Scrap box APRS iGate / Digipeater

 

So, no shit, there I was. Our Tompkins County Amateur Radio Association is getting ready to support the AIDS Ride for Life event this coming weekend. It occurred to me that it might be handy to have an extra fill-in APRS DigiPeater / iGate running at my house, which could serve some places that have poorer coverage. So, I thought "Self, what would I need?" "Well, self, I'd need a radio, a raspberry Pi running Direwolf, and a magic cable to attach the radio to the Pi." As it happens, I have the perfect radio. Years ago, I picked up an ICOM IC-2000 (VHF Only) radio for $20. It was non-functional. I repaired it fairly easily. If I recall, there was just a blown transistor in the power-on circuit. It's been sitting on the shelf ever since. This is a perfect use for it, so I can get it out of moth balls! 

 

 

 

So next, I considered the magic cable. I figured a decent one would have a CM108 audio card for the Pi, a few audio transformers, and a Optocoupler to isolate the PTT ground (I've run into problems in the past when I tried to do it with a transistor). So, with a rough idea in mind, I started digging through my parts bins. I pulled out my trusty box-o-CM108's, and lo and behold if I didn't find a "KF5INZ Easy Digi" kit board that I had built YEARS ago and completely forgotten. That board has the audio transformers and optocoupler built-in! 99% of my work was done! Though I have no recollection of messing with the Easy-digi, I'm sure my knowledge of what I needed to do was based on playing with it years ago. My brain remembers processes, not details, so that tracks.

 

 

 

So, I desoldered the bodge of wiring that was on it from whatever experiment I must have done (probably an allstar node), and put it all together. I hacked off the end of a CAT5 cable to plug into the Microphone port on the radio. That gives me Mic-IN and PTT controls. To get audio, I just had need to plug into the external audio port on the radio. PTT is driven from the Easy-Digi board. I just have to run a few wires to the Raspberry Pi for it. Direwolf can do the rest with a GPIO port. I did hook up a power supply and a little LED to test the Optocoupler to assure it worked as I expected. It did.

 

So, 2 hours later, I had the magic cable to plug between the Raspberry Pi and the IC-2000. 

 

 

The next day, I configured up a new SD card for a Pi in my parts bin.  I built it on Raspbian Bookwork, which turned out to be a minor hassle.  The version of Direwolf that ships with it (1.6) does not have support for the GPIO changes that were made in Raspbian.  I ended up having to download the Dev branch of 1.8 and build the code from scratch.  

 

Testing went very smoothly.   I had one scare, thinking the radio had failed.  It turned out that it had an Auto Poweroff setting enabled.  Everything else pretty much worked right out of the can.   The audio was pretty sensitive.  I had to turn it WAY down so that direwolf wasn't complaining about it being overdriven.  I also noted that the volume POT on the radio is dirty.  A few times, the volume went from "low" to "off" without touching the knob.  Just wiggling it solved the problem.  I'll spray some cleaner on it.

Since this is really a temporary setup, I just zip-tied the Pi and cabling to the radio to make it somewhat secure.  We ran this over the weekend for the event, and it worked great!