This page shows interactive timeplots for the experiment described here. These plots make use of MIT's SIMILE Timeplot widget written using JavaScript and DHTML. [NOTE: Some browsers may complain about an "unresponsive script" while loading this page. If that happens, click "Stop" and you should still see most of the plots.]

The gray vertical regions represent notable events, e.g. periods when the SPOT was taken outdoors for charging and the time (between 11:00pm on Feb 22 until noon Feb 23 when no samples were recorded due to a database table crash).

Figure 1: Total uptime (blue), time spent in deep sleep (orange) and time spent in shallow sleep (red) measured in seconds since the start of the experiment. Overall, the SPOT spent 95% of its time in deep sleep, about 4.5% in shallow sleep and less than 0.5% in active computation.

This time around, the SPOT stayed off the power grid from Feb 12 until Mar 3 -- slightly over 19 days (that's more than 1.6 million seconds) -- reporting light, temperature and other readings every 10 minutes. Its reported up time as well as the time spent in deep and shallow sleep kept rising at a regular clip throughout the experiment.

Figure 2: Variations in the USB voltage supplied by the solar panel (light blue), the output voltage measured at the SPOT's battery (dark blue) and the estimated remaining battery level (in red). Spikes in the light blue plot indicate periods when the solar panel circuitry charged the SPOT's battery and caused an increase in its remaining capacity (red).

It rained frequently during this experiment (click here for the local weather and look in the "Events" column under "Observations") so I kept the SPOT indoors for the most part and only occasionally took it outdoors when dry so I could recharge the SPOT more efficiently in direct sun light.

The normal discharge rate for the SPOT's built-in battery (rated at 700mAh) was nearly 12% per day and a full charge would have lasted about 8 days. However, the solar panel was able to replenish about 15-18% of the battery whenever it was sunny and I suspect that this figure could be bumped up to 25-30% with some simple optimization of its orientation.

Figure 3: These plots show changes in the light and temperature (°F) readings as measured by the built-in sensors on the eDemoBoard. Light readings are shown in light blue and temperature readings in dark blue.

Accidental exposure to rain disabled the SPOT and prematurely terminated the experiment while it still had nearly 10% of its battery life remaining.

Picture of a SPOT with rain drops