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.
This circuit is used to test capacitors with a working voltage above 150 V, detecting shorts or...
The circuit shown is used to reset TTL logic when power is established. The circuit uses a 7413...
This circuit was obtained in a Motorola manual from the 70s. The integrated circuit is from that...