Problem: 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?