Converting an old Robbe Starion RC transmitter to fly my Furibee F36
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So I wanted to fly my Furibee with a normal transmitter.
Got a Robbe Starion at hand, ditched out the original electronics.
I have had several ideas for achieving my goal:
- Wire the Robbe's potentiometers to the Furibee's TX and call it a day.
- Reverese engineer the protocol and create a PCB with some random MCU (STM8 preferred)
After some investigation the second option seemed to be a bit difficult so I have implemented the first option.
Back in the eighties it was not usual to MCU-s with ADC-s to the RC transmitters which would have made the low voltage alarms easy. However the Robbe engineers used a small galvanometer to display the battery voltage:
So I wanted to marry the Robbe TX's good old Alps potentiometers to the Furibee's TX.
The Furibee TX potentiometers were used at full range: their analog output goes from 0V to 3V3. While the Robbe potentiometers have different work range: when biasing them with 3V3 their range is ~1.2V -> 2.0V.
So we need to came up with some analog circuit which is capable of amplifying the input signal (4,125) and offsetting it with a negative offset (-1.2V).
This problem could be easily solved by an operational amplifier, but I have to note here that we need to use a rail-to-rail version since we need full range of output.
First I went to the TME's search and looked for the cheapest Rail-to-rail OPA with 4 gates.
It was the Microchip's MCP6004. It was available DIP package so it screamed for a quick and dirty solution.
At first I have hooked up the schematic in LTSpice, for simulation purposes. Also hooked up the schematic in EAGLE to help the population of the prototype board.
Miklos Marton
