This circuit was found in a Philips documentation from 1966. The circuit provides 1 mW with a power supply of only 1.3 V. Transistors support current BC series equivalents.
This 1969 Philips documentation circuit makes it possible to control an engine through the sound...
We found this circuit in a 90's Radio Electronics. The circuit can still be easily assembled as all...
This circuit was found in the July 1992 Radio Electronics magazine. Sensitivity adjustment is made...