A variable capacitor made from junk

cap

[Jezan] decided to introduce his son to electronics by building a small crystal radio. These crystal sets have been around for a long time, and make for a great beginner electronics project, but some of the required parts are a little hard to come by. The most difficult to source part for these radios is a variable capacitor, and not finding one in his parts bin, [Jezan] decided to make his own.

This variable capacitor comes directly from a piece of 1.5 mm thick aluminum sheet. Instead of fancy CNC machines, power tools, or even a pair of tin snips, [Jezan] cut the rotors and stators for his variable capacitors with a pair of scissors. The center hole was punched out with a piece of sharpened pipe, and all the pieces were filed down and sanded for a perfect finish.

Considering the variable caps you can get your hands on are either rare or very old, this looks like a great afternoon project for the budding electronics wizard or radio enthusiast. [Jezan]‘s craftsmanship is incredible as well and the finished part looks like it came off an assembly line.

Experimenting with a permeability tuned oscillator

[Scott Harden] has been working through a design for a variable inductor to use as a PTO, or permeability tuned oscillator. What you see above is the most recent fruit of these efforts. The variable inductor is made up of the green coil of wire with a threaded bolt in the core. Turning that bolt moves the tip in or out of the coil, affecting its inductance.

Traditionally, tuning RF oscillator circuits has been a function of an adjustable capacitor. But capacitance is only part of the circuit, with inductance being the other important portion. Since variable capacitors that are capable of affecting a large change on the frequency of a circuit can be quite expensive he set out to find another way. This is what prompted the development of his first PTO project.

[Scott] produced a demo video of the hardware seen above which we’ve embedded after the break.

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