Recent Posts

1

Test Equipment / Re: Choosing between entry-level 12-bit DSOs

« Last post by KungFuJosh on Today at 04:48:54 pm »

@KungFuJosh can you please set the scope to 500 Msa/s, low waveform acquisition rate (to make the TinySA's glitches less visible), low persistence, and record a video of a 30 seconds long frequency sweep from, say, 110 MHz to 270 MHz?

Coax connection with a 50 Ohm feed-through terminator, if possible, to make the test conditions the same as in my test.

It will be interesting to see at what frequencies (and at what ratio relative to the sampling rate) it will become first wobbly and then AM-like (if it will), to compare that to Rigol.

I'd love to play, but I don't have one of these scopes. I have an SDS2504X+ 500MHz scope. I can sweep up to 841MHz on my scope with the TinySA Ultra.

2

Test Equipment / Second bench PSU, am I thinking about this correctly?

« Last post by krby on Today at 04:47:08 pm »

I am very much an amateur electronics person, with a bit of G.A.S. I'm posting here to get opinions on my approach to buying another PSU.

I've got a 6+ years old Eventek 30V/10A PSU. I've used it for a variety of things, from powering RPis, Arduinos, other small circuits to testing strings of 12 or 24V LEDs, a stand in for 2S to 4S LiPo battery, a crude charger for a variety of battery chemistries, whatever. I don't often need beyond 3 or 5A, but have sometimes. I generally haven't been using it in places where the ripple (IIRC, somewhere around 200mV) mattered or I wasn't sophisticated enough to know it mattered.

Recently, I've been thinking about and doing more projects that I think will benefit from a better bench supply. My thinking is I would keep my existing PSU for anything that really needed >5A because I can't imagine a project I would do in the next few years that needed >5A and needed the accuracy and low noise. I'm also had a few I wanted 48VDC and just used a fixed swithing PSU (meanwell) I already have for another project, but would be nice to have this on the bench supply.

So, all this leads me to thinking about not-expensibe linear supplies that can do about 60V and 5A. This could be a one channel device, or multi channel 30V/5A that could do parallel/series across channels. I get a multichannel w/paralleling PSU, I guess I could ditch the current Eventek because that would be 30V/10A with cleaner output.

Since I'm not willing to spend a ton on this, it has me looking at the "best of the cheap" or "bottom of the quality" end of things. The usual suspects. Keep in mind I've been ok with 200mV ripple now. When I have need accurate voltage, I have verified it with a known good DMM and adjusted the supply until my DMM hit the number I wanted. So maybe the new PSU having voltage sense and feedback would be good?

- Siglent/Rigol The DP832 being the common one I see recommended here
- Korad KA3005 or KA3305 for multi output.
- Maybe super cheap RD6012P (it looks like in the 0-6A range it acts just like a 6006P) ? Should I even bother with  these sort of "20mV ripple SMPS" things or just go linear?

I'm not sure I'd actually use the multiple channels all that much. But maybe that's just because I don't have them now.
Is there anything else I should be considering? I don't know if I need memory slots, I'd use them for some common configs I guess, but not required. Since I'm upgrading I would like to be able to have some better input than just coarse/fine pots. But I guess that's not required if it saves a ton of money. I haven't looked deeply at what the computer interfaces do with these things, generally I'd say I would do without that. I haven't come up with complex control needs, mostly "set to a given max current, get the voltage I want, go". Then maybe "vary current and voltage a bit manually" if I need to see how things behave.

Thanks for any advice.

3

Repair / Re: Tek CG5011 calibration

« Last post by fmashockie on Today at 04:46:27 pm »

I have both manual parts for the CG5011.  Here's part 1.

4

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.

But the best idea is to synchronize the ADC, take many samples during on-time, and average them. Assuming enough load so that motor runs in CCM, then the same average is very closely true also during OFF-time. If you can only have one sample, take it at exactly the midpoint of ON-time, and you - theoretically - again have true average motor current, in CCM.

5

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.

6

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?

7

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.

8

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.

9

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.

10

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.