How low can the energy get?

From the previous slide, calculate energy per transaction.

• Assume an upper bound of 3ms per minimal transaction.

• Estimated TX power is 15mW (mostly TX power amp for 65nm chips).

• For 1.5v battery, this is 10mA. 0.015W * 0.003 sec = 45 micro Joule.

How long could a sensor last on a battery?

• An example battery: Lenmar WC357, 1.55v, 180mAh, $2-5.

• 180mAh/10mA = 18Hr = 64,800 seconds = 21.6M transactions.

• Suppose this sensor sends a report every minute = 1440/day.

• For just the BT LE transactions, this is 15,000 days, or > 40 years.

• This far exceeds the life of the battery and/or the product.

This means that batteries will cost more than the electronics.

• This sensor could run on scavenged power, e.g. ambient light.