Long duration timer for noisemaker

Hello All,

I am trying to design a battery operated device that can wait a duration of time measured in weeks up to months and then activate a piezo buzzer for a few seconds (between 3 and 10 seconds) then wait again for the same or a similar duration of time and do it all over again until the battery is run down. The thickness of the board and components need to be able to fit through a slit approximately 7mm wide (possibly a few mm thicker would be fine).

I've looked at 555 / 4017 options and while I'm open to exploring it further it didn't seem like I'd be able to get the components I needed to fit into the 7mm width I'm looking for. I'd be happy to use a microcontroller but I know absolutely nothing about them except what I learned in the last 24 hours browsing the web, not that I know much about circuit design in general.

So as far as my knowledge of microcontrollers go I like the TI msp430 series for their low power features. I would appreciate any code for any of the TI msp430 low power chips that could be programmed to do what I needed. Any ideas of implementation are greatly appreciated.

Also, it is important to note that I only need reliability to the day, the timing could be consistently off by hours and it wouldn't be a big deal, even inconsistencies of around a day would work.

Thanks,
Simon

I'm kind of guessing this device is intended as some sort of prank. It's going to be tough not to drain small batteries in a week, just using the timer portion. I just know enough about microcontrollers (AVR) to program basic stuff, still struggling to get control over the more advanced features. I do know that when the MCU goes into Power-Down Sleep mode, almost all functions are shut down until an external interupt wakes it up. Maybe somebody else knows if you can use the 'Sleep' instruction for a set period.
Most microcontrollers don't seem to burn up a lot of power, it's mostly what you are driving. ATTiny13L at 1 MHz, 1.8 volts, draws 240 uA in active mode. The internal clock can be set as low as 16 kHz (128/8), so guessing much lower current draw.

Clearer details would make it so much simpler to giver better solutions. This is kind of a 'unique' application, most likely won't find anyone who has done this before, so the more you put into your request, the more likely somebody here will respond with a useful solution.

I don't know of any batteries that would last that long in continuous operation. You may want to reconstruct your original idea to make it more practical/feasible.

Thanks for the replies, they were actually very helpful.

Yes, this is for a prank. And yes the slim profile is intended so that the device can be slipped in between the vent slits on an air conditioning vent. Please don't be worried that this is too malicious for your contribution because in the end it is a really light hearted joke that will not be doing any damage to anything (including egos).

As far as the power consumption is concerned, I am woefully ignorant. Basically I'm hoping the device will sleep for a week and then chirp, then repeat two more times for a total of three cycles (sleeping, then chirping) or three weeks. I assume there must be ways to do this at least with a microcontroller because of the cheap digital watches I've had that lasted years on single button cell batteries. I wish I could find a different power source but I don't think it would be particularly safe or practical, and the joke would pretty much be nullified if I didn't place the device in the a/c vent.

Some of the batteries I've looked at are found at:
https://www.batteryspace.com/index.asp?PageAction=VIEWCATS&Category=869
The PL-544792 lists 2500mah @ 2.5A max current drain. I assume that for a circuit drawing 3.7v at a few ma or micro amps that would be enough to run for quite a long time. Should I be looking at things like fall off voltage over time since it would be going without a recharge for three weeks?

Would it be feasible to use a long duration timer (say a 555 RC'd for 100 minutes) to wake the MCU and increment a counter then go back to sleep until the counter reaches a certain value?

Some newer PIC microcontrollers contain an ULPWUM (Ultra Low Power Wake Up Module) which can be calibrated to provide pretty decent timing. They (Microchip) even produced an application note showing how to compensate for temperature and battery voltage. I'm not certain how accurate you could make this over several months though.