Help Please - Retevis RA25 mini mic adapter - Anyone done this ?

Equipment
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Have made several electret mini mics based on Electret capsule and button press switch. For FX4CR, QMX, Radio-Kits Explorer and even made an adapter for Yaesu FTM 3100 to convert the RJ45 plug to 3 core jack plug, for a mini mic. But I’m really struggling to make an adapter for the Retevis RA25 to allow me to plug a mini mic into the radio.

The pin-out of the radio is different to any of the others that I’ve done, in that it has no PTT pin. Here is the Pinout

Pin 1 - Red - URX/Data

Pin 2 - Brown - 5V

Pin 3 - Yellow - UTX/Data

Pin 4 - Empty

Pin 5 - White/shielded - MICE

Pin 6 - White - MIC

Pin 7 - Empty

Pin 8 - Grey - Ground

During my research I came across a suggestion that grounding the URX/DATA pin to ground will put the radio into transmit. It does go into transmit. I get a nice +/- signal on the MIC pin too of approx 5mV. But when I release pin1 from ground the radio goes into scan mode and starts scanning through the frequencies. I’ve used a 2.2Kohm resister to bias the electret and a 4.7uF electrolytic capacitor (the right way round) and the reading in the MIC pin would suggest that this circuitry is OK. Pin 1 also looks like its at 3V when not grounded, I don’t know if it is supposed to be.

I’m at that point where I’m trying the same stuff and getting the same result and would really appreciate any experience from anyone who has done this or can help me understand something I can do with no PTT pin. Would a resistor in series between pin 1 and ground make a difference?

I really like this little VHF radio, 20W for 416g is great but the mic takes up a lot of space, weights too much and has too many buttons you can accidentally press during a cold/windy activation (including changing frequency with my nose during a transmission twice over the weekend!)

Any help much appreciated :grinning_face:

Blemcathra
Blemcathra1524×2048 416 KB

2

I suspect those two ‘data’ pins are used in the same way as the ones in the Mic socket of the Yaesu 8800/8900 mobile radios. They have a resistor network in the Mic and pressing different buttons (PTT, Up, Down) change the voltage presented to the radio.

It might be worth opening up the Mic and seeing what is inside.

As for the ‘Nose’ problem, does the Mic have a ‘Lock’ function that disables everything except the PTT?

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Thank you. On the lock button thing, a search and trying stuff out reveals that “Fun” then “Mon” on the mic keypad locks and unlocks the keys on mic and radio. Thanks for that I just needed to try a bit harder to find it!:grinning: Nice big slide switch on the side would have been nice!

On the voltage thing I’ll have a look and see if I can see what the resistance is between Pin 1 and ground when the PTT is pressed. I’ll let you know how I get on :grinning:

Many Thanks

Kind Regards

Ian M0JIA

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