The Spektrum transmitter has a small daughter board in it that contains the Unigen RF module, a voltage regulator, and a host microntroller. The microcontroller is used to measure the PPM signal from the transmitter's encoder and convert it to a three-wire (I2C) communication signal so that it can talk to the Unigen module. ....
This is a great thread !!! And I believe it confirms something I already considered looking at the transmitter chip: I2C communication. That brings me to my two questions:
1) On the transmitter side, could you actually put microcontroler between the PPM front end part of the transmitter, and the transmitter chip, bypassing the current PPM to I2C conversion step, or between the current PPM to I2C conversion step and the transmitter chip. I could see possibilities of actually adding some channels on the digital side of things which normally would not be possible on the PPM side. E.g a 4x 4-position switches packed into a single byte value, and two 128 step sliders with a yes/no switch packed into two single byte value, bringing the total for a DX7 to 10 "byte value channels" but 15 true channels ;=)) Would be very nice to have some additional controls for e.g. camera tilt, zoom and mode, and for choosing from a series of automated flight modes in a GPS and IMU capable VTOL camera platform (i.e. a quadrocoptor).
2) On the receiver side could you actually export the I2C signal from the receiver chip. If I understand it correctly there are two receivers, both of which will be generating an I2C stream which the current processor in the receiver most likely compares, rejecting streams with an incorrect checksum or some other check? Exporting the I2C would greatly simplify interfacing the Spektrum Rx into a microcontroled flight system. And it would of course be unavoidable if you wanted to decode the extra channels inserted into the transmission as per question 1).
Edited by Arthur P., 30 June 2007 - 03:52 AM.