The CR2032 battery powered TinySensor that I had set up to monitor my house’s power consumption has stopped sending packets yesterday afternoon, totaling 7.5 days of transmissions every 10 seconds. That would mean 6 * 60 * 24 * 7.5 = 64 800 transmissions were sent. Here is the battery discharge pattern:
It last sent around the 2.65V levels. I have BOD disabled and the RFM12B battery low level set to 2.2V. The Attiny is running @1Mhz and only speeding up to 4Mhz to send RFM12b packets.
I was expecting that it would work down to 2.2V, but I guess the CR2032’s chemistry is different and the power drop during transmission is too high. JCW has put up nice power survival strategies that involve not submitting for some time when battery goes below certain threshold to allow the battery to recover, this may squeeze out some more quice out of the battery, but this is about it.
So as a conclusion we have it send data full 7.5 days,10 seconds apart out of a 220mAh battery. Crude assumption will be that with two AA batteries 2200mAh it may last almost three months.
Martin – was the battery a ‘proper’ / branded make, not a cheap one?
I got a pack of 12, branded for IKEA, but am sure they are just cheap Chinese batteries.
Maybe adding a small cap could extend the sending time quite a bit. The RFM sucks more power when sending than the cr2032 is made for.
I have a capacitor on that particular build, didn’t help. I assume this is because transmissions are too frequent, and the capacitor could not build up charge. I never got back to experiment further though.