This repellent operates with frequencies from 30 to 45 kHz, serving for insects and rodents. The circuit is from 80s documentation. The transducer is a piezoelectric type.
Analog Devices ADuCRF101 Wireless Data Acquisition System Now at Mouser February 24, 2015 - Mouser...
Among other applications, the 1960 Sylvania transistor manual indicates this timer for chess...
This circuit is from a Motorola manual from the 70s. The circuit can be implemented with more...