PRC344 Scan Project

A drunken challenge accepted means that I am in the process of developing a controller that will give the Clansman PRC344 radio a scan capability. This is pretty frivolous to say the least! - the radios 50kHz steps means many active frequencies will never be heard anyway! But, its a fun thing to try and make happen,

The idea is to develop a means of controlling the tuning of the radio in timed steps, with received signals halting the scan. Initially, the system will be 'blind', that is, entirely self contained within the radio with no functions other than to start and stop it, and to override the halt to continue scanning. But later, by sacrificing one of the radios audio connectors, and external controller could be attached for more sophisticated operation.

This is no easy task. For a start, I have to take control of the synthesiser, this means 14 control lines plus a means to break the ground connection to the frequency dials. But, I also need to override the radios RF front end tuning, which means taking control of another 18 lines, and switching over a further three! I also need to accept control inputs from 3 different parts of the radio! Plus, I need an RS232 port. All in all, that means arranging for a minimum of 38 control lines on my controller!

And all this has to not only run on 3V to be compatible with the synthesisers logic, but switch tuning voltages up to 70V! And, when not selected to scan - have zero current drain!
 If all thats not bad enough, the entire thing must fit within the space left by the removal of the Tx control module!

Yet, I think I have the answer! And its all down to modern high performance microcontrollers and sophisticated logic chips. A string of resistors, a couple of 24v DPDT relays, two MOSFETs, a zener, a 3v regulator, three high voltage 8-port multiplexers, two 16-bit I2C port expanders, and a tiny little biddy PIC microcontroller! All built with SMT parts.

Just waiting on the prototyping samples to arrive. In the meantime, I have to do the daunting part that will form the heart of the system - Ive to learn to program in C...