I have a very simple project: ATTiny85V, a pir motion sensor, and an RF transmitter. From the transmitter's datasheet its current consumption is 8 mA and I can't find the consumption of the pir in it's datasheet (unless it is called the "Effective voltage" which is 0.2 - 1.5 - not sure if that represents it's current consumption in mA).
I'm trying to figure out how to choose the right battery(ies) and how long I can expect those batteries to last. I'd like to use coin cell batteries to save space.
I am polling the pir once every second and the transmitter will only send a signal when motion is detected (in my scenario motion will only be detected a few times a day).
Coin cells are good for a few hundred mAh? http://www.dipmicro.com/store/BAT-CR2032
225 for example.
Can the attiny be put in sleep, to wake up when PIR pulls a pin low?
Then send out some pattern - see the virtual wire library for the kind of sequence to send that a receiver can pick up on and interpert correctly.
Best method is to measure the current during the actual conditions, sleeping and transmitting.
Probablys see ~5-10mA while sleeping depending on the PIR, and a jump to 15-20nA while transmitting.
So 225/10 = 22 hrs.
Better off with a 1000mAh LiPo, can find them in niice small flat package.
Thanks - I'll look into putting the tiny to sleep.
I already have all the rf stuff working - and I am currently designing an enclosure for the unit that I'll 3D print. I just need to choose the right batteries so that I can finish the enclosure.
And I'd prefer to not have to change the battery(ies) every day.
Could I increase the number of batteries to increase battery life?
Increasing the batteries in series just increases the voltage - not the mAh.
If you connect in parallel then you have to start playing games to account for then running down at different rates.
I have a 1000mAh LiPo in a remote control running an 8 MHz promini that mostly sleeps, a 434 MHz Tx modukle, and 16 button keypad. Lasts several weeks to a month between charges. Added a Maxim 1811 charge control chip to recharge it from 5V source.
Bring the power in to an analog pin and measure it when the PIR wakes the processor up.