how to make an adjustable 5 minutes timer without microcontroller?

[gardenyu]

I was recently assigned this project. Build an adjustable timer to count as long as 5 minutes ( accuracy is not important) then trigger something.

Although programming a micro would have been easier, I rather not do that for now. But normal 555 and RC timers can only count very short time period.

Any suggestion?

 

[kpatz]

The 555 can time intervals more than 5 minutes with a big enough capacitor/high enough resistors.

 

[gardenyu]

Thanks, but this is for a LED circuit which is supposed to be operating for 50,000, I don't think large electrolytic caps is suitable there.

 

[crutschow]

Use a 555 timer at a higher frequency and use a counter to count the 555 clock pulses. For example an 8-bit counter would give you a 5 minute period with a 256/300 = 0.853Hz frequency from the 555. A 16-bit counter would require a clock frequency of 218Hz.

 

[microtexan]

supposed to be operating for 50,000 50,000 what?