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geekhack Projects => Making Stuff Together! => Topic started by: tee-eye on Wed, 11 January 2017, 19:17:29

Title: Question about a design. ATMega32u4 to IO Extender
Post by: tee-eye on Wed, 11 January 2017, 19:17:29

I was wondering if it would be possible to connect an IO extender(MCP23017-E/SP) to an ATMega32u4-AU via a usb cable. I figured if you connect up the SCL pin to the Data+ of the usb and the SCA pin to the Data- of usb, ground the 4th pin and power the 1st.. it should work. Am I correct with this?
Image example in Kicad schematic.

(http://i.imgur.com/SGAkOgC.png)

Title: Re: Question about a design. ATMega32u4 to IO Extender
Post by: suicidal_orange on Thu, 12 January 2017, 12:31:16

Wire is wire so you can certainly use a USB cable for this, putting ground/VCC on the edge pins is good as it ensures the chip is powered up before it's expected to communicate.

The only thing wrong with your schematic is SDA goes to SDA and SCL to SCL not VDD and VSS, and you should have resistors between VCC-SDA and VCC-SCL.  I'm ignoring the little VCC pad between pins 2 and 3 :thumb:

Title: Re: Question about a design. ATMega32u4 to IO Extender
Post by: tee-eye on Fri, 13 January 2017, 15:58:08

OMG I DID NOT EVEN SEE THAT LITTLE PAD! Hahaha!!
I'll add the resistors in :)
Thanks so much for the response!!