We need to pick a embedded cpu. The requirements are:
It must handle all of the GPIO (see part 1 for the I/O Table), or about 20 pins.
It needs a USB interface for a data link to talk to the host.
It needs to generate the BFO signal.
It needs a PWM output to drive the meter.
It needs to have a protocol designed for it. But I has to fit in to the Radio SubSystem or RSS architecture.
We need to design a interface card. It should have a relay for the Dial Lamps, and a connection to the Panel Lamp Dimmer. It should have a jack to connect the gain potentiometer to the audio system. It should also have an output for the ADF flags, in various instruments.
We also need to replace the syncro with static or absolute digital encoder. It must be static as when the system powers up there is no guarantee where the dial will be tuned to. Remember this is just a AM radio.
Here is a block diagram of the ADF system:
Now we must get the syncro out of the frame. Here is an abbreviated version, I will post some photos when I do the work. (TM 11-5826-255-35 page 3-12):
Loosen two Dxus fasteners located on rear cover, and slide the rear cover off the control unit.
Remove three screws and three lock washers securing retaining (rear) plate to frame.
Remove fixed resistor from retaining (rear) plate by removing the screw.
Remove four screws and nuts securing connector to the retaining (rear) plate.
Remove the retaining (rear) plate.
Loosen two setscrews on collar, and remove spur gear from shaft of helical gear. Note. If the setscrews cannot be reached, the tuning gear train must be disassembled.
Loosen two setscrews on collar, and remove spur gears from the shaft of transmitter syncro.
Loosen the three screws located around transmitter synchro at the shaft end.
Orient three rim-clinching clamps to permit removal of transmitter synchro and remove the transmitter synchro.
Remember re-assembly is just the reverse order. Make sure that you keep all of the screws, etc. in a nice safe place. What I like to do is to put the screws back where they came from.