Low battery indicator 555 (CB9551E)

This circuit can operate with different voltages, depending on the zener used. We found it in a 90s American documentation.

CW practice oscillator (CB7316E)
This circuit is from American documentation from the 90s. The configuration is very current and can...
Power Supply Monitor (CB14972E)
This circuit trips when the voltage set in the pot is exceeded. The tone depends on C3 and...
Simple Logic Probe (CB5911E)
This circuit uses only two general purpose transistors and can be powered by the circuit under...