MCP23017 Troubleshooting notes

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I used the command "sudo i2cdetect -y 1" to make sure RPi detects the MCP23017 board.  Unluckily it doesn't.  So I started troubleshooting.

I first executed the GPIO test programs for LED, buzzer, and button and found everything OK.  Then I used a multimeter to check the continuity of the connecting wires and also found everything OK.

So I gave up looking at the MCP23017 board and decided to try another piece of MCP23017 wired on a breadboard.  This time I had luck.  I2cdetect finds the MCP23017 in address 0x20.

This implies RPi side is OK, and the I2C connecting wires are also OK.  The fault must be on the MCP23017 protoboard.

Time I went to bed.  Perhaps tomorrow I should first try swapping the two MCP23017 to make sure the first one is not defective.

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