Circuit to countdown after a given pulse

[SScattered]

Hi,

Please see the attachment.

When I give input to opto-coupler it turns on the mosfet thus actuating the relays. Even after the power opto-coupler is removed, the relays will still be powered. So only way to reset this is to release the "Emergency Button".

I can't use a microcontroller for this. What now I need to do is remove the "Emergency Button" and implement some sort of circuit which reset the circuit (Like emergency button does) automatically after a few seconds when the input to the Opto-coupler is removed.

What I thought of to be used it a 555 IC timer, but I'm not sure how can I utilize it.

Basically,

1) Opto-Coupler is powered -> relays powered
2) Opto-Coupler is not-powered -> relays still powered
3) Timer circuit cut-off power to the relays after a certain time (Opening the circuit where emergency button is and the closing it)

[robzy]

I can't use a microcontroller for this.

Why not? Is there anything else you can't use?

Why don't you just throw away the whole circuit and create something new?

How will you be sure that the emergency button will still be safe?

[SScattered]

I can't use a microcontroller for this.

Why not? Is there anything else you can't use?

Why don't you just throw away the whole circuit and create something new?

How will you be sure that the emergency button will still be safe?

Actually this is for some project. Therefore cannot use a microcontroller in this case.
Emergency button works. I already made a prototype and tested.

[Benta]

CD4541/MC14541 come to mind.

[NiHaoMike]

Remove RL1 and add a 555 circuit between the optoisolator and MOSFET.