I want to make a timer that will run for more than fifteen minutes and power a device (deliver power for 15+ mins and then shut off power to the device). The longest amount of time I can get out of an LM555 monostable is 110 seconds only (using R=1 megaohm, C=100µF). I haven't been able to think of a good alternative. Are there other IC timers that can last longer, or is there a better approach?

 

Hello,

Another option is an oscillator with a divider and start / stop flip-flop.

In the link there is a sample with time setting possibility.
http://www.hobby-elec.org/e_counter.htm

Greetings,
Bertus

 

Hi,

You can make a long duration timer with CD4060 IC and drive the load via a transistor/mosfet/relay. Try by yourself, if you cannot do it, i will try to provide you the circuit i have made.

Thanks.