Recent Posts

1

Microcontrollers / Re: Incorrect current measusrement of BLDC motor using ADC

« Last post by Siwastaja on Today at 04:38:33 pm »

Without seeing a schematic, I would guess it's the usual case: current is only flowing through the shunt resistor during the PWM ON-time. If you synchronize the measurement during on-time and assume the current stays constant during the whole switching period (which is fair assumption given high enough f_sw compared to motor inductance), then you know the true motor current; because it is also flowing during OFF-time, you are just not measuring it.

But if you sample randomly (and remember to take enough samples for correct average, at least tens of samples per period!), you are also reading zero during OFF time, when in reality current is flowing in the motor. In such case, you need to multiple by the reciprocal of duty cycle.

2

Repair / Re: Rigol DP712 Output Shorted; Fuse? / I Screwed Up

« Last post by zanfar on Today at 04:37:52 pm »

I would guess due to the fact that it can be switched and therefore is not shorting the output during operation. But that's just a guess. This assumes that the thyristor is only used to discharge the cap, but the fet/resistor branch means there is still something unknown. I was casually working on reverse engineering a schematic of the output board; maybe I'll step that up and see what I find.

3

Projects, Designs, and Technical Stuff / Corrosion on DIP pins

« Last post by Alex Eisenhut on Today at 04:37:52 pm »

So I retrieved my PET 4032 from my parent's house. The 4032 is a 40 year old computer. It was in the basement for 30ish years. There was no flooding.
How do some chips have rusty pins but the next one over doesn't?

Those are RAM chips, but various 74LS also have the same rusty pins while the next one doesn't.
And the rusty/non-rusty RAMs are within one bank of 8 chips, so the difference can't be that one was wave soldered and the other by hand.

That rust means the end of that chip as the corrosion will crack open the two halves of the body and let humidity in the guts, right?

4

Test Equipment / Re: New 2ch pocket DSO+SG - Zeeweii DSO2512G

« Last post by chemary on Today at 04:36:57 pm »

That's OK, just don't overdo the calibration, it won't be like a multimeter.

For calibration, I need a more or less accurate laboratory power supply and a functional signal generator, which I don’t have.

If you don't want to spend much, I purchased a cheap device like this one https://www.aliexpress.com/item/1005006786894152.html it comes with a hand written paper with the real measured values with good equipment and also states the date and temperature when they were done, it can be used to know how good are the measures of your equipment.

5

Test Equipment / Re: New 2ch pocket DSO+SG - Zeeweii DSO2512G

« Last post by Aldo22 on Today at 04:32:14 pm »

For calibration, I need a more or less accurate laboratory power supply and a functional signal generator, which I don’t have.

It's not really necessary.
You have "Auto cal" in the Aux menu.

6

Metrology / Re: ESI RV622A Resistor Repair

« Last post by gmilliorn on Today at 04:31:59 pm »

Reviews of those cheap spot welders aren't very encouraging, and require an expensive LiFePo battery
or such.  The lead wires are about 1mm thich at least.

However, while searching, I found this comment from Earle Rich which discusses making just these
types of resistors:

https://hackaday.com/2021/06/16/review-battery-spot-welders-why-you-should-buy-a-proper-spot-welder/#comment-6357273

A bit too vague to replicate, though.

7

Beginners / Photodiode output emulation

« Last post by elki on Today at 04:26:47 pm »

Does anyone know if there is a simple RC circuit that could emulate the current output of a photodiode? I wonder if it is possible to achieve starting from a function generator, pass it through an RC circuit, and then using the obtained current pulse as input to a transimpedance amplifier. Any suggestions are appreciated.

8

Repair / Re: SDG830 another boot issue

« Last post by sgeets on Today at 04:19:37 pm »

At one point it didn't look good to get this unit recovered.  But I didn't give up. With the help of tautech, it was finally recovered and upgraded to the latest firmware.  Another device saved from the bin.  Many thanks to tautech. 

9

Beginners / Re: uCurrent Gold Schematic

« Last post by xvr on Today at 04:16:20 pm »

Strange arrangement of C6/R12/R16 and C8/R13/R17 - they short circuited.
OP circuit also wrong - they plugged without any feedback circuits.
I also would some protection for input circuit, for example - diode (or TVS) across J1. If CPU turn on wrong shunt resistor on high current it will just blow out.
Q1 placed upside down.

May be something more, that I didn't spot [yet].

10

Microcontrollers / Re: Has anyone used ASAN & MSAN, and relevance to embedded arm32

« Last post by ataradov on Today at 04:06:07 pm »

I don't think those would be very useful on embedded code. Asan adds instrumentation in the code and then replaces low level malloc() and free() calls with custom tracing versions.

This typically increases code size by 2-3 times, decreases execution speed by the same 2-3 times. And it also needs a lot more RAM to store all those allocation records. On embedded with custom allocators, you will essentially get one or no real malloc() calls, so the tool will be useless.

In theory, it might be possible to work with the instrumented code and match it with the custom allocators, but I'm not aware of anyone doing it.