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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This is the circuit for the HM-10ª, an instrument sold by Heathkit. The circuit is from a Radio...
This circuit indicates when the monitored voltage drops below the value determined by the divider...
This circuit, from a 1975 Motorola manual, uses a power Darlington transistor of the time. We can...