the ADXL 354

texts:
My project consists of the detection of a leak in a pipe using the vibration methode.
I am using the MEMS accelerometer ADXL354.
I selected the +/- 2g range.
My problem is that the static acceleration 1g is not cancelled.
I am scared that this would corrupt my data.
I don't have any data to show because I am at the design stage of my project.
I think that adding a high pass filter analog stage to the z axis will help me get rid of it but I also think that will attenuate some informations that I might need. So I guess that wouldn't work. Any other solution to my problem is welcomed.


texts: How can I run a 12 volt car clock on C or D batteries?

texts:
I have an old vehicle that I use a battery shut-off on so the clock doesn't tell the correct time.
I would like to figure out how to run it on alkaline batteries instead.
I have no idea how to do that.
update for clarity...i shut off the battery powered when i leave the truck.
Thank you very much to those who offered suggestions...I'm already working on them!!


texts: Understanding the mathematics in the following article about EMC

texts:
I am currently studying the following reference about EMC, and try to understand the mathematics done in chapter 2 "What do we mean by high speed". The link to the reference is given below:
https://www.cherryclough.com/media/file/EMC%20for%20PCB/Parts%200%20and%201.pdf
In chapter 2, the author writes:

The velocity of electromagnetic propagation is limited by the laws of nature, and in an FR4 PCB it is
approximately 50% of the free-space velocity of \$3*10^8 m/s\$, say 6.67ns per metre (2ns per foot). So
we can associate an ‘edge length’ in millimetres or inches with each rising or falling edge of a signal.
So a 1ns edge has an ’edge length’ in an FR4 PCB of approximately 75mm (3 inches).

Electromagnetic propagation in air is \$3*10^8 m/s\$, and on FR4 PCB, it is 50% of that. So:
\$0.5*3*10^8 m/s = 1.5*10^8 m/s\$
The inverse of that gives \$1/(1.5*10^8 m/s) = 6.67 ns / m\$.
That I understand. If we assume a 1ns (rising) edge on a signal, why do we have an edge length of approx. 75mm? Shouldn't it be \$1ns/(6.67 ns/m) = 0.150m = 150mm\$? Why does he have half of my calculation?
Also, going a step further, the author claims

The rule of thumb is that we usually need to design the PCB using transmission-line techniques
when the edge length is shorter than three times the longest dimension of a PCB. So for a PCB that
has a longest dimension of 150mm (6 inches) we would categorise edge rates of 3ns and less as
“high-speed”

Previously, we had 1ns edge having an edge length of 75mm. Now we are saying that a 3ns edge should be treated as a transmission line if the track length is min. 150mm. Also, the author seems to mix "edge [ns]" with "edge length [mm]".
Anyone here who can help me demystify the math, or is there really something odd in the text?
Thank you,


texts: How can I restrict current to 12 amperes on a 12V circuit?

texts:
What is the best way to restrict the current a motor draws? I am using a 12V DC motor which unrestricted (i.e. no current restriction) draws around 18 amperes. I need this to be limited to 12 amperes maximum. Is pulse width modulation (PWM) the only solution?
EDIT: This for a portable water pump unit, which is designed to be powered by the cigarette lighter socket in a car. However, not all cars can handle 18a through this circuit, hence I would like to adjust the current draw. If possible I would like to avoid having to change the motors (for a lower current option), hence I am searching for a cost-effective alternative to essentially reduce the power of the motor. It does sound like PWM is the only solution, potentially in-line on power cord, away from water?
I appreciate your comments!


texts:
How can headphone cables act as Antennas for built-in radios in smartphones ? Is it possible because of different frequency channels or what is the theory/mathematics behind this?

On a side note, what would be a hardware implementation for this application?


texts: SPI bus connections - to loop or not to loop?

texts:
I have a question regarding the physical connection of an SPI bus.

I have an SPI master (a PIC32 device) and a number of slaves (in this case PIC16 devices). I'm only writing to the slaves, and the protocol takes care of which one does what when, so there are no MISO or SS signals to worry about and I'm just paralleling the data and clock lines to all slaves. The total length of the bus is no more than a couple of feet (say 60cm) and I'm running the SCK at 8MHz.

Now, the physical placement of the slave devices (which are actually interface nodes on other boards) is such that the SPI bus loops right back to the master so that it would be possible to connect both ends of each loop to MOSI and SCK respectively.

The following diagram shows what I mean - I'm talking about the red dotted connections - and the question is: is it a good thing to do this or not?

I have power and ground doing a similar journey, and this is obviously - and demonstrably - useful because it minimises the voltage drop caused by the slaves. However, I have no idea if it's a good or bad thing to do the same with these signal lines. Should I instead allow for some kind of termination - resistors to ground(?) - or maybe resistors in series to suppress reflections, or what?

I've tried it both with and without connecting the dots, so to speak, and there's no functional difference and no changes I can see on the 'scope, but maybe if it was a little longer than 60cm or a little faster than 8Mhz, I'd have a problem? So I'm looking for advice on what to do that will keep me out of trouble if anything changes.

Although this question is particularly troubling me for a 60cm SPI bus @ 8Mhz, are there any general principles for other situations? Maybe pull-ups on an I2c bus should be placed differently?

Any links to suitable reading material would be welcome too - I've not found anything that covers this specific question.


texts: What's the purpose of two capacitors in parallel?

texts:
What's the purpose of the two capacitors in parallel on each side of the regulator in
 this power supply circuit

I've seen similar setups in other similar circuits and can guess that it's related to one being polarized an one not, but I don't really understand what's going on there.


texts:
I am designing PCB2 & PCB3 but PCB1 & PCB4 are set in stone.
My constraints are as follows:

1) The PMIC must be the 1st device to become alive.
2) As much as I would love to, I cannot use the 5V #1 supply for PCB4.  PCB4 requires 2A of service but PCB1 can only supply 1A of current.

As you can see, U2 is supplied by 5V #1 and it's output signal is referencing 5V #1 as well, but,  U3 is supplied by 5V #2 and it's input signal is (still) referencing 5V #1 (not 5V #2).

Note : All GNDs are common and the VIN (24V) originate from the same external 24V supply.

Can or will this (5V #1/5V #2) referencing mis-match cause excessive ground-loop/s, discontinuity and/or even function?


texts: Understanding motor controllers and example application

texts:
I'm rather new to the world of motors and motor control circuits - about all I know is that you need one.

My intended application is to take a DC motor and create a "servo", which I understand to mean a motor that I can control via angular position commands.

The motor I intend to use is the following: http://www.robotshop.com/ca/en/banebots-rs-550-motor-12v-19300rpm.html From my torque requirements, I've calculated that I can gear it up to what's needed.

Here is a demo video showing what I think it is I want to do: make this motor control a load with precise position: https://www.youtube.com/watch?v=2FpRb-oOZ6c

My questions:

1) To achieve my goal, what type of electronics do I need to use? Why? Example products would be super helpful.

2) How is position feedback implemented (I assume this needs a sensor of some type), and what is an example product? What type of accuracy could one expect, and what would be the next steps for increasing it?

3) Do I need one "controller" electronics thing for each motor? I'm hoping not, trying to keep costs down =) Ideally I'd like to be able to control 5 of these motors as price-efficiently as possible.

For background, I started working in robotics on the software / algorithm side of things recently, and decided that I'd like to build my own hobby hardware on the side to better understand the discipline. Thanks for your help!


texts:
Looking at chips such as

AP6502A
TPS5430

The output capability is rated in peak and continuous current. Why are they not rated in terms of power? What output voltage is this current rating for?

As for example a rating of 3A at:

5V = 15W
12V = 36W


texts: Dual-supply op-amp LDO does not work, but single-supply does

texts:
I'm designing an LDO with dual outputs (Vout and -Vout), and only the positive output is shown in the pictures below. I'm having large trouble using dual supply op-amps in the design, and my single-supply one works fine and is shown in the first image.

But my LDO using a dual-supply op-amp does not work at all in the same configuration, and I've tried a few different dual-rail op-amps. Am I missing something in the dual-supply design?

The design with a dual-supply op-amp just saturates to the positive rail.

The problem was that the dual supply could not get close enough to the rail.


texts: How can I build a small DC boost converter, similar to what exists on a flash camera circuit board?

texts:
So everyone knows that disposable camera flash boards have a small DC boost converter to power the tiny xenon flash tube.  I have read several sources on the internet that seem to suggest that the board does this in 2 steps:

1) 1.5V DC is converted to an AC wave through a small oscillator circuit, fed through the small transformer (larger of the 2 on a typical board), which boosts the source to 250-300V, and is stored in the notorious large capacitor.

2) When the flash switch is closed, the capacitor discharges, and it is again stepped up through a smaller trigger coil, jumping it to over 1000V to turn on the xenon.

My question is, how can I build the first section of the circuit with discrete components on a breadboard?  I am not sure of how the circuit works, how the oscillator works, and more and sadly many websites out there fail miserably at explaining it.


texts: Differential Pair Reference Plane Coupling

texts:
I am routing LVDS pair on a flex board. The signal is 264MHz. I used Saturn PCB design to calculate width and spacing between conductors. The targeted impedance for diff pair is 100 ohms, which is dependent on the width/space between conductors and hight to the reference plane. The reference plane is a ground which I choose to be layer 3 (of 4) in my design. Since this is the flex board it is very thin 8 mills total thickness, those it is difficult to create required hight to the reference plane. The reference plane is not far enough to accommodate 100-ohm differential impedance.

I created coplanar waveguide on the same layer as the differential pair to serve as a coupling for the diff pair. Unfortunately, the geometry of the board does not allow me to have this waveguide run all the way to the source. Those now I have a coplanar waveguide with a 6 mills spacing to diff pair guiding LVDS signal half way to the source and after LVDS signal coupled to a reference plane which is 3 mills away (Zdiff = 69 ohms). I also should mention that layer 2 is a power layer, those I believe LVDS signal introduces noise on the power supply. I could move power on layer 3 and have ground on layer 2. However, Zdiff going to get even worse then. I am torn here. Any suggestions on how to route differential pair on a very thin board? Would it be better if I only couple to the ground plane and not use a waveguide?


texts: Current transformer datasheet: confusion on turns ratio vs. max. rated currents

texts:
I have a SCT-013-000 current transformer that says it scales 100A:50mA, meaning it has a turns ratio of 1:2000, but the data sheet says that the turns ratio is 1:1800.

I'm pretty sure the turns ratio is 1:2000 but are there any test I could do to check?

Relevant part of the datasheet:

http://statics3.seeedstudio.com/assets/file/bazaar/product/101990029-SCT-013-000-Datasheet.pdf


texts:
I have a Electronic Speed Controller (ESC) being controlled with Pulse Width Modulation (PWM) from an Arduino.
When I put my hand close to the cables the signal goes screwy until I move my hands away. I checked for shorts but didn't find any. I don't have an oscilloscope or that would give me my answer.
What's happening here?
I also made this video to help explain the situation.
Rough Schematic

EDIT
Adding working Arduino code for future visitors
#include <SoftwareServo.h> // Download from http://playground.arduino.cc/ComponentLib/Servo

SoftwareServo myservo;  // create servo object to control a servo

//int potpin = 0;  // analog pin used to connect the potentiometer
int PIN = 2;
int val;    // variable to read the value from the analog pin

void setup()
{
  Serial.begin(115200);
  myservo.attach(PIN);  // attaches the servo on pin 2 to the servo object
}

void loop()
{
  char r = Serial.read();
  String inStr = String(r);
  if(r > -1) {
    Serial.print("serial in: ");
    Serial.println(inStr);
  }

  if(r <= -1) {
    // void
  } else if(inStr == "h") { // high
    Serial.println("HIGH");
    digitalWrite(PIN, HIGH);
  } else if(inStr == "m") { // medium
    Serial.println("medium");
    myservo.write(90);
  } else if (inStr == "l") { // low
    Serial.println("LOW");
    digitalWrite(PIN, LOW);
  } else if (inStr.toInt() >= 0 && inStr.toInt() <= 9) {
    int val = inStr.toInt() * 20;
    Serial.println(val);
    myservo.write(val);
  }

//  float t = millis() / 100;
//  val = sin(t / 10) * 1000;//analogRead(potpin);            // reads the value of the potentiometer (value between 0 and 1023)
//  //  if(val < 0) val *= -1;
//  val = map(val, 0, 1023, 0, 179);     // scale it to use it with the servo (value between 0 and 180)
//  val = millis() / 100;
//  myservo.write(val);                  // sets the servo position according to the scaled value
//  Serial.println(val);
//  delay(15);                           // waits for the servo to get there

  SoftwareServo::refresh();
}


texts: Reverse polarity protection in PCB design

texts:
I've fried the controller on this PCB when by accident connected 24V supply in reverse polarity. The PCB includes a SS34 schottky on a positive side. However the controller still got damaged (completely dead).
I already got a replacement controller and will replace it on the board. My question is -- why the controller got damaged even though there is a supposed reverse polarity protection and how it should be protected properly?
Notes:

I am not the designer of linked board
The board includes 3 separate power inputs. 2 were connected correctly, 1 was incorrect (reverse polarity), which should be causing short through the ground I presume?
The SD card that was inserted into the slot also dead, but nothing else appears to be damaged


texts:
I use gsm module, which makes current bursts up to 2Amps (maybe slightly more). That causes voltage drops about 0.5V on my power supply (I use lipo battery), and than device hangs up or starts glitching.
Now I use two 470uF, and smaller ceramic 22uF, 10uF, 1uF and 100uF tantalum caps. But they aren't enough.
Is it possible that my ground tracing is so bad that 470uF ones are enough but don't work? I put them quite close to  module input.
I decided to use a bigger one (3300uF, 6-10V) to try fix that problem.
However, do I have to use some special schematic to connect it? I mean that it will be like short circuit until get charged.
Thanks!


texts:
For a 20W amp, what are the determining characters, apart from speaker Impedance and Power rating, that affects a selection.

Example Specs -

(source - http://www.madisoundspeakerstore.com/approx-2-fullrange/aurasound-nsw2-326-8a-120-2-full-range-with-solder-pads/)

What are these
- Power capacity(RMS)
- Power capacity(peak)
- Maximum Excursion
- Resonant Frequency
- Total, Electrical, Mechanical Q
- Xmax
- Compliance

Any other notes.

Also, can I use this speaker.

Thanks.


texts: Multiple grounds from diode bridge? Safe or really stupid/dangerous?

texts:
I am making a hybrid tube preamplifier (one vacuum tube and one op-amp).  Both use very different voltages - the tube is getting somewhere about ~150V DC  and the op-amp gets ~6V  DC.  The differences are huge.

Can I connect the ground from 150v DC to  the ground of 6V DC?   Both are 'made' from a transformer and a diode bridge, filtered with capacitors.  I assume they both should be at 0V.  Based on that it seems to me that it should be somewhat safe.

Am I wrong?  Can it be done?  And can it be safe?  Or is it really stupid and should never be even considered?   I am just wondering, didn't actually try it - now I am asking.

*First stage of the preamplifier:    (~  150V   DC)

Second stage of the preamplifier:    (6v  DC)


texts:
I'm experiencing an interesting issue with Eagle's polygon copper pour. As you can
see below, the solid red is the copper pour area, while the dashed line is showing the complete polygon outline (I clicked on it to show it). I don't know if you can see, but the pour (the solid) actually has a bend to it that is somewhat noticible. It's not straight as it should be. This is the first time I've seen this. There isn't anything on any other layer that I know could be causing this. Does anyone know what could be causing this? Is this a bug in the software? I'm using Eagle  6.3.0.

[Edit] Interestingly enough, moving the outline specified by dimensions more to the left does remove the issue, although it makes the board larger.


texts: Why does my mic behave like an antenna only when I touch it?

texts:
I recently built this mic amplifier circuit (source):

The output is connected to a speaker, but it's not exactly working as intended: I can only hear myself at the output if I blow hard into the microphone, otherwise not much. However, when I touch the metal casing of the microhpone, it behaves like an antenna and broadcasts what seems to be an AM signal from Quebec. This is fine, I understand that the mic can behave like an antenna, but why does this happen only when I touch it?

I noticed this quite a bit with electronics, particularly when there's transistors involved that touching the electronics has an effect on its behaviour, why is this?

It's also interesting that putting the mic into contact with other insulating materials like my desk or paper has no effect, but only with skin contact in particular it seems to make a good antenna.


texts:
I am reading some C code and came across this declaration in the program:

unsigned char serv_ctr @0x0002;

Can someone point me to documentation, or explain what the "@0x0002" is for in the Mplab XC8 v1.35 C compiler?


texts:
I have an LED that is rated for 34V at 3A and about 100 watts. I am trying to figure out what power resistor I need with a 36V battery supply. I think I need a 10W 1 Ohm resistor but I am not sure. Did I calculate that correctly or will that resistor burn out?

Edit: Would a LM2596 DC to DC Buck Converter work instead of a resistor(s)?


texts: Showing QAM constellation diagramm on signal analyzer

texts:
I've been playing with some lab equipment recently in order to learn more about digital modulation techniques. I've connected R&S signal generator SMIQ 03B with the R&S spectrum analyzer FSIQ 3 and observed various modulated signals. I've managed to set up I-Q signal view, eye diagramm and constellation diagramm for BPSK, QPSK and 8PSK. But QAM16 gives me some trouble. Here are some examples:

For all my signals there are some common settings on both signal generator and analyzer:

Symbol rate: 100 ksymbols/s
Carrier frequency: 1 GHz
Output filter: squared cosine/0.9
IF bandwidth: 10 MHz

And here are some nice looking examples for various constellations: BPSK, QPSK and 8PSK. The problem is with QAM16 - the constellation is not expected 4x4 cell but rather some circular shape with no distinct clusters.

Question: which parameter has to be set on signal analyzer to obtain the classical 4x4 constellation? I don't mean only some device specific parameter - is there any common-theory known parameter that defines the constellation shape?


texts: 0-5V 1A Dual Output DC Power Supply - SOFTWARE CONTROLLED

texts:
I am interested in purchasing (or building but preferably purchase) a software controlled DC power supply.  Preferably, would like to control the output using LabVIEW.

I need two separate outputs that can be controlled from 0-5V as accurately as possible (5mV resolution).  Each output must be able to source up to 1A.

I am planning on using the supplies to control the brightness of two separate high powered LED's.

Can't seem to find much from Google.  Any help is appreciated!


texts: Hey I am trying to make a etchable pdf for a project of mine. It is supposed to be a 2x9inch board. But I cannot find a good software to make this. Eagle's free version will not allow me to make this size and I cannot understand gEDA. Is there other simpler option?


texts: Recapturing side and back lobe radiation from a directional antenna

texts:
When you look at the radiation pattern for a directional antenna, you see a major lobe where the greatest concentration of radiation is found and side and back lobes that have much less concentrated radiation.

I was wondering what methods, if any, have been developed to "recapture" the side and back lobe radiation and concentrate it in the main lobe for greater antenna performance?


texts: Calculating the voltage drop in a split-phase system

texts:
We are working with an electrician to install permanent wiring to a large trailer unit - it will be a 120/240 V split-phase system (the trailer itself uses a NEMA 14-50 dryer plug) delivering 50 amps at a distance of 300 ft.

I (think I) understand that this wiring set up effectively gives us three circuits - two 120 V/50 A circuits and a single 240 V/50 A circuit.

What I am struggling to understand is how I determine the proper wiring size for the system, given the parameters of the circuit and our voltage drop needs ( <3% ). Following Ohm's Law, I have been using the formula to calculate the expected voltage drop for particular wire gauges (4 AWG or 1 AWG):

Vd = 2 * L * R * A

Where:

Vd: voltage drop

L: one way distance (in thousands of ft)

R: resistance of wire (in Ohms per 1000 ft)

A: load current (in amperes)

Ex. 1 1 AWG wire, 300ft, 50A

Resistance of 1 AWG wire / 1000ft = .124 Ohms

Vd = 2 * 50 * (.3) * (.124)

Vd = 3.72 V

Ex. 2 4 AWG wire, 300ft, 50A

Resistance of 4 AWG wire / 1000 ft = .249 Ohms

Vd = 2 * 50 * (.3) * (.249)

Vd = 7.47 V

Based on this information, my numbers suggest that we would need to use 1 AWG wire, but the electrician has said that 4 AWG is more than sufficient. I have complete confidence in this electrician, so I am sure there is something that I am missing. How does the presence of the split-phase 240 V system affect voltage drop considerations (if at all?).

Any comments or help is greatly appreciated!


texts: Does EC11 Incremental Encoder need hardware debouncing and VCC for encoder?

texts:
I'm implementing an EC11E rotary encoder which has 3 pins + 2 pins for a switch. It seems like most of the projects I've seen online wire A/B and GND to the microcontroller, which to me, makes sense.
However, at the same time, I've seen a few references to schematics which include debouncing capacitors and resistors like below.

However, I don't understand why this is actually necessary. From what I understand, since the quadrature encoding effectively presents itself as a square wave, it shouldn't need debouncing, given the contacts either touch or don't touch.
Do I actually need these debouncing capacitors and resistors in my circuit?
As well, it seems like most breakout boards for encoders include a VCC line for pull-up. However, the MCU I'm using [AT90USB646] already includes internal pull-ups on all its GPIO pins. WIll I still need a pull up line then?


texts: Ac Adapters Pri & Sec ratings what can I use?

texts:
I am a complete novice and know very little about this so please stick with me.

I have a set of lights that came with an AC adapter that is now faulty. On the adapter it has:

Pri: 230V-240V ~50Hz.
SEC: 24V ~850mA Max 20.4VA

I have another adapter which works the set but this has the following:

Pri: 230-240V - ~50Hz
SEC: 24V ~ 300mA Max - 7.2VA

As this is lower rated and works is it safe to use or have I got it all around the wrong way and it is unsafe to use because it is a lower rating?

I can't seem to find any replacement adapter to buy that matches the old one.


texts: Is this phase shift oscillator design correct?

texts:
I found this design on the internet. It's a 180 degree phase shift oscillator.

Actually, it is a 203 degree phase shift oscillator. Because the frequency is 6.5 kHz and the capacitive impedance is 24485.37 ohm. So, the phase shift of each stage will be 67 degrees not 60 degrees.

The total phase shift of the three stages of the high pass filter is 203 degree.

Is it OK to have more than 180 degree of phase shift?

If it is OK, what is the allowable range? How do I know the range at which the circuit oscillates?


texts: Is there a universal guide-line for the mechanical dimensions and tolerances of Surface Mount packages across the industry?  I'm very new to SMT machine programming (<1 year), so I've been trying to look for a copy of JEDEC's JEP95 that wouldn't cost me over $1,000 but to no avail.  I have seen a few things related to IPC around the web, but I don't know what is most reliable and up-to-date, and would like guidance from someone more experienced than I.


texts: Does Armature current decrease as the load decreases?

texts: I am being asked to find the speed of a 16.5kW shunt DC motor that is being supplied with terminal DC voltage of 300V when operating at 50% rated load with an armature current of 30A. I need to use the armature current when solving this, and am wondering if it decreases due to the motor operating at just 50% load, or if I can use the 30A.


texts:
I am making a circuit to control a motor using an Arduino UNO and an H-bridge IC, but it's not working, rather something strange is happening.

Circuit's scheme:

When the motor is connected to pins 3 and 6 of the H-bridge nothing happens, but strangely when one of the motor's wires is connected to either 3 or 6 pins of the H-bridge, and the other wire of the motor is connected to ground the motor works! But I can't control it's speed with the potentiometer, neither control it's direction, or even it off using the push-buttons.

I suppose that the H-bridge deliver power to it's 3 and 6 pins because the motor works when connected to ground and one of them, but this shouldn't happen, one of the pins (3 and 6) should deliver power and the other should be ground, that's what I think.

How can I solve this problem?

Edit:
For some reason the wires connecting Arduino pin 2 with H-bridge pin 7 won't deliver 5 power unless I was touching the wire with my finger, (this also happen in the wire between Arduino pin 3 and H-bridge pin 2) I've tried connecting the pins with other wires, but the same thing happens, also I've used an 220Ω resistor and the problem is still happening. this thing happens with all Arduino pins, not just 2 and 3, but in before this project they were working very well. O_o


texts: How do i put a DC motor on an arduino motor shield and use it

texts:
I'm building a robot using an Arduino UNO and the standard Arduino Motor shield.

I have two 9-12V DC motors.  I'm open to the possibility of using servos, but I'm currently trying to use these motors.

How do I wire the motor to the microcontroller and program it to run? I've been looking for days on how to do this and returned unsuccessful.  I found the Makezine blog post the most accessible resource, but I'm still not sure how to do this.


texts: What PCB electromagnetic simulation tools are available?

texts:
I would like to perform electromagnetic simulation and analysis of simple PCBs (coupling, capacitance, impedance, EMI, etc.)

Are there any reasonably priced (sub £1000), or free packages available which will do this?


texts: A good 3V single supply OpAmp recommendation for a transimpedance amplifier

texts:
I have designed a transimpedance amplifier using OPA355, the datasheet suggest this Opamp can go down to 2.5V and still works however I cannot get it to work at 3V. If I provide 5V supply, everything works, when I reduce to 3V, things stop working.

I will further debug this but I am looking for a reliable 3V single supply OpAmp that I will use as a transimpedance amplifier. My signal is about 3MHz and I deal with small signals so I need something with relatively low noise.

I need help from the masters as I am looking for a proven part that somebody here made it work before as opposed to perfect datasheet part.


texts: Max startup current for Vacuum cleaner motor

texts:
We used the vacuum cleaner motor 2200W 220v in one dental device (vacuum former) as you can see here:

So now one of our costumers said when they used this device the power cable is warmed and when the vacuum motor started the dental clinic circuit breaker (25A C type fuses) trip (could be seen here:)

and disconnect the power of the whole system, so I guess it using 10A for steady-state but I don't know how much current this motor get for startup and could this situation be the result of this trips.

Based this site:

  Vpeak = IinR, where Vpeak = √2(V)

  and

  E = CV2/2

So we have 220v :
√2*220/15=20.74 A

I found this vacuum cleaner’s current waveform from here:
, which is similar, so is this the inrush current of this motor?

I need the causes, and if possible I want to know what is the proper way to solve this problem? Is it good to use soft starter?

Update:

  These Vacuum cleaner motor we used in our devices are Brushes.


texts: Normal current flow in LSF010x level translators

texts:
I am reviewing the datasheet and design documents for a level translator. TI has a great video explaining the operation of this device. I understand how the device works but my only concern is with current flowing into my lower voltage side source.

The video points out that under normal operation a few uA will flow into the VccA source. For my design, I have a TPS7A2025PDBVR linear voltage regulator (+2.5V). My higher side voltage is anywhere from +3.3V to +5.5V. I know that it is a only way street for a linear regulator and they cannot sink current, only source. But can it possibly source this little? If not, how can I divert this current if it really is a problem? Or perhaps I should switch the linear regulator for a switching regulator just for the voltage translator?
In case you are curious, here is the full video:
https://training.ti.com/tlm-lsf-bias?context=1134826-1139264-1134790


texts: It's been more than 10 years (since I designed hardware with RS-232), and we're still using RS-232?

texts: Are there any alternatives to this ancient yet still popular way of communication?


texts: Do you really need a satellite dish to communicate with satellites?

texts:
I'm doing a project where I have ground sensors that detect seismic activity and report their GPS coordinates via APRS if seismic activity is detected. I'd like to do the APRS over satellite.

The sensors are small and utilizing a satellite dish for each one would not suit my needs.

There is a product I came across called the Thuraya satsleeve for smartphones that is satellite-enabled and doesn't require a large antenna or dish to make satellite calls and send satellite text messages.

So would a small antenna work for APRS over satellite? If yes what kind of antenna would be appropriate? If no why?


texts:
I was recently learning about how a diode works, and I understand how a diode, in it's natural state, develops a sort of "pushback" voltage that pushes against any voltage that is applied, effectively lowering the energy of any electrons that pass (forward voltage). This part makes pretty good sense to me.
However, I fail to understand how to measure this "pushback voltage." Using a multi meter, I tried the setting which I use to measure the voltage out of a battery (200 mV setting), and I noticed that I got different values when testing my small LED's: 3.4 for the Red Led, nothing for the Blue Led, and 9.8 for the green LED. I'm not sure what's going on here. I expected the 3.4 Voltage drop to be normal, but the other LED's don't seem correct. And how can a multi meter even measure the forward voltage of a diode? As in, wouldn't any electrons that had the potential energy to cross against the induced electric field have already made the jump from the n-junction to the p-junction? Any ideas?


texts:
I have a bunch of random IC's from electronic goldmine and one of them includes the MM74HCT541 octal 3 state buffer.

So just a simple circuit to test it, I have 4x AA batteries and I am hooking this up on a breadboard. I hook up power to pin 20, and ground to pin 10, I then hook up power to A1, which is pin 2, and I hook up an LED with resistor from Y1 (pin 18) to ground. The LED does not light up. I tried it with other buffers in the IC, but it still didn't work. I have about 3 more of these, but just in case I was burning it out, I didn't want to try the others. So I am wondering what I am doing wrong here and what I can do to fix it.


texts: Time domain reflectometer looking for faults

texts:
I have a TDR with a sampling frequency of 200MHz that equals 1 sample very 5 ns. When I use a really long square wave the response will look like the left plot. Where delta t is the time of propagation through the cable * 2.
When I use a short needle pulse the response will look like the right plot. These plots are ideal plots without considering attenuation of the cable.
But lets say I have a little damage in the middle of the cable. The damage changes the line impedance by 10%. The damage has a length of 30cm. With a NVP of 2/3 that means the signal travels 30cm in 1.5ns.

When using a long square wave the width of the reflection will be 3ns?
Using a needle pulse or square wave won't show me the damage in the cable or am I mistaken?


texts: Are traces exiting a pad at an angle bad?

texts:
I have been told in the past that you should always have traces leaving a pad on a straight line.

The reason I was given was that it could create an acid trap. From what I have read this is not really much an issue in modern PCB manufacturing methods.

So is it just a looks/taste/aesthetics thing then?


texts: Can I use a USB keyboard with the PS2Keyboard library?

texts:
It is my understanding that most newer USB keyboards will not work with the PS2Keyboard library because they do not use the PS/2 protocol. Some, but not all, do have the ability to use the PS/2 protocol:

  Many keyboards and mice can connect via either USB or PS/2, selecting the appropriate protocol at power-on. Such devices are generally equipped with a USB connector, and ship with a passive connector adapter to allow connection to a PS/2 port. Conversely, modern USB keyboards and mice usually have only USB plugs and require an active adapter to connect to a PS/2 port.[1]

If it has the capability, would a USB keyboard select the appropriate protocol when wired to an Arduino automatically? If not, is there a way I can force it to select PS/2?

If the USB keyboard does not have the protocol selection capability, would an active adapter work with an Arduino?


texts: Efficient way of writing to flash memory without losing data

texts:
For my project, I am writing some code that gets some results and I want to store these results on external flash memory. The external flash memory in question is a MX25R8035F. I found that writing without erasing only works the first time I wrote something to an address.

But because of this I'm running into some memory issues. The smallest erase is a sector erase (4096 bytes.)  If I want to write to a specific address I would first need to read the sector that contains that address, change the bytes that I want to be changed and then write the whole sector (writing is only per page.)

Is there a more efficient way of using this external flash memory? Specifically using less memory to change one or two bytes.

The function I use now this can be found below:

uint8_t EXT_FLASH_write(size_t address, uint8_t *buf, size_t length) {

/*
 * The entire sector will be erased when writing to an offset inside that sector
 * Therefore this function will first retrieve all data inside the sector and update the retrieved
 * data with the values inside buff which and will then write the entire content back to the sector
 */

    uint8_t wbuf[4];
    SPI_Transaction transaction;
    uint32_t sectorBaseAddr;
    uint8_t temp[EXT_FLASH_ERASE_SECTOR_SIZE];
    uint8_t tries;
    size_t ilen; /* interim length per instruction */
    uint32_t bufIndex = 0;
    uint8_t pageIterations;

    while (length > 0) {
        // first retrieve entire sector so it can be erased on the chip
        sectorBaseAddr = EXT_FLASH_SECTOR_BASE_ADDR(address);
        EXT_FLASH_read(sectorBaseAddr, temp, EXT_FLASH_ERASE_SECTOR_SIZE);

        // Erase the sector on the chip
        EXT_FLASH_erase(address, EXT_FLASH_ERASE_SECTOR_SIZE);

        ilen = EXT_FLASH_PROGRAM_PAGE_SIZE
                - (address % EXT_FLASH_PROGRAM_PAGE_SIZE);
        if (length < ilen)
            ilen = length;

        memcpy(temp + (address - sectorBaseAddr), buf + bufIndex, length);

        bufIndex += ilen;
        address += ilen;
        length -= ilen;

        tries = 0;
        if (EXT_FLASH_writeEnable() != 0) {
            if (tries == EXT_FLASH_MAX_TRIES) {
                return 1;
            }
            tries++;
        }
        tries = 0;
        while (EXT_FLASH_waitReady() != 2) {
            if (tries == EXT_FLASH_MAX_TRIES) {
                return 1;
            }
            EXT_FLASH_writeEnable();
            tries++;
        }

        // programming the external flash can only be done in pages
        // so divide current sector into pages and write each page separately
         for (pageIterations = 0;
                 pageIterations * EXT_FLASH_PROGRAM_PAGE_SIZE
                         < EXT_FLASH_ERASE_SECTOR_SIZE; pageIterations++) {
            EXT_FLASH_select();

            wbuf[0] = EXT_FLASH_CODE_PROGRAM;
            wbuf[1] = ((sectorBaseAddr
                    + (pageIterations * EXT_FLASH_PROGRAM_PAGE_SIZE)) >> 16)
                    & 0xff;
            wbuf[2] = ((sectorBaseAddr
                    + (pageIterations * EXT_FLASH_PROGRAM_PAGE_SIZE)) >> 8)
                    & 0xff;
            wbuf[3] = (sectorBaseAddr
                    + (pageIterations * EXT_FLASH_PROGRAM_PAGE_SIZE)) & 0xff;

            // Configure the transaction
            transaction.count = sizeof(wbuf);
            transaction.txBuf = wbuf;
            transaction.rxBuf = NULL;

            if (!SPI_transfer(masterSpi, &transaction)) {
                /* failure */
                EXT_FLASH_deselect();
                return 1;
            }
            // Configure the transaction
            transaction.count = EXT_FLASH_PROGRAM_PAGE_SIZE;
            transaction.txBuf = temp
                    + (pageIterations * EXT_FLASH_PROGRAM_PAGE_SIZE);
            transaction.rxBuf = NULL;

            if (!SPI_transfer(masterSpi, &transaction)) {
                /* failure */
                EXT_FLASH_deselect();
                return 1;
            }

            EXT_FLASH_deselect();
        }
    }
    return 0;
}


texts:
I tried to open a file ff.txt and write into it some random numbers say seven times. I used EDA playground website for it. Below is the link for that code as well as that code.

http://www.edaplayground.com/x/TCC

When I try to run I get error as

** Warning: (vsim-3533) [FOFIW] - Failed to open file "ff.txt" for writing.

Permission denied. (errno = EACCES) : design.sv(6)

My question is why don't I have access to the file ff.txt?

     module fopenclose();
       integer mcd,number;
       initial begin
         mcd=$fopen("ff.txt");
         repeat(7) begin
         number=$random;
         $fdisplay(mcd,"Number is",number);
       end
         $fclose(mcd);
       end
       initial #2 $display("%d",mcd);
     endmodule


texts: short and over current protection for circuits using SLA batteries at high amps

texts:
I'm trying to build a robot that will use two motors at 24V. Yet to measure how many amps they will consume. My motors controllers can only do 23A. Planning on accelerating slowly with the hope that I never exceed 23A on each controller. I will also be running a wireless router (12V 2A rated), small computer (12V 3A max), arduino, couple of logitech cameras off a USB Hub (hub is rated at 12V/5A).

I'm considering using standard SLA batteries.

What is the best way to protect from shorts, accidental current overdraw, and reverse connections? I have seen some automotive circuit breakers rated at 50A. Is there a single solution that addresses all of these or will I have to have separate solutions to address each (shorts, over current draw, and reverse conditions)?

I see that this topic  addresses similar question, but is targeted for low amps. I need something that can handle 60-80A.


texts: Inductance of planar (spiral) coil near solid copper surface

texts:
I'm working on a electromagnetic levitation system, consisting of a flat spiral (planar) inductor positioned above a solid copper surface. The planar coil is parallel to the copper surface. (Consider both the coil and the surface to be 100% pure copper, and the surface infinite in area and depth.)

I know how to calculate the inductance of a spiral inductor in free space. In fact, there are a number of calculators online, like this one.

My question is regarding the change of inductance as the coil is brought near the copper surface. My thinking is to consider the copper surface as a "shorted secondary" in a coreless transformer. This would imply that the inductance of the primary is actually the effective leakage inductance based on the system geometry. I suppose that if the primary (the spiral coil), were brought infinitesimally close to the secondary (copper surface), the leakage inductance would be zero. As the coil is moved away from the copper surface, the leakage inductance would increase (up to the full inductance of the coil in free space, at infinite distance from the copper surface below). I think it is probably ok to consider the resistances as negligible (effectively zero).

I am looking for two things:

Guidance on my thinking, confirmation that I'm on the right track, or correction if not.
A formula that I can apply to calculate [the change in] the coil's inductance as it is positioned at different distances to the copper surface. (Typical distances would be on the order of 1 mm for a 25 mm diameter coil, FWIW.)

I realize that I could actually construct this system in some form and measure the inductance, and perhaps even empirically derive a formula. But I'd rather model it first if possible.


texts: How should I do an efficiency analysis of an AC motor driver in LtSpice?

texts:
I have two different AC motor drivers and I need to test them for energy efficiency in an analysis tool (I know only LtSpice).

But I don't know how to model an AC motor. Driver's circuitries are given. They are 3-phase AC motor drivers. Can you tell me how should I model an AC motor and how to do an efficiency analysis in LtSpice?


texts:
Is is possible to disable an interruption during its service routine to prevent it from happening again for some time?

For example:

void TIM2_IRQHandler(void)
{

    if(TIM_GetITStatus(TIM2,TIM_IT_CC1) !=RESET)
    {
        //(some code)

       **TIM_ITConfig(TIM2,TIM_IT_CC1,DISABLE);**
       TIM_ClearITPendingBit(TIM2,TIM_IT_CC1);
    }
}


texts: Op Amp as a buffer in lt spice for high voltage and high frequency

texts: I want to make a buffer which can drive my sine wave with an amplitude of ±25 volts and a frequency of 25 MHz. Which Op amp in LTspice should i use?


texts: Connecting two DC wallwarts in series - to produce dual DC supply

texts: I have two 9 V, 300 mA wallwarts and would like to connect them in series to produce +9 V, 0 V and -9 V. This can be done with two 9 V batteries (as seen below), but can I do this with two non-identical wallwarts?


texts: Why are different currents used for charging batteries with the same voltage output?

texts:
I'm trying to understand the behavior of batteries a bit more. I've noticed that chargers for given batteries have different current capabilities.  Do batteries need to be charged with a voltage that is near their nominal output?  E.g., a 12V battery should be charged with 12V?  If one charger for a battery has a 1A output and the other has a 2A output, is the higher current charger actually just supplying a higher voltage?

The batteries don't have some kind of semi-conductor-like physics going on which allows them to maintain a constant voltage drop with different current levels, do they?


texts: Does a shunt regulator protect other ICs from high current transient spikes?

texts:
Does a shunt regulator like 431L (datasheet), wired like this

(VKA is not connected to anything) help protect other electronics supplied from INPUT net (battery connection)?

INPUT net also supplies 4V directly to 4 small dc motors, which I believe generate quite large voltage/current spikes at start, stop, or from sudden stop (due to propeller hitting an objetc for example). INPUT net also powers an LDO that powers MCU, sensors, etc.

I am confused, because it is trying to keep VKA constant, then when the spike comes, VKA will change, then 431L should sink the spike fast to keep VKA at 2.5V, but there are two facts that go versus this: the 431L can only sink 100mA, that looks little, so maybe it burns? And there is 1K resistor before the 431L, so maybe the spike just ignores the 431L and goes directly to the LDO and next electronics, generating noise, maybe burning them? So the 431L would protect nothing?

Or maybe the 4V motor spikes are not so dangerous and I should forget about protection?

Please help me understand this, or point me to some reading about this. Thank you very much for your time.


texts: What is the Best Way to Reduce High Power Three Phase Rectifier Ripple?

texts:
If a three-phase 220V AC @ 50Hz(three lines having 127V RMS voltage if measured to neutral each) mains supply is rectified with a standard 6-diode rectifier looks like this:

I believe if 25 amps is drawn from output of rectifiers with a rectified voltage of roughly 310V DC, then it can deliver about 7.7kW of power.

I know in single-phase full bridge rectification the following formula is used to calculate voltage ripple: Vripple = Iload / (2 * f * C)

QUESTIONS:

Now the challenge I'm facing is how can I reduce the ripple to less than 1%, so I could deliver a steady DC power?

Am I right to assume in three-phase full bridge rectification the following formula can be used? Vripple = Iload / (6 * f * C)

Can I get away with a bunch of capacitors or is it better practice to use either a buck, boost, or buck boost converter?


texts:
I am making use of the LM2678 adjustable version switching regulator in the design of a 5.5V buck converter. I made use of the design equations detailed here: lm2678 datasheet

For the following design constraints:

Vout: 5.5v
Vinmax: 15v
ILoadmax: 3A

I worked through the design equations to obtain the circuit values shown below:

Next I imported the Spice model for the LM2678-adj from the TI website into LTSpice. I calculated a load resistance as \$R = \frac{V}{I} = \frac{5.5}{3} = 1.83 \Omega\$ and did a transient analysis simulation for 2ms. The result with input voltage (red) and output voltage (blue) is shown below along with LT spice schematic:

The output voltage value is 1.83mV. Removing the load results in an output voltage of just over 2V. The datasheet suggests a typical feedback voltage of 1.21V however when I measure the voltage between the feedback node and ground under load I get 367.17186µV. The output voltage is related to the input voltage and output resistors via the following formula: \$V_{out} = V_{fb}(1+\frac{R8}{R9})\$ hence the reason the output voltage is so low is because of the low feedback voltage. What is causing this feedback voltage to be so low and how can i fix this?

My goal with this buck converter is to have a stable 5.5V out and be able to draw a maximum of 3A from it at this voltage.

Any help would be greatly appreciated.

edit:

I've discovered that the spice model provided on TIs website is setup for the fixed 3.3v version of this IC. It means that the internal feedback resistors are incorrectly defined. I tried changing the values for the internal R1 and R2 feedback resistors to match those for the adjustable version (found on page 10 of the datasheet) however I still get the same error. There may be more incorrect definitions.


texts:
I am trying to use adum1200 isolator.
I want to know what they mean by 2/0 directionality


texts:
I am working on a project which require to activate a 24V Rated relay using a 3.3V rated IO. To provide adequate isolation I have added a Opto-isolater stage.

In order to increase the current output capacity I have added a NPN Transistor Switch and controlling it using the Opto-Isolator output.

The main issue I have encountered in past (Using only Opto-isolator to drive relay) is the output is accidentally connected to the 120V AC supply which potentially blow up the Opto-isolator.

I have following questions related to the over-voltage protection concept:

The transistor's reverse breakdown voltage (VEBO) is 6V, even if I use a over-voltage protection diode the Emitter will observer at least -25V upon AC application (if Zener is 25V rated), In this case how can I ensure that the transistor switch will tolerate the reverse bias (By adding addition components?)
Is there any other method can be used to provide the isolation with 120V AC protection?

Here is the circuit-

Transistor Datasheet:https://www.fairchildsemi.com/datasheets/MM/MMBT3904.pdf

Option A and B can be used to activate the Transistor switch

Relay Specification:

The relay I am using is Omron -G7SA-2A2B, rated 24V, Coil resistance 1600 ohm, Min vol = 75% of rated 24V, Max Vol =110% of rated 24V

The circuit is for the failure case when the 24 V/80mA rated output get connected to the 120V supply. In this case the transistor output gets +/- 120V.


texts:
I bought a WiFly shield ( http://www.sparkfun.com/commerce/product_info.php?products_id=9367 ) for my Arduino Mega board and am trying to hook it up.

I tried the wireless talker tutorial which seem to be very popular http://www.sparkfun.com/commerce/tutorial_info.php?tutorials_id=158

I tried running the first sketch, but it doesn't work. It just gives me a Bridge Locked up message. I tried changing the pin associations in the code as discussed in this post http://forum.sparkfun.com/viewtopic.php?f=13&t=22067&p=104343
but again no joy.

I tried the standard WiFly library that sparkfun ship from here ( http://sparkfun.com/Code/wifly/WiFly-20100519-023939.zip )
I extracted the zip files, put them under the libraries directory of the IDE, fired up the IDE, started the example and tried to run it, again no go. I put my credentials in the credentials.h file, changed the pin associations in the Spi.h file (for CS, MOSI, MISO, SCK) as suggested above to 53,51,50,52 respectively. Again, no joy. The terminal window just sits there showing "WiFly Shield Terminal Routine".

What am I doing wrong? Has anyone used the WiFly module by itself or with the Arduino mega board? Do I need to hook up the Mega's 50 - 12 pins to the WiFly shield somehow? There seems to be a similar discussion here with no resolution http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1270926864

PS: I am running this on Windows 7, 64 bit

Any help would be greatly appreciated.


texts: I too want to wire a 3 phase motor to a VFD. And the question has already been asked but

texts:
How to wire 3 phase motor to VFD
http://i.stack.imgur.com/KmuB3.jpg

My Baldor vm3556t 1hp motor shows the same wiring as the photo above and the wires are bundled as shown on the low voltage side.
My Teco FM50 was hooked to this motor in the past but someone took it off to run a handheld router.
Now I want to put it back to where it was but the diagram leaves me with a critical question; which of the three pair go to ground?

Woo Hoo!! You guys are awesome! I confess this is a freshman 101 student asking an advanced question with little understanding of the basics but:
The two machines in my description were dumpster rescues that used to be together. In the meanwhile someone had wired the VFD to a hand router by pulling the cord from the Baldor CLIPPING the red wire, and running green to ground. Must have worked for the hand router. Because your answer gave me the clue I went back to the manual, disassembled the cord, scratched my head, and followed instructions.
It worked!
It even spun in the right direction but that was luck.
I look forward to the day when I can answer a question.


texts: Small footprint constant current source / voltage regulator

texts:
I'm making an edge-lit snowflake out of acrylic. It's lit from the center; the LEDs are mounted straddling a circular (40 mm diameter) PCB.
I'm using 24 white LEDs, and since I don't want to work with huge voltages, my plan is to divide them into four 6-LED circuits, driven by a constant current source from 24 V, 20-30 mA, depending on how the thing will look like when fully it.
My original plan was to use through-hole LM317s, but now that I'm laying out the PCB, I've been tempted to use surface mount parts to keep the front-facing side nice and spotless. So far I've been able to find LM317 in SOIC-8 and SO-223, and it's a bit of a tight fit with those. I'm soldering with an iron so I'd like to keep the design as roomy as possible.
Are there smaller adjustable regulators or constant current designs (e.g. SOT-23) that would fit better?


texts: What is this part? (DIP, 14 PIN, Fairchild Logo, 5036516 -00 8432)

texts:
Found with a bunch of boxes with 74 Series Logic Chips.  Can't find a datasheet anywhere.

Text:

5036516

-00

8432

Indonesia


texts: Special Function Registers value expressed as Hexadecimal & Bit shift

texts:
I was wondering if someone could help me solve one problem, because I am very new to this and I was given the code of a former programmer to work with.
I'm trying to figure out the value of 0x8008 & ~(1<<15).
Maybe someone could also tell me what's the purpose of writing a value in this manner?

Code:

   // STSEL 1; IREN disabled; PDSEL 8N; UARTEN enabled; RTSMD disabled; USIDL disabled; WAKE disabled; ABAUD disabled; LPBACK disabled; BRGH enabled; URXINV disabled; UEN TX_RX;

   U1MODE = (0x8008 & ~(1<<15));  // disabling UARTEN bit

From what I understand:

0x8008 = 1000000000001000

1<<15 = 1000000000000000

~(1<<15) = 0111111111111111

so:
1000000000001000 & 0111111111111111 = 00000000000001000

This answer bugs me, because judging by it - UART is disabled, which is definitely not true.

datasheet: http://ww1.microchip.com/downloads/en/DeviceDoc/70000582e.pdf

I did some digging in the code and I found this line:

 U1MODEbits.UARTEN = 1;

Still don't get what's the purpose of disabling the UART first and then enabling it.


texts: Parallel capacitors with initial voltage

texts:
Suppose there is a circuit with two capacitors connected in parallel with a current source \$i_L\$, each capacitor with initial voltage \$v_i\$ and capacitance \$C\$. Is it correct to say voltage with respect to time \$v(t) = 2v_i + \frac{i_L}{2C}\$?

I got this by saying that \$v(t) = V_i + v_{current}\$, and \$v_{current} = \frac{i_L(t)}{C_t}\$.


texts: Can a CPLD be reprogrammed just like a Microcontroller?

texts:
Given that microcontrollers can be reprogrammed multiple times, does this apply to CPLDs as well? In particular, I am interested in Xilinx's CoolRunner-II. Until now, I was positive about the re-programability, but after looking at the specs at one of the stores, I got confused:

So, does it mean that I can program it only once?


texts: Making an omni anntena for PA+LNA+Antenna

texts:
I have several NRF24L01 RF modules that I would like to use to transmit data from a car to a ground station.

When testing the modules, I have found that the data transmission is only successful when the two antennas are facing each other. So after some research, I have learned that there are two different types of antenna: omni and directional.

I am wondering if it is possible to take the signal from the module antenna and resend it using a separate omni antenna, so that the data can be received at the ground station without relying on the antennas facing each other. Is this setup feasible?

Sorry if I am asking something that may be foolish but I don't have a lot of experience in this field. Thanks for answering and if you have any other ideas I would be happy to hear them.


texts:
I need to be able to power a device that accepts 15V with a USB-C cable.
The issue is not physical but the wiring.
I know USB-C can deliver 15V. But how ?
Do I simply need to wire the two wires to some specific pins on the usb cable ? Or do I need to add something ?

Thanks


texts:
Recently I had a problem with noises in my led driver. I realized that my PCB design was terrible, so I redesigned whole PCB following common rules.

Could you take a look and check if my new design is ok?

Thanks for all answers.


texts: Relay protection when proper TVS at load cannot be implemented

texts:
I'm currently developing a product which has a simple SPDT relay that can be controlled by an operator. To the end-user, only the common, normally open and normally closed contacts are available. The relay is driven by circuitry in our device, which has a proper flyback diode.

Recently we had a problem with one of our prototype units where a technician connected the relay directly to an inductive load, without any sort of transient voltage suppression, which resulted in our wireless comms getting knocked out due to EMI, and probably also resulted in contact arching.

After making sure the problem was due to inductive spiking, it was quickly solved by connecting a proper flyback diode to the load.

While in this situation we had control over the loads we were connecting, this made me realize that I cannot trust that our end-users will actually install proper transient voltage suppression devices when using our product with inductive loads, no matter the amount of warnings and typical applications schematics that we may offer.

Now, obviously there are many solutions to inductive spiking, but the particular set of situations in which this device must work is making it very tricky to implement TVS:

1) The relay is a general purpose SPDT relay rated for 250VAC/120VAC @ 10A or 30VDC 8A. This means that the TVS circuitry must be able to handle both AC (mains or not) and DC, and currents up to 10A. This makes it impossible to find a PTC fuse, since most will not handle mains voltage, specially not at 10A.

2) The device will be installed in places where it will be impossible to replace anything, and safety is a major concern for us. If the client does not install a fuse and the relay fails shorted (which is rare, but can happen), they will most probably blame us. This also means I cannot use MOVs, gas discharge tubes, or any other TVS device with limited lifetime.

3) Any TVS devices must never fail shorted, and if they do, I must make sure to protect the load against a short like that.

I've tried a simulation of a RC snubber network, but these alone will do nothing with big enough inductive loads. Also, using bigger capacitors means more losses when working with AC. Ideally, 1nF would give enough impedance (above 1Mohm @ 50/60Hz) to make any losses insignificant.

Here are the results of a simulation with a big inductive load. Changing resistor and capacitor values only affects the time that the oscillations take to settle down and not peak voltage, which will surely kill any resistor or capacitors, or arc the contacts.

Back-to-back zeners together with a RC snubber network effectively limit the voltage spike, but since they have to block mains voltage, they'd have to block more than aprox. 350V (mains peak voltage) until they would start conducting, and I fear this is still a high enough peak to kill any wireless comms nearby with EMI.

So, am I completely hopeless in this situation?

Are there other TVS devices / techniques I can use in such a situation? If so, can I guarantee that they will not fail shorted, or at least that I will be able to protect against a shorted TVS device?

Or is just a RC snubber actually a good solution to this problem? If so, why? And how can I select appropriate parts for this?

Please remember that I do not have access to the actual load, and I cannot make any assumptions about how a user might connect the load.


texts:
The Arduino UNO and GPS shield logs the coordinates by the use of the trigger inputs.  The trigger takes +ve 5 to 15v on a pin.  (See Image 1)
It is designed to be used to log, each time a solenoid valve(s) operates in the circuit in image 2.
How do i safely integrate this trigger/logging circuit into the circuit in Image 2 and protect the logging circuit?  Which components do i require and at what points should i install them?
Thank you


texts: Looking for some solar panels to go with this project

texts:
I've been looking around for some solar panels for a little homemade solar phone charger project. I recently found a portable phone charger project from a student at Cal Poly which I'm hoping I can add solar panels too instead of using batteries. I'm wondering two things. First, can I replace the batteries in this project with solar panels? Second, if so, what panels should I use?

I've been looking on Ebay and the Google and there are a lot of options. I'm hoping someone might be able to give me a more direct answer.


texts: How to make a constant current-pulse current charger for lithium ion?

texts:
I've been doing some research about battery charging system with the CC-PC-CV (constant current-pulse current-constant voltage) method. However I have some questions and need some guidelines for proper implementation.
Basically I am trying to find out if:

Is it possible to make the charging system with DC-DC buck converter?
If possible how to change from CC mode with output 1C-rate to pulse current 4C-rate.

If you don't mind, can you explain with PSIM schematics?


texts: Can I charge a lead acid battery with a lithium ion battery?

texts:
I am asking specifically about automotive 12V lead acid batteries but I suppose the principles may be universal.

If I were to connect a fully charged 15V Li-ion battery to a discharged 12V lead acid battery (at around 11.5V), would the Li-ion battery charge the lead acid battery?

My theory is that since the potential at the battery terminals is about 14.7V when the car's alternator is running, attaching a 15V battery will have the same effect. Is this correct or will it result in some horrible acid flinging hydrogen explosion?


texts: How can current flow in dipole antennas when there is no potential across them?

texts:
I have been trying to understand antennas and I've been trying to analyze how the transmitter's energy is transferred. It is clear that for current to flow there must exist a potential difference across two points. The accelerated charge (current) that is produced will then radiate EM waves. In the case of a dipole antenna as depicted here at Wikipedia there is an AC source but it is only attached to the ends of the wires with no electrical connection between them, and the animation shows the ac current when there should not be any since no potential exists.

If I continue with this logic, I become confused when I consider the scenario where there is a current carrying wire and I stood on a plastic stool and touched the wire does it mean that current will flow to me as well even though I am at the same potential as the wire?

The mechanical analogy I have in mind is that of a bowling ball that has been laid on a shelf where it rests with some potential energy, and in order to convert this energy into kinetic energy the ball would need to be dropped. This symbolizes the potential difference that the wires must have in order to allow charge to flow (ball to be dropped) and thus transmit energy.


texts:
I need to get 4 outputs from a 5V digital output as follows: 2 of them inverted and 2 of them non-inverted. I thought about using a 74 HCT 04 hex inverter in the following configuration:

simulate this circuit – Schematic created using CircuitLab

The 0 represents the output of an Arduino Digital GPIO pin and the output of the four inverters the outputs I'm going to use. Is this a valid configuration or am I going to run into problems whilst doing this? I am concerned because each inverter/buffer drives both another NOT gate and the actual output. The outputs I need to drive have a maximum low-level input current of -10 microA, and the the high-level input current 30-100 microA.


texts:
I am trying to use an Arduino to intercept and send out modified wheel speed readings on a 2014 Subaru Forester. The problem I am running into is the wheel speed signal.

From what I can tell the sensor is a Hall effect sensor. There are two wires going to it (12v and signal) All 4 wheel speed sensors plug into the chassis harness and end in the Vehicle Dynamics Control (VDC) unit. There are no teeth on the wheel the sensor is reading from so I am assuming it must be a magnetic encoder wheel.

With everything plugged in and the vehicle either running or just in the on position, I hooked my oscilloscope to the signal wire for the front right wheel and spun the wheel by hand. I was able to see a square wave with a period that varied based on the speed of the wheel. The issue is, the max and min voltages on the square wave only differ by ~160mV.

This is too low for the Arduino to read and seems strangely low for an automobile application. The only thing that I can think is that the comparator that is normally housed in the sensor its self is housed in the VDC unit.

I then disconnected the wheel speed sensor from the chassis harness to try and weed out electrical interference issues caused by the car running. With the sensor still installed in the wheel hub, I used my Power Probe III to provide 12 volts to the sensor and hooked the o-scope to the signal wire. The reading I got was just straight 12v with no fluctuation when I spun the wheel.

Basically I am a bit confused and lost. Do I just assume the 160mV square wave is correct and build a conditioning circuit with a comparator? or is there something else I am doing wrong?

Here is a link to the wiring diagrams I am working with in case that helps.

Any help will be much appreciated.

******Update*******
I got the MAX9921 chips and holy cow those are small. Luckily I was able to find some surface mount breakout boards for the form factor.

Using a bread board I made this circuit:

My only problem is when ordering parts I didnt notice that the capacitors on the input wires were .01uF caps and instead just ordered .1uf caps. I hooked it up with the .1uF caps and was able to get the output to trigger by touching the input to ground but when it is hooked to the wheel speed sensor and the wheel is spinning it wont trigger. I am guessing that the over sized cap is messing with the signal. Can anyone confirm what will happen to the square wave if a cap is added to it? I am going to pick up the correct cap and try it out.


texts: microstrip low pass filter design issues with sonnet

texts:
I am trying to replicate the microstrip low-pass filter in SonnetLite from the book by Jia-Sheng Hong - Microstrip Filters for RF Microwave Applications, 2nd Edition (Wiley Series in Microwave and Optical Engineering)   (2011, Wiley)

However, the S12 graph shows that it is not a low pass filter at all. Could anyone advise why ?

I have attached the SonnetLite design file here.

box resonance warning analysis logs

Run 1:  Sat Jun 22 00:27:07 2019.  SL291418.107194.
    Em version 15.53-Lite (32-bit Windows) on DESKTOP-DG59KC2 local.

Project:  C:\Users\kevin\Documents\sonnet\15.53-Lite\three-pole microstrip lowpass filter using open-circuited stubs\three-pole microstrip lowpass filter using open-circuited stubs.son.

Frequency:  0.001 GHZ

  Sonnet Warning EG2680:
  Circuit has potential box resonances.
  Circuit: primary structure
  The estimated box resonance frequencies are listed below.
  The calculations assume lossless materials, with a box filled with
  only the specified dielectric stackup materials.

  4.140 GHZ  TE Mode 1,0,1
  4.673 GHZ  TE Mode 1,0,2

  Only lowest order modes considered.

  See the chapter on package resonances in the Sonnet User's Guide.
  Date: Sat Jun 22 00:27:07 2019

  Sonnet Warning EG2680:
  Circuit has potential box resonances.
  Circuit: left box wall SOC magnetic wall standard
  The estimated box resonance frequencies are listed below.
  The calculations assume lossless materials, with a box filled with
  only the specified dielectric stackup materials.

  4.167 GHZ  TE Mode 0,1,1
  4.700 GHZ  TE Mode 0,1,2

  Only lowest order modes considered.

  See the chapter on package resonances in the Sonnet User's Guide.
  Date: Sat Jun 22 00:27:07 2019

Post-Analysis:
  Errors detected: 0    Warnings detected: 2.

Analysis completed Sat Jun 22 00:27:10 2019.


texts: Are input filters always required for switching power supplies?

texts:
This is a follow up to the questions here and here

I recently designed a PCB that contained a buck regulator (LM2576 5V). You can see the PCB layout in this question. After converting the input 12VDC to 5V, two linear regulators then bring that down to 3.3V (for a micro) and 4.1V (for a SIM800C GSM modem).

When the board is connected to other boards in the system (which contains a speaker), a loud GSM buzz is heard when the modem transmits. Bringing a mobile phone close to the speaker board also caused the buzz but it was much much quieter, which implied to me that the noise was being conducted through the cables, rather than being radiated.

In order to understand the noise, I did a simple conducted emissions test (using a spectrum analyzer and a Tekbox LISN). I captured the conducted emissions from 150kHz to 30Mhz (RBW 9kHz, step 5.4kHz dwell time 50ms) in a variety of different firmware configurations to try and understand where the problem originates from. Here are the scans:

Scan 1 with GSM modem transmitting as frequently as possible (roughly once every 750ms)

The large spikes spread throughout the spectrum are usually ~300kHz apart (closer peaks are about 90kHz apart - not sure how to interpret that. Could be multiples of the 52kHz switching frequency.)

Scan 2 with GSM modem turned off

So, looking at this, clearly turning the GSM modem off has reduced the conducted noise by a lot.

However, I then decided to solder a 4.7R power resistor to the output of the 4.1V regulator to simulate the GSM modem load continuously.

Scan 3 with GSM modem off and 4.7R load on 4.1V regulator

The overall noise jumps back up again to similar levels to the spikes that were present in the first trace with the GSM modem on. If I were to join the peaks of the spikes on Scan 1, I'd end up with a trace similar to Scan 3. This made me think that the problem may actually be the SMPS generating more noise at higher loads rather than it be noise caused by the GSM signal itself, and that the GSM noise was actually due to the modem demanding sudden bursts of power from the SMPS which was then working harder to provide that and generating lots of switching noise.

If this is true, it surprises me for the following reasons:

I tried to follow the recommended layout for the LM2576 as specified in the datasheet to minimize switching noise.
The 4.1V regulator has both large and small value capacitors on the
input and output, which I would have thought should be sufficient to
smooth out the current requirements of the GSM modem.
The GSM modem has 100uF tantalum, 1uF, 33pF and 10pF caps positioned close to the power supply pins, as recommended in the
datasheet, which should handle the high current requirements of the
modem.
Although there are layout issues with the board (especially underneath the micro in the center), the power supply traces seem OK
in terms of current loops (see the layout here).

The LM2576 datasheet makes no mention of any sort of input filter before the SMPS (only output filters).

So the questions I'm asking are the following:

Is my analysis of the source of this EMC problem correct? (SMPS generating input noise due to high load).
Are input filters always necessary in order to reduce SMPS switching noise, or can this problem be solved just by improving the PCB layout? If so, where are the layout problems that are causing this issue?


texts:
I am creating a guitar pedal. I want to mix together 3 sources:

Coming from electric guitar (or through another guitar pedal)
Coming from filtered PWM (for the purpose of generating sinusoidal signal)
Coming from audio dac chip headphones output

Generally the guitar input is usually around 500k - 1Megaohm . The other sources may not be so critical. DAC headphones output can drive as low as 16Ohms headphones and the PWM is coming through optocoupler with transistor output.

As all of you engineers know the best way is to optimize your circuits. So I am trying to spend as little as possible on the components and also save the space by not adding new components. But if this is still needed I will do so.

So far my candidates for mixing circuits are these.
A circuit with just 1 op amp - active inverting mixing circuit. To reach high input impedance there are 2.2MOhm input and feedback resistors. Is that OK?
My gut says me that this could be a source of problems. Am I right?
http://www.seekic.com/circuit_diagram/Audio_Circuit/4_microphones_mixer_circuit_with_TL081.html

The other candidate is the one where all the inputs are buffered separately
https://i.pinimg.com/originals/7a/46/9c/7a469c43499af2428a6fd79cbec51ac2.jpg

Actually the third option would be something in the middle. I could just create an input buffer for only the guitar input and then use the inverting active mixing circuit with one op-amp.

So could somebody give some advice about this topic?
What should I keep in mind designing this circuit?
How to choose the right solution?


texts: I am new to PIC microcontroller programming.  I tried to program PIC12F629. I simulate my program in Proteus, and it works fine. But when I tried to program it using PICKIT2, the band gap calibration value changes from 1000 to 0000. I have read the data sheet where it says the OSCCAL values and band gap calibration values should not change. How do I reset the band gap values, or get the PICKIT2 to not clobber them?


texts: Wiring a 6 pin On/Off/On toggle switch (DC) 2 Pole

texts:
I bought a 2 pole 6 pin On/Off/On toggle switch that's for DC power, (25A 12V)
see here:
Toggle Switch

The only issue is that I have no idea how to wire it, as mentioned, it has labels on the back, 1, 2, 3, 4, 5, 6 with no indication of what's positive and negative.

What I would like to do with it, is connect two power sources, and a main device, is that even possible with this switch?

Basically, I have a Monitor that takes 12V DC, and I want to use, USB-C (Which is converted to 12V through a buck converter) and a DC power adapter, but the switch is used to switch between them, so flicking to the first On will use USB-C, and then the second On will use the adapter, again, is it even possible to do that with this switch? If it is, could anyone help me with wiring? Because there isn't any schematics or diagrams that explain how this switch is wired.

Thanks in advance.


texts: How to drop the external source output voltage using Arduino

texts:
I would like to connect the 10VDC of my LED driver to Arduino so I can dim the lights.

I've found out that the lower the output voltage, the more I am able to dim the LED lights.

My question is, how can i control/lower the output voltage of external 10Vdc using arduino.

Note: I don't like to use photo-resistor because I wanted to manually control the dim light by entering some value on arduino TX/RX.

UPDATE: The 10Vdc were specially provided by the LED Driver for the purpose of dimming the LED.


texts: How can I decide relay on-off periods depending on the PID output

texts:
In my PID project, I am using discrete time PID formula as follows.

u(k)=u(k-1)+Kc * [(e(k) – e(k-1)) + (Ts*e(k))/Ti + Td/Ts * (e(k) – 2*e(k-1) + e(k-2))

As you know PID output increases over time if the actual point goes above the set point. I am using relays to give input to the system. Because of the thermal inertia, output increases even I turn off the relays. The main quesiton in my mind is, how can I determine the on-off periods of relays depending on the PID output? For example, in the second on period of relay, when should i turn off the relay to avoid overshoot?


texts:
Is there a way to determine the orientation of the LED in the image below?
The blue squares in the corners seem like they are denoting the orientation however it's not marked in the datasheet.

This particular LED is the Panasonic LNJ247W82RA.  It's size is 0402.  Is this a common way to mark 0402 LEDs and are there other common markings for the top side of 0402 LEDs?


texts: Why does small cache memory take less time to index

texts:
I was going though these slides (page 3) which are adapted from Computer Architecture: A Quantitative Approach, 4th Edition by Patterson and Hennessey.

The topic is about Advanced Cache Optimizations. It suggests that we can get fast hit times via small and simple caches and the reason it gives is "smaller memory takes less time to index"

I could not understand why? I mean if tags are compared in parallel. Why should the size matter?


texts:
A t flip flop needs a clock signal to operate correctly.
That clock signal will be provided by a LC tank circuit.
Can I just connect the CLK pin to one of the nodes of the LC circuit or is it more complicated than that?

Do I need to ground the LC circuit?


texts:
I'm calculating some load flow analyses so I need the parameters of the transformers. I have been able to find most of them but I have some doubts about their equivalences and relations.

What is the relation between copper and iron losses and on-load, no-load losses?
I also need the relative short-circuit voltage and I have the short-circuit impedance (%) and no load current (%). How can I calculate then the relative short-circuit voltage (V)?

PS: I also have the rated power and HV and LV values.


texts: I would like to know if there is something like AND gate logic for two AC power sources i.e, if two of the sources are on the light will turn on else it will stay off .Thanks


texts: How can I calculate the dead time to prevent shoot-through?

texts:
From Figure 1 is evident that to get the dead time I must define the values for RC. E.g my resistor is 220 ohms and capacitor is 0.1uF this gives me 22us at 1-time constant, however, when I measure this on my Pico scope this shows roughly 6.5us at the point of the dead time. Could some one help me understand where the 6.5uS comes from when using these values please ?

Image source: How is dead time in a half bridge implemented.


texts:
I've the following filter circuit:

simulate this circuit – Schematic created using CircuitLab

The transfer function can be written as follows (I think):

$$\frac{\frac{1}{\text{sC}}}{\frac{1}{\text{sC}}+\frac{1}{\frac{1}{\frac{1}{\text{sC}}+\text{sL}+\text{R}}+\frac{1}{\frac{1}{\text{sC}}}}+\text{R}}$$

  question: is my equation right?


texts:
I'd only like to know if the following is doable with minimum effort: I'd like to create a custom 7x7 two-color LED matrix, where each row of LEDs can be dimmed separately and set to a certain color. The whole thing would ideally be controlled by an Arduino or some other microcontroller.

I have extensive programming knowledge, however my electronics knowledge is limited; I can interpret simple circuit diagrams, but that's about it.

How hard would the above turn out to be for someone like me and is that whole thing possible at all?


texts:
I have been instructed to use KVL/KCL on the following circuit to try and figure out an equation for V+:

I've also been given a hint, saying that I can use the Vout from the previous time step of my simulation to solve for their values in the current step:

$$V^+ = F(V_{out}(n-1))$$

$$V_{out}(n) = A_v(V^+-V^-)$$

Can I be pushed in the right direction? I know I can represent V– as Vc(n-1), but I'm not sure how to go about V+.

edit: There are 2 answers I have come up with...

1) $$\frac{R_1}{R_1+R_2} V_{out}(n-1)$$

2) $$\frac{V_{out}(n-1)}{A_v}$$

edit 2: some values that may be of importance -

Vin = 0; % Voltage to the noninverting terminal

Vref = 0; % Voltage of the common port

Vcc = 5; % Positive Voltage Rail

Vee = -5; % Negative Voltage Rail

Av = 1e6; % Operational Amplifier Open-Loop Gain

R_1 = 100000; % Input Resistance, Ohms

R_2 = 100000; % Positive Feedback Resistance, Ohms

R = 7583.3; % Negative Feedback Resistance, Ohms (tuned for 60Hz)

C = 1E-6; % Capacitor Capacitance, Farads


texts: PIC programmer problems reading and writing program configuration memory

texts:
I was making a programmer for pic16f877a using arduino with the help of the programming specification document as I can't find any good one around here at the time.
I was able to write code in the user program memory and read it back in low voltage programming mode (and I'm very confident this process is successful) but I didn't write anything in the configuration memory.

The project didn't work (a simple blinking LED), so i made some research and found that it might be the 2 bits in the configuration word that define the type of the clock (supposedly RC oscillator by default) and it must be changed to another type. so i tried accessing and editing the configuration word using the commands given in the document but I always only read zeros whatever I do, even if I make a chip erase command at the configuration memory.

I know that this is very hard to answer as the programming protocol is specific to the device but I will really appreciate it if someone could give me a hint, and if there is any missing information just tell me in a comment and I will edit the question to add them.

Here is my code for accessing and reading the configuration word:

#define MCLR 8
#define PGM 9
#define DATA 10
#define CLK 11

  /*
    MCLR -> MCLR
    PGM -> RB3
    data -> RB7
    clk -> RB6
  */

void setup() {
  pinMode(MCLR, OUTPUT);
  pinMode(PGM, OUTPUT);
  pinMode(DATA, OUTPUT);
  pinMode(CLK, OUTPUT);

  digitalWrite(DATA, LOW);
  digitalWrite(CLK, LOW);
  digitalWrite(PGM, LOW);
  digitalWrite(MCLR, LOW);

  Serial.begin(9600);
  while(Serial.available() == 0);

  // Low voltage programming
  digitalWrite(PGM, HIGH);
  delayMicroseconds(1);
  digitalWrite(MCLR, HIGH);
  delayMicroseconds(10);

  loadConfig();
  for (int i = 0; i < 7; i++)
  {
     increment();
  }
  Serial.print(readData(),DEC);

}

void loop() {
  // no need

}

void writeBit(int a)
{
  digitalWrite(DATA, a);
  digitalWrite(CLK, HIGH);
  delayMicroseconds(1);
  digitalWrite(CLK, LOW);
  delayMicroseconds(1);
  digitalWrite(DATA, LOW);
}

byte readBit()
{
  byte _bit;
  digitalWrite(CLK, HIGH);
  delayMicroseconds(1);
  _bit = digitalRead(DATA);
  digitalWrite(CLK, LOW);
  delayMicroseconds(1);
  return _bit;
}

void sendCommand(char command)
{
  for (int i = 1; i <= 0b100000; i *= 2)
  {
    writeBit((command & i) >= 1);
  }
}
uint16_t readData()
{
    sendCommand(0b000100);
    delayMicroseconds(2);
    uint16_t value = 0;
    pinMode(DATA, INPUT);
    readBit();
    for(int i = 0; i < 14; i++)
    {
        value = (value<<1) | readBit();
    }
    readBit();
    pinMode(DATA, OUTPUT);
    return value;
}

void loadConfig()
{
    sendCommand(0b000000);
    delay(2);
}

void increment()
{
   sendCommand(0b000110);
   delayMicroseconds(2);
}

In short I am driving the MCU into low voltage programming mode, which appears to be working, the sending a command to move the program counter to the configuration memory, then incrementing the program counter till it reaches the configuration word address 2007h, then reading the word at this address.

There is another part for writing the code but I didn't add it here.

All of this is described in the programming document here


texts:
I'm an electronics newbie and I need some help/advice with a project.

So basically I need to make a sort of programmable power supply module (or at least that's what I think I gotta do). I got a DC Power Supply that outputs a voltage of 48V, and a maximum current of 20A, and I'm using it to charge a battery that can take up to 50.4V and 33A.
The problem with this power supply is that it doesn't limit the current when connected to a load that can take more than 20A, meaning it can easily surpass that maximum current value and "blow up" (don't know the term in english) the fuses of the power source.

So, I need to make a circuit that takes in the 48V from the power supply, and outputs those same 48V, but with a limited current, to a maximum of 20A. I also need the limit of the current to be regulated, using a potentiometer, and also some displays with the output voltage and current.

What I'm having trouble with is what should I use to limit the current. So far I've looked into simple current limiters and 'constant' current sources using BJTs or MOS-FETs, but I don't think they would work for this case.

Thank you for reading. Do you have any suggestions? Let me know if you need some more information.

EDIT: What I'm struggling with is just the part related to limiting the current. The displays and stuff isn't an issue. So far the type of solutions I've been looking into is really simple stuff. The most simple one is a constant current source using 2 MOS-FETs.

Someone gave me an explanation as to why this wouldn't work, I had to connect the positive terminal of the battery to VDD and the negative terminal to Vo, meaning the voltage wouldn't be set by the power supply, and the current would vary substantially. That added to the fact the the power supplied would be almost 1kW, makes this solution not viable.

Another one is using is some BJT's, to make what is called an "active current source". I've been told this wouldn't work, but didn't really get an explanation as to why.

Can someone explain why this last one wouldn't work?


texts:
I've come across a circuit I'm not too familiar with:

(Goggle Drive version)

How do I tune R1, R2, R3, and C1 to adjust frequency and duty cycle?

I get the general idea of how it works, but I've asked 4 engineers that I work with already, and the only answer I get is "That's an old school approach, ask the other guy". I'd like a better understanding of how this circuit works - Any help would be appreciated.


texts: How is it that this transistor drives the line such that we get a RESET event?

texts:
I am a bit confused on how this schematic works. It looks as if when we do not have any data coming in (i.e. 0V constant) from pin 3 on the DB-9 then the transistor will be off and the RESET will be pulled high as a consequence.

Now, say that the line 3 from the DB-9 goes HIGH, what happens then? Assuming the supply voltage from the connector is 5V, you can solve for the voltage at the base of the transistor, where you get ~2.57V.

Now that the transistor is on, how is the RESET driven low? Isn't it that the collector of a transistor is reverse biased in saturation mode? With that, we can approximate the collector voltage (and consequentially the RESET pin voltage) to be (2.57+0.7)V = 3.27V.

What is the threshold voltage for a RESET event generally?

Also, what are the purposes of each of the diodes in this schematic? Why is it needed to have a diode inline with the resistors off pin 3? Why are there diodes on pins 7 and 4?


texts: Why does an Ohmic contact contain non rectifying junction?

texts: I would like to know a simple explanation for the term 'Ohmic Contact'.I looked in wikipedia but I couldn't get what actually it means.I couldn't even get what do you mean by non rectifying junction.Could anyone help me.


texts:
In order to understand a tank circuit , I need to understand how inductors behave under differential voltage(discharging capacitor).I know inductors in AC behave like resistors but I don't know how exactly.
How does an inductor behave under the pressence of a differential voltage?


texts:
I'd like to program a LIS331EB which is an ST product with an integrated cortex-M0 core. ST says it can be programmed with ST-link even though it is neither an STM32 nor STM8. The lis331eb's core and SWDIO- SWCLK pins run from 1.8V.

When I'd like to program my device I can see on the oscilloscope that the SWDIO and SWCLK io levels are 3V, only the reset line got the core's 1.8V IO level.

Do you think it is OK? I did not find anywhere that the SWDIO/SWCLK pins would be 3V tolerant, so it seems like a problem to me...

(I use ST-link/V2 which should be able to program down to 1.65V target voltage.)


texts: How to determine proper capacitors to replace a battery for an Apple Magic Trackpad 2?

texts:
I have several Apple Magic Trackpad 2 devices and am finding that the batteries routinely go bad on these.  They swell and deform the trackpad such that it doesn't stay flat with the desk / tray surface and thus out of fear of fire, etc. I removed the battery from two of these that were bulging well beyond capacity.
Upon removing these batteries I found that with the devices plugged in they do still operate, BUT the magnetic impulse coil no longer functions to provide tactile (haptic) feedback.  It clearly needs the battery to act as a capacitor for a large enough electrical discharge to trigger the magnet for clicks / vibrations since the USB amperage is likely simply not powerful enough to provide this.
I prefer to operate these devices without batteries after this experience and basically losing hundreds of dollars since they are apparently out of warranty.
At this point I'd like to figure out how to spec and attach proper capacitors to these Trackpads in order to facilitate the haptic feedback engine's triggering.
Any thoughts on how would I go about ascertaining this?


texts:
I am a little confused on how to read the ratios of a transformer

Suppose there is a ratio of 1:6, is this read as the following?
Number of turns on Primary: Number of turns on Secondary?

so suppose a question asked that there is a voltage of 20 voltages rms and it enters a transformer of 1:6, is the Vout rms calculated as the following:

Vs/Vp = Ns/Np,

so Vs= VpNs/ Np

so Vs= (20*6)/1 which yeilds 160 rms?

does the distance and type of gauge wire effect the answer?


texts:
I've got a 2N7000 connected up to an AVR via a 1k resistor on a breadboard.  The top trace shows the AVR pin output, clocking at a couple of kHz.  The lower trace shows the source of the FET.  Clearly the rise time is as expected and the gate voltage is enough to go into saturation while the clock is high.  However, I don't know what's causing the slow falloff when the clock goes low - in principle it should be instantaneous.

The drain is tied to a 2.5V rail and the source is currently going straight into the scope.  If there's no gate voltage, the drain does fall completely to ground as expected so the minimum voltage when the gate is being clocked is due to the FET not having enough time to fall fully rather than anything else, I think.

Looks like there's some weird capacitive effect somewhere, but I'm not sure how to remedy the situation.  I did wonder if it was the probes that was causing it, but it seems unlikely.  The effect happens at low switching speeds too (if I manually plug/unplug the gate).  It's bound to be something daft anyway!

Any help would be appreciated :)

EDIT: Well that was enlightening, I just had it set up in a really weird way.  Should have been VCC->resistor->drain and then source->ground.  Seems to be working now.

But i'm still wondering why it's doing this when I connect it the other way round?


texts: Effect of VIA fence on grounded coplanar waveguie (GCPW)

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I'm working on a RF Frequency board with up to 6GHz signals. To connect components on the board (Mixer, Attenuator, ...) I decided on using GCPW. I designed my GCPW Using AppCad calculator (free software from Broadcom) for 50Ohm on RO4003. You can see the parameter in the below.

Then I see via fence is common in boards and my components reference designs (ex HMC1119) but neither AppCad nor Allegro (my layout software) not mention anything about how should via stitching be done around the transmission line.

Now I'm wondering how via snitching change the characteristic impedance and how can I calculate for that? Do I need a simulation in 3D simulator software?

Note1: I already found that Via fence should be around lambda/20 from each other nevertheless how far should via fence be from center of transmission line and how this would affect the RF performance?

Note2: Unfortunately my English is poor so please feel free to edit the post and fix my grammar mistakes. Thanks


texts: I'm routing USB tracks, which are 90R differential impedance from a USB hub to a downstream device, but the D+ and D- pads downstream are crossed over, and the device has an exposed pad, so I can't route behind.  Is there a better way of doing this than my solution (see image) to use vias right at the end of the routing for the smallest distance possible?


texts: Use AD5933 evaluation board for impedance calculation 1Khz-100kHz

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I recently got the AD5933EBZ evaluation board. After taking a look at the user guide, the AN1252 application note and the datasheet of AD5933 itself, I am trying to measure the capacitance across a capacitor that I have made. I'm using a feedback resistor (RFB)  = 714kOhm and a R(calibration) = 1.4MOhm. I have made a capacitor by sticking 2 copper plates to the back of a teflon backplate and then adjusted them such that the copper plates are 9cmx9cm and 40 mm apart. So, by calculation, it should give a capacitance of 1.79pF ==> Which should give me an impedance of 1.6MOhm at 30kHz.

However, when I check the value obtained, it shows 1.2MOhm ==> Which is nearly 4.2pF. I need to get an accurate value of capacitance since later on I will "disturb" the dielectric in between the 2 plates and observe the change of permittivity.


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I want to prove that demultiplexer is universal gate.
Can we build any logic gates using demultiplexer?
Can we build AND, NOT, OR gate?


texts: What benefit are opto-couplers for relay switching providing, if both sides share the same ground?

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I wanted to connect some relays to my Raspberry Pi (for 12V, not 230V) and I found the waveshare RPi Relay Board, which has the following schematic:

I like that they spend some thoughts on filtering the 5V supply, but what is the point of the opto-couplers? According to the schematic it appears like they won't provide any isolation.


texts: Ignoring nodes/wires when combining resistors to find equivalent resistance

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Is the 2nd step in the solution sheet wrong?
I don't know how they can just ignore the node where the 9 ohm resistor and the 12 ohm resistor were located. Wouldn't current be branched/divided when it flows from either the a or the b terminal through both the 18 and 9 ohm; and 12 and 6 ohm resistors, thus making the 2nd picture not a series circuit?


texts: Help choosing a transistor to drive an LED strip from a Raspberry Pi

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I'm sure this is a very simple question, but as a (near) complete beginner in electronics I would really appreciate a little help in choosing a transistor to switch a 5v LED strip from a 3V RPi GPIO pin.

The background is that the LED strip (20 x 5050 LEDs) provides illumination within a nestbox that contains an RPi and a camera, and I need to switch these lights on and off over a day/night cycle, and I may also run the lights at a lower brightness using PWM.

I have measured the current draw of the section of LED strip that I intend to use in this project at ~260mA (5Vdc), which will be powered by the RPi 5v rail. My understanding is that this should be OK with the 2A power supply I am using.

I can, apparently, run up to 16mA from the 3v GPIO pin I intend to use for switching the LED strip.

Now my question, which is, in a broader sense, how does one go about choosing the ideal transistor? I've spent much of the evening browsing parts lists and there seem to be plenty that would do the job - e.g. something like the MPSW55, with Ic of 500mA continuous and a current gain of 50 - 100 x. There seem to be many, many transistors that "fit the bill", but the data sheets also contain many values which I am unsure about. Are there any other values that I need to look for when choosing a transistor for a project, or can I safely assume that if my headline figures are met (and voltage ratings etc are high enough - which they all are for my needs), that the transistor will work?

Further to the choice of resistor, I have also tried to calculate the value of the resistor that I will need between the 3V pin and the base. Based on a 3V output, 0.7V drop across the transistor and, say, 6mA target (50x gain for 300mA), this gives an ideal value of 383 Ohms. Does this sound correct?

Thanks for reading!


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I have ordered a PCB for my circuit which includes transistor BC548 (Q1), SK100 (Q2) and a Zener diode (D2), but when I got the PCB it has no holes for those three components. Then I searched for SMD type equivalent of those, but their Pins are too distant as compared to my PCB.

So now, should I drill the holes or should I use SMD equivalent? And can somebody suggest the SMD equivalent for these three components according to my PCB image (attached)


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I want to Construct a priority encoder which implements the encoding of 0,3,1,2
with descending priority (i.e. 0 has the highest priority and 2 has the
lowest.
but i am confused about my KMAP I am getting same Equation for both Y_1 and Y_2 . Moreover i am getting I_0 term common in both equation .