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EspoTek / Labrador

EspoTek Labrador is a USB device that transforms your PC or smartphone into a fully-featured electronics lab. This repo holds all of the source code!
http://espotek.com
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Multimeter readings in V mode #190

Closed fijam closed 2 years ago

fijam commented 2 years ago

I have an issue with the multimeter in V mode.

With nothing connected, the multimeter stats show approx max 200mV, min 100mV, mean 145mV.

image

I have performed oscilloscope calibration and it looks fine, when I connect oscilloscope DC channel 1 and 2 to the USB shield I get 4e-05 mean on both. Disconnected both channels float at ~1.65V. But as soon as I switch to multimeter mode the mean is ~145mV.

So for example, if I connect the mutlimeter CH1 to PWR and CH2 to GND I get a reading of 4.95V. If I connect CH2 to PWR and CH1 to GND I get -4.7V instead.

EspoTek commented 2 years ago

That's a really interesting and quite concerning quirk! It's not something I've seen or heard of, but will look into it when I have time (probably around Christmas)

EspoTek commented 2 years ago

I've tried to reproduce this and am unfortunately unable to. I'm wondering if this was one of the quirks introduced by the performance-related bug (which only showed on low-end machines and is now fixed)?