Found in a 90's EDN this circuit can be used as a shield. The transistor is a general-purpose type and the frequency of the emitted sound is determined by R1 / C1.
This circuit produces a tone by a small loudspeaker. Frequency depends on C1 and C2. These...
We found this circuit in an 80's EDN. The circuit makes use of a MAX680, being given a table with...
Decade counters, such as the 4017, can be cascaded as sourcing signals with the frequency divided...