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Re: [Owfs-developers] Reading latesttemp
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From: Mick S. <mi...@su...> - 2020-10-08 13:08:17
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On 08/10/2020 12:26, Jan Kandziora wrote: > Am 08.10.20 um 00:31 schrieb Mick Sulley: >> On my test system I have 20 DS18B20 temperature sensors (all powered) to >> test out various things. I am setting /simultaneous/temperature waiting >> 2 seconds then reading latesttemp from all of them. >> >> I have just noticed that several are giving 85 reads. If I look with >> owhttpd this is what I see - >> >> owhttpd screen >> >> Also owread /uncached/DHW_Mid_Btm/latesttemp returns 85. This is after >> many cycles of simultaneous/voltage and latesttemp reads. >> > Reading /uncached/<id>/latesttemp reads the contents of the temperature > register from the chip. > > It never triggers a temperature conversion. But owwrite /simultaneous/temperature 1 should trigger a conversion? and reading latesttemp should then be correct. Here is another. Latesttemp returns 85 even after owwrite /simultaneous/temperature 1, but read temperature12 and it works again. I don't understand why! pi@pi4b:~ $ owread /DHW_Top/latesttemp 85pi@pi4b:~ $ owread /DHW_Top/latesttemp 85 pi@pi4b:~ $ owwrite /simultaneous/temperature 1 pi@pi4b:~ $ owread /DHW_Top/latesttemp 85pi@pi4b:~ $ owread /DHW_Top/latesttemp 85pi@pi4b:~ $ pi@pi4b:~ $ owread /DHW_Top/temperature12 13.5625pi@pi4b:~ $ owread /DHW_Top/latesttemp 13.5625pi@pi4b:~ $ pi@pi4b:~ $ I have a few more in this state at the moment, I am sure I could fix them all with a single temperature12 read to each and they would then be fine, but I would really like to understand what the problem is > > If you read 85°C from latesttemp, it means the latest conversion either > 85°C (unlikely) or the chip has been power-cycled since the latest > conversion (likely). As 85°C is the power-on value of that register. > > >> It seems to me that it is a useful safeguard to run a single >> temperature12 read on each sensor during the initialisation of the >> system. I cannot see any downside to this but just thought I would ask >> for your thoughts. >> > That doesn't make any sense as you will read back the value from that > initial conversion again and again if your simultaneous trigger isn't > working. You mask the error that way, which is likely not what you want. > > If a sensor reports a spurious 85°C, treat that as a power-cycle on that > sensor – check your hardware! > > Kind regards > > Jan > > > _______________________________________________ > Owfs-developers mailing list > Owf...@li... > https://lists.sourceforge.net/lists/listinfo/owfs-developers |
