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Help with sounds alarm after 30sec w/ battery saver circuit

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DaKandEKid

New Member
I'm trying to design a circuit that when power is switched on to the device it will generate an alarm sound via a bleeper after about 30 seconds.

The user would then turn the device off but in the event the user didn't get the message rather then draining the battery have it turn off after about 5 minutes.

The circuit needs to be powered from a battery which will i'm thinking of using a 3V coin battery but i could use a 9V also.

Power consumption is important.

Ideally it should also be easy to put together for labor reasons in putting multiple units together.

I have put together a 555 monostable circuit which works well for turning on the bleeper but it's adding the battery save function that will turn the bleeper off after 5 minutes which has me stumped.

If there was a simple IC which i don't know about that could go between the battery and the circuit which had a pin which would allow the circuit to be powered down that would work.

I could also use two 555 timers but i was thinking the amount of standby current used with the timers might be significant. I'd like to switch the power on and off to the device.

Any suggestions of good ways to do this?
Thanks in advance.
 

Sebi

Active Member
First change the normal 555 to 7555 (CMOS version of 555) for very low power consumption...
 

DaKandEKid

New Member
yep was planning on that.

I'm starting to think about possibly using a 8 pin PIC. I believe they can be had for under 1.50 and if so the cost might be cheeper then using a 7555 + other chips needed to go into power save.

I'm gonna look into the low voltage chips PICs. But, i really wanted to come up with a design not using a programmable solution.
 
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