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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
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