16 pF to 650 pF DIY variable capacitor from ordinary aluminium foil (alufoil), A4 paper and a cardboard tube from an empty alufoil package.
Roll one round of alufoil on the blank cardboard tube. Fix it with tape. Leave 5 cm / 2 inch free from alufoil at one end.
Roll a A4 paper around, but let it be slide’able, just about. Fix the diameter with tape.
Roll one round of alufoil over the paper. Fix the alufoil with tape. Again leave one end 5 cm free from alufoil, and the other 3 cm free.
The 3 cm end is supposed to grab the other tube without really adding capacitance.
Alufoil free areas are finger-touch areas. One at each end.
Add wire to each alufoil, at the ends, but let the outer be marked as “ground”. – Just tape the stripped ends of the wires to each alufoil.
Pushed all together: ~ 650 pF
Pulled out, except 3 cm: ~ 16 pF
Will be used for further experiments on various oscillators in the next few weeks. – Stay tuned, literally.
