Using the Adafruit 2.8" touchscreen with raspberry pi
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Using the Adafruit 2.8" touchscreen with raspberry pi

by tummychow on Sun Jan 27, 2013 2:10 am

I intend to use the Adafruit 2.8" touchscreen ( with the pi and I'd like to develop a good plan for how I intend to wire it up, before I order. As background, I have some Arduino experience and plenty of ability on the software side, not quite so much on the hardware side but I know my way around most simple ICs and I have no problem slogging through datasheets.

I've looked over the Arduino tutorial for the screen and it looks like it has 14 digital pins (reset, backlight, chip select, command/data, read, write, 8 data lines) plus 4 analog pins (x- y- x+ y+). I also intend to put a chronodot on it, maybe some other i2c toys, so I can't use the i2c pins as GPIO. Looking at the GPIO pinout (, there are not enough digital pins to make this happen without some expanders, and it would need an ADC anyway for the touchscreen pins.

I get the feeling that speed is a serious concern when pixel-pushing, and the literature I read tells me that i2c is a fairly slow bus so it sounds like SPI is the only way to go. I'm looking at an MCP3008 ADC (sold on adafruit already) for the analog pins. I'd rather use an MCP23017 for the digital pins (sold on adafruit, so I don't have to pay shipping to another retailer) but will it be fast enough?

One more thing: does occidentalis v0.2 include the hardware SPI driver?
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Joined: Sat Jan 26, 2013 9:35 pm