texts: External Wall Adapter Detection in MP8007?

texts:
I am reading the datasheet of MP8007. I found ambiguity in section Wall Power Adaptor Detection and Operation on Page 16. After reading the section, i am not able to understand how IC will differentiate between voltage from Adapter and PSE. Consider the equation given below:

Where, Vadp is adaptor voltage, Vdadp3 is the zener voltage, Radpup and Radpdown are the AUX divider resistors from adaptor power.

Considering the example given in Page 20 under section Wall Power Adaptor Detection Circuit (Radpup = 3K, Radpdown = 8.06K and Vdadp3 = 30V), the IC can safely accept voltages from 38.48 to 53.98 V (even more than that).

Now, I am confused how will the IC gets to know that voltage is from Wall adapter or from PSE? Because PoE voltage range is from 44 - 57V and since, there is common voltages between adapter supply and PSE power supply and the wall adapter power is also applied at Vdd pin of IC (as with PoE).

The detection circuit is given below:


texts:
I am new to this site and maybe I won't ask a good question but anyway.
I have come up with a voltage subtractor using two MOSFETs and a voltage divider well sort of.

simulate this circuit – Schematic created using CircuitLab
Vout = VCC - VM2
If Vu < Vtm2 -> Vout = 0
If Vu > Vtm2 and Vd < Vtm1 since R1 >> Rm2 -> Vout = VCC
If Vu > Vtm2 and Vd > Vtm1 since Rm1 || R1 and Rm1 << R1 the resistance of the loop is Rm1.
The resistance Rm1 depends on gate voltage (Vd) as well as Rm2 depends on gate voltage (Vu).
We want when Vd = Vu Vout to be 0 (substractor Vu-Vd). However if M1 is M2 then when Vd = Vu -> Rm1 = Rm2 -> Vout = VCC/2.
So the rate at which resistance changes according to gate voltage in the M1 must be bigger than M2 so that Rm1 << Rm2 << R1 -> Vout  = 0.
MSF1's resistance changes more rapidly with increase in gate voltage than MSF2.
However currents using MOSFETs are very big some amps while I would like this to work for mA. How can I achieve this?


texts: How antenna radiates(how currents flows through wire)

texts:
I don't understand how antennas radiate a signal.

I understand basics antenna(wavelength, electron E field, ...), but I simply don't understand how can current go through a wire that doesn't have negative pole.

Can you please explain that to me.


texts:
I need to do a lab that seemed like it was simple, but for some reason i cant get the right output for this function. its G(0)= T1T3'+T5T7'. These are data inputs.. I can only use NAND and NOR gates. The set up i have now is as shown below

I continue to get a constant low output for G(0). I would really appreciate it if someone could let me know where the schematic is wrong. Thanks in advance!


texts: Can´t get 8-bit shift register working (CD4014BE)

texts:
I can't seem to get my 8-bit shift register working. It's the CD4014BE.
The datasheet can be found here.
I've confirmed that the clock (pin 2) is ticking and the input (pin 4) is continuously switching between 0 and 1 on every clockcycle. I've tried multiple different setups, swapped components, but nothing works.

My code:

int clockPin = 2;
int dataPin = 4;

void setup() {
  pinMode(clockPin, OUTPUT);
  pinMode(dataPin, OUTPUT);
}

void loop() {
  digitalWrite(dataPin, HIGH);
  delay(100);

  digitalWrite(clockPin, HIGH);
  delay(400);
  digitalWrite(clockPin, LOW);
  delay(400);

  digitalWrite(dataPin, LOW);
  delay(100);

  digitalWrite(clockPin, HIGH);
  delay(400);
  digitalWrite(clockPin, LOW);
  delay(400);
}


texts:
I just saw a DIY solar panel setup, in which a single panel produces 12V output, which is then passed through a controller and stored in a 72Ah 12V car battery.
The stored electricity is mostly supposed to be used for night lighting of the outside, and currently consists of a single 12V 3W LED lamp (and of course the associated night-time detector.)
The question is, is there any sense  (from energy efficiency perspective) to use an inverter and 220V lamps and other loads, if the required items can be had in 12V versions?
I would assume 220V loads would be more energy expensive to run, as the voltage converter adds another step in energy conversion and every step results in some energy loss. However, as I understand, high voltage lines are a better way to transfer electricity across larger  distances. The distances involved here are hardly likely to exceed 10-12m though.


texts: I found that some laptops use a 3 wire CMOS coin cell. The construction is simple, 1 wire is spot welded to the positive side of the CR2032 and the other 2 to the negative. There is nothing like a sensor of any kind. Why is that so? I can't see the purpose.


texts: How could I generate a PWM signal from a control voltage

texts: I want to use a control voltage to generate a PWM signal that will drive a DC motor. I can't use a potentiometer with a 555 timer as I have to control it from National Instruments LabView software with a voltage output.


texts:
I'm trying to replace a rotary encoder with push switch from a Boss SE70 effects unit as the switch is broken; the same encoder is apparently used in a number of Roland products such as the JD-990, JV-1080, SC-880 and JV-880 (all '90s vintage I think).

This type of repair is normally straightforward: find something that is roughly the same mechanically and electrically. The part is listed as an RK09710WL, with Roland part number 13289196. I can't find any data on this part other than it was made by Alps (marked on the base). It has 20 detents.

I chose a Bourns PEC11R-4230F-S0024 as it was the right length, had a switch and had roughly the same amount of pulses (24 rather than 20 on the original) and detents. It even had pretty much the same footprint.

However it does not work. It seems that the encoder used by Roland gives a very different output to commonly used rotary encoders.

With the replacement encoder installed (that does not work correctly), the output from the two pins is as expected (direction reversed half way) for most rotary encoders:

With the standard (working correctly bar switch) encoder in place, the output is:

The stock encoder sends a short pulse (<50ms) on one pin only when turned in one direction and a pulse on the other pin only when turned in the opposite direction.

I've never seen a rotary encoder with this kind of output - does anyone know what it is and how to find a replacement? The dimensions are not too important as the encoder mounts on a small PCB (no other components on the board) and is chassis mounted so anything can probably be made to work, but that unusual output is needed.

Here is the excerpt from the schematic:

The rotary encoder lines connect to pull up resistors and debounce/filter resistors and capacitors, then to microprocessor pins as expected.

Can anyone provide any help, information or guidance?


texts: why Commutator power capacity is limited

texts: A commutator's power capacity is said to be limited to a few megawatts. What are the reasons limiting it? I thought it could be like brush resistance and spark strength. What is the maximum voltage limit to use a commutator?


texts: Could a significant amount of electricity be generated from public hand-operated generators?

texts:
So imagine you're at a bus stop at a train station. You're bored and have got nothing to do. So you see a big crank-handle sitting there doing nothing, and because you're bored, you decide to spin it for a bit. The crank is connected to an electrical generator, and when you turn it, it outputs free electricity, that goes into the Grid, or wherever it's needed. Then imagine that these generators are everywhere where there are people: transport stations, shopping malls, etc. There's no requirement or reward from turning the crank, but you can imagine how many bored people or children might want to spend a bit of time playing with it, and in doing so they're making free energy. There might be ways to incentivise using the generators too, for example by keeping a counter of how much power has been generated by that station (to gamers, it would be like levelling up a new skill!)

My question is: could this be a feasible and cost-effective plan reducing the amount of non-renewable energy? Obviously it wouldn't displace non-renewable energy, but do you think that, if done on a large scale and in places where lots of people would be likely to use it, it could generate enough electricity to be useful? Could a hand-operated dynamo even power a house? Or are we talking barely enough energy to power a lightbulb?


texts: How important is the temperature stability for gain - setting resistors?

texts: When two resistors are used to set a gain of an opamp, do I need to care about their temperature stability, provided resistors are from the same series, same manufacturer? Let's say my circuit will operate over temperature range of 85 degrees C and the gain of amplifier is 100.


texts: Measure universal motor inductance with LCR meter

texts:
I'm trying to measure the inductance and equivalent series resistance of an universal motor (from a sewing machine, 120V, 0.8A) with a B&K 879B LCR meter.
The measurements vary widely with the selected test frequency:

100Hz: 164mH, 60 Ohm
120Hz: 160mH, 65 Ohm
1kHz: 84mH, 285 Ohm

Measured in series-mode.
DC resistance (measured with multi-meter) is 40 Ohm
I would have expected that the motor, when not rotating, can be reasonably approximated by an ideal inductor with a resistor in series.
I wonder what the main culprit is that makes the measurements so frequency dependent. Stray capacitance between the windings? Skin-effect?


texts: Can pwm pulse damage High Side Solid State relay IC ,driving Bulbs as load

texts:
I am driving a 12V, 10W Bulb and 12V, 5W Bulb (parallel connected) on one channel of high side driver solid state relay IC. For dimming effect, Bulbs are driven by PWM (Intial 3msec) then continuously ON. After some use, the IC channel fails to work.

VNQ600AP-E IC spec:
Output current (continuous), for each channel   IOUT    15A
MAX ON-state resistance Ron 35mΩ
Current Limitation  Ilim    25A
Bulb inrush current is below 25A.

Can anyone please give explanation, why the IC is getting damaged.


texts: Will a computer fail sooner the more you use it?

texts: Is a computer like a car in the sense that the more you use it the quicker it will break down? Assuming that we have a regular computer with SSD that is running 24/7 versus a computer that is run everyday for only 8 hours. Which computer will fail faster?


texts:
I have tried my hand at designing a circuit for a tiny robot, but I am not sure at all if it will work. I thought about the robotics stack exchange, but this seems more suited to the job.
The questions:

Which parts of the circuits will not work

Where do the traces/wires need to be thicker for more current

(Sorry about different formats)
Motor Board

Main Board

The image at top is my attempt at designing the motors board for the robot, which also contains the batteries and charger. Assuming the microcontrollers are programmed correctly, which part is a bad fit/ has a wrong value.
To clear this up, I am using 80 mAh micro gearmotors, I think that the LB1836M IC may be too powerful for these tiny motors.
LB1836M IC
The gearmotor
The battery
Description:
The robot's goal is to be a low-cost (on the order of 10-30 USD) swarm robot. The five IR sensors act as proximity sensors / communication
Edit: Rephrased some of the question - thanks to Leon Heller
Edit: Updated Schematics for human-friendliness


texts:
I'm working on an analogue audio, video and sync board for my Dreamcast. Something I've been wondering about is the tolerance for analogue video, specifically RGB, in regards to the delta for trace length.

In my case my total Red and Blue traces are 61.382mm and my total Green trace is 55.964mm, and all three have a 220µF electrolytic capacitor (C1, C2 and C3) around the middle of their traces. The max voltage through the traces is 0.7VAC, they operate at 14MHz, my trace width is 0.414mm (for 75 ohm impedance) and the distance between them is around 5.50mm. Will that 5.418mm delta cause problems? Because I'm having a tough time exactly matching Green with the other traces.

This is my current circuit, in case it helps.


texts: microcontroller serial communication noisy on direct wire connection

texts:
I did a simple circuit to test data communication between two separate microcontroller circuits.
The big X is actually two wires (not touching each other) that connects the two circuits together.

Each inverter IC has its own 3.3V source from a regulated 5VDC source via voltage regulators.

The reason I'm using 3.3V is because I'll replace the wires with radio modules that can't accept more than 3.9VDC.

The microcontroller code itself runs as expected (I verified it in software simulation and on the board countless times with LED lights)

I even further debugged code by replacing a microcontroller with a max232 so I can collect data on the PC.

When I examined the data, much of it was accurate but there were some bytes that were not expected. The values were off by one bit being incorrect in most cases.

At the moment, I'm waiting for 74HCT14's in the mail and I will see if that makes a difference since they don't react terrible to sudden short spikes like the 74HCT04's do (or am I wrong?)

I'm also open to other IC's that work as drop-in replacements for 74HCT04 and LM1117-3.3 that would make the data transmission more smooth.

For my PCB I made my tracks short and wide (2mm width) and spacing is at least 12mils.

The data speed for communication is 38400bps.

I'm also tempted to throw in resistors somewhere in the receiving path (between inverter and microcontroller pin)

What else can I do to ensure the line is noise-free?


texts: What piece of technology is able to record the exact phase of microwaves?

texts:
I had this question on the physics community, but I thought this would be appropriate to cross-post here.

I read that in VLBI, the signals of microwaves (on the millimeter scale) are recorded and then later combined. A famous example of this is the Event Horizon Telescope which imaged the black hole. Presumably, the telescopes recorded the phase of the microwaves.

This tells me that it is possible to record the specific phase of a microwave, but I haven't seen any technology that can do this. Most oscilloscopes, for example, don't have high enough frequency to resolve such short time scales required to measure microwave phases.

My two questions are simple. Answers to either one would be helpful.

Is there any piece of technology that can measure the phase of a microwave? What technology is used anyways for VLBI to record phases?

Edit: When I said "phase" I meant to say the actual "magnitude" of the wave at any point in time, but I see it is more complicated.


texts:
Reference video: https://www.youtube.com/watch?v=U5-Fy4ULdPg

The chimp is climbing both wires out of phase (i would have to assume, it is in Japan), do the power lines have to be closed for the chimp to do that? How is it possible that the chimp is not electrocuted? It was stated that power was out for 1000+ people so i would have to assume the lines had to be closed for the chimp to survive climbing this?


texts:
I'm new quite new at electronics and trying to learn small tricks too.

In some schematics, I saw they're adding resistors or capacitors on the signal.

1) For example please check U1's 13th leg at the schematic below. Value of C5 is 100nF

CH340G schematic

2) In another schematic (couldn't find it again) I saw 100r resistors on SPI's MOSI, SCK and CS (chip select) signals. I applied schematic and it's working with and without those resistors.

I can only thing, they're tried to protect the IC.

Note: I do not have an oscilloscope

Regards


texts: Boosting a microphone for a noisy, low sensitivity input?

texts:
To avoid running into an XY problem, here is the problem I really have:
I have a RODE NTG2 microphone, and a Zoom H4n Pro recorder. The NTG2 has an XLR output, balanced, and it operates from either a single AA battery, or 48V phantom supply.

The H4n is a portable recorder that records to SD card, up to 24bit/96KHz uncompressed WAV or MP3. It has a combination XLR+1/4 jack input. If you plug a 1/4 connector, it is a line-level, unbalanced input. If you use the XLR connection, it's a mic-level balanced input. The recorder automatically switches between inputs depending of what type of connector you plugged.

The general consensus on the web is that this mic isn't "hot enough" for this recorder, as the recorder expects higher inputs. For example, I have to set maximum gain input in the recorder and speak right into the microphone to get -12dB peaks in my recording. This is not acceptable since this is a "shotgun" microphone and you're not supposed to speak right into it.

Also, when using the microphone with 48V phantom power, you get more gain out of the mic. Apparently +6dB. I haven't accurately measured, but indeed, switching phantom on and off, the mic sounds "much louder" with phantom than with batteries.

The solution proposed by most people online is to use a device called FetHead that will boost the mic +27dB and this makes it manageable for the Zoom. But this device is almost $100 and I don't live in the US so it's a long delay for shipping.

So I googled for several options and, as usual with audio circuit googling, I ended up on ESP's site, particularly in the Project 66.

In this project the first stage is two discrete amplifiers based on regular NPN/PNP general purpose transistors, and a opamp-based balanced to unbalanced stage.

Why does he use a discrete preamp? Is this just an old design?

Then I googled for other options. I found others with discrete preamp stages, others with instrumentation amp stages, another circuit with JFET, etc.

I have all sorts of ICs in my junkbox: NE5532, OP177, OPA2134. JFET I only have BF256. I also have BC847/857 for SMD. I don't have the more exotic THAT1512 which seems like an ideal solution.

Finally the question:
Should I use a balanced input/unbalanced output opamp, and take the mic-level output from my mic to line level? My recorder doesn't have line-level balanced inputs.

Should I just boost the signal from the mic from mic-level balanced to mic-level balanced? I was thinking I could use just the first stage of Project 66 for this. Leave out the opamp section.


texts: Effective Address calculation time on 8086/8088

texts:
I've started designing an implementation of an 8088 from scratch with the goal of being cycle-exact. I can understand the reasoning behind the number of clock cycles for most instructions, however I must say I'm quite puzzled by the Effective Address (EA) calculation time.

More specifically, why does computing BP + DI or BX + SI take 7 cycles, but computing BP + SI or BX + DI take 8 cycles? Note that this is the number of cycles for the whole EA calculation, which includes a shift plus add with a segment register (presumably this takes a couple of cycles to keep combinational delays as low as possible).

I could just wait for a given number of cycles in my design, but I'm really interested in knowing why there's this 1-cycle difference (and overall why it takes so many cycles to do any EA calculation, when an ADD between registers is just 3 cycles).


texts:
I need to generate signals at the output of a Mega Arduino to simulate the signals of a rotary encoder. I know how to generate frequency signals through the function below. How could I generate the signals as in the image below, with a time lag between them? I have to take into account that the frequency must be the same.

void Encoder() {
    tone(51,60);//Generates a 60Hz signal at output 51
    tone(52,60);//Generates a 60Hz signal at output 52
}

update:

I was able to generate the desired signal by doing the following:

void Encoder() {

        int i;

        for (i == 0; i <= 10000; i++) {
            digitalWrite(50, HIGH);
            delay(10);
            digitalWrite(48, HIGH);
            delay(10);
            digitalWrite(50, LOW);
            delay(10);
            digitalWrite(48, LOW);
            delay(10);
            digitalWrite(50, HIGH);
            delay(10);
            digitalWrite(48, HIGH);
            delay(10);
            digitalWrite(50, LOW);
            delay(10);
            digitalWrite(48, LOW);
            delay(10);
        }
    }


texts: What is clock cycle in a microprocessor?

texts:
can any body saying to me what is that the difference between a micro controller with 1 MHZ and 200 MHZ clock in a timer project or in a project that record sound by micro in a sdcard or in a servo motor project or in a counter project that use a laser and a sensor? surely clock is an important factor in a micro but where? please explain in a simple example.
can i say that in program viewpoint clock is the rate of all program repeat and checking all 'if' and do all loops and...


texts: What will a combinational logic circuit look like using any basic gates having the output=1 when the input=110 and 101?


texts: How can I make a simple circuit to trigger a buzzer for a 3-pin 12v DC fan when its stops working using the fan Sense/TACH/Yellow wire?


texts: Is there any reason to prefer one MLCC manufacturer over another?

texts:
I'm specifying some SMD chip capacitors for the first time and I note there are several manufacturers out there: muRata, Yageo, Vishay, AVX, Kemet in particular, perhaps others.

Is there any good reason to prefer one of these manufacturers over the others for chip capacitors?

They all look the same from the pictures, of course, and the prices seem to be quite comparable. Are these just a pure commodity or are there real differences? If there are differences, how would one typically go about discovering them, other than "asking around" like this? :)


texts:
I have a data acquisition board(A/D+Digital Signal Processor) and I want to check if a digital high-pass filter(implemented in DSP) at an extremely low cut-off frequency(0.05Hz) is actually working.

If this was a frequency I could generate with a signal generator it'd be easy to check, but 0.05Hz is too low and I can't generate it. How do engineers check this kind of filters?


texts:
We were looking for a very specific type of ADC in a small package for one of our projects, and found something suitable in a TSSOP. We wanted to save more space, so looked into getting bare dies; the manufacturer confirmed the dies are 2mm square, but said we'd have to order "some millions" to make it worth providing them. We needed maybe 500/yr and the budget is not huge, so that was the end of it and we decided to do something else.

But I was curious: What do people do when they want small numbers of bare dies? Does anyone decap ICs and use the dies in production? If so, can the process be made reliable, and roughly how expensive is it?

If anyone has examples of products or case studies, that would be really interesting.


texts:
My code is about button counter  .which appear on lcd 2x16 .pic18f46k20 .i want when i turn power off and turn on it again it should show the last number it count .
how to make data saved in pic and lcd when i turn off the power?


texts: Determine end of USB Data OUT packet on device (STM32)

texts:
I'm busy with a USB to Ethernet implementation (ECM) on an STM32 using the ST USB library (not HAL) and LwIP.

When I send a packet to the host (Data IN) that came from the ethernet interface, I know where is the end of the frame and therefore know when to send a zero length packet (ZLP) (when needed).

But how do I know when it is the end of a USB packet from the host (Data OUT)? So that I can send an entire frame to the ethernet interface?

I had a look at the endpoint parameters but none of them provide info on the the total packet (frame) length. Only per packet information is available.

I do not know the USB specification that well and not sure if this info in transferred with the initial/setup packet?

Maybe there is another method I can use to detect the end of a frame from the host?


texts: Variable output from Power Bank (24W = 12v * 2A and 5.4W = 9v * 0.6A)

texts:
I started with trying to find 2 UPS for 2 of my routers with the following input specifications:

12v 2A
9v 0.6A

I realised that buying 2 power banks will be economical than buying 2 UPS for the AC power source.

I started searching for the power banks with the output specifications which matches my routers' input specifications. I did not have issues finding the 9v 0.6A. However, I am unable to find the 12v 2A, except for car jump start power banks (which are very costly and I am not sure if they allow charging while connected to the router at the same time).

I thought of building one by stacking sufficient Lithium-ion 18650 batteries should not be difficult with configurable output voltage and amperes.

I came across these instructables

8v 0.6A
12v (Amps not mentioned)

But none of the above matches one of my router's input specs (12v, 2A)

I also checked other questions on StackExchange, but not very helpful, example:

Powering 12V 2A device from high-power USB portable charger - No conclusive answers.
Creating a Li-on backup for a 12v router - Good schematics and answer but the output specs does not match mine.

So, I landed up here to understand how this can be built. I am based out of Bangalore in India and I would prefer to procure materials available here.

My requirements:

Build a power bank which can charge itself and also power the router at the same time (work as an UPS)
Display output voltage and current preferably
Configurable unit on the built device which can moderate the output voltage and current.
Battery overcharge protection unit
Under and over voltage protection
Cost effective - I am ok to sacrifice point 2 from the above to cut down on cost! I can always use a voltameter to check the output specs manually ;) Fine with leaving behind point 3 as well and have a fixed output instead of variable one, however, I would love to have point 3 covered!

This is what I can think at the moment from requirements perspective, is there anything else I should consider?

I am very naive at electronics but very much interested to learn and build :) Looking forward to lots of fun and education from the community and a fruitful product!!


texts: Amplifying the output voltage from a coil (10Hz-20kHz) using an AD620 module

texts:
Disclaimer: I’m computer scientist.
I would need some help to get an AD620 amplifier module to work.
Some context is available here in a previous question.
Here is a physical view of the amplifier:

The documentation was unfortunately in Chinese, but I translated it. It is available here.
I managed to amplify the output of my generator (TieDie Handyscope H3-5) and adjust gain, but not with the exact same setup depicted in the image. I needed to connect the ground of the input terminal to the ground of my power source.
I didn’t manage to amplify the signal I need to amplify.
I want to amplify the varying voltage at the terminals of a coil that I didn’t manage to see with my oscilloscope (TieDie Handyscope H3-5). I was expecting that I would see at least the ambient 50Hz noise.


texts: Undefined std_logic_vector size parameter in procedure

texts:
I have written into a procedure the behavior of a simple SPI transaction that I use in my testbenches to make things easier to write and read.
Is there a way to make this procedure as generic as possible by not mentioning the size of the vector data given as a parameter? Or maybe add a size parameter as an integer?

Here's the procedure I'm using so far. For now I have one procedure declaration for each vector size I want to transfer.

procedure spi_transfer_3B(data : std_logic_vector(23 downto 0)) is
variable bitCnt : integer := data'length-1;
begin
    spi_clk <= '0';
    spi_mosi <= 'Z';
    spi_ss <= '0';
    wait until rising_edge(clk);

    for i in 2*data'length-1 downto 0 loop
        wait for SPI_CLK_PERIOD/2;
        spi_clk <= not spi_clk;
        if spi_clk = '0' then
            spi_mosi <= data(bitCnt);
            bitCnt := bitCnt -1;
        end if;
    end loop;

    spi_clk <= '0';
    wait until rising_edge(clk);
    spi_ss <= '1';
    spi_mosi <= 'Z';
end spi_transfer_3B;

What do you think?


texts: Why don't we use low voltage Power Sources for high wattage applications?

texts:
Super nooby question involving Ohm's law, but this has been on mind this morning.

Say I have a 60W device, and I want to power it. Usually this calls for a 120V source or something. However, why not use a 5V source and draw 12A with really low resistance? Is it for safety purposes mainly? Or is there an issue with getting the resistance low enough to achieve the 12 amps?

I tried googling this but not much came up. Probably really obvious but just wondering..

EDIT for duplicate mark: The duplicate suggestion is similar; however, it discusses series vs. parallel cells and adds interesting information, but isn't exactly what I was asking about. The answers provided on this post were much more useful to me.

EDIT 2: I added my original edit back now that the duplication mark has gone through.


texts: Unity gain op amp gives static, incorrect output

texts:
I have the circuit shown here:

where I'm using a switching regulator (not the linear 78xx shown) to provide me with 5V to power an Arduino and a little more circuitry that the Arduino is monitoring.  The Arduino is measuring (and logging) the voltage at A - ie I'm logging the input power supply voltage (which varies ~12.7 > 14V according to the solar charging the 12V batteries).

Without the op amp (ie measuring the voltage directly from the potential divider [and with resistor values ~1/2 of that shown]) the voltage logged is as expected.  I want the unity gain op amp so as I can increase the resistor values to reduce the current drawn.

However with the op amp in place the output (A) is a static ~3.74V.  I measured this directly at a time when the voltage to the +ve op amp input was ~3.85V, and I also know from reviewing the logging that the voltage on the output of the op amp was static throughout the previous day*.

I'm probably making some rookie mistakes, I'm new to the idea of an op-amp as a buffer - in this case I'm using an LM358 (datasheet pdf) as it's what I have available - I'm very open to suggestions of a more appropriate amplifier.  While I could get away without it in this case, I do want to minimise the current drawn here, and I will also be logging the solar voltage (~70V) so will definitely want > 10k resistors in that potential divider and will therefore need a buffer.

*the voltage is logged whenever the scaled measured voltage varies by 0.05V (ie battery voltage goes 13.1 -> 13.15).  Without the op amp this logged ~1000 entries in a day.  With the op amp it logged half a dozen, and these varied only within ~12.4-12.5V (despite the solar MPPT charger reporting the day max of 14V).


texts: Wired-or open drain with open collector outputs

texts:
I have a comparator with open collector output (LM311) and a gate with open drain output (SN74LVC1G06). I want join these two outputs to make a wired-or, with a pull-up resistor tied to +3.3V.

In a general way, is it appropriate to join an open-drain output with an open-collector output?


texts: Determining the shunt resistance for DRV8301 BLDC Gate Driver

texts:
I am trying to study how to drive BLDC (Brushless DC) motors, and got stuck in the current-sensing part.
I am using a DRV8301 Gate Driver IC, which contains with shunt amplifiers. My current understanding is that, knowing the voltage drop and gain used, I can calculate the current if the resistance of the shunt resistor is known. But I can't seem to find this info on its data sheet.
Am I expected to calculate this resistance myself? If so, how should I go about doing that?
Thanks for your time.


texts: Configuring fuel gauge IC (BQ35100) with USB-I2C converter

texts: I want to use TI's BQ35100 fuel gauge IC for my circuit. As per this instructional video, I would need an evaluation board and a communications interface adapter to configure the IC. Could I just use a simple USB-I2C converter (e.g. this Adafruit converter) to configure the IC instead?


texts:
I bought a 12volt, 80 watt aftermarket fan for a car. What I'm making is a portable swamp cooler for my tent when I move to AZ this summer. I plan to charge a 30 amp, deep discharge trolling motor by both a 400 watt power inverter in my car, as well as off a 24" square solar panel when the car is stationary. I needed the 12" size fan but I doubt I need the full 80 watts of power. I want the fan to run slower than it was built to run so it's not loud in order to allow me to sleep, and the 14" square wood-chip mat which water trickles down does not need a high volume fan to cool my tent efficiently.

What electronics are required to make this fan adjustable until I figure out just the right speed for coolness and decibels? Won't slowing down the fan also allow me to use less battery power every night? A rheostat may be easy to dial in, but I see that they are costly for a 80 watt load. Am I wrong in this regard?

I don't mind spending $20-$30 for the electronics, more if necessary for longevity since I plan to use this swamp cooler every night for the next 6 months. What gauge wire should I use and should it be stranded? I plan to hook it up directly to the deep discharge battery every time I use it. Thank you for your insight and help. Keith A.


texts: What happens if usage current exceeds DC adapter current rating?

texts:
I have a DC adapter 5 V, 350 mA. I'm using this adapter to be fed into a 3.3 V regulator which powers up my bluetooth device and a few LEDs.

My question is: what happens if I source 300 mA from this adapter or if I use all of 350mA or even exceed it? Will it run out of juice or will it get hot?


texts: Looking for gyroscope drift spec in datasheet

texts:
The product page of the BMI088 IMU makes the very impressive claim

  The automotive-proven gyroscope of the BMI088 has an unmatched bias stability of less than 2°/h

However, I can't find this claim anywhere in the datasheet. The datasheet does contain Zero-rate Offset, Zero-rate Offset Change over Temperature, and Zero-rate Offset Supply Voltage Drift, but not Zero-rate offset drift over time.

What would zero-rate offset drift over time be called in the datasheet? If it isn't included, can it be derrived from other specifications in the datasheet?


texts:
I'm trying to program a pic16f877a using PICKIT3 and MPLAB without success.
I'm powering the pic with the pickit.
I verified the connections almost 20 times, everythings plugged at the right place , every times when I try to burn the pic I get :
"Too much current has been drawn on VDD. Please disconnect your circuit, check the CLK and DATA lines for shorts and then reconnect." and "target device id (0x0) is an invalid device id. please check your connections to the target device".
I'm using a RC Oscillator with an arduino since the pic does not have an internal oscillator and I don't have any quartz or battery.
I made a quick schematic using paint to show you my connections using an image that I found on another similar thread(How to connect a dsPic30f2010 to pickit3 icsp).
Thanks !


texts: How do you design a switch input to a MCU for ultra low power consumption?

texts:
I'm trying to build a low power door monitoring switch.  I'm using an MSP430FR2311 with the below circuit.  The switch is a SPST reed switch and there is an internal pull-down resistor on pin P1.0 of the MCU.

When the switch is open power consumption is 1 uA but when the switch is in the closed state consumption is 100 uA.  I want to be able to run this on a small battery for years at a time.  Is there a circuit that will get me low power consumption in both the open and closed states of the switch?

simulate this circuit – Schematic created using CircuitLab


texts:
I have an MP3 sound chip module from Talking Products.
4.5 volt battery driven
40mA
with an 8 Ohm. 0.5 Watt speaker.
I briefly plugged in two 4 Ohm 3 Watt speakers and they worked (and sounded much better).
As a complete electrical novice will things be OK if I connect them or am I playing with fire?


texts: RC Lowpass Filter between Amplifier and ADC input

texts:
I have sensors (pyranometers that consist of thermopiles and measure sun irradiation) that ouput a low voltage signal so I need to amplify them using an instrumentation amplifier.

I have chosen the AD8237 for this task: Datasheet

I'm using a gain of 100 to amplify the initial low voltage signal (ranging 0-20mV) to 0-2V range.

I'm then feeding the amplified signal to the ADC (MCP3422): Datasheet

My sensor values change very slowly and I will read out the digitized ADC values only once every second, so speed is not important in my case.

Now as pointed out in the accepted answer in this question I need a filter between the IN-Amp and the ADC to filter the noise.
In many ADC-datasheets a simple passive RC-filter is suggested between the INA and ADC.
I did quite some research and I still have some questions that confuse me and I hope you can help me with:

I figured that a first order RC filter does not meet my requirements so I cascaded multiple RC stages:

simulate this circuit – Schematic created using CircuitLab

And this is the simulated filter response in LTSpice:

Questions:

Can I do that?
What would be the disadvantages using the proposed filter?
Capacitor values like 47µF or even 100µF give me a even better response (stronger attenuation,) would that have a negative impact on my signal or the ADC?

I guess resistor values should not be further increased to prevent voltage drop on my signal.

The filter response seems very promising:

Signals at 10Hz already attenuated by ~50% and at 25Hz already by ~90%. As I only care about the DC signal I guess that response should be fine (also 50-60Hz range is covered strongly by the filter.)

Resistors create voltage drops so how would these three cascaded resistors affect my amplified signal (thus my digitized value calculated by the ADC?)

Ohms law should apply, but I do not know the current...
Any clarification on this is highly appreciated.

Regarding speed/time constants:

As my data acquisition (readout ADC once per second) and change in sensor value is very slow, do I need to keep an eye on the speed/time constant of this filter?

As many datasheets suggest an RC filter stage this approach should not be too far off.


texts: Why is the square wave signal so distorted at the output of a push-pull pair?

texts:
I have this example circuit on my workbench:

simulate this circuit – Schematic created using CircuitLab

If I remove the RLOAD=1K resistor, then the output signal gets distorted.

Yellow is Node1 and blue is node2. With R load:

Without R load:

It is not easy to read from the picture but the lower part of the square signal starts at 600mV (one junction) and slowly goes down to about 50mV. Here is it zoomed:

The same thing happens at node1 too, but I'm less concerned about that. I wonder why there is distortion when there is no load?


texts: Refractive index of Infrared light through air and perspex

texts:
What will the refractive index of infrared light traveling to air and through perspex be?
So n1 is air and n2 is the perspex, I am using Snell's law to prove that as thetha 1 decreases so will thetha 3. But I need to the refractive indices of IR though air and Perspex first. Are the values for n1 and n2 correct?


texts: A zero mean random signal is uniformly distributed between limits –a and a and its mean square value is equal to its variance. What is the r.m.s value of the signal?


texts: How to best attach a wire to a switch without soldering?

texts:
I've got a switch like this one:

Now my (quite novice) question is: How do I best attach a wire to the connector without soldering, e.g. for quickly trying something out?

Right now I've folded the wire so that I got a hook at its end, put that hook into the hole, and wrapped everything with electrical tape.

Is there a better way?

(I can't use alligator clamps as the two connectors are too close to each other.)


texts:
I am looking for a balun to be used as a single-ended to differential converter, 1:2 impedance ratio, including range 1.5-2.5GHz, SMT and phase balance as good as possible (and return loss). Center tap (for common mode) would be nice but not required.

When I look at the Mini-Circuits site, I find the following options (which I do not see with other vendors like Macom or Coilcraft):

I know that the following would not work for the setup above:

D and Q (because it is unbalanced-unbalanced)
E (seems to be differential-to-single-ended (and not other way))

But for the rest: Is there any reason any of the others would not work as a single-ended-to-differential converter? Particularly, is there any reason why config K or N would not work?

Why does Mini-Circuits provide these different kinds of configuration but other vendors not?


texts: Can Vias be used on the board for branching tracks?

texts:
I need to split the RST line in two directions and also connect it to the opposite layer of the board.

I did it like this:

Is branching the RST line the right decision?


texts: If I have an 11.6 Ah 48 V battery, how many kWh does it take to fully charge it from empty? I calculated 556.8 Wh using the formula P = I * V  (11.6 * 48 / 1000), which works out to be 0.5568 kWh. Is that correct? Do you have to factor in the voltage and/or current of the charger at all?


texts:
I have a Scarlett solo like the one above and I need a way to split the output of the Mix boards Auxiliary output into two level controlled signals. This Scarlett puts the Instrument on the left channel and the Microphone XLR that I think is 600 ohms of impedance on the right channel.
I was hoping to do this with a passive circuit and still be able to keep the Zout of the Aux send at 100K zout if possible.
Would anyone have a circuit recommendation they could suggest?
Thank you


texts: Can I just use any soldering iron for logic board repair?

texts:
So, I got really inspired by Louis Rossmann videos to get into board level repair. I am only 17 year old, but I've been learning electronics on my own for about a year now. I definitely know the basics but I have no practical experience.

I don't have a lot of money to purchase equipment or even tutorials however, so please don't recommend any tool over $50.

The question I am asking, may seem dumb to most of you professionals but this is something that is not clear to me yet, so I would like to apologize i advance.

If I want to repair newer laptop motherboards including SMD, BGA, QFN and all of that, can I just use any iron or does it have to be a special micro soldering iron? Also, will every tip fit every iron?

Any recommendations for equipment would be really helpful!

Thank you in advance,


texts: Why don't microcontrollers generally have on-chip DACs?

texts:
In this answer I read that microcontrollers usually don't have DACs, while they do have ADC. Why is that?

edit
I appreciate that integrating resistors like in an R-2R DAC is expensive in terms of real-estate (thanks Mike, for your answer), but I thought switched current DACs can be made very small since they only need a handful of transistors.


texts:
TLDR; -
I want to connect such a low-value resistive load to a transformer that it draws ~1.6x the rated output current but I'll only do so for short periods of time so the transformer won't overheat. Aside from a drop in output voltage, is there anything that could occur that I should be aware of or transformers don't care as long as they stay cool?
I'm DIY-ing a JBC soldering station similar to Unisolder and MarcoReps' design and I have a question about the transformer VA rating that I need. This all started when I designed my station around a 130VA, 20V transformer and it worked really well, but the transformer barely got warm to the touch(IR thermometer clocked it at 36C) even when running at a high duty cycle while trying to heat a large copper bar. My iron works very similarly to JBC's and the above DIY designs where it only passes half or full waves to the iron with no phase control, reducing noise and interference.
This analysis of the internals of one of the JBC stations reveals that it only has an ~80VA transformer despite the station being listed as a 130W station. Further, based on the Vp values measured, the transformer appears to only output ~18Vrms under load instead of the 23.5V listed on the product page. I do see this other post about the power rating, so I understand to an extent how the voltage numbers make sense, but the power numbers still don't.
Based on all this, how would my transformer behave when I exceed the output current limit? My choice of 80VA, 18V transformer has an output current rating of ~4.4Arms. But the 2.5ohm cold-resistance of the tip would result in a 7.2Arms draw at least when the tip is still cold. From my research, the VA rating for large grid transformer applications is based on heating effects which won't be an issue for me since I'll be operating at very low duty cycles for the most part and my time-averaged power will be <80VA. However, could anything else occur due to these larger current draws? I was thinking saturation of the magnetic field in the core could play a role here? Will this just manifest as a slightly lower peak voltage?


texts: Designing Pick-and-Place-friendly CAD library parts

texts:
I'm working on a PCB design with surface mount components to be manufactured by a PCB assembly shop. I'm using CADSTAR, and I had to populate the library with some components, from scratch. I'm new to this, and I want to make sure I'm defining component outlines and origins in such a way that the pick and place machine will match the leads up correctly to the land area.

Consider a specific component, a humidity sensor from Honeywell. As I've defined the component in the CADSTAR library, the placement and silkscreen outlines are identical, while the assembly outline is smaller and is offset (lower) in the y-axis with respect to the other two outlines:

Should my component origin be defined at the center of the placement outline, of the assembly outline, or isn't it critical?

I have only the vaguest idea of how the P&P machine works. I understand that there's a camera that detects fiducial marks on the PCB, and so can match coordinates in the design with physical locations on the real PCB. But I'm a little fuzzy on how coordinates in the part definition are matched to a physical point on the part. For example, does the camera detect the outline of the physical package and try to correlate that with one of the outlines (assembly outline? placement outline?) in the part library definition? Does the placement of the component on the reel tape have something to do with it?


texts: How To Save A Matrix In Flash Memory In STM32

texts:
i'm new in stm32 and in embedded world in general. I'm using a nucleo64 f446re and I want to save a matrix in the flash memory.
Can I use CONST to do this?


texts: What is this connector of a stepper motor?

texts:
I have a Vexta stepper motor in hand with very short wires.

As much as I want to recrimp a cable, or directly buy a replacement for it, I couldn't find the connector type. It has 0.1" pitch and a lock to hold the cable in place.

What is its connector type?


texts: How should I modify this circuit to see exactly if the batteries fully charged or still not?

texts:
I made this circuit:

The op-amp is LM358.
The problem with this ciruit if the charging current get to drop about 0.10A the red and the green leds are flashing together. I want the following: if the current drops below 0.10A the red light stop to light and the green light get to light.
Do not flashing the LEDs.


texts:
Capacitors and inductors are duals of each other.

A transformer is made of two inductors, and transfers power through mutual inductance, through the magnetic near-field (right?)  Also, you can vary the ratio of voltages or currents by changing the ratio of turns on the core.  You could think of this as coupling a single primary loop with many secondary loops, and then stacking the secondary loops so their output voltages are summed.

Is there an electric dual of the transformer?  Something that uses capacitance and transfers power through the electric near-field over an isolation barrier?  Some way to couple a single primary capacitor with multiple secondary capacitors and then stack them to do power conversion by summing their outputs?

I know that an isolated supply can be built using two capacitors, but I'm not sure if that's exactly a dual, or if there's an equivalent to adjusting the ratio of turns:

 source

Or maybe something related to this?

 source

For example, there are capacitive voltage dividers, but these only reduce voltage, they can't increase it like an autotransformer.  There are charge pumps, but those require active elements like switches or diodes, which aren't present in a transformer.

More succinctly: Is there a way to transform power (1 V, 5 A on primary to 5 V, 1 A on secondary) using electric fields instead of magnetic fields, and passive components only?  If not, why not?  (Electric field screening?)


texts: Xilinx ILA to start recording after triger + Xnum clock cycles

texts:
I am trying to debug my system with Xilinx Integrated logic analyzer and there is only a limited number of samples (131,072) that can be captured after the trigger signal, whereas I need about 350,000 to reach to the place of interest. Is there a way set up the ILA to start recording 300,000 clock cycles after the trigger signal?

Initial problem: I am trying to debug what happens on the beginning of the second frame of the video processing hls IP. Thus, my trigger signal is TUSER (start of the frame), and since I need the second frame, I need the ILA to trigger only when the TUSER goes HI the second time (skip the first low-hi transition). Is it possible to configure the ILA this way?


texts: How do you calculate the drill diameter, given the ball diameter on a PBGA?

texts: Or is there just a typical value? Specifically, I'm using a 0.65mm-pitch PBGA with a recommended 0.5mm pad diameter.


texts:
I have a board with the ATSAM3S2BA-AU, which is a Cortex M3 uC. I need to use 2 PWM channel ,  here how I've done it :

 PIO_Configure(pPins, PIO_LISTSIZE(pPins));  //Pin mapping

/* Enable PWMC peripheral clock */
PMC_EnablePeripheral(ID_PWM);
PWMC_ConfigureClocks(EXCITATION_PWM_FREQUENCY * MAX_PWM_DUTY_CYCLE*2,
                     EXCITATION_PWM_FREQUENCY * MAX_PWM_DUTY_CYCLE,
                     BOARD_MCK);
/* Configure PWMC channel for 1  */
PWMC_ConfigureChannel( PWM,
               PWM_CHANNEL2,        /* channel */
                       PWM_CMR_CPRE_CKA,    /* prescaler */
                       0,                   /* alignment */
                       0);      /* polarity */

PWMC_SetPeriod(PWM, PWM_CHANNEL2, MAX_PWM_DUTY_CYCLE);
PWMC_SetDutyCycle(PWM, PWM_CHANNEL2, HALF_PWM_DUTY_CYCLE);
PWMC_EnableChannel(PWM, PWM_CHANNEL2);

/* Configure PWMC channel for 2  */
PWMC_ConfigureChannel( PWM,
               PWM_CHANNEL0,        /* channel */
                       PWM_CMR_CPRE_CKA,    /* prescaler */
                       0,                   /* alignment */
                       PWM_CMR_CPOL);       /* polarity */

PWMC_SetPeriod(PWM, PWM_CHANNEL0, MAX_PWM_DUTY_CYCLE);
PWMC_SetDutyCycle(PWM, PWM_CHANNEL0, HALF_PWM_DUTY_CYCLE);
PWMC_EnableChannel(PWM, PWM_CHANNEL0);

this works fine, but when I change the order of the configuration, meaning setting channel0 first than the channel 2 , only the second still works, so the question is why ? I'Ve tried to figured it out reading the datasheet but it didn't help !


texts: Flash datasheet information, why two input high levels?

texts:
I have an SST39SF040-70-4C-PHE 4 M flash memory. I was trying to program it using my Raspberry Pi.
Reading the datasheet Table 7 says:
Vih (Input High Voltage)= 2.0 V and Vihc (Input High Voltage CMOS)= Vdd-0.3 V.

You can find it at page 12 of the datasheet.
It is probably a very stupid question, but why do they specify two input high levels? Does the device recognize HIGH at Vdd-0.3 or 2.0 volts? If I use a Raspberry (only to program it) does the flash recognize a '1' with 3.3 volts or do I need a level translator from 3.3 volts to 5 volts logic?


texts: Suggestions for a thin contact sensor to check if there is contact between two surfaces

texts: I am doing a little experiment with my bagpack, making it into a smart bag by adding a contact sensor to pockets such that is any item is inserted the contact between surfaces break and vice versa. I was thinking to simply use 2 metal strips with magnets behind them so that if something is inserted, the circuit breaks but I am a little worried about the exposed end of the circuit (+5V). If I keep something that is sensitive to even small voltages, the exposed 5V surface might damage it. Also if I keep something conductive, it will not work. I was also planning to use a proximity sensor but I am not sure if they are durable/ thin enough to be disguised into a pocket's surface.


texts:
I am trying to design a bandpass filter that would have cutoff frequencies at 150Hz and 500Hz. The main purpose of this will be filtering notes played on a piano (or generated pure tones) that are outside this range.

I have been trying a lot of architectures on Multisim but unfortunately all of them seem to be giving frequency responses in highly negative dB ranges (-100s), and some don't even behave in the way I expect them to.

I also noticed that changing the op-amps in my designs changed the behavior of my filters quite drastically. For example using LM741 and LMC6464 caused very different frequency responses. Also, in some cases connecting the negative rail to negative voltage made a significant difference compared to connecting it to ground. Unfortunately, since I don't have a way to get negative voltage (or at least not one that I'm aware of) I have to use ground.

I would appreciate any tips on building this filter and also any insight you can share into why I get this sort of behavior (negative dB freq response, completely different response with different op-amps). Even though I'm mainly interested in building an active filter, I'm open to any suggestions and designs in building this filter. Thank you very much for your time and help.


texts: LEDs connected in series, parallel, and series-parallel combination

texts:
I have the following two circuits. And, there is a third circuit where all the LEDs are connected in series with one resistor. Could someone please tell me how each circuit works in terms of voltage and current flow. What is the switch on voltage doing? and how do the resistor or resistors limiting the current?

thanks


texts:
I am trying to read the ADC of a STM32F4. The code skeleton was generated by CubeMX, the HAL library is used. The read values are feasible but have periodic noise, as seen here:

The plot was generated by a loop doing single measurements with a 10ms delay.
Is noise of such magnitude to be expected or is something wrong?
Here is how I init the ADC:

hadc1.Instance = ADC1;
hadc1.Init.ClockPrescaler = ADC_CLOCK_SYNC_PCLK_DIV4;
hadc1.Init.Resolution = ADC_RESOLUTION_12B;
hadc1.Init.ScanConvMode = ENABLE;
hadc1.Init.ContinuousConvMode = DISABLE;
hadc1.Init.DiscontinuousConvMode = DISABLE;
hadc1.Init.ExternalTrigConvEdge = ADC_EXTERNALTRIGCONVEDGE_NONE;
hadc1.Init.ExternalTrigConv =  ADC_SOFTWARE_START;
hadc1.Init.DataAlign = ADC_DATAALIGN_RIGHT;
hadc1.Init.NbrOfConversion = 1;
hadc1.Init.DMAContinuousRequests = DISABLE;
hadc1.Init.EOCSelection = ADC_EOC_SINGLE_CONV;

The plot was generated with this code:

for (int i=0; i<128; i++)
{
   HAL_ADC_Start(&hadc1);

   for (int k=0; k<3; k++)
   {
       if (HAL_ADC_PollForConversion(&hadc1, 20) == HAL_OK)
       {
           uint32_t newValInt = HAL_ADC_GetValue(&hadc1);
           CanTxMsgTypeDef msg;
           msg.StdId = 0x500+i;
           msg.IDE = CAN_ID_STD;
           msg.RTR = CAN_RTR_DATA;
           msg.DLC = 8;
           *((uint32_t *)(&(msg.Data[4]))) = newValInt;
           can_tx(&msg, 1000);

           HAL_ADC_Stop(&hadc1);
           HAL_Delay(10);

           break;
       }
   }
}

Do you folks have any idea what the cause of that noise could be? Did I configure any (maybe seemingly unrelated) pin false? Is there a problem with the STM? Of course i could do averaging, however, I think the noise indicates some problem.

Edit:
The problem also occured without the delay. We found out that the supply voltage was not clean. After applying a circuit-filter, we get almost constant values with sigma~1.7. Thanks anyway!


texts: Two dimensional 512 byte (byte addressable) RAM from 16 byte chips

texts: Assume it is decided to design a two dimensional 512 byte (byte addressable) RAM from 16 byte chips. Each of the 16 byte chips has two select-lines. The chip is enabled only if both of the select-lines are activated. Your design must use only decoders of size 3 X 8 and 2 X 4. Need to show the components, the connections and size of each component!


texts: how to put led to indicate the signal is functioning

texts:
I want to connect an input signal to pc817 and the output to a microcontroller. I don't know how to put the LED at the input to indicate that the input signal is working.

For example my input is limit switch. My \$V_{in}\$ is 3.3V. Before the limit switch is closed, the voltage at the first pin of optocoupler should be the forward voltage 1.4V. After  the limit switch is closed, the voltage become 3.3V. So my question here is how to connect the LED to the input and how to connect the signal of the input to the optocoupler. other than limit switch i will use digital or analog sensor as input to be isolated and interface to the microcontroller. i would like to make the led as the indicator when the sensor is sensing object, and the led will light. so how to make the led work like that.


texts: How can I Further Reduce Power Leak from BSS84 MOSFET?

texts:
I am working on a device which is running from a 3V coin cell. A system timer enables a MOSFET which starts the actual circuit (MCU etc.) for a very short time.

The system timer (U1) only uses around 50nA of power while idle according to the specs. I checked this and it is true. When I measured current of the prototype I got something around 900nA. So it seems the used MOSFET (M1) leaks around 850nA current.

The circuit diagram looks like this:

simulate this circuit – Schematic created using CircuitLab

Is current leakage of 850nA a normal value for a BSS84 MOSFET?

Is there a simple and cheap way to reduce the leakage below 100nA?

MOSFET data sheet: http://eu.mouser.com/search/ProductDetail.aspx?r=512-BSS84 IDDS=-15µA, IDDS@125C=-60µA


texts: Device shutdown: harm from charged capacitors?

texts:
In my application, I have 220nF capacitors connected to the inputs of an A/D converter (MCP3204). Now I wonder what will happen when the circuit shuts down and the supply voltage drops below the capacitor voltage.

Similarly, I am sending the output of a D/A converter to the input of an LT1013 op amp. On shutdown, the supply voltage of the D/A would probably drop more slowly than that of the op amp, so it is possible that the maximum ratings of the op amp would be briefly exceeded.

My intuition is that both these cases probably won't cause any issues - the A/D converter will discharge the capacitor through the internal protection diodes at least, and the op amp input has a 10K resistor in front of it - but I'm not sure where the limits would be. After all, it does exceed the absolute maximum ratings, so generally it can harm the devices. How do you figure this out with some degree of certainty?


texts: Does anyone know what screen connectors or ribbon connectors for a smartphone like the galaxy nexus connecting to it's pcb and if simliar with other phones the screen connector that is, i'm finding it difficult to find what is compatible and not or any infomation on the ribbon connector is their a industry standard for something like that for touchscreens used in smartphones connecting the pcb? is a chipset exclusive setup thanks :)


texts: Can a ferrite choke/bead suppress unwanted audio signals (maybe mobile phone induced)?

texts:
I use a headset with a normal 3.5mm audio cable (not USB). Most times I have excellent audio quality, but in a large office building, I sometimes get very bad signals injected from an unknown source. I do not hear them myself, it's only affecting the microphone - a very lound buzz/humm. Needless to say, it is hopeless to identify the source as I don't have access to all rooms or even all floors. It may be the "usual" interference coupled from mobile phones.

Would one of the usual ferrite beads https://en.wikipedia.org/wiki/File:Ferrite_bead_no_shell.jpg likely help with audio signals? Or do those beads only make sense in high frequenzy (1xx kHz/MHz) ranges?


texts:
In a Dialog application note (AN-B-027), I ran into this rather curious antenna for 2.4GHz operation:

This is on two PCB layers connected with vias; the whole thing is shorted together at DC, but forms a sort of labyrinth pattern that switches back and forth between the layers.

How does it work?  The overall operating principle is a bit beyond me.  Is it basically a monopole with a bunch of inductors (the vias) used to load it?  Something else?

Why would one want to use this type of PCB trace antenna as opposed to something more common like PIFA or MIFA?  What are the pros and cons?


texts:
I am using an ATtiny88 in a pcb design. It is directly driving a LED matrix. I am only driving half bytes at a time, so the max current limit will be followed.

It is my understanding that I can dual purpose the icsp in the way that I have it. Since the ATtiny is driving the columns, when I go to program it, the reset pin is asserted, driving the pins tri-state, then allowing the iscp pins to be programmed.

Since the leds will be reverse biased while programming, they shouldn't cause any interference upstream.

Is this correct?

Also, the icsp labels go to a 6 pin programming header.

EDIT: Colums are the anodes, rows are the cathodes. It is a common cathode matrix.


texts: MOSFET H-Bridge Amplifier Unbalanced Gain

texts:
I have been designing a 100 watt, high frequency (20 - 40 kHz), bridged amplifier using MOSFETs. Although I have some systems and electronics background, the behavior of the MOSFETs is a bit beyond my understanding.

I have managed to smooth out the noise and remove most of the crossover distortion by adding a zener diode bias network. The left-hand op amp increases the signal (sine wave) to the full voltage range (within the swing of the op amp). The right-hand op amp takes the output of the left-hand and inverts it with unity gain. I know that this can amplify the distortion of the first op amp, but that isn't really a concern for this project. The output is shown below for the left (vl) and right (vr) sides:

The problem is that the unity gain amplifier (waveform vr) seems to not actually have a gain of 1, but instead 1.1 or 1.2 when I perform a simulation in LTSpice. This results in an unbalanced output waveform that is not desirable. Notice the higher peaks on the red waveform -- these should be the same amplitude as the blue peaks. I can reduce this effect by reducing R8, R9, R15, and R16, but then the power over these resistors becomes too great. Without the MOSFET bridge on the output, the op amp is indeed unity.

Is there an effect that I am missing that causes the op amp to swing
higher when attached to the push-pull?
What would be the course of action to correct this circuit? I am fine with minor distortion, but I would prefer a balanced output.

Also, is it wise to use zener diodes to provide the voltage bias to the MOSFETs? It seems to perform fine in simulation, but I'm not sure if it might not in a production circuit (with 100 W output). Is there a better way to provide this bias?


texts: Constant voltage source from battery and main power supply for power LED

texts:
I want to power a power LED from a lithium-ion battery and simultaneously from a 5V power supply if the device is plugged into the main voltage. My LED driver demands 3.3 V and up to 800 mA. The lithium-ion battery is just a single cell so the voltage will be something in between 2 V and 4.5 V during the whole discharge cycle.
I can ramp up the battery voltage from a DC/DC converter and get the voltage down with a LDO or build something myself like a discrete LDO from passive components, transistors and OpAmps (I don't have a lot of other IC's at hand). What would be the better option regarding power losses and what would be good topologies to build myself?
EDIT:
The design should work for every single cell lithium chemistry and the battery should discharge at least 80 % of its battery capacity.
I use the MCP73831/2 CMU.


texts: Using old notebook battery to power electric screwdriver

texts:
I have:

Dead notebook with live LiIon battery (HP HSTNN-CB50):
14.8V, 8 x 2500 mAh 18650 LiIon cells.
Rated at 73 Watt-hour.

I haven't managed to open the battery pack yet, but it's clear from the voltage and from the specification plate that the cell arrangement is "2p4s"
(2 x strings of 4 cells in series in each string.)

Live electric screwdriver (China/noname) with dead battery cells:
12 NiCd Sub-C cells, 14.4V 1200 mAh

It's possible to fit 4 x 18650 cells into the screwdriver.

I would like to have:

Live screwdriver
with Live LiIon battery from notebook in a shape of screwdriver battery.

I am on a budget for this project and the idea is to replace the dead NiCd cells in the screwdriver bat.pack with the LiIon cells and circuitry from the notebook battery. Does anybody have experience with this?

More precisely:

Is it possible to easily recycle the charging circuits from notebook?
What about the screwdriver discharge?

I do not have an idea in general if the Li-Ion battery from notebook will be able to handle the peaks from the screwdriver?


texts: Is a comparator the correct part to choose?

texts:
I have a device which puts out three different voltage-levels on its GPIO pin: Its voltage is either 0v, 0.8v or 3v.

What I need is a clear digital logic high or low, but I need 0.8V to be treated like a logical low. Additionally I would like the result to be inverted. In other words, 0v and 0.8v becomes a logical high at the output and 3v on the input becomes a logical low.

I was thinking of using an inverted buffer, schmitt-trigger and my latest idea was using a LM393 comparator. I'm comparing the voltage from the GPIO with simply 1v (created from a voltage div.). The output should already be inverted, if I feed the 1v into the + Input of the comparator and the GPIO into the - Input.

I just would like to hear some feedback, if the comparator is the best way to implement my needed behavior or is there a more simple/discrete way to do this?

Thank you!


texts: What type of voltage booster circuit is this?

texts:
I'm wanting to research the theory of operation for this type of voltage booster circuit, does this design have a particular name?  Early days for me, don't yet understand difference between buck boost, flyback etc.  Any help appreciated.

This particular circuit is from an old home computer that only has a single line +9V (unregulated) supply, but also requires +12V to power a couple of video ICs.  This circuit takes the +9 and provides +12.


texts: Would the frequency of LED be equal to that of microcontroller

texts:
Suppose I have a simple LED driving circuit i.e. an LED and a resistor in series which is driven by a pin of a microcontroller. Now I set the frequency of this pin to say 1Khz, will the LED flash with the same frequency?

There might be capacitances in LED but I assume them to be small to have any affect or I may even be wrong(Oh and yes the capacitance would just vary the rise and fall times but it is good to be sure ). What are the possible parameters which vary the frequency of LED?

Thankyou for your valuable time


texts: Synchronous motor base speed calculation

texts:
I would like to ask the following question.

How can I calculate the base speed of a Synchronous motor for variable speed applications controlled in dq frame?
I want to calculate the base speed for different Vbus and I suppose phase voltage is half Vbus.

Thank you in advance.


texts: sending signal to open car with microcontroller

texts:
I am interested in a way of how to open the caar's doors with a microcontroller device's extension hardware (I have an Arduino Uno Rev 3).
I know that the key can do it as well but I want to program things. The frequency of the signal is 433.92 MHz and the modulation is FM and AM. Therefore I need a device (a hardware that can be connected to the microcontroller) that can emmit/send and receive signals with this certain wave's frequency.

It is to be mentioned that, for me, it is not the most important thing to finally get to open the vehicle (the central locking system) but to work with it and to do experiments and to read what the key sends (this is actually the most important thing).

Can you recommend a hardware that can read 433 MHz signals ?
Are there differences among them?

I want to express my interest into that I want to receive the signal that is sent by the remote key.

(edit)
Later on, I can try to get some useful data out of the signal.

But, for the beginning, where do I know that all the remote keys work with the same method (I refer to this Wikipedia article: method of modulation). And this is what I meant with FM (frequency modulation) as an example.

By the way, ATA5811 sounds really good - I read the data sheet and it can use both ASK and FSK (modulation). How can I find out, what my car key uses (there are so many paramters!) ?


texts: Does a computer assembled only from CE marked subassemblies still need CE testing?

texts:
The FCC (bulletin 62) mentions an exception allowing someone to assemble and sell computers without the normal FCC testing requirement "as long as they start with an FCC-authorized system and add to it only FCC-authorized peripherals..."

Do the CE mark requirements have a similar exception?

(It is completely understood, by the way, that any answers are expressions of opinion, not legal advice)


texts: Need help on creating the most stable LED possible

texts:
I am currently trying to make a circuit to drive an LED with smallest amount of fluctuation as possible.

Background: Using an LED and spectrometer together to analyze small molecules. I can use the spectrometer to record the intensity of a light over time and that is how I read noise in an LED. I have tried a variety of LED linear drivers, and I am sticking to 5mm LEDs. My circuit consists of one driver (right now im using MAX16815) and LED, and some bypass capacitors at the IN and OUT pins.

Questions:

With a DMM, I found that the current decreases/increases for 15-20 minutes before reaching a steady state.

-How can I reduce this phenomenon?

I have a 35-100mA output 3.5% accuracy LED driver with a max 100mA 5mm LED. So far, I have been working on breadboard to do testing and analysis so there could be a source of error in there. I use an external resistor to control the current output of the driver. It currently takes 15 minutes to reach any current I choose with a standard deviation of 0.007 mA. I want to reach a standard deviation of 0.001 mA just to be sure.

What can I do to reduce variations in the intensity of the LED?


texts: Controlling an LED's intensity with a text file from an SD card

texts:
I want to control the intensity of an LED by reading a text file. Here is an example of a text file:

255,100,255,50,100,20,10,200,50,90,85,200,0,0,0,255

My equipment: Arduino Uno, microSD shield, power LED shield, and microSD card.

What I want is: during 60 seconds, my LED's light intensity is i and after that, the intensity is i+1, etc. In this example, that would be an intensity of 255, then one of 100, then 255, etc. I know how to read a text file and open a text file with the SD library, but I don't know how to parse my text file and get the good intensity at the time t. So I want something like this:

# Open and read the file from the SD card
# For t to the end of the file
      intensity = intensity at t
      analogWrite(led,intensity)
      delay(60000)
# For each time t, I want to have the intensity I on my screen
      Serial.println(intensity);

Next, I want to do that for two LEDs with two different arrays on the same text file.

How can I do this?


texts: Do usb and vga controllers consume power if there are not devices connected to them?

texts: Let's consider the following situation. There is a server, for example supermicro, that has 4 USB2 ports, 4 USB3 ports, and 2 VGA ports. At the same time we don't use these ports, I mean there are no devices connected to them. Do these ports consume any power in such a situation? I am asking as I need to understand if these ports draw any power from power supply.


texts: Are distributed element filters really distributed?

texts:
When looking at distributed filters etched into PCB, I have a hard time understanding why they called distributed. Most of them can be broken into sections and have basically a 1 to 1 correspondence with lumped element filters.
How are distributed filters really distributed?


texts: Switching frequency of a solid state relay?

texts:
I bought a SainSmart 4 channel solid state relay recently. I am planning to use an Arduino to control some Christmas lights I've put up around my home. My question is: How fast can you switch SSR's on and off? For example, what if I want to have a string of lights flash, what would be an appropriate flash rate so the relay won't get damaged?

This is the relay module I am using: http://www.sainsmart.com/sainsmart-4-channel-5v-solid-state-relay-module-board-omron-ssr-avr-dsp-arduino.html

On specs it says: OUTPUT EACH CHANNEL: Load voltage range: 75 to 264VAC (50/60Hz)

But the 50/60Hz isn't stating the max switching frequency, is it?

Thanks for any help.


texts: How to connect a four route MOSFET to multiple power sources?

texts:
I have this four channel MOSFET switch:

I have connected one RGB LED-strip to this, and controlling it from an Arduino, and this works great.

The problem is that I need to control four of these LED-strips, and they each need 12V. So I wan't to remove the 12V from connection to the board, and connect it directly to the LED's, and then control the RGB values on the LEDs from the board (the will all be controlled identically, so the are connected together). How would I go about doing this?

When I connected one LED-strip, I did what is described in this tutorial: http://arduino-info.wikispaces.com/Brick-4ChannelPowerFetSwitch

But I need to wire it more like this illustration, where the power is directly connected to the LED, so that I can control multiple LED-strips at once:


texts: Why is 3.5 mm audio jack so long (about 19 mm)?

texts:
The designers of 3.5 mm audio jack made the decision to keep it's length long (about 19 mm). They could have easily gone shorter lengths. Does longer length provide some noticeable improvements?

From what I see on Wikipedia, people have tried to do 15 mm & 17 mm
variants, but they seem to be incompatible.


texts:
I'd like to use OrCAD Pspice's "psp_cmd" to do three simulations using only one .cir file.

The problem is that execution of

psp_cmd mycircuit.cir

creates only one data file named mycircuit.dat containg the data alltogether.

I'd like psp_cmd to export three different simulation runs into three different data files. Is this possible?

Note that each job in the cir file is separated from the others with an .end.


texts:
I'm trying to find out if this kind of power plug for my laptop has a name, so that I can google for it more successfully.
I haven't ever seen any other like it, with its 4 pin connectors.
Does this style of plug have a name?


texts: What is mean by channel inversion in wireless communication

texts:
Regarding the title of the question, to my understanding, Channel Inversion means that "The transmitter adapts its power to  maintain constant SIR at the receiver."

It is a technique used for adaptive power control.

However, I am not sure if my understanding is correct.


texts: 2 phase vs 3 phase power density (switched reluctance motor)

texts:
I know 3 phase has the advantage of being able to start from any position unlike 2 phase. But my question is about power density...

In a 6/4 three phase motor, 1/3 of the stator is active at once, and only 1/2 of the rotor. In a 8/4 two phase motor, 1/2 of the stator and all of the rotor is active at once. Does this mean two phase is more powerful, and if so, by how much?


texts: What determines if a particular DAC is "good" for audio?

texts:
I want to generate low-end audio (sinewave, sampling rate 8kHz). How to determine if a particular DAC is okay for such application? Is it only the settling time (of course apart from resolution, interface, voltage etc.)?

For example the AD5601 has a maximum settling time of 10µs. At a rate of 8kHz a sample takes 125µs, so I would guess that this particular DAC could handle the sample rate. Is that correct?


texts: How to insulate a high voltage PCB trace?

texts:
I am making a PCB with a HV power supply module. Namely the C9619 module from Hamamatsu. The module produces up to 2 mA and 4 W of power so the heat won't be a problem

The module can produce up to 2000 volts, but I will be using it at around 1000 volts and it will deliver a current of around 400 \$ \mu \$A.

What insulator do you recommend to place above the high voltage copper traces?


texts: SIM800L - No response while sending AT commands

texts:
I'm new to this arduino world. I'm trying to communicate with my arduino nano and SIM800L. I read few things in the internet and found a basic code. I tried copying it and tried to work it out, but I'm not getting the response as expected. I'm posting the code which I tried:

#include <SoftwareSerial.h>

SoftwareSerial mySerial(11, 10); // RX, TX

void setup()
{
  // Open serial communication
  Serial.begin(9600);

  // set the data rate for the SoftwareSerial port
  mySerial.begin(9600);

  delay(1000);
  Serial.println("Testing SIM800L module");
  Serial.println();
  Serial.print("Sizeof(mySerial) = "); Serial.println(sizeof(mySerial));
  Serial.println();

}

void loop() // run over and over
{

  if( mySerial.available() )
  {
    char c = mySerial.read();
    Serial.print(c);
  }

  if(Serial.available())
  {
    String Arsp = Serial.readString();

    Serial.println("Serial available");
    Serial.println(Arsp);
    mySerial.println(Arsp);
    Serial.println("Serial available end");
  }

}

I tried to send AT command and the output I received was:

Testing SIM800L module

Sizeof(mySerial) = 31

Serial available
AT

Serial available end

I don't get OK, which I should receive, it's returning empty.

I don't understand what's going wrong. Can someone help me with it?


texts: Can driver for some device (for example LCD display), also be called library (a set of functions for work with)? If not what is the difference, and what term is used for what?


texts: Calculating constant current buck converter ripple current

texts:
For building a constant current LED driver, I'm looking at the TI LM3407 datasheet: https://www.ti.com/lit/ds/symlink/lm3407.pdf
For calculating the necessary inductor, there's several things I don't understand:

Under 8.1.4 Selection of Inductor The datasheet lists ripple current as
\$
I_{L(ripple)} = \frac{\left(V_{IN} - V_{OUT} - 0.198 \times \left(1 + \frac 1 R_{ISNS}\right)\right) \times V_{OUT}}{L\times V_{IN} \times f_{SW}}
\$

What I don't understand is where the term with the sense resistor is coming from,  my understanding of a buck converter is that it depends only on duty cycle, frequency and inductance, but not output current?
Edit: I guess that's the on resistance of the built in MOSFET - which is given as 0.77 Ohm typical, 1.45 Ohm max (at 80mA).

On the next page, there's Table 1. Suggested Inductance Value of the Inductor, which e.g. lists 22µH for driving 5 LEDs with 1MHz from 25V, with \$I_{L(ripple)} = 0.8 \times I_{OUT}\$. But inserting those values into above formula, I arrive at >250mA ripple current, indpendent of \$I_{OUT}\$.
E.g. with \$I_{OUT} = 100mA, R_{ISNS} = 2\Omega\$, that ripple current seems excessive?
The datasheet has some suggested output capacitor sizes, but no information at all for how output capacitor size relates to LED ripple current. What's a good resource to learn about this?


texts: HC-0X Bluetooth Module Difference between Slave & Master

texts: whats the difference between a Module HC-05 Master and HC-06 Slave? I have a slave module (HC-06) but im not sure whats the purpose of the word "Master" in the HC-05


texts: Relation between primary current and secondary currents in a transformer with multiple outputs

texts:
This applies for a flyback converter working in DCM.
Here is what the following document (https://www.infineon.com/dgdl/an-1024.pdf?fileId=5546d462533600a401535591115e0f6d) has :

Here is what I obtained :

(Edit: Replaced original image above, with one using improved contrast by Edin Fifić)
What is the correct answer?
------------------------------------EDIT---------------------------------------------------------
My answer is wrong but I am not able to understand why it is wrong.
If you consider a transfomer with two outputs and the number of turn for each winding equal to 1. Suppose a peak of 1A at the primary, then you should have a total peak of 1A at the secondaries. So if the winding are all equal to 1. It would mean 0.5A on each output. My formula doesn't not describe this phenomenom.


texts: Time delayed optionally postponable from a second input

texts:
I need functionality similar to that provided by true-off-delay relays, just a little different. I can't come up with a circuit.

I have two inputs (A and B) that I want to control one output (C).

Both inputs can act as resets for the timeout, but only one input (A) can activate the output (C) initially.

I've made an illustration:

"t" represents a 5 minute timeout, if it is reached then the output needs to switch low

I hope this makes sense!

Any help appreciated.


texts:
How to find the frequency of oscillations in this circuit CMOS circuit:

simulate this circuit – Schematic created using CircuitLab

Assuming the ideal CMOS gate with the threshold at 0.5Vdd.

And the output and the input waveform if an inverter.

R = 10kΩ; C = 1nF; IC = CD4069; Vdd = 5V

How would you approach it?


texts:
I have master device / board that is connecting to PC USB. On board is LDO (1A) with 5V USB input and 1.8V - 3.6V output. LDO powers master board but also slave boards (different boards designed by others, not me) that can be connected / disconnected to / from master anytime (hot plugging). There is option that master device takes power from slave boards and in this case LDO is disabled.

Problem is current surge. When the master device is powered and there is communication with PC, if slave boards are connected, due to surge current (charging caps on slave boards) there is voltage drop on LDO and master is reseted with lost PC connection. To handle this I used few ohm resistor between master / target VCC line. But now I am looking for better solution.

There are 0603 and 0805 PTC fuses (for example to hold 250mA and trip 500mA, with 0.5-2.3 Ohm) that can be found on many USB boards, but reaction time is (I guess) a little slow (0.1 sec).

I found that depletion N-MOSFET can be used as current limiter...

but problem is that, when master board is powered by slave boards current will flow in opposite direction, over FET diode, and thre will be (at least) 0.7V voltage drop / difference that is unacceptable, because master / slave devices should work on same voltage.

There is low cost microchip (bidirectional) LND01.

I found hspice model online, but don't know about diode connection, and how to define this in transistor description inside hspice, to simulate something...

M1 Vd Vg Vs ? LND01 W=40m L=1.5u AD=1 AS=1 PD=4 PS=4

Don't know if some J-FET's and how (for example J105) can be used for this.

All integrated solution that I found online, are not bidirectional, or / and not working on low voltage (1.8V). All commercial products that I know for, use two regulators to handle this, one for master, and another for target, and if master is "powered" by target than there is voltage sensing with adjusting master device LDO output.

EDIT: I an new to J-FET's, but there is no internal diode and I guess that they are symmetrical devices, so they can work on the same way, with Vgs= 0 or Vgd=0. If I simulate J105 with Vgs=0, connect one side to 5V, and another to 100 uF capacitor in series with 5 ohm resistor current will draw and other side (capacitor voltage) will end at 5V. If I switch direction D-S, current in opposite direction, cap is again charged to 5V. I can't see white smoke in simulator, so don't know if I am doing something wrong. Can with JFET Vgs=0 current flow in the both ways?

I found this...

Can't find DEI1600 datasheet, so don't know if this J-FET's are connected back to back like SIC J-FET's with internal diode, or not.


texts: CAN Split Termination Capacitor Calculation

texts:
I'm trying to use the split termination on a CAN bus, but I'm a bit confused about the calculation for the split termination capacitor. It is described in Figure 10 in the Texas Instruments app note SLLA270 Controller Area Network Physical Requirements but when I use the values of R = 60 Ohms and C = 4.7nF, I geta cutoff frequency of 564.379 kbps and not 1.1 Mbps like they describe in the app note.

I'm confused as to how they got 1.1 Mbps and why ? Isn't the RC low pass filter here created by the resistor and capacitor (60 ohms and 4.7 nF) ?


texts:
I have this old keypad sitting around, never used it because I could never figure out the pinout for it. Anyone know how this would be wired to something such as a picaxe/arduino?

Front of the keypad, with the plastic buttons and case removed:

Back of the keypad, same conditions as first:

Front of the keypad, with the buttons on:

Edit:
Forgot to say, the keypad was pulled from a fried 12v door lock.

This one, if anyone is interested: http://www.jaycar.com.au/Access-Control-%26-Automation/Access-Control/Keypads-%26-Standalone-Controllers/Self-Contained-Security-Keypad/p/LA5355


texts: Will the use of an isolation transformer improve the safety of my power supply?

texts:
I have a power supply design that makes use of a half-wave rectifier and a non-isolated buck Swtich Mode Power Supply IC to step down 120V 60Hz AC power to 12V DC.

I then use a Linear Voltage Regulator (78L05) to step the 12V down to 5V. The 5V will be used to control a micro-controller in a prototype, so there is a risk of people touching the pins.

In this design the Neutral line of the AC supply is connected to the 12V DC after the buck converter.

I realize that this could be dangerous since the 5V supply to the micro-controller is not isolated from the AC supply, so my question is:

Will the use of an isolation transformer just after the AC supply isolate the rest of the circuit from the supply. Will this make the design safer and/or less efficient?


texts:
I've just tried to crimp 'standard' 5mm TNC and BNC connectors onto a piece of Aircell 5. It didn't fit :-( The outer is far too big for the outer crimp to slide on and the inner is too big to fit in the pin. Bit of a bummer as my plane's now in bits until I fix it.

While I can just get a BNC connector labelled to be of the right size now I realise, where do I start with trying to find a suitable TNC connector? (And actually ideally, I'd rather get a right-angle BNC).

Hmmm. Turns out I'd been sent Aircell 7 instead of Aircell 5. No wponder my 'standard' 5mm connectors wouldn't fit. Nevertheless, question still stands as to what are the important dimensions of coaxial cable and connectors as they're not at all clear.


texts:
A side note: please be forgiving of me because I'm just starting out in Electronics so I'm still confused about certain terms.

Why are optocouplers used?

Yes I know they link a circuit together since there is an LED inside and a photoresistor. I also read that it prevents high voltages. But why use an optocoupler over another component? For example, to reduce high voltages we can use step-down transformers but why, in a certain scenario, we would use an optocoupler over a step-down transformer?

In what scenarios are optocouplers appropriate?

Hope my question is clear enough for anyone who can help.


texts: High power opamp-based constant current source circuit

texts:
I am currently working on a high-power 28S lithium-ion charger for EV. I'm on a constant current stage, so you don't have to worry about all that balancing thing, I just want a constant flow of 15A through my 28S cells. I looked upon some circuits online that achieve a constant current with a control loop with an op-amp and a current negative feedback as can be seen in the following image:

This is all fine and standard and I get how it works, basicly the opamp increases its output voltage until that is negative input current feedback is the same as its positive input.

However, I was looking for some other proper charger circuits and stumbled upon the an iMAX B6 like circuit, which is can be seen here: RC-Power_BC6_Charger

I am trying to analyse this circuit and my question briefly is: what those parts I marked are responsible for? I get R7 and C3 form a low-pass filter, as well as R17 and C14 and I think R14 adds a gain to the circuit. But I don't get what those marked parts are for. I though I was some sort of summing amplifier, but this got me nowhere.


texts: Negative Inputs For Diode Transistor Logic

texts:
I 've implemented this basic logic gate on a breadboard.  Only my circuit has +5 supply voltage.  The resistor values are 10K for diode inputs and 1K for collector of the transistor.  The transistor is a 2N3904 and the diodes are 1N4148.
Here's a pic:

I'm really confused about the inputs for this.  I've read that the inputs should be low voltage, but I've tried all sorts of voltages and nothing.  However, when I put one of the inputs to ground, the LED turns on.  This got me thinking, if in fact connecting input to ground was 1, then both of them being to ground "AND" would cause the LED to shut off.  If thats the case, how on earth do I implement this with a button or switch?  Also, is my circuit shorting somehow, or perhaps are these values not working with the +5V?  I've tested the RTL version and the 1K + 10K + 2N3904 works perfectly.

(source: jones at people.seas.harvard.edu)


texts: Circuit for reversible motor controlled using relays

texts:
I am very new to electronics and drawing isn't my strength either, so please forgive the bad diagram. But I hope it makes sense.

I want to be able to control a motor using relays and be able to change the direction of the rotation. From what I know, the rotation can be reversed by changing the power to negative and positive terminals. As far as I could understand, I won't be able to do that with one relay. So I plan on using two relays. The diagram shows this (badly). Basically the dashed lines represent circuit for one directional control and the solid lines show circuit for opposite direction.

As I am sharing the battery for both relays, when either of the relays are in open state the cable for the other circuit that is connected from motor to the battery would cause a short. To overcome this issue I will use a diode on both cables that run from motor to battery terminals.

So I guess the questions are,

Does my plan seems reasonable?
Is there a better way of doing what I want?


texts:
The data sheet for this LED gives the forward voltage range, at forward current of 20mA, of 2.8 to 3.8V.  How can I choose a sensible current-limiting resistor value for this device, given such a wide range of possible forward voltages?

If I have a 5V supply and the forward voltage is 2.8V, I would need a 110-ohm resistor to give 20mA forward current (the rated value).  But then if the forward voltage on a particular one was actually 3.8V, I'd only get about 11mA - and considerably less brightness.  And of course operating from a 3.3V supply it's going to pretty random whether the thing switches on at all.

Am I misreading something?


texts: Extracting amplitude of signal from FFT plot

texts:
I am busy with to extract peak amplitude of a noisy 1 hz signal. As you can see the image, the signal is very noisy. I need its average amplitude peak value.  However i can easily and perfectly find its frequency from FFT plot (i can find it after some smoothing algorithm). My aim is to reach average peak amplitude of this periodic signal. So can i extract peak amplitude value by using maximum amplitude of FFT plot?
If yes, how? Inverse FFT?
Thanks a lot,
Cem


texts: Initialization problem with 16F877A in C

texts:
I have some experience with PIC micro controllers ASM. But decided to move on to C. Having installed MPLABX IDE V3.55 and with the C compiler XC8. I now try to realize a program for PIC16F877A.

After initialization I try to set some output ports but there is no reaction in the simulator. When I try to change a port setting with a stimulus there is also no reaction. Where is the mistake?`

// Set PORTA and PORTE to digital
    ADCON1 = 0B00000111;
   // Turnoff PORTA comparitors
    CMCON  = 0B00000111;
   // Set I/O PORTE
    TRISE  = 0B00000111;
   // Set PORTB to input
    TRISB  = 0B11111111;
   // Initialize temperature routine varables.
   //  minLimit = 0;
   //  MaxLimit = cycleTime;
   // The switches SW1 - SW5 are pulled up against VDD
   // When unpressed RE2 must be high
   // Enter button SW3 open
    PORTEbits.RE2 = 0x01;`

Even in watch I can not change the value.
I can change the value in SFR.

Is it possible that I run into the R-M-W cycle problem?


texts: ETSI Tx Power standard for short Range Devices. I am Confused

texts:
I came across the European Telecommunication Standards Institute (ETSI) standard for non specific Short Range Devices which is documented in EN 300.200 .

On page 28 under Section 7.2.3 with Heading Limits, a table is mentioned which has regulations on max power of different frequency bands.

Owing to be under 1 GHz freqency range, all bands are long range bands. And some bands are allowed up to 500mW (+27dB) or 25mW (+14dB).

What I am confused that with this much transmission power how are these devices classified as Short Range Devices? Also with this high transmission power, what range can we expect from such SRDs?


texts:
I am trying to restore a bricked BBB device. Booting Debian from the SD card works fine (thanks to http://thethingsystem.com/dev/Bootstrapping-the-BeagleBone-Black-with-Debian.html ). Once the device is booted, I try to copy the Debian image to the emmc partition:

$ xz -cd debian-wheezy-7.2-armhf-3.8.13-bone30.img.xz > /dev/mmcblk1

This works but the boot partition is 100% full.

However, I need more space on that partition as I want to install a custom boot image with a display driver support (the Debian image from http://www.element14.com/community/docs/DOC-67958?ICID=BBB-feature-viewpanel )

So, once the BBB has booted with the SD card, I try to resize the boot image with:

$ [sudo mkfs.msdos -F 32 /dev/sdc1 -n LABEL1]
mkfs.msdos 2.11 (12 Mar 2005)

$ [sudo mkfs.ext3 -L LABEL2 /dev/sdc2]

from https://code.google.com/p/beagleboard/wiki/LinuxBootDiskFormat

How could I make the device booting from mmcblk1p1 ? Can I copy over the image from the SD card, how to do that?

Thank you!


texts: How much does it cost to etch your own PCBs?

texts:
I am at the point that my projects are becoming limited by the space on my breadboard. Rather than buying more, I have decided to look into PCB fabrication. My question is this: is it cheaper to make your own PCBs for prototyping, or should I send my plans away and have them fabbed elsewhere? If you do make your own boards at home, how much does it cost per square unit (approximately) and what method do you use?

If it helps, I am in Australia so I don't have many fab businesses close by.


texts: What is the function of the latch pin on my 74HC595 IC?

texts:
I am using this code with a 74HC595 IC to control a 4 digit 7-segment:
digitalWrite(latchPin, LOW);
shiftOut(dataPin, clockPin, LSBFIRST, "value");
digitalWrite(latchPin, HIGH);

I understand what the shiftout() does, but I don't understand why we need to put the latch pin low and then high. Can somebody explain this to me?
The latch pin is pin 12 on the 74HC595 IC.


texts: Pin compatible shift register with open drain outputs

texts:
I'm looking for a pair of otherwise interchangeable 8 bit output shift registers where one has open drain (or open collector) outputs, and the other has "normal logic outputs" (ie a pull up transistor and a pull down transistor, I've seen the term tri-state used, though I'm not certain that's exactly what I need). Can anyone suggest suitable parts?

I'm planning to build a PCB using large mosfets as final outputs, and these shift registers to drive them. I will only decide whether to use N-Chan or P-chan mosfets as high side or low side switches when I populate each board, the overall supply voltage to the mosfets will be anywhere from 3V up to 20 volts (I'm aware of the input voltage limits on mosfets).

For N-Chan mosfets I will use a "normal" shift register to drive the mosfet to 5v, or turn the mosfet off at 0v.

For P-Chan mosfets I will use a the open drain on the shift register to drive the mosfet down to ground, or let a pull up resistor float it up to supply voltage to turn it off.

I can find plenty of "normal" shift registers and a few open drain ones, but none of the parametric search tools are set up for telling me which have the same pinouts, and I'm not familiar enough with the parts to know which parts are a good place to look at. Many of the data sheets completely omit the details of the output circuitry.

Additionally I need latching and ideally PDIP, though I'll make the brave jump to SMD if I really have to. I'd like them to be cost effective, and I intend to run them at 5V, though 3.3v compatibility would be nice.

The closest I've found is the TI sn74ls595 and sn74ls596 which would do the job perfectly but are so old the datasheet on TI's site is scanned in and they cost a fortune to source.
An alternative would be a way to use a normal a normal 595 shift register against a 20v pull up, but I'm confident that wouldn't end well without using a row of 8 transistors in the middle, and that's a parts count issue I'd rather avoid.

[edited to fix mosfet naming]