Two NAND gates are used for the oscillator, and two as the control. If the two-tone speed needs to be altered, the 220 F capacitors can be changed (larger for slower operation). If the frequency of the oscillator is to be changed, the 0. 2 and 0. 1 F capacitors can be varied and the value of R1 can be increased. To change frequency range between
the two notes, alter the 1. 5 k (1. 500) resistor.