texts: How to convert RMII signals to LVPECL signals

texts:
As far as I understand the RMII output signal of an ethernet PHY is a TTL signal (at least according to wikipedia). I need to convert these into LVPECL signals.
So on the one side I have something like TX0 and TX1 from the RMII and on the other side I have Tx- and Tx+ for the LVPECL interface. How can I interconvert these signals (also LVPECL to TTL)? I found the MAX9370 TTL/LVPECL translater but wouldn't TX0 then split into two signals (same with TX1)? So i would end up with a four signal output from the MAX9370 translater. But I only need two signals as LVPECL input. I think I'm missing something important here.

UPDATE:

Some more details: the phy of interest is the LAN8720. According to the datasheet the RMII outputs LVCMOS signals.
These should be converted to LVPECL signals in order to serve as an input for an optical transceiver. My goal is to build a media converter.


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As an electronics hobbyist, I've already built a thing or two so this didn't seem like a complicated thing to do, but I was terribly mistaken. I wanted to build an FM modulated radio transceiver controlled by an Arduino board that would work anywhere between 86 and 520 MHz so that it'd include normal FM radio, VHF and UHF amateur bands and PMR and CB channels.
I expected there to be a miracle IC that would just require an audio and carrier wave input, rf amp and antenna, or that there would be plenty of similar projects already done that I could bounce off of, but hours of research gave me no answers, just more questions.
I came here to ask why are the radios built always in specific bands like 136-148/200-260/400-430 MHz instead of working continuously - is there a legislative or physical limitation? And my second question is whether is there a way to approach this problem that would be friendly for someone who usually works with digital stuff (like an IC or module) instead of analog/radio electronics.
Thanks.
EDIT: Thank you all for your time, you were very helpful.


texts: What does "For disconnect use only" mean on a connector?

texts:
I recently bought some Andersen connectors for connecting high-amp devices to my camping setup in my truck. The idea is they hold together through much rougher conditions than a regular cigarette lighter 12v plug would, as well as being superior in virtually every other way as well.

However they have this notice on them:

  FOR DISCONNECT USE ONLY

I am unclear what that notice actually means. The French above it

  NE PAS EMPLOYER POUR LA RUPTURE DU COURANT

Google Translate tells me means

  DO NOT USE FOR CURRENT BREAKDOWN

This seems to indicate that the connector should not be unplugged when the system is under load, which makes a lot more sense...

What does this warning signify?


texts: VHDL initialize vector using readable integers not long binary string

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So I am only starting out my VHDL journey. One thing I am finding a bit of a nuisance is the following format:

signal sig_A : unsigned (3 downto 0) := "0101";

being that "0101" is just a string which somewhere down the line gets converted to bits. Is there a way I can initialize this to where its a bit easier to read, especially when I get to bigger numbers. For example

signal sig_A : unsigned (9 downto 0) := "753";

which for the life of my I cant think of the binary or hex equivalent unless I whip out a calculator.

I just do not know the language well enough yet to figure this out. It seems like a trivial thing but I have tried a lot of variations with no success. I was thinking like a prefix dec"753" or "D753" I really have no clue but it surely has to be implemented in the language somehow I cannot imagine people really typing out 32 bits or trying to compute hex constantly.

Before anyone mentions it, I am not expecting it to throw 7 and a 5 and a 3 in there literally. Just as I dont expect it to throw an "F" in there when typiing hex. I am expecting it to decipher the number to its binary equivalent based on a string just how it deciphers the  "010101"  string.


texts: Do you get correct graph of transfer characteristics(CNTFET), if you take +ive Vds(constant) value instead of -ive. As mostly CNTFETs are p chnl FETs

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I'm studying transfer characteristic curve of CNTFET to get value for mobility, S.S, etc.
According to my basic background knowledge, NMOS curves lie in the 1st quadrant. While for PMOS they lie in the 3rd quadrant. As mostly CNTFETs are p-channel, I was expecting mine one to lie in the 3rd quadrant (-ive Id current, -ive Vgs).
But in my case, the curve lies in 2nd quadrant, current is positive, due to which slope comes out to be negative(calculated it for mobility).
I think I've made a mistake. While taking Vgs Vs Ids(graph attached), Vds is constant. I just took positive values of Vds. for example for the given graph(attached) constant Vds is 0.1V. Now I've come to know that one has to take -ive constant value for Vds when calculating Transfer characteristic for p-channel mosfet.
Questions:
Are my all reading wrong?
what should I do? I can't perform the experiment again.
Kindly help is there any way for my readings to be correct? If they are already correct then any explanation for this behavior?
I even connected my MOSFET for both kinds of biasing (for n channel and for p channel), that's because CNTs I've used are mixed(semiconducting plus metallic). So I thought I might get good results for n-channel one.  For p-channel, the curve was in the 3rd quadrant while for n channel biasing it was in 4th. So not in the one it should be(1st,3rd).
Keithley source meter was used to obtain IV-curves.
kindly help, I hope you are getting my point and sorry for typing mistakes as my electronics is not that good enough.


texts: Beads and self resonant parameter in supply circuits

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I've a consideration on beads self resonant frequency. The beads have self resonant parameter and I wonder how it affects on my supply circuit. I have read many post and i suppose that self resonant freq is very important in circuits with DC/DC converters and other elements which work with some switching frequency, and I can't admit to situation where the switching frequency is equal or close to self resonant frequency? Am I right? What about circuits where I don't know what noise can occur in circuit? For example, I have SFP+ transciver supply circuits given by the manufacturer:

and my question is: Is self resonant frequency important in this case? What is your point?


texts: Thevenin Equivalent circuit for T feedback network of inverting ideal op amp

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simulate this circuit – Schematic created using CircuitLab

I am trying to reduce the T feedback network(R2 R3 R4) into a Thevenin equivalent circuit looking into the network from the v- (inverting) terminal. The Thevenin equivalent circuit I get is this:

simulate this circuit
It is easy to see that Voc is just a voltage divider. To calculate the equivalent resistance a test source would be inserted then Isc (short circuit current) would be calculated and then the equivalent resistance is given by $$R_{th} = \frac{V_{oc}}{I_{sc}}$$ This bring me to my question: Is it possible to short the dependent source since $$ A(V_{+}-V_{-})$$ will equal some finite value that is independent of the thevenin equivalent; thus the VCVS is actually independent of this equivalent circuit and can be shorted like an independent source?

The book I'm reading gives the equivalent resistance as $$R_{th} = R_2+R4 || R3$$ Which would suggest that the dependent source has been shorted. To my knowledge we have to use a test source to determine equivalent parameters when there are dependent sources. Is this just a coincidence or can someone explain why we are able to short this VCVS.


texts: MAX 6675 K-type unstable to say the least

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have two breakout boards with MAX6675. I have 3 different K-type thermo elements. The MAX is connected to an AVR (atmega8) for communication, driver my own, communicates to PC on UART.
Now none of the combinations of MAX and K-type element works well. The only main feature is that you cannot touch the cable or probe, or even come in vincinity of the cable/probe with my hand without values falling drastically, eventually going to 0 if you take hold of the cable.
Also the value drifts substancially when just left alone.
Dont get any grip of whats going on, is the amp oscillating, and then why, what to try for remedy.
Thanks for any help  (not allowed to tag with the only useful tag MAX6675)


texts: Can I wire a dimmer switch into a soldering iron?

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So I have a really cheap soldering iron and a dimmer switch meant to be wall-mounted. The soldering iron has a standard, ungrounded cord. The dimmer switch has four wires: a green (for ground), a black and a red, and another red that's "only for use in 3-way switches". How can I wire this into the soldering iron to allow for variable soldering iron intensities?

I tried cutting the soldering iron cord, binding neutral back to neutral and binding the positive to the dimmer's red, through the dimmer, and back through the dimemr's black to the other side of the positive. This did not work. I also tried it with the red to red, and the black to the other red, and neither worked.

Is it possible to insert a wall-mounted dimmer into a standard appliance cord such as a soldering iron?


texts: Impedence Matching of Antenna and Coaxial Cable

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There is a scenario based question which is confusing for me
Antenna had four rods each 15cm arranged as a plus sign. its brass shielding was cut and it had two 75 ohm coaxial cables in it. one 10 cm long was connected to rod A and C whereas other was 17.5cm long connected to rod B and D. On measurement you found good impedance match between antenna and cable. both the cable got combined at the other end into one input connector

Find Center Frequency
Predict polarization
Plot radiation pattern.

Can you tell me how impedance matching works, do length matters and how can we know if antenna with given length is having a good match with coaxial cable with given length


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I have a 350 ohm bridge with 04 fixed resistors, later on one of them will be replaced by a strain gauge sensor. In the meantime I am trying to understand where the drift is coming from.

This bridge is connected to an in-amp with 1000x gain.
In order to calibrate the bridge and unbalance it (so I can have, say 1V output at the in-amp output) generally I use a very high resistor (around 500k ohms) in parallel with one of the resistors on the bridge.
These 350 resistors are 0.02% tolerance and 0.2ppm/C. The opamp is a AD8571 (extremely low drift and offset).

Unfortunately I have been struggling for months with a drift that shows in several different ways:

Temperature - Only by blowing some hot air briefly, the output varies +/-10mV
When the voltage output is increased by any external factor that is removed afterwards, it never goes back to its initial value
There is a voltage drift without any temperature change, I managed to have a very precise temperature sensor mounted on the top of the circuit to confirm.

All components are very high quality, spec'd for this particular application, low drift, low offset and really expensive. I do not know whatelse  I can do to get rid of this annoying drift, unpredictability and lack of repeatability.


texts:
Brief description of the context (not really necessary to answer):

I built a quadcopter. The motors (small DC motors) and the electronics are powered by a single 3.7-4.2v battery. To prevent the microcontroller and the sensor to reset when there is a current spike in the motor's circuit, I put a 1000uF capacitor near the electronic part's supply and a schottky diode between the battery "+" and the capacitor, so that only the electronic circuit can use the capacitor's charge when needed. I also built a simple remote control which communicates with the quadcopter trough a couple of cheap 433mHz rf modules (on the receiver stands "xy-mk-5v").
At this very moment I can send all the needed settings to the quadcopter, calibrate it to remain as steady as possible and eventually tell him to fly: it takes off and flies for 3 seconds, then it automatically shuts down (as I wrote in the code for safety reasons). But during the flight there's a lot of noise in the circuit and the quadcopter can't receive any rf message (so I can't control it).

The question:

What I need now is a rf sistem which works with a noisy supply. I think I could:

a) filter the power supply;

b) change the rf modules (I payed something like 2 USD for the actual ones, but I could spend 20-30 $);

c) change the antennas (now I use a 172mm wires)

Would these things help? What else could I do? And how could I do these things (how could I build a good filter? What shape should the antennas have?)


texts: Common emitter amplifier with load resistance

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I can't seem to grasp how to calculate the values for a common emitter with a load resistance, to cascade an amplifier in multiple stages.

I'm trying to obtain an 8.5-9Vptp output from a 12V supply on a 5520 ohm load resistance. Not trying to achieve much gain since it can be achieved in earlier stages so ~5.
I took:

Ic = 10mA

DC emitter 0.5V about ground

Vce min = 1V

This is what I've got

However, once I actually built the circuit on a breadboard the output ended up being 4Vptp, half of what I actually had in the simulation.
What am I doing wrong?

Complete circuit:


texts: How did they get to the SR-latch with 2 NOR gates?

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I understand SR latches and how they work, but I was trying to recreate the SR latch to see if I can get to the same well known circuit with 2 NOR gates.

However if I write the following logic table for an SR-latch
| S   | R   | Q   | Q+  |
| --- | --- | --- | --- |
| 0   | 0   | 0   | 0   |
| 0   | 0   | 1   | 1   |
| 0   | 1   | 0   | 0   |
| 0   | 1   | 1   | 0   |
| 1   | 0   | 0   | 1   |
| 1   | 0   | 1   | 1   |
| 1   | 1   | 0   | x   |
| 1   | 1   | 1   | x   |

and solve the K-map for this table, I get Q+ = S + Q!R and !Q+ = R + !Q!S.
Even if I apply DeMorgan, I get Q+ = S + !(!Q + R) and !Q+ = R + !(Q + S) and the resulting circuit:

simulate this circuit – Schematic created using CircuitLab

So how did they get to that simple form using only 2 NOR or NAND gates?


texts:
I have a problem in which I need to capture (spy on) an RS232 signal through an opto-isolator. This isolator needs to be high speed since the RS232 signal can reach up to 115200 baud. The main problem is as follows:
Device #1 and #2 talk to each other through a RS232 signal (only Tx and Rx). I would like to capture the Tx signal from device #1 without interfering on their communications:

For safety reasons there needs to be a bit of isolation, so I can't just 'tap' the line and a simple diode would only capture the positive bits of the rs232 signal. I have tried it with a simple diode, but then I get interference on the devices.
I came up with the following; The 6N137 opto isolator (high speed) will take the Tx as input signal. This IC needs 5v Vcc, so I need a L7805 as a voltage regulator to get 5V.  I use a pull-up resistor on the output of the 6N137 so the signal will be 'inverted' (and would actually be TTL Logic). I then take that signal and put it through a MAX232 (which also needs 5v) to get a proper rs232 signal again:

The things I'm not sure about though, is if the 6N137 would work properly with the RS232 signal. This normally ranges between -9V and 9V right? Can the opto-isolator handle that? Also, do the capacitor and resistor values make sense? Also, if I 'tap' the line, can it be that I draw too much current away from the line, so that Device #2 can't interpreted the signal anymore?
Is there maybe a completely different method which suits way better?
I'm quite novice when it comes to electronics (I'm more of a programmer myself), but very eager to learn. Any help is much appreciated!
6N137 datasheet: https://www.tme.com/Document/23c5dd4e02a7db41ce8ad9637e6eba2e/6N137S-L.PDF


texts: FFT in oscilloscope measuring Frequency spectrum

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I am using a Keysight InfiniiVision MSOX3054T Scope having Bandwidth of 500MHz and Sampling rate of 5Gsa/s.

I am learning to use the FFT Option in the scope.

Below is the waveform I captured of my QSPI Clock signal (48MHz)

My start frequency is 30MHz and Stop Frequency is 60MHz.

What is the threshold and the excursion levels (marked in red) mean? How to play around this value?
And how is the -4.97dBV calculated (again marked in red)? Can someone show the calculation for the -4.97dBV value?


texts: Unkown distortion in low power push-pull amplifier

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I'm trying to make a small headphone amplifier, and I started out simple: I'm using a LM358 opamp to drive a push-pull stage with a pair of BD transistors.

I started by trying a single channel (only one of the sides of the headphone) so I could check it and then double it to the other channel.

Here's the diagram for the circuit I built:

The load impedance (my headphone speaker) is 32 ohms.

In the input, I added a 1K resistor to the ground (before the capacitor) just to provide some relevant input impedance, as the headphone output expects some.

The circuit keeps every DC point where it should be: The voltage in the opamp output is VCC/2, the voltage in the push-pull output (before the capacitor) is also VCC/2, and there's a constant 0.2V voltage across the emitter resistors (which gives a quiescent current of 10mA).

However, there's a strange distortion. When I play anything in a very low volume, the sound is perfect. If I turn the volume up, it starts distorting really badly all of sudden, specially in low to mid frequencies, and if I keep turning it up, the distortion get's weaker, and the sound seems better again (but still distorted).

Of course, If I turn it up even more it'll start distorting again as the output voltage swing will reach the max peak and will start clipping, just the classic overdrive.

If I play a (quiet) sine wave on it and then start turning up the volume, the impression that I get is that, at some point, a square wave of the same frequency is suddenly "mixed in" in the sound, but as keep turning the volume up, the square wave doesn't grow louder in the same pace as the sine wave, so the distortion gets less perceivable in contrast.

It doesn't sound like crossover distortion (I mean, it is similar to it in the actual sound but the scenario doesn't point to it), the transistors are well biased, even too much, 0.2V is a bit much for the voltage across the output resistors. And if this was so, there would be trouble in lower volumes too, but the sound is perfect.

Maybe the output stage is requiring too much current from the lm358 output?

But if it is, why this distortion doesn't grow worse and worse?

I can't figure this out and the simulations doesn't help, they just show clipping after the output amplitude reach +-2.4V, but with this amplitude I should get something near 80mW RMS in the headphone speaker, which should be quite loud.

This sounds like the amplitude I get in the high volumes before overdrive, so my guess is that this distortion I'm getting doesn't appear in the simulation at all.

Any ideas?

Thanks!

Ps.: If someone saw my trouble with lm358 in my last post, just ignore it, it was a simulator flaw, it works well in reality. When I say things work in the simulation is because I simulated it with both a 741 opamp and an ideal opamp, and the result is the same, that distortion doesn't appear.

Using a 741 in the place of this LM358 in the simulation, and using an AM voltage source with a 100Hz carrier and 1Hz modulation (just to have an increasing amplitude sine voltage in the input), I plotted the output voltage, and you can see that no distortion show up except from the overdrive when it clips:

Plot in the low volume range, the horizontal scale is 20ms/Div and the vertical scale is 100mV/Div:

Plot in the same time window but now with a 1V/Div vertical scale:

Plot with the same vertical scale as before but further in time (when the voltage of the AC source increases and reaches overdrive)

As you can see, no distortion appears before the overdrive

Here's the plot differential voltage over R5 in the same time window of that first plot and with a 200mV/Div vertical scale:

As it's visible here, in that time window, the PNP transistor reaches full cutoff but this causes no distortion on the actual push-pull output, as shown by that first plot.


texts: How to produce five outputs, one low, shifted on clock edge. 74HC logic

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I want to produce five outputs, one of which should be low, unless the circuit is in reset, when all should be high.

The repeating sequence, on a rising clock edge, should be:

      qqqqq
reset 01234
  1   11111
  0   01111
  0   10111
  0   11011
  0   11101
  0   11110
  0   01111
      .....
  1   11111
  0   01111
  0   10111

Holding the circuit in reset should cause all outputs to be high.  When the reset is released the bit pattern should begin again from 01111.

Can I do this is 74HC logic?  I've looked at shift registers, but one problem is that they have a "clear all" input, not a "set all".

Is there a different approach?


texts: EMI difference between Ferrite (powdered iron) and Iron

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In an EMI application where I'm applying a snap on style ferrite core around a cable.  What's the difference / benefit of the typical powdered iron type and just using a similarly sized piece of iron with a hole in it?

I could see where it would be easier to manufacture a powdered core and maybe more rust resistant?  I don't know what the electrical differences are.


texts: Return Path of Bypass Capacitor in a PCB with 2 Grounds

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I have a PCB with two power rails, 5V and 12V, and two ground pours, GND-5V and GND-12V, respectively. The two ground pours are tied at one point (close to the connector).
I'm powering a DAC off the 5V rail and buffering its output using an opamp that is also powered off the 5V rail. The output of the buffer is fed to the control pin of a DC-DC converter that is powered off the 12V rail.
The datasheet for the DC-DC converter suggests a 0.1uF bypass capacitor for the control pin.

Should the return path of the bypass capacitor (shown as Cb in the image below) be GND-5V, as any spikes would be coming from the 5V rail, OR should it be GND-12V as that's the converter's return path? Note that the both the opamp and the DAC have bypass capacitors as well.


texts: Is there an electronic device that stays "on" until the current through the device reaches a certain level?

texts: I have the vague recollection that a device like this exists. The device is gated on, after which it approximates a short circuit, until the current through the device rises to a set level, at which point the device turns itself off until the next gate signal. Am I making this up, or does such a thing exist?


texts: How to control a matrix of electromagnets

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I'm trying to design a matrix of electromagnets, but I'm having trouble on figuring out the control schematic. I need to control the 12V 70mA coils using an Arduino Uno (5V 40mA max output).

Originally I was thinking of each coil having a transistor and it being controlled by shift registers, but that amount of transistors and signals (1 transistor and 1 shift register pin for each coil basically) is quite a lot, especially since my matrix is 18x10.

My next idea was using optoisolators to use standard multiplexing but have it act as a transistor. Each coil would have one, and I was fine with this because it minimizes signals (only row and column signals). The problem is that I could not find an optoisolator that could by itself handle the load. So I had to include a complementary transistor and resistor, which made the PCB extremely clogged and will make me sad when I have to solder everything together (180 times).

Is there a way to use multiplexing or something that can reduce the amount of components I have to use.

If it helps, I will never have more than 1 coil on at the time in each column.


texts: Effect of capacitor type in an active filter circuit?

texts:
Below is a unity-gain low-pass filter implemented with a Sallen–Key topology:

If C1 and C2 is large, are electrolytic capacitors recommended?
Similarly, if C1 and C2 is small, are any type of ceramic capacitors recommended?

What types of capacitors can be used if C1 and C2 are in uF range and nF range for a good filter application?

I cannot find information on this.

EDIT:

Lets say the desired LP active filter cut-off is 50Hz.

I go to this amazing Sallen-Key Low-pass Filter tool and set R1=R2=3.3k and C1=C2=1uf.

And I obtain 48Hz cut-off.

These tools do not show the types of the caps.

And depending on the opamp I get TOTALLY different results in SPICE simulations.

So basically some tools do not suggest an opamp and some tools do not suggest capacitor types. And some tools offer weird resistor values like 3.1235869804k

My specs are as follows

Bandwidth -3dB = ___Hz
Frequency tolerance = ___%
Gain at DC = ____  with tolerance ____%
Bandstop rejection >=____ dB  at frequency ____ Hz
Band pass ripple <1dB Butterworth?
Maximum R value should be___ ?  due to Iio error=___uA

I have tried http://www.ti.com/lsds/ti/analog/webench/webench-filters.page

and my result is ......


texts: How to improve peltier efficiency, use a CPU cooler?

texts:
I could really use some advice here.

I am currently using a cooled/heated seat cover in my car that uses a peltier circuit to either cool or heat water and that water is then pumped through a matrix pad that is on the seat bottom and back.

Here are some photos of the product in question so you can get an idea of what is involved (all photos from the retailer's website):

I was curious if the cooling/heating ability of the peltier circuit would be improved if I added a CPU cooler like this:

I am not an engineer, and I don't play one on TV (or the internet) so I was hoping to get some educated advice as to whether or not a CPU cooler would help this product cool the water even more than it already does.

Not sure if it is relevant or not, but I am in south Florida and drive a convertible, so in-vehicle temperatures are closer to ambient than they would be in a hardtop.

Here is a photo of the heat enchager/pump unit in the car. It sits behind the passenger seat:

Thanks so much for any layman-friendly help or advice you can offer.


texts: Name of a single-conductor coax test cable

texts:
Alright, bit of a silly question but I can't seem to get Digikey or Mouser to show me what I want.
I'm wanting to replicate Fig. 7 of this INA116 datasheet almost exactly. Before I go and buy this expensive IC, I'm mapping out how I'll build the coax setup at the top of Fig. 5; I'm having difficulty figuring out what cable and connector I'll use, though.

What I'm imagining is a single conductor coaxial cable that features a BNC or SMA at one end and a minigrabber / alligator clip / kelvin clip / similar at the other end (I use a mix of custom and standard electrodes with both planar and pin contact geometries); the BNC or SMA allows me to tie the coax shield to my guard loops on the PCB. However, the search terms I'm using for Digikey and Mouser turn up either unterminated coax spools or BNC test cables where the connector shield is just a separate wire (therefore, not coax at all).
Does someone know what the correct search term is for what I'm looking for? Or is this something uncommon enough that I'll have to make custom cables?
Thanks!


texts: full wave rectifier is not rectifying the wave properly

texts:
the following rectifier does not create a wave that is rectified evenly. according to the books this should work when using a centre-tap transformer.

scales : (Y = 10ms/div) & (X = 5V / div)

peak values : (smaller pulse = 1.53 V) & (larger pulse = 3.59 V)

Software: NI MultiSim 13


texts: What are the resistors for in bipolar transistor based NOR gate?

texts:
In general I think I understand how this NOR gate works.

What I don't understand is, why (in a very general view) there is a need for the resistors in this circuit.
Especially the 4.7k Ohm one.

I assume the 10k Ohm resistors are normal base resistors to limit the base current?


texts: Decoupling capacitors in a bjt amplifier, polarity

texts:
The circuit is not important, my quesiton is for example, for C3, while using an electrolytic capacitor(I assume for a 100uF, electrolytic is the most common one); which side should be connected to the + terminal of the capacitor? Right or left? Why?

Thanks.


texts: How is heat generated to start combustion in an incinerator?

texts:
I see many diagrams on the internet that show a layout diagram of an incinerator that has a combustion chamber connected to a boiler or gas turbine to capture the energy mechanically or generate electricity and a gas scrubber to filter the exhaust from different types of particles before discharging to the atmosphere.
For example:

What's missing is the apparatus to start the combustion. Typically, it could be natural gas or fossil fuels in the same way a campfire or barbecue pit.
Is it possible that electricity alone can be used to generate heat that would cause the incinerated materials to start combustion and provide the fuel for more incoming materials?
For example, if I had a three-phase existing oven, could the heating element be used as part of the incinerator component?
If electricity is solely used as the fuel source without a combination of other fuels to start the first combustion, how effective would it be to generate back the electricity/heat energy from subsequent combustion?


texts: Non-standard frequency crystal replacement

texts:
I'm new to DIY electronics therefore this might well be a noob question.
I'm trying to upcycle a brushless DC motor salvaged from a printer and I accidentally broke a crystal's pin [edit: on the associated driver's circuit].
I tried to find a replacement on the usual RC,Mouser but I don't seem to find the frequency stated on the pcb or the part no printed on the component: XTAL1 4.437M - D437D0C(not sure if the penultimate character is a zero or a letter O)
I guess that it's a 4.437MHz crystal and it might be custom made, be damned patented parts :)
The closest I found are these:
http://au.mouser.com/Passive-Components/Frequency-Control-Timing-Devices/Crystals/_/N-6zu9f?P=1z0wmuu
I don't have a scope and my multimeter cannot measure above a few KHz to test the actual frequency.
My question is whether it's safe/viable to use a crystal with similar frequency or, alternatively, build a frequency multiplier without having a major in physics.


texts:
I've got a couple of these 9001-05-01 reed relays. I've tried activating them by applying 5 VDC voltage through pins 2 / 3. This connects pin 1 to pin 4, as I expected. But, after disconnecting pins 2 and 3, the pin 1 remains connected to pin 4 indefinitely (for days, at least). I thought this particular relay is not a latching relay. Have I misunderstood something, or do I have defective units? Or, do I need a diode?

To the best of my knowledge, I do not have strong magnetic fields around.


texts: How to bypass minimal load limitation on a power switch?

texts:
I got a power switch which seems to have minimal load that makes it incompatible with LED lights.

Schneider GUPA1411BSS 1 Gang 1 Way PIR Switch  — after unpacking I found it has only L, L1 and earth connections and a min load of 20W (220v). When mounted it fails to fully power my led light which are probably around 16W and is buzzing (lights blinking).

Product page at https://www.schneider-electric.co.uk/en/product/GUPA1411BSS/ultimate-screwless-flat-plate---occupancy-sensor-with-override---flush---2-wire-/ seems to miss that aspect.

Is there something I can do to make it work?

Updated info from the instrusctions:

  Rating 230V ~50Hz
  Max Load 150W/150VA
  Min Load 20W/50VA

  When using 12V electronic transformers, ensure that the minimum load
  on the circuit is no lower than the approximately 70% of the rated
  transformer load i.e. for a 65VA transformer, the minimum load would
  be 50W.

The transformer that I have on the LED lights seems to be 35W but I have no idea which is the effective load. It came with the lights and it has a feature where if powered down-and-up <5s it would switch the LEDs to dimmed mode. Sadly I can no longer reach the transformer a huge mess in the ceiling as the light panel was glued to it, so I am looking for a solution on the light switch side (wall).


texts: Im trying to run FreeRTOS on ATMega328P and with two tasks its works well, but when i put one more  task, no one is scheduling, I got the return of CreateTask of all tasks created and is right, all of it returned pdPASS, so all was created, and the vTaskScheduler() is executing, but if i try to print something from within of the task no one show something, so no one is in the ReadyState i think, the idle Hook function also dont execute.


texts: How to detect if a TRS cable is connected to a MP3 player output?

texts:
Imagine I have a MP3 player and one male-to-male TRS cable that could be connected or not to the output of that MP3 player on END1. By having a multimeter on the other end END2 of the cable, how could I detect if the cable is connected there or not?

How do I have to do in order to proceed on that?

This is the multimeter I have:

and this is END2 which I will use for my measures:

Could  you let me know on what position do I have to configure the multimeter and how to interpret the measures? I'm a bit new on electronic so details are welcome for me.

Thanks!


texts: Can one use 5A transistor for motor driver of BLDC motor 920kv?

texts: I am designing an esc for 920kv motors. For Code testing purposes on microcontroller, I want to make a low speed circuit but only have TIP122 (5A transistor) available in hand. Can they handle ESC control of EMAX 920kv. I will be using 3s battery to power the motor.


texts: What is the difference between SDA protocol and I2C?

texts:
A manual for Sound Design Technology's "DSP Programmer" programming box has the following statement:

  Hearing aids based on the Sound Design Technologies Wolverine platform
  can be programmed from a PC and fitting software using an I2C
  compatible programming interface box. The Wolverine platform natively
  supports standard I2C communication across the PC interface (PCIF)
  with 7-bit addressing and the 400 kHz fast mode communication rate.
  PCIF also maintains communication with the SDA protocol.

A related document, "Application resource Kit (ARK) User's guide" from ON Semiconductors has the following statement.

  When this option is selected, the software determines if the selected
  programming box and connected device support I2C communication. If the
  software determines that the I2C protocol is supported, the software
  sends commands to the connected device using the I2C protocol. If the
  software determines that either the selected programming box or the
  connected device do not support the I2C protocol, the software sends
  commands to the device using the SDA protocol.

I am using Sound Design Technology's DSP Programmer v3.0 programming box and the ARK software to communicate with a DSP chip (R3910). The chip has SDA and SCL pins for programming (firmware update, parameters update). When I update some parameters for the chip from the ARK software user interface, I can see a stream of bits transmitting in the SDA pin on an oscilloscope, but the SCL pins stays high. I was assuming the ARK software on PC and the programming box were using the I2C protocol to communicate with the chip, but since the SCL pin did not change at all I am not sure what is going on.

What is the SDA protocol? Searching google is only giving me descriptions of the I2C protocol, as almost all of them contain the text SDA. Searching for something like "difference between SDA and I2C protocol" gives me the same results. The manuals for ARK and programming box are clearly differentiating between I2C and SDA, but I am not sure what keywords I should be searching for on google.

What exactly is the SDA protocol and how is it different from I2C? Also please provide a link to a page or document.


texts: Does a CE amplifier draw more power when it is amplifying than it is sitting idle? In quiescent mode the power consumption would simply be Vcc * Icq. How about the power drawn from the DC power source when it is driving output at full swing? Would it be the same as in quiescent mode?


texts: How do I come up with a list of requirements for a microcontroller for my project? How can I then find microcontrollers that fit?

texts:
I have been working on an eBike control project on the Arduino MEGA2560. The program runs 3x PID control loops, one battery capacity control loop (interpolation based on lookup tables), a speedometer (samples based on a reed switch) as well as an LCD screen to display information. Its inputs are 3 analog signals: battery voltage, current and user throttle input as well as a digital input: speedometer (reed switch) on/off signal. Currently, with all this running on "long" arithmetic the Arduino manages to complete 10 loops per second. As the TFT LCD screen takes tremendous amounts of computational power, I am thinking of replacing it with an Alphanumeric screen.

The outputs consist of an analog throttle signal going to a motor controller, the LCD screen and potentially a few other devices requiring analog signals. Thus, ADC converters are essential and DAC would be very useful although I am currently using the Arduino PWM output with an RC low pass filter. Similarly, the capacity to read digital and analog signals without interrupting the processor would be great.

I would like to potentially make a consumer product out of this, hence I want to build my own platform from the ground up with a different microcontroller that could give me at least 100 samples per second (10 times what the Arduino is achieving). Also, to avoid floating points, my calculations use long variables and consequently numbers larger than 16 bits, so I'm assuming a 32bit MCU would be a good idea. Also, a MCU able to do floating point calculations could be interesting to simplify the maths in the code.

In the end I am not sure how to start looking for MCUs that would satisfy these requirements and allow a swift transition from the Arduino environment. Any guidance on how to go about finding such MCUs would be greatly appreciated!


texts: What is difference in the design steps between designing an OPAMP vs Miller-OPV?

texts:
I am given a task as:

  Design an operational amplifier (Miller-OPV, 0.35μm) according to the
  introduced design plan and the given lab technology that meets the
  following specification:

What is the difference between normal opamp and miller opamp?

Are there any good design steps for Miller-OPV?


texts:
A common photodiode amplifier circuit (Horowitz and Hill 2nd edition, pg. 253 figure J)  looks like this:

simulate this circuit – Schematic created using CircuitLab

I am currently working on a project that requires detection of power in an infrared (1550nm) laser. The photodiode/phototransistor is from an older project in the lab I work in and I cannot find its part anywhere online.

My question is this:
There are 3 leads. One of them is presumably for grounding, and the other two have the signal across them. Assume I operate the photodiode in photovoltaic mode. Since the two leads that have the signal also have the characteristic diode drop of .7 Volts, this amplifier will have a DC offset which will cause it to rail. How can this possibly be a functioning circuit?

I suspect that my misunderstanding stems from the fact that this is a transimpedance amplifier, so the DC offset is somehow irrelevant, but I would like some clarification and insight.

Edited my question to include a question!


texts:
I'm pretty new to ESP8266 and all these low-level stuff. I recently purchased a ESP8266-01 and started learning about it and playing around with it, and I have a few questions:
First, I found on the web the following table

which specifies the GPIOs of the ESP8266 processor. From what I'm getting, these are the pins on the bare-boned ESP8266 itself, which is embedded in the different versions of the ESP8266 like my ESP8266-01. This means that I can't really use these, rather I can only use the broken-out pins (In the 01 version these include GPIOs 0,1,2,3). Am I getting this right?
If so, it brings me to my second question: I've started reading a bit about the different communication protocols such as SPI, UART, I2C, and I've read (here and here) that the ESP8266 can communicate using these protocols. So for example GPIOs 12-16 are used to communicate using SPI. GPIOs 1&3 are used to communicate using UART, and 4&5 using I2C.
I wonder what exactly does this mean. There are 2 ways I can sort of understand it:

Those pins are connected directly to the processor, and the processor is communicating using these protocols. So if we take UART e.g., the processor knows it needs to send or receive packets in with this number of bits, 1/2 stop bits, baud rate, etc.
Those pins belong to peripherals, meaning that there are dedicated hardware components on the chip for those communication protocols, and the processor talks to those peripherals using the bus.

This question is for educational purposes.
Another question which is more practical is: Since the GPIOs for SPI are not broken out in the ESP8266-01, how can I use SPI?


texts: Is it better to route Ethernet on the top layer, or to use vias?

texts:
I'm making a circuit board with Ethernet (PoE if that makes a difference) coming in through an M12 connector, passing through magnetics and a PHY and going to a micro. I've always heard that there are two things to be avoided when routing high-speed signals: vias because they mess with impedance (which I've matched pretty closely to 100 Ohms) and routing on the top/bottom layers because EMI/EMC.

I've already had to use some vias when routing from the M12 connector to the magnetics due to pin layout, but the stretch from the magnetics to the PHY is currently on the top layer only. I'll only be using 10/100 speeds, the routed length is about 20mm, there can/will be a ground plane underneath the signal, everything is length-matched.

Which is the greater evil? Having vias or routing on the top/bottom layers? Does it matter at all at that speed/trace length?

Here is the original layout:

Here is the layout after rerouting the input to eliminate vias. Since only 2 pairs are used in 10/100, I didn't bother with length matching/single-layer routing for the other two:


texts: Ideal analog switch to replace BJT / MOSFET in the modern world

texts:
When tackling with the very common need of toggling a current with an output from a microcontroller or similar chip, solutions have varied over time.
The oldest solution is to just use a BJT. This works reasonably well, but one has to verify that the gain is suitable for the use and requires the microcontroller to constantly drive the transistor when switched "on". The current may be neglible, or it may not.
The next solution is to use a MOSFET. Modern MOSFETs seem to switch nicely even with 3.3V voltages and have very low on resistances. Gain is no longer an issue, and no need to constantly drive the MOSFET but the microcontroller still has to drive the MOSFET when it is switching. These currents are sometimes pretty high, so the MOSFET needs to be selected carefully.
Then there are Analog Switches (bilateral switch) which require separate voltage inputs but which seem to offer even nicer characteristics: very fast switching speed, very low power usage, very low drive currents, very low on resistance, etc. And obviously having a SPDT switch is nice in some situations.
So, I am asking, what is the modern world ideal component for these sort of situations? Is analog switch the holy grail, or is there something even more suitable? Or are MOSFETs actually better if you just pick the right one?
The usage situations I am thinking of are just switching low voltage low current lines with no special requirements - the sort of solutions that would've gotten a 2N2222 transistor years back.
The wishes I would have for an ideal component:

Supply voltage either 3.3V or 5V
Input voltage suitable for LVTTL, TTL, CMOS inputs
Low on-resistance (<1 ohm?)
Fast switching times (<100 ns?)
Bidirectional current flow (although usually not really necessary)
Safe for the microcontroller (no back-current?)
No need for high current operation, 100-200mA is probably fine.
No need for high isolation, although it would be nice if the switched voltage could be 12V
Cheap-ish, let's say sub-$1
Small SMT package

In general, something that could be used to replace 2N2222 or say BSS138 in most simple situations.

To quote wikipedia on 2N7000 MOSFET:

The 2N7000 is a widely available and popular part, often recommended as useful and common components to have around for hobbyist use
The 2N7000 has been referred to as a "FETlington" and as an "absolutely ideal hacker part."

I guess what I am looking the analog switch equivalent of this, if such a thing still holds any benefit over just using something like that.


texts: How can I scan a One-Wire (1-Wire) bus for all connected devices and list their IDs

texts:
I have written a One-Wire (1-Wire, OW) controller in VHDL for FPGA designs. Currently I use a USB-OW adapter from Dallas/Maxim on my PC to get the sensors' IDs. I would like to scan the bus directly from the FPGA and collect all IDs on that bus.

How can I do this? It should be possible, because the shipped software from the USB adapter can list all devices on the bus.

Enumerating all devices is to slow, because OW has very long IDs. I used this technique on I²C, because there are only 127 addresses to scan :).


texts: Interpreting Fourier transform of Images

texts:
I'm new to image processing and am learning about the Fourier transform. I've read that FT decomposes a function to its constituent frequencies. However, I'm not sure how to tell which is a low frequency or high frequency region in an FT image and why the transforms are shaped in the way they are.

For instance, in the image above why is the FT of the line oriented in the opposite direction and why is there a bright dot at the center of the random noise image? What are the ways the FT can be helpful here? Also, is there a trick or a general method of analysis that would work for a better understanding of FTs across a variety of images?


texts: What is the difference between a super capacitor, an ultra capacitor, and an industrial capacitor

texts: What is the difference between super capacitors, ultra capacitors, industrial capacitors and hybrid capacitors?  I see these names thrown around but they seem to have blurred definitions.  Are there specific properties for each type?


texts:
What is the normal convention(safe and reliable), should one connect NPN transistor base to ground or should a resistor be used?
My logic tells me that in common emitter mode, shorting base to ground turns off transistor so no current flows between emitter and collector and also base current must be zero. If current is zero there is no need for resistor?
At the same time I think there should be some minor base capacitance that will discharge when base is shorted and thus could exceed rated base current? (However I cant see base capacitance mentioned in  BC817 datasheet)

simulate this circuit – Schematic created using CircuitLab


texts: How to (cheaply) measure power usage of a 250V socket

texts:
My air conditioner runs off a socket providing 250V, 15A. I'd like to figure out how much power it's using in a cheap way, so I can budget how long to run it.

Ideally, I'd be able to plug in something like a $25 Kill A Watt. But no, that's 120V-only. Everything else is just damned expensive (I may as well run the aircon all month instead of paying $200 for The Energy Detective...).

Is there anything I can do? Looking at the electric meter isn't an option, I don't have easy access to it in my apartment block.


texts: Calculating the Running Corrleation of two signals in Matlab

texts:
I am currently using https://www.eecs.umich.edu/courses/eecs206/public/lab/ to advance my matlab skills. Sadly I am stuck at lab2 task 2. First, i cant run the pcode file to get the proper solution because matlab always complains about Warning: Skipping argument 'run_corr_demo', no MATLAB code found.> In pcode (line 211)
and my second problem is the output of the correlation, which should be zero because there is no correlation between these signals right?

Running Correlation of Code1 and Code 3
Maybe anyone has an idea of what I am doing wrong?
Here my code:
function out = run_corr(x,y);
%function out = run_corr(x,y);
%
% RUN_CORR -- This function implements the "real-time" running
% correlation algorithm.
%
% Input Parameters:
% x -- the signal to correlate with (i.e., the transmitted signal)
% y -- the signal to correlate against (i.e., the received signal)
%
% Output Parameters:
% out -- the resulting correlation signal with size equal to
% length(x) + length(y) - 1
% Written by Mark Bartsch, Winter 2002
% Modification History:
% 8/16/02 -- Added modification history (MB)
% Initialize the output vector to all zeros. It should have
% length(x) + length(y) - 1 elements.
out = zeros(1,length(x)+length(y)-1);
% Make x and y column vectors, regardless of incoming size
x = x(:);
y = y(:);
x = x.';
% Beyond the end of the signal y, the input is zero
y(end+1:end+length(x)) = 0;
% Buffer is just a column vector. We initialize it to
% all zeros (with the same size as x) to begin with.
buffer = zeros(size(x));
for n = 1:length(out)
% current_sample is the single-sample input to our "correlation box"
current_sample = y(n);
% Update the buffer. Discard the first sample in the buffer, and put
% current_sample at the end of the buffer.
buffer = ([buffer(2:end), current_sample]);
% From x and the contents of buffer, we can calculate
% the next output sample
out(n) = x*buffer.';
end


texts: How to get LiPo battery protection circuit's function and schematic

texts:
I have three single cell 500-730 mAh LiPo batteries at home. I would like to know if they have an on-cell protection circuit (I can see it in one of them, and I think the others also have it) and what this circuit exactly does. If possible I would also like a schematic of their circuits (with the name and value of each component). I tried to find that on Google, but since I was't able to find a specific datasheet and I haven't any idea of what the circuit in my batteries looks like it's really hard for me to find something useful.

Where could I find the schematics of those circuits? (This is not essential for me, but I'd like to have them...)
And, more important and useful, what does this kind of protection circuit do?

Here is a picture of my cells, I don't have any other information about them (I bought them quite a long time ago and I don't have any receipt or something like that).


texts: WIll the multimeter continuity test on the SOIC - DIP adapter spoil my IC?

texts:
IC : L9637D for ISO 9141 bi directional serial comm. Multimeter: Mastech

I am mounting an SOIC 8 IC on an adapter(regular Soic to dip adapter), so I can mount the adapter on a bread board for use.

I want to ensure that the pins of my SOIC pins are clamped correctly and firmly, so i use the continuity test between the DIP pin (say DIP pin 1 of the adapter) and the SOIC pin (pin 1 in this case), to see if there is contact in Pin 8, and repeat this for 8 pins.

Will this type of testing damage the IC? Obviously i thought that current wont be flowing directly through the IC in this case. These ICs are incredibly tough to get and common sense tells me it wont but just to be sure.

PS : i am not testing between pins of the same SOIC, just between the adapter and the SOIC. Thanks for any of the help :)


texts: What is happening, physically during a Transmission Line Reflection in a closed and open circuit scenario?

texts:
I am having trouble understanding what is happening physically during a transmission line reflection, in particular the short circuit and open circuit case. I understand that when when a transmission line is terminated with a resistance equal to the transmission line impedance, then

$$ \Gamma = \frac{R_T - Z_o}{R_T + Z_o} = 0 $$

which means that there is no reflection, and physically it makes sense because the resistor is dissipating power through it, and so therefore the wave cannot propagate back. However, I don't understand what is happening in the closed and open circuit cases.

In this post On a transmission line why are voltage and current waves reflected at a short circuit? the answer makes sense in a power perspective for the short circuit case, but I don't understand why the reflected wave is inverted. This post Transmission Line reflection. I would like a non-mathematical explanation seems to answer the question with

  But now we have another unstable situation: That end of the line is at 0V, but the rest of the line is still charged to Vs/2. Therefore, additional current flows into the short, and this current is equal to VS/2 divided by Z0 (which happens to be equal to the original current flowing into the line). A voltage wave (stepping from VS/2 down to 0V) propogates in the reverse direction, and the current behind this wave is double the original current ahead of it.

but I don't understand why additional current flows into the short. Is this some application of Len's Law? Or is there something that I am missing? Also, what happens when the reflected wave reaches the voltage source? There would be an enforcement of some voltage so would it be inverted again?

For the open circuit case, I understand that voltage "Piles up" at the end of the transmission line since there is no path for it to continue traveling, but why is it twice as much voltage as what is started with? Mathematically, it makes sense, but I still don't understand this physically.

Any help would be great, I am very confused about this topic and would like to get a firm physical understanding before accepting the equations. Thank you!

edit:
I walked through the equations a few hundred times, and was able to figure out what is happening physically.


texts: Operating a stepper motor through a driver circuit

texts:
I currently have what I've gathered is a rather old custom made stepper motor driver attached to a stepper motor and am unsure how to actually operate it.  I have looked around online and gathered a typical setup for driving this type of motor involves 2 H-bridges but I'm not sure how the setup I have will translate to properly operating them.

I believe the stepper motor is a bipolar 2-phase stepper motor.  You can see several specs at the top including TTL, input voltage, output current, and clock input (I don't exactly know what clock input means).

Here is a picture of the driver:

The inputs and outputs are labeled (and in parentheses are the configuration I found them in):

  1-Motor Phase 1 (hooked to motor)
  2-Motor Phase 2 (hooked to motor)
  3-Motor Phase 3 (hooked to motor)
  4-Motor Phase 4 (hooked to motor)
  5-Outputs off (grounded)
  6-4 phase/3 phase (no wire)
  7-Enable (looks like it is wired to 13)
  8-Enable A (wired to nothing)
  9-Clock Selection (wired to 12)
  10-Direction ccw (wired to nothing)
  11-Clock cw (wired to nothing)
  12-GND (wired to 9)
  13-Voltage supply (wired to 7 with another wire going to nothing)

I have found some information for other products that seems to indicate I would need to put the specified input voltage to 13, pulse 9 with 15 microsecond square pulses, then hold 5-8 and 10-12 either at 5V or ground to change basic operating configuration.  Is it that simple or am I missing something critical?
I apologize that this may be rather low level stuff here but any information on how to operate this would be very much appreciated because there is no manual for this piece of equipment.


texts: Why can't I assign pin 18 on Lattice MachXO2-256-HC FPGA in my design?

texts:
I'm using a Lattice spreadsheet view inside of Diamond with a MachXO2-256-HC-4TG100C.  When I assign pin 18 to a port on my design, I get an error:

ERROR - The pin [18] is not user assignable and cannot be assigned to the port [clk_sel_in]; for details, please refer to the device datasheet.

phys pin on board is connected to slide switch, gnd on one side, n/c on other side, pulled up in fpga.
datasheet says pin 18 is just PL7B on Bank 1
there are no special functions associated with the pin.
all special functions (except JTAG) are disabled just in case in global preferences
I don't see any asterisks anywhere in DS1002 for the pin/package.
Other datasheets / docs I've checked TN1199, DS1035, TN1204, DS02056, Design Planning Guide, Diamond Users Guide.

I've only used one lattice on one other project so very possible I'm doing something silly or don't understand something about how they do things.  Does anyone know what may cause this?  I'm using Lattice Diamond 64-bit on Windows version 3.11.2.446.  Thanks in advance.


texts:
My question is about the resistor for termination in a CAN network.
From an electrical perspective why should we add this resistor (commonly 120 Ohm) between the CAN_H and CAN_L?
Thanks in advance.


texts: Why is a 12V 3-wire CPU fan very slow at 12V input?

texts:
I play around with an old 3-wire CPU fan from a dell server PC.
It is this thing: 3612KL-04W-B66 https://www.coolingsurplus.com/index.php?option=com_content&view=article&id=86:3612kl-04w-b66&catid=6:92mm-fans&Itemid=7

It was mounted at the end of heat pipe over the CPU. It was pulling the air from the CPU to the outside of the case.

I found a datasheet here (https://www.electronicsdatasheets.com/manufacturers/nmb-technologies/parts/3612kl04wb66) but this particular model B66 is not in it, only B50 and B60 and other round numbers and they are all 2-wire fans.

According to some info I found about dell fan wiring, black wire should be GND, red wire is +12V and white wire is TACH feedback.

As I understand the basics of 3-wire brushless fans, I can control the speed by varying the voltage (10.5 - 13.2 V according to datasheet) or low frequency PWM the 12 V input.

As a less experienced fan user I would expect the PWM method to cause the fan to slow down while running at full speed at 12 V. But the fan acts in the opposite way, at least for me.

It spins up to speed for a short period after connecting the positive wire to 12V PSU (made from ATX PSU), then it slows down to very low speed.

When I connect and disconnect the positive wire manually in short succession (0.5 Hz by my fingers judgment) the fan speeds up significantly.

I ask you guys for some advise how to actually control the speed of this fan, roughly and manually.

Edit: I managed to resolve the mistery behind the low RPM at 12 V continous. There is some speed controll built into the fans board. I can see a small part coming out from the side of the stator case. Might be a temperature sensor. I pointet a heat gun at it from behind the air flow. The fan revived to significant speed :-) I am stil curious, what is the white wire for (seems not to be TACH, only bias on the analog scope) and how to get rid of the internal speed control

Edit: Shorting the leads of the termistor (youtube.com/watch?v=AVovy7UWDQ0, is exactly the same fan by the way) lets the fan run at full speed and I can control RPM now by lowering the voltage. The question about the function of the white wire stays in the room :-)


texts: Derive transfer function from block diagram

texts:
I have this block diagram which I already reduced pretty much:

Now I want to derive the transfer function from phi_o1 to q. However I have trouble with the feedback loops since they multiply with each other and I do not know how to reduce that.

How do I derive the transfer function?


texts:
Suppose I have the discharging free source RC circuit as shown below (I am referring to figure a, not figure b):

From this, I can easily calculate that the charge on the capacitor as a function of time is
$$Q(t)=Q_0 e^{-\frac{t}{RC}}$$
where \$Q_0\$ is the initial charge on the capacitor.
I then note that \$I=-\frac{dQ}{dt}\$ and so taking the derivative of my calculated formula \$Q(t)=Q_0 e^{-\frac{t}{RC}}\$, I get that the current as a function of time is
$$I(t)=\frac{Q_0}{RC}e^{-\frac{t}{RC}}$$
But now from Ohm's law (\$V=I\cdot R\$) I can get the voltage as a function of time simply by multiplying my function \$I(t)=\frac{Q_0}{RC}e^{-\frac{t}{RC}}\$ by \$R\$, so that I have
$$V(t)=\frac{Q_0}{C}e^{-\frac{t}{RC}}$$ or since \$V_0 =\frac{Q_0}{C}\$ I get
$$V(t)=V_0 e^{-\frac{t}{RC}}$$
I know that this is the correct answer since multiple sources corroborate it. But now suppose I have a source-free discharging RLC circuit like this one shown.

My textbook (Electricity and Magnetism, Purcell and Morin) calculates that the voltage with respect to time is of the form
$$V(t)=e^{-\alpha t}(Acos(\omega t)+Bsin(\omega t))$$
and I can easily follow the steps as to why.
Then since for our circuit we have that \$I=-C\frac{dV}{dt}\$, we can calculate the current by deriving the voltage formula and we get that
$$I(t)=-C\frac{dV}{dt}=AC\omega (\sin(\omega t)+\frac{\alpha}{\omega}\cos(\omega t))e^{-\alpha t}$$
But now if I simply applied Ohm's law by dividing the original equation for by voltage \$V(t)=e^{-\alpha t}(Acos(\omega t)+Bsin(\omega t))\$ by \$R\$  I get a totally different answer:
$$I(t)=\frac{1}{R}e^{-\alpha t}(Acos(\omega t)+Bsin(\omega t))$$
In this form of the answer, the phase difference between the current and voltage seems to have completely disappeared, so why does the straightforward application of Ohm's law not produce the correct result?


texts: Sensor for very low temperature (liquid nitrogen)

texts:
I'm looking for a way to measure temperatures in range of 40 to -200 °C (100 to −320 °F). The usual DS18B20 digital thermometer works only down to -55 °C (-67 °F).

A precision of 2 °C would be good enough.


texts: Is there a Semisynchronous Buck Topology which mixes the advantages & disadvantages of both?

texts:
I was looking at "What is the purpose of using MOSFET instead of free-wheeling diode in Buck topology?" and the referenced PDF which discusses the trade-offs between a traditional asynchronous Buck with the lower Schottky diode, and the more complicated but more efficient MOSFET which replaces it.  Then I thought, "If you allow the Schottky diode to remain, but parallel it with a MOSFET, you could use comparators to sort of notice the Schottky conducting and turn the MOSFET on, and then turn it off again when the flowing current has decreased enough.  This would improve efficiency, prevent the possibility of shoot-through, and take the synchronous complexity and move it out of the switching chip."  Yet I haven't seen it, so perhaps there is some reason why this isn't done.

So if this does work, it would produce yet another possible set of trade-offs which could be considered.  Meaning that the Schottky diode wouldn't have to dissipate as much heat, and the efficiency of the circuit would improve, at the cost of additional circuitry?  Thanks ahead of time.

=========== EDIT ===========

More recently, I stumbled on something that, to me, makes answers related to this question more important for achieving better efficiency.

In this TI app note about designing an Isolated Buck (Flybuck) Converter, there is a Synchronous Buck with three outputs, as shown:

As you can see, only Vout1 has had its Schottky diode replaced with a MOSFET, and the other two outputs are still sustaining the same Schottky diode efficiency losses as would a standard non-synchrous Buck.

Can those isolated outputs be easily made synchronous?  I haven't seen it so far, but even so, I believe that there are significant efficiency gains to be realized by this method, especially with multiple isolated outputs.  And the cost of extra MOSFETs should be partially offset by smaller heatsinks, and lowered cooling costs because of less heat generated in the isolated output Schottky diodes.

So, does this method exist, and if so, what is the name of this method, and if not, I will in the future ask how it may be done in a separate question, and link to it here.  Thanks ahead of time.


texts:
I'm using an IGBT in a wireless charger circuit as a swtich to send 'pulses' of power across the gap. I have 14V coming from the mosfet driver and I can see around 5v on the collector. I have the emitter connected to ground and the gate connected to the output of the mosfet driver.

Has anyone any idea why I'd be losing 9v across it??

Thanks


texts: How to deal with strobe and balance pins of this comparator for single supply operation?

texts:
I want to use this LM311 comparator with a single supply. But these are pins called balance and strobe which confuses me. What are these for?

In a forum I read someone suggests pin 5 and pin 6 shorted for single supply operation. Should I also ground them? But the data-sheet says: "Do not connect strobe pin directly to ground, because the output is turned off whenever current is pulled from the strobe pin"

These pins should not be kept floating, but how should they be connected in case of single supply operation as a comparator or schmit trigger?


texts: Hartley oscillator with ua741 amp in pspice

texts: I'm trying to simulate a hartley oscillator in Pspice using an ua741 amp. The results are not oscillations..I don't understand what's the problem..


texts: Crystal tolerances and what that means for timer interrupts

texts:
I'm developing a system that needs to periodically wake up and perform a process. We're currently targeting for an hourly wake up (give or take, this spec is very loose).
The key here is the unit cost and I really hope to avoid a real time clock on board. We're even trying to avoid an external crystal, if possible.
I expect some amount of drift if we decide to rely on the MCU's internal clock for timing. However, is there any way to minimize this drift? Is it common practice to calibrate the interrupt timer to reduce drift at the factory?
Are there any other options I'm not considering?


texts: Solar charging a lipo battery with ESP8266 as a battery load

texts:
I am trying to add solar harvesting capability to my IoT device based on esp8266. I am using linear charge controller (MCP 73831) with solar input to charge a 500maH lipo battery.

An observation when the device is active (connected to a wifi AP) and solar input is available, the linear charger goes into CC mode even if the battery is fully charged. Possibly because esp8266 draws around 80-90mA of current on average during wifi connection process. (Solar charge current available is around 30-40 mA on average)

Is this safe? can this result in possible overcharging of the battery. More pointers on this will be highly appreciated.

Adding a diagram of the setup:


texts:
In my parents house, the door is 'unlockable' via a switch. As long as the button is pressed, the door is unlocked.

Since I often forget my keys, I thought to make a WLAN-Switch, which is controled by an app.

The software development part is not a problem, but I have absolutely no clue in electronics. A first thought is some kind of WLAN-module, which is attached on a wire to the existing door opener, and gives an impulse if activated. But

what possible 'thing' exists out there?
where is the best address for such electronic toys?


texts: I am making a schematic of a PCB in Orcad Capture. I have to place a jumper. Does anyone know the part number for a jumper or the library where it can be found?


texts: In a flyback transformer with multiple windings, how are voltages controlled for different current loads?

texts:
This is the flyback transformer I will be referring to:  Wurth 760871543

There are three output windings as follows, 24 V at 0.30 A, 5 V at 1.15 A, 14 V (unspecified but in mA range aux winding).

The voltage which I need to control precisely is the 24 V winding using secondary side sensing.

Here is my question: If the output I am sensing has a very low current load (1 mA), but the 5 V winding has a very high current load (1 A), won't the voltage at the 5 V winding drop much faster than at the 24 V winding?

If this is correct, how would I then go about controlling all the voltages simultaneously?

For example, if I instead sense the 5 V output winding for feedback, would switching the flyback transformer more frequently (to compensate for the larger current load) cause the voltage at the 24 V output winding to increase more than the regular 24 V?

Just some additional background on my design...
I am using a Power Integrations TinySwitch-4 switching controller. The 24 V will get increased to 1 kV through a converter and voltage multiplier. The 5 V will power a Raspberry Pi. The 14 V auxiliary winding will power the switching controller IC.


texts: Interfacing an inductive proximity sensor with a Microcontroller using a sort of PNP-NPN transistors combination

texts:
I'm trying to repair an old circuit based on the Micro-controller S87C751 interfaced with an inductive proximity sensor similar to one already posted here

The sensor is powered +24V.

I followed the circuit paths from the sensor until the input of the Micro controller and i found it wired in the following way:

The uC is powered +5V.

As you can notice, the circuit designer used a PNP transistor combined with an NPN transistor.

My questions are:

1/ What is the purpose of this transistors combination ?

2/ Is it a level shifter ? if yes, is it really necessary ? As i already seen Arduino interfaced with such sensors with only a pull-up resistor not matter power source of the sensor.

3/ During simulation in Proteus ISIS, i simulated the inductive proximity sensor as a switch.  the circuit didn't work, and i get always 0V at the uC input, what could be wrong with my drawing?

Thank you in advance for your help.

EDIT:

I plan to use the following level shifter using two NPN TRs instead of an PNP-NPN  TRs, is it possible ?
I would like to include an LED in this circuit that gets ON when there is Metal detected to save one of the pins of the uC, how can this be possible? i tried including it however a voltage drop will occurs so i'll not get the 5V output.


texts:
I am trying to interface my ATmega chips to the computer using a serial interface. I have read that this can be done directly by connecting the appropriate pin between the chips and the serial pin. But it is advised that I use a MAX232 chip. What is the purpose of this chip and do I really need to use it?

I ask this because in a project I am making, there is a big size constraint and the chip might take up valuable space.


texts:
When shopping for components it's common to find a lead-free or RoHS-compliant version of the part along side one that is not. Under what circumstances does it matter that I chose exclusively lead-free or RoHS (or whatever other lead-free designation is out there) parts? What would motivate me to pick a lead-free part over a cheaper non-lead free part?

On a side note, some explanation of what all this lead-free business is about would be interesting to me.


texts:
I am trying to design a driver circuit for a coil that I am planning to use as an electromagnet. The coil is rated at 12V @ 3A. The part number is FC-6521.

The MCU will output a 3.3V through GPIO (~20mA). I have simulated a design shown below:

The transistor and diode I chose were parts that I own just to make it easier for me to test. I am not very familiar with the resistor values that I need. Can I get some advice for what I need to change? Thanks!


texts: How do sound cards cope with negative voltage?

texts:
I feel this is a basic question but I found no answer for it so far.

Let's take a random sound card that lives within a PC. From the connections at the end of the datasheet I assume that it is powered by 5 V and uses the computer's ground. Maybe it is a faulty assumption, but by some small experiments with my laptop it seems that the audio input and output ground is connected to the overall ground of the computer. So the sound card does not have any fixed negative voltage to refer to.

The waveform of the input and audio should have negative and positive regions. How do the ADC and DAC handle that? If there is any external circuitry that shifts the voltage it doesn't seem so.


texts:
I am trying to design a DC to DC UPS using a Li-ion 5000 mAh battery where my load is between 5 V/4 A - 7 A. My system requires keep running after an outage about 20 mins. The load is a RPI3 with extra hardware and a small motor.

My major concern is the in the boost stage, I am looking for any DC-DC step-up/Booster for 7 A+, but I could not find any most are up 4 A.

I tried some solutions from Texas Instruments, Linear Technology and Microchip but no one fit my requirements

Does any one on the past face a similar situation?

I would like use a lead acid battery, but a big size and weight is not option for me.

details:

DC-DC step-up input range 3-4.2V (it is in Li-ion Battery)

DC-DC step-up output: 5V / 1A to 7A


texts: How to correct/adjust floor temperature sensor resistance to account for calibration error?

texts: I have a heating system with 10kohm floor temperature sensor cable connected to controller unit. The controller displays floor temperature around 7.0 degC higher than reality, the sensor is installed in a channel inside the floor above insulation and below floor boards (directly between heating elements). I do not believe (although cannot confirm) that the sensor head location is compromised in any way, I can withdraw the sensor from conduit and leave it exposed in the room above floor and the display temperature remains the same. The sensor cable is installed in its complete calibrated length. It is the right sensor resistance for the controller, yet the 7.0 degC discrepancy persists. I've tried swapping controller and replacing sensor. I have adjusted the heating set point upwards to account for the discrepancy; the heating system modulates effectively and the relative temperature tracks correctly, but it annoys me that the controller displays heating at 28 degC when it's really around 21degC (confirmed by thermostat in lounge room). Any ideas what I can test or try next?


texts: Trouble understanding Charlieplexing problem

texts:
I am trying to make a circuit that uses 3 pins to drive 6 LEDs using charlieplexing. The cicuit im using is this:

What I don't understand though, is that when I want to turn D1 on, PB0=1, PB1=0, and PB4=high impedance. That turns D1 on, but also D5 and D4, as shown in the other image. I don't understand how to avoid that. Could it be because im using different color LEDs with different forward voltages?

Thanks in advance


texts: How can I produce an analog control signal from -2 to 12V?

texts:
I have a sensitive micro/nano positioning controller that takes -2V to +12V signals as input.  This controller then produces high voltage -20V to +120V as it's own output to actuate a piezo crystal, which contracts and expands microscopically depending on the potential it experiences.

I am aware of how to produce a range of signals from 0-12V DC using a potentiometer and a 12V battery, however, I am not aware of a way to produce -2V to 12V DC signals.

At first I was a bit confused since the potential difference between -2 and 12V is going to be 14V (i.e. "0" to 14V), but then I realized that the controller device itself has it's own "0V" ground, so it's indeed possible to have -2V and +12V relative to that.

I am open to anything since it's critical to get this right, but I don't have too much experience in building electronic circuits using op-amps.  Since I am controlling very small movements using this piezo crystal, I would ideally like to produce these -2 to 12V signals with a digital controller - maybe something that goes from 12-bit or 16-bit PWM input to a -2V to 12V output.  If there is a way to use a potentiometer I could also use a stepper motor to turn it, but I am still confused as to how to get the -2 to 12V.


texts: What "type" of impedance is a schematic referring to when talking about differential signals?

texts:
I'm trying to learn a bit about routing high-speed differential signals. One thing that is confusing me is that often schematics talk about routing certain signal pairs with a specific impedance (usually 90 or 100Ohms). Though while reading into the topic there seems to be quite few different ways to calculate impedance depending on how the signal is propagating through the traces. I'm presented with odd, even, common and differential impedance and when I want to calculate a specific impedance for a microstrip with this tool, it gives me the impedance for all four types mentioned before.

How do I know what the schematic is referring to? Differential impedance sounds obvious but it seems to be a very complicated topic so I don't want to jump to false conclusions.


texts: How to calculate power loss & voltage drop in three phase power cables

texts:
What is the correct formula/method to calculate cable power losses in a three phase system? i'm unable to find any IEC standard outlining the same.
If you consider 3C/4C cables, the manufacturer datasheet specifies the resistance in ohm/km (R). Does this imply the resistance per conductor core or is it for all the three cores added together?
The standard three phase power formula is $$ \sqrt{3}V_LI_LCos(phi) $$
where $$ V_L $$ is the Line-Line voltage (e.g; 415V) and $$I_L$$ is the Line current.
Would my cable power loss be calculated as $$ 3I_L^2RL $$ or $$ \sqrt{3}I_L^2RL$$
with voltage drop as $$ \sqrt{3}I_LR$$ or just $$ I_LR$$ respectively for the above?
$$L$$ is the total cable length.
As I Understand, R values are measured/specified on the basis of IEC 60502/IEC 60228. how is the resistance measured in the case of 3C/4C cables (in terms of setup & process)?
My question in general relates to cable sizing and selection for three phase power applications.
Although I have seen Annex G of IEC 60364-5-52 (which seems quite complicated) as far as voltage drop is concerned. Is there a prescribed way to calculate power loss and voltage drop from the Cable Manufacturer datasheet alone?
This maybe quite simple, but has been bugging me for some time. Thanks in advance for your valued responses.


texts: Car battery capacity in colder countries

texts:
The capacity of the battery is affected when the temperature drops, particularly Lead-acid batteries. So how in cold countries this situation is solved.

In this PDF about automotive batteries at low temperature, they have mentioned the specific gravity of the electrolyte is affected when the temperature dips proportionaly the charge as well. This also observed from the graph.

And also is there is any possibility, I have load of 2 amps apart from starter will it function when the battery capacity is reduced to certain low percentage(eg. 50%)  at the time of temperature drops.


texts: How can I tell if my banana fits in the banana hole?

texts:
Are all banana plugs the same? Can I use these Fluke brand banana plugs and plug them in to this Extech brand phase rotation tester? Will they fit?

What defines banana plugs anyway? Is there an ISO standard or something?
MSC Direct has a better picture of the phase rotation tester that makes it look to me like it uses standard "banana" connections.

But what really IS the standard for banana connections, and how can I be sure that my banana fits into the banana hole?


texts: Common mode filtering a shunt: "active" vs. "passive" strategies (diff. amp vs. common mode choke)

texts:
If you are trying to observe a relative small voltage across a shunt resistor and you are finding common mode noise interference induced in the signal, in what cases would you choose to use something like a differential to single end amplifier across the shunt VS. a common mode choke?
Would a diff-amp topology be used for smaller (instrumentation?) signals in the mV range and a choke for "power supply level" voltages?


texts: Finding datasheets for these transistors

texts:
I have 9 very odd transistors (as I think) that I got from a surprise electronic package from the electronic goldmine. The packaging is the oval metal cases with 2 wires sticking out and the case is the ground (I think). I did a datasheet search and found nothing so I am wondering if anybody has any info on these. I am also wondering if there is any cool circuit I can build with it, and if any are power MOSFETS I could use for a flyback driver (using my 555 PWM generator) Here is the list of what the labels say.
1. Motorola logo
A8W
MEX
8605
2
1587538-1
8734
3
HY-386
40PI
8939
4 Motorola
3007838-00
Mexico
8821
5
12258819
19207
8848
Some are repeats, so that's why there is only 5.


texts: Reading measurements from an oscilloscope. Figuring out rise time

texts:
I have this picture (Sorry for the glare):

The two verticle bars are a at 0.5v and b at 4.5v, or at least roughly at this spots. I need to get the rise time from 0.5v to 4.5v, but I don't understand the measurements on the top right. is it 100 microseconds? or 124.6 nanoseconds? I'm guessing it is the 124.6 nanoseconds.

Thanks for any help!


texts:
On the internet, it always shows that each pin of the IC has its own Boundary Scan register (the yellow boxes)

But looking at BSDL files there are actually more BS registers than pins.

So for the questions:

Is it right to say that there are always more BS registers than pins?
What are the other BS registers used for OR Why are they there?
How can we use JTAG(TAP controller, state machine etc) to find out which are the pin's                                                BS register?

P.S. I have posted this question on StackExchange Reverse Engineering but there werent any reply.
https://reverseengineering.stackexchange.com/questions/9119/jtag-finding-bs-registers-for-ics-pins


texts:
I'm not good at physics, but I'm trying to make a lantern. So I have an LED with this characteristics:

N = 3 Watt
I = 0.7 Ampere
U = 3.4-3.6 Volt

So I connect it to 6V battery, but need ~3.5 V. What type of resistor do I need?

I calculated internal resistance with R = U / I and got 3.6 / 0.7 = 5.14 Ω.  And using this formula I =  / (R + r) I got total resistance of 6 / 0.7 = 8.57 Ω. Here 8.57 - 5.14 = 3.42 Ω of external resistor. Am I right?


texts:
I'm using the LTC5598 IC for modulation. I am confused as to how to properly feed my BaseBand analog signal into the chip.

According to its datasheet:

  The circuit is optimized for a common mode voltage of 0.5V which
  should be externally applied. The baseband pins should not be left
  floating because the internal PNP’s base current will pull the common
  mode voltage higher than the 0.6V limit. This condition may damage the
  part. In shut-down mode, it is recommended to have a termination to
  ground or to a 0.5V source with a value lower than 1kΩ. The PNP’s base
  current is about –68μA in normal operation.

If I understand this correctly, if I want to feed it an instantaneous signal of 0.4V do I set:

BBPI = 0.9V
BBMI = 0.5V

This should satisfy the requirement of having a common mode voltage (Vcmbb) of 0.5V?


texts: How to calculate how long a supercap can provide power

texts:
What's the formula to calculate how many seconds a supercapacitor can provide power when employing a buck/boost converter?

Also, how different would that calculation be when using a pair of supercaps in serie (eg. 2x 2.7V @ 1F)

Example data:

Supercap:
5.5V, 1F;
Panasonic EEC-S5R5V105
http://www.mouser.com/ds/2/315/ABC0000C22-947554.pdf

Buck/Boost (5V out):
XL6009, 94% efficiency; are there other relevant specs?
https://www.pollin.de/productdownloads/D351434D.PDF

Load:
5V, 250mA (Raspberry Pi)

(intended application: to provide a few seconds to save settings at power loss for an embedded RasPi)


texts: Is it better to use a MOSFET with a gate driver IC or a MOSFET with a lower VGS,on?

texts:
I am building an RGBW controller for my room. I will be using an ESP32 with four MOSFETs for each channel. I want to know which is best for fast switching. Do I need to use a MOSFET driver IC such as the ICL7667 with IRFZ44n or is it better to use a lower VGS MOSFET such as the AO3400, or something entirely different?

I'm open for suggestions.

What are the cons and pros for both, since it's only one time investment cost is not the issue?

I will make the PCB, so I prefer SMD components.


texts: On many Arduino sensors, there are most likely a port for, gnd, vcc, and signal/s. On some other sensors, I see there is an "out" replacing an "s". This confuses me because "s" normally goes in analog and output goes to Rx. I am deeply confused. What is the difference between "s" and "out"? I've tried looking at tutorials but all it says is attach "out" to rx. I have an "s" label and there are no other models like mine.


texts: Does all bluetooth modules support RFCOMM?

texts:
I am about to order a Bluetooth module and I wonder if RFCOMM is such a basic feature that it is always (or close to always) supported in Bluetooth modules?

Let's say for Bluetooth 2.0+.

Previously this has never been a problem, and it have always been there, but this might be good to know.


texts:
I am doing a circuit to drive a 5V 70Ohms relay using ESP8266. The max GPIO source current of ESP8266 is 12mA. I got this information from the forum here https://bbs.espressif.com/viewtopic.php?t=139#p600

According to my calculation, the required current to turn on the transistor will be around 7-8 mA. Can someone please cross check this and let me know if my calculation is wrong or correct and I doing it the correct way?

Initially I thought I'd be using an N Channel Mosfet, but I could not do that as I could not fit the LED easily like this. LED is important. I am open for any suggestion using Mosfet.


texts: How would it be possible to avoid contention for a Network on an SoC (or more specifically an FPGA) from two or more nodes?

texts:
In a classical chip, you have a main CPU to perform general processing and it acts as the master on a some bus and other slaves (IO, Memory) usually do not send command or data autonomously. (or at least that is my basic understanding, the master knows and waits a certain amount of time for a response)
Let's say I want to implement something similar to a TPU or NPU. I want to have four processing element cores that receive work instructions from some scheduler. The scheduler can manage when to send instructions for the processing elements to perform work on, but it would have to wait for one of the processing elements to return status of when it finished.
This seems to be like a great theoretical example of using a network protocol instead of a bus to transmit command/data. However, if I were start thinking of implementing it in an FPGA for example, wouldn't the PEs have to drive the same write back to the scheduler? If that is the case, how would I know my scheduler received the correct data and not that of which another PE overwrote due to timing and the distance between the PEs to the scheduler?
I think there is a standard that indicates a PE can attempt to send out data by first reserving the network for a certain amount of time. Then if another PE also attempts to do this, the PE with either higher priority or waited longer would take it. However, I am trying to see how this would work in simulation.
In simulation, I have no info on how to "sense" another PE is attempting to reserve the network. What if I run into a simulation in which two PEs are attempting to establish a connection. Let's say I have an edge detect (where the network routing wires are weak 0 ('L' in VHDL) when idle and a PE attempting to reserve time drives its output as 1) on a PE. If two PEs attempt to reserve network time, how would I disposition that if both PEs just drove the same routing wires?


texts: How does an swr meter directional coupler work?

texts:
How does the directional coupler in an swr meter work? How are the forward and reflected waves separated out from the standing wave on the feeder?

I would like an answer in terms of sine (or cosine) waves, phasors and complex numbers, as well as a non-mathematical description. please.


texts:
What happens when the resistors of an op amp amplifier circuit are replaced with capacitors? Or inductors?

What is the frequency response of such an arrangement?


texts: How can I power my 6-pin PCI Express card without using an ATX power supply?

texts:
One of my older computers has a 365-watt power supply that, for various reasons, cannot be replaced with a new power supply. I would like to upgrade the graphics card in that computer, but all the acceptable cards I can find demand the extra 6-pin PCI Express power connector. After using a few power supply calculators, I've come to the conclusion that the additional 6-pin power connector would push my little power supply over the edge (not to mention my PSU lacks a 6-pin connector anyway).

So, would it be possible to create my own 6-pin PCIe connector that plugs into a regular wall outlet? I assume it would be possible with some horrid freakshow of power adapters tangled together, but I don't know where to start.

Some Wikipedia background info about the power connector I'm referring to:

  PCI Express cards are allowed a maximum power consumption of 25W (×1: 10W for power-up). Low profile cards are limited to 10W (×16 to 25W). PCI Express Graphics 1.0 (PEG) cards may increase power (from slot) to 75W after configuration (3.3V/3A + 12V/5.5A). PCI Express 2.1 increased the power output from an x16 slot to 150W so that some high-performance graphics cards can be run from the slot power alone. Optional connectors add 75W (6-pin) or 150W (8-pin) power for up to 300W total.


texts: Are creepage and clearance value in common standard relative to ground?

texts:
So I have been researching creepage and clearance for a few weeks now and I think I have a pretty good understanding of the concepts. However what I do not understand is some of the interpretations of the standards.

My Question: When UL 61010 standard states a voltage, is that the difference between the two adjacent conduction pairs or is that voltage relative to ground. I think it would be relative to ground but thought I'd ask here.

I am asking because theoretically you can have 2 1000V lines very close to each other and from what I understand there is no potential difference to cause an arc, however I highly doubt that you would pass any certification doing this.


texts: ARM cancel execution of pre-empted interrupts

texts:
I can't seem to find an answer to this in google or the Definitive guide...

Is it possible to from one interrupt, cancel the return to any pre-empted interrupts? For example, I have an ISR which is called when an interrupt driven process needs to be aborted. Presumably, I will have been in an ISR when this interrupt is triggered, so I would like to reset the state of my state machine and cancel the completion of the previous state processing since there was an error. I know I could set a volatile flag but then I would need to check it constantly in the normal process code. I would prefer a much more direct, deterministic way to cancel the pre-empted interrupt.

Additional Information from the comments

I have a 2 processor system with an SPI command/control bus. The slave waits for a command from the master, then executes it and sends a response back. This is driven with some handshaking signals since the STM32F4 series has a useless hardware CS design. The problem I am experiencing from my other question is that after some time, the data returned to the master from a command is complete nonsense (specifically the last value received by the slave x transfer length). The master is able to detect this error and sends an abort signal. When received, I want the slave to cancel its DMA/SPI transfer, and return its state machine to waiting for a command. I can accomplish resetting the state machine no problem, I just want to make sure that when the abort ISR exits, it does not return to continue a DMA or USB ISR which is no longer valid.


texts: Are electrode based, water level monitoring systems safe?

texts:
I want to install a pump control with water level monitoring system.
I've seen all kind of sensors, ultrasonic, infrared, mechanical (Based in pressure switch's / float valves), etc.
One of the most interesting systems, its based on electrodes submerged in water, apparently the system consist of 3 or more electrodes. There is a "Common anode / catode" in the bottom, and other electrodes placed at different heights to detect the water levels. I suppose the controller detects an small electric current between the common electrode and the its counterparts.

What i like, is that there is a lot of commercial systems, so no need to start from scratch. They can detect levels on multiple tanks and activate / deactivate the pump depending of the water levels. But what I'm worried about:

Generally systems require you to submerse electric cables to your tank. If we are talking about drinkable water, it could present a risk of chemical leaching overtime. Most electric cables have PVC with fire retardant's. Probably negligible, but if i can get away with my water being free of phthalates and bromine / halogen compounds it would be much better.
Systems use copper,  stainless or bronze  electrodes. They work at 12V, Maybe there is a possibility of an small electrolysis / galvanic corrosion over time?. That could affect the water quality placing trace amounts of this metals on the water?, that would eat the electrodes overtime?.

I could manufacture or purchase an electrode system without exposed electric cables, and using mostly innocuous plastics as rigid PVC for water or polyethylene with small exposed electrodes made of copper or stainless steel, solving the first issue. But not sure if can solve the second one.

So, are this type of systems reliable and safe?, or should i start looking for other solution?


texts: Home automation on Cat5e again: is this a reasonable multidrop protocol?

texts:
Previously I have asked about running I2C over CAN PHY over Cat5e cables for my home automation project. Now after a round of money saving and experimenting, it seem to me that abusing RS485 chip MAX1487 may be a cheaper idea than I2C-over-CAN. Now I need a protocol to allow the host device (with Ethernet) and satellite nodes talk with each other.

Environment

The environment is the same: Cat5e in very hostile alien crosstalk environment, cable already have RJ45 crimped on in TIA/EIA-568-B pinout, and budget is very tight. So is this a suitable pinout that carries both power and signal to the target device:

N/C
N/C
D+
+5V
+5V
D-
GND
GND

Also an extra constraint: all chips used here MUST be available in DIP package. Preferred MCU for me is ATtiny85 for the satellite nodes and ATmega328P for the node with Ethernet access.

Physical layer

And since all devices in the system have some kind of MCU in it, I can make the bus talk peer to peer. However I do need to avoid collision. Will this physical protocol and collision avoidance scheme work:

Talk using RS485 physical layer chip MAX1487 at UART baud rate 9600bps and 8/N/1.
Resistive bias/termination network makes the line float at 1. Drive the bus only when sending 0 (since MAX1487 can tri-state its drivers.)
Talk when the bus is idle, a.k.a read as 1, for at least 5 bit of time.
Read every sent bit back immediately after transmitting, as well as before transmitting the next bit. Whenever a mismatch is found, abort transmission and back off for a pseudo-random amount of time before retransmitting.
First transmission of every node that just come online have to be delayed use the same pseudorandom backoff time as collision backoff.

Talk here means drive the bus. I chose the MAX1487 chip that can have its transmitter turned off when not used. Normal bias network:

simulate this circuit – Schematic created using CircuitLab

Link layer

And since it is multidrop, some kind of addressing have to be used, which leads to this framed protocol:

Frame format (using C structure syntax):

struct frame {
    uint16_t magic;          // = 0x55aa
    uint16_t source_address;
    uint16_t target_address;
    uint16_t payload_type;   // Like EtherType
    uint16_t payload_length; // Exclude padding, if any
    uint8_t  payload[];      // Padded to 2-byte boundary
    uint16_t checksum;       // CRC16 of entire frame before this frame
}

Source and target addresses are hard coded into the chip, either during programming, or use some chip-specific value during manufacturing like the AVR's RC calibration value. Target address 0xffff means broadcasted frame.

Questions

Will this protocol be good enough as a home automation controlling protocol?
Will this protocol be able to be extended into carrying IPv4 or IPv6?


texts: What kind of IC drives this safety LED night light?

texts:
This night light LEDs circuit has three 4 positions:

off
fast blinking
slow blinking
LEDs always on

The big central component is a switch.

I was wondering what IC drives the LEDs ? From what I can read on the PCB, I expect:

PY55 to be the LED model
7340 to be the integrated circuit

However I couldn't find any reference for a 7340 IC online.

What IC drives the LED ?


texts:
I'm planning to use a ULN2003A 7-channel Darlington driver (datasheet) to control 4 to 7 LEDs in common-anode configuration from a Teensy MCU:

(The "trident" is a common-anode RGB LED).
The ULN2003A has a set of "clamp diodes" or "free wheeling diodes" which I gather are present to protect against voltage spikes when switching inductive loads. Those diodes are common-cathode out to pin 9 on the IC:

My questions are:

Do I need to connect pin 9 to anything if I'm just driving LEDs? (My guess is no.)
If I were driving motors or something and needed diode clamping here, what would I connect pin 9 to? The positive voltage of the motor side?


texts: Why is the energy density of 26650 Li-ion cells lower than that of 18650 cells?

texts: I have an application where I need a rechargeable battery in a very tight space too small for two 18650’s but large enough for a single 26650 cell. I have done some research on these cells and currently the highest capacity commercial 18650 cells are pushing 3500mAh’s (and here). Since the 26650 cells have a little over twice the volume as an 18650, I expected the capacities to scale proportionally, but the highest capacity commercial cells are a little over 5500mAh. Why are these high cap cells not closer to 7000mAh?