MIC/PTT Interface for Baofeng Type Radios

If you have a Baofeng radio or one of the many other similar Chinese hand portables then this may be of interest. Love them or hate them, these rigs are now very much part of the amateur radio hobby and I have to say I think they are great fun! The information given on this page relates to the external speaker/mic connector (also used for channel programming via CHIRP) which takes a 2.5mm and a 3.5mm TRS jack plug cojoined together. Although this type of connector is officially called a 'Kenwood K1', it now seems to be the standard for many different radios coming out of China. Full disclosure here, I don't acually own a Baofeng, I have a Retevis RT85, but I used 'Baofeng' in the title as they seem to be the most popular

For reference, a typical wiring diagram for a 'Cheapo' Chinese speaker/mic is shown above (they don't all have the LED). It can be seen that the 2.5mm plug carries the ground connection for pretty much everything. As a point of note, I would probably omit the LED as it could impact the transmit audio quality due to being an extra load across the microphone, possibly reducing the supply voltage to it as well. The interface circuit is shown below, consisting of just a PTT rocker switch and a stereo 3.5mm jack socket (without the ring connected), all housed in a Hammond 1551HBK enclosure

This simple interface came about because I wanted to convert the double jack socket to something more useable so that a desk mic, for example, can be easily connected. The first thing I needed was a double jack plug. These can be obtained with cable attached from eBay, but it actually cost less to purchase the cheapest external speaker/mic I could find on Amazon to use as a donor for the plug and cable (and you also get a speaker and a microphone for the junk box!). As these jacks are intended for an external speaker/mic, the internal speaker will mute when the plugs are inserted but there is an easy fix. By removing the tip of the 2.5mm plug with side cutters and then rounding it off with a file, the 'break' contact in series with the internal speaker cannot be pushed and so the speaker still functions

Internal view