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• Notes about the "volt control" indicator

  Miklos Marton • 08/12/2017 at 11:58 • 0 comments

  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:
  

  
  I have decided to repurpose this. I have connected it to a PSU and checked the voltage levels corresponding to the notable poisitions: full scale, red area start:
  - RED start: 1.3V
  - Full scale: 2.37V
  

• Walking at the analog way

  Miklos Marton • 08/08/2017 at 19:27 • 0 comments

  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.
  

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