I need to switch ON a NE555 timer relay from 12V DC supply when the DC supply is switched ON. Also, when I switch OFF the 12V DC supply, the relay should switch ON again as it is a timer relay.
What I am doing currently:
I am connecting 12V DC to an NPN transistor. The 12V supply gives power to the collector and the emitter emits 12V and gives it to a 4700uF/25V capacitor and also to the timer relay and the relay switches ON and OFF (because it is a timer relay.) Now when I switch off the power supply the capacitor discharges immediately and as I guess it is not allowing the timer relay to de-energize there by not switching on the relay. I have tried adding resistor and it still doesn't work. But when I try to discharge the capacitor directly to the relay, the relay operates.
My use case:
I need to switch ON and OFF a CPU(NUC) from the ignition of a car battery. That is, when I switch ON 12V I need an ON pulse and when I turn OFF the 12V supply I need an another pulse. Just a pulse is enough (like pressing the switch to ON or OFF the CPU.)
Maybe if even my capacitor starts discharging after a 2 second delay when I switch off the 12V DC in the circuit I have provided, would be great.
Is there any device to delay capacitor discharge start timing or any modification needed in this circuit?