Topic: Adding an I2C device to a Chumby
The Chumby has an I2C bus that makes it possible to control peripheral boards with 2 wire control. They currently use it to control some internal devices like the Radio and the accelerometer.
I wanted to be able to add additional (non-servo) PWM ports for external LED control. One option is to add USB based PWM devices using something like the Nifty Pololu USB servo control boards http://www.pololu.com/catalog/product/1350. I needed my USB ports for other things so I instead went with adding an I2C device. A lot of I2C devices require a 5V interface but JeeLabs makes 3.3V I2C devices that are compatible with a 3.3V Chumby / Infocast.
The folks at ladyada.net have an example program that shows how to talk with the built-in accelerometer via a regutil like command line tool and via custom code. The i2c demo program can be used to talk with any device via shell scripts. You can find some notes on using a I2C dimmer on a Chumby at http://joe.blog.freemansoft.com/2011/02 … umby.html.
It turns out to be a 5 wire connection for the LED dimmer board, 3.3V, ground, SDA, SCL and optional power to external items plugged into the ports of the added I2C device. A compass or pressure sensor would only need a 4 wire connection.
I also have a JeesLabs non-PWMhigher current "output board" that I hope to play with.