This circuit provides an audible signal when testing a TTL circuit. The circuit is from an old documentation, being fed with the 5V of the circuit under test.
In the figure we have a simple timer with the 555 feeding a relay directly. The circuit is from...
ON Semiconductor NTMJS1D5N04C 40V Industrial MOSFET Available from Mouser Electronics, these ON...
To control relays safely with double insulation, we suggest the circuit in the figure. The optical...