Yeay! – The JeeNode made it through the night on a 0.47F supercap, for the first time ever at JeeLabs:
Sorry for the awkward / missing scale, here’s some context:
- vertical is voltage: 50 = 2V, 100 = 3V, 150 = 4V, 200 = 5V
- blue is VCC before sending, green is VCC after sending
- graph runs from 11:45 yesterday to 10:45 the next morning, i.e. 23 hours
- that’s two VCC measurements and one packet transmission every minute
The supercap had been charged by the solar cell for 3 days, no load. When connecting the JeeNode (BOD set to 1.8V, on-board 100 µF i.s.o. regulator, already running), I placed it in a cardboard box to block out the light:
- the first upward blip is at 12:45, during 5 minutes of exposure to sunlight
- then back into the box until 18:30, depleting the supercap for a few hours
- after that, the node was kept in the light to try and charge up enough for the night
- at 20:00, the charge had gone up to 4.42V and 3.86V, respectively
- at around 6:30 the next morning, the lowest point was reached: 3.44V and 2.88V
- from then on, the cell started charging again from the morning light (no direct sunlight yet)
- looks like about 10% of the packets never arrived (probably mostly due to collisions)
At noon, the cap voltage had risen to 4.9V (note that the RFM12B is now operating above its official 3.8V max).
So there you have it: one packet per minute powered by solar energy, harvested indoor near a window.
Update – FWIW, this setup lasted a second day, but then it died again… we’re not done yet!