This 50% active cycle TTL clock generates signals from 4 to 20 Hz. Its power must be supplied with 5 V and other frequencies can be generated with capacitor replacement.
We found this circuit in a 90's Radio Electronics. The low power circuit activates a 12 V relay...
This circuit sources a Constant current to a load. The current is determined by R2. In the...
This page shows a crystal oscillator for 2 MHz. Other frequencies can be produced depending on the...