Older 3DR radio and APM 2.5? Which pins to which pins?

A friend gave me an older(?) 3DR radio?

Anyway, it has 4 leads/wires coming off the "flying" portion.

Can someone take a look at the pic and tell me which of the 6 board connections need wires soldered to them, and to which pins on the APM 2.5 they should go?

And...maybe this isn't worth the trouble?  Maybe I should just get a new 3DR telemetry setup?


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Are you sure it is a 3DR radio and not a clone? I have the 3DR 900MHz telemetry radios and they do not have the type of connector (Hirose) that is visible in your picture. The 3DR radios use the 0.1 spaced berg style pins and connectors.

I would buzz the pads on the back side of the radio to the wires in the connector, so you know what signals are on the cable, and then see if the other end of the cable matches the input on the APM2.5 connector.



Thomas... As far as I know... It is an actual 3DR radio... But really, I can't be sure.

The main issue is that there are supposed to be 5 wires going IN to the APM 2.5 from the radio (though only FOUR go into the APM 2.0...and this is why I think this isan "old" radio, as it appears it is wired for an APM 2.0?).

I am pretty sure that if I can solder 5 wires to the correct 5 pads on the back of the radio (and not use that connector at all), and connect those 5 wires to the correct 5 pins on the APM 2.5, I just might be able to get it to work.


Even if I get those wires correct, I wonder if there is something else about thos old radio... Firmware... Whatever... That will prevent it from working with the APM 2.5?

Here is an explanation of the connections


Thanks Kenobi!

im having the same problem.

i bought an 3dr radio online from ebay. it came with 5 seperate female-to-female headers, unlike the apm 2.5 3dr radio socket.

Thank you so much, I just realised that the Socket i had for my LEA-6H gps matches exactly the telemetry socket.

I'm thinking about using that 5 pin socket for telemetry after some soldering.

I'm going to use old style gps socket for gps which i had a cable in spare. Do I have to make any changes to use old style gps socket? or does it work as you plug?

OK...I took some good pictures...this is how the the wires are connected, assuming a person has the 3DR "telemetry adapter cable" plugged into the APM:


This cable comes included with the purchase of an APM 2.5+, and is also available on it's own for $2.00.

APM wires --> older 3DR radio wires

Red (furthest toward the "inside" of the APM) ---> 5V (red)

Black, 2nd from inside --> RX (white)

Black, middle --> TX (blue)

Black, 2nd from outside --> CO (no color, see pic)

Black, "outside" -- GND (black)

The "older" 3DR radio has a FOUR wire harness coming out of it...they are marked RX/TX/5V/GND...but FIVE wires need connected to the APM...that 5th wire connects to the "CO" pad on the radio...I soldered mine (see pic).

That said, at first I hooked up just the 4 wires from the harness, and as a test, was seemingly able to connect and have the radios send/receive data to each other...I don't know what the "CO" does, but I connected it anyway.

I had originally soldered all the wires from the APM to the back of the radio, that's why there is all that solder mess, then decided to use the wire harness with the white/blue/red/black wires.

Hope this helps.


This helps!! Thanks

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