Make: Volume 87

the circuit in Figure J after the power is pulsed

very briefly. The circuit has a small amount of

resistance, so the current gradually loses energy

in the form of heat, and the oscillations die away.

But in our circuit, logic gates X1 and X2 feed

back just enough power into O1 and O2, through

resistors R1 and R2, to keep the oscillations going.

The frequency is then determined by capacitors

C1 through C5, the value of the inductor, and the

diameter and number of turns of the sensing coil.

Oscillators are fundamental in radio, when you

want to receive a station or change the frequency

of a transmission. We have been writing a book

titled Make: ...