This device has the requirement to go into Ultra Deep Sleep (UDS) and wake up every hour or once a day, transmit some data via LoRa and go back to sleep again. UDS is not like the deep sleep function in an ESP 32 chip as it can shuts down multiple modules, including the MCU and completely isolates them from the power supply. It's very easy to get current leakage into modules that are supposed to be disabled and UDS cures this problem very nicely. The modules that currently require isolation from the power are the 5.5V buck booster, the ESP32 MCU and the EBYTE LoRa and any sensors wired into the device are automatically put into UDS by default. There's even a sleep sate beyond UDS which even seems to shut down the logic gates called Beyond Ultra Deep Sleep (BUDS). This state is controlled by the AEMLION energy harvester and reduces the quiescent current down to an obscene 60 nA! UDS has been measured at 240 nA, which aint to scruffy either.
The UDS time is set by a resistor switch bank by simply flicking various switches in the correct order and the longest time interval is 2 hours which means the ESP32 needs to momentarily wake up, count how many times it has previously booted up and go back into UDS if the count is not high enough. Fortunately, the number of electrons needed to do this is fairly minimal.
In theory, this project should have been fairly simple but, unfortunately, the timer chip did not behave as described by the data sheet and currently the longest time interval is a pathetic 10 minutes. Rather than settle for mediocrity, it seems to be worth wrangling with some logic gates to make use of the short pulse that can be reliably detected from this chip and turn it into something more useful.
Once finished, the device should be fairly useful and various sensors could be wired into it or just used 'asis' to hack into the neighbour's WIFI (with permission, of course!). Having onboard 1 watts of LoRa means it's much more likely that the radio waves transmitted can reach a local node and communicate with the Interwebs. If it only transmits once a day it should be able to retain a good amount of charge in the battery, even in the depths of Winter. A winter on the North or South pole might be challenging though!, but with BUDS it might well just wake up in the Spring and start transmitting again. Hopefully there would be a LoRa gateway in range.
Project partially sponsored by Seeed Studio: https://www.seeedstudio.com/pcb-assembly.html
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