On Mon, 26 Jun 2006 13:33:42 -0500, John Fields
>Neglecting the buzzer for a moment, if the rest of the circuit draws
>500 microamps from the battery, all the time, and the battery has a
>capacity of 500mAH, that means you can expect about 1000 hours out
>of the battery. About 6 weeks.
>If the buzzer needs 50mA and it runs for 15 seconds a day, that's
>only increasing the load on the battery by about 9 microamps, so the
>life would still be about 6 weeks. The trick here would be to get
>the timer to run on as little current as possible. I think 100
>microamps is doable and that would get the life up to about 10000
>hours. About 417 days.
Checking Eveready's site gives 625mAH for their 9V alkaline, so with
a 100µA load that's 6250 hours, or about 260 days.
Professional Circuit Designer