This circuit was found in an Electronics World of 1966. It has a range of 5 to 25 000 Hz at 1 dB and the diagram includes the power supply.
Found in old documentation, this circuit uses components that are still common on the market. The...
This circuit activates a relay by activating one of a series of optical sensors that can be...
We found this circuit in a 1996 publication. Equivalent components can be tried, especially in the...