I recently purchased a Deltronics CONTROL IT buffer box from the online tat bazaar eBay, with a view to connecting it to my Commodore VIC 20. The Control IT buffer box is a general purpose interface that gives you easy and protected access to the computer’s user port. It was designed to connect to the BBC Micro or other suitable computer.
The box has a 25 way D-type socket on the back and the connecting cable is terminated with a 25way D-type plug. I had to make up a lead as the box wasn’t provided with one, luckily I managed to find a pinout for the 25way D-type socket on this website.
The buffer box contains its own mains power supply which is stabilised and protected internally against overloads and short circuits and the key switch on the front selects either 12 V or 6 V but I don’t have the key. The full supply voltage of 6 V or 12 V is available between the red and black sockets at all times. Because of the voltage drop across the buffer box internal circuitry the voltages available at the blue and grey sockets will be less than the supply voltages. The voltages are blue to black 5.25 V(6 V range) 11.25 V(12V range) and grey to grey 4.5 V (6 V range) 10.5 V (12 V range).
The Control IT buffer box can be used with the following BBC Model B, BBC Plus, BBC Master 128, BBC Master Compact, RML 380Z, RML480Z, RML Nimbus and Sinclair Spectrum although it can be used with any computer that provides access to eight input and eight output lines at TTL levels.
I connected the output lines to the user port on my VIC 20 and wrote a quick bit of BASIC software to turn the outputs on in sequence.