Admittedly – the tones that come out of this box are rather scruffy. In return, the model-making synthesizer convinces with its original appearance and the clever use of old technology. Because its six buttons belong to a controller that was originally used to control model railways from the East German manufacturer Berliner TT-Bahnen. With photo resistors, LEDs and an oscillator circuit, the Berlin hobbyist Marc has built an interactive instrument out of it that just fits into the original box.

The basis of the synthesizer is a small circuit with a Hex-Schmitt trigger, which we use in Make 1 / 18, from p. 48. The chip contains six identical circuits with which six different tones can be generated and thus fits perfectly with the keyboard. It practically tolerates between 3 and 01 volts and always delivers defined output signals: square waves, one of the basic forms of sound generation . The frequency of the vibrations is determined by the built-in capacitors and resistors. By flipping the console’s buttons, you can set whether or not current flows. The pitch (or frequency) is then changed via the photo resistors, which react to differences in brightness. Six LEDs also visually indicate which tones are currently sounding.

Model building synthesizer (4 images) Test setup of the circuit on a breadboard

(Image: Marc) The circuit is “normal” soldered on a small breadboard, but in order to cram the entire project into the little box, Marc had to get creative with the installation . He shortened the cables so that they could only be connected when the lid was already half closed. So that the contact points do not lead to short circuits, he insulated them with liquid rubber. Heating shrink tubing was not an option in a flammable cardboard box. After all, the 9-volt block also fits perfectly into the box as a power supply. The keypad is firmly attached to the cover with four screws.

Particularly effective music can be elicited from the model-making synth when you Wears black gloves to play with and has a flashlight or flashing bicycle light ready. A mini amplifier is still required, but the project remains easy to transport. Marc has put many pictures, further explanations and of course an acoustic demonstration on his website. Since German is not his mother tongue, he would also be happy to receive help to further improve the documentation. (hch)