DS18b20 hard reset ?

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uxhamby
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Joined: 29 Dec 2016, 18:13
Location: Toronto Canada

DS18b20 hard reset ?

#1 Post by uxhamby » 22 Jan 2019, 18:04

Hi,

I have a couple of esp8266's in service, running espeasy (one is version R120 and the other is version mega-20180809) where from time to time the DS18b20 connected to it will apparently become unresponsive, leaving espeasy reporting the same temperature indefinitely, regardless of how ambient behaves.
DS18B20 Technical specs: Usable temperature range: -55 to 125°C (-67°F to +257°F)
I am safely within that range I'd say.

I periodically need to manually hard reset the whole esp to recover from this and find that a soft reset of the esp alone does nothing for the DS18b20's state of mind.

I realize that the sensible thing to do is to change out the relevant DS18b20's but it occurs to me that with an appropriate gpio pin toggle, I could likely hard reset just the DS18b20 remotely if I were to power the DS18b20 using a gpio pin directly or via a transistor. Plan A

Alternatively, I could wire the power to the whole esp8266 and DS18b20 via a Normally Closed relay contact which I could open with a gpio toggle which operates the relay. Plan B.

I suppose I could power just the DS18b20 via a N.C. relay contact and toggle its power by gpio pulse but don't see any advantage to this over my previous strategies. Plan C.

Any known precedence for any of this?

Thoughts, admonitions, warnings ?

Thanks,

Brian H.

Wiki
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Joined: 23 Apr 2018, 17:55

Re: DS18b20 hard reset ?

#2 Post by Wiki » 23 Jan 2019, 11:28

The GPIO pins of the ESP8266 can easily power the few µA the Dallas needs. So I would solder the VCC pin of the Dallas to a free GPIO configured as output high and reset them by pulling the pin to low using a pulse.

In my network I have several DS18B20 running using parasite power, no problems at all (except readings sometimes report NaN).

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