texts:
I have a problem of adding two numbers in base of two's complement (6 bits!!!)

1100(2's C) + 0101(2's C)

I notice that the first number is starting with 1 which means it's negative
but since it's 6 bits, I have to change those two numbers into 6 bits and I have no clue how to find those numbers in 6 bits..

I need help please

Thank You


texts: Negative Half of Sine Wave Passes Through Off MOSFET

texts:
I'm trying to design a MOSFET based switch which allows a sinewave through, however I noticed that when I was simulating it in LTSpice, whenever I try to turn off the FET the negative half of the sinewave still passes through.

Why is this and how do I prevent this from happening?


texts:
I'm experimenting on a breadboard how to use the programmable interval timer 8253 (actually I'm using the new 82C54, it's the same thing).
datasheet:
http://www.intersil.com/content/dam/Intersil/documents/82c5/82c54.pdf

what I don't understand is what kind of clock should I use with it.
I only see 1 input pin for each clock channel, but usually I use 2 pins crystal resonators (as clocks for microcontrollers).
so what kind of clock should be connected to this timer IC?
I guess I can't use the usual 2 pins crystal.

thank you


texts: Generic tablets and single board computers

texts:
I've been pondering the idea for a while now in regards to a project I've had in mind. Essentially, I was wondering how I would go about obtaining generic tablet/phone motherboard designs? Would I be able to license them from anywhere in order to have them manufactured someplace else if need be?
The same goes for single board computers like the Raspberry pi zero W; My brother has a project he has in mind and was wondering the same question. Would we be able to buy generic ones in mass from a vendor, buy the schematic or would we have to design our own?
Obviously, I expect this to not be easy what so ever, but It's a long term project and I would like to have all my options to consider now rather than later.


texts: How to set an oscilloscope for measurement of interrupt service routine execution time

texts:
I have been developing control software and I need to know how much time it takes to execute an interrupt service routine (ISR).
I have decided to use a dedicated GPIO pin of my microcontroller and an oscilloscope for that purpose. I set the pin to high at the beginning of the ISR execution and then reset it to low at the end of the ISR. I have configured my oscilloscope in such a manner that the trace record is triggered by the rising edge of the specified channel.
My idea was that, in case I measure the pulse duration via the oscilloscope, I will have the actual execution time of the ISR. This method works but I have found that the execution time fluctuates due to the internal logic in the ISR.
I would like to measure the worst case execution time but I am not sure how to set the trigger on my oscilloscope to be able to record the longest pulse. How can I do that?
Oscilloscope: Tektronix TDS2014


texts: Do the contacts on a SIM card and card holder always match?

texts:
I am trying to choose an SMD SIM card holder for my PCB but while doing so noticed a few inconsistencies for the C1-C8 locations on a product's footprint.  It has got me wondering if all SIM cards and holders use the same locations for C1-C8 on their footprints.  Like, for example, is the location of Vcc (C1) standardized for both the card and card holder?
TE Connectivity's 1981959-1 is the component in question.
If I look at the datasheet I find the diagram below for SIM card contacts and corresponding pads on the component's footprint.
If I go on Mouser and download the SamacSYS (2nd image below) footprint I see that the location of C4 is on the back-row of the contact pads instead of on the front with C1-C3.
This has gotten me confused.  I am guessing this is just an error on the SamacSYS footprint.
Can I expect that the SIM card I am using was designed with the SIM card pin assignment below?  That is C1, C2, C3 are Vcc, RST and CLK respectively and so on?


texts: Can anyone make a device that uses pcie?

texts: As the title suggests, can anyone make a custom board that connects via a pcie connector?  Do you need to purchase the rights/license to use it or is it all open to the public?  For example my use cases would be communicating with an fpga that's on a custom board as well as communication between two of said boards.


texts: Is there a reason why we don’t supply power to a 2.5 mm or 3.5 mm jack?

texts:
Is there a reason why we don’t supply power to a 2.5 mm or 3.5 mm jack or why it hasn’t evolved to be used it as a wall outlet protocol?
It seems it would use less space, easier to use (can’t insert it incorrectly), and disconnects more easily.


texts: I am using an MCP41HV51 digipot IC to convert digital signals from an STM32 board to analog voltage. The datasheet states that the control circuit of the IC need to be powered up first, then the analog circuit to be powered after it in order to maintain the last wiper position before power off. I was wondering, is there a way to achieve this power up sequence using only passive components?


texts: Where can I learn to safely deal with mains electricity?

texts:
I want to start working on projects that directly interface with the mains in my house. I know this is dangerous. I don't want to design something that will fail in a year and burn down my house. We had one lecture on mains electricity in my EE program. So I basically know a bit about inductive and capacitive loads, and that is about it.

Things I would be interested in learning:

-Directly power a microcontroller from the mains lines.

-Sense power running in a line

-Switch loads

-DIM lights from a micro

I want to do this properly. What classes could I take that would teach the appropriate knowledge?


texts:
So I am trying to get a 74ls139 to work, but am having a little trouble. I hooked up inputs a and b to flexible jumpers, and all the outputs to leds. I then went through all the input combinations, with each one giving the expected output. When I got to both inputs high, things started going weird. Only one led lit up, and the rest turned off. I though that maybe it was a problem with the led or connection to the led, but then I realized that then the led wouldn't have turned on for any of the inputs. I tried the same circuit with 10 different chips, but they all did the same thing. Is this an error in my wiring, or a problem with the ic itself? (video link below)

video


texts: Why not keep distribution transformers secondaries floating? Why do we need to earth them?

texts:
We use isolation transformers for many reasons, one of them is may be safety. So why not just keep the distribution transformers floating? If they're floating, then someone touches the live wire, I don't see how this would present a safety hazard.

The closest earthing system to this configuration is "IT". But I don't want to keep the impedance in the leaking current path, we'll keep it as high as possible, floating.

Also,it does not look like we're still using the earth as a conductor for economic reasons since the neutral wire is pretty much always provided.

What am I missing here?


texts:
I wanted to loop through the addresses in that flash M29W800D, so I started a counter from 0 to 0xFFFFE, then I try to write an unsigned int to an address, but it fails. When I made the loop counter to increment each even addresses, it worked.
but why ? what's so special with that chip that doesn't address all the addresses ?

here is a link to the datasheet http://www.datasheetcatalog.com/datasheets_pdf/M/2/9/W/M29W800D.shtml
I'm using blackfin 533 with the chip.
I'm using 16 bit mode with the flash


texts: Equivalent resistance of Resistor measurement matrix

texts:
To measure a lot of (high resistance) resistors in an harsh environment, I want to setup a matrix of these resistors under test (\$R_{00} \dots R_{nm}\$).

The resistors \$R_{x0} \dots R_{xn}\$ and \$R_{y0} \dots R_{ym}\$ are switches to select the resistor under test. These switches have no infinite isolation resistance when open, so I drew them as resistors. An ammeter combined with a voltage source is connected between + and GND.

I want to calculate the error, the rest of the resistor matrix is causing, when activating one resistor.

For example if the switches \$R_{y0}\$ and \$R_{x0}\$ are closed (set to \$0\ \Omega\$) and the other switches are open (set to \$10\ G\Omega\$) to measure the current through \$R_{00}\$, I have to consider the other resistors as a parallel resistance, causing an error for the measurement. How do I calculate this resistance?

When all resistors under test are considered to be equal, and all open switches are considered to be equal, I feel like there has to be some simplification like considering all rows to be connected to each other and the columns to be connected to each other? But I am somehow stuck at proving this and have no real approach.

Update:

Like Neil_UK suggested, the following would be a better setup to allow guarding out the current that would go through the rows not having the resistor currently measured. Supposing, the guarding works perfect, the error could be calculated as an parallel resistance of all the isolation resistances \$R_{xn}\$ plus all resistors in the measured row \$R_{xn}\$.

simulate this circuit – Schematic created using CircuitLab


texts: MEMS microphone gain calculation for MCU ADC

texts:
I've got a Knowles SPH1642HT5H-1 (pdf link) analog MEMS microphone that I'm planning to connect to one of the ADC inputs on an STM32. I've done what I think are the correct calculations to determine the gain and offset that I will require but would like someone to just check that my interpretation of the datasheet is correct.

The sensitivity of the microphone is -38dbV/Pa and the MCU AVDD is 3.3V. The small signal is carried on a relatively large DC offset. I calculate for the signal:

$$
Vrms = 10^{-38/20} = 12.589mV\\\\
Vpp = Vrms . \sqrt{2} = \pm 17.8mV\\\\
Gain = \frac{AVDD}{2 . Vpp} = 92\\\\
Offset = \frac{AVDD}{2} = 1650
$$

To make full use of the range of the single-ended ADC I need to design a pre-amp with a gain of 92 and an offset of 1650mV.

For reference, these are the datasheet parameters:

Edit

Based on the @JRE's comments below I can recalculate as follows.

If I want 70dB SPL to be full scale on the ADC then, using this calculator I convert dB SPL to Pa and get 0.0632Pa. The new gain calculation will be:

$$
Gain = \frac{\frac{0.5 . AVDD}{\sqrt{2}}}{10^{-38/20}. 0.0632} = 1466
$$

Based on @Andy aka's answer I can adjust further based on how things actually perform in the real world.


texts:
I need reference for comparator and considering option between using one made from voltage divider and the one from precision reference.

Basically, if i were to use voltage divider, it will be simple voltage divider dividing voltage from voltage regulator.

As it is used for zero-crossing detector for timing critical application, the stability and noise performance is very important.

Can I expect a significant advantage from using precision reference in my application?


texts:
This is essentially a revival of an old thread (from Nov 2016), but I am a newbie and am not able to make comments or ask further questions on it...

Canon no longer makes CanoScan 8800F AC adapters, help needed to replicate its functionality

In a nutshell - the Canon Canoscan 8800f scanner has a unique external power supply unit which supplies 32V dc, plus has a second 32V dc line which has a 1.5k resistance across it for 3 seconds. These Canon power supplies are almost impossible to get, and somebody had the good idea of taking a particular HP printer power supply, which also gives 32V dc, and inserting a circuit on this second supply line which performs the function of giving it the 1.5k resistance initially, then removing it with a timer, as this scanner requires.

In this previous thread, as linked above, two users here kindly offered designs for this delay/resistor-bypass circuit. At first I tried the second one, because it was more simple, submitted by 'Whit3rd'. This circuit functions, but it kicks in too soon, almost instantly. The scanner only responds and switches on if the delay is 2-3 seconds.

Looking now at the first circuit design, offered by 'ThreePhaseEel', it has more components, and I am about to order the components I haven't got to make it but...

I've three questions:

A: With Whit3rd's version, which components can I experiment with to increase the delay of it's response? Any suggestions of configurations to alter this?

B: With ThreePhaseEel's version, again, which components would most impact the delay, so I could substitute parts to get the right result?

C: Again also with ThreePhaseEel's design: could somebody please clarify/confirm the choice of capacitor in the design: ThreePhaseEel writes that '...the timing capacitor should be a stable, low-leakage type such as a polyester film or a good grade of tantalum cap...' - yet the cap is listed as 100uF which seems large for a Tantalum and is near-impossible to get as a Polyester Film... Is this correct? I have electrolytic caps this size. And what voltage for this cap? 50V seeing as the circuit is 32V?

Thanks in advance for any responses. I am not trained in electronic engineering, more an intermediate-level tinkerer. I can easily make these circuits, as designed by other people, but I don't claim to understand them to the point that I can modify or redesign them.


texts:
I am testing below LED Driver Circuitry on breadboard using LM3410X.

Input Specs:

Vin & DMM = 5V,

L = 20 uH

R=2 Ohm

Only thing is I have'nt connected LED ( I am testing with 10k resistor as dummy load)
But somehow  I am getting 4.86 V at o/p ( across 10K load resistor  )

Can anybody help me to figure out. Do I need to connect LED string?

Thanks in advance. :)


texts: Current calculation in Capacitor drop supply?

texts:
In the above two circuits the only difference is post rectification zener and pre rectification zener arrangement is used.
According to my understanding
in both the cases i=240/Xc1+R1=15 ma

and voltage at C2=Vz=5.6 V in post rectification zener

and voltage at C2=Vz-Vd2=5.6-0.6=5 V in pre rectification zener.
so my questiion is what is the advantage of pre rectification zener when it provides less voltage at output.
does it provide higher output current, if yes then how?

also how to find the value of C2 in this case it is given as 470 uf .
if I replace by 1000uf then will I get high current even though it is known that input current is limited by 0.2uF cap?


texts:
So, I already understand that the maximum resolution of a radar system is λ R / L, where lambda is the wavelength, R is the range to the target, and L is the diameter of the antenna, and that for a phased array, L would be the maximum distance between antennas (correct me if I'm wrong  :)  ). But there are two things I don't know:

1) How would one go about calculating the maximum bandwidth of a phased-array system? I know that they can be retargetted "in milliseconds" and different portions of the array can be used to track different targets at the same time. But when sweeping across terrain, what determines how many return datapoints you can read per second?

2) How does one calculate / estimate range accuracy when measuring distances to the target? Again the multiple antennas throws me off a bit because I know that in a single antenna system you generally have the antenna switch between pulses and waiting for returns, but I imagine that on a phased array when you have many antennas that it might be different.

This is all concerning terrain mapping from a lighter-than-air vehicle. Just trying to calculate what sort of data quality could be gathered, and it seems that most radar questions on stack exchange are in this section. :)

On that front...

3) Am I wrong that phased array is the ideal radar choice for this application?  I know aerial terrain mapping is usually done with SAR, but a) a lighter than air vehicle moves much slower than an airplane or spacecraft (bad for SAR), and 2b) spreads out over a large physical area (good for phased array).  Correct me if I'm wrong and SAR or some other type of radar else would be superior from a mass perspective for a given resolution.


texts: Which is a better conductor, a very thick rubber wire or a very thin copper wire?

texts:
I read somewhere that very thick wires are generally better conductors than very thin ones. Is this true? If yes, then would a very thick rubber wire be a better conductor than a very thin copper wire?

Edit: By rubber wire, I mean a wire made entirely of rubber, not a copper wire insulated with rubber. This is purely a theoretical question.


texts: reusing a phone(LG) bluetooth component in arduino

texts:
I have a older LG 150 mobile phone with bluetooth. Is it possible to remove the bluetooth component and use it in an arduino project?

My concern is that there might be some propriety assembly or instructions that would make compatibility difficult or impossible.

Anyone have any experience or suggestions?


texts: How do (unused) electronic components age?

texts:
For a fictional text, I was wondering whether, and how, electronic components are affected by oxygen and moisture in the air, natural background radiation etc, over the course of years or decades.

Silicon, for example, is usually protected against corrosion by passivation. A lot of plasticizers slowly evaporate or decompose, so plastics become brittle over time. I'm not sure about copper, I think it might be fine as long as it's dry enough. Another source of degradation might be temperature stress (freezing / thawing) leading to broken connections.

I realize this is a pretty broad question, but I was hoping there are some typical examples, maybe there's typical storage requirements for electronic equipment or typical failures of components that have been in, say, a mountain hut for too long. I would guess that there might be some sources from the cold war on topics like that (think bunkers).


texts: Parallel LTC3127 based software controlled supercapacitor charger

texts:
I am trying to charge 3 supercapacitors rated for 2.7VDC-300F connected in parallel, giving a total of 900F@2.7V. The IC I am trying to use is the LTC3127 from Analog Devices(Linear Technologies). I have been through the IC datasheet but as a beginner, some of the things are still confusing to me.

https://www.analog.com/media/en/technical-documentation/data-sheets/3127fa.pdf

I want to fully control this IC using a microcontroller such as the Raspberry Pi or ATtiny or STM32F0. By fully control I meant: enable or disable(on or off) the IC, set the programmable input current limit(0.2A-1A) and set the output voltage limit(1.8V-5.25V). All this through software on the micro at 3.3V logic level.

Typical Application (Datasheet):

This typical application schematic shows the charging of 2 supercaps in series. But, I want my bank in parallel. Furthermore, I want to stack this same IC 3 times in parallel to allow more charging current to the supercaps when needed. Also, controlled by software to allow different charging current through: IC1(min) or IC1+IC2 or IC1+IC2+IC3(max) on (0.2A-3A) range.

Questions:

What type of resistors or RC filters I would need on the MODE, SHDN, PROG and FB pins for connecting them to a micro. For protection of the IO pins on both sides as well as precise control.
Should I need to do any value modifications to any of this typical schematic components for better reliability and performance in terms of charging the super capacitor bank mentioned above?
What characteristics of an SMD inductor should I consider to provide better reliability, less heating and overall good performance headroom?
I am planning to use NP0/C0G MLCC for all the capacitors mentioned in the schematic. Will this be a good approach? Would tantalum SMD caps be more useful in any way for this case?
How should I go about stacking 3 of this IC together? Should I share the typical passives needed? What about the control side of things? Surely want to control 3 of the ICs individually.


texts: Does reactive power of induction motor vary with load?

texts: I know that the power factor of an induction motor varies with load and is very low at no load and high at full load, but does the reactive power vary as well? If so, how much can it vary?


texts: Does a wireless receiver need always power?

texts:
In a wireless switch system,

does the receiver always have to have power or
are there methods that allow to power the circuit only when it has received the signal?


texts: All three indicators of a Spike guard/ Spike buster shining leading to shock like sensations

texts:
A standard Spike buster/ Spike guard has 3 LEDs in a horizontal line to indicate if the connections are OK, open or reversed depending upon which one or two of the LEDs are shining. This information is usually printed just below the row of LEDs. It however does not mention what it means when all three indicators are shining.
In our house, we use this spike guard to attach a mobile charger,  monitor of a desktop, modem and laptop charger. Usually the first and the third indicators lit up  implying "all OK" . However, intermittently, all of a sudden, the middle indicator also lists up a for variable period of time. During this interval when all three LEDs are shining, we get shock like sensation on touching metallic knob of geyser in bathroom (which is not connected to the spike guard), keypad of the laptop and cabinet of the desktop. As and when the third ( middle) LED stops shining, this current like sensation also disappears. We have changed the spike guard multiple times, sought help of electricians, checked and changed earthing and have performed Google search but in vain.
Nobody in the family is related to to electrical engineering. Could you please find out the fault and let us know what we should do to avoid this current like sensation. Thank you.
Attached herewith is an image whilst the middle LED was flickering along with stable first and third LED .


texts: Why is there such a strong preference for 45 degree angles in PCB routing?

texts:
I've always wondered this: every single modern PCB is routed at 45 degree angle increments. Why does the industry prefer this so much? Doesn't any-angle routing offer more flexibility?

One plausible theory would be that the existing tools only support 45 degree increments and that there isn't much pressure to move away from this.

But having just researched this topic on google, I stumbled across TopoR - Topological Router - which does away with the 45 degree increments, and according to their marketing materials it does a considerably better job than the 45-degree-limited competitors.

What gives? What would it take for you personally to start routing arbitrary angles? Is it all about support in your favourite software, or are there more fundamental reasons?

Example of non-45-degree routing:

P.S. I also wondered the same about component placement, but it turns out that many pick & place machines are designed such that they can't place at arbitrary angles - which seems fair enough.


texts: Operation Amplifier: + and - with equal voltage

texts:
I understand the basics of Operational Amplifiers, but I am curious, what would happen if the + and - input pins have the same voltage, does the output pin (x) give a high or a low voltage output?

simulate this circuit – Schematic created using CircuitLab


texts: AC Current Source - Modifiable Amplitude and Frequency

texts:
Just a heads up, I am not an electrical engineer. I need to build an AC current source of the following specifications. I have looked into IC chips, but none meet my specifications. I have started looking into the Howland Current Pump circuits and audio amplifiers.

Specifications:

Amplitude of AC Current:

0 - 1A (peak to peak). Should be able to change the amplitude.
Frequency of AC Current:

0 to 75 kHz. Should be able to set the frequency as well.
Load:

Copper coil with a resistance of 0.5 Ohms and 5000 nH inductance.

Questions:

I would like to know if there is a way to change the amplitude and frequency of the output current when using a Howland Current Pump circuit.
My load is a coil and is inductive. I have read that the Howland circuit becomes unstable for inductive loads. Any advice on how to make it stable.
Any other alternative circuits that can meet specs?


texts:
I've asked a similar question before but this one is a bit different.

I would like to split a microwave signal from a source and route one to the RF and the other to LO.  I will intentionally introduce an adjustable phase shift to the RF to see the change in the IF. (Since both RF and LO have the same frequency, IF should be DC)

Since the oscilloscope is going to read a DC signal, I am not worried about the impedance mismatch.

I am worried about what's going on inside the SMA Tee though.

Except for the impedance mismatch between IF, output of the mixer, and the oscililoscope, which is ok because it's DC, is there any other impedance mismatch?

When SMA Tees or BNC Tees are designed, is everything 50 ohm impedance matched?


texts: While using arduino to close a circuit (the output to transistor's base), is it necessary to connect negative of circuit to ground in arduino?

texts:
Please refer to the following image:

I hope the quality is not too bad. Anyways, as can be seen, the circuit has its own external power supply from a wall wart (AC to DC transformer). The arduino is being used only to close the circuit by means of providing the signal current to the base.

My question is: is the only thing that needs to be done is to connect the Arduino output to transistor's base? Is there a need to somehow make use of the GND pin in the Arduino (for example, by connecting the -Ve of wallwart along with the emitter to the GND)?

While I am at it, I have another question: how to find the +Ve and -Ve on the female DC jack?

As can be seen, there are 3 pins sticking out of the DC jack, (it is centre positive I think. I bought the jack because it makes it easy to connect the wall wart to the motor, i.e., without having to cut open the adapter's male jack).


texts: Voltage-boosted switching boost converter

texts:
I refer to my previous question which may be found here. With the LT1172 the highest output voltage of the booster is about 60 V, or slightly more. Now I need more, say 100 V.

Linear technologies' Application Note 19 reports an interesting voltage-boosted boost converter (see page 43) which makes use of a tapped inductor. But, the formulae are reported without an extensive explanation, and I am unable to reconstruct it. I am unsure about how to estimate the proper inductor specifications, especially in view of the need for a snubber, and when I try to calculate the value for the snubber resistor I fall into nonsense values, such as zero or negative ones.

In conclusion, I would need some advice on this topic, and possibly a reference for further reading.

EDIT: I have advanced somewhat, thanks to the readings suggested in the comments. Now I am trying to design the snubber. I am trying with a Zener diode, but I need some help with it: I need it to be about 50 V, with the ability to sustain repetitive current spikes of a bit more than 1 A, but from my computation the average power over the Zener seems to be less than half a W. I have not been able to locate such a diode.

From further investigation, I am considering Transient Voltage Suppressors: is this reasonable or are they only suitable for extraordinary events? Are these diodes rated for repetitive current spikes? (As far as I have seen, in Zener data sheets the surge current is specified as "non repetitive.")


texts: testing no leads packages for pin to PCB pad connectivity

texts:
After having spent 4 hours to hot air solder, multimeter probe, apply flux around the sort circuiting pads, re- hot air, re- probe and finally apply wick & iron to get rid of those shorts I am now concerned with possibly having overwicked them. Can't tell for sure if there is pin to pad connectivity and wouldn't know how to test for it. Also wouldn't want to go on soldering the rest of the board only to find out at the end that my no lead packaged chip is not working.

Is there any way I could test this connectivity for a LGA package ? it does not expose its pins on the side, it only has bottom pins. I don't know if the multimeter probes are touching the solder joint or just the bare solderless pads underneath.

edit

Tried the resistance to GND measuring method from @Some Hardware Guy answer. My  joints are a wreck... Aside from that, I can understand cases 1 and 4 below, but how about 2 and 3 ?

DMM reading of 1.4 M     - probably for the healthy solder joint
DMM reading of 1.0 M     - how so ?
DMM reading all over the place, or slowly decrementing, or slowly incrementing
DMM reading out of range    - probably no contact between the pin and pad


texts: The reason for using air coils in LC tank circuits

texts:
I noticed that in LC tank circuit designs very often people use air coils as the L element as opposed to an axial inductor. I understand that the problem with the axial ones is that they tend to self-resonate. But I also thought that using an air core coil allows for much smaller inductance (on a scale of nH), as opposed to the usual uH scale of axial inductors. This in turn allows for a larger capacitance of the capacitor in the tank so that the other capacitances in the circuit don't influence the resonant frequency as much.

Would it be reasonable to conclude that using larger capacitors and smaller inductances (air coils) is a more robust approach to designing LC tank circuits, or should the effect be negligible and the main concern be reducing self-resonance of the inductor?


texts: How to Compute bias Resistor for phototransistor Value?

texts:
I want to use this phototransistor in an Arduino project: https://www.kingbrightusa.com/images/catalog/spec/WP3DP3BT.pdf
I calculated the value of the phototransistor bias Resistor (R1) by the following computation:

R1 = (Vs - Ev) / If

where:
Vs = supply voltage, which is 5V on Arduino board
Ev = emitter forward voltage, which the data sheet states as 0.8V
If = emitter continuous forward current in Amperes, which the data sheet states as 100nA
Applying the formula, we get the following:

R1 = (5V - 0.8V) / 0.0001A
R1 = 42K ohm
then I used R1 =10K ohm to use the phototransistor  as switch (either saturate or cut state).
I am not shure from my choose.

So, my question is:

Did I compute R1  and choose it correctly?


texts: Why are SRAM based FPGA used more than NVM based FPGA?

texts:
SRAM based FPGAs need to load the bitstream again after power off. Meanwhile the Non-Volatile based one don't need that.

I wonder, why are more experiments and security research done on the SRAM FPGA than the the NVM based one, it seems that the volatile technology is more used regardless of its security limits (when it comes to ensuring secure boot).

(PS: I have no statistics, it is a personal observation)


texts: Can I locate the object by reading its signal with RFID readers?

texts:
Say, I have a moving object [X] inside some territory and a set of long-range RFID readers [<]:

-----[<]---------------------[<]------
|                                    |
|                                    |
|                                    |
|                                    |
|                   [X]              |
|                                    |
|                                    |
|                                    |
|                                    |
|                                    |
|                                    |
-----[<]---------------------[<]------

The idea is to make possible to track cattle or chicken walking around a fixed area range.

Is it possible to get the time signal goes from the object to readers and thus locate it in real time?

How can it be performed?


texts: SGEN amplitude measurement doesn't match oscilloscope

texts:
I don't understand the measurements regarding the voltage of the oscilloscope of the JDS6600 signal generator I recently bought.

Being the SGEN specified amplitude 5V I'd expect the Vpp on the oscilloscope to be 10v. Instead, I get 5.76V. Even if the amplitude in the SGEN actually refers to its  Vpp, it still doesn't match the one reported by the oscilloscope.


texts:
I need somehow to manage pallet movement in one of factory sections. Since my controller can't work with interruption from I/O I need to get I/O reading cycle. But for this reason I need my persistence sensor generate high level when pallet moves in and still be in such position till I reset it to low level by using controllers output. Sensor should stay in high level even if palette move out.

Is there any classification of such sensors?
How to search for them online?


texts: How does a super diode work when the diode is directed towards the output of the op amp?

texts: I saw this problem  on a sample test and was stumped by the purpose of the diode. Since it's an ideal op amp, the 2 inputs (Vp, Vn) are the same. You know that Vp = 2Vi and so you also know that Vp = Vo = 2Vi. This leads me to think that Vo is totally unaffected by the diode. That was my intuition at least. This led me to believe that this  would be the answers to part A and B, but apparently it's this.  This obviously means my rationale is wrong that the diode actually plays a role in all of this. Please help me understand where I went wrong. Thanks!


texts:
I need to do when the module have connected power supply, it will automatically turn on the module. Because is there a PWRKEY button, probably grounding it or give on that pin VDD_EXT will not work.
I've read whole Hardware documentation, but I found only schemes where is turning up via transistor or button, but nothing about automatically turn on. This feature have for sample SIM800L coreboard, but scheme of that board isn't available.


texts: What kind of cable can be used to power a mobile electric machine running of 6 kV AC?

texts:
I'm looking into the specifications of Hitachi hydraulic excavator model EX8000E-6 with electric motor. The spec says the motors are of type HITACHI TFOA-KK and run off AC 6 000 - 6 600 V / 50 Hz, each of the two motors is rated at 124 amperes. In the picture (left bottom corner) there's a cable:

The cable looks as if it was a domestic vacuum cleaner cable - simply laying around.

Crafting such a cable looks like a major challenge - it has to be flexible and have enough insulation to withstand the 6 kilovolts in the wires. All the high voltage cable I've seen so far were designed for being buried underground and so were not really flexible. Even they have untrivial design.

How are such flexible cables for voltages around 6 kilovolts designed that they feature flexibility and capability to insulate the high voltage?


texts: How do we know the direction to draw the arrows for voltage drops and current direction when drawing a circuit diagram for an ac circuit?

texts:
In an ac circuit the polarity of the voltage source changes periodically. So too will the current. However my circuit course has the voltage source labelled with a positive and negative as seen in the schematic below:

simulate this circuit – Schematic created using CircuitLab

This software used to draw the schematic also provides the voltage source icon with the positive and negative signs on it. Using the polarity of the source we can draw the direction of current flowing towards the resistor in the loop. My main source of confusion is that ac alternates the direction of current therefore why do we draw current in one direction and polarise the sources?


texts: AC Current Calculation from wattage and Voltage

texts:
There is one simple formula to get Current drawn by the appliance i.e P = V * I
I am running an appliance its wattage is 1000W as per the specs. It works on the nominal voltage range between 220-240V 50/60Hz (As per the specs).

I used the multimeter to calculate the current drawn by the appliance, it's 3.8A.

The AC voltage currently is 224V, but when I plug in the appliance to AC socket it drops by 10V. It's 214V when the appliance is plugged in. Why did the voltage dropped.?

If we do the math

P = V * I
1000W = 214 * I;
I = 1000/214 = 4.16A

On the multimeter, it shows 3.8A. Why the difference in values?


texts: I am designing a robot using the PIC16F877A microcontroller that will avoid walls and obstacles.  I plan to have it run off of 4 AA batteries.  I was wondering how i would convert the 6 volt input voltage to the 5 volts that the pic needs.  I need to use 6 volts because the h bridge circuit/the motors that I am using require it.  I also need exactly 5 volts, because i need a 5 volt reference voltage for my ADC and to run my sensor off of.  Using two batteries is an option, but I would hope to avoid at all costs.  Finally SMD products won't work, because I would like to build this on a breadboard.  I did ask a similar question here How to get input voltage of 5 and 6 volts but my needs have changed since then and the answers wont fit my problem.  How would a normal project overcomethis problem.


texts: 2 sequence detector using state machines

texts:
I was given a problem to design a 2 sequence detector. I was able to make the State Diagram but don't know how to proceed to make the state table.Can someone please guide me how to make the state table?

Here's the problem-
Design a sequence detector to detect 1101 and 1011, both sequences should be detected with the constraint that overlapping is allowed. There shall be one output. One output should be high when any of these two sequences gets detected. Consider LSB of each stream to be first bit to enter in sequence detector.

Here's what I got to

Input is a data stream for example 00011010110 and would like to the design the circuit using flip-flops and mux.


texts: Implementing function with NAND only quickest way

texts:
I'm trying to remind myself how to implement given function or karnaugh map with NAND or NOR gates. I remember how DeMorgan's laws work.

Let's say I have some Karnaugh Map and I want to implement the obtained function only with NAND gates.

To be efficient: should I group together zero's or one's? (Should I obtain PoS or SoP form of function to get to my result as fast as possible with least number of boolean algebra transformations?)

And same for NOR gates: should I group zero's or one's?

I understand that it all depends, but let's say that the Karnaugh Map is uniformly distributed with 0-s and 1-s and it is equally difficult (or easy) to group either.


texts:
Why won't the value of output changes? It has been clocked and the inner loop should update? In the simulation, the output's value is always 9. Please help what I may be missing. I would like the code to update output when the inner loop updates.

 library ieee;
    use ieee.std_logic_1164.ALL;
    use ieee.numeric_std.ALL;

entity test is
    port(
        clk : in std_logic;
        output : out integer
    );
end entity;

architecture behave of test is
begin
process(clk)
begin
if (clk'event and clk = '1') then
for x in 0 to 9 loop
   for y in 0 to 9 loop
       output <= y;
   end loop;
end loop;
end if;
end process;
end behave;

I would like to use values of inner and outer loop. It could be used as counter for my system.

The desired waveform would be like this.

I would like to use value of y and x if possible/


texts: battery overdischage oscillation protection

texts:
I previously asked asked an advice on power control of battery operated system.

The problem was to cutoff the battery when low to avoid overdisharge.
I have built the device according to Olin Lathrop's advice to add hysteresis to avoid oscillations. Unfortunately this does not work. The oscillations still appear in very unpredictable way.
Is there a way to add a control with stable hysteresis and preferably with reset button.
My current schematic is: stable voltage is compared with battery voltage at the comparator, when certain threshold is achieved the comparator switches and switches off the load via power mosfet, 200mV positive feedback from is added to input of comaparor to add hysteresys. It work perfectly fine in simulation software but still oscilates in real life.
The problem might be in capacitance of the load or whatever. I need a different approach, something that would latch and hold the OFF state.


texts: Why overshoot happens in Inductor voltage in an open loop DC-DC buck converter?

texts:
I am extremely confused about why this overshoot occurs in the Inductor voltage waveform in buck converter and also why the time to achieve steady state reduces on increasing the load resistance.
These are the waveforms that have been formed for two different load resistances (1. 12 ohms, 2. 36 ohms).
Please help me understand why the two waveforms differ on just changing the load resistance. Please do provide a good reasoning as I am extremely confused after hours of googling!
Waveform 12 ohms:

Waveform 36 ohms:


texts:
I connected a 1.3" SH1106 Oled via the I2C pins to a i2c-to-usb adapter (UMFT201XB from FTDI) and on my Linux Box (Z83 mini pc with Ubuntu 18.04) I can see the device under /dev/ttyUSB0.

This is the dmesg output:

[16123.056915] usb 1-2: new full-speed USB device number 15 using xhci_hcd
[16123.212789] usb 1-2: New USB device found, idVendor=0403, idProduct=6015
[16123.212806] usb 1-2: New USB device strings: Mfr=1, Product=2, SerialNumber=3
[16123.212816] usb 1-2: Product: UMFT201XB
[16123.212825] usb 1-2: Manufacturer: FTDI
[16123.212834] usb 1-2: SerialNumber: FTWCN8T5
[16123.216185] ftdi_sio 1-2:1.0: FTDI USB Serial Device converter detected
[16123.216361] usb 1-2: Detected FT-X
[16123.216947] usb 1-2: FTDI USB Serial Device converter now attached to ttyUSB0

Now I want to write text/graphics to the OLED screen but I cannot find the i2c device with i2cdetect -l. After plugging in the USB, I don't see a extra device there (maybe there should not even be one?).

I use the luma.oled library on the Linux Box, but for the initialization, I need the i2c port and i2c address (somewhere in the docs they mention 0x22, but what port?).

How can I find the port for the USB adapter, if there is even one. I am a complete noob with i2c and virtual serial ports, so maybe my approach is completely wrong.


texts: multimeter input impedance calculation discrepancies

texts:
To measure the input impedance of a multimeter, I have built a voltage divider circuit with equal resistances R1 and R2 and measured the voltage across one of them using the multimeter. Considering that a multimeter is an ideal voltmeter in parallel with a resistor with value equal to input impedance I derived the following equation: $$R_{ii} = \frac{R_1R_2}{(\frac{V_s}{V_{meas}} - 1)R_2 - R_1}$$
The circuit is as shown below:

When I measured the voltage using 10kohm and calculate impedance using the above equation, I get a value of 2.58Mohm but when I repeat the same with 100kohm and 1Mohm I get values close to 9Mohm for input impedance. Why does this discrepancy exist? Please explain with equations if possible.

NOTE: I measured the values of the resistances that I used in the circuit with the multimeter so I get that it is a circular problem with using the multimeter to measure circuit resistances and using the circuit resistances to measure the multimeter impedance, but I am at a loss for measuring the impedance in other ways without involving another meter. Please also give ideas on how to measure the impedance otherwise without the use of a secondary meter.


texts: Why do we need Frequency Divider for external clock (GPS reference signal) for Frequency Counter?

texts:
Our senior project is to build a precision frequency counter which is using GPS signal as a reference. I looked up somebody else project online and found that I have to divide reference signal (normally >7.2 MHz in my project GPS freq. signal is 10MHz) and then it will feed to Microcontroller.

So my question is why do we have to divide reference signal like 100-200 times smaller (the output of my Frequency Divider is ~ 76KHz) before send it to Microcontroller which have speed of 16MHz for example. I assume that I will use this signal as an external clock instead of using internal clock of Microcontroller.

Please help, this is very confusing for me.


texts: Is zero input zero output test of an electrical network is necessary and sufficient condition for network to be linear i.e for example if  I have electrical network of N-port and I measure current and voltages across all the N-ports without applying any external input and got zero output at all the N-ports,  so now  is it sufficient to assume that this network is linear?


texts: What is best way to generate PWM to drive LEDs without 555 and microcontroller?

texts:
I want to drive my LED circuit at 40-60% duty cycle to reduce the power consumption. How can I do this without using any microcontroller? Is there any switching IC to do this?

Details:=
Input voltage to the LED panel is 5 volts.
Every LED has a series resistor. And then they are connected in parallel.
4 LEDs: 3 volts, 20 mA.

EDIT:
I don't want to use many components. Something like op-amp ICs; we can just select two resistors based on the gain requirements to amplify the signal.


texts:
I am trying to build a robot with the minimal components and an Arduino UNO.

It needs 7V to 12V input or 5V. So I thought as a replacement of using 6AA, I'd use 2 li-ion of 3.7V in series.

My question is, is it safe to place them in series and use them without any other components controlling it?


texts:
Is there a PCB guideline paper or book that discusses how to design PCB layout and components that meet IEC60079 (-0, -11, -7) and how to limits the use of encapsulation or conformal coating.

In my case, I have an off shelve certified Zener barrier module attached to 4-20mA sensor device (protected input). The unprotected signal/power from Zener Barrier is then attached to my DAQ PCB, it has current limiter build-in on 24V terminal which avoids overheating in event of shorting faults. My DAQ board has lot of 0402/0603 res/cap but avoided tant/elec cap. (An expert for initial review suggested this board with 0603/0402 and small IC along with tracking layout does not qualify in IEC60079-11, I'm unsure why or which clauses in that standard apply). The power consumption of the board is less than few watts and mostly 5V/3V3 with 24V to 4-20mA sensor.

The IEC60079-0  (clause 5.3) defines a component with surface area, do they also apply to PCB as a component with 11,000 mm2 surface area? or do they apply to discrete parts?

It says Max Pd = 1.3W for +40C ambient, do they apply only for discrete part or whole PCB as a component?

How thick conformal coating, how to decide on that?

The DAQ unit resides in Zone 2 (Group IIB, T4).

(Ref: PCB design for intrinsically safe equipment to 60079-11 standard)


texts: What is the best way automated relay switches can work with manual switches for a two way skylight motor?

texts:
I am installing a pair of skylights and considering if I could automate them with a Raspberry pi. The same could apply to windows or blinds, so I am hoping someone has done similar.

Is this a safe and effective way to use two automated relay switches to control a two directional actuator used to open and close a skylight?

The idea is to never allow both Open and Close circuits to be live at the same time. This is the way I thought that could be achieved but have little to no experience.

This follows on from: Can this double-pole double-throw switch be simplified for controlling a motor (skylight)


texts:
With a continuous rotation servo I can control the direction and the speed of the servo, but I need to control the position as well. I know it's not possible directly due to lack of feedback control in a continuous servo, but I found some hints about adding an encoder to let you control the position.

Is it possible to add an encoder to a continuous servo to control its position, and if so, how?

Also, can I add a thing to block the motion of the servo like the picture below or would having such a stop effect and damage the servo?


texts: Circuit or device for avoiding electrical overload

texts:
Is there any device that can limit current to 2 appliances connected in parallel on the same outlet?

Let's say both devices A and B can draw upto 10 amps but can work under reduced current as well (say 5A each).

So I want something to be installed in the outlet (rated for say 15-16A) that will limit the current to 10 amps so that the circuit breaker doesn't trip.


texts: Attempting to make a stopwatch using two 74hc161n chips with decoders and seven segments

texts: I have been tasked with constructing a digital clock in my electronics class. I had a problem with multisim and had to change my design but now I can't figure out how to make these counters reset correctly. The problem I have is this circuit counts from 0-50 and then resets to 1. My least significant counter works fine, always from 0-9, but the most significant one counts from 0-5 and then instantly to 0 instead of waiting for another 9. Any help will be greatly appreciated!


texts: Can anyone tell me what a 'double diode' is used for? For example, a BAV99. I'm not sure of the correct name for it and so can't find it in any of my reference books. I've come across one in a circuit, between an output pin on a micro and an input clock pin.


texts: External gain-independent offset-nulling for a buffer

texts:
Related

Non-inverting amplifiers Offset Nulling - but with different constraints since that has a non-zero gain and uses a different op-amp
How can I do offset nulling for this opamp circuit? - that has a large gain and uses a different op-amp.

Context
For now I am using a cheap MCP6002 as a rail-to-rail voltage follower. It has a worst-case input offset of +/- 4.5 mV and typical input offset of +/- 1 pA. The application is for a low-output-power (<= 1 mA) low-frequency (< 100Hz) output stage after a microcontroller-based resistive ladder DAC.
The chip I have has an offset of about 2mV. This is fine for my application and does not strictly need correction, but as a thought experiment and for learning purposes I decided to see what it would take to null this offset. The 6002 does not have nulling pins. I realize that the proper solution for a production circuit would be to replace the op-amp with one that either has a laser-trimmed offset or is configured as a chopper, but that's not the purpose of this exercise.
Example solution
The following solution would be able to null a fixed offset of +4.5mV.

simulate this circuit – Schematic created using CircuitLab
To maintain unity gain and cancel the offset,
$$
\frac {R_4} {R_5} = R_3 \left( \frac 1 {R_1} + \frac 1 {R_2} \right)
$$
$$
\frac { V_{DD} R_3 } {R_1} = V_{off} \left( 1 + R_3 \left( \frac 1 {R_1} + \frac 1 {R_2} \right) \right)
$$
Issues

This doesn't take into account input offset current at all.
In its current configuration this can only cancel a positive offset, not a negative offset
Whether R1, R2 or R3 is made a trimmer to make the nulling variable, the gain will no longer be unity.
The divider of R4/R5 decreases input impedance, defeating one of the purposes of a buffer.
Even disregarding the issue where a trimmer anywhere breaks unity gain, exact unity gain will be difficult to achieve without extremely precise resistors and won't be as close to unity gain as the bare, non-nulled solution
Power consumption will be increased as compared to a non-nulled solution

Questions

Have I missed anything in the list above?
Is there a better strategy for external offset nulling, or is this a lost cause?


texts: Convert\Modify Air fryer from 120v to 220\240

texts:
Dash Compact Air Fryer

i wanted to ask if its possible and\or practicle to convert an 120v air fryer(1000w) to work on 220-240 outlet ?
it has a heat spiral and a fan (if it helps)
if more info is needed so please tell me and ill provide.

im not a pro in electronics but i understand basic stuff and can solder.

Dash Compact Air Fryer

sorry for bad english and thanks in advance :)


texts:
I'm designing BLE devices and other low power embedded systems that can consume very low energy in the range of a few micro-amps.
I can't afford any expensive precision multimeters. Hence, I'm trying to design a simple system to measure micro-amps with the INA series chips and a micro-controller. I currently don't have access to designing custom PCBs with SMD chips and precise components. Therefore, I'm sticking with the INA series modules which can be found easily on aliexpress.
I found 3 modules the INA219, INA226 and INA3221.
They are very similar using an I2C bus to communicate but have different resolutions. Based on the datasheet, taking INA219 for example has a max shunt voltage of 40mV and a 12-bit ADC which gives a LSB step size of 10uV. By using a 10ohm resistor as a shunt, I get a resolution of 1uA.
In theory, this should be perfect to calculate microcurrents. However, I read in multiple forums that INA219 series are great for measuring milli-amps but not micro-amps and recommended using a traditional op-amp amplifier circuit. I'm currently not able to do so, so I'm trying to see why do these modules cause problem in measuring low currents and what I can do to improve it?
[EDIT]
Answering some of the questions from the comments.
Firstly, I perfectly understand that SMD components are unavoidable in professional design. However, at the current situation I need a quick low cost and relatively reliable solution to measure uA to a single digit. Hence, the question and I'm also curious why it would be a problem if it is?
As this will act as an ammeter, I can attach the shunt resistor in either high-side or low-side of the circuit. The system is operating in a standard room temperature of about 27 degrees Celsius. The precision needed is to have a step size of 1uA.


texts:
Recently Samsung came out with the new Galaxy and Edge phones which are advertised as IP68 rated.The mircro USB ports on these phones are completely exposed, yet are still IP68 rated. My question is, how do you achieve a water resistant rating on these ports while still exposing these pins to the potential of a short circuit?

The only thing i can think is that the phone will use some kind of smart circuitry  too prevent it going into USB host mode and supplying any voltage when exposed to water. Or prehaps some kind of special nano coating around the charge port?


texts: Part identification: 4 pins, 2 marked with squiggles, one each marked with + and -

texts:
This component has 4 legs. I don't know what it is, 2 of them go to VCC and GND, the rest of them I don't know.

What is this thing?


texts: Arduino Laser Engraver cd drive - what do i connect where?

texts:
I am a beginner in the world of circuit boards and electronics, and this is my first real project. I am making a DIY laser engraver, following the instructions in this instructable.

Here is the circuit layout

As you can see on the two A4988 stepper motor drivers, 1B, 1A, 2A, and 2B pins have the two A's in the middle with the B's on the outside.

When I watch the guy in the tutorial connect the board with the x and y axis, which are directly connected to those pins, he does it straight, with the leftmost pin on the leftmost solder point on the CD drive.

However, when I use the multi-meter on continuity, I have that the two left solder points on the CD drive are a pair, as are the two right solder points. Should I cross the wires over, connecting the two left solder points with the two middle pins, or do it straight from left to right as he did?

Here is the pcb gerber file.


texts: Is an ideal transformer an ideal current source?

texts:
I define every circuit element of a primary coil of a transformer that is connected to a voltage source and calculate \$I_1\$ (current of the primary loop).  I then connect it to a secondary coil with a known number (\$N\$) turns.

Regardless of the values of the secondary coil, I always can calculate \$I_2\$ (current in secondary coil) by using $$I_2=\frac{N_2}{N_1}I_1$$ Does it mean that an ideal transformer is an ideal current source?


texts: Increasing output current of the inverting voltage doubler charge pump circuit, implemented with MAX1720

texts:
I have a +3.3V voltage rail available. And I want to generate a pair of negative and positive symmetrical supplies out of it. The magnitude of the output voltages must be less than 7V and should be higher than 5V; anything around 6V is fine.

These voltages will supply a couple of analog switch ICs, which will consume current around 50mA at total from the both supplies rails. My charge pump controller IC (MAX1720) itself can supply that much of current, but its output voltage drops down to undesirable levels when that much current is drawn. So I decided to enhance the output stage by using a NPN/PNP pair as suggested in the datasheet (page 14, figure 42).

I have no problem with the design of the positive voltage doubler circuit. But, the datasheet doesn't suggest any way of increasing the output current capability for the inverting circuit. Can I do the same thing in the inverting one. If yes, how do I do it?


texts:
Why is the base to base characteristics of UJT a straight line passing through the origin?
and what do you mean by offstate resistance of ujt??


texts: How to wire a PIC32MX795 so it can be used as a Host (OTG) or device

texts:
I know that the pic32 can not do both at the same time.
In device mode the pic32 should be powered by micro B usb connector and act as a HID/Serial.
In host mode it should give power to a USB type A connector and support things like a keyboard or a mouse/touchpad. I think supporting mass storage is too difficult compared to using an sd card so i want to keep the functionality of the USB to its basic needs.

I would like to be able to switch between those modes by way of a switch(es) or jumper(s).
The simpler the better.
I have checked most of the schematics microchip provides but none have this worked out and my understanding of USB is unfortunately not adequate enough.

Did any of you guys figured this out yet?


texts: Garage door openers - BLDC x AC monophasic - Is that possible?

texts:
As far as I know, electronic control boards for garage doors, they basically control two main types of motors:

AC induction monophasic, one neutral and two phases, driven by TRIAC or relay. It takes long time for close/open garage door.

BLDC, driven by inverter. With it it is possible to reach much faster opening/closing time of the garage door, around 4 seconds for a complete cycle.

A representative of companies that makes electrical motors told me that there are few companies selling an "additional board" that connects to the control board from any standard garage door already installed (I mean only the one which controls AC induction motors) and also to the motor. He said that using that addon board the AC motors can reach almost the same speed of closing/opening the garage door compared to the BLDC type, a much lower time compared to the original installation (without the addon board).
Could that be really possible? How would be the electronics of such thing?
Regards.


texts: What would be the best way to design a real time clock for the MSP430?

texts:
Basically that. The way I am doing it now is with the TimerA set to 1 second interrupts. But I think that it's very annoying. Are there any other ways to do it?

I want to basically set timers on that clock, like, shutdown until 40 seconds have passed...


texts:
So I had to design an amplifier with a 'floating' output. (I don't know if floating is the right word, it's the direct translation from dutch.)

See the picture below ( I drew it whilst sitting in the train so it doesn't look very nice)

I don't know the theory behind this but I suspect that one of the signals works as sort of a reference signal for the other one. So the electric potential alternates over the load.

Can somebody verify/clarify this for me?

Thank you,
Matthijs


texts: How does temperature affect voltage references, resistors etc.?

texts:
I have a 0.1% 3V reference with a temperature coefficient of 100ppm/°C.

Does this mean it will be off by 8500ppm (0.085%) on top of my 0.1% when operating in an environment at 85°C?

Does something similar apply to resistors?


texts:
I'm generating a sine wave to apply to a transistor in the push-pull configuration.

I am using a symmetrical source with 741 operational amplifier, + the IC 555 with plym 60 Hz 50% duty clycle, + another 741 with a filter passes the band at its input.

the problem is that when I measure in real life the circuit with the negative input of the oscilloscope on the ground plus the other on pin 6 of the 741 filter, I get a square wave.

Why do I get this square wave?.

Where am I going wrong?

formulas for the bandpass filter are these.

R1 = Q / (2 * 3.14 * F * G * C)
R2 = Q [(2 * Q 2 -G) * 2 * 3.14 * F * C)
R3 = R4 = 2 * Q / (2 * 3,14 * F * C)
Q = quality factor.
c = capacitance in farady.
f = frequency.


texts: Is this normal for a 12 bit Microcontroller ADC (STM32F303)?

texts:
I am using an STM32F303 with a 12bit ADC to read an output voltage using the ِADC itself.. as far as I know the Vref of the ADC is the same as the VDD of the device. Am I right?

However, when feeding the output of the VDD pin of the microcontroller to the ADC, it gives a value of 4043 instead of 4096. Is such an inaccuracy normal in my case?

Thank you all.


texts: What are these cream plastic-like blobs on my circuit board?

texts:
I see these white/cream colored blobs all over the board (I've surrounded them with red rectangles in the image above), something which I've never encountered before. They're plastic like in texture, deforming with small amounts of pressure applied to them. Does anybody have any idea what these might be, and whether or not they're indicative of some kind of failure?

Context

My motorcycle's EFI control unit is complaining about not getting enough supply voltage (it is, I've checked the input pins) after breaking down recently (and this is now preventing the bike from starting up), so I figured this electronics degree must be worth something, right?

Hoping it might be as simple as a blown capacitor or damaged track, I removed the control unit from my bike and pried off the metal cover covering the pcb, which was attached with some kind of waterproof sealant (somehow without damaging the circuit board myself). The image below is what I found myself presented with.

Also, if anybody happens to notice anything obviously wrong in the circuit board above, I'd appreciate very much if you could post a comment and let me know!

p.s. The supply rails on either side of the board measured ~5mV across with the bike's ignition turned on (what the hell? basically nothing). The Infineon CPU seems to be rated for 3.3V of supply voltage... so one thing I tried was putting a small 3V DC supply in parallel across the rails, hoping it might stop complaining about having low voltage (it didn't), was this stupid? Yes it was.


texts: What should i do with BJT when BJT has other two pins

texts:
The commomn BJT has three pin for B,E and C,but i use the virtuoso to choose bjt504tnpn from analoglib and find it has five pin,i surf the Internet,
guessing these five pin is B,C,E,S and Th,however,i don't know what is Th here,and also wonder what should i do with S and Th when i want to make the schematic below


texts:
S11 for marker 1 says -47.661 dB

Two Questions

1st ..... What is | S11 | ^ 2

2nd

Is this accurate ?

g = 20 log_10(-47.661)  dB


texts: What is the the physical meaning of inductance? We know that the resistance "R" of a conductor is how easily the electrons flow through it, etc., but what about the inductance "X"?


texts: In cold weather, sensor on garage door opener malfunctions

texts:
I have an electronics question, I hope this is an appropriate forum. I have an electric garage door opener. It works just fine in the summer, but when the weather gets cooler (not below freezing, I live in Australia) something funny happens. I press the button to open it, it opens about a foot and a half then stops, and starts going down again. I stop this by pressing the button again. Then I start it going again, and now it goes up to about 3 feet high, then stops and reverses again. I stop it, then press the button, then up to 4 1/2 feet or so, then stops and reverses again. But now when I press it it goes all the way up. My guess is that somehow the sensor gets messed up when it gets cool, but I have no idea why or how to fix it. Then again, I know nothing really about these things, so maybe my guess is wrong anyway. Has anyone seen something like this, and have any suggestions?
Greg


texts: What makes TPM chip Endorsement Key Non-migratable?

texts:
I know that the endorsement key (EK) of TPM is stored in non-volatile memory (e.g. EEPROM), which is non-migratable to ouside the TPM. The Storage Root Key (SRK) is also non-migratable.

What makes them non-migratable? It is achieved by protective code or the design of the internal IC structure?


texts: Can a digital meter be damaged when reading resistance but connected to AC voltage

texts: While testing with multimeter like a fluke 177 or fluke 334 clam meter in ohms range, if it is connect to ac voltage up to 50 volts, does it damage the multimeter?


texts: Why diode series on Input of boost converter?

texts:
Simple question:
I'm new to electronics, but have one straight forward question. I know all boost converters are made up of diodes, caps and coils with some sort of feedback system to regulate voltage.
I bought a 150w boost converter: BMT DC/DC BOOSTER 12-35VOUT 150W
SPECS:

Module Properties : Non-isolated Step-up Module (BOOST)
Input Voltage : 10-32V
Output Voltage : 12-35V (adjustable)
Output Current : 6A (max)
Input Current : 10A (max) (Please Enhance Heat Dissipation if more than 10A)
Output Power : Enhance Heat Dissipation 150W (MAX)
Conversion Efficiency: 94% (measured at Input 16V, Output 19V 2.5A)
Output Ripple : 2% (max) 20m-Bandwidth
Operating Temperature: Industrial (-40 ~ +85°) (ambient temperature exceeds 40°, lower power use, or to enhance heat dissipation)
Full load temperature rise: 45°
No-load current: 25mA typical
Dynamic response speed : 5% 200uS
Short Circuit Protection : None (Please Install fuses and protection circuits at Input port.)
Input Reverse Polarity Protection : None (Please Series diode at the input port.)

In short it recommends to place a diode (out of interest I've bought a schotkky 10SQ050) in series at the input port to protect against reverse polarity, but what I don't understand is; do I simply just place the diode (with Cathode connected directly to the in+) inline of the In+ line? see figure 1. OR must it be placed in parallel with the in+ and in-? If so then in which direction would the diode be placed? see figure 2
I would really like to understand more. It doesn't make sense to me that the diode is to be placed in series with the input, despite it stating it needs to be in series, so I just want to understand. Please help me understand! Thanks a ton for your time!
Figure 1:
Figure 2:


texts:
I want to know that is it possible that a Slave I2C device which is a 32-bit MCU, for example STM32F407, I write its I2C data send function and send data through it after every 1 sec? I am asking this because my understanding is that I2C is a command-response protocol. A salve will not send data unless it will receive a command to do so. So for the case of fixed I2C based sensor chips this logic or protocol is embedded in the chip silicon. It's state machine will not send data unless it gets a command first.

But in the case of an MCU in which I2C is a peripheral and it is configurable and programmable.. will it be possible to call the I2C_Data_Send() library function in my test program that will send for example 1-byte of test data over and over again?

So essentially what I want to know is that when an I2C Slave is a peripheral in an MCU then does its SEND and RECEIVE digital logics are implemented independent from each other in the hardware or they are logically tied together? If it's the later case then obviously I will not be able to invoke the SEND_DATA logic without first receiving the COMMAND from a I2C Master. But if its the first case and SEND and RECEIVE logics are independent then I can start an I2C_SEND_DATA() case anytime from my firmware (specially at the time of testing the setup to see if my data sending logic is working or not).

Overall I will have single Slave device (an I2C MCU) and no Master. I want to see if I can make to to send data without any master giving it a command or ACK/NACK or START/STOP signal. I will be looking at the output on an oscilloscope by pulling-up the SCL, SDA lines of the Slave device.


texts: Biasing high frequency BJT cascode amplifier

texts:
So far, no one in the course has gotten both primary spec: 14.125 (with 1 V/V swing either way) nor 3dB-bandwidth of 500kHz to 20MHz using the 2N4427 (datasheet).

Vcc = 9V

I_CQ = 10mA-15mA

I have four questions about the cascode BJT amplifier.

1) I found some practical advice, here and here, saying this:

  [I]n the real world, for frequencies above 2MHz, a second emitter
  follower buffer stage is needed to prevent loading of the output
  stage, and reduced frequency response.  The capacitance from even a
  1MHz scope probe will roll the frequency of this amplifier off at 2
  MHz.  To measure frequency response on a scope, measure on the output
  of the cascode through a buffer.

Do they mean a third BJT?

2) Another student's circuit below reaches the desired gain (23+/-0.5dB), but when implemented, the gain was half! We are soldering our circuits to perf board. The leads are kept short. Our professor suggested grounding surrounding pins. Any other practical suggestions or design tips?

3) I designed the circuit below to reach a higher gain (since the student's gain above, implemented, had too low of a gain). Although, my biasing calculations for R1 and R2 are guess and check in the B2.SPICE simulation. R1+R2+R3 = Vcc/I_CQ. So R_th = 900 Ω. And R3 = V_CE/I_CQ = 75Ω. Although, I feel like I should be using higher resistances (in the kΩ) from what I've seen in other designs. Why should I?

4) ilkhd commented from a similar question, "This is not a typical cascode circuit. Usually you'd keep the bases unconnected; you'd connect top base to a reference voltage and feed the signal into the bottom base."
Would the configuration below be better than the configurations above?

ece.tamu.edu/~kentesar/ELEN326/lab9.pdf

EDIT

I haven't implemented the JFET emitter follower yet, but would I have the highlighted capacitor in there:


texts: Inverting Buck-Boost -12V converter Schematics

texts:
I saw two schematics for inverter switching converters for -12V output. I wonder, the first schematic uses many components compared to the second one but still, the output current rating of 2nd one is more.
Is it safe to use 2nd one? Won't there be any problem if I implement the 2nd one on the PCB?

Using TPS40200 and the link is here: https://www.ti.com/tool/PMP1903#technicaldocuments

Using LM2576 and the diagram is in pg-19 in the datasheet: https://www.ti.com/lit/ds/symlink/lm2576.pdf?ts=1608612202416&ref_url=https%253A%252F%252Fwww.google.com%252F


texts:
Our sewing machine's foot controller is running continuously and I need to change the capacitor but I cannot find the same value capacitor i.e 0.05 μF and 250 volt AC.

I just want to know that can I replace it with 0.047 μF  250 VAC  or  0.15 μF   275 VAC. Please advise me if I can use different capacitor value on this foot controller.


texts: Transfer function and graphic (Scilab error)

texts:
I'm trying to solve this problem with a Scilab code:

I'm trying to follow this code, but in the step [b,a]=ss2tf[A,B,C,D], it shows the error ("Wrong number of input arguments.")
The code of Scilab that I try to make is the following:

clc;
clear all;
close all;
A=[-1 -2;42 -0.9]
B=[1.5;1.1]
C=[0.7 2.1]
D=[0]
[b,a]=ss2tf(A,B,C,D)
H=tf(b,a)
figure
step(H)
grid

How can I fix this code?


texts: Support for MSP430x5xx processors on MSP430-gcc

texts:
How would I add support for a new MSP430 processor type on MSP430-gcc? E.g. msp430x5xx series.

I understand I must produce the relevant .h/.o files but how do I generate/integrate those in msp430-gcc ?


texts: Chip Identification - Electronic sound toy

texts:
I just bought this toy called fridgezoo. It's a small plastic animal that you put in the fridge. It has a light sensor and a button. As soon as there is light, it plays a sound, and when you press the button it plays another sound.

I figured that it may be possible to hack this thing by dumping memory, identify and replace sound content and flash it back onto the device.

There is only a single SOIC-14 chip inside the device, labelled with

NY4P065614
P55101F

There is not much else on the board, just some passives. The chip must contain everything (Storage, amplifier, analog part for light sensor) as there is no other chip on the board.

The thing works with 3 LR44 batteries (so 4.5V).

Do you know how to source some more information about that chip?
What kind of interface (if any) would one expect from such a chip? JTAG?

Thank you


texts: Finding a I/O expander that supports 18 PWM outputs or another solution for MOSFET control

texts:
I am a student working on a university project.
I need help figuring out how I can supply 18 PWM signals to 18 gate drivers, in a 3-phase inverter.
The inverter is built up of 3 half bridges, with 6 transistors per half bridge, 3 on the high side and 3 on the low side.
The gate driver takes a simple HIGH/LOW signal, and has a built in signal inverter for low side.
The switching frequency is at 24kHz.
I want a I/O expander or a slave microcontroller to supply the PWM, as the main controller sits quite a bit away from the 3-phase bridge.
My wish is to turn off some of the transistors when the inverter is running at a low load to improve efficiency.
As far as I am aware, using GPIO pins is out of the question, so I need dedicated PWM pins, my issue is that I don’t have enough PWM outputs.
I have been looking at I/O expanders, but the vast majority I found only gave GPIO. I have also been looking at LED drivers, but I am not sure if they are the best choice.
Another option might be using AND gate logic, supplying the PWM to one input, and the ON/OFF command to the other input.  This way I might be able to reduce the PWM to 6 outputs.
Thanks.


texts: Relation between transformer core material and application frequency

texts:
Regarding the following excerpt from a text:

The text mentions that at RF air core transformers are adequate, but for 50/60Hz low freq. applications iron core needed to obtain a low reluctance.

The text does not explain the reason. What is the relation between the frequency being low and the need for low reluctance medium? Low reluctance intensifies the magnetic field but why particularly at low frequencies it is needed?


texts:
Alright so I learned all the fundamentals of the AVR and now I am thinking of building a clock as a project. I will use the ATMega328P along with the DS1307 RTC. The time will be shown on an LCD or OLED display.
What I want to know is how the general structure of the overall program will be. I know that there will two modes; one to set the time and one in which the clock runs normally. I need some help as to how I will implement these modes and two switch between them using external buttons.
It would be great if someone could shed light on this. Thank you.


texts: What is the two-pin polarity indicator for a PCB?

texts: I inserted a two-pin header (P1) into this circuit using EasyEDA.  Does the square outline mean that is the positive pin, or is there another meaning?


texts:
I have been running small batches of production over a year without a problem. Today, I found a problem that is never happened before. I have changed the PCB to gold plated in my recent batch and I see mold build up at a certain location 20 out of 500 units. I am unable to understand the root cause.

The production environment is humid (it is in Asia) but for mold to build up more things are needed especially sugar or some other type of food which I believe hard to come by in such environment.

What would be the cause of such build up? Is gold plate more prone to organic exposure?

update

I look under the microscope and now I think it is corrosion.
Here is the photo.

What process mistake would cause a problem like this?


texts: Vary equivalent resistor linearly between two values

texts:
I'd like to use a potentiometer (with a value like 1kOhm) in a resistor network to achieve a close to linear variation between 35 and 250 Ohm. I've tried several configurations, but I'm having a hard time finding a possible configuration.

I've tried the following circuit:

R2 needs to be around 220 Ohm to allow this variation. Not only there aren't potentiometers with this values, as the response curve is very non-linear:

The response doesn't need to be super-linear, but needs to allow the user to vary it continuously.


texts: finding ADSP-BF518 JTAG connection on the board

texts: I have a PCB board with ADSP-BF518, I want to use its jtag pins. (It is not an evaluation board) there are some VIAs on the board that comes from its jtag pins. but by using Continuity Test I couldn't find any header that was connected to these VIAs. Is there any special points here that make me couldn't find headers of VIAs? or Is it possible these VIAs don't connect to any header?


texts: How to make a low pass filter of current, instead of voltage?

texts:
Is there a way to low-pass filter current, rather than voltage?

Let's suppose there is a circuit consisting of a current source and a load.  The current source may have a little bit of current noise at high frequencies.  I'd like to figure out what can be inserted in between the source and load in this case to suppress that.

(Note: the load may not be resistive, and may have strong nonlinearities)


texts: Technology used in LED stumps and bails in WorldCup-2015?

texts:
I just know that when the bails are taken off from the stumps the LEDs will glow.Could somebody explain how exactly the concept works in case of LED stumps and bails which have been used in the World-Cup tournament Or provide a link which explains this.

The image below depicts the terms used in the title of the question.

EDIT (For those who don't know Cricket):

Objective of the LEDs are to detect whenever Bails (Horizontal sticks) are moved away from Stumps (The vertical wooden sticks) or not.
In game, A player will throw "Ball" from a distance to dislocate Bails from Stumps. If he succeeds, he gets a point. To detect easily, Cricket Organizers added LEDs to bails.
Video: https://youtu.be/dumkGXj0F5E

This is picture of a real stumps and bails.


texts: Hartley oscillator and feedback fraction

texts: Do we decrease the the feedback fraction and increase  the amplification fraction if we increase the value of L2? (similar to Colpitts oscillator where we by changing C2 capacitor)


texts: Why doesn't the MCU's pin go high on time?

texts:
I have a STM32F103 and I downloaded this program to it(a simple blink program):

/* Includes ------------------------------------------------------------------*/
#include "stm32f10x.h"

#define SYSCLK_FREQ_72MHz

/* Private functions ---------------------------------------------------------*/

GPIO_InitTypeDef GPIO_InitStructure;
NVIC_InitTypeDef NVIC_InitStructure;

void GPIO_Configuration(void);

void delay(uint32_t a){
    while(a){
        --a;
    }
}

/*******************************************************************************
* Function Name  : main
* Description    : Main Programme
* Input          : None
* Output         : None
* Return         : None
* Attention      : None
*******************************************************************************/

int main(void)
{
    GPIO_Configuration();

    /* Infinite loop */
    while (1)
    {
        delay(0x44AA200);
        GPIOB->ODR ^= GPIO_Pin_0;

  }
}

/*******************************************************************************
* Function Name  : GPIO_Configuration
* Description    : Configure GPIO Pin
* Input          : None
* Output         : None
* Return         : None
* Attention      : None
*******************************************************************************/
void GPIO_Configuration(void)
{
  RCC_APB2PeriphClockCmd( RCC_APB2Periph_GPIOB , ENABLE);
/**
 *  LED1 -> PB0
 */
  GPIO_InitStructure.GPIO_Pin = GPIO_Pin_0;
  GPIO_InitStructure.GPIO_Speed = GPIO_Speed_50MHz;
  GPIO_InitStructure.GPIO_Mode = GPIO_Mode_Out_PP;
  GPIO_Init(GPIOB, &GPIO_InitStructure);

}

I expected that delay(0x44AA200); works for 1s but but when I run it, this delay take 6s!!

Why?

Is it related to the 3 stage enhanced pipeline?

this is the RCC configuration and I thing everything is ok:

and this is the assembly code:


texts: What lead-free solder type is convenient to use for hand-soldering?

texts:
I have read some discussions about the lead-free solders on the forum, but could not see what solder type is easier to use for hand soldering (among lead-free ones)?

As an example, I see only two RoHS compliant solder alloy options (e.g. on Mouser at this link).

SAC305
Sn96.5/Ag3/Cu0.5

Available types:

rosin activated
water soluble
no clean wire
spool solder
Glow core no-clean

Which properties would you recommend for the one that would melt at a lower temperature and be convenient to use?

I have this lead-free solder that is not pleasant to use because of melting temperature.


texts: ALU implementation in Verilog: how to handle negative numbers?

texts:
I am designing a simple ALU with and, add, load operations for 16-bit inputs. This is what I have so far:

module ALU(overflow,out,in1,in2,select);
input[1:0] select;
output[15:0] out;
output overflow;
reg[16:0] out;
reg overflow;
always @(in1,in2,select)

case(select)

   0:out <= in1 & in2;    //and

   1:{overflow,out} <= in1 + in2;    //add

   2:out <= in1;

   default: out<= 16'bx;

endcase
endmodule

I am confused how to deal with negative numbers and how to handle when my inputs are negative: what should I do?


texts: Fast and easy way to get formula of circuit?

texts:
What would be a fast and easy way to solve problems like these? I seem to get a lot like these in my course.

Also the other way around; Questions like: How many NAND gates are at least needed for a particular formula?


texts: How to chose resettable fuse for 24 V DC to 5V DC converter?

texts:
I want to use a 24V to 5V DC converter, the PYBJ10-Q24-S5 (https://www.mouser.fr/datasheet/2/670/pybj10-om-1548233.pdf).

Page 7 of the datasheet, they specified the EMC Recommended Circuit which includes the fuse I'm trying to choose :

If I understood correctly the datasheet, the converter accepts a maximum input current of 508mA and has a current overload protection of at least 110% :

So if I'm correct, in the worst case scenario it should not exceed 558mA.

I was planning to use a resettable fuse. If I understood correctly, the holding current is the maximum current such as the fuse won't trip.

The tripping current is the minimum current such as the fuse will trip.

In conclusion, I have to choose a resettable fuse with a holding current = 508mA and a tripping current = 558mA.

Problem is : in this configuration, I can't find exactly the right fuse.

Knowing all this, how do I choose my fuse from all the existing models?

For example, I found some fuses with currents of 550mA versus 1A but I'm afraid that 1amp is much too high for my converter.

I guess I'm missing something.


texts: Can I protect areas of a MCU's flash from reprogramming/reading by arbitrary code executing in that MCU?

texts:
Consider a microcontroller with self-programmable flash, for example some ATSAM MCU.
I put a bootloader on it, which has the additional capabilities of receiving programs, ex. using USB, in whatever format I use, and storing them in a given part of the flash. It then allows execution of these programs. This is public and anyone can use that feature.
In some given part of the flash, that the bootloader won't overwrite, there's data (could be the bootloader code itself) that I really don't want anyone to be able to read.
Is it possible to somehow protect that flash area from a program loaded through the bootloader that would simply try to read it and report it however they want, ex. using USB ? Are there specific features enabling this ?
For the record I'm coming from the Arduino world and new to the actual MCU world. Thanks.


texts: How to find \$R_{eq}\$ in this situation?

texts:
I am having difficulties understanding where a parallel resistor situation is occurring in order to help me find \$R_{eq}\$.
My first thought was that \$v_{ab} = v_{ac}\$, but that would mean \$v_{bc} = 0\$ which is not correct.
Does anyone have any tips for how to think/approach this problem?


texts: Fixing conmutation for high voltage switching with power MOSFET

texts:
I have an issue with a charge circuit for a capacitor as load.

I want to switch approximately 400 V DC to charge a 1000 µF 600 V capacitor. I'm using a power MOSFET for this application. I need it to charge instantly as soon as it turns on, or in a few milliseconds. The problem is that to do that I saturate the MOSFET and then turn it off using a 10 V signal to gate source to drive the MOSFET.

It works the first time, as soon as I send the signal it charges, but the problem is that the capacitor gets damaged and all the terminals get shorted. The MOSFET is a IRFP460, it is a 500 V, 20 A and 0.27 ohm MOSFET. I choose it, because it seems to be the correct for this application. I put a 10 A fuse next to the MOSFET to verify if it was being damaged by some inrush current, but it wasn't because as soon as I turned on the MOSFET the fuse didn't pop and the current I measured was not above 5.5 A, and the MOSFET broke down anyway.

The only thing that could be causing the problem is the commutation therefore, the problem must be in gate-source or the driving part. Another thing that called my attention is that if I apply almost 8 V to gate-source the capacitor charges, but only to a half of the voltage with a single pulse of a button, and the MOSFET does not suffer any damage.

The driving signal for the MOSFET will be a pulse that can go from 55 ms to 1 second. So it has to charge the capacitor within these times too. I looked for snubber circuits that can handle this, but the ones I found were parallel to the MOSFET and would get 400 V as soon as the power supply is connected, so I would need components to deal with this and I don't have them. Even if I would get them I don't know if it would work.

This circuit will have another part to discharge the capacitor, but first I need the charge to work. I would like to know if I can implement some kind of snubber for gate-source or what can I do to avoid damaging the MOSFET and switching the voltage needed.

I think the MOSFET could be leaving the safe operating area (SOA) when switching. I also tried to put a diode with a parallel resistor on gate, but no results. How can I do this?

This is my circuit:


texts: ESD Protection for 1Gb Ethernet pre-magnetics able to withstand PoE?

texts:
I am looking for suggestions on protecting a gigabit ethernet port from ESD between the jack and the magnetics.
Due to the nature of the equipment design, the magnetics cannot be placed next to the non-standard (ie not RJ-45) circular connector. The transformer is about 3 inches away after the signals traverse a flex and onto a PWB. Currently using a Semtech Rclamp0524 device on the flex right at the connector for the high-speed Low-C ESD protection that doesn't affect the eye diagram of the PAM-5 differential signals.
However we have found that when connected to some network routers/switches with PoE (which tends to be turned on by default on those pieces of equipment) the TVS diodes get destroyed (sometimes short -> port quits working, or sometimes open -> port works but now unprotected). The theory is that the V/I characteristics on these during the PoE probes makes the port look like there is a PD controller on it and the PoE runs the voltage up and destroys the diodes.
We are going to move these TVS diode arrays to between the transformer and the MDI/PHY port to protect the phy. However I also need to protect the other circuitry on the PWB (near the flex interface) from seeing the ESD transients (every other interface port has ESD protection right at the back of the mil-circ connectors to keep it off the main PWB). The concern is that any TVS capable of withstanding PoE voltage has too much capacitance and will degrade the eye diagram to the point that 1Gbs operation won't work.
Does anyone have recommendations for parts and/or an alternate solution that could be used to kill ESD on the flex/connector circuit?
Circuit Layout:
Simplified Schematic:


texts: High voltage sampling with microcontroller potential divider affecting signal

texts:
I am trying to sample a LED light driver signal which is DC signal with an approximate mean voltage of just over 50V and a 3V pk-pk ripple. I would like to sample the signal with a microcontroller which has a maximum 5V input on it's ADC.

I tried building a simple potential divider circuit with 1M and 100K resistors, and then opened up the lamp and connected my potential divider in parallel with the LEDs being driven in the lamp (there appear to be 9). This did the trick for lowering the voltage, however it completely changed the shape of the signal. I'm assuming this occurred because I'm changing the load on the driver?

Here's some images of my signal before and after the potential divider. The stepped down voltage not only changes shape, but also becomes slightly unstable. The peak to peak voltage of the wave fluctuates ocassionally getting bigger, as well as the signals frequency which decreases (so the wave spreads out and gets bigger).

Pre:

Post:

Does anyone have any advice as to how do I should go about stepping this voltage down, while still preserving the original signal shape? Thank you.

Edit: So this is my schematic.

The LED lamp is a normal lamp for domestic use, which is powered of 240V AC mains. The black box is the driver circuity connected to 9 LEDS in series. I didn't design this, the friendly lamp makers did. (As I can't post more than 2 links per post with a reputation below 10, I have had to include the pictures as I have below, if you copy and past it into your URL bar it should work however)

FakeMoustache, the scope itself does not have a ground connection and is connected to mains via an isolating transformer so that the ground is floating. I don't entirely know what you mean by "switched from the positive side". They're all in series connected positive to negative though :).

When I measure the across the LEDs and add the potential divider the signal does not change. It does however change when I tap into into the potential divider. Also pretty strange, but probably down to me doing some rooky mistake with my scope, the signal shape changes with the attenuation factor on the probe.

Here's some measurements AC coupled. The first two are with x10 attenuation on the probe (with the oscilliscope set to x10). The second two are with the probe and scope set to x1.

I will be sampling at 1Khz, but I have yet to actually try it, will do that today and plot the graph to see how it compares to what I'm getting out my scope.

Stray capacitance is a possibility as I'm using a couple of roughly 1.5-2m wires to connect the lamp to my potential divider. But wouldn't that affect the signal across the whole divider as well as from the middle?


texts:
A plane electromagnetic wave has the shape:
\$\vec{E}(\vec{r},t)=E_0\cdot cos(\vec{k}\vec{r}-\omega t)\cdot \vec{e}_y\$
\$\vec{B}(\vec{r},t)=(B_1\cdot cos(\vec{k}\vec{r}-\omega t)+B_2\cdot sin(\vec{k}\vec{r}-\omega t))\cdot \vec{e}_z=B_0\cdot cos(\vec{k}\vec{r}-\omega t+\phi)\cdot \vec{e}_z\$
In what direction is \$\vec{k}\$ facing?
Determine the amplitude \$B_0\$ and the phase change \$\phi\$ between \$\vec{E}\$ and \$\vec{B}\$.

I asked this question in a physics forum but they said that the actual exercise is more mathematical because of trigonometric identities for finding \$B_1\$,\$B_2\$ and \$B_0\$ as well as the phase angle, so I'm sorry if this is also the wrong place.
We got this one in our lecture of experimental physics and it kind of bugs me because I can't find the right approach to this one.
Since \$\vec{E}\$ only got a component in y-direction and \$\vec{B}\$ got only a direction in z-component that the k is either in -x or x-direction.
About the second part: In general \$E\$ and \$B\$ are in phase, right? Since that's not the case here, can I assume that it results from a reflection on a surface? But how would I get to \$B_0\$ and the phase change without explicit values for \$\omega\$ and such?


texts:
I have the task to build and control 35 heaters, 10 W each. I first thought about using power resistors (like in this datasheet) as heating devices, but they'd need high currents in order to get the desired dissipation (10 W each):

case temperature about 100 °C,
10 V supply,
1 Ohm resistors

I'd need 35 linear regulators in order to control them appropriately. PWM might also work, but that would put timing requirements on the sensing algorithm (I could only sense voltage drop and current while they are on).

The next idea was to use high power BJTs instead, such as the MJB45H11 (PNP, D²PAK). I could just give them a small current through the base, and they can happily dissipate 10W as well - the derating curve tells me that's OK. To me this seems to be a good idea, I've just not done anything like that before (also I have no real electronics education, just hobbyist knowledge).

Apart from being a bit harder to control, are there any reasons not to use BJTs instead of resistors for heating?
If you don't advise against this plan in the first place: is there a recommended "front end" for controlling the base current?


texts: Running digital ground at AC line potential (not neutral)

texts:
I've run across an interesting WiFi dimmer module known as a Shelly dimmer.   This bright green module is designed to be used inside an electrical box.  Most of it's user interface is over line-voltage screw terminals (or via WiFi.)

In addition they have a recessed reset button and 6-pin programming/debug header.  It is mostly documented as for being used when not connected to A/C mains.

Doing some more reading, I understand that the "GND" pin on this is generally running at A/C "line" potential.   The power supply is clearly not galvanically isolated, which seems OK given its intended operating environment.

My primary question is what advantage is there to choosing L rather than N to make the digital ground?

Second question, any guess as to what sort circuit they use to generate their 3.3V DC supply while connected to the mains?


texts:
I need to switch on my APC UPS at 2 AM and switch it off at 8 AM every day. Would like to switch on/off the mains power to the UPS too.

I am not an electronics guy, but started to learn and have built some basic circuits.

My initial plan was to build a timer based switch circuit, which when activated would switch on the UPS after a predefined (based upon value of resistor & capacitor and IC pin connections) time period (like 30 mins, 2 hrs etc.) and switch off the UPS after another predefined time period. The problem with this approach, I think is, somebody will have to switch on the circuit every day. My logic says, it must be possible to reset timer for every 24 hour or so. Can I?

The other approach was to build a programmable timer circuit, which will be always powered on, has a Real Time Clock, with battery backup and will power on/off the UPS and mains at the specified times. I have no experience with microcontrollers, but I can learn. Is this approach an over-kill?

The UPS powers my DSL modem and torrent box and is in a remote place and have remote hands (to activate the circuit if needed, in case of first approach) available at location till 11.30 PM

Please suggest which method is better or any alternative way.


texts: Can I use aluminum tape or naked two paralleled striped cables to connect parallel LED strips?

texts:
I need to parallel connected couple dozen cut LED strips.
The total current reaching them won't exceed around 2 amps.

My constraint:

I can not order any more components for the job.

My tools:

Lots of cable, soldering wire, solder, aluminum tape.

My question:

Instead of soldering wires for each strip piece and later connecting them together, can I get hard plastic, put on two parallel lines of aluminum tape and solder cables directly from strip there?
Or: Can I glue stripped cable on plastic and solder cables coming from strips on it?

That way I have the parallel aluminum or just one set of cables at the end.


texts: What mechanism controls a ceiling fan speed?

texts:
Are all ceiling fans AC induction motors?

Since any ceiling fan can accept any off-the-shelf fan dimmer switch and any wireless remote unit that fits in the base, that means they've all got something in common and the way to control the motor speed is similar among all fans.

What is the mechanism used to control the fan speed for a fan dimmer switch vs a 3-speed wireless remote? Do they use the same mechanism? Are the electronics and method of control universal?


texts: Resistor Between Voltage Reference and + Input of Op-Amp? Why?

texts:
something I commonly see in schematics which include op-amps set up as inverting amplifiers is the inclusion of a resistor between the non-inverting "(+)" input of an op-amp and a strong voltage reference such as ground, power, or a voltage reference set up using an op-amp buffer.

What is the purpose for this? The (+) input of op-amps are high impedance, and the references mentioned above are strong sources of current, which aren't vulnerable to crosstalk in the way a weak reference would be.