Power Analysis

A project log for Star Trek Communicator Badge

In the true spirit of Star Trek, this communicator badge is completely autonomous, while fitting in the form factor of an original badge

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...