This circuit mimics the heartbeat with the softest sound played through a small speaker. The circuit is from an Electronics Now issue of January 1997.
This stage was found in a 1964 Electronic Design. The transistors are of the time and the shape of...
The traditional circuit was taken from a French magazine Radio Plans that no longer exists but can...
This circuit, which is present in other points of this website, was found in a 90s Hands On...