Thursday, 5 May 2011

Adding a composite output to a ZX Spectrum

Tonight at BuildBrighton we have Sinclair night! One problem that we have is that the Spectrum, ZX81 etc (and a lot of other 1980's home computers) do not have composite video output sockets but rather were designed to run on an analog TV set tuned to the correct channel to pick up their signal. Analog TV sets are getting a bit hard to find these days, so this is an inconvenience...

Many years back I got my Spectrum to run on an old greenscreen mono monitor I was given. I don't have that speccy any more but decided to try the same trick on a spec I picked up on eBay earlier this year. With a composite output it is possible to hook it up to most modern TVs and many computer monitors.

Well, technically there is nothing to it... the Spectrum already has the composite signal (it is fed into the UHF modulator box that converts it to a TV signal) so its just a matter of getting the signal to the outside world.

I already had a 3.5mm mono jack to coaxial video lead from an Olympus digital camera (its the lead for showing your pics on the TV set) so I decided to simply add a 3.5mm socket so I could use the same lead.

The modulator is the nice little tin box on the inside of the Specc's TV connector. Take care when lifting the lid off the speccy or you might accidentally pull out the keyboard ribbons

 Connect the SIGNAL (jack plug tip) to the connection going into the box furthest back from the TV socket (on my speccy it had a white plastic insulator). Connect GROUND (jack plug barrel) to the metal box itself, using solder to make sure you get a good connection.
 Fit the socket... ah hot glue, how thee makes a craftsman of any pleb!

... get out the swiss army knife and scratch a groove to accomodate the socket in the lid so it can close

And the proof of the pudding... a "Specbook"