http://www.blogger.com/blogger.g?blogID=1840459474737789074#editor/target=post;postID=5794842964770282384
Now I have started assembling a new MCP23017 board. Last time I used 2N7000 to shift RPi's 3V3 to 5V0. I don't like the pulling up circuits which I think is not that flexible. So this time I directly use MCP23017 at 3V3, and do the level shifting using ULN2803 (+ HC04 to do another inverting to give the original logical level) and SN74LVC245AN.
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