get rid of that MCP23017 and go for an tiny ARM cortex M0 from NXP like: http://www.nxp.com/documents/data_sh...PC11XXLVUK.pdf that way it could be used for other cool stuff too And price is around 3.5EU on fernell for the 32Kbflash + 8kb ram variant. http://de.farnell.com/nxp/lpc11c14fb...qfp/dp/1812185