Found in a 1964 Electronic Design this circuit compares two signals by providing the inverse of the algebraic sum of their frequencies. The circuit can be made with modern equivalent transistors.
We found this circuit in Popular Electronics from 1992. Time is given by C1. The circuit provides an...
A Popular Electronics from the 90's suggests this circuit that is based on a low voltage...
The frequency of a 555 oscillator depends on the capacitance of capacitor C. We can take advantage of...