I'll post on the sensors perhaps later, but right now I'm working on reducing their power consumption. They have an approximately 1 uA sleep current, which I currently don't know how to reduce further.
Initially, when measuring every 5 minutes and transmitting 3 measurements at a time over the radio, I got an average current consumption of around 2 uA. Initial current consumption over time is show in figure 1. This was measured using the setup described in the previous post and using the data port of my UT61E.
|Figure 1. Initial current usage.|
The measurement time used by the sensor (Sensirion SHT20) is significantly reduced when the measurement resolution is lowered. According to the data sheet of SHT20, the measurement with full resolution takes a maximum of 350 uA for 114 ms, which translates to about 40 uC of charge. The measurement with the lowest resolution however takes a maximum of 350 uA for 15 ms, which translates to about 5 uC of charge. This was the first course of action to reduce current consumption. The result of the first try of this is shown in figure 2.
|Figure 2. Current consumption with what I thought was reduced resolution measurements.|
|Figure 3. Current consumption with reduced resolution measurements.|