Topic: SHT21 as alternative to SHT11

[dataworx]

I came across this sensor board and was considering whether it could be used as an alternative to the SHT11 in the older stations. I appreciate that there are a bunch of technicalities, so if anyone here has some info to share, I'd be most interested:

http://www.ebay.com/itm/SHT21-Digital-Humidity-And-Temperature-Sensor-Module-Replace-SHT11-SHT15-AM-/253076359731?epid=939419517&hash=item3aec86ca33:g:DMsAAOSwPK5ZgwVS

[azchrisf]

This was something I was thinking about earlier, if we can get a list together of sensors that can improve the Davis's accuracy, yet still be pin for pin compatible and work with the software, if possible, that we can replace.

[dataworx]

I've sourced one of the sensors linked to above - I'm quite happy to test it but I'm hoping that one of the more knowledgeable members will be along to help me with a pinout so I don't immediately wreck it by hooking it up incorrectly. I have a couple of stations here so I can easily do a side-by-side comparison to test accuracy.

[johnd]

I guess you need to explain why you might want to use SHT21 in place of the SHT31 that's readily available from Davis as a drop-in replacement for SHT11? OK, you need to apply the prescribed temperature offset to the console temp, but that's easily done. Maybe cost is an alternative factor, but the SHT31 board cost isn't exorbitant.

[dataworx]

I think there are a few factors, one of them being price ($6 versus $40-$50, which is a considerable difference). The primary reason though is that I'm an inveterate tinkerer. With Scottish blood. So if I can find a cheaper, effective solution I'm all for it, especially for stations that are a decade old and need to be kept in service.

[jerryg]

Well unless something has changed it won't work with the davis software it needs to be the ls series and i don't think they make it in that version. I tried one and it would not work, i believe it is i2c only.

[dataworx]

Thanks jerryg, I was fairly sure someone on the forum would have tested this sensor at some point. Perhaps something has changed - since I already have the sensor I'd like to test it anyway. Are you able to help me with the pinout?

[jerryg]

No i don't have the pin out anymore because it won't work with Davis station so saw no need to keep any info.

[dataworx]

Thanks jerryg

I have a dead Davis sensor here, and I have a schematic of the sensor itself, so I'll see if I can strip the protective coating and establish the pinout.

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[belfryboy]

As jerryg points out the sht21 uses i2c serial communication, but the Davis vantage pro 2 uses legacy sensibus communication. The two are not compatible. Although you probably won't damage your equipment your results will be disappointing. If you get the two data sheets side by side it should become clear.

[dataworx]

Thank you belfryboy, that's the sort of information I was looking for. With my rudimentary knowledge I've been unable to determine whether there would be a communications protocol issue. I have to assume then that nobody on this board has yet found a drop-in, non-Davis replacement, whether SHT11, 15, 21 or whatever?

EDIT: sorry to waste everyone's time, I just found this thread from last year, looks like this is an avenue that's been well explored:

https://www.wxforum.net/index.php?topic=29500.0

[dataworx]

Pardon the resurrection - I'm still digging around looking for a replacement to the Davis SHT11 chip/board. I have 7 of these original sensors here, all with varying faults.

Has anyone here yet come up with a suitable replacement at a sensible price?

[johnd]

The answer really hasn't changed in the past 6 years, for all the reasons previously stated. For a VP2 T/H sensor to operate correctly then it needs to use the Sensibus protocol. And the only known source of Sensibus-using Sensirion T/H sensors is Davis themselves.  To my knowledge, no-one has ever been able to find an alternative source, in part because - Davis-aside - Sensibus seems to be EOL.

Presumably one day Davis will need to redesign the ISS SIM board input to use eg a standard I2C input for the T/H sensor, but I can understand why they hold off doing so for as long as they can source the Sensibus part and can preserve full backwards compatibility for all VP2 stations with digital sensors back to 2006.

[AndreGermain]

After much web searching and reading documentation, it was clear that finding an SHT31 or other variant with Sensibus was impossible unless one bought 1000 from the OEM. I wasn't in the mood to spend 120$ CDN to get the Davis replacement owing to xchg, taxes and shipping. I had the dreaded SHT11 out of bound humidity signal, and I chanced upon a gent on ebay with a dozen of them intact in their original packaging for 19$ CDN to my door. I replaced the part and it works, problem solved. He still has many left as of Oct 2024, give him a try: https://www.ebay.ca/itm/235549498480?itmmeta=01JB9FAE5J02S89J8AJ5269Q51&hash=item36d7d81c70:g:-A0AAOSwOEhmNlGx

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Note the old one is labelled BAD... I knew it!

[davidmc36]

Thanks for the heads up.

I picked up a 4 pack to keep in stock for upcoming retirement budget.

Get a few toys during this last 11 months of work. 

[AndreGermain]

You're welcome, and I had already noticed! Ontarians need to help each other I'm down the road from you near Alexandria, also about to retire, too many projects to work on. We're part of the BIB SHT11 crew.

But consider how few there are on the planet, if anyone is in desperate need, consider selling one.

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[dataworx]

Thanks for the info @AndreGermain, I ordered one, we'll see how long it takes to get to the bottom end of Africa...

[davidmc36]

... near Alexandria,
....

Cool. I am out that way quite a bit. Doing service of Stand By Generators these days. We go all over lol

[Sawadee]

Does anyone know what sensor is used in the current release of the 6263?
I just ordered this station and was curious.  Thanks.

[AndreGermain]

To anyone wanting an SHT11 Sensiron, still 10 left on Ebay canada, and for Canadians the shipping has dropped to 2$, so 17$ CDN.

https://www.ebay.ca/itm/235825036240