ArduCopter RSSI voltage modification


i am flying a long range quadcopter with APM 2.6 external compass question is how can i modify RSSI voltage reading of the APM since my RX at maximum signal is 1.5volts..? and in full parameters list it seems to have only 3.3V and 5.0V ..

It ll needs to have buffer ?

my receiver is Rmilec 4047lite

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  • Developer

    Hello everyone,

    This is solved with pull requests #1603 and #1604.
    Hope it pass the developers review and they merge them in master soon...


  • Developer
    Hello everyone,

    I am trying to resolve this. I have modified actual code introducing a new parameter called RSSI_MIN_RANGE, RSSI_RANGE has been changed to RSSI_MAX_RANGE. You can see this in github, pull request #1568:

    Regards from Spain,
  • Developer
    If a parameter is not shown in the Full Parameter View its the APM Firmware version. The parameters are automatically defined and sent from the autopilot to the GCS. All teh GCS does is correlate the param name to a xml file to show description etc... If available
  • Saqib, it could be your APM code, but try mission planner instead of APM planner. 

  • What version of apmplanner are you using? I dont even have the rssi_range option on mine. My rssi is on 160% because its set on the max 5v i think. Im using a 3.3v reciever. Is there any other way of changing the parameter?
  • A small rail-rail op-amp would be good for this. I use the TLC2272 but recently got in some MCP6401; a single op-amp in a much smaller SMD package. A bit tricky to use if you don't have a circuit board. R-R allows a simple circuit with full voltage swing and few or no power supply issues.

  • Developer

    Look at page 11 The Non-inverting DC Gain diagram in the datasheet. 

    If you used R2 as 1MOhm and R1 as 470KOhm, you get a gain to 4.6V at 1.5V (+- some % error). That's 2 resistors and a 8 PIN DIL OpAmp chip. Add a small cap on the input in parallel and small one on the output to reduce noise, and there you have it.

    the part is available here 

    I'm sure we can figure out the size caps required, but amplifying the signal before the ADC will make it much more reliable solution.

    Anyway, just a suggestion. :-)
  • Bill does have a good point; RSSI doesn't just lineally step down from 100% to 0% when you fly farther and farther away.  When you're flying near the end of your range your RSSI drops fast and quick; that extra resolution might be helpful.  However there's nothing wrong with a simple software test; maybe turn on the failsafe and see how it does with less resolution.

  • i agree  Bill with you but i m building something very lightweight and with long flight time and of course ..and i don t want to make any circuits.. 

  • Developer

    That variable will scale 3.3V signal read on the input 100% in code when using a 5.0V ref on the ADC. The looses resolution for convenience.

    If you set it to 1.5V when using a 5.0V ref voltage you will loose a lot of resolution as you are only using a small part of the voltage range on the input. You would be much better off creating a small circuit that amplifies the 1.5V to 5.0V range to have the full resolution.

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