I wanted to interface my Baofeng UV-B6 using a K5INZ “Easy Digi” board from eBay for PTT control.

The K5INZ “Easy Digi” boards are very inexpensive interface boards, which are available on eBay. You can find them by searching here. The Baofeng UV-B5 and UV-B6 feature a Kenwood-style 2-pin 3.5mm and 2.5mm connector on the side of the radio. Although the radio supports PTT keying, you have to take care to wire it correctly.

I found the pinout on the Miklor site confusing. After a quick search, I found this better image of the pinout:

Source: http://ham.stackexchange.com/questions/1891/whats-the-pinout-for-kenwood-2-5mm-trs-3-5-mm-trs-connector

Going off this, you can see that the 3.5mm shield is the PTT, which gets pulled to ground to enable. You can also see that the grounds are on the 2.5mm side (ring and shield) and are for the speaker, mic, and PTT.

This should work for all Baofeng 2-pin cable compatible radios, such as the UV-5R (and variants), the BF-F8+ (and variants), and UV-82 (and variants). This should also work for all 2-pin cable compatible radios from other manufacturers, as long as they use the same pin out.

Special Note for UV-82 series: The UV-82 series supports dual-PTT keying. As such, the pinout is slightly different. The rest of this article will give you a working setup, but will key PTT for the bottom display only. The top display is keyed using the tip of the 3.5mm jack instead of the shield. See this page on miklor.com for more details. 

I used a USB A-to-B cable and cut off the ends. This left me with 4 conductors, of which I only needed three. I wired the RTS, DTR, and digital ground to a DB-9 female connector, with a little bit of electrical tape to keep the cable shield from causing any problems.

Pinout source: http://www.db9-pinout.com/

Then wire the connections to and from PC audio in the usual manner. On the Easy Digi the polarity is not marked, but if you follow the wiring diagrams included, you will see the two negatives are in the center, and the positives are on the outside. I marked them myself with a silver marker to help during assembly. For this I used two 3.5mm stereo cables, and wired tip (+), shield (-), and left the ring disconnected.

Next I took a 3.5mm stereo cable and connected the ring to mic in, the shield to PTT high, and left the tip disconnected. (UV-82 series owners only, this is where you want to connect the tip instead of the shield if you want top display PTT instead of bottom display PTT)

Next, I took an Arduino jumper and cut it in half. Put one pin in mic ground, one pin in PTT ground, and twist the free ends together. Tin the twisted end, and solder and snip the excess pin leads. You could use any suitable wire for this jumper. It should end up as shown here:

Next, solder on the audio in using the tip (+) and shield (-). The radio side of this cable needs to go down to 2.5mm, and can be mono or stereo, but if it’s stereo, be sure to leave the ring disconnected. You can use a 2.5mm to 3.5mm adapter, such as this one from Monoprice, but either wire your own plug or test the adapter before use.

Take the jumper lead you made previously and wrap it around and solder it to audio ground. If you’re using the Easy Digi case, don’t go around the long side of the board (as I did in this photo), go around the short side of the board. You won’t be able to fit the board back in the case if you go around the long side. you could have also made the connections from the bottom side of the board if you so desired.

You should have your board fully assembled now.

You can now control PTT with either DTR or RTS control over your serial port, and it works fine with USB-to-Serial adapters.

This works great for an EchoLink simplex repeater, or for APRS digipeating use.

Audio leveling: I found this to work best when the Baofeng volume is set between the 9 o’clock to the 10 o’clock position, and the PC mic input is set to 20 with +20db boost. I found that the PC volume level may have to be set anywhere between 20 and 50, depending on the particular PC and software. You will likely have to adjust to your own environment.

NOTE: If using this with DireWolf v1.2 for APRS, you will need to specify both DTR and RTS control in the DireWolf configuration file, or DireWolf will hold PTT down. All other programs seem to work normally. Example configuration line for DireWolf:

PTT COM4 DTR RTS

Comments are welcome.