Back in the mists of time, I spent a while at the University of Manchester Institute of Science and Technology…1980 so no mobile phones back then. No internet, social media or even fax machines. Decent computers were housed in large air conditioned rooms and had a team of dedicated staff to provide the tender loving care they needed.
Today I was testing a very basic circuit to successfully combine the ignition pulses from my Matchless G12 650 twin, to drive an analogue tachometer. Most twins use a single coil and distributor based ignition system…like a car which has four or more cylinders. It also means you can fine tune the ignition timing by turning the distributor housing. From 1964 to the end of production, Matchless decided to do away with the distributor and have two contact breakers and two ignition coils…I assume it was cheaper.
Neat and tidy design
The aftermarket tachometers on the market need one pulse per revolution of the engine to read correctly. Four stroke twins normally provide this, but not directly with separate coils for each cylinder.
My bike is also positive earth, so there are a few changes to the circuit diagram. Rather than solder a prototype, I decided to dig out the Powered Prototyping Board I’d built as a First Year Project at UMIST. It needed a clean and I checked it over before powering it up on a VARIAC. All was well after over forty years and it made the job of checking out my modifications to the tachometer circuit easy.
I still remember building this thing. We had to cut the metal then file and drill it, bend and solder the case, paint it, assemble the circuit board, test it and put it all together. Electronics was already my hobby before I went to university and I’d already built many things, so this project was finished in no time at all…I ended up being retasked to help others build theirs.
Testing underway
Universities and schools still taught practical subjects like woodwork, metalwork and electronics back then. I wonder who will be able to do them in the future? When I last returned to my old high school, all the workshops had been turned into IT suites.
I actually get a great deal of pleasure from using things I’ve either made from scratch, built from a kit or repaired myself.