That moment when you discover a use for an old (rotten!) mic cable (or how to make a programming cable for an FT-90R using an Arduino!)

Since setting up my ‘new’ shack, I’ve been using my Yaesu FT-90R for 2m/70cm FM.  I must have bought it the late 1990s and it was used extensively in a mobile environment, moving from car to car for a number of years right up until I replaced it with my FT-857D when that got replaced in the shack by an FT-450 fairly recently!  The only problem with this radio is that over the years the sheathing on the mic has degraded and in places has split (and is getting worse with each use!)  Fortunately, replacements are cheaply available on eBay for pennies and mine arrived today!  Not wanting to waste anything and knowing that the radio has a clone facility, that enabled it to be programmed by a PC, it got me to thinking ….

Studying the FT-90 operating manual, the pin-out of the mic socket is as below.

Pin 2 – Data, Pin 4 – Gnd

How does a single data pin talk to a USB to TTL converter which uses 2 data pins?

A bit more Googling (GIYF people!) soon led me to an answer!  Using this as inspiration, I once again reached for my Arduino …

Configuring the Arduino to access the USB to TTL chip is exactly the same as my previous post about how to program your rig with an Arduino , if you haven’t seen it, pop over there now to see how, I’ll wait right here!

OK, got that sorted?  Connecting it up is slightly different however!  After a few false starts, I settled on the following configuration …


As you can see, the green wire from the previous post has been removed and replaced by a diode bridging the Tx and Rx pins on the Arduino.  Watch out for the polarity of the diode – the cathode should be towards the Rx pin.  Now there are two wires that can be connected to the mic jack of the rig.  The yellow wire in the picture goes to pin 4 of the RJ12 connector (DATA).  The red wire goes to pin 2 (GND).  It’s as simple as that!  To make it even easier, I used the old mic cable and plugged the jumper leads straight into that and the RJ12 at the other end into the rig.


Once this is done, all that is left to do is set the FT-90 into clone mode, swap the mic for the new ‘cable’ and fire up chirp!  There’s a nice video here by VR2XKP of the process in action.


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