Showing posts from February, 2011

Adding an I2C device to a Chumby

Chumby I2C The Chumby is a 3.3V device.  This means that you have to use 3.3V signal compatible devices.  Several of the JeeLabs I2C devices are 3.3V signal compatible. It is possible for some of the 3.3V I2C devices to control higher voltages either through their intrinsic design or through the use of opto-isolators or relays. I2C connection pins are available on the Hacker Port on most models. There are some internal devices at certain address so you have to make sure that you don't add additional devices that conflict.  I cut one end off of a JeesLabs extension cables and soldered it to the connector.  We don't use the IRQ line so it can be removed or taped off to avoid shorts.  This is pretty straightforward. I2C uses 7 bit addressing on a bus that does 8 bit transfers.  The thrifty I2C folks make use of the extra bit as a R/W bit.  They standardized on the addresses in the upper 7 bits and the R/W bit as the least significant bit.  This means that the address is sh