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By kameo4242
#80691 Hi dear community,

I'm looking to use Lorawan as a way to receive my probe measurements instead of the less energy effective wifi.

The problem is the following: on a Lorawan access, you can only send 140 messages per day.
The "RTC clock", rather the RTC cristal used to pace during deep sleep periods, is temperature sensitive and somehow inaccurate with quite some drift over a day.

If you have a 10 minutes deep sleep sessions, some seconds of activity to poll the probe and send the results, you can theoritically reach the 140 messages per day. (10 minutes and 17 seconds I guess) So if the device is inaccurately spamming at an imprecise rate, it could end up having message discarded by the network.

So question is : since it is not possible to sync directly to a NTP server over a Lorawan connexion, are there any option to keep a decent timing, let's say around +/- 1 seconds accuracy over a period of 10 min?

__
Philippe.
User avatar
By villTech
#80713 140 messages / day is for sigfox iirc. haven't read anything saying it's the same with lorawan. is it?

<= 1sec / 10min is your target drift for rtc. that is > 2mins per day.
What temperature are you looking at that even a less accurate DS1307 will fail to that amount?
And there are still other more accurate rtc chip.
User avatar
By kameo4242
#80792
schufti wrote:AFAIR the error for deepsleep was an average of 3% on several samples. Taking this into accout (initial adjust) plus the varying time to get the message ack'ed I got a 15min interval stable to about +/-10s


It's quite decent in the end. The error margin does vary (like with temperature) or it's kind of a one time calculation?