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A matrix display using light bulbs


My first from-scratch design was inspired by a box of flashlight bulbs handed down from my grandfather's workshop. I was around twelve at the time.
I made a panel that held the screw-base bulbs in a 5 x 5 matrix, by drilling holes in a sheet metal panel, cutting a radial slit in each hole, then using a screwdrive to bend the metal on one side of the slit up and the other side down, so the bulbs could be screwed into the holes. That sat on top of a board with a corresponding array of screw heads for the center contacts of the bulbs to make contact with. A hand-twisted cable containing a wire for each bulb in the matrix plus a common for the sheet metal panel went to the control board, which had another matrix of screw heads, and one side of the power supply (a heavy duty filament transormer). A wire with an alligator clip went to the other side of the power supply. I then cut digits and letters out of tin, sized to fit the matrix of screw heads on the control board. I could then clip the alligator clip onto the letter or digit I wanted to display, set the digit or letter on the matrix of the control board, where it completed the connections for the corresponding bulbs on the other end of the cable.

The project was pretty primitive, but I learned quite a bit in the process. Including the that connectors and wiring usually end up being a bigger and more time consuming part of a project than you expect. And the importance of reliability as the number of connections goes up!

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