Wireless sensor node - watch battery (8)

Back in part 4 I made some improvements and did some sums and convinced myself that I could run my TX node on 3x AA batteries for more than a couple of years. Here are the sums I used.

Entering the following figures into this website:

• Battery capacity: 1700mAh
• Sleep current consumption: 0.006mA
• Wake current consumption: 8.5mA
• Duration of wakeup: 2000ms
• Number of wakeups per hour: 12 (once every 5 minutes)

The result: 2.6 years.

It occurred to me that the wakeup time of two seconds is pretty long. I used this time to allow for 3 transmissions with high power sleeps between them. However, if I use low power sleeps between retransmits I can be running at high power for a much shorter time and hence get a much better battery life. The results are pretty impressive.

• Battery capacity: 1700mAh
• Sleep current consumption: 0.006mA
• Wake current consumption: 8.5mA
• Duration of wakeup: 100ms
• Number of wakeups per hour: 36 (once every 5 minutes * 3 transmissions of each reading)

The result: 11.38 years! It seems pretty unlikely that my batteries would actually last for a decade but this long battery life means that I could get away with a much smaller battery. A single CR2032 watch battery is very cheap, 3V and usually has a capacity of 225mAh.

• Battery capacity: 225mAh
• Sleep current consumption: 0.006mA
• Wake current consumption: 8.5mA
• Duration of wakeup: 100ms
• Number of wakeups per hour: 36 (once every 5 minutes * 3 transmissions of each reading)

The result: 1.51 years! That's an ideal length of time - I think I'll be using CR2032 batteries with my wireless TX node.