I poked around on the Internet looking for a schematic for the HM-219 hand mic. Believe me, Icom didn’t make it easy to find, but eventually I came up with a few helpful results I was able to piece together.
Now, I know that if I’m going to build my own headset, I will need to come up with an acceptable microphone. Since I liked how the mic in the HM-219 sounds, I decided I will take that and figure out how to get it mounted on a boom. There is also the small matter of a diode, a resistor, and a couple capacitors that must be placed between the mic element and pins 1 & 7 on the mic jack. In order to make this microphone perform as similarly as possible to the HM-219 I will need to locate this bit of circuit near the mic element – a problem for later. For now, I just want to verify that what I’ve found on the Internet is correct.
I started taking apart the HM-219. A small phillips head screw driver got things started.
I compared the color codes and labels on the PCB. Everything matched up. So far. so good.
The PCB from the mic body is too big to tuck into the new headset, and I wouldn’t want the PTT and Up/Down switches anywhere up there, so I decided I wouldn’t be reusing that for this project. However, I could certainly use the mic cable and element, so I broke out some more tools.
Here the silver mic element is seen to the left between the foam and the plastic housing which holds it in position inside the body of the hand mic.
The mic cable included a fat section of strain relief molded around the outside where it seats inside the hand mic body. I won’t be able to use that oddly shaped custom fit for my project, so I used an exacto knife and carefully trimmed away the strain relief. I will have to come up with my own solution for this later.
It only took a few seconds for my trusty iron to free the mic element and cable from the PCB. These are the only two parts I will be salvaging. The rest will go into the scrap parts bin if I am happy with how the headset turns out. Otherwise, I will just put the HM-219 back together (with alternate strain relief).
In Part 3 I will salvage the rest of the parts I’ll need and begin some rough proof of concept testing. Stay tuned!