Battery Solution

[Keith]

I am trying to figure out battery requirements for a project I need to put together. First what is the best way to determine this ... what and how to I calculate this?

My project consist of a one LED, Pic16L88, a bluetooth transceiver and an Analog Devices Accelerometer. I believe all 3 will operate at 3 to 4 volts. Full power maybe 7 sec then off. Do this 25 to 50 times an hour.

As with most battery projects I am trying to use the smallest and coin operated if possible.

Thanks in advance...

[jessey]

Hello Keith

I've just started working on a battery operated circuit of my own and from reading the archives I was able to calculate approximately how long my batteries would last based on the current draw of my circuit. To calculate how long a battery will last, when you know what the current draw of your circuit is, you simply divide the milliamp draw (calculated over a 24 hour period of your pic circuit) into the capacity of the mAH (milliamphours) of the button cell battery that your considering using.

I don't know what your circuit draws but, for an example, say that your current draw is 1.5 milliamps for the 7 seconds of on time and if you do that 25 times an hour then your circuit would be consuming that 1.5 mA for 7 sec X 25 = 175 seconds each hour then X 24 would be 4200 seconds divided by 60 would equal 70 minutes of consumption per 24 hrs which would be close to 1.17 hours X 1.5 mA = 1.76 mA per 24 hours. Assuming my logic is correct, if your button cell battery has a capacity of say 170mAH then the single button cell battery would last 170mAH / 1.76mA which would be close to 97 days.

Here's a link that shows the capacities of some button cell batteries and some considerations when choosing the right battery for your particular application.
http://www.falconryelectronics.co.uk/page17.html

I think I got it right but I'm sure if it's wrong, someone here will correct me. I hope this helps.

jessey