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01:14
If I wanna make a primary and secondary inductor with magnet wire in a 12:1 ratio, how many turns should the primary have so it performs 'ok enough' ?
All I will be doing is calculating $\mathcal{E} = \frac{2\pi f N_s N_l \mu A_s}{l_s}$
$\mathcal{E}$ is the emf on the large coil, l_s length of small coil, N_s and N_l number of turns on large and small coil, f frequency of small coil signal
 
1 hour later…
02:34
@georg if you're making a transformer you need to start with the voltage and operating frequency first
 
1 hour later…
03:49
hey there @EricUrban and @NickAlexeev
hi @sh
@Shalvenay
im trying to implement a schmitt trigger
so...I'm wondering if a question about the tradeoffs of using setscrew-attached vs solder-attached vs spring-clamp attached banana plugs would be on topic on mainsite, or best left to chat?
hmm, good question
is this in general or do you have a specific application?
I'm designing a set of test leads for my bench supply
the wire is 18-22AWG stranded, PVC-insulated (it's UL AWM style 2468 "zip lead" typically found on the DC output cables from wall transformers -- I need the 22AWG for lower current leads to header pins, while the 18AWG is for banana-to-barrel plug, banana-banana, and the likes)
04:24
not sure
 
10 hours later…
14:41
Quick question...
> After two minutes running at full power, I saw the tell-tale sign of a dying unit on the power meter when the power draw began to suddenly climb. I saw 670 watts right before the unit went down silently for good.
Did something go into thermal runaway?
by that amount of information its very clear to figure out...
hi guys,
I am searching for a (replacement) for a 168dimm sdram, 256MB with two banks.
Do you know where to get such RAMs? I am in Europe and everywhere i search, they are obsolete or in small numbers (< 20), mostly had a look at the fast distributors like digikey, farnell and co.
100 to 200 pieces would be nice.
why would one need that much?
14:56
For maintenance.
20 years are a long time.
sounds like somebody failed to plan that through
15:21
period
16:09
hello, how can I calculate transconductance of jfet having some measured points (Ugs, Id, Uds) ?
16:52
@bwDraco You the owner? Those pictures better not be the best quality available, because not a single well reasoned analysis for peak voltages and duration can be made from those. Far too few samples displayed.
@Eggi Seoul, South Korea, Yongsan District, near the Dragon City Hotel, there's an Electronics Market. Lowest level. Ask people there. There might be an idiot there with a box of Hyundai modules.
An increase in current draw on a stable load at elevated temperatures sounds like some MOSFET went into thermal runaway, but not 100% sure.
@bwDraco On device scale that vastly depends on control schemes and such.
@EricUrban Was that a preamble to a question? If so, just post it (not directly @ me) and possibly someone will know to answer it
 
2 hours later…
19:32
Looking at this Instructible: https://www.instructables.com/id/3-channel-Dimmerfader-for-Arduino-or-other-microco/
Which suggests this TRIAC: https://www.eoo-bv.nl/triacs/1636-t1m5f600a.html
But I can't find that one.
Is this one https://www.digikey.com/scripts/DkSearch/dksus.dll?Detail&itemSeq=243118301&uq=636456428233666383 the same? Or close enough?
The diagram comes from this note on PowerPath controllers, MOSFET ideal diodes, and such.
How would the floating 15mV voltage source be actually created in a circuit like this?
@NickAlexeev If you had a resistor from the amp's inverting input to ground (or SUPPLY) to provide bias current to the whatever-it-is, it wouldn't change the behavior.
Of course the fact the + end of the "source" will be at the SUPPLY voltage makes that a bit tricky.
Maybe it just represents an offset voltage deliberately designed in to the amplifier?
19:48
@ThePhoton There's a body diode in the pass MOSFET. It would provide a startup suppply.
@NickAlexeev Right, but that's tied to the - end of the source...how does it generate a higher voltage than what its supplied with?
I'm leaning toward they just deliberately design the amplifier to have an offset voltage in the appropriate direction.
@ThePhoton Maybe these controllers have a charge pump for the gate driver. There's also a P-channel flavor of these circuits. From what I see, majority of these controllers are made for P-channel. I can't seem to find a single datasheet for the N-channel flavor.
20:14
morning
Suppose I have a 12bit I2C DAC chip. If it supports 100 kbps, 400 kbps and 3.4 Mbps. Which modes can be used to produce sound?
According to my calcs: 4096 * T_update = T_fmax
so f_update should be at minimum: 4096 * 20khz (for sound) = 80MHz... So none of them could be used? :\
20:37
@Zeta.Investigator Where does the 4096 factor come from?
@ThePhoton Using 12 bit precision to its max... like 4096 points for a sine wave
@Zeta.Investigator You only need to send 12 bits per sample, not 4096.
Practically, you probably can't just stream data over I2C. Every so often you'll need to stop and start a new transaction...maybe for every sample. Which adds an extra 8 bits plus ack.
@ThePhoton I still don't get it. Suppose I have an analog sine wave like v = 1 * sin(20e3*2pi*t). I have 12 bit dac...so I can divide 1-0 by 4096 to get 4096 distinct levels. How many datapoints do I need to represent the sine wave?
Well at least 4096 data points?
20:54
@Zeta.Investigator I2C is not that conducive for full quality audio (might work for 4kHz phone quality). Digial audio applications usually run SPI-based serial bus. Note that I2S (which is often used for audio) is an SPI-based bus, and it has nothing in common with I2C.
You need to send at least 40,000 samples per second, preferably 80,000 or more. But each sample is only 12 bits.
So that's 960 kbits per second (at 80 kSa/s).
You don't need to send a bit for each possible level of each sample.
Like Nick says, I2C is not really designed to stream data continuously and to maintain a constant clock frequency, so it's not really a great fit for audio.
On a different note, I wonder if this would be on-topic for EE.SE ?
0
Q: Increase processing use of DSP

user2982010I have a DSP with a very well defined application, (this explication will be simplified) The DSP uses TDM frames to receive audio information, the audio information is processed (simple IIR filter) and then outputted thru TDM, mainly the application works on 2 interruptions: Interruption 1: [4 ...

@ThePhoton Does this >40,000 Sa/s come from Nyquist?
@Zeta.Investigator Yes. For example, CD quality audio is 44ksps.
@Zeta.Investigator Yes, you need sample rate at least 2x the bandwidth of your signal. So 20 kHz signal needs 40 kSa/s.
But that would require a very well-designed anti-aliasing filter on the output if you don't want a very distorted signal.
21:05
@ThePhoton Yeah, I've read somewhere that rule of thumb is 10x
@NickAlexeev AFAIK most CD players will digitally interpolate and the drive the actual DAC at a higher rate.
@ThePhoton But suppose that I want to be able to produce a 20khz sine wave out of a MCU. I should load (at least) a 40k * 12bit = 60 kByte array into the ROM and have an interrupt output each element of the array to the dac? What would be the frequency of interrupt?
I guess it should be the same as >40kSample which is >40khz
21:24
What am I saying? I think I should sleep :\ Thanks @ThePhoton @NickAlexeev
Anybody know, is Python goofy with recursion?
@NickAlexeev its not really a good question to start with. its like waffling about what you buy for bbq dinner, then ask how many native americans are in the red inflatable boat...
@ThePhoton define goofy. recursion isn't one of its strenghts and I doubt it has tail recursion optimization
I wrote a recursive function and it looks like the recursive call is clobbering variables in the parent call
thats because scoping in python is a bit goofy... everything is per default passed by reference afaik
I am doing recursion here because I know the call depth will never be more than ~10 (and my test so far is no deeper than 3)
@PlasmaHH These aren't values that were passed, just local variables inside the function. After making a recursive call, it seems the values are changed to what they would have been set to by the child call.
No, I'm stupid.
21:32
@ThePhoton well, a test case to show what you mean could be useful here. but remember that also things in data structures are references. So when you put the local variable into a datastructure and act in the next call on the structure, the local variable appears to have changed
@PlasmaHH Figured it out.
rubberducking at work
I was seeing a print() call from within the recursive call
Not the one from after the call
in some of my python code all my outputs are routed through a special print function that outputs (depending on configuration) line number, file and stack depth (optionally as a tree)
21:56
Hm, what makes more sense for a bunch of safety interlock switches for an enclosure... have them all directly switch main power, or have them switch a relay that switches main power...
22:20
also wow, type b(+) gfcis are fucking expensive
22:41
Anybody used Cypress ezUSB (USB 2.0)?
22:51
Holy crap
20 dB gain, 1.2 dB noise figure, 5V supply, 8 GHz bandwidth, $140 each
So I think I have an answer to my question, would someone like to discuss it wth me?
0
Q: How can I perform pulse shaping from an op-amp providing overcurrent protection?

Eric UrbanI built a circuit using an 555 as a flip flop to drive an IRFZ44N controlling an inductive load. The circuit uses two voltage sources configured to provide narrow pulses. Together these actuate the set & reset functionality of the flip flop. This generates a square wave clock signal driving the M...

Basically I was thinking "pulse shaping" when what I need was some sort of "sample and hold" type circuit
without the requirement to hold an exact voltage, just hold the state.
I used another MOSFET and a PNP transistor on the reset line to build a positive feedback loop. Once the gate charges up the MOSFET turns on pulling the reset line down but also turning on the PNP transistor which can charge up the gate.
a 1n4148 (or any fast diode) prevents the op amp from turning off the MOSFET by discharging the gate
The reset clock also is used to drive another circuit that clamps the gate to ground through a 470 ohm rresistor.
23:21
The high price of Altium is apparently to pay salesguys to send every user at least two emails per day.
@EricUrban I pretty much stopped reading when you said "using a 555 as a flip-flop". Maybe you had a good reason to do that, but I wasn't going to read a wall of text to try to figure out what it was.
Could you suggest an alternative?
What problem are you actually trying to solve?
I am still learning to be honest
so i am driving a MOSFET to run a square load, but want to limit the current by just stopping the pulse once the current hits a certain preset amount
hence, op amp
@EricUrban I'd use a flip-flop. But which one depends on Vcc available, speed, etc.
are there flip flops that can source enough current to drive a MOSFET gate directly?
23:27
@EricUrban -- what's the Qg on your FET and what speed are you driving it at?
@EricUrban flip-flop with a buffer of some type
hey there @ThePhoton
wouldnt a flip flop + a buffer mean I'd need two components on the board?
63 nC is the gate charge of an IRFZ44n
how fast are you trying to drive the thing?
23:42
@EricUrban Is that a problem? You've got a bunch of crap on your board to support your 555 already.
hmm, well.....ok
I do like my squarewave example plot: i.sstatic.net/HoAYR.png :)
what is this jon?
shows the harmonic content of a squarewave and equally what happens if you pass said squarewave through filters
50lines of python :)
and thats lazy python
what library ?
23:49
numpy and matplotlib
neat.
I recently learned how to use LTSpice, so I'm pretty happy with myself.
I can't stand LTSpice
but I am probably spoilt with matlab and SIMextrix

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