-
End of test results
11/05/2015 at 23:18 • 0 commentsIt works! After a total of 14 days running purely from the capacitor, I have verified the memory contents to be entirely intact. The module was left unplugged on the bench for the duration of the test, with no special attempt to insulate it from RF, magnetic or other noise sources. In fact, it was a few inches away from a display with a noisy power supply, and within about 3 feet of an unshielded 300 watt induction heater. This suggests that the pull up/down resistors used are the right value to protect against noise.
Here is a final graph of the voltage over time:
-
Initial test results
10/29/2015 at 13:39 • 0 commentsSo far the results are much better than expected, the module has been storing data without external power for over ten days, and is still well above the cutoff voltage. Here is the graph of the voltage over time, with a comparison to a linear drop in voltage:
It looks like the RAM takes less current to run as the supply voltage drops. Even if the curve does not flatten out any more, the module should retain data for another two weeks, in addition to the ten days it has already run!
The one caveat here is that I haven't been able to check the memory contents since starting the test. Applying power to the chip to read the RAM would of course recharge the capacitor. So I have no idea if the memory has been corrupted by noise. I will probably wait a few more days before stopping the test to run verification, just to bring the run time up to a nice even two weeks.