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I bought some of the Xbee3 LTE-M modules a few weeks ago and they had hardware version D printed on them, so they appear to be the latest version. I also updated their firmware to a version that came out a few weeks ago which supposedly has some improvements too. Digi also states in the manual several time (including with big warning symbols) that Bypass mode has been deprecated and should not be used because it causes instability in the cellular connectivity. So I’m now switching ours over to transparent mode to see if they are more stable. Previously in Bypass mode, I had the same issue that Cal did where things would work fine for a few days, but then the module would stop responding and require me to reset it. I’m hoping that operation in transparent mode will be better.
Something else that I discovered lately is that because of the workaround we did with using the SJ13 option for powering the Bee socket pin 1 directly from LiPo is that the module is now constantly powered. This is great as long as the Mayfly is turned on and can put the LTE-M bee to sleep by asserting the bee’s sleep pin high. The Mayfly is able to keep that pin high even when the Mayfly is asleep (if you write your code correctly). However, when the Mayfly gets turned off at the main power switch, the Bee module is no longer kept in sleep mode by the Mayfly, so it wakes up and stays on permanently until someone turns the Mayfly back on. The LTE-M bee draws about 7ma when idle, so it’ll drain a battery after a short while if you don’t have a solar panel connected. So for now, I just remove the Bee module from the socket when I turn the Mayfly off. It’s possible that you could solder a pullup resistor to the bee sleep pin, but that gets messy and could cause other issues. So our next version of the Mayfly board will incorporate some new changes to how all the Bee socket stuff is handled to fix this problem and to add some other functionality.