Reworking a FrSky D4R-II Receiver

Since i want to use telemetry with my soon-to-be-finished uavp-ng quadcopter i decided to use a FrSky two-way-telemetry system. Unfortunately the enigneers at FrSky choose to invert the serial signal which wont work on the hw0.24-mini.

Thats why i took a closer look at the receiver pcb. Fortunately it was quite easy to identify the UART-Pins with TTL levels. I removed the two transistors and some resistors which arent needed anymore.

The pinheader was also removed in this process. I added a bridge on ch3&4 to active CPPM-mode.

As a additional modification  a voltage divider was installed. The AD2-Input of the receiver works up to 3.3Volt. With a 3k3 and a 10k resitor i was able to build a network with a convenient 1:4 scale factor. With 4*3.3Volt > 13V i can monitor the voltage of a 3S LiPo 🙂

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