Temperature sensor current consumption

1 year with batteries - temperature sensor project

Temperature sensor with alkaline batteries

Just a quick update on my XBee/ LCD/ temperature sensor project which I originally started in 2011 (last blog entry: XBee temperature sensor project ). I  had to replace the already used battery cells which I put into the sensor about one year ago (August 31 2012) because I got some timeouts on my receiver. The
voltage came down to 3.34 volts and this is a point where the low dropout regulator (MCP1700) keeps quit working sometimes even when the load is only about 25 mA every four minutes when the XBee (end device, sleeping) sends the temperature data to the coordinator.

Voltage development temperature sensor

The three battery cells had a voltage of around 4.1 volts when I started using them for the sensor, so they were already down from their original voltage/ capacity which is around 1.5 volts per cell for unused batteries.
Why did I use used battery cells and not new ones? Because they were lying around and I was wondering how long some spare, already used cells would last during time and different weather conditions. And they lasted almost one year!

The temperature sensor is located outside and we had temperatures of around -15 to +30°C during the year. The chart you see is far from scientificly accurate but gives you a raw picture of the voltage curve for those cells (GP super alkaline).

Next I will replace the batteries with some rechargeable batteries. There are some nice energy harvester ICs on the market - maybe this will be the next power supply for my sensors. Stay tuned.