MCP23017 I2C 16 I/O Port Expander

[7H3LaughingMan]

I have recently ordered a MCP23017 to mess around with for a project on my Raspberry Pi and I am having issues with the address randomly jumping around whenever I am trying to run "sudo i2cdetect -y 1". I have even gotten it a few times where it says there is a device on 0x20 and 0x27 at the same time just about. I have nothing else hooked up to the I2C Bus and I am using a Pi Cobbler to connect my Raspberry Pi to the Breadboard, I then have 4 wires coming from the Pi Cobbler to the MCP23017 Chip for 3v3, Ground, SCL, & SDA. I have gone over the connections 20+ times now and I am 100% positive there is nothing wrong with the wiring but I am having the issues where the Address is jumping around randomly.

[adafruit_support_bill]

Post a photo showing your soldering. And make sure all your breadboard connections are firm. The spring contacts do tend to loosen up over time. If it does not grip the wire tightly, try an adjacent hole in the same row.

[7H3LaughingMan]

[adafruit_support_bill]

Looks like your address pins (15,16 & 17) are floating. You should tie them to ground. From the datasheet: http://www.adafruit.com/datasheets/mcp23017.pdf

The address pins should be externally biased
even if disabled

[7H3LaughingMan]

Going over that datasheet I noticed the reset pin is externally biased as wrll so I would have to ground thst as well, right? In the tutorial for using this with the Raspberry Pi it should say that the address pins need to be grounded for normal operation like it says for the reset pin so it is clear.

[adafruit_support_bill]

Reset is active low, so it should be pulled high. And yes, that would be good to mention in the tutorial.

We welcome comments & correction on the tutorials. If you post them in the "Feedback? Corrections" link on the left side of the Adafruit Learning System guide, it will be sure to get back to the author.

[nigelf]

I had the dreaded random detection of address and it would clash if all pins for address were selected

so I tried not connecting pin 17 to ground but to supply ie hold it high rather than leaving it floating ...

this seemed to do the trick