Review power-saving modes when battery is low

[jdavid]

When reading the battery charge in every loop we set the static variable battery to one of these 3 values (see readBattery() in power.cpp):

• BATTERY_HIGH
• BATTERY_MIDDLE if less-than-equal 70% (lithium) or less-than-equal 11.6 (lead)
• BATTERY_LOW if less-than-equal 35% (lithium) or less-than-equal 10.5 (lead)

For instance, lets say we run loops once every 5 minutes.

If BATTERY_MIDDLE we run actions half as often (every 10 minutes in our example). If BATTERY_LOW then we run actions 1/3 as often (every 15 minutes in our example).

Besides this there're some special cases:

• If BATTERY_MIDDLE the XBee network will only run once every 3h
• If BATTERY_LOW the mote will not run networks (XBee, 4G, Iridium)
• Actually, if BATTERY_LOW the mote will immediately sleep after waking up, so really nothing will be done, except logging to disk. So the condition above never happens.

[jdavid]

Discussion :

• The first thing we need to stop, or to run at a much lower frequency is the network.
• Maybe the GPS as well since it takes quite a bit of power, but the GPS is sampling data.
• At a lower level we need to completely stop the network, and the GPS?
• And maybe reduce the frequency of sensor readings
• At the lowest level we may need to stop sampling completely and sleep for a long time

[jdavid]

Basically the thing is 1st reduce frequency, 2nd stop. Starting with the network, following with the GPS, and finally the sensors.

[jdavid]

For example:

• Low-level-1: run network every 24h
• Low-level-2: stop network, run GPS every 24h
• Low-level-3: stop GPS, sample every 1h
• Low-level-4: stop sampling, sleep for 8h

[johnhulth]

Iridium Austfonna.xlsx

This is how I would like it to work on the two stations that i install on austfonna.

[jdavid]

Ok that means these changes:

• cooldown=4 for both middle and low levels
• stop network and gps if low
• adjust thresholds, middle 70 -> 80, and low 35 -> 30

I think we can do that for every mote, since this power-saving behaviour is coded. It looks to me better than what we've now.

Since we're changing thresholds for lithium-ion battery we change them as well for lead-acid batteries?

[johnhulth]

We don't use Lead-acid any more, so no need to adjust these values.