Thanks for the offer to help and sorry for the late response.
I have a bit closer to the problem. This is the schematic (at least I hope I did not make any copy-paste mistakes):
Yellow boxes indicate INA219 breakout boards and blue box indicates INA1540 breakout board
What works:
- When using the boards and wiring as indicated, I can read both INA219 sensors.
- When replacing the ISO1540 breakout board with a bare ISO1540 chip in a socket like the following, even without the capacitors at the power lines and without the pullup resistors (in the blue box), it works as well.
(Source: makershop.de)
Problem
- As soon as I replace either the ISO1540 breakout board or the bare chip in the socket with one soldered on a breakout board (see below), I still get sensor readings but only for a few seconds, then the communication fails. It makes no difference whether I add the 4 pullups and 2 capacitors or not, the result remains the same. Since both above methods work (socket and commercial breakout), it is likely a soldering issue, but then why do I get sensor readings for a few seconds before the communication fails?
Anyone has ideas how to narrow down the source of the error?