This circuit was found in a 90s American publication. The same configuration appears in several places on this site, obtained from different sources. The lamps can be replaced by LEDs.
The circuit shown in Figure bellow generates frequencies of 50 Hz, 100 Hz, and 200 Hz. The circuit uses a...
This circuit rejects frequencies around 1 kHz and can be adjusted using C1. Equivalent operational...
From stereo inputs, this circuit generates a modulated and multiplexed signal to be transmitted in the FM...