This simple circuit can work with either 4.5 V or 6 or 9 V if a 1k resistor is added in series with the set of LEDs. The circuit is from an old French publication.
The circuit shown was found in the National Semiconductor's Linear Applications Handbook of 1994....
This circuit was obtained from Linear Technology documentation from the 80's. Powered by 5 V it...
This simple injector and signal follower employs a high impedance headset. Transistors can be of...