I'm trying to get multiple i2c devices talking to the RPi and at least one is a 5V i2c device (a servo controller - SD20, based on a PIC micro controller).
I have set up a level shifter similar to the circuit on http://playground.arduino.cc/Main/I2CBi ... velShifter
(but using 2N7000 MOSFETs) and whilst I can communicate with the 3.3V devices just fine, I cannot communicate with the 5V device (sudo i2cdetect -y 0 only reports the 3.3v devices). The only difference I am aware of is the SD20 communicates at 400KHz whereas the other devices run at 100KHz... do I have to add special coding to talk at the higher speed (I haven't found any mention of how to!)
I've used as close to the 1.8KR pullups the RPi has on the 5V side (no pullups on the 3.3V side as RPi has those).
Any ideas what I might be doing wrong?