So I built the ATiny13A led flasher and achieved an average current draw of 30uA over several hours by measuring the discharge of a 0.78F capacitor. This is around 25% of the discrete version.
Which is crazy compared to what I was expecting. After poking and prodding I determined that some of the difference was due to not allowing for the internal resistance of the pin driver on the ATTiny13A. Instead of getting 20mA I was getting 7mA of current through the LED. However, this did not explain all of the difference between what I measured and what I expected.
With some more tweaking of software and hardware I achieved a LED that flashes for 10ms every 2 seconds drawing 10mA. That's the rated maximum for a single pin. I was thinking of using two pins in parallel but it seems bright enough for my purposes.
As a sanity check I put a new but several year old AG3 battery onto one of these Tiny flashers on 9:30am on Dec 6th. I believe the battery was rated at 25mAhr when new. I expected this battery would run the led for 10 days. Note the makeshift button cell holder below.
However, after 10 days of operation it appears there is still substantial life left in the battery.
Day Voltage
6 1.35
8 1.32
9 1.31
10 1.30
11 1.28
I can't explain the observed result which is way better than I expected. What was supposed to be a sanity check has sent me back into my spreadsheet looking for an error. Wherever the error lies I am amazed that the AG3 cell looks like it will run the Tiny Flasher for 20 days.
It would seem that based on the range of outcomes at this point the Tiny Flasher will run for around 4 years from a single AA battery.
The only way to be sure is to monitor the one running on a fresh AA battery to see what happens.
More on this in 2027?
No comments:
Post a Comment