Circuit design needed

Normally I would suggest a 555 timer if you want to build something, however, you equire a rather longer time than what a 555 is suited for.

Look up a CD4060B or BC circuit example for a long timer.

Fairchild has a clean looking PDF file on this.

This chip comes with its own oscillator that you can configure and it has multiple frequency dividers that allows you to select a range of times This may help you better understand..

Jamie

1. Must the 3 volt power source be used to run the timer or is there another supply available for that?
2. How much current must the 3V power source deliver into the load?

John Fields

I agree. In the 80s I made my mum a kitchen timer - 3 cascaded 4017 decade counters (with the middle one wired to reset on the "6" for 10's of minutes. IIRC there was also a divider between the 555 and the first (minute) 4017.

It was very stable and repeatable once calibrated. The OP's 15 minute period will be no problem.

1. the 3v is 2 D batteries powering an igniter and regulator for a propane water heater. I bought this heater to circulate water in a relatively small swimming pool, but the heater shuts of at regular intervals in which seems to be a built-in unit of time. Turning off the power off then on again res tarts the gas regulator immediately.