Sunday, 3 February 2013

More Battery Life

Based on the last test the GoPro isn't going to last the night (at least not in winter) without some help. This test uses a charge interval after each image capture . The example data here run for ten hours (before I couldn't resist having a look) previous tests have run for twelve hours. (There's currently a test running under the stairs that started last night at 10pm which I'll have a look at in the morning.)

A ten hour test using a two second lighting interval and charging the GoPro for five seconds between each capture. The exact GoPro start up time and initial capture timing is unknown. If these can be measured the lighting duration could be reduced. If there isn't enough light the system behaves erratically, the camera can produce black or corrupt files and the system can get out of sequence. Subsequently it has been hard to deduce the timing window from trail and error and it has been safer to leave the duration at two seconds than risk jeopardizing the experiment. If the demands of the lighting subsystem on the overall battery status are insignificant compared to the charge duration it might not be worth the time it would take to investigate this properly.

The charge in the GoPro camera is slowly creeping down so I'm running the current test with a slightly longer charge interval.

The debug LEDs can be turned off, and the board is still taking 40mA idle which could be improved on. Ultimately these factors may also be insignificant, but it might be prudent to look at sleep intervals - particularly during the day. (The data logging interval period and SD card flush frequency are going to be longer in the 'real thing too, which may make some really small difference.)

These result look hopeful. Even if the NiMH battery doesn't perform so well in the cold, a lithium ion battery or lithium polymer would offer a better charge density albeit at a greater cost.

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