03/26/2018

Just finished the third Cricket power test. Like the last one, I am reading/logging sensor data every minute and broadcasting LoRaWAN updates every 10 minutes. I am also using a low duty cycle of one GNSS fix every two hours like the last time, and a high duty cycle of once per minute when motion is detected. This occurs ~once per day manually. Both tests started witha fully charged 105 mAH LiPo battery.

The key variable is the GNSS fix accuracy EHPE, which was either 10 meters (minimum practical value) or 50 meters (a reasonable low-power value. EHPE sets the cutoff for ending the satellite acquisition/tracking and entering power-saving sleep mode):

EPHE       hours       average current         number of fixes      rms location accuracy

10              196              536 uA                         ~110                        ~ 5 meters

50             327              321 uA                         ~180                       ~ 15 meters

So with a single AA-sized LiSO2Cl 3.6 V, 2600 mAH low-self-discharge battery the Cricket would last:

202 days at EHPE of 10 and 338 days at EHPE of 50.

This time could be longer if the low duty cycle frequency were to be increased to three or four hours, which makes practical sense because the ephemeris data goes stale after about four hours. So three or four hour fix update is a sensible criterion for the long cycle.

Overall battery life will depend on the amount of motion experienced by the device; the more motion the more fixes per day and the less the battery lifetime. For a 2600 mAH battery, total number of fixes will be limited to between 2700 (EHPE of 10) and 4400 (EHPE of 50). Of course, one could always just use two 2600 mAH batteries in parallel to get out well past one year ;>