Use of Microhard P900 with HolyBro Pixhawk 4

Hello everyone,

I’m currently trying to use a pair of Microhard P900-ENC ( to serve as the Telemetry radios for the HolyBro Pixhawk 4. Because the radios use an RS232 connector, I’ve also acquired a TTL to Serial convertor (

While both radios have been configured correctly to talk to each other, I can’t seem to get any information to be transmitted over the radios from the Pixhawk to the ground computer. I’m not too knowledgeable about serial radios, so I was hoping some folks here could help provide some insight as to what I can do to try to troubleshoot it?

Thanks in advance for the help.

This should be possible, I have a p900 radio that communicates with my GCS, however it was sold with a commercially bought drone so I wasn’t the one to configure it. My best guess is to try swapping the RX and TX on the converter as there may be some ambiguity on how it is labeled

Hi Jake,

Thanks for the input! I’ve tried switching the RX and TX on the TTL-RS232 Shifter, but it didn’t work either way unfortunately.

I know you mentioned that you hadn’t configured the radios yourself, but I was wondering if you had ever poked around in the settings portion of the microhard radios? Was curious to know if I could potentially compare settings to see if there might be something I’m doing wrong on my end.

EDIT: Also, just to confirm, is it a Microhard P900 unit that you have, or a P900-based unit from a third party manufacturer?

I have not poked around with the settings unfortunately, It is a P900 unit on a custom carrier board produced by the manufacturer of the drone, or at least they stamped their name on it. It looks pretty similar to the board in the enclosed unit but there are certainly some differences

Ah I see - ok thanks for letting me know. I appreciate the help!

I’ll have to keep poking around to see if I can get it working with the stock carrier board.