I've recently built the PS2M mouse adapter for my A1200. To programme the PIC16F84A chip, I built the COM84 serial port programmer and used WinPIC software. The mouse adapter worked first time. Total cost was around £10 (inc. programmer).
All components were sourced from ESR Electronic Components -
www.esr.co.uk (highly recommended).
Next job is to build a PC keyboard adapter - should cost no more than about £7.
