It turned out that modifying the HobbyKing HK310 transmitter in order to change the behavior of the AUX (CH3) channel is quite easy:
WARNING: This and other DIY projects are purely "at your own risk". If you are at all uncomfortable or inexperienced working with electronics, please reconsider doing the job yourself.
All documentation details and sample source code for Arduino and PIC microcontrollers can be found at https://github.com/laneboysrc/hk310-expansion.git.
With the information found in this project you can modify a HobbyKing HK310 or a Turnigy X-3S transmitter to send arbitrary information on the three channels to the receiver. This allows for example to:
- Change the AUX channel from a two position switch to a three position switch
- Change the AUX channel to an analog channel
- Perform custom mixing on any of the channels
- Transmit arbitrary data over the AUX channel to a custom decoder as to expand the system to a large number of on/off channels, e.g. to control lights and accessories on a scale RC truck
- Build your own custom transmitter by just reusing the wireless module