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2 votes

How can I debug why the Pi will only recognize some of the GPIO expanders over i2c?

Power the MCP23017 from 3V3 or use level shifters on the Pi GPIO. When powered from 5V they need more than 3V3 at their inputs for the inputs to be reliably seen as high.
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2 votes

How can I debug why the Pi will only recognize some of the GPIO expanders over i2c?

That rats nest of wiring is just asking for trouble, particularly with all the uninsulated junctions. WHY are you powering with 5V? I use MCP23017 (admittedly not so many) powered by 3.3V Normally ...
  • 54.8k
1 vote

How can I debug why the Pi will only recognize some of the GPIO expanders over i2c?

Sadly, the answer turned out to be dead simple. In trying to wire the RESET pins to power, I misread the datasheet and instead wired the INT pins to power. I think I made this mistake once wiring the ...
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1 vote
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How can I debug why the Pi will only recognize some of the GPIO expanders over i2c?

Two more options to try for troubleshooting in addition to previous suggestions: Since the behavior is not very reproducible, try getting rid of open reset pins on MCP23008. I.e. pull up reset pin (...
  • 196

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