MCP23017 Troubleshooting notes

http://www.blogger.com/blogger.g?blogID=1840459474737789074#editor/target=post;postID=4879392034702340187

So I found out the MCP23017 no detection problem is not on the RPi side, and that the 3V3 and I2C wiring are OK because they work for the MCP23017 #2 on the bread board.

Therefore I am coupling as loosely as possible the RPi from the two MCP23017s.  Now the RPi hardware interface is summarized below.

1. AC power, LAN, HDMI cabcle

2. DC 5V0, 3V3

3. I2C (SCL1, SDA1, and RPi GPIO Gen 6)

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