This circuit oscillates in the fifth harmonic of the crystal frequency. The circuit is from a 90's documentation. L1 must be according to the desired frequency.
This circuit is from a 1979 publication. The sensor consists of plates or screens that, when...
The circuit is from a Radio Electronics from August 1989. The cells used at that time did not have...
The automatic modulated siren circuit shown in the figure really produces an interesting sound...