God creates, others copy. It is also true that "necessity is the mother of invention". Here are some things I like to think I have created. Maybe one day I will add to this page some specific design information.
GAUGE OO INERTIAL MODEL TRAIN CONTROLLER (age 16)
Model trains are typically controlled by a rheostat or potentiometer from a 12V dc supply, at least they were before electronics came along. The knob is effectively a speed control. If there is dirt on the track the speed isn't even smooth.
"Driving" such a train lacks realism. In reality a train has inertia and slows down when climbing and accelerates when going downhill. A very simple way to simulate interia and reduce the effect of dirt is to supply the train from a constant current source, and the easiest way of doing this is to start with a higher supply voltage (say 24V dc or more) connected to the train via a series rheostat. This effectively controls the motor's torque and not its speed.
Arrange for the minimum current to be non-zero and able to be trimmed to the point where the motor just overcomes friction on the level, and you have a pretty good and beautifully simple inertial controller. The maximum current must also be limited to save burning the motor out. At a given setting it will struggle up a hill and race downhill, just what the doctor ordered.
GAUGE OO AUTOMATIC SIGNALLING (age 16)
I acquired four 4-pole changeover relays from an old telephone switchboard - this was the foundational step of the design. The target track was a circuit divided into 4 segments. I made my own current sensing relays by casting contacts in a mixture of polyfilla and white glue with a low resistance coil connected to a short length of track. With one sensing relay and one 4-pole relay per track segment my design was able to control a 3-colour (red, amber, green) signal, an isolating track length, an automatic choice of one of two controllers and a mimic panel. In this way two trains could be run on separate controllers simultaneously on the one circuit. The design target for total reliability and maximum usage of components was achieved. Later I tried to redesign using TTL logic and failed miserably! Relays rock!
MUSICAL SLIDE RULE (age 17)
Using a printed see-through tube fitting over a plastic tube, so that the outer tube could be moved longitudinally and circularly, I created a "slide rule" to calculate the notes of any musical scale (major, minor, any key) or to calculate the interval between any two notes. I created this to help me through the theory for music O-level and it did.
