Latching timed circuit control

[bigbadmac]

OK... I've been looking at various circuits using 555 to build the timed portion of the circuit but I'm not sure I need this level of complexity. Here's what I'm trying to achieve.

I'm building a battery powered filtration and evac system for another unit. I would like to have the circuit operational between 4.5vdc and 6vdc. This circuit will be in a non powered state until the activation button is pressed. Once active, the circuit should remain powered for about 3-5 min at which time it will shut off. A second switch can activate and hold the circuit from counting down via a pressure activated switch. It will close at aprox 30 lbs of pressure. Once released, the circuit would then remain powered for about 3-5 min. A third n.o. switch can be pressed to shut the circuit down and remove power to conserve battery. Correct me if I'm wrong, but I was thinking I could do this completely analog using a capacitor with a controlled charge rate to act as my timer.

Any thoughts?

 

[schmitt trigger]

That it could be done fully analog, of course, it can be done. Whether it is practical or economic, that is another matter.

I consider myself an analog guy, but this is one of those instances where the simplest microcontroller would achive those same results in a more straightforward and economic way. With better tolerance, too.