Drifted over time ?

[pete_dl]

Hi,

I have a R1 bought in 2018 with original firmware. I have not used it in a while and have noticed that with the inputs shorted, it reports 0.0mA, 8uA and 8nA when i manually select the ranges.  In order to tweak the offsets, I tried connecting it to my windows 10 computer. Arduino software reports a new port when i switch it on, but the serial monitor does not show any text or respond to question mark.

Should my firmware have offset adjusting functionality ?

Thanks,
             Peter.

[Felix]

That's quite old but should not have any significant drift.
I believe at that time 1 ADC bit meant 8ua/8nA over the OLED. Do you see a constant 8ua/na on the OLED?

The firmware is vastly improved since then, but those early units came with the old samba bootloader so it's a bit more involved to update them than a drag-and-drop firmware file.

In any case, I always said that the OLED should be secondary and only for quick measurements, rather than high precision, due to the low resolution at range extremes. The raw output is what should be most accurate and that can be read with a RMS DMM.

[pete_dl]

On further testing with a resistive load, it is only the mA range that makes sense, so I imagine i damaged something in the nA and uA path.

Pete.

[Felix]

That's quite possible given the readings you're seeing.
Especially if you're seeing a constant reading in those ranges.