This can also be done in hardware. I borrowed a section from Andrew’s 5001-DC with march time drawing. I added a supervision blocking diode and a shunt diode across the regulator. I also went with 1N4004 diodes just because I like the higher voltage units. I changed the resting relay contact from N/O to N/C to pass the supervision voltage to the rest of the circuit. I did not verify any of the existing 555 timer circuit. I figured Andrew had already done that.
