texts: I made an RC curcuit on a breadboard gave it a of 25V measured the voltage across it with an oscilloscope. During my experiment it has come to my attention that the peak voltage level was getting over 25V by a very small factor during the pulse switches ie. in 5T time below the graph. The value was 25.002V. Why would this occur, the maximum voltage i can supply to my capacitor is 25V? It doesnt make sense to me.


texts: ESP8266 Power Supply source Recommendation

texts:
I have a regulated power supply with rating 17V@900mA. The LED display is attached to it and consumes maximum current of 600mA @17v. I have to attach ESP12F WiFi module to it which requires 3.3V @ 500mA.

The DC DC converter in the market can solve the purpose, but how reliable they are and can ESP12F sufficiently draw current from it? Is remaining 400mA sufficient to drive DC DC converter?

I am considering this cheap inexpenisve module based on Monolithic Power System's IC MP1584

Any suggestions would be of great help.


texts: Why is the digital out acting as ground on arduino?

texts:
I was following LED Light bar project in Arduino Project handbook and I noticed some odd behavior in the Arduino.

I accidentally didn't ground the back half of the breadboard (because I didn't realise there was a break see in the circuit below). I figured that out but noticed it seemed to make the digital pin 2 behave as ground and not light the LED when the ground wasn't connected to the back of the bread board. I tried Googling this but can't find any explanation. can anyone explain why this happens?

UPDATE
To make it a bit clearer I thought it was acting as ground because before I connect the ground between the right and left of the board (the connection I originally forgot to add, see the image) I would of expected only the front 4 LED's to light but what appears to happen is all BUT the LED connected to pin 2 lights up. When I bridge the gap in the ground rail all LEDs including the one connected to Pin 2 Lights hence why it appeared to me to be acting as ground, as the LED clearly works.

Update 2
Here is a video of the result:
http://youtu.be/5dg0PHDOorA


texts:
Edit 1/1/17: I was going to take a picture of my NI Elvis breadboard as the first fee suggestions didnt work. I removed several ICs (counters) that I was going to use for the other digits and some spare wires, and now the circuit works as it is supposed to with or without the 1 nF cap. I dont know exactly what the culprit was, but as I continue to build the rest of the circuit and put the other ICs back in, the problem may present itself again, if it does I will put in another edit.

Original question:

I'm not home so can't post a schematic at the moment, but hopefully I can describe what's going on and always add one in later.

I have a 1 Hz clock signal going into CLK A, 74LS90 set up in divide by 10 mode, with both reset and set pin pairs grounded. QA goes into CLK B. QA QD QB and QC all are connected directly to QA QD QB QC inputs on the 7441 and the 0-9 outputs to a nixie tube. Both ICs have 0.1 uF bypass caps to ground.

When turning it it sometimes counts 0-9 for only one time, then it only counts 1-8. I tried inverting the 1 Hz signal, and tried buffering but only 1-8. Next I got out my scope and the QA QB QC QD signals looked ok, and I realized when my scope was connected to QA, the nixie displayed correctly, 0-9. Then, Not sure why, but I thought adding a bypass cap between QA and ground would fix the problem. I tried I think 0.1 uF first and the display was way off it only cycled a few digits. Then I tried a 10 pF and it counted 1-8. Finally I tried a 1 nF cap and now the circuit works, I get a 1 second count of 0-9.

Can someone explain what is going on? Similar designs I have seen do not mention a required cap between the BCD counter and the nixie driver. Thanks!


texts: Is RTS & CTS important in UART communcation

texts: I am starting with UART communication in PIC32MX795F512l. This UART will communicate with PC. I was just wondering that it is important to connect RTS & CTS or just connecting Rx Tx GND will make the communication? Some websites say RTS & CTS are also important but some say that its not important. I am really confused. Please help.!


texts: Single-IC solution to the problem of spurious high on NodeMCU powerup

texts: I am currently trying to find a method to use all the IO pins on a NodeMCU to control an 8-Relay Board. However, some pins on the board briefly switch to high during startup and that is a problem for my use. Thus I've decided to use an AND Gate IC and connected all of the Input As to a NodeMCU pin that is safe to use during boot. Is there an IC which does this or something similar internally as illustrated on the picture below (just a quickly photoshopped diagram of a 74HC08 IC)?


texts:
As per circuit above, what's the purpose of the HPF in that array?
The Foot SW is actually an old graphite pile rheostat (which works fine).

Something happened, it got defective I suppose, the circuit went on being continuously closed, thus I removed it along with R1 and the setups works fine without it.

And now I can't figure out its purpose.

I though that HPF's were supposed to block current with low frequencies, based on a calculator it stands at 1Hz for the values given. Well, mine lets even DC current pass, which, I suppose, means it's defective. But if it lets high frequency current pass wouldn't it keep the circuit continuously closed even working?


texts: Can UPS with small internal battery used with large external battery ? what are the issues?

texts:
I have APC BX1100C-IN 1100VA 230V Back UPS UPS , there is internal battery in it. Its gives 15 minutes backup in case of power failure.

I am planning to increase the backup time from 15 minutes to 6 hours. By using External Tubular 12 volts 180ah battery.

What are the possible issues in doing so ?

Can UPS be kept online for 6 hours ? will it heat ? or burn ?

Can this UPS be able to charge my 12volts 180ah battery ?

are there any other issues ? in doing so ?


texts: I have finished the schematic layout for my design which contains transformer. I also found the optimized design 100%, but the transformer background should be black while I'm having only portion of it black, any idea on how to do it?


texts:
My project in PAhead 14.7 have 6 different synthesis run and 6 implementation runs. Each implementation run have her own parent synthesis run. The differences between synthesis runs are some generic parameters to customize each synthesis to a country. These custom generics have been introduced in the "More options" parameter of each synthesis, for example -generics {g_COUNTRY="CANADA"} -shreg_min_size 6

In order to synthesize and implement quickly taking advantage of modern multicore processors I have wrote a tcl script that:

Reset outdated implementation and synthesis runs
Launch outdated synthesis runs
Wait for completion of synthesis runs
Launch outdated implementation runs
Wait for completion of implementation runs
And finally generate the bitstream file

Here some main parts of the launching runs tcl code

# Launch all the synthesis runs with a maximum of $jobQuantity jobs
launch_runs $synthRuns -jobs $jobQuantity
# Wait for completion of all runs
foreach synthR $synthRuns {wait_on_run $synthR}

# Launch all the implementation runs with a maximum of $jobQuantity jobs
launch_runs $implRuns -jobs $jobQuantity
# Wait for completion of all runs
foreach implR $implRuns {wait_on_run $implR}

The big problem is that when all the runs have finished, in the GUI I found inconsistent results. For example, when I open each synthesized run in PAhead GUI to verify her customization, always is opened the results of the active synthesis run the tcl script was executed.

Each synthesis report file has been verified and is correct.
Each ngc result file in each synth directory has been verified and is correct.

But PlaheadGUI always open the active synthesis run during the launch command, even when changed the synthesis active run to other.

And worst. When launching the implementation runs, all the implementation runs have taken as synthesis parent the active synthesis run. So all the implementation runs have the same and incorrect results. These same wrong results have been verified in FPGA Editor for each implementation run.

The TCL script have been executed in GUI mode and interactive mode with the same wrong results

What's going on? PlanAhead 14.7 is not capable of manage multiple runs? Any setting could be wrong?


texts: Is a digital bit represented by any two discrete signals?

texts:
I am trying to understand computers from the building blocks up. I know computers use transistors to amplify voltages, and this is used for arithmetic, such as a MOSFET.

However, what really makes up a typical computer bit? Is it just two input currents, one higher and one lower? Two possible states? Is movement a bit (run or walk)?

How can I make a bit? Do I just need an emitter, current, and multiple passages?

Would I have a bit if it couldn't be amplified (i.e. a two-series circuit with no amplification of current)?


texts:
I was doing some experiments with mosfets I have at home. Everything works but there's something I can't really explain yet.

simulate this circuit – Schematic created using CircuitLab

The schematic is quite basic, the gate is connected to a dangling wire and I connect it manually to positive current to open the gate.

The load I have is a DC motor.

When the gate is connected to V+, the motor turns, when I disconnect the gate goes back to gnd and the motor stops.

The strange moment is that when the gate is to ground, the scope displays some kind of sine/triangle wave. The motor doesn't turn. I guess I'm sensing a voltage because the MOSFET allow a very very small amount of current to leak from the source to the drain.

My power source is of 7v and the voltage on the scope goes from 0v to 10v when the gate is closed. The frequency of the wave is of 100hz. I don't think it's AC noise because it should be of 60hz and go below 0v and probably not as high as 10v.

Is it normal to see something else than 0v when the gate is connected to ground? I was expecting to see maybe a really low voltage as I read that MOSFETs would behave like power resistor when the gate isn't completely open.


texts:
Is there any difference between the name "recycling count sequence" and "count sequence"?

I have a digital system book saying that a MOD-12 counter has a recycling count sequence of 0001 through 1100. However, I think that a MOD-12 counter would count from 0000 to 1011.


texts: I/O pin driving PCB? Problem, Bug, Feature?

texts:
I built an PCB board housing a couple of ICs and the PCB communicates with a PC over USB with a Saxo board (contains FX2 USB controller and Cyclone FPGA). The Saxo board sits on my PCB as daugther board and is powered via USB.

The FPGA's I/O is 3.3V which I want to convert to 1V. Hence I use a logic level shifter, namely ADG3308 from Analog Devices.

Now consider the following setup:

The PCB is completely powered off. All connections disabled (except for the Saxo Board)
The Saxo board is powered via USB and sets one I/O pin to high (3.3V).

In an isolated sense, this means I have an ADG3308 with only 3.3V supplied at an I/O pin (say, Y1). VCCA and VCCY (the supplies of the ADG3308) are connected to the circuit but the supplies are off.

Now the following strange observation: Measuring VCCY, it is actually 2.7V! This can only happen through driving the I/O pin!

But: VCCY is supposed to be connected to a 3.3V benchtop supply and there is a connection to an on-board voltage regulator that generates 1V (and 1.2V). Lo and behold, VCCA (which is the output of this voltage regulator) is also 1V. Which means that the 3.3V I/O pin drives the VCCY pin of the ADG with 2.7V which is enough for the 1.0 and 1.2 regulators to work.

Furthermore, more ICs (which require the 1V supply) are pretty functional! In total they would draw about 60mA from the benchtop supply!

Question 1: Can it really be that the single I/O pin of the FPGA drives the complete PCB - indirectly - sinking tons of mAs?

Question 2: Is this a problem? Bug/Feature? Does it have implications about a startup sequence? I feel not quite comfortable driving the whole PCB with an I/O pin over the USB interface. That would mean that I want to power on first before I connect USB. But this seems not like something "normal" to do.

Clearly, ground is shared between the PCB and the saxo board (and hence USB) but no supply is shared.

Here is a sketch to facilitate understanding (red: measured voltages):


texts:
I have a Linear position sensor attached to an outboard motor to provide input to an autopilot. It looks like a linear potentiometer with 3 wires and a shield. It has Red, Green, and Blue wires that connect to the controller. The autopilot is giving an error of motor position sensor failure.
From the controller I read 5v being supplied between the Green and Red wires, Green ground and Red positive. When with the motor straight or sensor barrel half way out the Blue wire reads 5V. Turned all the way one direction (barrel out) it reads 2.2v and all the way the other direction (barrel in) it reads 2.8v.
The voltage readings on the Blue wire as you slide the barrel in or out look fairly linear but as it gets close to the mid point the values jumping around until you get to the mid point where it settles on 5V. I would expect a Linear pot to fail at the mid point since that is where most of the movement is as the autopilot makes lots of small corrections to stay on course.
I was thinking the sensor is just a Linear Potentiometer but that doesn't make sense to me since the wiper voltage (my assumption of Blue wire) starts at 5v with the wiper at mid point and goes lower in both directions. Do they make Linear potentiometers that work this way? Any other suggestions for how this sensor is working or what type of sensor it might be?
Thanks


texts:
Probably a silly question but I'm still a total noob on electronics. I got my hands on an old  non-functional XR2206 based function generator and I wanted to bring it back to life and in the meantime upgrade it with newer components.

From the old circuitry I could rescue the power supply, that delivers +5, +15 and -15V. I'm powering the XR2206 with 0 and + 15V and I got it to generate nice 1V amplitude waves (it works fine also in pulse mode).

The problem comes when I want to amplify the signals.

What I came up with is below:

(I'm using a LM358 but I have also the LM324, +5V is so far unused but I'm thinking to connect an Arduino to control the LCD/8 segment screen to show the frequency)

My idea is to get the signal from the 2206, couple it to AC and then use the +-15V to generate the output that goes to a second buffer op amp and then will go to a third op amp to regulate the final amplitude.

When I probe with the oscilloscope after C2 and with the op amp disconnected everything is fine (sine/triangle wave centered on 0V) but when I connect U1G2 the wave jumps up (depending on the values of R1 and R3) and the op amp outputs just +15V without any signal.

UPDATE:

Think twice, check trice. It turns out it was a faulty LM358. As a note to this, some commented that the LM358 is a horrible op amp. What would be a better choice?

Note 2: how do I reduce the crossover distortion? Resistor to GND?


texts: What are the functions of the diodes in this BLDC controller circuit?

texts:
I'm trying to understand the function of the diodes in this snippet of an automotive BLDC controller.  I believe that D102 is for over-voltage protection, and reverse polarity protection.  Also, I think D104 is for reverse polarity protection.  I can't figure out what D103 is for.  Any ideas?

ETAT_MJP - this is an open collector output PWM diagnostic to the vehicle ECU.
ETAT_MJP_PIC - from the PIC for the diagnostic output.
PIC_ETAT_Monitor - monitoring the output diagnostic (input to PIC).
CDE_MJP - PWM command from vehicle ECU.
CDE_MJP_PIC - PWM command going to PIC input.


texts: Power LED light from battery when mains fails

texts:
I'm attempting to design a circuit for some LED lighting that will be powered from a mains connected 24V DC transformer but if the power fails then the a battery should take over as the power source and automatically switch the LED lights on.

In the circuit below the idea is the LED light D1 is normally powered by V1. When V1 has power relay SW3 would switch from the position shown in the diagram and thus break the B1 circuit meaning D1 LED would be controlled by V1 and SW1. When V1 loses power SW3 would be in the position shown and the LED light would be powered by BAT1 and always on.

Is my analysis on the right track or is there a much simpler way to accomplish my goal? If I am on the right track what sort of relay should I be looking at for SW3?

Update:

Below is my revised attempt. The polarity on the SW1 terminals needs to be reversed. I don't think there's any need for a diode between the + terminals of BAT1 and V1 since they will only ever be connected if V1, the mains supply has failed in which case it will act as an open circuit. I think there is a problem with this new circuit in that the SW1 relay will always be off while SW2 is open and hence the LED will be lit by the battery. I need SW1 on even if SW2 is off.


texts: Transitor keeps base turned on even at zero volts in dual power supply system

texts:
Circuit Description:
I am powering transistor with two power supplies. One supply is providing 5-VDC to its collector load through ammeter (+Ve - ammeter - load - collector - emitter - common/ground.) The decond supply is providing 0.0-VDC to 0.9-VDC to its base (base - emitter) with no resistor between.
Problem:
A strange (to me at the moment) phenomenon is happening

Start-up is normal - at 0Vbe there's no current through the ammeter
Starting cut off is also normal as up to 0.4Vbe there's no current through the ammeter
Starting active region is also normal as from 0.5Vbe to 0.8Vbe the current flows through 0mA to about 97mA
Strange after getting in active region once, the transistor can't be turned fully off. Once conducted it keeps its collector-emitter junction turned on and about 40mA current keeps on flowing even at 0Vbe
More Strange After getting active once the transistor shows two active regions one between 0Vbe-0.4Vbe and second between 0.5Vbe-0.8Vbe
[0.0Vbe-0.4Vbe | 40mA-50mA Ice] active region is less linear its Vbe to collector current is not the same all the time but is likely (I'm guessing could be limitation of my equipment as my power supply volt meter has only one significant digit after decimal.)
[0.5Vbe-0.8Vbe | 6mA-97mA Ice]  is kind of linear
Back to Normal Now even though there's 0Vbe but when I short circuit the base and emitter through a piece of wire then the transistor turns off and there's no collector current or if I pluck out supply probe from base then too the transistor turns off and there's no collector current

My Questions:

Why is the transistor not turning off at 0.4Vbe to 0.0Vbe as this is its cut off region?
Is there a problem with using dual power supply or is my equipment faulty?
Am I still illiterate on this particular phenomenon and all transistors do have two active regions after getting activated once?

Equipment/Component Details:

Transistors: C828 NPN, A1015 PNP
Load resistors: Two 100 ohms (1/4 watts) resistors in parallel
Collector emitter power supply: Custom power supply with 220VAC -> step down transformer 12 + 12VAC (One 12VAC side of transformer) -> bridge -> filter 2200uf/25V -> 7805 -> filter 104pf
Base emitter power supply: 1501D by M&R
Collector ammeter: DT9205M digital multimeter, selector switch is at its 200mA range

Circuit diagram:


texts: Measuring RF and heterodyned frequencies

texts:
I have a question about RF measurement techniques.

The partial schematic above is the front end of an AM radio receiver kit.  I have assembled the kit.  The kit manual states,

Transistor Q7 not only amplifies the RF signal, but also simultaneously oscillates at a frequency 455kHz above the desired radio station frequency. Positive feedback from the collector to the emitter of Q7 is provided by coil L5 and capacitor C31. During the heterodyning process the following four frequencies are present at the collector of Q7.

The local oscillator frequency, OF.
The RF carrier or radio station frequency.
The sum of these two frequencies, OF + RF.
The difference of these two frequencies, OF – RF.

When I measure the ground referenced voltage at Q7, with the radio playing a local station, all I see on the scope's (Tektronix TDS-380, 1996 vintage) FFT display is the OF signal, which is very distinct.  That OF signal changes with the movement of the tuning dial and is about 495 kHz, not 455 kHz, above the received radio station frequency of 990 kHz.  The scope probe is set to 10X.  When I set it to 1X the station disappears, which I think means that the 1X probe is loading the signal(s) at the collector of Q7 with the scope probe.

Should I be able to see the RF carrier as well as the sum and difference frequencies when measuring with an oscilloscope in this manner?


texts: What is the Thevenin Norton equivalent of the folloing circuit

texts:
I am trying to find the Thevenin Norton equivalent of the folloing circuit. I am familiar with the procedure.
However, when I am taking off the voltages to calculate the equivalent resistance, I am not sure how to deal with the fact that instead of the voltages I get two branches on the sides, with no resistors at all..

Any help will be most welcome

Thanks

Edit: I am looking for both Thevenin and Norton equivalent. But any of them will help. Also, The middle resistor is Rload=$R_L$. This is where I need to measure resistance, Voltage and current. I.e "what does RL see"?


texts:
I am getting pretty familiar with microcontrollers and now want to connect it to the internet.  What are the minimum requirements for a microcontroller to be able to do this, specifically, an AVR one if possible.  Secondly, what else is required?  I read about ethernet controllers, but am not really sure exactly what they do and how they are to be interfaced with the micocontroller.

What are the needed components to get a micocontroller online (no Arduino shields)?


texts:
I'm trying to trigger a logic fall signal on my raspberry pin input which is set with a internal pullup resitor (on 3V).
The input raw signal I have in actually a 0V which change to -5V during a really short period of time (see below).

Here is the schema I use:

simulate this circuit – Schematic created using CircuitLab

The problem is my logic input reads always 0 and I guess it's because of the voltage divider which is connected to the ground through R2.

Is it the right approach? How should I do to resolve this issue?


texts: How can electrically short these terminals?

texts: Shorting red + white 1 moves the garage door up and shorting red + white 2 moves the garage door down, I’m using a micro controller but not sure how I can electrically short these terminals.


texts: Why AC is not used to excite synchronous machines?

texts: In synchronous machines rotor is excited with DC and rotated so that due to change in mf falling on the conductors in stator an emf is generated.if we use Ac as an exciting means to excite rotor and then rotate rotor so that we get more change in flux due to which we can generate more emf. But we r not doing like that. can any one explain me?


texts: Combine Bluetooth Buttons (Volume up / Next, Volume Down / Previous)

texts:
I have a question regarding the control of a bluetooth device, which I would like to connect to some old headphones.
Bluetooth SMD Module - BC127

There are some pins on which I can connect the headphones, micro and some buttons (vol up, vol down, previous, next, play/pause)

let's assume...

pin 1: volume up
pin 2: volume down
pin 3: next (track)
pin 4: previous (track)
pin 5: play/pause

I'm not that into building circuits, so my question is...

Is there a way to combine two buttons via a hardware circuit (i.e. volume up & next track)?

-> So if I shortly press the button once the signal goes to pin 1 (volume up) and if I hold the same button for about 2 seconds the signal goes to pin 3 (next track).

I don't have a microcontroller connected to the bluetooth device, so I would have to do it via a hardware circuit (if possible)...

kind regards, Guti


texts: Low Battery Indicator for 2x AA Batteries

texts: How would I create a circuit which turns on an LED when the voltage goes below 2.5V? I am using 2x AA batteries


texts:
I have a question about detecting RFID tags at long range. I understand there are LF, HF,and UHF RFID frequencies.

I'm looking to detect a tag from a minimum distance of 2 meters (actually, 5 meters if possible). I would really like to us HF chips, but I'm not sure if it's possible to detect those from that distance.

I was thinking of using passive tags, but if it's necessary to use an active one I wouldn't be so against it.


texts: PCB microscope digital zoom vs optical zoom

texts:
I am looking for a PCB microscope and am noticing that there are many affordable digital microscopes out there that offer 1000x+ zoom.  Is this enough to see very small details on a PCB, like inspect individual pin's soldering on a fine pitch MCU?  Does anyone know if the image will be clear at this level of digital zoom?
Another subset of PCB microscopes uses optical zoom, the magnifications I typically see are much less though maybe 40x, and they are typically more expensive.  But I imagine the image is more clear, is this enough zoom though?  Both technologies offer HD video feed of sample.
Does anyone have experience examining PCBs with microscopes and can offer insight into which type of microscope is best for fine details?


texts: Why does this schematic have a "Do Not Mount" component? Why not just remove it from the BOM and drawings?

texts:
While reviewing the reference design for the TI CC2541EM 2-layer board, and the associated parts list, I noticed one component (C254) states "DNM - Do Not Mount".

What is the reason for this?  Why even draw this on the schematic if you don't intend the component to be populated?  if they go to the trouble to change the schematic to read "DNM", why not just remove the component altogether?

OR, are they using the two unpopulated SMT pads as a capacitor?  That seems strange.

OR, is this a placeholder for a cap that would be added later, to properly tune the antenna if needed?


texts: 3 watt LED plus LiFePO4 battery (1 cell), no resistor, no regulator. Is there anything wrong with this?

texts:
I read that you should "always" have a resistor in series between an LED and its power source.  But what if the power source already has its voltage set to a suitable max for that particular LED?  Why would you need a resistor then?

So here's what I want to do:

Power a 3 watt LED with a single cell LiFePO4 battery.  The only other things in the circuit would be a switch and maybe a fuse (mostly to protect the battery).
The LED charts I'm looking at show the LED comfortable and productive in the voltage range between 3.3 and 3.5 volts.   This is perfect for a LiFePO4 battery with 1 cell.   My charger is a Turnigy Accucell 6, which can be set to always charge the battery to 3.5 volts, or any other voltage I tell it to that is reasonable for LiFePo4.   I can get a good chunk of the total energy capacity of the battery just running it from 3.5 down to 3.3 volts, which is the range where the LED works ok, without over-current or over-voltage (according to the mfr charts for the LED).

For a straw-horse LED, we could look at this one, which has nice charts available here:  http://www.rapidonline.com/pdf/170197_da_en_01.pdf

In this pdf, page 15 has the chart for Vf vs If, with 1 amp being the max If allowed, this happening at 3.5 volts.
Will this work ok - as long as I am careful to never let the battery voltage go higher than what produces max allowable current in the LED?


texts: How big a magnet do I need to wipe my portable HDD?

texts: According to this article, I need a really big magnet to wipe the data off my HDD. Thing is, I don't know how strong a "laboratory degausser" is, so I'll ask it in my own terms: I have a pair of magnets that would crush my fingers if I let them close on my hand. Is that likely to be strong enough to wipe the data on my damaged portable HDD before I let the repair guys fix the dinky connector between casing and drive proper? It's a sleek WD Passport that I can't open up myself without ruining the aesthetics. Don't care if they give me a new one, do care if someone gets to poke around the data in the old.


texts: Diode stops conducting. Conducts again after applying higher voltage. What happened there?

texts:
I have the following circuit for providing regulated 5V from a 12V power supply:

I have several hundreds of PCB with this circuit, and they work fine. However recently I have had a few of these PCBs stop functioning. I have tracked the problem to diode D1.

When applying 12V to the input I have measured 1.8V on the cathode of the diode, and no appreciable input current (the power supply shows 0.000W output power), so I have discarded a short-circuit down the line as a possibility.

Now comes the interesting part. I tried slowly increasing the voltage to see if there would be any change on the output current. To my surprise, the diode started conducting at around 16V, and when I measured the voltage drop across the diode it was back to its normal 0.7v to 0.8V. After this the PCB was functioning normally again, and I was not able to reproduce the behavior. As matter of fact, now when applying a 12V input, it works as intended.

I have seen this behavior on at least 3 or 4 PCBs out several hundreds identical PCBs.

I am assuming this is a defective diode, but it is the first time I observe this mode of failure and I would like to get more information about it.

EDIT: I would like to add that I made sure that the connector and cable were not at fault here. Also the measurements are on the pins of the diode itself.
Furthermore, when increasing the voltage on the power supply, I made sure I was not touching any of the cables or PCB because I suspected that could be one of the problems, but it is not apparently.


texts:
I found a photo in my grandfather's effects that I believe to be of an RF GaAs FET. He was working in a GaAs FET lab at the time this photo was dated (1975). It was labeled on the back "300μm gate width on mesa".

I believe it was related to US Patent US4160984A filed in 1977; he is listed as one of the inventors.

The structure is foreign to me; where are the gate, source, and drain? Any additional information on the structure would be appreciated.


texts: L293D driver DC motors need help to start rotating

texts:
I set up this circuit which uses L293D motor driver IC to control two DC motors.

+6V input is connected to unregulated power supply. It's current rating is 500 mA.
There is a connection between Arduino's ground line and power supplies ground line. There is a parallel 0.1 uF capacitor connected between motor terminal pins.
There is a wheel at the end of the motors but they don't have a gearbox. The wheels are suspended so that they can rotate freely.
The source code of the software is as follows.
#include <Arduino.h>

unsigned int firstMotorPositive = 8;
unsigned int firstMotorNegative = 7;
unsigned int enableFirstMotor = 9;
unsigned int secondMotorPositive = 5;
unsigned int secondMotorNegative = 4;
unsigned int enableSecondMotor = 3;

void setup()
{
    pinMode(firstMotorPositive, OUTPUT);
    pinMode(secondMotorPositive, OUTPUT);
    pinMode(enableFirstMotor, OUTPUT);
    pinMode(secondMotorPositive, OUTPUT);
    pinMode(secondMotorNegative, OUTPUT);
    pinMode(enableSecondMotor, OUTPUT);

    // All motors are off
    digitalWrite(firstMotorPositive, LOW);
    digitalWrite(firstMotorNegative, LOW);
    digitalWrite(secondMotorPositive, LOW);
    digitalWrite(secondMotorNegative, LOW);
}

void speedControl()
{
    digitalWrite(firstMotorPositive, HIGH);
    digitalWrite(firstMotorNegative, LOW);
    digitalWrite(secondMotorPositive, HIGH);
    digitalWrite(secondMotorNegative, LOW);

    for (int i = 0; i < 10; ++i)
    {
        for (int i = 200; i < 255; ++i)
        {
            analogWrite(enableFirstMotor, i);
            analogWrite(enableSecondMotor, i);
            delay(20);
        }
    }

    // All motors are off
    digitalWrite(firstMotorPositive, LOW);
    digitalWrite(firstMotorNegative, LOW);
    digitalWrite(secondMotorPositive, LOW);
    digitalWrite(secondMotorNegative, LOW);
}

void loop()
{
      speedControl();
      delay(1000);
}

The problem is they need help to start rotating. They will only start rotating if I physically twist the shaft with my fingers first.
As far as I know the motors used in this circuit are two 6 volt DC motors.
When I measure the maximum voltage between motor terminals I read about 0.5 volts. If I twist the shaft I read about 4.5 volts.
It is interesting that, if I connect a small 1.5 volt battery between motor terminals they spin.


texts: uC IO pin driven "low", but voltage sits at 0.3V, not 0V

texts:
This is an Arduino MKR WiFi 1010 board, which runs at 3.3V.

PA18_OTG is an IO pin, which by default is driven HIGH (3.3V). In this state I measure the OTG pin at 0V.

I need to drive OTG high, so my intuition was that I can do so by inverting the PA18_OTG pin. So, I'm driving it LOW. However, measuring the output, it sits at 0.3V, not 0V. In turn, I then measure the OTG pin at ~0.1V.

I don't understand enough about uC outputs or even this (probably very simple) MOSFET circuit to understand if this is all completely expected, or pointing to some faulty component?


texts:
I've got a 500W ATX PSU (more info about it here) and I would like to use it as a sort of bench power supply. I know that there are many guides about how to convert an ATX PSU to a bench lab power supply, but I'm not sure about how to connect a potentiometer to make a variable power supply, and on the internet I found many contrasting opinions.

My first idea was to take a 10k potentiometer (or maybe a 5k is enough?) and connect it to the -12V wire on one side and to the +12V wire on the other side, so that I get a maximum output of 24V, and I can use the potentiometer to vary from 0V to 24V. Is this going to work?

I also saw on this website that there is another way to do the same thing:

  Find the resistor which goes from pin 14 on the PWM IC to pin 2. Now simply place a 10K potentiometer in series with this resistor and pin 14. What this does is mess with the regulating reference. Pin 14 is the internal regulated +5V from the IC. The resistor we put a potentiometer in series with is part of a voltage divider, which supplies ~2.5V originally. Turning the pot decreases this voltage and the PWM IC thinks the output voltage is increasing, so it compensates by reducing the duty cycle. Reduced duty cycle means less power and less voltage. Regulating the voltage down can be done without modifying other components.

I understand the main idea, but I'm not an expert about this stuff; what is exactly a PWM IC? And where can I find it inside the PSU?

Do you know a better way to do what I'm trying to do? Or which one of these two ideas is better? Thank you in advance.


texts: What's the difference of placing multiple resistors and one resistor for limiting the current of LEDs?

texts:
I'm looking at a diagram and wondering if I could use just one resistor to limit the current of the LEDs instead of multiple resistors so that the cathodes are all connected to the same resistor.

JL


texts: How to ground external AC voltage (18V) to Arduino?

texts:
I have a project where I need to read 0-18 Volts AC in Arduino's input (0-5V DC).

So I did a circuit with a diode (half wave bridge), voltage divider, and a RC circuit where I tested some values for the RC part where the speed of the AC to DC converted voltage were enough for me.

Three levels of AC voltage are sent in these terminals depending on button presses (18, 17 and 16V).

I wired my circuit directly over the AC terminals and got readings that varied from 1 to 3V DC,  which are enough for me to read in Arduino

When I connected the circuit to Arduino, I grounded one of the AC terminals (the one where the diode blocked current flow) to Arduino's ground.

When I turned on the circuit, connected to Arduino, a fuse on the AC line blew, like there was some short circuit.

So, my question is: How to ground this separate AC circuit to my Arduino, in order to be able to read this converted/lowered voltage? Did I wire it wrong, according to  the schematics? How should I correct it?

Edit1: This AC line is a secondary in a big transformer that outputs different voltages. Is there a possibility of any of these two wires not be grounded?


texts: Power Converters - Small Ripple Approximation

texts:
Hi,
I'm having some difficulty understanding what they mean when they said they are able to replace the 'exponential or damped sinusoid waveforms' - what exponential or sinusoid waveforms are they referring to? Is it when the sinusoidal v_ripple(t) is plugged into the derivative terms of the capacitor/inductor equations?
Secondly, they say this is only valid when the switching period is much less than the natural time constants. What do they mean by the natural time constants? Is that the natural response of the LC assuming some initial conditions?
Thanks


texts: Specifications for a charger needed to charge LiFePo4

texts:
I have a project with three 4-Cell LiFePo4 batteries.
The battery specs:

4S at 3.3V
4200mah
30C

I want to charge all 3 batteries in a range of 45 - 75 min (Preferably one hour)

What are the specs of the charge I would require to accomplish this?


texts: Parallel RLC Step Response with Voltage Source

texts:
I am learning about RLC circuits in my Circuits Analysis class and I had a question regarding Parallel RLC step responses.

In the book, they only provide examples of RLC circuits with a current source, such as the one below.

simulate this circuit – Schematic created using CircuitLab

The circuit and equations that go along with it make sense to me, but I started thinking about voltage sources, such as the one below.

simulate this circuit

This brings up a couple of questions:

Does the voltage change across the resistor, inductor or capacitor? According to KVL it would be 12V once the switch is closed. Does this produce a step response at all then?
When the switch is closed, the voltage across the capacitor goes from 0V(assuming no energy initially) to 12V because KVL would be violated otherwise. Wouldn't this be an instantaneous change, which cannot occur in capacitors?
What happens when you put a current source in a series RLC circuit? This raises similar questions.

Thanks for any help provided.


texts: Is there a device to prevent a main circuit breaker from tripping and give an added layer of protection?

texts: I would like to install some additional appliances in a room that already has a couple of heavy equipment machines running in it. These are sensitive machines, so instead of having the main circuit breaker trip when there is an overload, is there a device that I could connect to the outlet and then connect the new appliances to these devices? My goal would be to have power to these specific appliances cut off instead of tripping the breaker.


texts:
I know how to divide numbers in VHDL (or using one of the Xilinx IP core generators) but I do not know how to do it in the case the numbers are complex.

In my case I have defined a complex number as this:

type complex12 is record
    re  : std_logic_vector (11 downto 0);
    im  : std_logic_vector (11 downto 0);
end record;

So my complex number it is just two vectors of 12 bits, one for the real part an other for the imaginary part.

Let say that now I have a and b complex numbers:

signal A : complex12 := (re => (others=>'0'), im => (others=>'0'));
signal B : complex12 := (re => (others=>'0'), im => (others=>'0'));

I know that the theory for dividing to complex numbers tell us two approaches for doing a division:

$$
c = \frac{a_r + j\cdot a_i}{b_r + j\cdot b_i} =  \frac{(a_r + j\cdot a_i) \cdot (b_r - j\cdot b_i)}{b_r^2 + b_i^2}
$$

Alternatively:
$$
c = \frac{|a|}{|b|} \cdot e^{j (\angle a - \angle b)}
$$

But both approaches seem very difficult to implement in VHDL. What would be the preferred approach? Is there an easy way to divide complex numbers? Is there any Xilinx block that can save the day? I am bit lost on how to approach this.


texts: Do solar flares affect the software when the hardware is turned off?

texts: Do solar flares affect the software when the device is turned off? Like for example, would the windows os got corrupted even when the hard drive is off?


texts:
I am trying to design a current limiter that limits current through R4  based on a typical transistor-MOSFET topology like the one in the picture:

This circuit works fine. When the voltage accross R3 is Veb (0.65) current begins to be limited (at 0.25 amps) by means of the MOSFET.

The problem is that I want to limit the current from a negative voltage source. For example, if VS1 would be -5V or -10V. Of course, then the current flows in the opposite direcction and the circuit does not work. I've tried changing both transistors (to npn and Nchannel) without success. Also I tried changing the arrangement of components (bipolar circuit to the right and MOSFET to the left), also without success.

Could you hint me how to arrange components to obtain my goal?
Thanks

PD:Other topologies are also accepted.
PD2: No ICs if possible

UPDATE:
Should this topology work (note the minus sign in the source) for limiting current through RLOAD?  Or should I keep the old trt and mosfet?

Thank you very much


texts: Sizing of and Type of Power-loss / Brown-Out Protection Capacitor

texts:
I found a few resources and this question here: power-loss protection

I'm using an MCP16301 step down regulator to turn 12v to 3.3v

I'm having trouble determining I in this equation:
C=I×t/ΔV

with a minimum of 6v input I get this

ΔV = 12v-6v = 6v
t = 5seconds
I = ?

Question 1:
If my output current is 1A max, and assuming 90% efficiency, does that mean the input current is 1A/.9 = 1.11A?

Question 2:
What's the correct type of capacitor for this application?

Question 3:
How do you actually detect the power loss? I'm aware than I can use an interrupt to handle the event, but what's the correct circuit?

simulate this circuit – Schematic created using CircuitLab


texts: What is the difference between a Sallen-Key Band pass filter and a band pass filter?

texts: Am currently doing an assignment on sine wave generation and am using a sallen key band pass filter - i am unsure what the difference between the band pass filter and the sallen-key band pass.


texts: Equation for the average power of a signal

texts:
I'm reading the book "Introduction to Electromagnetic Compatibility" by CR Paul, and in Chapter 3, I come across this equation for the average power in the waveform assuming a 50% duty cycle and \$\tau_r\$ = \$\tau_f\$ :

Is this a general way to compute the average power? So far I've only computed the average power using the area under the waveform, and I can't understand how this equation is derived. Can anyone help me?

BTW, the waveform in this section of the book is a trapezoid.

ETA: Added the diagram of the waveform.


texts:
I'm trying to set up a transimpedance amplifier reading the response from an avalanche photodiode (Hamamatsu S12572-100P http://www.hamamatsu.com/resources/pdf/ssd/s12572-025_etc_kapd1043e03.pdf) and a low-noise operational amplifier (TI LMV793 http://www.farnell.com/datasheets/1771351.pdf).

The dark current is around 0.15 uA, and the signals I'm expecting to measure correspond to around 0.8 uA current on the APD. My feedback resistor is 1.27 MOhms. However, after building this circuit on a PCB I just get about 0.09V on the output of the amplifier, in a situation where it should saturate, and no variation at all. I've replaced both the APD and the op amp thinking they might be damaged, but the problem persists.

The biasing is being achieved by setting 70V across a 2 KOhm load and connecting a 1 KOhm resistor in series with the APD, as suggested by the datasheet. The breakdown on the APD is 67V, thus I assume the APD is pulling around ~35 mA from the biasing supply, but I don't get any output.


texts: Are ten 2W speakers as loud as two 10W speakers?

texts: If all things are the same (e.g. total magnet weight, manufacturer, cone material) and I have two 10W speakers as compared to ten 2W speakers would the decibel level be the same?


texts: L293D heating quickly under 0.5 A (driving a DC motor using adafruit motor shield v1)

texts:
I am using Adafruit's Motor shield to drive a DC motor I got out from an RC car...

Powering the Arduino from USB. And powering the shield from a 12V / 1.5 A Power adapter (the shield is using an L293D)

I checked the datasheet of the L293D and it says max current is 0.6 A and max power dissipation is 5 Watts.

I measured the drawn current from the supply and it was : 0.5 A. (with running motor)
As soon as the motor turns on the chip gets hot quickly (withing 1 sec) & the motor's speed drops down.

Another weird thing is that when I connect the motor directly to the power supply it starts turning for 1 second then turns off for 2, then it turns back on & so on... I am suspecting that it's exceeding the power adapter's max current (1.5 A) which is also weird because the motor is small and doesn't look that powerful.

Can anyone please help me here?


texts: I hooked up a crystal oscillator (4 pins) to Vcc + Gnd and observed the generated waveform using my scope. I think everyone will agree the waveform shown is very distorted and I am not sure why. Any ideas?


texts: I have EMC issue and there is spike at 64 MHz on my 6 layer PCB design. I have used many decoupling capacitors and ferrite beads according to the datasheet. Is there any cad tool to measure on which part of the PCB, there is the high emission and by changing the capacitor and ferrite bead to see what happen to the electromagnetic behaviour to optimze and select the best bypass capacitor value and ferrite beads?


texts:
We have an issue with our TFT display. The display constantly flickers while displaying. What are common causes for flickering in this type of display? How can we resolve this issue?

It's a 3.5 inch local TFT display

We are using Arduino Mega for programming, with AdaFruit graphics and AdaFruit TFT LCD library. The driver IC used is 9341.


texts:
How can I simulate the below circuit to show its transmission coefficient?

I have developed the circuit as in the diagram but what is missing to view the transmission coefficient?


texts: Copper sheet thickness to use between Peltier and CPU

texts: I'm going to use a TEC-12726 (50mm by 50mm, 240W QMax) to cool an FX-8120 (40mm by 40mm, 125W TDP) CPU, and I want to use the full size of the TEC by putting a sheet of copper between the CPU and TEC, but I what copper sheet thickness should I use? Or should I not bother with a copper sheet at all?...


texts: Why resistor is used at the output of OPAMP?

texts: I'm reading this note and in Figure 1(page 1), there are two resistors R5 and R10 whose use I don't understand. From my understanding, R5 would cause offset due the input bias current and R10 would load the output. What's the purpose of these resistors and how to calculate their values ?


texts: Generator Power factor Calculation with varying Output Power

texts:
We are operating a generator (Stirling engine in particular) that outputs a certain active power in the range of 6.5-8.9 kW. The power output is adjusted with pressure variation. The electrical machine is rated at 400V and 15.5A nominal voltage and current. For calculating the power factor is it correct to assume that the power factor varies between 0.62 to 0.83????
I'm not sure whether changing the power output changes the current draw so as to lower the apparent power and maintain the same power factor at different loads, or the apparent power is defined as S=sqrt(3)VI with the nominal values?
One thing to mention, there is no information concerning the set power factor of the engine. The results I provided are the actual output of the engine.
Your help is appreciate in advance


texts: Why is it okay to swap a resistor and source in series?

texts: I need some help understanding why it is okay to swap resistor and source in series in the following problem. Mesh analysis of the problem is rather easy, but the nodal analysis appears to have two super nodes. I was able to get the correct answer by switching the source and resistor so that the circuit looked like the second problem, however, I don't fully comprehend why switching them is permissible. In case it is necessary, the question is looking for the voltage at R3.


texts: Uart Transmit every 1µs Interrupt StM32 NucleoF401-Re

texts:
I am using the STM32 Nucleo F401-RE and HAL libraries.
I would like to send value through UART to the PC console every 1µs interruption.
Actually  I want every 1 µs interruption to increment a counter so it will act like a timestamp,then send this value every 1µs,so when there is interruption every 1 µs -> Incrementation of a counter (++count) and send the value of the counter.

My code that doesn't work like I want it to be  :

My Clock : 84Mhz

I Used MicroElektronika timer calculator to calculate for 1µs interruption the period and Prescaler.
Timer configuration :

__TIM4_CLK_ENABLE()
;
TIM_Handle.Init.Prescaler = 0;
TIM_Handle.Init.ClockDivision = 0;
TIM_Handle.Init.CounterMode = TIM_COUNTERMODE_UP;
TIM_Handle.Init.Period = 83;
TIM_Handle.Init.RepetitionCounter = 0;
TIM_Handle.Instance = TIM4;   //Same timer whose clocks we enabled
HAL_TIM_Base_Init(&TIM_Handle);     // Init timer
HAL_TIM_Base_Start_IT(&TIM_Handle); // start timer interrupts
HAL_NVIC_SetPriority(TIM4_IRQn, 0, 1);
HAL_NVIC_EnableIRQ(TIM4_IRQn);

And the TIM4 IRQ handler :

uint32_t count=0;

void TIM4_IRQHandler(void) {
if (__HAL_TIM_GET_FLAG(&TIM_Handle, TIM_FLAG_UPDATE) != RESET)
        {
    if (__HAL_TIM_GET_ITSTATUS(&TIM_Handle, TIM_IT_UPDATE) != RESET) {

        __HAL_TIM_CLEAR_FLAG(&TIM_Handle, TIM_FLAG_UPDATE);
        ++count;
        printf("%ld\r\n,count");

    }
}

}


texts: How to set the load to "on" by removing voltage from the resistor base?

texts:
I know how to power the load with the transistor when the base is "on".

simulate this circuit – Schematic created using CircuitLab

But I sometimes need the opposite, to power the load when the base is "off". How to do that with transistors?


texts: Does the input polarity matter for a 12V DC adapter?

texts:
I bought a car cigarette DC adapter yesterday with the following specs:

Input:  DC 12V
Output: DC 17V

I'm planning to connect it to a 12V battery I have at home, but I was wondering if the adapter input polarity matter or could damage the adapter if reversed?


texts: How to change the final value of several NetLabel at the same time - Altium Designer 21

texts: I need to change the final value of the string in several NetLabel in Altium Designer 21. For example, I need to change RED0_U1 to RED0_U4, RED1_U1 to RED1_U4 and so on. I would like to know if there is a simple way where you can change the value of all similar nets at the same time without having to change one for one.


texts: What does the "side-band" and "in-band" mean in the context of digital circuit?

texts:
I read below content from the Intel On-chip System Fabric (IOSF) spec. AS I understand, the IOSF is a technology for chip reuse and interconnect.

  The sideband message interface covers most communication that is not
  sent using inband transactions on the primary interface. Although IOSF
  allows sending in-band message transactions on the primary
  interface (such as interrupts and power management requests), some
  implementations may choose to use the sideband message interface
  instead.

I looked up the sideband, the explanation is from electric signal transmission context and seems not fit in.

So what does "side-band" and "in-band" mean in the quotation?


texts: Antenna Tuning for Source Impedance not equal to 50 Ohm

texts:
I have designed a setup for 433.92MHz wireless device (a key fob). The source impedance is not equal to 50Ohm. The load impedance may or may not be 50Ohm depending upon the choice of the antenna. For now, I have given a block diagram for a setup with a PCB loop antenna below.

The antenna tuning setup block diagram is show below.

Usually, the antenna tuning guides tune the antenna for 50Ohm source impedance. But in this case, the source impedance is not 50Ohm. So, is the tuning procedure same regardless of the source impedance?
Also, I've not done antenna tuning before. Is the antenna tuning setup correct?
Some of the articles I referred:

Nordic Semiconductor - Antenna Tuning - White Paper
A stackoverflow question on antenna tuning
Antenna Tuning for beginners

Suggested matching network design schematic from Atmel Antenna Design Guide.

The equivalent representation schematic of the system is given below:

Here, Source Resistance = 465 Ohm,
Parasitic Capacitance = 1pF,
So, Source Impedance = (166 - j223) Ohm


texts:
This is the most baffling question of all other concepts. I ask my teacher

"How does the computer choose a path?"

"They program it"

"How do they program it?"

"..."

I have a basic understanding of how a transistor works, how the CPU handles things, and the latter, but how does the CPU physically choose a path!? I want to learn the college level stuff, but google is not helping!!! All I get are these novice translations! Please help because I'm crying over not knowing the answer. Literally.

 EDIT:  I need a thorough answer explaining what is going on in the hardware please.


texts: ATX power supply doesn't cut the current after being turned off

texts:
I made a power supply for my electronic projects using a ATX power supply of a older computer and used a button connecting the black and green wires to turn it on/off.
I noticed that sometimes when I turn it off, the power supply didn't cut the current and still keeps the circuit operating. I have to remove the power cable of the power supply.
Actually when I don't apply any charge to the power supply it turns off normally, but after I put some load it still operates when the button turn off is pressed.
complete schematic:

Any ideas what is happening?


texts: Interface conditions and surface current density

texts:
let's consider the interface condition for magnetic field strength:

1) I do not have a clear idea of what js represents. If I have understood it correctly, it is a linear density ([A/m]) of a surface current density. What does it represent? Which is its direction and which is the dimension it is referred to (height, length, depth)?

2) what does it happen if both 1 and 2 are conductors?


texts: Maximum input voltage ripple for FOC ESC

texts:
I designed a FOC ESC using TMS320F28027, DRV8305 and InstaSpin-FOC. Everything works great and it spins different motors very well.

I want to choose input bulk capacitors for it and I wonder what is acceptable voltage ripple on the input power.

I am trying different kinds of capacitors with different capacitances and get varying results (from 1V to 15V ripple). So, what is acceptable?

The system is powered via 22.2V 10Ah LiPo battery. The motor is 5212 BLDC with max currend draw 30A. Wires from battery to ESC are 60cm.

Thanks for any help.


texts:
What I understand about working principles of ideal transformer:

We apply an alternating voltage at the primary side. This creates a flux inside the transformer core (\$\Phi_p\$). Some voltage is induced on the secondary side winding according to the Lenz's Rule (\$\mathcal{E}=-\frac{d\Phi_p(t)}{dt}\$). This voltage crates a current through the load (\$i_s(t)\$). And this current creates an opposing flux in the core (\$\Phi_s\$). The amount of this flux that is generated by the secondary winding is equal to the one generated by the primary winding (\$\Phi_s=\Phi_p\$) because the transformer drain that much of current from the primary side power supply according to he formula \$\frac{V_1}{V_2}=\frac{N_1}{N_2}\$. Therefore, there mustn't be any flux inside an ideal transformer.

But all these don't make any sense to me because of the following reasons.

Primary side inductance of an ideal transformer is so large, so no current flows through it if no load is connected at the secondary side. If we connect a load after powering up the primary side, there still shouldn't be any current at the secondary side, because no current if drawn from the primary side, thus there is no flux in the core. Even if we assume that there is some flux in the core, the opposing flux (\$\Phi_s\$) will cancel it out, and the net flux in the core will drop down to zero (\$\Phi_{net}=\Phi_p-\Phi_s=0\$). So the power transfer will stop.

Some flux must stay inside the core during normal operation, but all these facts(?) I told about claim that there mustn't be any flux in the core. Why does a contradiction like this occur? I understand that, in electronics, some circuit model won't function when built with ideal circuit elements (e.g.; flip flops won't take initial state, phase shift oscillator won't start, etc). We usually have some sort of realistic effect that starts the operation. Does the "magnetizing inductor \$L_m$" which we connect parallel to the primary side in the realistic transformer model have something to do with this?

How does flux exist/stay in the transformer core? Please explain it.


texts:
simulate this circuit – Schematic created using CircuitLab
I am using the following circuit with given component values.
I am not getting a proper level of output from Ho or Lo pin to drive the MOSFETs. The voltage level is in mV. Also, the square waveform that I should be getting from Ho and Lo pin is not very crisp.
I have not connected the load yet.
This circuit is being used for Class D Audio Amplifier.
Any suggestion why the the Driver IC2104 is not working?


texts:
I know about the ghost voltage concept. As far I as understood for example in an SMPS there is "Y" EMI filter and that little capacitance creates a RC voltage divider and we see the ghost voltage high if we measure with a device with high input impedance. I'm not going to write about details because there are many question on the mechanism of it which is basically caused by some sort of capacitive coupling.

But my question comes from my own experience in life. When I touch my laptop's surface sometimes I can feel that ghost voltage but not at every place's. So at home I don't have that but in another place the phenomenon is there.

So this made me think that if ghost voltage was caused by the capacitive coupling of the mains voltage why doesn't it happen everywhere? If the leakage capacitance is the same and we have the same AC at two different place why am I experiencing this at only some places? Can that be the mains at two different locations have some fundamental differences leading this issue?


texts:
Below is a simple dimmer circuit using a triac, a cap and resistors. As you can see, the resistor Poti changes with time and the load current change can be seen in the plot. It seems like one can use this circuit to control a light bulb light or a single phase AC motor according to the simulation.

But in many literature or tutorials, always a diac is connected to the gate of the triac (and sometimes a fuse added to the Line). Here is an example:

http://www.eleccircuit.com/wp-content/uploads/2010/09/ac-lights-dimmer-with-triac.jpg

My circuit and the circuit in the link have differences. I have the following questions:

1-) Why is a diac used instead of a resistor?

2-) In my circuit I used R1 as 1k value. What is the best value for R1? How can I calculate it?

3-) The circuit in the link has a series 10k resistor next to the potentiometer. Why would that be needed?

4-) Here is another variant: http://www.electronicecircuits.com/electronic-circuits/filament-light-dimmer-circuit What is the job of C2 and R2 here? Suppressing what?


texts: How to draw sprites using DMA2D with transparency using stm32?

texts:
I am using STM32F429I-Discovery board I want to draw sprites on TFT-LCD with transparency on top of background image , I used black color as the transparent color for the images that I want to draw and used DMA2D at blending mode but the black color is not transparent and the sprite was drawn with a black color surrounding it.
the sprite color mode is RGB565 (I have tried ARGB888 also with no hope) .
The code:
void DrawSprite(uint32_t img , uint32_t SprNo , uint32_t w , uint32_t h  , int format){

/* Configure the DMA2D Mode, Color Mode and output offset */

  Dma2dHandle.Instance          = DMA2D;
  Dma2dHandle.Init.ColorMode    = DMA2D_RGB565;
  Dma2dHandle.Init.OutputOffset = 240 - w ;

  /* Foreground Configuration */
  Dma2dHandle.LayerCfg[1].AlphaMode = DMA2D_NO_MODIF_ALPHA;
  Dma2dHandle.LayerCfg[1].InputAlpha = 0xFF;
  Dma2dHandle.LayerCfg[1].InputColorMode = format;
  Dma2dHandle.LayerCfg[1].InputOffset = 0;

  if(SprNo == BACKGROUND)
  {
      Dma2dHandle.Init.Mode = DMA2D_M2M ;
  }
  else
  {
      Dma2dHandle.Init.Mode = DMA2D_M2M_BLEND ;

      /* Foreground Configuration */
      Dma2dHandle.LayerCfg[0].AlphaMode = DMA2D_NO_MODIF_ALPHA;
      Dma2dHandle.LayerCfg[0].InputAlpha = 0xFF;
      Dma2dHandle.LayerCfg[0].InputColorMode = DMA2D_INPUT_RGB565;
      Dma2dHandle.LayerCfg[0].InputOffset = Dma2dHandle.Init.OutputOffset;

      /* Configure DMA2D Stream source2 address */
      WRITE_REG(Dma2dHandle.Instance->BGMAR, (uint32_t)RenderBuffer);
  }

  /* DMA2D Initialization */
  HAL_DMA2D_Init(&Dma2dHandle);

  HAL_DMA2D_ConfigLayer(&Dma2dHandle, 1);
  if(SprNo != BACKGROUND)
         HAL_DMA2D_ConfigLayer(&Dma2dHandle, 0);

  /*DMA2D Transfer Start*/
  HAL_DMA2D_Start(&Dma2dHandle,(uint32_t) img, (uint32_t)RenderBuffer, w, h );
  HAL_DMA2D_PollForTransfer(&Dma2dHandle, 100);}


texts: How can a microcontroller be more efficient than an FPGA?

texts:
If we don't count the cost of both (MCU, FPGA) are there any applications where a microcontroller can be more efficient than an FPGA? It is easier to program a microcontroller than an FPGA (embedded C vs VHDL, for example) but if someone spent time and implemented the MCU design inside an FPGA, then the FPGA could be used for the same application as the MCU but more efficient because we can implement more than a single MCU in an FPGA.

I was wondering if the only application that an MCU can be more efficient than an FPGA is when we connect an analog sensor to the MCU (for example an analog source that harvest entropy in case of producing random numbers etc)? Is this correct or I am totally wrong?

edit(as gbulmer suggested):
My criteria for efficiency are speed of execution and throughput/watt


texts: TDA2009A speakers making a ticking noise

texts:
I've bought a brand new TDA2009A IC in my local electronics store and all the extra components needed from the schematic, which is provided work this post.
If I connect a speaker (8 ohm, about 10W) to the right input or the left input, the sound is just great. I'm running the IC @ 8V. But when I connect another speaker (the same as the first one) to the other output (either right or left), one of the speakers starts a weird ticking noise on the bass speaker.
I've built this according to the schematic provided in the images, but I've changed the capacitor connected to VCC and GND at pin 9 of the IC to 3300 uF and 220uF with no change (I've done this because of my lack of capacitors at home).
Is there any way to stop the weird ticking?

Video: https://www.youtube.com/watch?v=nSWqJsfmkEE

You can see there, that if I reconnect the speaker to the other output, it still doesn't tick.


texts: 555 Monostable delay circuit misbehaving

texts:
I have designed a basic application of a 555 in a monostable configuration to delay the LOW/off state of an output signal. (The output drives some power electronics through an optocoupler).

As per my simulations and breadboard tests, when the foot pedal is depressed and held the output should remain high until it is released where the output remains high for a further ~0-10s depending on the value of the adjustment R5.

The idea is that C7 discharges through Q4 until the pedal is released where it charges up to 2/3VCC and then turns the output LOW. Unfortunately, when I had this circuit board printed and I populated it, it behaves as expected only for the smallest values of the potentiometer (delays up to around a second), after which, at around 100k or so the output just stays high indefinitely until I turn the knob back down below this value.

I cannot think of any theoretical reason this should be happening. Is there something I'm missing?

Any advice is greatly appreciated, thanks.


texts:
I am trying to make a PCB that works as a 433mhz amp and filter. However I am having trouble calculating trace widths. I am planning to use an FR4 board. I assume I need to have my signal paths matched to 50\$\Omega\$?

I was using the following calculator to try and calculate what the thickness needs to be and got a result of approx 1.9mm, this seems very large?

I used the following parameters:

\$\epsilon\$r = 4.35

Substrate Height = 1mm

Trace Thickness = 35\$\mu\$m

Frequency = 433.75MHz

Have I made any obvious mistakes or is this actually correct? I have checked on other calculators and obtained the same results.

Many Thanks


texts:
I was reading about op-amps and found this schematic.

What is the role of those capacitors?

Lets call them:

10uF - Cap A
250uF - Cap B
0.05uF - Cap C

As of now, capacitor positioning and capacitance values choice seem so random to me. What am I missing?

Thanks!


texts: How to stretch ON time of a pulse train when keeping the periods unchanged?

texts:
I'm receiving varying frequency pulse train with very short ON time and I want to convert these to pulses with longer ON time but without changing the pulse periods. On time is now around 100us. Pulse period varies between 1000us and 2500us.

The flipflop halves the frequency and skips one rising edge which I dont want in this case.

How can I achieve this Duty cycle doesn't have to be fixed just the frequency of the pulses should remain the same.


texts:
I'm planning to get an oscilloscope and a signal generator.

It seems to connect the signal generator to the oscilloscope. And it seems a 50 ohms terminator is needed.

I wonder if I can use a BNC T junction, and put the terminator on one end, and the other end with a cable towards the oscilloscope, or should the terminator be inside the chain?


texts: I was just learning about the port configurations of the GPIO pins. I came across the open drain configuration, and I was bit confused. I could not understand this properly. When this should be enabled or disabled? Should this be always enabled when the port is configured for output while transmitting?


texts: To Activate RFCOMM in CSR8670 Audio Development Kit

texts: I have a device CSR-8670 which act as SINK and on another side I have Android phone which act as Source. I am able to connect through RFCOMM when my both server and client is ANDROID phone but not able to connect when sink is CSR8670 Audio Development Kit and source is Android phone. Is there any way to enable or connect RFCOMM so that I can connect the kit with Android phone and can send data byte serially.


texts: Can Arduino Mega handle 6 motors independently

texts:
I wonder if anyone can help me

I am modifying an ROV and thinking of using Arduino Mega

I am new to electronics and robotics and wonder if the Arduino Mega can control 6 DC motors independently as well acquiring data from a few sensors over a tether of about 150 m. I know that some kind of multiplex is needed but I don't understand fully the theory

Thanks a lot . Appreciate the help


texts:
I am trying to design an oscilloscope/BNC input circuit for a side project and to learn more about filters.

The requirements are:

150-200 MHz -3dB bandwidth
1 megohm impedance
50 ohm termination option (I can omit this if it causes problems.)
Can be switched between 2x and 20x attenuation
Measures up to 80Vpk (160Vp-p), tolerates up to 400Vpk (800Vp-p) (5Vpk on 50 ohm mode.)

I designed a neat circuit that allowed switching between 2x and 20x attenuation while keeping 1 Mohm (or thereabouts) attenuation, as below:

                499k        442k
( Input ) -----/\/\/---+---/\/\/---+----- To JFET input buffer
                       |           |
                       /           /
                  499k \           \ 49.9k
                       /           /
                       |           |
                       +---+   +---+
                           |   |
                            \       relay to switch
                             |     attenuation 2x/20x
                            ---
                             -

(All resistors 1%.)

However, then I learned oscilloscopes have input capacitance, and I'm not sure how to add it. Also, if I want the input to tolerate 400Vp-p swing but on the wrong input range (2x attenuation leaving 200Vp-p to damage the inputs of the JFETs), I couldn't use diodes as the lowest capacitance I found was 0.13pF for an RF diode, which would limit me to about 612kHz for two diodes (one to each rail, reverse biased.)


texts: How can I accurately find the distance between two drones over moderate distances?

texts:
I am currently taking part in a project in which I am building drones using Arduinos and Raspberry Pis, and I need to be able to measure the distance between the drones. After some research, I realized that many people use ultrasonic sensors.
However, I want to build a system that can measure the distance through walls and over moderate distances (up to 100 meters.) I figured that ultrasonic sensors won't have this range, and might not work through walls. I am honestly stumped with how to solve this problem.
Is there a way to do this, or is that just not a practical idea?
I want to have an accuracy of at least within half a meter.


texts:
I recently bought some LiPo battery packs from Ali,

Now im trying to figure out what type of plug it has!

Anyone knows the answer? Would be awesome.


texts: Will an SPI flash memory chip have the same issues with non-atomic write operations as a dsPIC's internal EEPROM?

texts:
A while back I had some intermittent trouble with the internal EEPROM of a dsPIC. Every so often, some value in the EEPROM would be found zeroed out on power-on. I tracked the problem down to when the chip lost power after the erase step of the write cycle, but before the write had completed. It was all about the timing of the power-down relative to the firmware execution, which was (in normal operation) random. I solved this by adding a buffer section to my EEPROM, to ensure that an incomplete write-cycle could be completed on restoration of power. I had to turn EEPROM writes into an atomic operation.

Now I'm using a different dsPIC without internal EEPROM, and I'm trying to use an external flash memory chip to store persistent data. I'm wondering if I should have similar concerns. Should I be worried that my external flash chip will power down mid-write and lose data, and write a fix for this in my firmware like I did for internal EEPROM? Or does the chip itself guarantee atomic write operations?

For further detail, my buffering technique defines an area of persistent memory that consists of three fields: address to write to, data to be written, and a READY flag. A "write" consists of four steps: write to buffer, set READY flag, write from buffer, clear READY flag. On power-up, you check the READY flag. If it's set, execute whatever's in the buffer. This worked well in EEPROM, but I'm not sure if it will work well in flash.


texts: Auto start and stop water AC motor using these two circuits

texts:
Problem:
    I have a AC motor (pump) which pumps water from the      ground floor to 4th floor. On 4th floor, I have water tank. The problem is I have to start the motor in 5AM in morning. I have installed a water alarm buzzer which beeps when tank is full. I want to automate this using some circuits.

Solution: Automatic solution which will start motor at 5AM daily in morning. There is no automatic turn off (based on time). Motor will stop automatically when water tank is full.

I have purchased Two items

Daily Weekly Programmable Electronic Switch.
http://www.ebay.in/itm/Daily-Weekly-Programmable-Electronic-Timer-Switch-220V-AC-16A-MCB-Digital-Relay-/191748990517
Water Level Controller.
http://www.ebay.in/itm/Water-Level-Controller-Tank-Level-Controller-Works-On-12VDC-AC-/111819716037

There first device has capability to turn on motor at scheduled time. The second circuit behave differently. Second circuit start motor when water is below certain level and automatic switch off when it certain level.

Can i use these two device and create something which I want ?

May be I need to purchase some more circuit/devices. Please help to guide to make this hack.

final thought : I want, my AC motor pump to auto start at 5 AM in morning and automatic switch off when it full.

I do not need     any     other kind of logic that if Water is below at certain level then auto start motor. Because, there is no use to start even if water is below certain level because in my area water supply happens only for 4AM to 6AM.

I am software guy and understand basic  electronics. Solution like have a Pi board or use GSM kind of things will not be helpful, because I want a minimum solution for my problem and not a fancy luxury solution like (app controlled switch etc).

I searched a lot on Internet and found these two cheapest circuits which can help me.
Let me know if you know any other cheaper way to achieve my goal.
I have purchased first device in $13 and I am going to buy second circuit in $4.

Thanks
========== Update 1========
After reading answers, and with my limited understanding on electronics, I have created this circuit picture !

Let me know If I want need to add extra resistors or this circuit will blow my house !

Image attached here.


texts: Unstable readings in photoresistor matrix with Arduino, OK with Ohmmeter - what's wrong?

texts:
I'm working on a photoresistor array with my arduino, and I'm having a little trouble getting stable readings.

I'm driving 7 rows one at a time with Arduino's digitalWrite(pin,HIGH) command and floating the other outputs with pinMode(pin,INPUT); Problem is, I got NO READING from my analogRead() voltage dividers unless the column is hooked up to my ohmmeter. Whats up with that?

Only the column connected to my ohmmeter outputs anything at all, all the other columns read zero.  Whats in my ohmmeter that suddenly makes that sensor work?

So if I connect my Ohm-meter to the positive rail of P1 and to MEGA Analog 0 (A0) connection, suddenly the whole column gets readings! Otherwise, zeros everywhere.

void readArray()
{
  for(int i=0; i < ROWS; i++)
  {
    for(int k=0; k<ROWS; k++)
    {
      pinMode(rowPins[k], INPUT);
    }

    pinMode(rowPins[i],OUTPUT);
    digitalWrite(rowPins[i],HIGH);
    delay(250);

    for(int j=0; j < COLS; j++)
    {
      holdVals[i][j] = analogRead(j);
      Serial.println(holdVals[i][j]);
    }

    digitalWrite(rowPins[i],LOW);
  }
}


texts: I would like to use a 430mhz RF antenna and a 1575mhz GPS antenna. Both antennas are chip and drive current in the ground plane to radiate. The RF antenna is only useful 1s every minute. The GPS has an LNA. I am wondering if the two antennas could share the same monolithic ground plane or should they each have a proper ground plane joined in a single point ?


texts: why is this microcontroller brown-out level detection at 2.6V and 3.4V

texts:
The default brown-out detection level for the ATmega32u4 is 2.6V (typical) in the range of 2.4V to 2.8V. The table of possible values:

2.0V
2.2V
2.4V
2.6V default
3.4V
3.5V
4.3V

Unfortunately there is a large gap between 2.6V and 3.4V. Another possibility is "brown-out detection disabled" which is not in my table but it certainly exists.

My application uses an Adafruit board at 3.3V and 8MHz. The application is non-life threatening but accuracy is always of interest so I ought to benefit from brown-out detection, if feasible. This board aside, 3.3V seems to be a popular voltage for a microcontroller Vcc level so the default 2.6V brown-out level seems to be a good choice  except for the fact that the datasheet also has this graph.

One interpretation is that at 2.65V (which is above the default brown-out level) a frequency of 8MHz is in some way unsafe and the safe frequency is somewhat lower by extrapolation. I don't want to run slower than 8MHz. Another interpretation is that the graph gives you information about the maximum frequency between 2.7V and 5.5V and no other conclusions should be drawn. There should be no extrapolation.

My question is: What were the design considerations that caused there to be a large gap between 2.6V and 3.4V on the brown-out level table? It seems wasteful to have to choose a 3.4V brown-out level in a battery powered application.


texts: Why is in some cases that the messaged received from the demodulation process has slightly more amplitude  then the original message?


texts: Do multi-core processors reduce power consumption?

texts:
I have been reading some tutorials about power consumption on parallelized system. I have been following this tutorial.

Tim Mattson (Intel): Introduction to OpenMP: 02 part 1 Module 1, YouTube

At about 3:50 min of this tutorial, the mentor mentions that.

lets say if I have a processor that operates at frequency f.

The output power is

$$ CV^2f $$

where V is the voltage, and C is the capacitance.

If we have the two processors that operate on the frequency f/2, and they are connected in parallel. Then total output power will be P1 + P2. And for each of the processor, voltage will be V (they are in parallel). And the Capacitance will be 2C (C1+C2) for parallel.

So total power will again be

$$ P = P1 + P2 = 2( CV^2 f/2) $$

which will again be equal to

$$ CV^2f. $$

But the mentor mentions that the power consumption will be decreased to 40%.

Can anybody explain? Do multi-core processors reduce the power consumption by such a high value?


texts: High Frequency Pulse Rate Generator - Science Fair

texts:
( For our High School Science Fair) I am trying to find a pulse rate generator capable of producing 2.5Hz - 20,000 Hz utilize with over 10,000 LEDs all at once with several milliseconds in between pulses. Any ideas? Aside from the generator, how could I accomplish this?

We are doing an experiment on photobiomodulation (affecting cells with light). Living cells respond to and have different frequencies ( ex Brain Freq range 72 MHz). Living cells also respond to different wavelengths of light (ex 660nm).

Our group is utilizing something similar to a tanning bed, outfitted with specific wavelength LEDs. We are attempting to control pulse rate. We want to be able to set different pulse rates at 2.5Hz to 20,000Hz for 20 minutes.
Our goal is to see if there is an added affect to the cells on top of the light response by adding the same pulse rate as it is accustomed to.

Typically in Photobiomodulation, they will pulse lasers to prevent over-heating of the tissues. I asked for a pulse generator because a paper discussed that the same could be applied to LEDs.

We are trying to find ways to be able to program this (the ability to pulse frequency) into our light bed. We want to have an LCD screen that controls different programs that would change frequency of the 660nm + 850nm LEDs to preset programs or customized options. What components would you suggest. Can this be done?

Sorry to be vague I am 16 and this is for our science fair.


texts:
I am currently trying to get a basic Ethernet communication between a laptop and and FPGA Development board working correctly, however, I seem to be facing an issue where the auto-negotiation is timing out.
I have the Ethernet port on my device plugged into a an Ethernet cable which is going to an Ethernet-to-USBC adapter, and this adapter is plugged into my laptop.
Prior to this I have attempted to assign an IP-Address to the device and then ping that IP address (but no response was received). Additionally, I have followed the Ethernet Firmware API for initialization calls (parsing through the code I found that this auto-negotiation happens in the first initialization call)
Would anyone have any idea on what I may be doing wrong?
For reference I am using Microsemi's M2S150 FPGA development board which has a an m88e1340 PHY from Marvell, and an ARM M3 Cortex


texts: Circuit analysis of a emitter follower with bootstrap

texts:
I'm trying to analyse the circuit below (from Art of Electronics, 2nd edition, p. 96). What are the small signal input and output impedance of this emitter follower?

I can analyse an emitter follower, but I'm doing something wrong with the capacitor.


texts: How to connect/disconnect signal line electronically?

texts:
I sometimes do electronics projects as a hobby and as far as I know if you want to switch something in a circuit electronically, transistors are the way to go. And I have used them successfully before to control high current loads such as LEDs or DC motors with a micro-controller.

But what I'm trying to do now is to turn a TTL serial connection on and off. As if I was physically disconnecting the TX wire from my micro-controller's RX pin. And I have realized that every tutorial I've ever read about using transistors as switches (this one for example) assume that you are using the transistor to turn a load on or off.

I found a few similar questions on the Internet but they all are drifted away from the subject one way or another and left unanswered. (This and this for example).

I have actually managed to do it myself, with the following circuit:

My though process behind this is: A transistor connects the Collector to the Emitter when it is saturated, so when I "turn on" the transistor, TX should get connected to RX. And it actually works!

When nothing is connected to the base my micro doesn't receive anything. When I connect 5V to the base the micro starts receiving serial data. I'm outputting this data to a serial console and it's valid, non-gibberish data.

But having learnt from previous experiences, after achieving this I started searching the Internet to see if this is the proper way to do it. But I couldn't find anything about how to switch a signal/data line on and off. As I mentioned, they are all about switching loads using NPN or PNP transistors to connect to GND or VCC respectively.

What I want is something that acts exactly like a physical switch, that I can put anywhere in the middle of my wire and connect/disconnect it. Which my circuit seems to be achieving.

So am I doing it right or am I just getting lucky?

I have a feeling that I'm just getting lucky.


texts:
Is VBEn turn on voltage, if so why is it changing?

It says when \$V_I\$ is increased, voltage at the base of Qn increases and
\$V_O = V_I + V_{BB}/2 -V_{BEn}\$

Can you please explain me how does increase in \$i_{Cn}\$ result in increase in \$V_{BEn}\$ voltage?
Firstly, I didn't get why was it increased because \$V_{BEn}\$ must be constant, because it is turn on voltage.
Secondly, If it is able to change, why was it increased but not decreased?

Thank you

Edit: new link of the
circuit


texts: Large-value ceramic caps  in small packages?

texts:
I'm looking at some capacitors, namely ceramic, 10µF 50V caps. Here are the search results on Farnell UK.

Most are in big packages, 2220 or some form of stacked capacitor. But then there are the occasional X7R and X5R caps in 1206 and 1210 packages, like this one: GRM31CR61H106KA12L. It seems too good to be true, it's half the size of others and very low cost. It's not available yet, otherwise I would have bought some and tested them.

Any opinions? Has anyone tried these?


texts: If a high frequency signal is passing through a capacitor, does it matter if the capacitor is charged?

texts:
If I have a signal generator I want to inject into mains or DC systems. Does it matter if the capacitors are charged or not, does it make a difference?
If for a example, the reactance at 5MHz at 50nF is 6mohm, if we then charge the capacitor to 230V 50Hz or 60V DC for example, would the 5MHz signal see a different impedance? Or would it be the same?

simulate this circuit – Schematic created using CircuitLab


texts:
I am trying to repurpose a scavenged motor, however the wiring diagram that's on it has a schematic symbol I have never seen and could not find on the Internet.

Anyone know what this is and what it means?

For more context, here's a reproduction of the entire schematic:

Update:

The symbol is for a thermal switch/contact. This particular kind is normally closed and opens on temperature rise (http://www.industrial-electronics.com/Electricity-Refrigeration-Heating-Air-Conditioning_5b.html)


texts:
I have a LiPoly battery (3.7V 650mAh, similar in size/shape to a standard AA) that was part of an e-cigarette assembly. While attempting to remove another part of the assembly, I accidentally separated the battery from the assembly.

The battery still has both leads attached and is fully charged. I would like to fully discharge this battery for safety reasons, and am not sure exactly how to do that. As the battery is still in good shape, I would optionally like to keep the battery for some other hobby use so destroying it is not ideal.

What should I do to safely discharge this battery so I can store it without worry?


texts:
Suppose we have this circuit:

simulate this circuit – Schematic created using CircuitLab
Z = 4-3j
I = V/Z = 1<0/5<36 = 0.2< -36 A
But when I use Ohm's law on the capacitor i get this which doesn't make any sense:
Vc = IZc = 0.2< -36 -3j = 0.2< -36 *3< -90  = 0.6< -126.
Any help appreciated


texts: Use a postive linear regulator for regulating a negative voltage

texts:
Can I use an LT78L05 (https://www.st.com/resource/en/datasheet/l78l.pdf), a postive voltage regulator for regulating 5V, for regulating a -5V in this configuration :

simulate this circuit – Schematic created using CircuitLab
In this way, it sources current.
Thank you :)


texts: JK flip flop integrated circuit (7473) toggle malfunction

texts:
I built a state machine using JK flip flops, I tested it but I kept getting seemingly random results. I decided to test each jk flip flop individually.
Here is the schematic for my testing:

simulate this circuit – Schematic created using CircuitLab

Both LEDs should toggle whenever the clock goes high to low (everytime I release the push button) and thats what usually happens but every few tries the toggle doesn't occur at all or it happens when CLK goes high and when it goes low.
I made a video of the aforementioned test:
JK flip flop Test

I tested 4 different IC (8 flip flops) and they all presented the same behaviour.

All flip flops' set, reset and memory worked perfectly.

Why does this malfunction happen and how can I prevent it from happening?


texts: Is the orthogonal spacing of dq axis of AC motor with respect to electrical or mechanical angle?

texts:
In FOC of AC machines, we try to align the stator flux to Q axis and maximize the value. The idea behind this logic is when rotor flux and stator flux are orthogonal, we generate max flux. But is the dq axis orthogonality with respect to electrical or mechanical angle?
An extension to the above question: In case of a 8 pole pair machine, I think the angle per pole (three phase) in stator is 45 deg (360/8). If dq is spaced orthogonal electrically does it mean that d and q axis are compressed between the 11.25(45* 90/360) deg in mechanical angle?
Btw, my picture of ac motor is that there are 8 repetitive segments of ABC phase in the stator and each segment corresponds to a magnetic pole. Each segment is complete electrically by 360 deg.


texts: How to convert 3.3V from Raspberry Pi to usein a Remote Control Car which needs 3V

texts:
I need a 3V ( 2 1.5V batteries) for a RC car transmitter and I have a Raspberry Pi Model B giving out 3.3V. How can I convert the 3.3V from Raspberry Pi to use it in my RC car Transmitter ?
Basically I'm trying to run the RC car with the Raspberry Pi GPIO pins 1, 3V3OUT, and Pin 39 GND.


texts:
I'm using an STM32F429 Discovery board and using the FW_F4_V1.25.2 firmware. I have SPI3 configured as a full-duplex slave (currently used only to send) which sends data out to a Beaglebone as a Master. The Beagle supplies a 10MHz clock and SS to the Disco board. The clock is pulsed/polled every 2ms to get the header after which the data is clocked through, this loops.
My issue is that every so often the MISO pin stays low after the header is correctly sent and no data is clocked though, as verified on an oscilloscope. This seemingly happens at random, sometimes it may be once every 100 or so transfers and other times happens after just a few transfers. For larger transfers, (simply increasing number of words to be sent), I don't seem to have this problem at all.
I tried the latest FW_F4_V1.26.0 and don't seem to have this problem. However in this version the discovery board sometimes stops responding to the Beagle clock altogether and the HAL_SPI_Transmit command times out repeatedly until eventually it starts to work again at random and sends data.
As a side note, I don't understand why I need to specify the first 2 words / 32 bits as highlighted in the code below, in order to actually just clock through one 16 bit word. If I specify 1 word, no data is ever clocked through. However in the case of the header, 4 does mean four words are clocked though.
My transfer routine below is very simple.
HAL_SPI_Init(&hspi3);
if (hspi3.State != HAL_SPI_STATE_BUSY_TX)
{
HAL_SPI_Transmit(&hspi3,(uint8_t*)&header,4,50);
}
if (hspi3.State != HAL_SPI_STATE_BUSY_TX)
{
HAL_SPI_Transmit(&hspi3,(uint8_t*)&data,2,50);
}
HAL_SPI_DeInit(&hspi3);

-------------------------------------------------------------------------------------------------------------
 hspi3.Instance = SPI3;
 hspi3.Init.Mode = SPI_MODE_SLAVE;
 hspi3.Init.Direction = SPI_DIRECTION_2LINES;
 hspi3.Init.DataSize = SPI_DATASIZE_16BIT;
 hspi3.Init.CLKPolarity = SPI_POLARITY_LOW;
 hspi3.Init.CLKPhase = SPI_PHASE_1EDGE;
 hspi3.Init.NSS = SPI_NSS_HARD_INPUT;
 hspi3.Init.FirstBit = SPI_FIRSTBIT_MSB;
 hspi3.Init.TIMode = SPI_TIMODE_DISABLE;
 hspi3.Init.CRCCalculation = SPI_CRCCALCULATION_DISABLE;
 hspi3.Init.CRCPolynomial = 10;

Please could anyone help with this?
Thanks
EDIT: I've played around with the GPIO parameters for the SPI pins but this hasn't helped. Can anyone offer any suggestions?


texts: Raspberry Pi to Digital LEDs, No Soldering

texts:
I have a Raspberry Pi laying around right now that I'd like to put to use, and I'm also going to be buying a string of digital LED pixels from Adafruit (the string of 25 WS2801 pixels).

I know I can easily control the pixels from the Arduino based on the Adafruit tutorial, but I'd prefer not to buy a new Arduino if I can do this from the Pi.

Based on several projects I've seen, such as PixelPi, it's obviously possible, but because I have no space for a soldering iron (I live in a dorm hall, and stuff like that is not allowed for obvious reasons), so I can't do any soldering. I would like to be able to learn how to solder and simply go to a hacker space, but I don't see having that much time any time in the near future...

Is there a way to connect the RGB pixels to the Raspberry Pi without any soldering? The only way I could think of doing that would be to use some sort of adapter for the header pins so I can push the wires into them (without having to solder), but I'm not experienced enough with electronics to know exactly what to look for...

Alternatively, if no one knows a way, I guess I might as well just spend the extra $20 and get an Arduino...


texts:
What is the best way to measure the state of a latching switch using a micro controller?
Keeping in mind the voltage level of the input to the switch is higher then the maximum voltage input to a MCU as show below:

I have attempted to solve this myself using the following circuit (a simple voltage divider) however i'm not entirely confident in my solution due to my lack of experience. Below is my attempt however I am worried that when switch is open the input appears to be floating, which could yield some incorrect reading?


texts: Troubleshoot load capacitance (crystal not starting)

texts:
I am using a MAX11060 ADC in a project, I have established SPI communications and am able to read and write registers, however I am unable to get any readings, I believe this is due to the crystal not operating correctly.

This assumption is based on before enabling the oscillator 0V when probed, after enabling the oscillator I see a flat 800mV or so.

To backtrack a bit to fix a screw-up in our board design (wrong footprint) we have manually broken out the package and encased in epoxy (as in I REALLY don't want to re-solder this).

I presume the extra capacitance and/or larger loop area has pushed the crystal out of its operating zone.

Is there any way to measure the load capacitance and then adjust, is this as simple as using a multi-meter to measure between each side of the crystal and ground ad adjust to match the rated value.

Can this be done with the crystal in place.

(Also yes I understand mounted like this the chip will not be able to reach its 16 bit performance, the project has reached a it would be good if it would work at all state)


texts:
To introduce myself I am a first year EE student and an exam on AC circuits is comming up. Whilst practising I noticed one question I couldn't solve. No way I tried managed to get me the answer (which I do have)

The first question was easy so I got that one. But when trying to solve this I keep getting different values of the gain. I tried multiple ways of connecting the resistor from the backgate effect to solve it but I either get ~-12V/V or ~-14V/V
I am not asking for people to do my homework as I really want to understand this course but this one I cant solve.
to save some time:
gm1 = 4 (20*0.2)
gm2 = 10 (8*0.5)
ro1 = 25kOhm
ro2 = 10kOhm


texts: Protecting RPi against lightning and high voltage

texts:
I'm making a remote weather station with a Raspberry Pi 4 and a few sensors.
Problem 1: the anemometer is held on a iron rod (was already there, can't change), dangerously exposed to lightnings. Inside it has a reed switch connected to GND on one wire and to a GPIO on the other. Wires go down to the RPi box. What's the best way to  avoid hazarous high voltages from burning everything? I was thinking about gas discharge tubes, commonly used in ethernet protection. Would they be OK and what type should I get for a 3.3V signal? How to connect them properly?
Problem 2: the ethernet Cat 6 cable that connects the RPi to the LAN will stay underground, a few cm below walking level. Shall I add a surge protection to it, too?
Problem 3: the board will stay in the same box as 220V wires, which power the station. Is it fine? Or will it interfere with the delicate electronics?
Thanks
EDIT: block diagram


texts: Can power be distributed to USB devices from central supply?

texts: I own some inexpensive yi home cameras.  I don't like having a cable run to a wall wart for each camera.  Is it possible to run low voltage wires in the walls to a central 5v power supply with sufficient wattage, and splice to the VCC and GND wires in USB cables?  Or does power over USB require communication?


texts:
I have this NEW heat recovery unit from Amazon (shady quality, branded as made in UK but actually made in China) with this motor inside. It was supposed to have two speeds (Low/Hi).

Question:
How to connect the wires?
Assuming that BROWN and BLUE and the "main" 230V wires, where do I connect the BLACK and WHITE?

Here is what I got by disassembling the unit. (Yes, the schematic I show is correct. I double checked.) Did they connected the capacitor to the wrong wire?

Here is the user manual, which makes no sense:

Internal resistance measurement:

Blue-Black = 500ohm
Red-Black  = 680ohm
Blue-Red   = 1200ohm


texts: What do these question marks next to heater resistance mean?

texts:
This is from a sensor called MQ306A used for sensing gas.
My problem is that this same series of sensors from the MQ category have the same tin dioxide layer but they claim to sense various gases.
How is this possible?


texts: Multiple diodes in series reverse biased

texts:
I was thinking about a question that was just up here, someone's interview I think.   Anyway I'd never really thought about what happens when you have two diodes in series but reverse biased.

simulate this circuit – Schematic created using CircuitLab

Why is the voltage drop shared, or 10V across each of them?  I mean I understand if it were resistors there'd be a current flow, I suppose here it's the very small reverse bias current flow?  I just don't understand what's happening at a low level :)

Then having Vdrop be VCC/3 seems like a text book answer, like the real answer should be each diode's characteristics are a little bit different so depending on how much current each one is handling, however small somehow leads to the voltage drop across it.

So how does that work in real life?


texts: Circuit to first turn on an FPGA, with an enable pin from FPGA so it can shut itself off

texts:
I have an inquiry and searching on Google didn't help.  If I have a voltage regulator, with active low shutdown pin, and the output of the voltage regulator powers an FPGA/ASIC/CPLD, how can I implement a "hand-off" circuit paired with this voltage regulator such that the FPGA turns on when the voltage regulator is initially powered on, but the FPGA can turn itself off by driving the shutdown pin low, and keep this voltage regulator off?  By the way on this voltage regulator, the active low shutdown pin, when either tri-stated or driven high both keep it enabled.  So it MUST receive a logic low.
If my specific question doesn't make since, I'll ask a more general question: How can an FPGA power itself off with a shutdown signal to the circuit which powers it?
Thanks in advance!


texts: what means starting and Maintaining voltage in this specification?

texts:
i want to drive a pneumatic ejector(open and close), is specifications in following:

Starting Voltage : 100V
Maintaining voltage : 12V
Resistance Value :18Ω
Frequency(Hz)：800-1000
Maximum instantaneous power : 200W
Standby power : 3W

what means starting voltage and Maintaining voltage?
do is correct that 100 volt is for on and 12 volt for off ? if yes what is best circuit for it?
do is below circuit appropriate ?
Solenoid Driving Circuit