This small tone generator was found in the November 1987 issue of Radio Electronics magazine. The phototransistor is common and controls the sounds generated. The basic frequency is given by C1.
T1 and T2 can be BC557 and T3 a TIP32 for lamps up to 3 A. The supply is made by voltage of 12 V...
This fourth-order filter was found in American documentation from the 90s. The circuit applies to...
This resistance meter uses a two-transistor oscillator as basic configuration. The tone produced...