texts: Why aren't SR Motors used in all the heavy load or heavy duty applications ?

texts: Most of the machines with such applications require less maintenance due to SR motors, while these are expensive, but aren't they more reliable and better than the other kinds of motors ? So why aren't they prefered over other kinds of motors for such applications  ?


texts: Which is more efficient over 300 to 500 miles high voltage AC or high voltage DC?

texts:
BEFORE you jump to answer or flag as duplicate read please read this first!  I always assumed like yourself that AC would be more efficient and in part that is what Tesla and Edison fought over to reconcile and AC won and the rest is history....enter. "Scientific American" page 20 June 2017. Article titled " Electric Renaissance" by Annie Sneed.  says

" Technology for power transmission advanced in the 1970's, allowing direct current to return as a viable option-and for lines more than 300 to 500 miles long, DC out competes AC.After a certain distance , AC systems become more costly to build than DC and have larger power losses along the line because of issues such as higher resistance. " Using DC lines is a much better solution for moving power from big, remote wind or solar farms",says Gregory Reed, director of the University of Pittsburgh's Center for Energy and Energy GRID Institute...."

I always thought DC sources were converted to alternating current for efficiency sake not to just accommodate the AC infrastructure that is all ready in place.  Obviously you have to step down the AC before it is allowed to get in side the house but isn't the reason DC was never used to begin with was because of the  resistance in DC power transmission and that the lines would have to be as thick as a telephone pole not to mention you need a power source at every corner. Can some one clear my obvious confusion.  Thank you again!


texts: Multimeter shows OL or 0.00 or 1.00. What's wrong?

texts:
I've got a UNI-T UT33D multimeter that's not working like I want it to, and I'm not sure how to find out what's wrong or if it's salvageable or not. The unit is new, but may possibly have had its battery inserted backwards at some point.

I've tried it with two three different batteries, two of which seem healthy when measured by another multimeter, and the third one being new from the store.

Resistance readings I can get are as follows:

Setting | open | shorted
200M | OL. | OL.
20M | -0.00 | 1.00 -- battery indication for both
200k | -00.0 | 10.0 -- batt. ind. for both
20k | -0.00 | 1.00 -- batt. ind. for both
2000 | -000 | OL -- batt. ind. for both
200 | OL. | OL. and batt. ind.

There have been times when the shorted readings have been 243, 24.3 and 2.43 instead.

Voltage readings for 20V and 200V DC on a healthy 9V battery are OL and battery indicator.

All of the above readings are taken with black lead in COM and red lead in the fused connection.

I have checked the following:

Battery appears healthy
Battery is correctly inserted
Test leads are not broken
Fuses are okay
Connection from test leads to inside fuses is okay


texts: How is voltage exactly created in a citcuit?

texts: I just began studying electricity and concept of voltage and this particular concept of voltage is so confusing. I have searched answer for this question everywhere and every answers stops short at saying that voltage is created by chemicals in a battery and nothing beyond this. You don't need to go deep into explaining chemistry but I just need an idea of how electric potential is created in batter and how it "forces" electrons in circuit to move. Like how is charges spearate in first place. If battery is not one to supply electrons in first place, then how come potential difference is created in battery which would then force electrons in wire to flow. If anyone can shine light on this, I really appreciate it.


texts:
In Germany the wifi(5470-5725 MHz-Subband 2) maximum output power is 1000mW.
I would like to buy a Airmax5 which has 200mW(23dbm) output power. In the Airmax5 there is 13dbi built in directional antenna according the documentation the maximum distance is 20km.I would like to replace the directional antenna with 12dbi omnidirectional antenna or a 16dbi sector antenna. Also on the coaxial cable there is minimum 2-3db. I would like to establish a connection within 2-3km.

The 1000mW is the maximum module output power, or with the antenna?
How can I calculate weather do I exceed the maximum output power?
Is it possible to estimate the maximum distance between two wifi antenna?


texts:
I have some confusion about capacitors.

There's mention that at DC T=0, a capacitor should be considered as short circuit.

So how does it work when we use it as a filter capacitor?

Won't it be shorted to ground as the sketch in a flash?


texts: Relation between RTL and Verilog modules

texts: I am taking a digital design course and I didn't get something. RTL design includes datapath and controller, that's ok but what's the relation between these and verilog modules. For example, is controller a module in verilog? Generally, how RTL can be coded in verilog?


texts: Replacing a 5V female barrel connector on USB hub with female USB micro

texts:
Is it possible (and relatively easy) to replace a 5 V power plug (barrel connector) on a USB hub with a standard USB Micro power-only female?  If so, is there anything special (besides hooking up the +5 V and GND connections)?

I have been trying to find some information about it, but I haven't been able to.  I keep reading stuff about using a 200Ω resistor between pins 2 and 3, but that is for making a custom plug (the USB micro male).  Would that also apply to the female?

I'm very much a beginner when it comes to this kind of stuff.  I can handle a soldering iron, but I'm quite new to actual electrical engineering concepts.

Some clarification (based on the comments):

This is to swap out the barrel connector for the power to the USB hub - nothing to do with the actual USB ports that will be linked.
The USB hub is a Belkin F5U404, which makes for a killer little hub for the Raspberry Pi Zero. Problem is the power plug was faulty (if I wiggle it barely it powers off) and quite frankly, when I got half a dozen Pi Zeros, I would like to be able to plug them into any phone charger and not carry around the power cord.
I picked up some USB Micro Female connectors from Adafruit
The standard power supply for the USB Hub is 5 V / 2600 mA - I'm hoping my 2000 or 2500 mA USB plugs will be sufficient.


texts: I read in many websites that transformers can only be used, to step voltage up or down, with AC current (which is why AC is preferred for power transmission since they can transfer huge power in the form of high voltage over thin wires instead of thich ones then they can be stepped down again), but then I started studying car mechanics and I discovered that the ignition coil also acts as a transformer and can step voltage from the 12V battery to ~30kV, but from the DC car battery, so the question here is: Is a transformer only used with AC? And if so, how does the ignition coil step up voltage. And if it can be used with DC too,  so why use AC current in the first place??


texts: Does LED matrix scanning reduce overall brightness?

texts:
Using scanning (or multiplexing) of an LED array, such as below:

Such that only one row is powered ON at any given time, would this cause a reduction in LED brightness?

My rationale is:  In this 4x4 matrix, row 1 will only be turned on 25% of the time.  This seems awfully similar to PWM control, which is also a common method of controlling LED brightness.  In this example, would all the LEDs be operating at 25% of their maximum brightness?


texts: Deliberating shorting PTC to toggle between FBR and HBR

texts:
We're designing a board that needs to interface with a variety of different furnace control boards, some of which have full-bridge rectifiers and some of which have half-bridge rectifiers. Depending on the design of the furnace control board, our PCB should have a matching rectification circuit to prevent damage to either board (we want to prevent this from happening).

We thought of putting a PTC in the mains line and connecting either the HBR or the FBR. Depending on if the PTC blows, then we'll know if we chose the correct rectification. In the case that the PTC does blow, we would toggle a mechanical jumper (something like this) to short different pins of these 3-pin connectors, selecting the other rectification method.

Is this sane??

UPDATE: We rolled this board to manufacturing and, surprisingly, the setup conducts when two devices are hooked up both with FBR, both with FBR, and with one of each, even though latter should, in theory, cause a short across the FBR and blow its fuse.


texts:
Altium is killing me! I am basically doing a semi-volunteer project to learn Altium, my previous workplace used Eagle. I made a library from scratch and compiled it to an integrated library. The library compile without any issues, and all of the symbols are associated with a footprint.

When I want to 'compile' from schematic to PCB, some of the parts complain about not being able to find their PINS. Their is also an error about not being able to add components to a class, I didn't create the class and I am not sure what the purpose of it even is.

When I go to the library for the capacitor, Pin 1 is mapped to pad one on the footprint and Pin2 is mapped to PAD2 on the footprint.

Any Ideas?

I am not sure how to embed the pictures bigger, but if you right click them and choose open picture they are bigger.

Thanks!


texts:
I am trying to understand a concept of Gilbert cell.
I have the next figure.

Quastion1:
If +1V is set up in (3), then in (4) is admitted -1V, and for (5) is -1V, (5) +1V.
The current source is sume up with LO-Input. (1) represent the symmetry between  A and B.
Will be my conclusion correct?

Question 2:
can someone explain me more about this?


texts: IC forces <260℃ solder temperature; socket needed?

texts:
For a school project, we are using LN324-N OP-amps packed in a DIP.
Specs can be found here.

We need to solder these to a PCB board. However, section 6.1 of the specsheet says:

  Lead Temperature (Soldering, 10 seconds) - min N/A, max 260℃

  Soldering Information - Dual-In-Line Package - Soldering(10 seconds) - max 260℃

I take it that we can't solder at >260℃ without an IC socket.
However, I noticed that people rarely solder at <300℃(I wasn't able to find out why - the only pages that show up when I google "low temp solder disadvantages" or similar are related to other commercial products).

So the question is:

Am I right about how we can't solder at >260℃? Or am I missing something?
So do we need a socket? Or can we just solder at 250℃ without a socket? Will there be significant consequences of soldering at such a low temperature?


texts: How to limit coin cell battery voltage to 2.0V and below?

texts:
The backup battery voltage for my device is specified to have a maximum voltage of 2.0V, whilst coin cells are normally around 3.0V.

How would I be able to limit the voltage to 2.0V, but in a way that does not draw much quiescent current to deplete the coin cell?

At such low currents (backup battery voltage rail current is specified with a 150nA limit),

TPS78230 linear regulator has a quiescent current of 500nA which appears to be good! I wonder if there are any lower quiescent current solutions?


texts: Electricity theft from radar transmissions

texts: I recollect reading in a newspaper in england, maybe 20 years ago, that someone had been prosecuted for stealing electricity from a radar. This was detected because the air defense radar had a black spot in its propagation field and apparently he hooked up a load of wires in his roof. I an certain I read this, but it seems physically impossible. Is this false memory syndrome or could it have happened? Could it happen with a microwave link if they pass over head? Thanks – dave


texts: electronic speed control of 3 post compound DC motor

texts:
I've got a 12V DC winch motor with two field posts and an armature post (compound motor). Currently direction is controlled by four solenoids.

Here's a diagram which boils this down two the two modes:

I think speed can be controlled via PWM, but the standard H-Bridge most brushed DC motor controllers come with doesn't seem like it would support this configuration.


texts: How to use UART rx data from ISR to main loop?

texts:
I am using PIC18F and currently trying to interface it with SIM900. I am using UART Rx interrupt. ISR is working correctly but I wonder how to get data in main loop. Lets say :

#pragma interrupt hi_prioriint
void hi_prioriint(void)
{
   if(PIR1bits.RCIF==1)
   {
      Rx = ReadUSART();  //store the received byte in Rx
   }
 }

Now I want to use Rx  in main loop. For example, if I send AT command then I need to check if I received OK or ERROR from  SIM900. (For the time being I am just testing it with a single byte and will convert it later into receiving strings because response from the SIM900 is in string form)

Example:

 putrsUSART("AT\r");        //sending AT command
 delay(500)                 //delay of 500ms
 if(strcmp(Rx,"OK")==0)     //checking the response
 {
    //if received OK then proceed further
 }

So how to use RX data of ISR in main loop?


texts:
Our instructor gave us the assignment of creating a working schematic using a 555 Timer and a 74LS192 IC using 9 LEDs. The 9 LEDs will blink counting in seconds particularly 9 seconds then it's going to loop from the beginning to start the counting again.

The instructor is not teaching us how to understand the pin configurations of the 2 ICs and I've been searching around the net but haven't found anything.

The parts would be:

A number of resistors if need be
A single or more capacitor if need be.
1 555 timer
1 74LS192 IC
9 LEDs

Can anyone help me?


texts: Why don't we use 7075 aluminum Ethernet and USB cables?

texts:
Since the skin depth of copper at 1Ghz is about 2.3 micrometers, it doesn't seem like aluminum would provide a worse signal to noise ratio.

7075 aluminum is also much more resilient and stronger than pure copper, so it should be able to bend more without breaking.

The main problems seem to be splicing wires (due to oxidation) and Power over Ethernet, but for other uses, aluminum wires seem like a cheaper and lighter (for aerospace) solution.

So why do we still use copper for data?


texts: How to make a open-circuit cable fault detector?

texts: There are projects like this one over here: Underground Cable Fault Distance Finder, which checks if a given line is short-ciruited with any of the other lines. The location of the fault is also calculated by a voltage divider method. I want to know if there is a method to detect an open circuit fault on the line, using just a single wire, similar to the resistance voltage divider. This should mimic a real implementation.


texts: Can I get 24V from ATX PSU using 12V and -12V cables?

texts: ATX PSU's have one -12V cable, and a few 12V yellow ones. Could I power up a 24V device by connecting 12V to + on the device and -12V on -?


texts: Differential amplifier input voltage higher than the supply voltage

texts: I want to measure current at high side of circuit but input voltage is higher than the op amp supply, is it ok to do the input voltage division like schematic below?


texts: Connect to Arduino Mega serial interface by C code

texts:
I'm having trouble talking to an Arduino Mega using serial port commands on Windows. Identical code works fine to connect to an Arduino Duemilanove but doesn't allow connection to the serial port with the Mega. Also, I can access both cards from the Arduino IDE software, on both Linux and Windows.

I have serial port code that works fine on Linux for both Duemilanove and Mega. But I can't write code that works for the Mega on Windows, even though it works fine with the Duemilanove at this stage.

My only thought is that perhaps something is different in the way that the Mega's USB-to-serial hardware is set up, and perhaps, at least on Windows, I need to add some additional command (maybe on the Arduino, or maybe in my C code) to enable the interface to be correctly visible/accessible.

Any thoughts anyone? Anyone else had this problem?


texts: Looking for a mechanism similiar to a watch's stem in rotary encoder type form

texts: The watches stem can be pulled out at two different levels to provide two sets of adjustments of the date and time. Is there something like that in the form of a potentiometer or rotary encoder?


texts: Why does nobody make a discrete OLED in an SMT or thru-hole package, like we have with LEDs? Is it a cost thing or a limitation of the process?


texts: How does the current limiting resistor for an LED affect current and voltage drops?

texts:
I'm having a bit of trouble understanding currrent limiting resistors in simple LED circuits. I know that I can determine the optimal resistor like so:

\$\displaystyle R=\frac{V_{s}-V_{f}}{I_{f}}\$

But I'm having a hard time understanding how this one value modifies the voltage and the current to the correct values for the LED. For example, if my calcuations for a super bright blue LED (with \$V_{f}\$ being 3.0-3.4 V and \$I_{f}\$ being 80 mA, and a voltage source of 5 V) gives me 25 ohms (using the lower bound of the forward voltage), that's fine. So the current throughout should be 80 mA and the voltage drop for the resistor and LED should be 2 and 3 volts, respectively.

But what if I used a 100 ohm resistor instead? Or any other value—how would I calculate the voltage drops and current? Would I assume one of them stays the same?


texts:
I have an idea for a project, which needs to be able to measure temperatures up to 260°C. The accuracy is not crucial (±5°C is fine) but it is important that it can measure lower temperatures too.

I initially thought of using a silicon diode such as the 1N4148 as forward voltage is proportional to temperature with a nice linear slope of -2.1mV/°C. The current will be <100µA.

However, it looks like these diodes cannot survive a temperature this high, although it is not specified exactly what failure might occur. Can I expect the silicon die to break down and not work properly at this temperature, even though the current is low? The environment will be 260°C for 3-10 minutes, so it looks like any soldering rating is irrelevant.

If this does not work, what other low cost options are there for measuring high temperatures?


texts:
I have a two prong led that when power is supplied to it, it twinkles and changes colors.

How does that actually work? It's too cheap in my opinion to have a micro controller in the diode and it looks like a normal "radio shack" diode.


texts:
I've multisim 14.2.
I not succeeded in make a phototransistor or photodiode to work.
I've tried a circuit like this

But no way to work.
Any clues? I don't know how to do it.
Thanks a lot.


texts: Sensing voltage with respect to virtual ground

texts:
I want to sense a near-ground voltage in this circuit which is Vsense, but its maximum voltage would be 0.5 V so I designed an op amp amplifier with a gain of 10.

I used another op amp to split the 12 V supply into +6 V and -6 V to power the amplifying op amp.

The problem is: the amplified output of UB is measured referenced to the virtual ground (GNDREF in the circuit) and I want to send this voltage to a microcontroller to sense it. But since the MCU uses a different ground, I'm afraid there will be a problem.

I thought about simply connecting both grounds and everyone will be happy but it came to my mind that MCU's ground is the same of battery's 12v ground which is the same negative rail of the op amp so I want to know if that would be a problem.


texts: Which servo motors for a precise but not powerful robotic arm?

texts:
I've just got into electronics with an Arduino explorer kit from Oomlout and I have learned a lot about electronics so far, but now I want to start my first proper project. A robotic arm.

It should be precise but barely needs to lift any weight at all (a laser pen). I would like it to be 30cm or so long, it would have one servo at the bottom for rotating the whole arm left and right, another up and down, then two more to lift the other segments up and down. Does anyone have any recommendations on servo's I should use? They don't need to be fast or powerful, just precise. And, of course, being cheap will be a bonus.


texts: Are there surface-mount pin header footprints for KiCAD?

texts:
I'm designing a small module that breaks out a DIP SPI EEPROM to a 2x5 pin header socket(more info here: SPI-10). I want to mount the socket on the end of the board, with the pins lying parallel to the board.

I think two 5x1 surface-mount header footprints, on both sides of the board right near the end would do the job. Trouble is, KiCAD doesn't come with such a footprint(if it does, I haven't found it yet). Where might I find one? If one doesn't exist, that's OK; I'll have a shot at making my own.


texts: Removing silkscreen paint which overlaps copper padding after printing

texts:
I am new to advanced PCB printing and, as it turns out, my PCB printing vendor prints the silkscreen white text over some copper padding according to my design, which i don't know that would happen. Is there any way to fix this issue, Should i try using rubbing alcohol, and would that damage the copper padding?

Here is what it looks like


texts:
To calculate the input capacitor for buck converter, I follow TI Application Report SLTA055–FEBRUARY 2006 "Input and Output Capacitor Selection".
It says to determine the input capacitor "75 mVpp is recommended for maximum input voltage ripple. This will yield approximately 22 mVrms of ripple voltage"
The question is how we select this value 75 mVpp?
thanks


texts: Need advices on an AC fan control circuit

texts:
I've setup a small system where I can control an AC Fan by a data-acquisition board's DAC. Here is my final schematics(please left-click to enlarge it):

The first issue was to hack the manual speed controller which powers and controls the speed of the AC fan. And thanks to @transistor, I could achieve it by soldering an LDR in parallel to the potentiometer and optically varying LDR's  value by varying LED lights. I experimentally made it work which means I was able to control fan's speed by adjusting LEDs current by a power supply. Here was the relevant question: Controlling a single phase AC fan with a 0-10V DC input

But then the second issue was that the DAC was not able to deliver enough current to LEDs(this DAC can output max 5mA current in 0 - 10V DC range). This issue was solved by adding a voltage follower and a transistor as seen in the above schematics. Now I was able to control the speed of this fan via the DAC.

And finally the problem was that this type of fan and controller was not able to totally stop rotating unless someone manually switched it of from the controller's mains switch. Therefore I decided to add a solid state relay and set it up such that under around 400mV DAC output it should switch the speed-controller hence the fan off. You can see this under the Comparator in the schematics.

Speed_controller circuit and the AC_Fan parts of the schematics is irrelevant to my question and they are just representative since they are complicated to draw and I have no schematics of these units.

When I simulate I can see the behavior I want from the system. The comparator switches to around 11V when the DAC signal is more than around 400mV and the relay turns on; and since now the speed controller is powered, the fan speed can be controlled by the LED current.

My questions are:

1-) Is my non-inverting comparator good enough? I mean do I need some extra caps around any nodes? R2 and R3 sets the threshold, but are they okay in values? Do I need a pull-up resistor from the output to the Vcc?

2-) I haven't experiment the final circuit and haven yet bought the relay. Do you have any suggestions regarding inrush currents, decoupling caps or any safety issues or anything related?

3-) And finally, is there a way to separate AC neutral and GND in LTSpice? You see in my circuit it doesn't represent the real life scenario since AC neutral is ths same with GND in my schematics.

I would be very glad to have your opinions before I set it up for use.

Info about the components and the equipment:

Two LM324 is used for voltage follower and a comparator

Transistor is an NPN BC547B

Green LEDs

A 300k LDR

This is the relay I'm going to use: http://uk.rs-online.com/web/p/solid-state-relays/0346895/

The fan: http://uk.rs-online.com/web/p/axial-fans/2781543/

The controller: http://uk.rs-online.com/web/p/fan-speed-controllers/6685345/?origin=PSF_438361|acc

The data.acq board: Controlling a single phase AC fan with a 0-10V DC input

edit:


texts: Memory deallocation exception when using free()

texts:
I am currently working on a project that requires some allocation and deallocation of large arrays on a PIC32MX775. I have a dedicated heap memory size of 1500 bytes, which should be more than sufficient and I have previously had the system allocating and deallocating memory correctly when using standard float types. However, I have recently introduced a new variable type:

typedef struct{
char index;
float gain;
float freq;   }RM_EQ_SORT_ELEMENT;

With this replacing three separate arrays I have had problems deallocating the memory using the 'free()' function ever since. An example of the arrays and how I'm trying to free them is below:

float* freq = (float*)malloc(NO_OF_FREQS*sizeof(float)); // For the unsorted average frequency
RM_EQ_SORT_ELEMENT* sortArray = (RM_EQ_SORT_ELEMENT*)malloc(NO_OF_FREQS*sizeof(RM_EQ_SORT_ELEMENT));

//**Some more code here that uses the arrays**

if(freq != NULL){
   free(freq);
}

if(sortArray != NULL){
   free(sortArray);
}

Whilst debugging, the code will jump into the 'excep_bp' loop found at the bottom of the included exceptions.c file, when the PIC32 hits either of the above free statements. If their order is changed the same result occurs.

Are there any common problems that might occur when deallocating memory like this with a PIC32? Also I understand that I might be able to debug this problem more thoroughly, any advice on what to do in this situation would help.


texts: Impedance matching at the boundary between two PCB's

texts:
I am using two evaluation boards in my circuit. Counting the one I'm designing, there are three. I know the impedance of tracks on Board #1 and have control over the impedance of tracks on Board #2. The input impedance of the tracks on Board #3 is unknown. There is no termination at the end of the lines on Board #3.

At the interface between Board #2 and Board #3, I need to control the impedance. To that end, I will be source matching at the driver on Board #2, but what is the best way to deal with boundary?

Would it be best to have a termination at the end of the line on Board #2? Perhaps a shunt or AC Termination? This assumes my driver can support the power drain of the shunt.

Perhaps I should use a quarter wave transform? Ending the transform right at the input header to Board #3 might be effective?

The simplest solution might be to place the connector physically close to the driver so they are lumped. If I then add source termination resistors to the driver to match it to the impedance of Board #3, would the two boards communicate smoothly?

Since I don't know the impedance of Board #3, would it be reasonable to accurately measure the track's width and its distance from the ground plane and roughly calculate it?

Specifics:
Speed
The edge rate of the data is ~750Mhz - 1GHz. I'm working with a rise time of about 1ns. I have space for a larger capacitive load if recommended. The output drivers of choice are the 74VCX245, but am open to changing them.

Board Layout
Board #2 will have a solid ground plane between the output drivers and the connection to Board #3.

Connector
Board #2 and Board #3 will connect via a 2x20 rectangular header. I am open to other suggestions.

Board #3
Board #3 is Texas Insrument's DAC7741 EVM. If you look at the data sheet, you'll see that there is not much information on the track design. The most I was able to extract was that the minimum track width is 10 mils, it is 1oz copper plated, and the layer (dielectric) thickness is approximately 0.014"

Physical Configuration
The connection method I had in mind looks like this:

Thanks.


texts: Why does switching power supply output AC

texts:
I've been trying to troubleshoot some a 3D printer. It wouldn't power up. I checked the power supply (NES-350-24). The positive and negative outputs measured 0VDC, and 8VAC rms (confirmed with o-scope). I figured it should be outputting DC, and that the supply must be broken. I replaced it with a similar PS (LRS-350-24). Connected it to 120VAC power, and the outputs are still 8VAC RMS (60Hz).
Is this supply behaving normally? Is there some other issue? What am I overlooking? I would very much like to understand better what the issue is here, but I am no expert in these kinds of devices.
Edit: The new supply appears to be working as expected. I am still not able to ascertain the reason for the failure of the old supply. There are no obviously burned out components. Thank you all for your input.


texts: The brightness of light bulbs in this circuit

texts:
What will happen to the brightness of bulb A and bulb B in the circuit shown in the figure when we move the wiper of the rheostat from point x to point y?

When the wiper moves from point x to point y we get a smaller resistance, and hence, we get a larger intensity of current flowing in both bulb A and bulb B, so I guessed that the brightness of both bulbs will increase. However, the answer to this question in my text book was that the brightness of bulb A decreases and the brightness of bulb B doesn't change. I got confused, so what is the correct answer? And Why?


texts: Detecting when AVR ICSP header has a cable connected

texts:
I have a bunch of Atmega16A MCUs laying around so I want to use them with an ESP8266 to relay temperature and such in each room of my home to a server.  The thing is, if I need to update the firmware on them, I need to take the device from that room to a different one to update the firmware.

The issue is once i plug in the programmer, it will supply power to the controller and it'll start detecting the temp of the room and tell the server the room it was in is the temp of the room it is currently in.  The server doesn't know the difference so it'll skew my results and such.

So is there some way I can detect when the ICSP 6-pin header has the programmers cable connected?  Just some simple thing that will tell the controller, "Hey we may not be in the right room, don't tell the server any measurements"

For clarification, the header that I'm going to use is this one:


texts:
I'm trying to derive from scratch the differential equations that characterise Chua's circuit.

Here are the ODEs I obtain from that diagram. Current is positive if conventional current goes + → –.

equations http://imageshack.us/a/img822/8892/diffeqwithdim.png

This thing is, wherever I look, the IL term in the dV2/dt equation is positive instead of negative, with everything else effectively the same. (Also, beta is generally positive).

Why am I getting the sign of that IL term wrong?


texts: Analyzing the push-pull output CMOS stage

texts:
My problem is, when V2 is 5V, M2 will cutoff obviously. So now if I measure the open-circuit output, which result will I get? Since the source of M1(NMOS) is floating without connecting to anything, I don't know how to analyze the state of M1(NMOS).
But the simulation from LTspice shows that, when V2 is 5V, output is also 5V. This is what confusing me. It seems like even source of M1(NMOS) is floating, the NMOS is working somehow in the triode region or saturation region.
Can someone give me a valid explanation of method of analyzing? Thanks!


texts:
My first idea was to use a JFET as the heart of the switch. I opted for the JFET because of its normally closed property. See below for the circuit.

V1 is at 2.5V dc, 20mA max. And V2 is at 1.1V ac @10Mhz, 1mA max. To drive the semiconductor switch J, the user closes switch S and J will have to open, so no current is allowed to flow through the channel anymore. Making
the switch open. I soon learned that a JFET is not really suited to act as a switch.

So my question is : what would be a good semiconductor or analog ic-switch to replace the JFET is this circuit?

NB: This switch is intended as a silicon version of an everyday household-switch(although with lower voltages). So no signal or data flow has to be switched.


texts:
In Eagle, is there any way I can remove the empty space around the pad here?  I would like the polygon to connect to the whole pad.

Note that this is a pad from a part and not a via.


texts:
How do you change the tuning of a PID controller to deal with changing thermal properties?

The project: I am making yogurt. It cultures at 110 deg F for about half a day; you put in milk and a little starter culture and get yogurt. Save a little for a starter for the next batch and eat the rest. Easy and delicious.

The setup: I am taking a food safe container (pan with lid) placing it over a heater, adding a type k thermocouple, SSR and PID controller all wired pretty much per the reference implementation of any PID controller you care to name. This works well if I am using a crockpot (225W, approximately 3/4 gal) as both my pan and heating element, but I want to do larger batches (1 gal).

The problem: With a larger heater to thermal mass ratio (1000W hot plate and stainless steel pan instead of ceramic). There is increased instability during the later part of the cycle. The PID controller is tuned with water (milk is a little more expensive) and holds temperature within 2 deg F for the first couple hours, but as the yogurt cultures I am noticing pronounced temperature swings, and unlike using the crockpot I am seeing whey separation (presumably either due to over temp or increased condensation on the lid due to the same). I am fairly sure that the larger thermal mass was dampening the noise of the change of the thermal conductivity during the culture, but I am unsure how to proceed to more precisely control the temperature during the later stages without excessively compromising temperature regulation at the beginning.


texts: Logic circuit shutting off at target voltage

texts:
I deleted the old question and posted another one because I felt the question is now substantially different.

I have a potentiometer connected to a current source and I want the logic chip to cut off the current altogether when the voltage across the potentiometer reaches a certain value.

I am looking at CD74HC4052E as my chip of choice.

I have learned how the logic chip works by applying 0V to the inputs and confirmed that the output was 5V. Also, when either of the inputs went up, the output voltage was 0V.

I thought as I increase the potentiometer value from zero, the input voltage will go up and once it registers the high voltage threshold, the output would go from 5V to zero.

I think I see why the circuit would not work the way I want it to, the input voltage of the NAND is not really defined the way I would like it to.

I want to know if there's a way I can simply place the logic switch in my circuit in series, or if there's a simple circuit I can implement.

I want to come up with a circuit with a constant currents source where as you increase the potentiometer value, the voltage goes up and once it reaches the cutoff, the output would go to zero.

Any help would be appreciated.

simulate this circuit – Schematic created using CircuitLab


texts: What's the output of a record cartridge playing an out-of-speed record

texts:
I'm very interested in vinyl records and analog music, and the belt of my turntable got loose. Upon such situation it piqued my curiosity, what is the output signal at the end of the arm cartridge wires for a known waveshape if the speed is not the correct one.

Say the record was mean to play sin(wt), a pure sine wave, at 33rpm, then, because of a loosen belt or any other reason, it rotates at a different RPM, how to calculate the changes in such sine wave?

I'm not considering the filters that the cartridge might apply on the signal, whether it is a low pass, band pass, or high pass nor any other impedances that might alter the signal in any circumstance, just a supposedly ideal stylus and cartridge.


texts: Hardware to Detect EMG or Skin Resistance

texts:
I have been given assignment to design a device that can detect emg signal of Skin Resistance change while moving
fingers.

actually i need to track finger movements using some hardware containing micro controller

My idea was that i will apply voltage at two points one finger tip and one elbow.

and measure voltage change by amplifying it.

Today i tested this idea by applying 1 volt and measuring by Ossiloscope .I donot know why there was 50 Hz AC wave detected there and there was very very slight change.

but i am not much happy with the results.

any idea?may be something mile a glove that sends computer a signal through some PIC/AVR or what ever
Any Idea or help is required.Consider what would you do in this case keeping in mind safety?


texts:
Given the following diagram:

Both conductors are moving at the same velocity, and the same direction, and are in the same magnetic field. They should induce the same ϵ even when their shapes are different?

ϵ = -vBL , my assumption that they should be the same.

My apologizes for the simplistic diagram, I don't have the proper programs to draw this a bit better.

Edit:


texts: 120VAC to 90VDC Power Supply (for DC Stepper Motors)

texts:
I'm currently an electrical engineering student working on building a 3 degree of freedom motion simulator using three 90V DC Stepper Motors. Each motor can draw up to 5 A so I need to find or build a 90V DC power supply that can handle up to 15 A (1.35 kW). I've tried looking around for an already built power supply that I could buy but for this amount of power these become very expensive (~$3000). I'm working for a client whom recommended that I use a Dual IGBTMOD H-Series Module (Datasheet: http://www.pwrx.com/pwrx/docs/cm50dy-12h.pdf) to convert 120 VAC to 90VDC.

The picture above shows the schematic for the module and I've tried searching for circuit diagrams of power supplies using similar modules and but I haven't been able to figure out how these work. From my understanding I imagine that 120 VAC would connect to C1 and E2 terminals and a PWM signal would be fed to the gates G1 and G2 to get the desired output at C2E1. However this is just speculation and I'm not sure if what I'm thinking is completely wrong or if there may be a better solution altogether. Any help would be greatly appreciated, thanks.


texts: What's passive about the passive sign convention?

texts: I've heard and read about the passive sign convention, but don't really understand its  meaning and importance in solving electric circuits. Is this because of conventional current which flows opposite electrons or is it something else?


texts: Need help to design voltage regulator circuit with LT1959

texts:
I am planning to use LT1959 IC for making a voltage regulator circuit for 3V 1A output. The datasheet does not mention maximum allowed value for input capacitor for the circuit.

In order to meet the ripple current requirements for the input capacitor(I RMS(MAX) =I OUT/2 = 0.5A), I am planning to use 7-10 100 uF electrolytic capacitors (in parallel configuration) with 0.1A max ripple current rating. This is because of time and cost constraints. So, my effective input capacitor value would be 1000 uF with 0.7A-1.0A ripple current rating.

I am again going to put about 10 electrolytic caps of 100 uF in parallel for output capacitor. I will also use few 0.1 uF ceramic caps in parallel with the electrolytic output caps. So my effective output capacitor would >1000 uF.

The evaluation board manual for LT1959 demo circuit designed by Linear Technology uses only 25 uF input capacitor and 100 uF output capacitor.

Questions:

1) Should I be concerned about the relatively high effective capacitance value of input and output capacitors which I am about to use, as compared to the company design?

2) Would there be any other problems in the circuit if I continue with this design?

3) Should I place any extra ceramic input cap in parallel with the input electrolyic caps?

4) Should I place output ceramic cap close to IC or closer to load?


texts: 433MHz RF transmission only working when holding usb cable in the air

texts:
I'm really puzzled about this. I have a simple transmission between two ATTiny85's going on with a 433MHz receiver and transmitter.
The transmitter is in the basement so the signal is rather weak but here is weird thing.
If I hold my USB to TTL cable, that connects the ATTiny to my PC, at a higher position like shown in image #1 I get a steady stream from my transmitter down stairs.

If I put the cable down (touching the cable isolation makes no difference) like shown in image #2 I get no signal AT ALL. Just nothing. I could repeat this behavior several times.

I really don't know much about antennas and radio transmission so this doesn't make sense to me in any way. I guess he USB cable must act as some sort of antenna/repeater but how? It only provides 5v power to the receiver and ATTiny and reads the serial output from the tiny.

High-res: http://i.imgur.com/mmH910U.jpg

High-res: http://i.imgur.com/y6fIKOo.jpg


texts:
My syllabus shows that I have to study about transistor amplifiers - including small signal analysis.

What exactly does small signal analysis mean? I googled it but I couldn't find an exact answer.


texts: What will happen if for a BJT transistor, it's emitter terminal is treated as collector and collector as emitter in a common emitter amplifier circuit?


texts: I read somewhere that in a mixed signal ckt , the analog part and the digital part are supposed to be better when they have different power rails and ground lines , but to avoid floating of the ground , the different ground lines and power lines have to be connected at a point called the star point , so that there is a single ground point and power point. But can someone explain this in a better way , I basically want to understand why a star point is used and its advantages in a mixed signal board .


texts:
I recently picked up a faulty Hitachi V-1150 'scope and after fixing a problem in the power supply it now starts up. However, it only uses the very middle of the screen vertically, and goes wild if I try to lower the volts/div.

My theory that the oscilloscope "thinks" that the screen is smaller than it is is also backed by the fact that turning the vertical position knobs to their extremes only moves the trace up and down a tiny amount.

As you can see from the pictures, the entire trace is also shifted to the right.

  The largest I can get the trace so the waveform is displayed
  accurately:

  When I decrease the volts/div:

Does anyone have any ideas about the cause(s) of these problems?


texts:
My question is can a thermoelectric generator(input:heat difference to output:electricity) module also work as a peltier module(Input: current to output:cooling effect)?

If I buy a thermoelectric generator, can I use it for cooling if I pump current into it?


texts:
Let's say we have an arduino or Rpi gpio pin connected to (accidentally?) 12V rail with resistor limiting current to ~50uA. I wonder what will happen to a microcontroller. Will it survive or magic smoke pops out? Well without current limit it's dead for sure but does that very small current change cards a bit?

Edit: This is just a theoretical question. I would like to know what happens under given circumstances.


texts: Converting Positive Logic to Negative logic. 7 Segment Decoder

texts:
I was looking for a truth table for a seven segment decoder and saw that in order to display a three we must input a 0 for D, 0 for C, 1 for B and 1 for A. This will allow us to output the segments 1111001 which will display a 3. However if we wanted to convert this to binary logic would we just change the 0's to 1's and 1's to 0's?

Thanks for the help very new to this.


texts: Quadrotor flight controller and actuator dynamics

texts:
Do off the shelf flight controllers for quadrotors, such as pixhawk or cc3d, take into account BLDC actuator dynamics? For example you can design a controller to compute propeller rates, and then assume the propellers instantly achieve those rates, or you can build the actuator dynamics into a model and account for the difference between actual and desired propeller rates in closed loop control.

I previously assumed the former was true, and I am building my flight controller with this assumption (the motors achieve the computed rates instantaneously) but am running into problems with attitude stability. I am beginning to suspect might be because of the assumption about the motors, but I'm not totally sure.


texts:
So I was wondering if I could power my 8 or at least 4 ip cameras from my old pc psu.

I have: *500 W psu, where 12 V can use up to 360 W

*GV-EBL1100 ip cameras which require 12 VDC / (IEEE 802.3af), not sure if 7.4 or 15 W per camera (confused from documentation)

*non-PoE router I think (nWay switch)

*CAT5e cables

I want to make a diy injector with at least 4 sockets which connect to ip cameras (data + power) and 4 sockets which go back to router with data only.

Is it possible to connect all 4 cameras CAT5 cable power pairs parallel to a single psu 12V power pair using DC-DC transformer to 48V?

Does this particular ip camera communicates to negotiate power supply over data cables?

Will it work if CAT5e cable is splitted the way that power goes to ip camera but blank to router via (unused?) pairs?

Or just buying the poe switch is the only option here?

Don't hesitate to ask if something is unclear, I don't know if I provided enough information and clearly.

Thanks in advance.


texts: Pad size for JEDEC 1.0mm pitch 27x27 device

texts:
I have a JEDEC 1.0mm pitch 27x27 device. The only missing information I need to build a footprint for it is the size of the pads.

What size of pads should I use for a JEDEC 1.0mm pitch 27x27 device?


texts:
I was reading an electronics book and came upon this circuit.

I am having a difficult time understanding why the voltage across D1 is 0.6V. I understand that that the reason is because the input signal's pp voltage is lower than 0.6v C and R1 make a differentiator then D2 rectifies that but none of that would work if the signal is less than 0.6v. I just don't understand why D1 is at 0.6V and how that makes D2 be higher than 0.6V. I was going to post a diagram but I don't have enough reputation.


texts: How to find and compare two regulators' output impedances

texts:
I want to compare output impedance of TL780-05 and LM7805, and also AC output impedance. Which parameter indicates these?

Both are fixed 5V regulators.

I can only see that one of them has 1% accuracy and the other 4%.


texts: Which form between solar panel and wind turbines requires less cost in servicing?

texts:
I found that the average life of a solar panel is about 25 years and that of the the wind turbine is also somewhat close to 25 years.
But the wind turbines require alternator in order to generate electricity which is showing an average life span of 7 years.
One factor does add up to the cost of solar panels which is the cost to clean the panels in order to keep it dust free.
Even after adding that cost to the solar panels it appears that it must be requiring very  less cost in servicing.
I did some research but no proper information was available that after a 7 year time span of the alternator the whole alternator need to be changed or just some parts of it as this will vary the cost of servicing prominently.
If anyone in this community have any information regarding the above mentioned field please share it.


texts: Stereo to mono amp solution with mono bridge

texts:
I have these stereo amplifiers - Adafruit 20W and Sure Electronics 15W.

If I connect this passive stereo to mono bridge at its output, will it technically be a good solution? Will the amps work correctly?

I have searched and searched for modules which can take in stereo inputs and output mono, but there isn't just any available.

Anyway, is there any other technique to help with this. Or any other amp which can support simple twisting of wires to get it play only mono from a stereo.

PS - Got a 15W driver with 4 ohm. Need to work with 4 ohm.


texts:
I am designing a electronic lock using a electromagnet(coil).This is my circuit:

simulate this circuit – Schematic created using CircuitLab
When the switch is closed it will short the circuit and current will stop flowing the inductor-> the lock will open.
I was wondering if I should add a diode in series with the inductor just like this for protection:

simulate this circuit
in order to prevent any significant current flow in the opposite direction in case a voltage opposite to the battery is induced somehow and damage the battery and generally to block any voltages opposite to the battery.
Should I do it?


texts: Thermal Noise autocorrelation and time domain analysis

texts:
I have some doubts about the termal noise of a real resistor.

The equivalent model of a noisy resistor is this one (here the reference):

Here there is the model of a noisy resistive network:

I have the following questions:

1) From the previous relationships for parallel and series resistances, we see that it is possible to add the noise powers of each resistor included in the network. But this is true, from a signal processing point of view, if and only if the Cross-correlation of those noises is 0, i.e. the noise of each resistor is uncorrelated with others. Why is it true?

2) Thermal noise is white noise (approximately), i.e. its power spectral density is constant with frequency. But this means that its autocorrelation is a dirac delta, i.e. a single pulse. It seems quite strange to me: I'd say that its behaviour is like the following one (which is also what I have found while searching "Time domain simulation of thermal noise"):


texts: Does melting microwires cause internal shorts

texts: If you overheat a chip, you can melt the microwires attaching the wafer to the package. When this happens, can the melted microwires cause shorts between the pins of the chip, inside the package of the chip? The result of this would be short circuits even though the circuit externally appears to have none.


texts:
The datasheet of the chip UC3843 recommends to add an external resistor of about 10-20 ohm in series with the MOSFET. Can anyone explain how to calculate the power dissipation in the series resistor? I'm operating the circuit at 200Khz. Other parameters are as follows:

Vin= 10V
Vout=18V
Ouput Current= 3A
Mosfet: FDP5500


texts: 12V DC LED and motor circuit - overheating

texts:
I'm trying to build a model lighthouse (don't ask). :-)

Essentially I'm trying to have an über-bright LED with a motor rotating at 2rpm, both powered from the mains (120V AC).  The problem I am having is overheating...

I have constructed the following circuit:

simulate this circuit – Schematic created using CircuitLab

These are the components I am using:

Power source: 12V DC power adapter, 1A

LED: Cree 10W high-power, 2.9-4V forward voltage, 3000mA forward current, 10W power dissipation, 2.5°C/W thermal resistance

Resistors: 1x 3ohm 25W (R1) and 1x 3.3ohm 50W (R2)

The motor part works wonderfully.  I can adjust the speed down to 2rpm and everything is good.  The LED on the other hand is causing a headache.  Initially, I had calculated a 3ohm resistor (R1) based on (12V-3V)/3A.  But this caused the LED to flash intermittently - I assumed overloaded - so I bought a slightly larger R2 (3.3ohm), thinking maybe the voltage across the LED was 2.9 and so I should go for something a little larger.  Still blinking.  On a whim, I put them in series (as in the diagram), and then it stops flashing and everything works as it should.

However, the LED is getting VERY hot, as are the two resistors.  I don't run the circuit for longer than 5 minutes because I'm worried about it burning out.  The LED comes pre-mounted on a flat heatsink disk, and I could attach a slightly larger heatsink to that, but I'm limited by the lighthouse design and therefore would really like it to get less hot.

The resistor power should, I thought, be 3A*(12V-2.9V)=27.3W.

I feel I must be miscalculating what kind of resistor I should be using.  Or maybe there's something I'm missing entirely wrong with the circuit.  Any thoughts on this and/or ideas as to how to stop this LED circuit from self-incinerating would be hugely appreciated.

Thank you all!


texts:
The V-I characteristics of MOSFET lies in the first and third quadrant. Therefore it should be passive device acc to me. But I have read that it is an active device. Can somebody tell what is wrong here or what am I missing?

Because for passive elements \$P_{out}\$ should be less than \$P_{in}\$ which correspond to \$V_1 \cdot I_1 + V_2 \cdot I_2 > 0\$ for a two port network. For those devices whose V-I characteristics are in first and third quadrant this condition will always hold.


texts: STM32F103 - TIM5 doesn't exist on medium density devices ? How do I tell what else is missing?

texts:
I've tried setting TIM5 as a timebase timer with an interrupt, when the compiler gave me the following error:

  39: error: 'TIM5_IRQn' undeclared (first use in this function)

Than I though I'll search for this definition in stm32f10x.h , and I noticed this:

#ifdef STM32F10X_HD
...
TIM5_IRQn = 50,     /*!< TIM5 global Interrupt  */
...

I guess this means that my device, which is Medium Density, doesn't have a TIM5 interrupt. Does that mean the device doesn't have TIM5 peripheral at all ?

The only reference I have found about this is in the medium density datasheet "features" page which states:

"Three 16-bit timers..." - I assume these are TIM2/3/4

"16-bit, motor control pwm timer..." - I assume this is TIM1

Here is a bit from the Reference Manual (RM0008):

This is so confusing, according to this table you'd think TIM5 and TIM8 are available.

How can I tell what other peripherals am I missing in my Medium Density device ?


texts: MP3-25 flexible solar panel providing low current

texts:
I am working on a project where I need about 20 mA to come from a particular solar panel I am in possession of. The solar panel is an MP3-25 panel, I actually have 2 which I am trying to get to work. The panel is rated at about 25 mW, and I got it to output that much power, even indoors, for a few seconds. I was testing it continuously with a multimeter, and for some reason it put out about .21 mW instead of 20-25 mW the rest of the time. I wonder if something would need to be done to lower the voltage, as it is possible at a very high voltage the panel cannot output the proper current. I am right now unable to make it produce the proper amount of power, which is quite frustrating.

What steps can I take to get the solar panel functioning? I have tried making a good connection to it in several different ways, and I have brought it outside and it still only output about .66 mW in broad daylight.

Right now I am directly shorting the panel through a current meter, perhaps that is the issue. Is there some special way to measure the current? Solar panels are meant to output current near the current they would provide in a short circuit, so I doubt this is the issue but it could be.


texts: What is the technical name for fan that produces electricity?

texts:
I'm wanting to create a wind powered LED similar to this one, but weather proof.  I know there's tons of them out there, but I'm wanting to build it from scratch.  My issue is that I'm completely novice when it comes to electronics, and I don't even know what to search for.

For example, when I search "fan that produces electricity", I mostly get hits for fan motors, or huge wind turbines.  Is there a specific name for fans that produce electricity?


texts: Why are the outputs of these gates tied together in the Apollo Guidance Computer?

texts:
In looking at the AGC schematics, I'm finding a lot of instances where the outputs of some of the NOR gates are tied together when feeding into another gate. The most dramatic example being here, where 4 NOR gates all have their outputs tied together.
More commonly though, the gates tied together look something like this:

simulate this circuit – Schematic created using CircuitLab
I can't imagine there'd be a reason for doing something like this in modern digital logic, since it seems like there'd be contention if one gate's output was low, and the other high.
So what's going on here, exactly? My first thought was that maybe it's some kind of "poor man's OR gate,"  allowing the next gate in the stage to see a high if at least one of the gates is high.
Is there some quirk with RTL logic that would allow it to work this way, or is the reason for this something else entirely?


texts: Power supply for Precision Current Source for Medical Instrument

texts:
I am trying to implement power supply for constant current source(LM334) for medical application. I have 24V,3A SMPS to generate required output (38V) to operate LM334 Constant current source of 10mA.
LM334 is followed by I/V converter and OP-amps and then ADC.

Considering fact that LDO generate less noise than switching converter and LM334 has less error at higher operating voltage, I have come up with 2 schemes as mentioned below:
Scheme 1:

Scheme 2:

Which is better option ( in terms of noise , since signal strength is very less )to generate 38V for LM334 ? Please someone guide.
Thanks in advance !


texts: Simplest 5 Volt power supply circuit design

texts:
I am doing a project related to power supply. In that i have designed 5Volt supply some what largely(using transformer,diodes, capacitors) therefore it occupies more space. So can you suggest me a very simple form of 5Volt power supply.

Edit (based on author comments)

Input voltage: 230V

Output current: <1A


texts: Error in this Countdown module? (Verilog)

texts:
My professor looked at this code for a good 10 minutes, but could not find the problem. So, I'm hoping a fresh pair of eyes will see something both of us missed. As always, I'll be grateful for any hints you can provide.

Context: A module that counts from FFF to 000, then repeats.

Problem: Only lowest 2 displays decrement, skipping several numbers at a time and then jump back up to FF at a seemingly random point.

Assumptions: 1. SevenSegment driver is working properly. It has been checked manually and will display the hex number it is given
2. The ClockDivider module works as intended. The countdown decreases every 1 second as it should (CLOCK_50 = 50 MHz)

Possible Hint: Verilog warns that "cd" is an inferred latch and retains its value through one or more paths in the "always" block

module ClockDivider( input CLOCK_50, output reg[ 31:0] count );
parameter clockDivisor = 50_000_000;

always @( posedge CLOCK_50 )
    if ( count == 0)
        count <= clockDivisor;
        else
            count <= count - 1;
endmodule

module Test (

    //////////// CLOCK //////////
    input                       CLOCK_50,
    //////////// SEG7 //////////
    output           [6:0]      HEX0,
    output           [6:0]      HEX1,
    output           [6:0]      HEX2
);

//ClockDivider Output
wire                [31:0]          cout;

reg                 [11:0]            cd;

ClockDivider a( CLOCK_50, cout);

always @(cout)
begin

if (cout == 32'h0)
        if (cd == 12'h0)
                cd <= 12'hFFF;
        else
                cd <= (cd - 12'h001);

end

SevenSegment    C2( cd[11:8],  1'b0, HEX2 );
SevenSegment    C1( cd[7:4],   1'b0, HEX1 );
SevenSegment    C0( cd[3:0],   1'b0, HEX0 );

endmodule


texts: Lucid (Verilog) intermittent generated clock signal

texts:
I'm just starting out in the world of FPGAs.  I've picked up a Mojo running a Spartan-6 from Xilinx and I'm attempting to create an arbitrary clock for use with a SENT peripheral.  At this point I haven't made it beyond attempting to generate a tick clock (eventually 1.2us) from the base clock (50MHz).  I'm using the divider below to take the 50MHz clock as an input and currently divide by 500 which should provide a 100kHz output that I'm feeding directly to a pin connected to my logic analyzer.

File: divider.v

module divider (
    input clk,  // clock
    input rst,  // reset
    output reg out
  );

    parameter DIVIDER = 500;

    reg [15:0] count = 0;

    always @(posedge clk) begin

        if (rst == 1) begin
            out <= 0;
            count <= 0;
        end
        else begin
            if (count == (DIVIDER - 1)) begin
                out <= 1;
                count <= 0;
            end else begin
        out <= 0;
                count <= count + 1'b1;
            end
        end
    end

endmodule

File: mojo_top.luc

module mojo_top (
    input clk,              // 50MHz clock
    input rst_n,            // reset button (active low)
    output led [8],         // 8 user controllable LEDs
    input cclk,             // configuration clock, AVR ready when high
    output spi_miso,        // AVR SPI MISO
    input spi_ss,           // AVR SPI Slave Select
    input spi_mosi,         // AVR SPI MOSI
    input spi_sck,          // AVR SPI Clock
    output spi_channel [4], // AVR general purpose pins (used by default to select ADC channel)
    input avr_tx,           // AVR TX (FPGA RX)
    output avr_rx,          // AVR RX (FPGA TX)
    input avr_rx_busy,      // AVR RX buffer full
    inout sent0
  ) {

  sig rst;                  // reset signal
  sig data[12];

  .clk(clk) {
    // The reset conditioner is used to synchronize the reset signal to the FPGA
    // clock. This ensures the entire FPGA comes out of reset at the same time.
    reset_conditioner reset_cond;
  }

  divider tick_clock(.clk(clk), .rst(rst));

  always {
    sent0.enable = 1;
    sent0.write = tick_clock.out;

    reset_cond.in = ~rst_n; // input raw inverted reset signal
    rst = reset_cond.out;   // conditioned reset

    led = 8h00;             // turn LEDs off
    spi_miso = bz;          // not using SPI
    spi_channel = bzzzz;    // not using flags
    avr_rx = bz;            // not using serial port
  }
}

What I'm seeing though is that while the clock signal outputs a 100khz waveform as expected it drops out periodically.  I haven't been able to draw any conclusions as to why this is happening.

I am expecting a semi-clean 100khz waveform with the supplied code.

I've been banging my head hard against this for a while but I can only assume that it's my lack of Verilog experience that's getting me and not anything to do with the hardware that I am attempting to use.  This seems to be similar to existing examples for UART and I2C master modules.  But there must be a small detail that is missing.

Can anyone offer any advice regarding producing a clean clock signal to drive an output pin?


texts:
I have some experience with highfrequency circuit analysys. However I am a newbie in PCB design. I am analysing this circuit:
http://www.ti.com/lit/ug/spmu365b/spmu365b.pdf (starts on page 36)
and regularly see things like "OMIT" for headerpins or components like resistors or so.

e.g.:

p41 (6/6): the boxheader(?) on the left.
P40 (5/6): R48 on the dev board are two small surfaces with some soldering on it but no component apparently. I can hardly see myself (de)soldering resistors on my new dev board...

Why is this being mentionned? What do the people who made the PCB mean by this?

I mean if this part has to be omitted, why did they even place it on the PCB?

Thx


texts:
I have noticed that there is some current (not dangerous levels) in the shield around the power supply in my computer.

Would it be safe to measure the current (Amps) going through the shield with a multimeter, or is that a short circuit? The shield is grounded, so I fear this might look like a parralel circuit, which is not good for Amp measurement.

I know that you can measure voltage and resistance via a parralel circuit, but to measure current you need to measure serially.

Or should I just measure the resistence and voltage to determine the current via Ohm's law?


texts:
I want to design a custom PCB to connect to my addressable RGB motherboard.
My question is, I have researched the WS2812B led, which seems to be capable of addressable RGB connection.
Would it suffice to just connect an addressable RGB header with decoupling capacitors on the VCC and connect the D pin to Din, and the Dout of the led to the next Din and so on?
Or am I missing something.
And if people have a suggestion for maybe a better/easier design, let me know.
*edit for clarification:
link to led I found:
https://www.seeedstudio.com/document/pdf/WS2812B%20Datasheet.pdf
link to addressable RGB: https://www.msi.com/blog/top-5-accessories-for-rgb-gaming-pc-build-guide
An RGB connector sends as far as I understand 5V to power the leds, and D signal for the colors and brightness.
*edit after some more research:
I found a picture of the ledstrips which use the WS2812B led.

*update 1:
I made the first prototype and found out (if I had read the datasheet a little bit more closely) that the data send to the leds, is only for 3 leds chained together. So I adjusted my design and will post an update in a few weeks if it works (with pictures).


texts: How to monitor one wire "kind of" protocol

texts:
In the current network, there's 1 master device, which gathers data from over 20 devices. Nameplate says the baud rate is 2400. In the bus cable there's one data wire, 12V and GND. A friend of mine connected oscilloscope to Data-GND and checked there's 0-12V voltage level.

I want to reverse engineer the protocol used, so I'd like to connect my PC to check byte frames. Is it safe to connect Data to RxD and GND to GND of COM port, or will I damage the ports by connecting it that way?

EDIT:
Today I had a chance to connect device to logic analyzer. Here's the screenshot of sigrok:

I used UART and inverted Rx cause it looked somewhat reasonable. Afterwards I connected Data and GND to usb/TTL converter to hopefully get some data to work on, but sadly serial port monitors show nothing... Any idea how can I capture the signal?


texts: Is supply current lower than output current in voltage regulator circuits?

texts:
Say I have a 5v linear voltage regulator circuit with a supply voltage of 24v.

If the 5v citcuit is using 20amps how many amps will the 24v supply need to deliver? Or will the current be the same?


texts: What does "MCS" means in intel's microcontroller MCS-48, MCS-51, and MCS-96?

texts: Like the title said, I would like to under stand what does "MCS" refer to?


texts: 3 phase AC motor wont start after overloading

texts: A 3 phase induction motor is stuck with a heavy load and was making hum noise. After it is unloaded it still wont start. Any ideas where to start trouble-shooting? Would overloading activate the circuit breakers in an AC motor?


texts: Test cases for a calculator test bench in VHDL

texts:
I just wrote down a calculator core with VHDL which actually does a multiplication, additon, an Xor operation and an AND operation and I have to write a test bench which should simulate all four functions for all possible combinations of the two 8 bit operands.
How could I write down a similar test bench since I have a button to increment the operands and the opcode value and one to select the operation and a last one a reset button.
When I tried a test bench for only one case for each operation it was so long I think that there is another way to do it to test all the operand.


texts: Vibration motors burning out under PWM control

texts:
I have 16 dc vibration motors bought from Ali, rated at 0.1A, Vdc 3-9v.

In fact they consumed 0.15-0.18A from 9V. Starting resistance varied from 20 to 30 ohms.

I connected all 16 motors to PCA9685 16-channel pwm controller that runs at 1.6 kHz. I have 8 identical pcb boards as shown below, each pcb is connected to its pair of motors. The power source V1 is supplying all boards and is capable of 11A / 9V.

The diode and capacitor is near the motor. Each motor is connected by two copper multi-strand non-shielded wires, 1.6 mm sq diameter, 16 ft. length.

During testing I had been having blown fuses and motors with degraded resistance (almost short circuited). Not all of them, not in one time. I haven't observed any spikes on power source terminals.

Some motors heated more than the others. I've got two motors at 60°C but quickly disarmed them. Others were not more than 10°C above ambient temperature.

As a safety measure I programmed soft pwm transition, lowered maximum duty cycle, lowered the power source voltage to 8V. So far looks like it helped.

The actual questions are:

What else can I do? I have a low budget so I cannot implement current sensing. Do you think linear voltage regulators could help to protect the motors?
From your experience, can you say that the motors were doomed to burn in my setup or not?

simulate this circuit – Schematic created using CircuitLab


texts:
I am making a differential amp with a non-inverting amp with a gain of 4.9 with the use of an AD822 which is a dual rail-to-rail op amp.

My input signal on the diff amp is on the range of 2.5V to 3.45V and then i am subtracting 2.47V from it. The output then goes to the non-inverting amp for it to be scaled up to about 0.15V to 4.8V for the arduino ADC to read it. My problem is I'm not having the gain of 4.9 which I want, im getting a gain of 6 and above at my output.

I am thinking that buffering the diff amp output before going to the non-inverting could solve the problem but that would need another rail-to-rail op amp. What other solutions could I do?

FYI, the input from the diff amp is a load cell output using an in-amp(AD620). And the 2.47V is provided by a shunt regulator(TLV431)


texts: using the mcp42010 for audio attenuation

texts:
I would really appreciate some help here, I've spent a lot of time on this and can't get it right. looking at datasheets and answers here actually made me even more confused...

I'm trying to control the gain of an audio source (300mV pp) with the mcp42010 digipot as a voltage divider powered from a single supply of 5V. after I do that, I plan to pass the attenuated  output through a buffer and sum it with another audio signal with a summing amplifier.

I understand that this IC is not the best candidate for audio (it is linear and does not have zero crossing function) but I have it working nicely with my setup and need somthing working quickly. I'm ok with some minor zipper noise.

My problem is that I don't understand what is the "right" way to connect the signal to the pot: should I bias the signal before it enters the pot (on pin A) to 2.5V? if so, what should the voltage on the other pin (B) of the pot be?
it looks like people say that you should not have DC voltage across the pot, so ground is not going to work.

simulate this circuit – Schematic created using CircuitLab

I also found this example, where they have another funky way of setting it up with two voltage dividers with resistors of different values on each side of the pot, somthing like this:

simulate this circuit

and in this example (page 18 figure 11) they bias the B pin of the pot to 2.5 and the input is between positive and negative 2.5V:

simulate this circuit

which I understand even less, since the pins on the pot can have maximum ratings of 0-5v, so pin A will see a negative voltage...

could someone please suggest the right/best setup for this IC and explain why this is the case? also could you please explain why that is the case?
thanks!


texts: Is it possible dimension a braking resistor according to a specific stopping time for a DC motor?

texts:
Assuming that a DC motor is running at 1200 RPM and there is a power cut, the motor will stop in 40 seconds. Now when the power cut occurs, a braking resistor is switched on.  What  would its value be for stopping the motor in 10 seconds?
How can I get a general formula for this?


texts:
I build and measure loudspeakers at home as a hobby. But I have never had a decent mic preamp for my unmodified Panasonic ECM capsules. I use a USB sound card to accept the mic audio and analyze it with ARTA software.

After thinking about it for awhile I decided to go to the mountain and use the Linkwitz circuit for my measurement mic preamp, but with a couple changes. See here at Microphone http://www.linkwitzlab.com/sys_test.htm

The Linkwitz circuit is designed for capsules that are cut. That means the capsules are referenced from ground to V-. So I thought why not design the circuit so that it can handle uncut as well as cut capsules. My capsules are all uncut but I may try out cut ones in the future.

So, I figured a switch could be used to switch the capsule reference from "ground to V-" to "ground to V+". That change is on the schema below. Thoughts?

I believe my Panasonic capsules put out about 6 ma at 90 dB SPL which is where I do most of my testing. The Linkwitz circuit has a gain of about 10 dB. But the cut capsules are more efficient than uncut. I am uncertain what gain I need to properly feed my sound card, so I figured why not make the circuit variable gain to provide for the uncut capsules. What I figured was to use a rotary switch to change the resistance of R3 in the schema below. A four position switch with the resistances shown should be able to provide a gain variation of 10, 20, 30 and 40 dB. But at the higher gains the effective R3 starts to get pretty small. Am I in trouble there? Would it be smarter to only have two levels of gain, like 10 dB and 20 dB? How High should I go to get a proper level to my sound card? Would it be smarter to vary R4? Suggestions?

The output of the circuit will go to line-in of a sound card. Cables will be very short, a few inches. So do I even need R5 and C2?

As for the pot, it may not even be necessary given the switched gain choices in the circuit. Thoughts?

I can use any value for the Pot if it makes sense to have it at all. Suggestions?

The resistances in the circuit were chosen by Linkwitz to keep noise down. Is there any good reason to change them? Especially considering the uncut capsule interface with the circuit? I understand the uncut capsules like an input impedance of about 20k or higher. Thoughts?

The LM833N OPA is a dual chip. Is there anything smart that can be done with the second amp?

And last, how long a cable can an uncut capsule push signal down before the high frequencies begin to be cut? I have seen home theatre mics with cable lengths of 20 feet or more. How far can I go with mic cable? Linkwitz suggests less than 30 ft with a cut capsule. What about a stock capsule?

Here is my schematic:


texts:
I have this line at the beginning of a Gerber file generated by Altium.

%FSDAX23Y23*%

According the the Gerber Spec, the FS  parameter should be followed by <L or T><A or I>. Nowhere does it mention the meaning of the D. Surely this isn't a bug in Altium.


texts:
I'm currently using a demo-board from sparkfun for quick prototyping of a hall-effect sensor application. The specific chip I'm using is the ACS723-5AB, a Hall-Effect sensor that can measure between -5A and +5A.

Now that I'm done using the demo-board from sparkfun I'm looking to just directly use the sensor chip in my final circuit design.

One of the improvements I wanted to make was to add a low-pass filter on the sensor output for smoothing the signal a bit by adding a simple RC filter, but when I look at the circuit-design of the SparkFun board, they don't use an RC filter but just a capacitor to ground on the output line.

I can't imagine anything drawing current from the sensor output, so decoupling doesn't seem likely.
It doesn't really create a filter without a resistor (as far as I know?)

My question is: What is the purpose of capacitor C2 on Viout?

link to circuit diagram of daughterboard

Link to sensor datasheet


texts:
I am working on developing Patch antenna for 5G Applications. As the first step, I am trying to understand the working and properties of Microstrip patch antenna.
All the resources I have read state that electric field is zero at the center of patch, maximum at one side and minimum at another. However, I haven't come across any solid proof or even explanation for the same.
If anyone could enlighten me on this, it would be really helpful !


texts: EXTI stops working after jumping to the new firmware STM32L4

texts:
I am working on an application on the STM32L4 microcontroller. The idea is when I press the user button, the bootloader jumps from the main application (0x08000000) to the second one (0x08080000).

The second firmware is just a blinking LED application. The jumping is fine and the LED starts blinking, but my problem is that when I want to go back from the second application to the first one (0x08000000) the exti won't work!

Here's my code:

First firmware:

if (((*(__IO uint32_t*)APPLICATION_ADDRESS) & 0x2FFE0000 ) == 0x20000000)
{
    /* Jump to user application */
    JumpAddress = *(__IO uint32_t*) (APPLICATION_ADDRESS + 4);
    JumpToApplication = (pFunction) JumpAddress;

    /* Initialize user application's Stack Pointer */
    __set_MSP(*(__IO uint32_t*) APPLICATION_ADDRESS);

    __disable_irq;
    SCB->VTOR = FLASH_BASE | 0x80000;

    HAL_RCC_DeInit();
    SysTick->CTRL = 0;
    SysTick->LOAD = 0;
    SysTick->VAL = 0;
    __set_PRIMASK(1);

    printf("Starting Firmware 2 . . .  \r\n");
    HAL_DeInit();
    JumpToApplication();
}

The beginning of the second firmware:

  SCB->VTOR = FLASH_BASE | 0x80000;
  __set_PRIMASK(0);
  HAL_Init();

  SystemClock_Config();

  HAL_InitTick(1);

...

This is the exti callback from the second firmware:

void HAL_GPIO_EXTI_Callback(uint16_t GPIO_Pin)
{
    HAL_NVIC_ClearPendingIRQ(EXTI15_10_IRQn);
    HAL_NVIC_DisableIRQ(EXTI15_10_IRQn);

    if (GPIO_Pin == GPIO_PIN_13)
    {
        if (((*(__IO uint32_t*)APPLICATION_ADDRESS) & 0x2FFE0000 ) == 0x20000000)
        {
            JumpAddress = *(__IO uint32_t*) (APPLICATION_ADDRESS + 4);
            JumpToApplication = (pFunction) JumpAddress;

            __set_MSP(*(__IO uint32_t*) APPLICATION_ADDRESS);

             HAL_NVIC_DisableIRQ(EXTI15_10_IRQn);
            __disable_irq;
             SCB->VTOR = FLASH_BASE;
            JumpToApplication();
        }
    }
}

Why is this not working?


texts: Is it the right use of the RTC RV8523 to wake up an atmega328p?

texts:
I'm using the RV8523 to wake up every 2 minutes an arduino atmega328p. The rtc is wired like this :

Where INT1 is wired to Port D pin 3. The internal pull up resistor is activated and yet it's working properly. It wakes up sometimes every 2 minutes but sometimes not.

There is the code to program the RTC :

#define I2C_ADDR (0xD0 >> 1)

#define TIMERA_CLK 0x03
#define TIMERA_PERIOD 0x02

void Rtc_init()
{
    Wire.beginTransmission(I2C_ADDR);
    Wire.write(byte(0x00)); //control 1 register
    Wire.write(byte(0x00));
    Wire.endTransmission();

    Wire.beginTransmission(I2C_ADDR);
    Wire.write(byte(0x01)); //control 2 register
    Wire.write(byte(0x02));
    Wire.endTransmission();

    Wire.beginTransmission(I2C_ADDR);
    Wire.write(byte(0x02)); //control 3 register
    Wire.write(byte(0x00));
    Wire.endTransmission();

    Wire.beginTransmission(I2C_ADDR);
    Wire.write(byte(0x10));       // Timer A Clock register
    Wire.write(byte(TIMERA_CLK)); //
    Wire.endTransmission();

    Wire.beginTransmission(I2C_ADDR);
    Wire.write(byte(0x11));          // Timer A register
    Wire.write(byte(TIMERA_PERIOD)); //
    Wire.endTransmission();

    Wire.beginTransmission(I2C_ADDR);
    Wire.write(byte(0x0F)); // Timer & Clkout register
    Wire.write(byte(0xBA)); //
    Wire.endTransmission();

    pinMode(INT, INPUT_PULLUP); // <== Sleep mode from RTC

    delay(100);
}

ANd there is the "main" code :

#define INT 1
void setup()
{

    Serial.begin(9600);
    while (!Serial){;}

    mySerial.begin(9600);

    mySerial.println("Start ");

    // Setup RTC
    Rtc_init();
    mySerial.println("RTC Init Done");

}

void loop ()
{
    mySerial.println("\n\nWAKE UP ");
    delay(1000);
    mySerial.println("\n\nGoing to sleep");
    mySerial.flush();

    attachInterrupt(INT, Push, FALLING);
    LowPower.powerDown(SLEEP_FOREVER, ADC_OFF, BOD_OFF);
    detachInterrupt(INT);
}

void Push()
{

}

All the library are included and there is the signal from the rtc interruption pin (INT1) :

If you have any clue to guide me to the right direction for debugging, I'm out of ideas :-/

EDIT : I should precise the atmega is powered up by a 3.3V voltage just like the RTC.
EDIT 2 : The signal visible on the scope repeat correctly 1 times every 2minutes BUT the atmega doesn't wake up :


texts:
To my understanding the reactive components in a converter should not store energy over a switching period, otherwise they will blow up. An in inductor for example abides by volt-second balance, which translates to zero average voltage over a switching period- no flux linkage/ no average energy stored.
That being said, the inductor current waveform will be switching at rate Fs ( switching frequency) and will introduce a ripple on the current waveform.
Now if we consider the transient time of buck converter. There will be no energy stored in the capacitor by the inductor at t=0.
My question is how do we calculate the transient time of the buck converter? And what is the circuit analysis reasoning were the inductor current increases and settles at a DC offset? (Why doesn’t the waveform ripple go back to zero at period [DTs - Ts] - how does the capacitor hold the charge in period [DTs-Ts] and not discharge through the load connected on the output terminals


texts: Are fins necessary/required for cooling in a closed room

texts:
i am trying to design an efficient cooling solution for my project.
I planned placing a IoT computer in an aluminum housing which is completely closed.
In this case, do I really need fins and large surface areas INSIDE the aluminium housing when my main goal is to dissipate the heat to the housing itself as fast as possible?
I'd really appreciate your help!
Here is some more information:
Ambient temperature: 25-30 degrees celsius
Max. Power: 10W
Time Period: The device is intended to work 24/7 (of course NOT with max. Power but with 20-30% of what's possible. However I think that a great product is designed to also handle 100% Power over a vast period of time!
Internal temperature: The CPU itself (surface area of 10mm x 10mm) reaches a max of 80 degrees.
Surface area of the enclosure: 0,05735 m2
Enclosure material: Aluminium sheet metal (1mm thickness)
Space between CPU and inside of the enclosure: 14mm
Maximum Volume of the Heatsink: 60cm3


texts: Circuit Testing, Verification & Certification Standards for Biomedical Devices

texts:
Please note: I would have posted this question on HealthIT.SE but they are apparently now closed for business, and I believe this site is the next most appropriate place to ask this. I believe this question is on topic because it involves circuit verification and certification.

I'm very interested in the open source OpenBCI device and the bevy of apps and devices I could see it allowing integration with. Their open source license allows derivation (provided attribution), and I think this is going to open up flood gates with respect to commercial devices that build off of its hardware design.

In the commercial domain, I was curious as to what regulations/standards may come into focus for any companies selling OpenBCI and/or hardware componentry built up off of the OpenBCI mainboard. I ask because the biodata being streamed from the OpenBCI is EEG (brain wave) data, EMG data, EKG data, etc... this may very well constitute biomedical data that may be protected by things like HIPAA, etc.

I've heard of IEC 6061 but that is the only biomedical/technical safety standard I'm aware of.

So I ask: if I was building a commercial device that used OpenBCI as its core, and that was streaming EEG/EMG/EKG data from it, what sort of standards (besides IEC 6061) might I have to have the electronics verified/certified to?


texts:
I'm working on setting up a heater bed for my 3D printer, and looking for some help / sanity check on adjusting the heater input.  I've got a Kat's Automotive Heater pad (150W, 4" x 5") attached to an aluminum print bed.

My problem is that the 150W heater is too hot.  I'd like to have a 50W heater, but haven't found one the right size (plus I have this one on hand).  So I'd like to add a resistor inline on the cord to make this approximately a 50W heater.

I believe that I need to add a ~200ohm resistor to the circuit.  My reasoning is it's a 150W, 120V device.  My electronics knowledge is very rusty (20yrs since I've had an electronics class...), but if I recall, Watts = Volt * Amps, so I'm expecting 1.25 Amps across the device.  Using those values and V = IR, that means there's 96 ohms in the system, which I'd expect to be the heater pad itself.  If I want 1/3 of the Wattage across the heater, I need 188 (~200) ohms added in.  That should reduce the amps across the circuit to ~0.4 amps across all components.

So, my plan is to hop down to the local friendly Radio Shack, purchase a 200 ohm resistor, cut my wall outlet cord, and solder the resistor inline.  Problem is, what I see online seems to be mostly 1/2 Watt rated resistors.  I should have ~32 watts across this resistor.  Does that mean I need to find a 200 ohm, 50 watt resistor?

Thanks in advance!


texts:
hello to all,

I'm working on I2C Based Communication Device bq27742-g1(Texas Instrument) Battery fuel gauge which is Slave Device address is 0xAA. I have put in the 10K pull up resistor.

In this I'm using Kinetis series Cortex M4 micro controller as Master device.
The microcontroller works with another I2C device.

I have tested the bq27741-g1 Battery fuel gauge with an MSP430 Launchpad board using I2C scanner and it works fine.

I have attached screen shot of CRO Signals (SDA(PINK) SCL(Yellow)) of I2C Device in the 9th clock pulse of SCL when SDA have undetermined state. Why does this occur at this level?  Is this issue from the pull up resistor?


texts:
I have an Atmega328P MCU that is driving a stepper motor driver using its digital I/O. However, I'd like to use the same pins to drive the motor externally as well possibly using a different MCU or hardware. When the external driver is driving the motor using these same pins, the Atmega328P MCU maybe powered down and its state would be unknown. I know that its not safe to drive the Atmega328P MCU's pins with logic levels when its powered down and it will in fact destroy the chip.

To overcome this, I thought of adding low power Schottky diodes between the Atmega328P MCU's pins and the motor driver inputs (as shown in the image). Would this be ok or can any one recommend a better solution? I know I could use an optocoupler but I do not space on the board for placing so many of them.

UPDATE: This is what I'm finally thinking of doing (see image). The buffer chosen here can sustain upto +6.5V on its output terminals when powered down. I also realized that even when an external logic control is used, the board still has to be powered on for the motor drivers to work. This means that the onboard Atmega would also be powered on. However there is the possibility of the user inadvertently forgetting to power on the board before plugging in an external control source. In this case the onboard Atmega would experience 5V on its I/O pins when its powered down which obviously is not good. These buffers take care of that.


texts: Analog dinosaur needs simple buzzer when timed power source ceases

texts:
OK, as my profile states, my electronics knowledge is extremely limited and so is my use of correct terminology and symbology considering I come from a mechanical background.

I'm adding liquid agitation to my 3D printer's modified wash station, and I'd like to add an audible signal when the timed wash cycle is complete.  I have a cheap timer from Amazon that does what I want based on my breadboard experiments.

To keep things simple I'm using all 12VDC components.

What I had in mind was to use the 12VDC that runs the agitators to also charge up a capacitor that will be used to activate the alarm when the power is discontinued at the end of the wash cycle (typically 15-minutes).

My idea is to use a 12VDC automotive relay (have plenty) to hold open the switch contacts when energized.  When the wash cycle is over, the switch contacts close dumping the capacitor's charge to the alarm for 10 - 30 seconds.  Would my simple circuit do the job?

At this point in time I have no idea what the Farad rating of the capacitor or the OHM's value of the resistor or potentiometer should be.

Now that the holidays are over and life (e.g. unexpected house repairs) have been completed for the time being; I have had a chance to calculate and understand this stuff better, or at least I think so.  Thanks to 'Transistor' for the 'Must Calculate' link!

I have two buzzers in mind that I found at Digi-Key.  CPE-253 or CPI-42533C-120.  For a 10-second discharge I calculated anywhere from 5mF to 11mF depending on the buzzer.  I can get those capacitors at Digi-Key for reasonable prices; but I see what both of you're saying about needing a big capacitor.  The buzzer might be omitted.


texts:
My circuit does not work as I thought it should and I'm really confused now.

What I want?
Two LEDs which will pulse to audio LEFT and RIGHT channel separately.
And same for display BACKLIGHT, but there is going to be SPDT switch, which will switch between direct voltage or voltage from transistor - in order to react to sound.

So far I have this:

 .

1.) It works when I don't use power supply of GameBoy but external for the circuit.
This is what it looks like

2.) LEDs with no transistor will light UP when I use GameBoy power supply.

3.) Somebody told me before to put ground from audio to actual ground, not to emitter, but it works like that. When I tried to connect it to ground it stopped working. But still don't know why it works with audio ground on emitter.

4.) It is really weird, but when I switch the switch, it works as expected, BUT it switch LEDs not BACKLIGHT.

I really can't find any logical explanation in my head. I started with electronics few days ago, so there must be things I cannot see.

Thanks in advance!


texts:
How to mark unused components in Orcad?

Often there are resistors/capacitors/other-components that you don't want to be assembled in the final product, but you wish to leave them in the schema in order to apply different features of the product at other times.

What kind of field should I add to the component and how to do that technically?


texts:
I'd like to power up a PCB that I'm design with USB-C. The main reasoning is that the connector is low-profile, reversible and can carry 5A at 5V. This PCB will have an ATmega2560 chip onboard, which will be programmed via USB.

What do I need to take into consideration to do the following:

1) Power the PCB via USB-C, providing 5A (where possible)

2) Use the USB-C to program the chip

Does some sort of negotiation need to be done between the sink (my PCB) and source (wall transformer)? Alternatively, can I just read the necessary voltage on one of the CC pins? Also I only need to use the D+ and D- lines of the USB-C as I only need to run at USB2 speeds.

As an aside, this similar question mentions:

  Keep in mind that a typical Type-C receptacle needs a thin PCB (0.8 mm), which is fairly inconvenient for DIY projects

I can't see any mention of that in data sheets I've seen. Any further info?


texts: Recommended first steps with the BeagleBoard

texts:
How can I easily start off professional development with the BeagleBoard XM?

Which OS should I work with? .. my choices include:

Ubuntu
Android
MeeGo
WinCE
QNX
Angstrom  (preinstalled)
Symbian
Gentoo

How do I install an OS onto the board?
Which IDE do I use?
How do I debug or run my code on the target?

I bought a brand new Beagleboard XM to interface to a camera module, capture video and do some image processing. The camera uses an 8-bit parallel port interface to transfer images.

What do you recommend?


texts: What will motivate me to provide an isolation boundary in a motor controller?

texts:
This Analog Devices technical article describes a motor controller that uses their digital isolators to provide an isolation barrier between the 3 phase bridge/DC bus and the microcontroller.  It is mostly about how digital isolators are better than optocouplers, but they do mention this:

  The motor
  power electronics are floating at high voltage potentials
  while the ADSP-CM40x processor is referenced to earth
  ground, thus the need for isolation.

I have designed similar circuits, but I always tie the negative DC bus voltage to the same ground as the microcontroller.  In this way I can measure the DC bus directly, and my pwm outputs directly drive the FET drivers.

Edit:
In other words, I have earth referenced the micro and the DC bus minus.  Now the motor works from earth gnd to whatever DC+ is.

Can anyone discuss the advantages of providing this isolation?  I realize you would protect your microcontroller if you had some failures in your power stage, but you'd be replacing so many components at that point it isn't likely to matter.  Someone could probably also make an argument for not putting all the motor noise into your microcontroller ground, I have seen this problem trying to communicate over usb while driving a motor.

What else you got?


texts: I am currently controlling 120VAC solenoids with panel-mounted switches. Each solenoid controls the air line for a single disk brake. Now I need to incorporate an NI CompactDAQ. My boss has asked that the solenoids can be controlled either by the DAQ's digital control module or the panel-mounted switches we are currently using. The picture below is a simplified diagram of what I want to do. What is the best way to do this?


texts: Powering Thin Client PC from car's battery

texts:
I have a thin client PC manufactured by HP (t5720). The following specs are written on the power supply:

Input: 100-240V AC 50-60Hz   2.4A(2,4A)
Output: 12V DC  4.16A(4,16A)
Max Output: 50W

I would like to use the thin client in my car, but don't have any power supply for it. Now my thoughts and questions:

Do I even need some special transformation device as the supply's output is around 12V? The car has between 10.5 and 13 V, depending on whether it's running or not. How tolerant is a device such a thin client? Could this actually damage the car?
If  I actually need some transformation, what would it be?

There are websites selling such transforming supplies. But some of them cost a lot of money and before buying something I would like to know whether I even need it.

And I wouldn't want to just try it out and plug the thing in before I know what could get damaged. I have some very basic knowledge about electronics but I can't estimate it.


texts:
Question:

  A DC Motor, when supplied from a 195V power supply is observed to rotate under no load conditions at 1730 rpm. A stall test shows that the winding resistance is 1.66 Ω. The motor is connected to a load whose torque-speed characteristic is Torque = 0.128 × ω.

  Find the speed (in rpm) at which the motor will drive the load.

So far, I have tried to use the following method:

$$\ K= \frac{V}{\omega} = \frac{195}{1730*\frac{2\pi}{60}} = 1.0764 $$

$$\ Torque= K*I = 1.0764* \frac{195}{1.66} = 126.4446 $$

And from the question, \$Torque = 0.128 \omega\$

$$\ \omega = \frac{126.4446}{0.128} = 987.85RPM $$

Can anyone tell me why this is wrong?


texts: Getting started with PCB Layout for BGA Packages

texts:
Are there any good resources for learning the intricacies of PCB layout when dealing with BGA packages?

I'm very familiar with layout for almost every SMT part that has leads on the edge (QFP, TSSOP, QFN, etc...) However, I have not ever had a chance to work with BGA parts because of the difficulties involved in their assembly, as the shop where I work does not have the facilities to do so.

Anyways, I've been looking into farming assembly out, and am hoping for some reference material for dealing with BGA devices.

I'm interested in both general and specifics. Escape routing, blind vias, vias in pad, SMD pads vs NSMD pads, filled and open vias, etc...

I've done a lot of sporadic reading (blogs, mainly), but am missing the bigger picture, namely how different techniques interact and a lot of basic common sense knowledge that likely comes through actual experience, even if only by proxy.

So far, I have spent some time studying any open-source project that uses BGA I can find (the BeagleBoard, Mainly) but most open source projects are not at the level of complexity that requires a BGA device, and the ones that do are rather rare.


texts: AD8217 High Side Current Sensor Output at Low Currents

texts:
I am using an AD8217 high side current sensor to measure currents up to 20A.  It works as expected when testing with lower currents and sense resistors of 1\$ \Omega \$ and 0.3\$ \Omega \$ and currents of 660mA and 130mA.

For the eventual 20A, I will need to use a 5m\$ \Omega \$ sense resistor.  The output of the AD8217 is not what I expect using this resistor and the 660mA or 130mA currents.

At 130mA, I expect an output of 13mV but I measure 34mV.  At 660mA, I expect 66mV but measure 115mV.

Directly measuring the differential voltage across the sense resistor looks right (e.g., 3.3mV with 660mA which should produce an output of 20 x 3.3mV = 66mV).

The application note (https://www.analog.com/en/analog-dialogue/articles/high-side-current-sensing-wide-dynamic-range.html) says that a differential voltage across the sense resistor of at least 1mV is fine.  I don't think that the AD8217 offset voltage or bias current can account for what I am seeing.

Thanks for any ideas.

This is the circuit I am using with a 12.5V battery, either 18\$ \Omega \$ or 100\$ \Omega \$ load resistors and 0.3\$ \Omega \$, 1\$ \Omega \$ or 0.005\$ \Omega \$ sense resistors.