This circuit uses the LM2931 which is not a common component today. What it does is to activate a lamp causing it to blink at a frequency determined by the capacitor.
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Found in a 1968 US publication, this circuit is designed to measure very weak signals. The...
The sensor can be made using two bare wire or two screen with a piece of tisse between them. One...
This circuit serves as a binary demonstrator using 3 LEDs. The circuit can be scaled up for a...