I stumbled across a manual for the Hand Held Control Head and discovered it did not run on 8v as I previously thought (based on something I saw on the datasheet for the LED driver). It is supposed to run entirely on 5v. I also now have the entire schematic which is invaluable for determining how to interface with the various controls. When I moved the control head power off the radio's 8v bus to it's 5v bus, it wouldn't run at all. I put a meter on it and found that it was dragging it down to around 1v. Further experimentation with the control head and a power supply revealed that it draws over 120mA when the LEDs are lit. I needed a new 5v supply. I tossed a 7805 and the requisite capacitors on the breadboard and tied it to the switched 12v bus. While I was at it, I fed the Arduino from this as well. I found the 7805 was quickly reaching temperatures hot enough to burn my fingers. I added a couple of aluminum clip-on soldering heat shields to help cool it and consulted with #Hacker Channel, where I learned that between the voltage drop from 12v to 5v and the current draw I was going to have a pretty serious amount of heat to dissipate. While discussing how I intended to provide the heat sink, one of the members pointed out that ground loops would be an issue if I simply bolted it to the frame of the radio. He suggested looking in old power supplies for ground isolation mounts for TO220 packages. I had a dead PSU in the junk bin and found not only three mounts but a nice heat sink screwed onto the board. I pulled the whole heat sink out to use. I decided to split things into two separate 5v buses. One switched for the control head, and one unswitched to run the Arduino. I mounted both 7805s on the heatsink with the ground isolation kits and stuck them on a small breadboard and wired them up.

With the power supply sorted out, I'd like to fix the issue where flipping the power switch between ON and SCAN turns the radio off and back on. I'll get into more detail in the next log.