Frsky Telemetry Matek F405-Wing and r-xsr receiver

I have been trying to get telemetry to work for literally months. I have tried everything I could find. A max3232 converter did not work. Several circuits I found on the internet did not work until I built the attached converter. It must be supplied with 5V. 3.3V does not work. 2n3904 transistors can be used instead of BC547s, but the pinout is reversed. I think the problem is the voltage levels needed by the r-xsr receiver, but it could also be the max232 mini converters I got from amazon. I got one out of 10 to work with my pixhawk FC. The circuit came from a german website, kudos to whoever designed it. !