I am looking at bringing the system power down to extend battery life. The power breakdown in idle mode is as follows:
Component | Active RX Power | Sleep Power | Avg. Power | Notes |
RFM69HCW | 17mA | 0.7uA | 9mA | 50% sleep duty cycle |
Teensy LC | 5mA | 150uA | 2.5mA | 50% duty, w/ bootloader |
Microphone | 155uA | 155uA | 155uA | Always on |
LIS3DH | 11uA | 11uA | 11uA | Always on |
Totals | 22.16mA / 73.1mW | 317uA / 1mW | 11.66mA / 38.5mW |
The battery I have chosen has a capacity of 150mAh @ 3.7V. The system runs at 3.3V so energy rating of the batter at 3.3V is 150*(3.7/3.3) = 168mAh @ 3.3V. This means the standby time is 168/11.66 = 14.4 hours. That's a full day of standby time!!!
I think we can push the sleep duty cycle longer than 50% to save even more power. Probably by as much as 80% duty.
Now to measure the full system during streaming mode:
Here, I put the whole system into stream mode and measure the supply current (measured on the battery voltage rail).
Mode | Power | Max Duration (based on 150mAh) |
STREAM_RX | 37mA @ 3.7V | 4 hours of talk time |
STREAM_TX (31 power setting) | 39.6mA @ 3.7V | 3.8 hours of talk time |
STREAM_TX (15 power setting) | 38.9mA @ 3.7V | 3.85 hours of talk time |
STREAM_TX (0 power setting) | 38mA @ 3.7V | 3.9 hours of talk time |
Wow, 4 hours of talk time! There must be something missing... there is, the speaker. The speaker driver can source as much as 120mA when driving a lout signal. Therefore The talk time is limited to more like 1 hour of receiving.
Summary:
12+ hours of standby
1+ hour of talk time
Actually, not too far off from an old Nokia bar phone...
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