I did another battery test using a modified version of Ted’s code which makes the pagers broadcast their battery readings, and turn off automatically at a reading of 1600. The modified versions of sampADcC.nc and sampADcP.nc can be found here:
http://docs.google.com/Doc?docid=0AWGN0bxAc29yZDdqZG5zd183aGI4bWgyZjk&hl=en
http://docs.google.com/Doc?docid=0AWGN0bxAc29yZDdqZG5zd182ZnZ2cXpnZzU&hl=en
The following table and graph summarize the data
The motes exhibited some strange behavior after the test. mote 244 ended at a reading of 1607, which should correspond to a voltage of about 2.5v. When I measured the battery voltage, however, it read 3.2v. I turned it on again after the test, and it broadcast a reading of around 1980, which sure enough corresponds to 3.2v. I’m certain it was not plugged in between the time the test ended and I read this voltage. In the last test, both motes exhibited the same behavior, but I let it slide since they had been plugged in for some time (1-2 minutes) before I checked their voltages.
Both of the other pagers in this test had a battery reading of 0v, suggesting the automatic shut down didn’t work for them, and they drained their batteries overnight. The test results seem to suggest they turned off at the right time, however, and I don’t know why the automatic shut down would work for one pager but not the others.
Great work, Greg. I’m glad you checked on the batteries the next day to see what happened to them. It may be that they don’t completely turn off, just that they turn off most of their functions. I would have thought that their power drain was so slow that they wouldn’t be at zero the next day, however. Perhaps we should shut them off a little earlier, before they get into the steep descent part of their curve. As for the difference between the 3.2v and 2.5v readings, I wonder if the battery voltage drops when sourcing a current when the battery is mostly depleted.
Comment by gthomas — February 24, 2010 @ 12:30 pm