We found this circuit in the old Mullard transistor reference manual from 1960. The circuit is powered by a single battery and the transistors are germanium common at the time.
This circuit can generate signals in the range from 1 to 20 kHz, depending on the crystal. The...
The basis of this circuit is an LM380 that drives a speaker that emits sound when moisture is...
Using the ICM7555, CMOS version of the 555, this circuit produces a 1 kHz signal. The circuit has...