Found in Popular Electronics from the 90's, this circuit uses 555 integrated and common transistors to generate two tones determined by push buttons S1 and S2.
This circuit, obtained from a 1965 magazine, can still be assembled using some modern equivalent...
We found this circuit on an Elektor from the 90s. The frequency is given by capacitor C1. The...
This powerful regulator, shown in the figure is for 5V (TTL) is suggested by Motorola and makes use...