C1 will discharge through the 555 but a diode across R1 will speed up the discharge.
View attachment 352710

Did you try the BAT42 in the circuit?

 

Did you try the BAT42 in the circuit?

Yes I did. Discharges fully in under 2 seconds.

 

Yes I did. Discharges fully in under 2 seconds.

OK. I don't have one and didn't breadboard the circuit.
However, when simulating with LTspice, the timer doesn't trigger correctly (extremely short time ~180mS).
I tried different vendor BAT42 spice models but all work the same. The timer works correctly with 1N4148 or BAT54.
Anyway...that's the reason I asked.

 

Seems strange not working with a BAT42.
180ms is probably about right if the diode is installed backwards.
It definately works on the breadboard though.

See if you get the same results with this circuit.
LED should remain OFF until the button is held for 5 or more seconds.

 

I don't think you can get simpler than this:

View attachment 352687

You can change the capacitor value to get a precise pulse width -this depends on the characteristics of the MOSFET. I assumed that the MOSFET does not need more than a few volts of gate drive.

Solution Alert!!

 

Seems strange not working with a BAT42.
180ms is probably about right if the diode is installed backwards.
It definately works on the breadboard though.

See if you get the same results with this circuit.
LED should remain OFF until the button is held for 5 or more seconds.
View attachment 352814

It works if I use 1N4148 or BAT54, but not with BAT42.
I'll check the BAT42 models. Thanks for you help.

 

Transistor version with fast cutoff after appx 5 seconds.
View attachment 352707

i really like the simplicity of this one, so I'm going to get a sample board made from JLC. thanks for your suggestion

whilst i feel i've got an understanding of how it works, would Q1 not need a resistor between the base-emitter?

also, would this work for a higher power load, like a brushed motor pulling roughly 5A? with a suitably rated N-ch Mosfet

 

The purpose of the resistor from the base to emitter is to assure that the transistor actually shuts off when it is supposed to be off. In the case of this very nice circuit, when the transistor is supposed to be off its base and emitter are shunted by the drain-to-source resistance of the MOSFET through R1 which is probably enough to keep the transistor's collector-to-base. leakage from turning the transistor.