texts: Why are external AC/DC adapters almost always single supply rail?

texts:
If I have a product that requires several voltage rails internally, why does it make sense for my external power supply to only source a single rail.

For instance, if I have a product requiring the following DC supply rails internally

5V @ 2A, 10W
3V3 @ 4A, 13W
1V8 @ 4A, 7W

and having an external AC/DC adapter, what are the reasons for generating a single higher voltage (e.g. 24VDC @ 1.25A, 30W) within the adapter when I would still need to step that voltage down using 3 DC/DC converters within the product?

The benefits I see for two stage regulation are,
- Better line regulation due to two filter stages
- Lower cost for DC power entry plug/socket and cable due to fewer conductors
- Lower cost for DC power entry plug/socket and cable due to lower current rating
- Better line/load regulation due to colocation of supply and load.
- Reduced noise cross-coupling due to single voltage in cable

The benefits I see for single stage external regulation are,
- Lower BoM cost due to removal of one regulator stage
- Increased power efficiency from removal of one regulator stage
- Increased thermal performance due to removal of one regulator stage
- All regulator losses occur outside of the product
- Reduced product size due to removal of regulators (within the product)

Is there anything else I've missed?

If a products primary design constraints are size and heat dissipation, why wouldn't this be the logical choice?


texts: Why is pin number 7 GND and 14 VCC in 7400 ICs ( logic gate ICs) ? Could the designer have put VCC and GND in some other pin number? Is there a constraint for that specific number? (Except a few cases, like 7490, Please consider gate ICs for example)


texts: Does putting solder mask over a ground plane influences its heat exchange with the air?

texts:
If you want the best thermal exchange with the air, is it preferable to leave a thermal/ground plane raw or to cover it with solder mask? And how important is the difference?
(Dave from EEVblog is pretty self-confident saying it's more efficient without solder mask: https://youtu.be/q3RhWuXFixU?t=782)


texts: Can I communicate with any sensor/device using a transceiver if they use the same frequency?

texts: If I have a transceiver using 868MHz and connect that to e.g. a Raspberry Pi and start reading from it, will I be able to see all traffic on that frequency happening nearby? So if I have a sensor that is sending some data periodically on that frequency I will see it somehow?


texts: I'd like to know that by soldering a circuit board, what causes the potential difference between the soldering iron and the board. Is it just static electricity (like by hands), or is the power source of the soldering station involved somehow?


texts:
I'm working with a PIC32MX564F128H in MPLABX 2.35 with pickit3. I'm trying to parse a message from UART. The character is received properly, but I'm stalling when I attempt to copy a character to a buffer. This is the part in my main loop:

                unsigned char*buffer="efg"; //dummy string
                GetDataBuffer(buffer, 3);

_

  UINT32 GetDataBuffer(unsigned char *buffer, UINT32 max_size)
    {
        UINT32 num_char;
        num_char = 0;

        while(num_char < max_size)
        {
            UINT8 character;
            while(!UARTReceivedDataIsAvailable(UART1));
            character = UARTGetDataByte(UART1);
            if(character == '\r')
                break;
            *buffer = character;  **\\PROGRAM STALLS HERE**
            buffer++;
            num_char++;
        }
        return num_char;
    }

Symptoms:

In debug mode, after unsigned char pointer declaration: buffer address: 0xA0008010 Value: Invalid Address

After being passed into GetDataBuffer: buffer address: 0xA00071F8 Value: 0x9D005ED8 *buffer=0x65 ("e", at this point not written over.) Continuing, program stalls at point shown above until the debugger halts at an unknown location.


texts: PID control at small PWM values for a DC motor

texts:
I've set up a PID controller to control the shaft position of a brushed DC motor that I control via PWM and an optical encoder. I'm basically reconstructing an RC servo.

Now that I think I've found the correct tuning parameters (all three parameters non-zero), I'm facing with another problem: the shaft arrives at the desired angle with some approximation (look at the black stick at https://www.instagram.com/p/BTg25HngIDo/), then stops moving further. I hear a "buzzing crescendo" from the motor, that ends after some seconds with it moving a little further, but now too much. So there's another buzzing crescendo, and so on. It almost never reaches the target angle exactly.

By looking at the output/error output, I see that during the buzzing the controller is sending small PWM values, too small to start the motor (as I could experiment by myself, see https://www.instagram.com/p/BQYBZsShq9x/). I guess this is some kind of non-linearity, while a PID can only work with linear processes. Because the motor is stopped at a nearby position, the error accumulates in the I branch and so does the output, until a threshold is reached.

What is the usual approach to solve this issue? I'm thinking about linearizing the output as suggested in this answer (i.e. implementing a "dead zone" function so that the motor never receives small PWM values), but I'm worried that the linearizer will add more independent variables in the system.


texts: I can't communicate a subcircuit wiith the main sheet through bus cables

texts:
how are you?. I'm doing a project in Proteus whose I wanna do it as modular as possible, from the principal sheet I've an LCD screen (see the Image 1 and Image 2)

and its terminals are been  moved with bus cables to a subcircuit and inside the subcircuit I put another bus named as the terminal bus on the external part of the subcircuit, dimensioned to manage all the necessary signals.

Inside the subcircuit (se Image 3) all is connected but when I run the simulation the LCD terminals in the main sheet appears floating which means that the interconnection doesn't be made apparently by an error of mine, if I use normal terminals for one connection then the simulation works fine.

How can I solve the problem with the bus cables.

Thanks in advance for the help.


texts: How to use Altium Multi-Board to define SODIMM board and socket connections?

texts:
I am attempting to use Altium 18.1.9's new "Multi-Board" feature to connect a 200-pin SODIMM board ---> to a SODIMM socket connector ---> on my mainboard PCB. This Altium article is just about the only documentation I can find on how to go about doing this, and I don't think it explains what I need.

For the SODIMM board, I have created the schematic library symbol with all 200 unique pin names and functions. I have not created a PCB library footprint for this board, because I did not design the board, and I'm not sure I even need a footprint.
For the 200-pin SODIMM socket connector, I have created the schematic library symbol and PCB library footprint layout, which will connect (1) to (3). I added the "System: Connector" part parameter as shown in the Altium doc link above.
I have created my mainboard schematic (which includes the SODIMM connector), created the PCB, and placed the SODIMM connector footprint on it. Because of adding the "System: Connector" parameter in (2), I can see the connector in Altium's Multi-Board schematic project:

I am not sure what to do next. Should I create a new PcbProj just for the SODIMM board, add it to the PrjMbd, and define the SODIMM board as a "System: Connector"? Do I add another SODIMM socket to that project also?

I have no idea what to do next.


texts:
I've designed some PCB's in the past but never really had to worry about load and safety. Now I need to build a small PCB with some 230v AC cirquits. The load will be minimal, but still I have healthy respect for working with AC voltages.

What I need is a few simple push button switches that send an impulse to a connected device. the load here will be about 0.5 Watt.

1) I'm assuming this can be done on a PCB. How do I go about figuring out how wide to design my tracks and what are safe distances?

2) are there any really small push buttons out there (in the 6mmx6mm range) that are able to deal with these voltages? everything I find has contact ratings at 12v.

Thank you for your advise!

EDIT:
Let me add some context.
I have a bunch of in-wall-switches that I've upgraded to smart switches by adding a Sonoff Mini behind them in the mounting box.

in this setup the original switch functions as signalling switch to the Sonoff, on the Sonoff the swich port is 3.3v DC (i think, might be 5v).

So far, so good.

But, because the space in some of my mounting boxes is very limited I can't always do it like this because the combination of switch plus sonoff is just too deep to fit.

Here comes my project. I've designed and 3d printed a setup that replaces the switch with a plastic contraption that allows mounting of the original switch face plate and that houses 2 micro switches. This saves 15mm of depth compared to the original setup and works great!

All was good in my life.

Now i want to do the same with a Shelly dimmer which is connected thus:

So, the Shelly switch port functions at 230v AC. I contacted Shelly, they gave my the 0.5w specs. (i will measure myself when i receive my dimmers). clearly I can't just hookup my jig now.

So, i'm looking to come up with a solution for this limited space, potentially 230v setup problem. preferably i will over engineer it, because, you know... I can :)


texts: opamp comparator circuit question battery discharger tester arduino

texts:
http://forum.arduino.cc/index.php?topic=8377.0

I have wanting to build a battery discharger/tester for age. I saw this circuit years ago, and thought it's great, but was too complicated to me to build back then. now I come back to this, and I have few questions for this circuit design.

why there isn't a current limiting resistor between the output of the op-amp and the base of the NPN? and won't this current from the op-amp added to the total capacity of the battery?
D2 is the voltage reading point. It uses a 0.5 ohm resistor as current sensor. if the discharging current is 500ma, then the voltage is v=IR= 0.5A * 0.5 ohm = 0.25v; 1A>0.5V; 100ma>0.05V; For an arduino analog pin with limited resolution.(5-0v 1024; 5/1024=0.0048v) How accurate will it be?
A relay is used to end the discharging process. Will it be more simple by using a LOW digital output on the base of the NPN instead? Or maybe it's also okay to use a LOW digital output on the Vref of the op-amp?


texts:
I'm trying to design RTD measuring for industrial use which has EMI/EMC/ESD.
I have 3 wires input to the board.

obviously 3 wires out of the board are going to 3-wire configuration PT1000
 1- 3V3 (RTD 1)
 2- B   (RTD 2)
 3- B   (RTD 3)

Vout is going to MCU ADC
in second image i attached you can see i have different resistor for op amp gain.

and what I'm thinking of is the following:
1- add capacitor for (B) before the (+) of LM358 to filter noise
2- add 3 TVS diodes to the 3 wires (to GND)
3- add current limiting 10k resistors before the RTD sensor (as shown below)
4- no 10k resistors but add PTC fuse on the 3v3 rail to the sensor to protect shorting?

Protection Questions:

is protection with TVS is required actually?
do you see any flaw or mistake in the circuit, any suggestion is welcomed.
i don't know if industrial designers protect all inputs/outputs from applying certain level of voltage like +-24v? or it always
depend on the project and i don't need to think about it here. so
should i think about it here?

wheatstone Questions:

every time the wire length (going to RTD) changes will need to change
software compensation variable?
as you can see I'm simulating the circuit but is't practically going to work efficiently?


texts: Bluetooth 24 Pin IC Identification - 1942UDZ - GEP5436.69 - win-668 - Logo

texts:
I'm trying to identify the 24 pin Bluetooth IC below. Google returns nothing related. Any clues would be much appreciated. Maybe even the manufacturer logo would be a start AA, AV, VV, VA?

The chip shows up with the name "win-668" when connecting via bluetooth.

Thanks.


texts: Help designing an inverse polarity and overload (crowbar) protection circuit

texts:
There are some great resources on the internet and on this site about designing various protection (crowbar) circuits. For example, Leon's answer to a general circuit protection question.

I'm looking for a little more specific advice on selecting type of components and/or values for my application. I'm a little confused about whether to use a standard fuse or a PTC fuse; whether to employ a Schottky diode or a simple rectifier diode...

Currently my prototype is built on a 2-layer PCB and uses an AMS1117-5.0 voltage regulator (SOT-223 pkg) for 5 volts. It uses about 32mA on average (fluctuates between 22 and 42mA). I'm not sure what the startup current is or how to measure it.

Based on the datasheet for the regulator, with a dropout voltage of between 1.1 and 1.3, I am speccing the device as requiring between 6.3 and 15 volts. (If I use a Schottky, I'll need to increase the minimum accordingly.)

What I would like to accomplish is the following:

Protection against inverse polarity
Protection against overvoltage and overcurrent (exploding parts, fire, etc.)

Typical operation will utilize 6 series AA cells, either NiMH or Alkaline (7.2 to 9V). These have current capacities of 2300-2500 mAH (though I'm not sure if such cells can actually deliver more than 2.3 to 2.5A).

I'd like for polarity reversal to do no damage and not require a fuse replacement. Overvoltage and overcurrent conditions can blow a fuse. I'd also prefer a minimum of parts and cost as another design goal is small size. Surface mount components preferred.

Current schematic with no protection:

So my question is thus:

Of the components: Schottky diode, rectifier diode, "normal" fuse and PTC fuse; what combination of these (or other suggestions) would best serve my requirements?
What criteria should I use to select appropriate values?

It's been suggested here and elsewhere that doubling the normal current use may be a valid starting point for selecting a fuse. I found a Littelfuse 1210L005 resettable PTC which has a hold current of 50mA and a trip current of 150mA, but I am not sure if these are desirable values.


texts:
I want to temporarily solder a pin on my pcb where I know for a fact that it's going to be moved soon. Is there a better way? Is there like a plastic piece I can attach to the other side of the exposed wire that will allow me to temporarily attach this wire there?

I realize that's where a bread board is used but unfortunately I'm doing testing on an existing PCB and I don't want to keep applying solder only to have to remove it.


texts:
This is a question following on from my previous one "How can I improve my testbench for testing a 1024x4 RAM memory in Verilog".
Basically, I have modified the previous solution in an attempt to test a 1024x4 RAM memory, which uses coincident decoding and was implemented using gate-level description.
I have modified the code to use a for loop to run through the coincidental addresses of the decoders, for both the write and read operations.
My test bench works with regards to the write operation and as long as the read portion of the code  is commented out.
Please see code below:
module tb_RAM_1024x4();
wire  [3:0] Mem [0:1023];
wire  [3:0] DataOut;
reg   [3:0] DataIn;
reg   [4:0] X_Address,Y_Address;
reg   Enable, ReadWrite;

RAM_1024x4    M0 (DataOut, DataIn, X_Address, Y_Address, Enable, ReadWrite);

  initial begin
  Enable = 0;
  DataIn = 4'b0000;

  #10 ReadWrite = 0;

  end

  // Write random data to specific addresses
  initial #28830 $finish;
  integer  i, j;
  initial begin
     for(i = 0; i < 32; i = i + 1) begin
        #5 X_Address = i;
        for(j = 0; j < 32; j = j + 1) begin
           #5 Y_Address = j;
           write(X_Address, Y_Address, $random);
        end
     end
  end

//      initial begin
//      Enable = 0;

//      #20 ReadWrite = 1;

//      end

    // Read data from specific addresses
//      initial #28830 $finish;
//      initial begin
//         for(i = 0; i < 32; i = i + 1) begin
//           #5 X_Address = i;
//           for(j = 0; j < 32; j = j + 1) begin
//              #5 Y_Address = j;
//              read(X_Address, Y_Address);
//           end
//         end
//      end

 task write (input [4:0] addr1, [4:0] addr2,[3:0] din);
    begin
       #20 X_Address = addr1; Y_Address = addr2;
       #1 Enable = 0;
       #2 Enable = 1;
       DataIn = din;
    end
 endtask

 task read (input [4:0] addr1, [4:0] addr2);//, [3:0] dexpect);
    begin
       #20 X_Address = addr1; Y_Address = addr2;
       #1 Enable = 0;
       #2 Enable = 1;
     end
  endtask
endmodule

Also provided is the waveform for the write operation. When the read portion of the code is uncommented, it affects the operation of the write operation for some reason which i haven't quite figured out.
Therefore, any insight that anyone can provide will be very much appreciated.


texts:
I am trying to understand the MOS-Capacitor band edge shapes. When negative voltage is applied for gate, why does the band edge across the insulator shift upward (and linear decreasing band edge)?  Similarly, when positive voltage is applied to gate, why does the band edge across the insulator shift downward (and linearly decreasing band edge)?

When gate voltage is positive, why does the energy level of metal shift down in band diagram? And vice versa?

I looked up previous questions relevant to this topic and couldn't find this question. Please direct me to that, if you think someone has already answered this question.


texts: Can I emulate BLDC motor torque control with a speed controller?

texts:
I am looking to use a BLDC motor to control a reaction wheel. Since this will be used to provide balancing torques for my system, I really only care about the motor torque, not speed (assuming I stay within the max motor speed). Unfortunately, all of the controllers I can find online are speed-based. Since I do not want to make my own controller from scratch, I am wondering if I can simply integrate the desired torque profile to get a velocity profile, and command that velocity profile to the controller. The quality of this controller will depend on how smoothly I can change the velocity profile, the settling time of the speed controller, overshoot, etc.

Will these factors, among others I have not considered, significantly degrade the quality of the torque controller? The (much simpler) alternative I am considering is just using PID control on the PWM of a standard ESC.

For reference, I am looking at using something like TI's DRV10975 controller. I am avoiding general hobby ESCs because I cannot find specifications for converting signal-in to torque or speed output. Though I might be able to tune a controller that is stable, I would prefer to have a sound mathematical model to tune/debug.


texts:
Ethernet up to 100Mbps uses only 2 of the 4 twisted wires in an ethernet cable while gigabit is using all of them. Connecting an LED to one of the gigabit-only pairs should therefore make it easy to detect a gigabit transmission.
Well, actually not. Problem is, that PoE may or may not be used, the ethernet data is AC while an "this is gigabit"-led is DC, ethernet has no fixed current and I have no clue what I'm talking about.
I really ain't versed in electronics. A rectifier between ethernet and the LED would solve the AC problem, but this can't be the whole solution. Ethernet has no fixed voltage as described in here. Is there a module that counters fluctuation in a way that the LED gets the power it needs? Even with the low energy from a ethernet cable? If yes, would this work with PoE injection on the unused wirepairs as well?
Background: An intrusion detection system based on Microsofts ATA has to have a physical connection to the network so I've built a network tap with a maximum throughput of 100Mbps. I forward only two of the wirepairs, forcing any network clients to use a maximum of 100Mbps. This may obviously cause a giant bottleneck, but while not preventable, I would at least like to know when this is a problem. A litte status LED would be nice, flickering upon gigabit data connection.
First post and glad about criticism. Thanks


texts: Why do i have a high DC component at the output of this circuit?

texts:
I want to create an sine wave from a uC PWM with a very low DC offset. I did some research and decided to simply make a Band-Pass filter, composed by one pole passive High Pass Filter, to filter the DC component, followed by an active 3-pole sallen key filter to make the square wave sine-ish.
The result is the circuit in the figure bellow.

At the breadboard i didn't face any significant problems, i got a wave with a good sine shape and with a low dc offset(10mV), but now on the PCB i'm having a significant DC offset (100mV) at the output. I tracked the signal with oscilloscope and this DC shows up right after the HP filter, in the node between R25 and R26.

Does anyone has a hint on what is going on and how can I reduce it?

Edit: PCB  layout added. I applied the cooper plan in top and bottom with ground signal. I placed several vias to avoid  the ground loop.


texts: Will using a resistor in series with a LED to control its voltage increase the total energy expenditure?

texts:
This might sound like a stupid question, but I want a confirmation. I watched a video on Youtube about using LEDs. Those LEDs required a voltage around 2 volts at 20 mA.

In order to power one LED using a 5 volts power supply, the author used a resistor in series. He calculated he needed around 150 ohms (using U=RI, 5-2=3 volts, 3V/20mA=150ohms).

What I find disturbing is that the resistor, in order to control the voltage must be consuming energy too. P=UI, so 3x20mA=60mW, on top of the LED 2x20mA=40mW. In other words, adding +150% energy consumption to the actual need for lighting up the LED.

Am I missing something or is it typical to spend extra energy just to be able to use electronic components that require a lower voltage?
And second question, is there a way to avoid doing it for this type of circuit (5V source, 2V LED)?

-Remarks-

I use the term of voltage instead of current because this is how Ben Eater in his video presented it
I am mostly interested in the general issue of using extra components in order to reduce consumption locally while introducing a waste when taking the circuit as a whole. This is not just about LEDs, which serve here as an example so suggesting this is a duplicate of "How can I efficiently drive an LED?" is missing the main point (although I agree the second part of my question is related).


texts: I have managed to salvage the LCD screen from an old Tom-Tom (the model number of the screen is LTE430WQ-F0B-0BS). It comes with a driver for the screen on the back, but it doesn't look humanly possible to solder/interface with it in any way. However, this driver connects to 4 wires going into the LCD, which look easy to solder. I was wondering whether it'd be possible to skip the driver already there, and simply connect the 4 wires to the GPIO of an Arduino or something similar. I have looked for some time for this solution, but only found data sheets which referenced the on-screen driver.


texts: How to programme constant current of a LED Driver for various current levels?

texts:
I need to design a backlight unit that will change its duty cycle and constant LED current via a microcontroller. My supply is a SMPS with 12V - 20A output. I need to drive 16 * 16 = 256 LEDs(seperate 16 LED strings each combined of 16 LED). LEDs have 2.1 forward voltage and typical current is 60 mA.

Most of the LED Driver chip work in the same way. To output a reference voltage and let us to adjust constant current via an external resistor to flow from. Like this below:

However, once you put the resistor there you are not able to change the current. So, I draw this circuit:

driver chip is lm3410 and analog switch is NX3L1G3157G.

You see, I thought that I can switch between two external resistors via a deMUX this way I will be able to have at least two current levels. And then I can use few of the same configuration to get what I need.(Red circles are external resistors and the switch)

The thing is, I couldn't find any other switch that supports more than 350 mA and 100m Ohm resistance except NX3L1G3157G. And it has only 2 switch. Also, probably I will have to change the LEDs to another one with higher luminance and higher current flow so I will need a switch which can support up to 500 mA. Also, I need 5 current levels like 100% DT(Duty Cycle) - X mA, 50% DT - 2X mA, 33% DT - 3X mA, 25% DT - 4X mA and 20% DT - 5X mA. I could still have managed to do that if we don't need to care for the PCB area, but we do!

Also, I am aware of some LED driver chips provides limited current adjustment register like MC34844 but they do not let more than 30 mA to flow per each channel so useless for me.

So, since I had all my hidden answers from this forum, again, I ask help from other experienced engineers. Do you have any suggestion for my trouble? I need to adjust the current flow through LEDs to 500 mA (20% DT), 400 mA (25% DT), 300 mA (33% DT), 200 mA (50%DT) and 100 mA continuous. Regards.


texts: Bringing compiled device to market (and how to power)

texts:
(Preemptive apology if this is the wrong place to ask; pointers to the right place appreciated)

I've thrown together a device using a Raspberry-pi, touchscreen (plugs into pi) and small monitor type thing which has its own power cord and brick. I've for the time placed everything into a small radio shack project box.

Right now, there is an extension cord with 2 outlets on it that run into the box which the pi and other device plug in to. The idea is that there is only 1 cord that needs to be plugged in for power; would much prefer if there weren't multiple power cabled needed.

This device is not so much to sell for now, but as an adjunct to an existing (very small; read: no budget) business. I have no idea where to go from here. Several google searches for "selling electronic device" etc have provided no help.

I'm trying to determine if there are regulatory or other regulations that this would fall into. FCC? UL? CE?

NB: I'm in the US with no immediate plans to use the device overseas.

Where would be a good place to ask for details? If the answer is lawyer up, what kind of lawyer should I look to talk to?

Also, are there resources I could look to to try and find a better way to power the devices? The Pi is powered via mini-usb and a transformer that came with it (think iDevice power brick). The block did not fit into the project box as it was, so I had to disassemble it. This makes me nervous because fire. What would be the recommended way to break out power from a single cable from wall to multiple devices?


texts:
I am slightly confused about Ohm's law. I understand V = IR, and I did a simple experiment on paper. The results are slightly confusing, so I was hoping someone could tell me if I'm right?

First, I have an input voltage of 5V at 1A. I then pass it through  a 1 Ohm resistor to get 5A at 1V. If I pass it through another 1 Ohm resistor, I get back to my starting voltage and current of 5V at 1A. Is this correct/normal?

simulate this circuit – Schematic created using CircuitLab

Edit: Would this work any better?

simulate this circuit


texts:
I'm wondering something. It's purely theoretical.

Let's say I'm in home automation etc and I've got lots of little modules, for examples to control lights, access codes, doors locks, etc... All these modules uses DC voltage. But houses mostly are wired with AC circuits.

Does it sound ok for you to have some tranformers in the basement, (for example 5VDC/10A, 9VDC/10A, 12VDC/10A) and then wire the house with DC circuits in addition of the classical AC circuit ? Are there some limitation ? (cable length) Or any specific care about ?


texts: Tune L C resonant circuit with semiconductors

texts:
I have an air coupled transformer consisting of a primary L C resonant circuit fed with feedback transistors and a secondary L C circuit feeding a bridge recitfier to power a small circuit over an air gap.
It is almost identical to this circuit: https://en.wikipedia.org/wiki/Royer_oscillator

I also use a FET shorting the rectifier on the secondary side that is triggered occasionally to pass a signal back to the primary circuit.
It looks like this example, the secondary coil and resonance capcitor is on the left, in this case a forked light barrier is used as source of the signal to be transmitted:

The lowered resistance leads to a small change (about 2%) in frequency which can be sensed on the primary side. That worked well in several places, but if the constant power consumtion is higher, it sometimes fails: While the signal is triggered, it tends to overload the primary circuit, giving an trashed non-sine waveform.

However, by changing the capacitance C4 mounted to the secondary resonator, the frequency can be changed easily over a broad range of about 30% without much additional power consumption.

So I wonder if there any way to change the AC capacitance with the FET or some other simple circuit?


texts: Connect Ethernet pairs directly to PCB with 'magnetics' IC instead RJ45 MagJack?

texts:
I'm working in an application where I have to use different connector type system as a Ethernet plug. I did test this already in a single cable inserting this connector in the middle acting as a breakout and it works.
For the final design one of the solutions is to populate a standard RJ45 on the PCB and then make an adapter from the Ethernet plug to our connector system. This should work fine but the problem is that it takes quite a lot of space into the PCB enclosure.
Another solution which would solve the space issue is to use a magnetics IC like this one and solder the Ethernet pairs directly into the PCB board but not sure if this would work fine, I have not seen any working examples/applications of this...
Does anyone know if this last solution (magnetics IC + soldering pairs) would work fine?


texts: Incomprehensible high level interrupt behaviour

texts:
I am a newbie and trying understand how high level interrupts are handled by a microcontroller. I am using a LPC1347 with Cortex M3 CPU. I understand how edge interrupts works but level interrupts has unexpected behaviours.

Until now I thought that a level interrupt is a notification that a device needs attention. As long as IRQ line is asserted we get an interrupt.

LPC1347 has different behaviours. Firstly I have to clear IRQ status which toggles the level type. For example if I set interrupt to high level and change the state of pin to high I get first interrupt, then I clear interrupt status and the interrupt type automatically toggles to the low so the next interrupt occurs when the state of pin toggles to the low. As a result I always have two interrupts; when the state of pin toggles from 0 to 1 and from 1 to 0.

Is this only a different concept of level interrupt handling or do I not understand it correctly?


texts: Need help finding pin layout diagram for GSM module (SIM800c RPi development board)

texts:
I'm having a bit of a conundrum. I bought a SIM800c development board off of ebay but the pins are not labeled at all and I have no idea which pins Rx and Tx are. I really want to hook it up to my COM port and test it out with putty. In case you weren't aware, these GSM modules communicate via the UART in AT commands.

Anyways I do have some helpful hints to solve this mystery. Here is a link to the item that I purchased.

https://www.ebay.com/itm/202041471362

You can see a picture of it on there. I also found what looks like my module along with a pinout->

https://www.itead.cc/wiki/RPI_SIM800_GSM/GPRS_ADD-ON_V2.0#Pinmap

Its not exactly the same as the one that I bought, but its the best thing I was able to dig up. I'm not sure if this is the correct pinout?

I tried hooking it up to some pins labeled "Test pins". There were pins for power and ground, along with two pins, one labeled R and the other labeled T. I thought those must be it, but when I test the AT commands in putty, there is no response from the GSM module. I'm pretty sure these can't be the right pins.

Please someone with knowledge, can you tell me which pins are Rx and Tx? If you have a schematic, please share.

One more thing I'd like to add is that I tried contacting the seller on ebay, but they told me "They are only a customer service and they don't know anything technical. Please research the internet."


texts: Choosing the best DC motor to use as a generator

texts:
I'm designing and will be building a wind turbine.  What characteristics do I look for in choosing a motor to use as a generator?
I know this might not be enough information, I'm not an electrical engineer.  What I'm really looking for is the details I need to look for when choosing a suitable motor for the job as generator.
For example:  AC or DC, brushless, RPM, high torque or not?
I want to generate the most power possible, right now I don't know what rate the wind turbine is going to spin at.
My design for the prop at the top of the wind turbine:


texts: Why doesn't work this circuit? I would like to sense the temperature raising

texts:
I would like the following:

Once the led gets active, stays active until I disconnect the power supply.

I tested it with this simple circuit, but it didn't work. When the temperature increased the NTC value decreased and the led went active, but when the temperature desreased the led went inactive. Why?

The NTC sense the temperature and if the temperature is too high the LED is go active and I would like to keep it active to see if the temperture was too high.
NTC is 10k.


texts: Adjustable DC/DC converter and/or LDOs for space application

texts:
I am currently designing a system for a satellite and I am looking into the components to generate the required low-voltages, and I was wondering if maybe the collective knowledge of stackexchange could be of some help.
Some specs:

input voltage: exact value still TBD, but min 5V and up to 20V if needed
output voltage: range 1V up to 5V
ideally, the value should be adjustable during operations (controlled by an FPGA)
rad hard: TID > 100 kRad, SEE > 60  MeV.cm2/mg

At the moment, I selected a couple of LDOs from TI and the plan would be to control them following this scheme (a DAC in the feedback loop of the LDO): link to control scheme
I was wondering if you knew either of some other control scheme or maybe of components which include such capability directly in one chip package, instead of having a separate DAC.
Thanks for any help you can give me!
EDIT: some additional information:

this is the first space-project of my organization (research institute, not a company), so I don't really have tried and tested product recommendations. We got the rad hard requirements for TID and SEE that I wrote in the post, and that's basically it (we got them from the project office).

Here are the datasheets of the components that I selected. These are a basic starting point for what I need, but I am not married with these choices

TPS7H1101A-SP
TPS7A4501-SP


texts: Multiple driver error for SystemVerilog initial value

texts:
In my code I have an always_comb block coded as follows:
always_comb
begin
    if ( x == 0 )
        z = some_value ;
    else if ( y == 1 )
        z = some_different_value ;
end

some_value and some_different_value.
z is defined and given an initial value ( for simulation purposes ) as follows:
logic z = 42 ;

When I compile - I get an error: "Multiple drivers to always_comb output variable z detected".
Is it a bug in the tool?


texts:
I was looking for simple pseudocodes for a PID controller and found this code.

If I am not wrong this Ki_Prior is wrong and should be e_integrated otherwise we will also be adding this Ki gain with this term So according to the psuedocode should look something like this

I = I + e*iteration_time

D = (e -e_prior)/iteration_time

output = Kp*error + Ki *I + Kd *D

or am I missing something here ?


texts: Controlling the power from a 9V battery with a potentiometer

texts:
I'm working on a project where I'm powering an LCD screen backlight via a 9V battery. As it is currently, I'm powering the LCD via a 9V battery.

This works great, but I'd like to have the ability to easily change the brightness via adjusting the voltage with a potentiometer. I have a 10k Ohm one currently, but that only works when it's fully on. Anything less, and the screen is off.

Would a higher Ohm potentiometer solve this issue, or is there a better solution?


texts: This flash memory works without connection to a power source or gnd?

texts: I am doing a project where I need to store information into flash memory and read it back using an mbed. I can't get it to work right, but I noticed that even if there is no connection to power or ground, I can still read non-zero bytes from it. Most of them are 0 but some are 255. Why is that?


texts: Video encoding is a computationally heavy task. I like to ask, are the video specs that can be managed with a ARM M4 (STM32F4 type CPU) type CPU? Perhaps low frame rate (10fps) and only VGA quality.


texts: +-33V Overvoltage and reverse polarity protection

texts:
I found on this forum a schematic (Zener + MOSFET overvoltage protection).
But It does not work and I can't figure out why. this is the schematic:

I want to protect the power supply of an opAmp form voltage above 33V (and symetric -33V). It's maximum votlage is +-45V.
For some reason M3 is always conducting and doesn't deactivate when M1 is conducting.. Which should bring M3s gate to the same voltage than M3s source, thus deactivating M3.
I know there are many other circuit possible do achieve what I want to do. But I'm wondering why this doesn't work because thoereticly it seems ok to me. For my academic knowledge ^^.
Thanks for your help.


texts:
How quickly should that state machine cycle through the digits so that the digits don’t appear to blink?
Need some help with this question.


texts: Replacement battery voltage mismatch tolerance?

texts:
I want to try replacing a proprietary battery in an electronic of mine as a first electronics DIY project.
Thing is, the stock battery is 3.6V, and the phone battery I have on hand that I would like to use is 3.8V. The replacement battery also has a charge voltage of 4.35V, and the AC adapter for the electronic is 5V. I've tried looking up if this will be a problem, but everything I've read is written waaayyyy beyond my skill level.

Are either a .2V difference in the batteries or a .65V difference between the battery and AC adapter significant differences that makes this build unsafe?

Also, is 24awg wire sufficient for wiring everything up? I would be soldering the replacement battery to the pcb inside of the proprietary battery.

Thanks in advance, and sorry for asking such basic questions.


texts: How to emulate a capacitor discharge curve using a microcontroller output pin?

texts:
I require a configurable amount of capacitance, without using a bank of dozens of actual capacitors and some kind of complicated switchboard, like this:

Not only would this be an unwieldy solution, but I need to be able to change the capacitance in software.
I figured maybe I could emulate a capacitor discharge curve using a microcontroller. That is, the output will initially be at VCC, but quickly decay exponentially to zero, at a speed dependant on the amount of current drawn.
For example, a real capacitor would behave as shown, when the switch was opened:

I want an output (via some simple interface circuitry) that emulates such a discharge curve. I would like to be able to specify some desired capacitance, and have it produce an output consistent with the expected discharge curve of a capacitor of that value.
Possibly this could be achieved by having a real capacitor of the largest required value, but in some way affect how much charge it gets, or modify its discharging current in such a way as to simulate a smaller capacitor.
The emulated "capacitor" will only need to source current, from a starting position of "fully charged", and with its simulated cathode at ground potential. It doesn't need to simulate a charging curve, or do anything fancy like take part in a Pierce oscillator or the like.
I realise that such a solution may need to take current draw into account. Either the "simple interface circuitry" could factor this in somehow; or - failing that - I could just measure the current being drawn (e.g. using an INA219).
Is there some feasible way of achieving this, without insanely complicated and/or expensive circuitry?
NOTE: I guess it would be acceptable to merely approximate the curve, using a series of discrete digital voltage levels. In other words, the output could decrease in steps, rather than being a smooth curve. Provided the resolution of these steps is fairly reasonable, it should be good enough for my purposes.
--
EDIT: Removed explanation of my eventual use of this device. I included the explanation to avoid accusations of the XY problem; but it has merely resulted in people obsessing over relays rather than addressing the actual question I have asked.
The question, in a nutshell, is: How do I output an analog signal emulating the discharge curve of a specified size of capacitor? Bearing in mind, of course, that this curve will depend on the amount of current being drawn.


texts:
What is the metallic component, labeled Y1, just at the right of the integrated circuit and at the left of the small C4 and C5 capacitors?

When I search for “N24.000” on Google, I find only other boards with the same component, but no information about the component itself.

If I search for “electronic component N24,” all I find are references to a bipolar transistor, however the component has only two connectors and therefore is not a transistor.

Searching for “7C20PF” doesn't give anything useful either.


texts:
I have signal coming from DAC ranging from 0 to -1V. I want to be able to adjust the VPP from 0 to 10V and adjust the offset from 0 to +/-5V. To do this, I am using digital potentiometers (Rf for VPP and R1 for offset). Does this circuit seem viable?

simulate this circuit – Schematic created using CircuitLab

The other option I thought to use was a differential amplifier circuit as stated in :Differential amplifier opamp with gain and offset adjustment

Thank you for your help!


texts: There is a problem with this circuit. The original document specified 3V for power supply. However, the capacitor 13 is only charges to around 0.8v and then stops when I used 3V and it doesn't trigger SCR 7. I tried 9v and it works sometimes with this voltage. When I disconnect the gate of SCR 7, it seems to be charging fully. I am using TICP106D SCR. In the original document the SCR was BRY55. Both are sensitive gate SCR as far as know, so they should (?) be interchangeable. I don't understand why the current is leaking this much through the gate. Do you have any suggestion?


texts: Need single-shot 1 minute delay-off LED circuit

texts:
What I would like to do is have an LED turn off 1 minute after the power is turned off. The LED would be on all the time when power is on. Thus:

Turn power on: LED comes on immediately.
Turn power off: LED stays on for 1 minute and then turns off.

This is to signal when someones eyes have adequately adjusted to the dark in a darkroom.

Thanks in advance.


texts: Is SWD with an FTDI chip a universal programmer solution?

texts:
I have searched high and low (in fact I have spent the recent months on and off trying to find an answer). Maybe I'm not asking the right questions, or am staring the answer in the face, I'm not sure. I have been too nervous to ask, but I am at my wits end, so here goes.

I am creating a project that due to size constraints needs to be very small. That means small MCU and small programming interface. It is also open source so I would like to keep the programming interface as cheap and simple as possible (also as a student I don't want to spend a lot if I don't have to).

This Article I found seems to indicate to me the possibility of a universal solution. Those FTDI chips are a lot cheaper than any other (legitimate)  JTAG programmer. Broadly speaking (for posterity), will they be able to interface with and program any ARM MCU that includes an SWD interface?

Specifically (if it's relevant), I am looking to integrate the SiLabs BGM121 SiP module into my project and am trying to figure out how I would program it. I don't even necessarily care about debugging at this point, just trying to figure out a cheap solution. Also between the SiLabs CP2102 and the FTDI FT2232H, which is more likely to work?


texts: Ground loops in a PCB with large hole in the middle

texts:
I'm designing a board for a client with some unusual constraints. My question is well illustrated with the following simplified example.

Assume the positions of everything are fixed. Let's also assume a 4-layer board for simplicity. The outer layers are signal layers, and the inner layers are two planes for Power and GND.
As can be seen from the image, there is a large hole in the middle of the board. The board will transmit data at 16 MHz (wavelength ~18m) from the ADC to the "Master" board via a connector.
Is there any concern that digital signals leaving the ADC will return to the connector in both clockwise and counter-clockwise paths?
Would it be better to break the plane such that this cannot occur?
Some quick LTSpice with arbitrary simulation parameters seems to suggest that NOT breaking the loop is the way to go. As seen below, leaving the loop decreases the return's inductance since the two paths are essentially in parallel:


texts: scaling voltage with Op Amp for microcontrol

texts:
simulate this circuit – Schematic created using CircuitLab

So I am having trouble trying to figure out how to scale voltage from 22-32V to 0-5V. I know that Vout= 0.5Vin - 11 will give me the proper voltage values I need. I am trying to monitor the voltage of a battery with my Arduino.

I tried doing a voltage divider for R1= 54K and R2=10k. When Vin=32 I do get Vout=5V, but when Vin=22 Vout=3.43. I have read that a third resistor or Op amp will help but I am just not sure how to pick the third value. How can I include the bias needed? Any links or examples would be greatly appreciated.


texts: Roadmap for learning Electrical Engineering

texts: I am just starting to learn electrical engineering, but I am confused about what I should do. Should I be reading about it, taking online classes, or just make projects? If possible can you provide me with a roadmap of what I should do in order to best learn about electrical engineering? I am really interested in making exciting projects related to the field. Any suggestions?


texts:
First of all, my question might be dumb, but i've just started designing microwave circuits, I don't have any experience.
I'm designing a simple FET-mixer. For the FET,I chose the low noise ATF-33143. And its datasheet says that the STATZ FET model can be used for designing.Of course, the model parameter values are also avaiable.
And there is a section below, which looks like a detailed modeling circuit, containing the FET, ,capacitances, TXlines, inductances etc.
My question is that for the designing the mixer, I should just pick and place the Statz FET model, and setting the model parameters, or I should also build the detailed FET model in the mixer cirxuit, with the many capacitances and txlines?
Thanks everyone


texts: Using digital input pin to read variable resistance from sensor requiring supply voltage

texts:
I intend to use air contaminants sensor TGS 2602. The internal resistance changes if a given gas is detected. It requires an input voltage V_C = 5V to operate.

According to the specs, the basic measurement circuit is:

simulate this circuit – Schematic created using CircuitLab

The problem I am facing is I want to read the measurements with digital IO pins, specifically I want to use Raspberry Pi for this. I found a simple solution to a similar problem here:
Reading Analogue Sensors With One GPIO Pin. Essentially it involves using an RC circuit and measuring time lapsed until "high" voltage occurs on our digital pin.

In this case I would then be inclined to simply switch R_L with a capacitor but by doing this I would quickly cut off the supply voltage for the sensor (it requires V_C). I then thought I should maybe add the capacitor in parallel with R_L. But the R_L voltage drop is low, so I would never reach the "high" voltage on the capacitor to be able to read it with my digital pin. Should I perhaps use op-amp to drive the V_RL up? But is it not over-complicating things?

My question is then how should I measure value of R_S with a digital reader?


texts: How to send string in serial communication in AVR-C

texts:
So as the title states, instead of sending a byte of information at a time, I would like to be able to send a whole string. What I tried to do was that I tried to put the user input in an array and get each element of that array to be transmitted. However I was only able to get the first few letters to transmit not the whole array, here is my code:

//tx serial
#include <avr/io.h>

#define F_CPU 16000000
#define BUAD 9600
#define BUAD_RATE_CALC ((F_CPU/16/BUAD) - 1)

int main(void){

    char ar[]= "hello";

    //High and low bits
    UBRR0H = (BUAD_RATE_CALC >> 8);
    UBRR0L = BUAD_RATE_CALC;
    ////////////////
    //transimit and recieve enable
    UCSR0B = (1 << TXEN0)| (1 << TXCIE0) | (1 << RXEN0) | (1 << RXCIE0);
    UCSR0C = (1 << UCSZ01) | (1 << UCSZ00);  //8 bit data format
    ////////////////////////////////////////////////////////////////
    int i = 0;

    while (1){

    while (( UCSR0A & (1<<UDRE0))  == 0){};
        for (i = 0; i < strlen(ar); i++){
            UDR0 = ar[i];
        }
    }
}

What would the problem be with this?


texts: Maximum reliable speed of GPIO pin given only capacitance and no resistance

texts:
I looked up information about my microcontroller AT89S52 and I can't seem to figure out the maximum speed I can operate a GPIO pin at.

I'm running it with a 22.1184Mhz clock, and I notice sometimes when I modify a port value, it won't update right away without adding several NOP statements but I don't want to guess. I want to know values so I can adjust code.

This is information from the datasheet I got:

It lists the pin capacitance, but I see nothing about the pin resistance. How do I calculate the resistance here? or is there another way to calculate the maximum reliable pin processing speed?


texts: Is it possible to use a IR proximity sensor as a dust optical sensor?

texts:
I'm doing an automatized-ish windshield wiper project, which requires some kind of dust sensor. I have an IR proximity sensor and I could only find people using it for rain detection on windshields.
Can I use it or it's sensibility isn't enough?


texts: Can a Verilog function return an array indexed from one to the value passed in as an input parameter?

texts: If an input parameter to a Verilog function is integer "lg" then can the function return an array of integers indexed from one to (lg)?


texts: How do do V=(white(2e6*time)/10) noise on voltage source with LTSpice?

texts:
I am trying to inject noise into the Voltage Source as shown in this thread. The NOISE function looks like this: V=(white(2e6*time)/10). I am new to LTSpice. How to actually use the white function? Where do I go in the LTSpice tool to enter this function?

I can right click on the voltage source and I see this window. Where do I enter the white function?


texts: use RS-485 or Normal Voltage as Input over 10 meters

texts:
Newbie when it comes to data transmission, no test equipment or any so i can't verify it actual, much of a idea so i would to ask those who have practical expertise. I have this setup where i came up on a long distance SPI using rs-485. Distance is about 10 - 20 meters. Now what bugs me will be the CS/SS.

This is a dumb Question of me (i guess) so sorry if i had to ask. should i use rs-485 transmitter and receiver for my CS/SS (image below)

EDIT: SPI here is a slave sensor that is being read by uC upon selection.

EDIT: i used this solution for applying long distance SPI to RS-485 http://www.ti.com/lit/an/slyt441/slyt441.pdf

or just use plain voltage input switched by a transistor/mosfet and uC (image below should i add bypass cap at the end near cs)

Is there a concern of transmission response, propagation, noise, etc?

Thanks :)


texts:
Complex numbers contain imaginary numbers as we all know but often it is used for solving real life practical problems such as taking the impedance of a capacitor, inductor etc.

Even in Signals and systems we use complex form of Fourier series,in AC circuit analysis we use complex numbers and i guess there are still more applications to come in my coming semesters.

How an imaginary number in real life can have a practical significance?

So what really makes complex numbers such a powerful tool in electronics?

In layman's term why do we use it?How does it helps us?


texts: Converting Arduino Due 3.3V digital pin to 5V

texts:
I'm a real novice so please bear with my terminology
I've got an Arduino Due which outputs 3.3V signal when digital pin is set to HIGH. I have a driver that needs to receive at least 5V from this digital pin. I've been googling all day and it sounds like I need to amplify this 3.3V signal using a transistor but I'm too novice to really appreciate how to implement a simple amplifying circuit. Can anyone help me out?
Thanks in advance!


texts:
I am planning to build 4 LED-strips using two different 'white' settings (1+1 strip x 4). The LEDs will be driven by a 24V constant voltage dimmable RGB-DALI driver (up to 5A per channel). My idea is to control the two strips (2700K and 5000K) using the R and G channel and the PWM mode for dimming. I drew and calculated the necessary circuit:

The parts are both from this series. (Warm white LED 2700K, Cool white LED 5000K). The resistors are standard 1206 SMD. My calculations for a target illumination of ~500lm yield (for 2700K):
\$ 20 \times 23...26.5lm = 460...530lm\$
In order to satisfy the 24V I need to split the strip into 4 paths with 5 LED each.
\$ 5 x V_{led} = 5 \times 2.8...3.3V = 14...16.5V\$
\$ R_{pre} = \frac{V_{in} - 5\times V_{led}}{I_{LED}} = \frac{24V - 5\times 2.8...3.3V}{60mA} = 125...166\Omega\$
Choosing a 180\$\Omega\$ resistor gives an effective current of
\$I_{path} = 41.6...55.5\leq I_{forward} \$
For all four strips I would come to
\$ P_{max1} \sim 4W \$
Now my questions:

Are there more parts (filter, overvoltage protection) necessary to build an LED application? It seems too simple for decent light source.
Is my calculation correct? (Heat and prematurly degradation should not affect my circuit, since I am under the recommended forward current).
Can aging both in the driver and the LEDs produce a state where the forward voltages cant be produced?
Should an LED in one path fail the entire path is lost, but no current is induced in the other paths since the driver regulates the draw. Correct?


texts: Understanding datasheet for SMPS transformer

texts:
Looking at different datasheets of SMPS transformer, I found that the manufacturer always specifies voltage in a certain frequency range. Why is this parameter important?

For example this transformer:

https://www.weonline.de/katalog/datasheet/750311564.pdf

voltage is only specified for 40 V @100kHz.

Is this voltage-frequency parameter somehow related to volt \$\times\$ second or saturation?

EDIT:
Removed the insulation part.
 I went to fast through the datasheet. So, the part of the insulation voltage is quite clear, I am interested in the relation between voltage-frequency and the magnetic properties.

Does it mean that if If I would apply 80v at a higher frequency (>200 khz)that the core would not saturate since the increased voltage is compensated with lower “seconds”


texts:
It is believed that one lightning bolt can carry enough energy to light a 100W bulb for 3 months. Why do so many people get directly hit by lightning bolts and survive?

One argument can be, the electric shock period is really small (a fraction of a second) but on the other hand, if someone is hit by lightning bolt from a high tension wire for example, he is almost instantly killed.

That lightning is also for a very short period of time.


texts: Monitoring voltage without a known reference

texts:
I'm working on a little sensor platform that runs off of batteries.  I'd love to be able to trigger an alert when the voltage gets too low.  The problem is that anything I use to measure that voltage will be powered by that same voltage source.  For what it's worth, I'm running Arduino Pro-mini clones (3.3 V) off of 4xAA rechargeables (4.8 V to start with, but the system seems to work right down to 2 V or so, including the XBee transmitter).

Does anyone have any clever ideas for how to work this?  It seems like anything using the analog inputs of the ATmega chip will just be comparing the input voltage with itself.  Maybe checking the difference between what comes from the regulator and what comes from the batteries themselves?


texts: Why can't we command two DC motors with just 2 relays for each in opposite directions with a same power supply?

texts:
We managed to control 2 DC motors with 2 relays for each one.It worked great except one thing:
we couldn't  make them turn in opposite directions at the same time .We noticed that there was a shot circuit.
Can somebody explain it please?
Thank you for your attention.


texts: Can you store energy in an inductor and use it later?

texts: My company uses supercaps to power the device if power is cut. I was wondering if you could do the same thing with an inductor. If you can't, why not?


texts: Heatsink selection and datasheet specifications for Thermoelectric Generator

texts:
I have bought this TEG. I am planning to use it as a generator, for energy harvesting applications.
I am having trouble though understanding both the diagrams and the meaning of the TEG's specifications in the datasheet. To be specific, how can I use the info provided in the datasheet to determine for example, what heatsink would be required for the TEG, while having a DT=20 degrees, and also what would its output power, voltage, current be at that DT ?


texts:
I'm unable to figure out how to use the current dependant voltage source in KVL

The following are the equations I've found, up till now:
20i+V2=10,
V2=50i1,
20i+50i1=10,
i=i1+i2


texts: Chip with one oscillator provide different brightness (PWM) for multiple LEDs?

texts:
I'm working with the PCA9531 chip described as

  The PCA9531 is an 8-bit I2C-bus and SMBus I/O expander optimized for
  dimming LEDs in 256 discrete steps

It is a chip that provides 8 PWM outputs for driving leds. It has two PCS (for defining the oscillator frequency) and two PWM (for defining the duty cycle) registers which define the characteristics of the "blink". The documentation also stats:

  The initial setup sequence programs the two blink rates/duty cycles
  for each individual PWM. From then on, only one command from the bus
  master is required to turn individual LEDs ON, OFF, BLINK RATE 1 or
  BLINK RATE 2. Based on the programmed frequency and duty cycle, BLINK
  RATE 1 and BLINK RATE 2 will cause the LEDs to appear at a different
  brightness or blink at periods up to 1.69 second.

My understanding so far is that I have two Led groups (based on the blink rates) and it isn't possible to have all 8 leds to have different brightness at the same time.

However, (I'm using a Linux kernel driver to work with the chip) I've seen it possible to have all leds having different brightness at the same time, so it's happening somehow.

Below is the block diagram of the chip which shows two BLINK inputs going into the summation block.

I would like to know can this happen logically from the perspective of the chip.


texts: Identify coils end in 3 phase AC induction motor for star-delta configuration

texts:
In general if I look at a 3 phase AC motor outlet wires there are six wires that comes out of motor, three of them are marked to show coils end and other three are not marked which show coils other end.

Sometimes what happens these marks are worn out due to the reason that motor is rewinded and winder guy forgot to mark the coil ends or due to other reasons.

Six wires also comes out of a star-delta motor starter,
now how would I correctly identify outlet wires which are coming out of motor so that I can configure the star-delta connection correctly?


texts:
I'm currently working on a problem that wants me to obtain a gain of 500 using a mix of CG CS CD or cascode amplifiers or just a single topology. The Vout will be powering a resistive load of 50 ohms. I need a step in the right direction on what topology to use.

VDD  = 3v
VDSTAT = 0.25V
AV = 500

Update::::

So I have only been able to obtain a gain of 400 and cant get much more. Any ideas on where im going wrong. Here is my HSPICE Simulation. max length and width of the mosfets is 10um and min is 0.15um.

Vdd 2 0 DC 3
Vb 3 0 DC 1.75
Vin 5 0 DC 1.25

X1 1 5 0 0 nmos_ee435 width=4u length=10u
X2 1 3 2 2 pmos_ee435 width=8u length=10u

.SUBCKT nmos_ee435 d g s b width=4u length=10u
M1 d g s b nmos_internal W='width' L='length'
+ AD='width*2e-6' AS='width*2e-6' PD='4e-6+width' PS='4e-6+width'
.MODEL nmos_internal NMOS LEVEL=1 uo=400 vto=1 lambda='1e-6/length*0.1'
+ tox=6.903n gamma=1 phi=0.6 cgdo=0.5n cgso=0.5n cj=0.001 mj=0.5 pb=1
+ cjsw=0.1n mjsw=0.5 capop=0

.ENDS

.SUBCKT pmos_ee435 d g s b width=8u length=10u
M2 d g s b pmos_internal W='width' L='length'
+AD='width*2e-6' AS='width*2e-6' PD='4e-6+width' PS='4e-6+width'
.MODEL pmos_internal PMOS LEVEL=1 uo=200 vto=-1 lambda='1e-6/length*0.1'
+ tox=6.903n gamma=1 phi=0.6 cgdo=0.5n cgso=0.5n cj=0.001 mj=0.5 pb=1
+ cjsw=0.1n mjsw=0.5 capop=0

.ENDS

.OP

.tf V(1) Vin

.END


texts: Current decreasing while measuring the current through a constant current source resistor

texts:
My Circuit :

The above is my circuit.

The Forward drop of LEDs is typically 2.8V and a maximum of 3.15V.
I designed the current through the string to be around 21mA, so the emitter resistor is 33ohms.

Now, while performing the actual measurement, I try to measure the current through the 33ohm resistor using the multimeter (Link attached below).

But what I am getting is that, initially, the current reading that I get from the meter is around 21mA, but if I let it measure for some more time, like for say,1-2 mins, the current reduces to 20mA.

This trend continues. The longer the time I measure the current through the resistor using the multimeter, the current reading keeps on decreasing. I kept the reading ON for like 5 mins and the reading turned out to be around 16mA. I didn't extend beyond that.

But I do not see the intensity of the LEDs decreasing. The Intensity and the brightness of the LEDs are the same (Like if the current through them was actually 21mA. No change in the LED brightness). If I measure the forward voltage of the LEDs, it is around 2.74V.

Any reason why this is happening?

Multimeter Link : 6 and half digital multimeter


texts: How to implement 8x1 multiplexer using 3x8 decoder and 3-state buffer

texts:
Suppose that AB and CD are 2-bit unsigned binary numbers

(a) Find the truth table for the function F with 4 inputs A, B, C, D to satisfy the following condition

if AB >= CD, then F = 1, otherwise F = 0

(b) implement 8x1 multiplexer using 3x8 decoder and 3-state buffers

Am I right?


texts:
In the book "Electronics For Dummies" there is a paragraph called "Creating a timer".

  If you’ve got a buzzer that requires a voltage of 6 volts in order to sound off,
  and you’re using a 9-volt battery to power your little scare circuit, you can
  build an RC circuit like the one in Figure 4-5 and use the capacitor voltage to
  trigger the buzzer. The idea is to charge the capacitor to about 6 volts in the
  time you want your flatmate to think about whether she wants a beer or a
  lager and reach out for one, but then blast her with the buzzer.

The idea is that by choosing a time and knowing the capacitor value we can calculate the resistor value so that the capacitor charges up to 6 volts in the chosen time from the equation 2/3T = 1RC (2/3T because 6V/9V = 2/3).

Then as the buzzer requires 6V to trigger it should alarm after the specified time.

How should I connect the buzzer?


texts:
I work in possibly gas filled environments.  As such safety recommendations are that I don't use my cell phone, camera and computer while touring around these areas that explosive gas may be present.

My job contains elements where using some digital devices is would be absolutely beneficial that aren't available from a vendor.  For example, (I am not aware of) a device that can detect wireless router signals that is also intrinsically safe.

I wish to design such a device (or another), but I don't know what makes a device intrinsically safe at which lower voltage and the amount of space between components and such.

Is there a standard or a guideline or formula that defines this?

Edit:  There are cell phone devices on the market that are rated intrinsically safe such as: M-Safe 28 or the Atex Advantage 1.0.  I am thinking they aren't perfect but near perfect.


texts: I am trying to make an adjustable power supply with an LM317 and a potentiometer. The only problem was that there were some conflicting schematics online about how to connect everything. Can some please verify that it is correct or identify what I need to change?


texts: Physical operations of discrete - time circuits

texts:
I have a basic doubt about discrete time circuits.

A discrete - time signal is a sequence of values which are taken at specific time instants (let's call them sampling instants), as we can see from the following picture:

So, from what I have understood, a discrete - time signal is in general like an analog signal which has been sampled, and it is not exactly equal to a digital signal because its values have not been quantized yet (so they may assume values inside a continuous set of numbers).

My question is about the physical implementations of discrete time circuits (for instance discrete - time filters).

For instance, this is a switched capacitor integrator:

If I have understood it correctly, it performs integration during the sampling instants (in which the capacitor C1 acts like a resistor).

But my question is: obviously the circuital elements (op - amp etc) are ON during all time, in general, and at the output we will have a signal for each time. What does it happen during the time between two sampling instants and how discrete - time filters manage it?


texts:
I recently got a new heat pump which has 3 parts:

Indoor pump
Outdoor pump
electrical heater

The picture below shows the configuration in the fuse box

Before the main fuse (FI in my country 230V@50Hz) is an energy meter SDM-72 to monitor the heatpumps power consumption. In the specs the basic current is rated at 10A and the maximum rated current at 100A.
From my simple calculation I get

L1: 13A + 6.5A ~ 20A
L2: 13A + 14.3A ~ 28A
L3: 13A

This would mean, that the energymeter is always operated over the basic current, which affects its accuracy and lifespan. Should I replace it with an higher rated energy meter?
Also there is some concern of the position of the energy meter since the FI should trigger when a delta current of 30mA is recognized. If there is an additional consumer between the FI and the circuit breaker there is also an additional impedance which might delay the reaction of the FI. Should the energy meter before or after the FI?


texts: Statistical accuracy of multiple resistors in series or parallel

texts:
I'm having a senior moment and would appreciate clarity.

I'm working on an inverting amplifier design where I need to add low-pass filtering and a voltage clamp.

Without the filtering and clamp, the op-amp configuration would simply be a feedback resistor from output to (-) input and the input resistor from signal source to (-) input.

Worst case error is the sum of the resistor tolerances but statistical averaging usually gives better results than worst case.  The figure that I've used in the past is the inverse of the square-root of the number of components (about 0.7% if using 1% resistors).

Now I'm going to split the input resistor into two equal-value resistors, half the value of the original single resistor.

Intuition says that the statistical average error now decreases slightly to the inverse of square-root (3) or about 0.58% if using 1% resistors.

Am I out to lunch or is this a reasonable assumption to make?

Note: the worst case error is still 2% in both cases.  Worst case error is what I use when I'm calculating my total error, statistical average is the number I use when estimating the typical error.

simulate this circuit – Schematic created using CircuitLab


texts: LUT - Maximum error of linear interpolation approximation

texts:
I'm currently using an LUT (Look-Up Table) stored in a microcontroller, to read the temperature from an NTC sensor. I'd like to achieve a precision which is known, it doesn't matter if it is not so high.

The first step in which I'm stuck is to know well the error introduced by evaluating an interpolation of two values in a LUT.

What I thought: If the LUT have 1°C steps, the maximum error using the intermediate value as discriminant, is 0.5°C. And (what I thought) the only final solution to this is that I can print on a display the value interpolated (i.e. 24.8°C) instead of the LUT (i.e. 25°C), but both have 0.5°C of error. The case of 24.8 +- 0.5°C it doesn't seems so meaningful. Maybe 24.5°C could be a better solution.

The second thought is that interpolating using two points separated by 1°C, are bringing an error which can be smaller than 0.5°C, since it is related to the ratio of second derivative of the curve and a factor of 1/8 times the step of the function (here 1°C) (https://en.wikipedia.org/wiki/Linear_interpolation#Linear_interpolation_as_approximation). But I'm not sure at all of what I am reading: supposing that I have the Steinhart-Hart equation, I do not have the second order derivative. Am I right? Any suggestion? Is this analysis necessary to make a correct estiamtion of the error?


texts: Routing multiple video and power through one multicore cable

texts:
I currently have three cctv camera feeds each with a dedicated cable, I assume a 4 or 3 core of some layout (not sure if this is shielded or otherwise). Currently each cable has a dc pair end connection and a bnc connector.
My question is how best to combine these 3 feeds via a single multi-core cable? The requirement would be for one dc pair overall, and capability for 3 separate video feeds.
I am familiar with calculating voltage drop so specing the dc cores is no problem but what about the video cores? Can any of these be combined for the ground? Is a shielded cable preferable? Is there a minimum cross section for video feed?
Also Could the negative and video ground be combined possibly?
Hoping I am in the right place and can pick someone's brains on this.
TIA


texts: Use of a single cell lipo for VIN enough to power motors and board

texts:
I successfully powered two tiny brushed motors and an MCU using a single 1S Lipo (3.7V) battery 300mAH. I did this by supplying battery power directly to the motor controller and VIN in parallel. Per datasheet, the external power supply inputs voltage range for VIN should be 7-12V. The motors spun even though I am below that range, why? In this case, using just 3.7V for VIN.

This makes me believe that 3.7V can be used for the +5V input as well to run the motors. If that's the case, then I won't even need the LD1117 voltage regulator if I plan to use a 1S to power everything, correct? I would still need the LD39050 voltage regulator if I plan to add logic devices.

Questions:
Is there a more efficient, less power drain, or reliable way to share a battery between MCU and motors than in parallel as done above? I read that I may need to decouple the shared supply for noise.

Is there anything I need to be aware of when using a small 1S Lipo to power everything as a standalone unit besides less battery life?

A 5V voltage regulator is unnecessary if my power supply is not above 5V, correct?

I am trying to make something like the jumping parrot drone without the jumping, but make it smart enough that it doesn't just die because of terrible design flaws. I have plans to incorporate wifi, sensors, and battery management IC on top of the motor controller. My goal is to have it drive but only using the 1S. The brushed motors I used are taken from a quad and they have no specs on them that I know of other than 5.5mm diameter and 18mm length. I just know they use 1S Lipo.

STM32 Nucleo-64 boards page 60/66


texts:
I am defining a controller using the mixed sensitivity approach, and I have the following specifications:

a low frequency attenuation of 60 dB
a maximum resonance peak of 2

and I have chosen to use a weight on the sensitivity function and on the control sensitivity function. My code is the following:

s = tf('s');
G = 10/((s+10)*(s-1));
K1 = 10*(s+1)/s;
W_bt1 = 0.5;
W_bs1 = 0.25; %same cross over frequency as the previous point
M = 2;           %peak of the sensitivity
A = 0.001;      %attenuation
Ws1 = (s/M + W_bs1)/(s+W_bs1*A);   %sensitivity weight
Wt1 = (s/M + W_bt1)/(s+W_bt1*A);   %control sensitivity weight
%bodemag(1/Ws),grid;
[K2,CL,GAM1] = mixsyn(G,Ws1,[],Wt1);  %define the controller with the mixed
sensitivity
display(GAM1);
K2 = minreal(K2);  %define a minimal order controller

the problem is that I have a frequency response which is:

and I don' t think it is a good frequency response since it is not a smooth response. So I think the problem is given by how I have chosen the weight for the control sensitivity. In fact, by using the A I have chosen, I obtain a low frequency attenuation of 60 dB as desired, but I am not sure I have to use it also for the control sensitivity weight.

Can somebody please help me?

[EDIT] I didn't mention in my question that I have a pole in the RHP, so this should also influence the frequency response of the system, in the sense that it imposes a lower limitation in for the bandwidth.


texts: Amateur question: how circuit analysis methods are applied in "complicated" circuits?

texts:
This will sound maybe stupid, but I'm amateur in electronics and I'm in process of learning.
I have previously analysed some basic circuits involving opamps, diodes etc.
Although some circuit looks simple (only few opamps, diodes, resistors, capacitors and sources), mathematics that describe that simple circuit can be very complicated, especially if we want to calculate full response of circuit (not steady state).
I was wondering, how then some complicated electronics schematics are analysed?
I mean there are devices containing hundreds of components inside it, it would be impossible to apply some circuit analysis methods there (KCL, KVL etc), right?
How important are those network analysing methods we are studying in school in practice (in repairing electrical devices)?
To clarify what I mean, lets look at one switched-mode power supply schematic I found on the web:

(source: 320volt.com)
Probably, professionals doesn't see there something terrific complicated, but to me, it is very complicated. If one has to repair this device for example, which knowledge he need to have? If he start measuring some voltages, or tracing signals waveforms on oscilloscope, he must need to know firstly what he should expect in normal circumstances (when device is working), so he can detect exact problem. But how can he know that if he doesn't analyse circuit mathematical, which would be quite impossible in this case, what returns us to first lines  of my question :)


texts: How to design a voltage follower/Unity gain buffer circuit using MOSFET?

texts:
I am trying to design a voltage follower to drive a resistive load using MOSFET as a peripheral circuit. I am using this simple circuit using two NMOS transistors. The output is following the input. But the problem is output is becoming load-dependent. If I change the resistance of the load, I am getting an increase/decrease in output voltage.
How can I solve this problem?
Is there any CMOS based stable voltage follower/Unity gain buffer circuit which can be used to drive a resistive load?

simulate this circuit – Schematic created using CircuitLab


texts: Understanding how current is 0A in secondary circuit of this potentiometer - misprint?

texts:
I'm learning some basic electronics, and I'm using an old textbook (Basic Electronics for Scientists, Brophy, 1966) to wrap my head around some fundamentals.
At the moment, I'm looking at potentiometers, and I'm trying to understand a particular circuit in the textbook (I've included a photo of the circuit diagram.) The potentiometer has a secondary circuit, which is connected to an ammeter and a reference voltage source. The textbook suggests that the variable resistor \$R_A\$ should be adjusted so that the current passing through the ammeter labelled \$M_1\$ is equal to zero. However, I cannot see how this is possible given the orientation of the reference voltage source \$V_S\$, both conceptually and using Kirchhoff's voltage/current laws.
Can somebody tell me at a glance whether or not the book is misprinted, and if the terminals on \$V_S\$ are supposed to be swapped around the other way? If it is a simple misprint, then I can understand how everything should be working. If it isn't a misprint, I'd really like some feedback on my working re: my KVL analysis of the circuit (which I'll provide).
I'm still not 100% sure that I understand how this works. I'm considering the simplified example below. I've condensed \$R_A\$ and all of the series resistors into a single (variable) resistor, although I've left \$R_S\$. Please excuse my terrible sketch:

So, my question is, under what conditions can \$I_3\$ ever be zero? Here's my analysis of the problem:
First, let's consider the loop abcd. This yields the following equation (KVL):
$$ V - I R_1 - I_2 R_{S} = 0 $$
Next, consider the loop abef, which yields:
$$ V - I R_{1} + V_{s} = 0 $$
Finally, consider the current at junction c:
$$ I = I_2 + I_3 $$
I can substitute this expression for \$I\$ into my two KVL equations. This gives me:
$$
V - (I_2 + I_3) R_1 - I_2 R_{S} = 0
$$
$$
V - (I_2 + I_3) R_{1} + V_{s} = 0
$$
I can now rearrange these two equations by putting the voltages on the left-hand side, yielding:
$$ V = (I_2 + I_3) R_1 + I_2 R_{S}     $$
$$ V + V_{s} = (I_2 + I_3) R_{1} $$
Rearranging the second expression for \$I_2\$ yields:
$$ \frac{(V + V_S) - R_1 I_3}{R_1} = I_2 $$
And substituting this value for \$I_2\$ into the \$V =\text{ ...}\$ expression gives me a somewhat messy equation:
$$ V = \left(\frac{(V + V_S) - R_1 I_3}{R_1} + I_3\right) R_1 + \frac{(V + V_S) - R_1 I_3}{R_1} R_{S}     $$
Expanding this out (I'll skip a few steps) gives me:
$$ 0 = V_S + \frac{R_S}{R_1}V + \frac{R_S}{R_1}V_S - R_SI_3 $$
Finally, rearranging for \$I_3\$ gives me my final expression:
$$ I_3 = \frac{1}{R_S}V_S + \frac{1}{R_1}(V + V_S) $$
Clearly, every term on the right-hand-side of this equation is positive, and neither \$V\$ nor \$V_S\$ can be negative, because I'm (hopefully) accounted for their polarity when I initially set up my simultaneous equations. So what am I missing? How can \$I_3\$ ever be equal to zero? At first I thought that adding an unknown voltage across the series resistors would change something, but after I went back to have a look, I realised that I still don't understand the problem.


texts: Fourth-order bandpass filter Bessel - I can not solve the final part (math accounts)

texts:
With the previous gain function you calculated, design a Bessel fourth-order bandpass filter with center frequency \$f0 = 10 kHz\$ and bandwidth \$Bf = f0/10\$.

I did the calculations with the Mathematica program and even the factorization part is fine. Now I am trying to match the coefficients obtained, with the transfer function of the previous problem, to get the value of the capacitors and the resistors, but even assigning values to the capacitors I can not solve.

\$F(S)=\frac{1}{1+a_1S+b_1S^2}\rightarrow F(s)=\frac{1}{1+a_1\big(\frac{s^2+\omega_0^2}{Bs}\big)+b_1\big(\frac{s^2+\omega_0^2}{Bs}\big)^2}\$

\$F_{BP}(s)=\frac{1}{1+\frac{a_1s}{B}+\frac{a_1\omega_0^2}{Bs}+\frac{b_1s^2}{B^2}+\frac{b_12\omega_0^2}{B^2}+\frac{b_1\omega_0^4}{B^2s^2}}\Leftrightarrow\$

\$F_{BP}(s)=\frac{s^2}{s^2+\frac{a_1s^3}{B}+\frac{a_1\omega_0^2}{B}s+\frac{b_1}{B^2}s^4+\frac{b_12\omega_0^2}{B^2}s^2+\frac{b_1\omega_0^4}{B^2}}\Leftrightarrow\$

\$F_{BP}(s)=\frac{s^2}{\frac{b1}{B^2}s^4+\frac{a_1}{B}s^3+\big(\frac{b_12\omega_0^2}{B^2}+1\big)s^2+\frac{a_1\omega_0^2}{B}s+\frac{b_1\omega_0^4}{B^2}}\$

2th order Bessel coefficients:

\$a_1=1,3617\$

\$b_1=0,618\$

\$Q=0,58\$

Values of frequency and bandwidth:

\$f_0=10 KHz\$

\$\omega_0=2\pi\times 10^4 rad/s\$

\$B_f=1 KHz\$

\$B_{\omega}=B=2\pi\times10^3 rad/s\$

Substituting the values of the coefficients and frequencies in the transfer function:

\$F_{BP}=\frac{s^2}{1,565\times 10^{-8}s^4+2,167\times10^{-4}s^3+124,6s^2+855581,34s+2,44\times 10^{11}}\Leftrightarrow\$

Factoring in the Mathematica program:

\$F_{BP}(s)=\frac{6,38978\times 10^7s^2}{(3,69555\times10^9+6690,03s+s^2)
(4,21887\times10^9+7156,62s+s^2)}\$

The transfer function of the previous problem is as follows (it is in this expression that I have to match the values):

\$H_{B}(s)=\frac{G_1(G_4+G_5)C_2s}{G_2G_3G_5+\frac{G_1G_4C_2}{G_2G_3G_5}s+\frac{G_4C_1C_2}{G_2G_3G_5}s^2}\$

My problem is now: I can not solve the system. Could you please help me?

System of equations:

\$G_1(G_4+G_5)C_2=\sqrt{6,38978\times 10^7}\$

\$G_2G_3G_5=3,69555\times 10^9\$

\$\frac{G_1G_4C_2}{G_2G_3G_5}=6690,03\$

\$\frac{G_4C_1C_2}{G_2G_3G_5}=1\$

I know I have to give values to both capacitors and to one of the resistors. G is the inverse of the resistance. But even giving values, I can not solve, gives me a mathematical incompatibility.


texts: How can I determine the max frequency of the clock signal for a 3 bit ripple counter

texts: I can't figure out how to determine the max frequency at which a ripple counter functions properly.


texts: What is the simplest way to introduce a ~ 1 second delay in powering on a 230v AC device?

texts:
I have three separate lighting controllers which all have a programmed sequence of slowly dimming lights up and down. These are wired in parallel as I want to be able to turn these on and off with a single switch at the wall (for aesthetic and ease of use reasons).

When switched on at the wall, I want to introduce a delay in when each lighting controller receives current. So the circuit is switched on, and the first lighting controller receives current immediately. After approximately a 1 second delay, the second lighting controller receives current. Then, after a further 1 second approximate delay, the third lighting controller receives current. This will produce an effect where the lights are no longer operating in sync with each other. To be clear, this delay would be a one-time thing each time the circuit is switched on at the wall - it does not need to continue to happen during operation.

The delay does not need to be especially precise or especially repeatable.

I'm new to learning EE, and I'm wondering if there's some off the shelf component or product that will fulfill this function? Ideally I am looking for something which is small in size.

I am working with an experienced electrician to build this device but I would like to design it myself as a learning experience. Please let me know if I need to provide any further information.


texts: Is it possible to upload/download memory from/to external files in Atmel Studio?

texts:
In the old AVR Studio 4 there was an easy option to upload eepeom to the chip from an external file, and also to quickly download either the whole or a specified range of flash or eeprom or RAM memory and write it to an external file.

How is it possible to achieve something similar in the Atmel Studio 6, or in the current Atmel Studio 7?

While I'm in debug mode and need to upload a different eeprom file to the chip (while the EESAVE fuse is set, so I can keep the changes I did to the eerpom while testing), then I have to do the following tedious journey:

stop debugging
switch from debugwire to SPI
edit the fuse settings (to disable eesave)
edit the file containing the eeprom data in the project
rebuild the project so the everything is written to the chip
edit the fuse settings again (to enable eesave)
start the debug session again (which will automatically recompile and re-burn everything again)

There is an old forum thread from almost 3 years ago describing this problem, with a hint that the feature from AVR Studio 4 will soon be added.

Is there a simper approach to upload and download the eeprom in Atmel Studio 6? The above lengthy procedure is too impractical if I need it often, and it provides no possibility to just download part of the memory into a file to be analysed by some of my custom-built tools.

Is this really a feature that no one needs besides me?


texts: I've been following TI precision lab, I didn't understand how the Req is derived. Can somebody explain, I am curious to know.


texts: Why will my led not light up & why does my input voltage fluctuate when I add a wire?

texts:
This design is suppose to light up the LED When the sensor is under light, and turn off the LED when the sensor is covered.

I noticed two problems:

My LED won't light up.
When I measure the voltage input difference (expecting
+15- V) without the wire connecting the second prong of my 50k potentiometer (25th node) to the second prong of the op-amp, I measure 15 volts. But when I insert that wire how it is in the picture, my same input voltage measurement starts fluctuating. I assume this is a problem

Of course, I tried changing the values of the potent. and sensor but had no luck.
I also tested my op-amp and it seems to be working correctly.
The LED is also working correctly because it lit up in a different scenario. & Yes, I am also aware there is no voltage input in the photo. These were taken after I unplugged
The input.

Will you please look over my design and help me locate the problem?

EDIT: New circuit based off new understanding

EDIT2: Just talked to my instructor. I indeed originally wired the purple wire wrong, but it should be fixed in the last two photos. I also confirmed that my resistor is not shorted and the photo is just confusing everyone, so I will upload a new one once I get home.

EDIT3: Less confusing photo (made sure you could tell the led is not shorted)

SOLUTION: Thank you @jonk and @TonyStewart!

My circuit was wrong in that I did not realize my potentiometer should not connect to the op-amp's 3pin (basically I didn't understand the schematic).

Later on, @jonk helped me come to the realization that there was something wrong with my op-amp, so I used a new one and it now works.


texts: Deriving the small signal model of this transistor

texts:
Given that the current equation for a graphene transistor is given by equation (1) I'm trying to find the small signal model of the transistor.

$$(1)\space \space i_D(V_{GS},V_{DS})=\frac{W}{L}μ(C_{ox}V_{GS}+a)V_{DS}\\
i_G=0$$

Small signal models were always given in the courses I've had. So, a problem like this is unusual for me. I gave it a go though. I used the Taylor series around the bias point for two variables and ignored the non-linear terms:

$$i_D(V_{GS},V_{DS})=i_{bias}+(V_{GS}-V_{GSbias})(\frac{\partial _{i_D}}{\partial V_{GS}})_{V_{GS}=V_{GSbias}}+(V_{DS}-V_{DSbias})(\frac{\partial _{i_D}}{\partial V_{DS}})_{V_{DS}=V_{DSbias}}\\
Δi=ΔV_{GS}(\frac{\partial _{i_D}}{\partial V_{GS}})_{V_{GS}=V_{GSbias}}+ΔV_{DS}(\frac{\partial _{i_D}}{\partial V_{DS}})_{V_{DS}=V_{DSbias}}\space \space (2)$$

I'm confident that this is the small signal equation for the current. However, this equation is causing me some confusion.

What is the transconductance gm and the resistance ro for this model?


texts:
I'm designing a 4 layer CC2541 board. I'm using recommended balun from TI. I'm also using the same layer stack as in CC2541 Keyfob reference design.

I'm following exact antenna dimensions mentioned by TI. I'm using MIFA type pcb antenna.
One part of pcb antenna is connected to GND and feed line is connected to Balun's antenna pin. How can I mention this two things in Altium?


texts: SMT soldering for QFN package without legs

texts:
I have soldered through-hole and SMT before but this is the first time I have to do SMT (QFN) package which has no legs. I tried the traditional approach, Flux, solder, then heating the component. But here the pads are underneath that it's been a nightmare to reach em to apply heat.
I worked with somebody back in the day who soldered in a different way. He applied something on the pads(very thick paste), I'm guessing Solder/flux paste. It managed to keep the components right where there are. Then he put the board in a microwave and ran it for a few minutes. Then the components were soldered perfectly. No issues what so ever.
My question is, what's that paste? Is my guess right? What exactly is it called so that I can buy one?
If I'm wrong, then how does one normally solder these components?
My component is a micro msp430fr2433.


texts: Why are "devices utilized exclusively in any transportation vehicle" exempted from FCC compliance testing?

texts:
I was researching whether do we need to do FCC compliance testing for a device we developed for a client. Curiously, it seems to be in the list of exemptions (passage taken from here):

  A digital device utilized exclusively in any transportation vehicle including motor vehicles and aircraft.

This got me wondering why such an exemption is there in the first place? Aren't badly-designed intentional radiators just as bad when mounted on a car?

My guess would be that in the past, motor vehicles used ignition systems which are known to cause interference, so EMI-wise, the situation is bad enough already. But it certainly strikes me as odd if that rationale lives on in the 21st century!

Could somebody shed light? (I'm mostly just curious, but the rationale behind this exemption might be of importance to us).


texts:
Datasheet: http://www.analog.com/media/en/technical-documentation/data-sheets/ADV7125.pdf

Assuming R0, G0 and B0 are the least significant bits of each channel, but cannot find it specified anywhere in the datasheet explicitly.

Is there a convention for this that the higher the bit number, the higher its significance?


texts: Unknown component on PCB - rectangular, white, 4 terminals, marked 3215

texts:
I found a component, which I couldn't recognize, on a printed circuit board.  Does anyone know this kind of component?

Edited :The unknown components are the white squared ones. There are many of them.

The person that ask me this didn't tell me what this circuit does.

I attached a photo to help in the recognition:


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I couldn't understand why can't you get electrocuted touching one wire of an isolation transformer, as showed in the image:

The man in the right touches one wire of the isolation transformer and presumably get electrocuted, however I couldn't figure why -
He touches a live AC wire with 230V, the ground potential is 0, therefore for t such that 230sin(2pi50t) != 0, there is a potential difference between the wire and the ground,
Therefore a current should flow from the wire to the man, and to the ground, no?


texts: If watts is power and amps is current, what is volts

texts: I know power is measured in the terms of watts, current is measured in amps, so is there an X for voltage?


texts: Do electronics companies publish the diagram of their electric boards

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I'm new to the electronics world, and I came to know that electronics companies (As Fairchild) provide datasheet for the components they produce (As IGBT, Triac, etc.).

Do electronics companies (As Samsung, LG, Sony, etc.) provide a datasheets & a diagrams for the electric boards in their devices?

If the answer is NO! Then how can you tell what component is connected to other components in an electric board that you are fixing for a better diagnosis of the problem, especially with the existence of the "Surface" components as (Capacitors, Resistance, Optocoupler, etc.)?

If the answer is YES! Where can I find these diagrams?

Thank you in advance


texts:
I am new to electronics and I am trying to build an audio amplifier with an input signal of 100mV @ 60 hz using 12V as VCC and expect an output of 70-75W power.

I have the following circuit:

I copied this one from my notes and simulated it just to find out that it does not amplify. I believe there is something wrong with the biasing. What could be the problem?


texts: Magnetic path length and Permeability relation

texts:
In a transformer, increasing the magnetic path length reduces flux and permeability and increases reluctance of the core?

if yes, why does the equation of relative permeability of a gapped core show that permeability is increased as you increase the MPL?


texts: Surface mount transformerless 230v to 3.3v on a small board

texts: I am trying to design a 3.3V mains power supply to go on a PCB approximately 50x25mm in size (this will include other functions too!). I've come across the Supertex SR086, which is almost perfect, except that it can only pump out 60mA, which is likely to be too little for my application (Atmel AVR, Nordic NRF24L01+, triac, MOSFET, zero crossing detection, possibility of powering an LCD from it). I would appreciate any suggestions or case studies for similar solutions.


texts: Is the output DC voltage of any rectifier (Halfwave, Fullwave or bridge) simply equal to \$\sqrt{2}\$ times Phase to neutral AC input voltage? Or does every rectifier circuit have its own formula to calculate DC output voltage?


texts:
I would like to implement the HART protocol and am searching for specifications of the protocol.
I found that the Hart Communication Foundation manages the protocol and on this page it says that

  The HART Protocol was developed in the mid-1980s by Rosemount Inc. for
  use with a range of smart measuring instruments. Originally
  proprietary, the protocol was soon published for free use by anyone,
  and in 1990 the HART User Group was formed. In 1993, the registered
  trademark and all rights in the protocol were transferred to the HART
  Communication Foundation (HCF). The protocol remains open and free for
  all to use without royalties.

However when I try to download the documents from the same site it only gives me the TOC so I'm a bit confused.

Any idea where would the protocol documents be available?
If users have had previous experience in implementing this protocol, I would love to hear about their experience.


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i have written in dsp.stackexchange.com, but guzs have written me this question would be better off on this site.

I have questions according to how to measure s- parameter.

I have a two-port network:

Normalized incident voltage

Now I would like to derive from measurements by setting the value of the incident signal \$a_2=0\$, which:

\$S_{11}= b_1/a_1\$ with \$a_2=0\$.

How to set \$a_2=0\$?

How I have understood I need a wave which go in other direction compare with \$a_2=0\$. Can I reach this condition if I connect resistor with 50 Om


texts: Microprocessor instructions per cycle clock

texts: Could you please explain this issue: can a microprocessor perform on average more than one instruction per clock cycle?


texts: Design a differential op amp (subtractor)

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For my electronics lab course I need to find the values of this op amp's resistors :

I found & tried these equations :

My question is : How can I find R1,R2,R3 & R4 ; considering I want Vout = 0V when V1 = 5.6V and Vout = 7V when V1 = 5.3V and considering R1=R2 & R3=R4.

(V2 is always 9V, Vcc+ = 9V & Vcc- = 0V, wanted current 100mA, using DC power supply)

All this information was given by my teacher but I couldn't use the equations properly to find the resistors & that's why I am asking for help.

thank you for your help !


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I am working on a project of wireless power transfer system for EVs. On the secondary side there is a full-wave rectifier which output current charges the battery. Of course, after the rectifier stage there needs to be a filter that will reduce load's current and voltage ripple (see the picture)

Now, since I decided to use 'Pi filter' as an output filter, and have chosen the values of the inductance and the caps, I am not clear about few things when I want to build my schematic in EAGLE, because this is my first project and I am inexperienced in circuit design.

1) How should two caps and inductance be connected in the schematic between the rectifier stage and the load? Since I doubt that it will be a simple connection between one L and two C-s (there may have been some additional small caps and resistors)

2) What type of inductor should it be (common type, etc..)?

3) If I am not wrong, caps going to be used should be film capacitors.


texts:
For my project i would like to waterproof (or at least moistureproof) a PCB. The PCB is to be used without housing and during operation/handling there will be some skin contact (mainly hands).
Now i have read about different kinds of conformal coating like silicone or acrylic. I would like to go with silicone because most other coatings (including nail polish) tend to become brittle and chip off. Also i don't want to use things like resin because it is more difficult to apply and i may need to rework the PCB at some point.
The silicone conformal coatings i have found seem to do exactly what i need but i am concerned about the health of the users of the coated PCB (as well as my own health). I had a look at the safety data sheets of two silicone conformal coatings:

MG Chemicals 422B: https://docs.rs-online.com/7be1/0900766b814ccb6b.pdf
(productpage german: https://ch.rs-online.com/web/p/schutzlacke/1462878/)
Electrolube FSC15ML: https://docs.rs-online.com/1c83/0900766b80b7e787.pdf
(productpage german: https://ch.rs-online.com/web/p/schutzlacke/0535525/)

They seem to list quite some health risks (especially the 422B one).

Are these risks mainly due to the solvents?
Will the dangers go
away/become negligible once the coating is cured?
Are there any alternatives that i don't know about?
Is there a better place to ask this question? If yes, where?