I’m putting together an autonomous system with a Photon that I want to last for hopefully ~week-ish (or longer) on a single battery charge (battery TBD) but because of it’s out-of-reach nature it will be controlled via wifi (another Photon acting as a ON/OFF [sleep] switch). My idea was that when the system gets an “OFF” message from the switcher Photon, that it would go into a deep sleep and then wake itself up after ~10-15 seconds in order to save battery by disabling wifi but having wifi back on in a reasonable enough time to check for another “ON” message to break the sleep/wakeup cycle.
My question is: Is waking up from deep sleep at short intervals like this more energy expensive than just leaving wifi on and not putting the Photon into any type of sleep cycle? If so, is there any other way to save energy and increase battery life with this type of system that you would recommend?
@tomz, if one device can be powered on all the time while the other (battery operated) one cannot, then are they in physical proximity? The ideal scenario is to NOT wake the Photon every 15 seconds to check for a ON/OFF state which it could only do via direct TCP/UDP comms with the ON/OFF photon or via publish/subscribed via the cloud. Your battery will not last for your target duration.
Ideally, you put the battery operated photon to sleep and wake on interrupt or a high transition on the WKP pin. This could be done with a external hardware like a IR receiver if you have line-of-site to the ON/OFF photon or a low power 433MHz receiver (used in cheap remote controls). I’m sure others could come up with other ideas.
@peekay123 awesome thanks for the advice! That makes sense. I briefly considered a RF receiver like you mentioned but assumed it would also need to be powered all the time, but I guess you’re saying it would just require significantly lower current draw than a Photon in a frequent wakeup/sleep cycle would?
@tomz The total current draw on your battery greatly depends upon the circuitry around the photon, that will also consume some current and you will need to take into account how to turn off the power to any peripherals without impacting the wake operation on interrupt. I can vouch that the WKP pin works very well to wake the photon from deep sleep mode - but you then need to consider that waking from deep sleep effectively resets the system. The datasheet current consumptions are as follows:
Operating Current (Wi-Fi on)
IVIN avg
80
100
mA
Operating Current (Wi-Fi on)
IVIN pk
235[1]
430[1]
mA
Operating Current (Wi-Fi on, w/powersave)
IVIN avg
18
100[2]
mA
Operating Current (Wi-Fi off)
IVIN avg
30
40
mA
Sleep Current (5V @ VIN)
IQs
1
2
mA
Deep Sleep Current (5V @ VIN)
IQds
80
100
uA
The overall benefit of cycling through sleep (rather than deep sleep) is that the WiFi reconnection is automatic and there is no loss of variables in RAM. I use a cycle of 15 seconds awake (average 70mA) and 5 minutes sleeping (average 1-2 mA). If you have an external wake signal then using the WKP pin makes more sense.