Resetting Timer Circuit

OK here is the Idea: Contact switch is engaged for desired time ( changeable from 5-30 min in 5 min increments) then a pleasant chime sounds. If contact switch is released prior to desired set time then unpleasant buzzer time sounds and resets to start over.


I have been looking at some 555/556 circuits but wonder if there isn't something out there already doing this in some form that I could adapt. Thanks in advance for any advice.

Nothing I can think of off the top of my head. Maybe you are the sort that would prefer to work with time-delay relays. They run about $30-$50 apiece, have adjustable time in the minutes and seconds range. You will need three of them, as well as a buzzer, door chimes, 24V doorbell transformer and a switch. If you have more money than you have patience to wire up 555 timers (and the drivers and the power supply) this is the usual alternative.

Thanks Duffy I may look at that and just starting to play with the Idea but it does need to be inexpensive and was starting to play with a schematic that uses a battery I have tried to post it here but can't for some reason now

Delays beyond a few minutes are a problem with the 555 due to the high value of the required timing resistor and capacitor. A better way is to use a oscillator/counter such as this. This also allows varying the delay by the 4060 output selected and by changing oscillator frequency.

hi,
You could configure an astable using a 7555 timer for 5 minutes and clock a 4017 counter/decoder, to give 5 min intervals from 5 min to 30 min

This could all be done with a simple 8 pin micro: PIC12F675 - including the sounds.