Parrot repeater for 446 MHz PMR radio

My friend asked me to make a voice repeater for his PMR radio.
It had to be remote controlled by DTMF and it should be capable of record and play 60 sec.
I built it with a PIC18F2520 mcu. The built in adc working at 8kHz and every sample is stored in a 256kB static RAM.
Because of i/o port saving the addressing is done by a 4040 counter.
The transceiver microphone input is drived by a TDA1545 D/A converter.
The MT3271 dtmf decoder is connected via serial link to the mcu.

Parrot repeater modul on the rear of the 446MHz radio


Schematic