We found this circuit in an English publication from the 1980s. The circuit uses current components and can be tuned for frequencies between 300 and 1500 Hz.
With this luminous remote control, which we found in a 1990 publication, using a flashlight you...
We found this circuit in a 1967 Electronics World. The circuit can be designed to control other...
This circuit can be used in a signal level indicator with LEDs. The circuit is from an Electronics Now...