Found in a 90s Popular Electronics, this circuit uses a 741 to generate frequencies from 0.1 to 30 Hz. Observe the phototransistor feedback.
This circuit is recommended for alarm systems since it has a good output stage. The circuit is...
) Suggested by Philips in a 1968 documentation this circuit has very high 10 ohm on-load voltage...
No information is given about the transformers in this circuit suggested by Motorola in a 1968...