FrSky S.Port/F.Port inverter

Inverter for FrSky's S.Port or inverted F.Port signals, using a CMOS logic IC.

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After my XJT module died (at least a thought so), I had a real cause to get the R9 system. I was lucky, and could buy the module from a guy for around 13$. I also ordered the R9 mini receiver, which was a mistake. The R9 mini, as opposed to the R9 mm, doesn't have an inverted S.Port pin (which actually means uninverted), so I needed to invert the signal. After two days of experimenting with different transistor designs, I settled with a CMOS one. The transistor inverters were unreliable, because of the bad signal levels. CMOS is better, as it has a wider supply range, and also the correct voltage levels.

My first design used a CD4069UBE in DIP package, which I had laying around at home, built on a perfboard. It seems to work well now, but I will still test it more.

I designed an other one in EasyEDA, using a much smaller IC, the NC7WZU04P6X. This version fits on a 6.6 x 9.2 mm  (0.26 x 0.36 inch) board, that costs 0.45$/3pcs at OSH Park. I'm currently waiting for the PCBs, so as soon as I get them, I will test their reliability, and publish some more photos. 

This circuit should work with a 5V supply. If you would like to use it  with 3.3V, I recommend changing the diode to a schottky with a lower forward voltage. 

Also, I appreciate all kinds of feedback. And if there's a need for it, I might sell some on Tindie. 

EasyEDA project link

OSH Park link

The Gerber files for the PCB.

x-zip-compressed - 5.71 kB - 07/10/2019 at 10:07


  • 1 × NC7WZU04P6X Logic ICs / Gates and Inverters
  • 1 × 1N4007 (SOD-323 package) Discrete Semiconductors / Diodes and Rectifiers
  • 1 × 10uF 0603 ceramic capacitor
  • 1 × 0.1uF 0603 ceramic capacitor

  • Prototype working

    Agoston Garad07/23/2019 at 19:18 0 comments

    The CD4069UBE has gone through some more testing (FPV racing competiton, and practice sessions) and it has been working fine, there were no problems. Also, OSH Park has shipped the PCB's, so soon I will be able to start to put the first PCB's together. 

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