| Electronics > Projects, Designs, and Technical Stuff |
| DIY DC Current Probe? |
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| Jeroen3:
Yes, I've thought about the USB port. The other method I considered was using 18650 cells. Both methods do require a boost/inverter +-12V regulator for dual rail. The LT3471 is on the list for later. |
| joeqsmith:
For DC, I have an old Tektronix current probe along with a few LEM sensors. The Tektronix is good into the MHz. I also modified a cheap UNI-T clamp (UT210E) which can do a couple of KHz without changing the front end. Depending what you needed, you could do some simple digital modulation across some optos or maybe some magnetics off an old Ethernet board. Rare I would use a meter to read current but even the UT61E has the link if you don't need much BW. |
| Jeroen3:
The CMS3005 is here. So, whats on it? - AD829A - 8L08A - OL S4N - AL S48 - A7W 44 - Some custom silicon. On a ceramic pcb. I get the price now. |
| Leo Bodnar:
--- Quote from: Jeroen3 on September 23, 2017, 04:02:43 pm ---While I was looking into method to get DC current on my oscilliscope I discovered this is an expensive hobby. You can get DC current probes, for high currents. But what if you want to measure milliamps? So I thought, why not make one? :-// --- End quote --- Here is completely wild and pointless idea - if your measurement range is reasonably small and you are not looking for lab grade accuracy, you can use [a pair of] VOM1271 either directly into the high impedance scope input or via a buffer amp. At least it wins by requiring no power at all. 1271 is my favourite solution when I can't be bothered doing a proper driver for high side or across isolation barrier. Somebody characterised its transfer performance and it is reasonably good: http://www.edn.com/design/power-management/4425510/Isolated-AC-linear-power-control Cheers Leo |
| Jeroen3:
A linear optocoupler could be useful to add to the parts list. Yet, I would still need additional circuitry, such as isolated power and an shunt amplifier for that way. How would such linearity hold when exposed to non-room-temperature situations? I've played around with the CMS3005 today. Cool thing, it's spot on, and it detects 1 mA without issues. (The noise on my breadboard made it somewhat inaccurate here) It also gets remarkably hot when doing nothing, so that might be one of the reasons why ceramic was chosen. When probing on it, I did not find any voltage regulators. So those sot-223 are doing something else. It isn't greatly affected by unbalanced supply (eg: 12 and -15), only a few mV. So it does contain a reference. No super precise supply required, but it should be a stable one. No switching noise, since running it from an RP-1215D directly didn't work very well. |
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