Simplest hardware inverter for flight controller

Together with increasing popularity of STM32F4 flight controllers, telemetry became hard topic again. Why? Most popular telemetry protocols, SmartPort and FrSky telemetry , requires inverted signal. Zero becomes one, one becomes zero.

In case on STM32F3 that was not a big problem. Those CPUs have built in inverters. STM32F1 and STM32F4 does not. So, if flight controller designer did not put external inverters on UART ports, FrSky telemetry, SmartPort and even S.Bus would not work.

Luckily, simple inverter for FrSky telemetry and S.Bus can be build using only few electronic parts:

  • Small logic level N-channel MOSFET transistor. One of the best choices is 2N7000
  • 10kOhm resistor
  • few cables

This device is so simple, that it can be built without PCB. Cables and resistor can be attached to the transistor, and everything can be put inside heat-shrink tube.

11 thoughts to “Simplest hardware inverter for flight controller”

    1. Better choise is using 2SK3019 NFET transistor intead of 2N7000. 2SK3019 has match lower Gate Threshold Voltage arround 1,2V.

    1. that one is bidirectional. This one is unidirectional and only to connect SBus to F4 flight controllers without dedicated SBUS pin.

      1. thansk Dziku, I missed your answer! Due to the fact I have many units hardware components for doing “Pixhawh Frsky inverter”, I suppose I could use this to here? Is it a correct assomption ?

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