Author Topic: Temp/Hum sensor pinout  (Read 938 times)

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Offline azchrisf

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Temp/Hum sensor pinout
« on: February 09, 2018, 09:25:29 PM »
Does anyone have any ideas or a diagram which color wires go to which pins on the SHT31?

Offline azchrisf

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Re: Temp/Hum sensor pinout
« Reply #1 on: February 10, 2018, 08:12:21 AM »
Since noone seems to know, I tore a sensor open (did not want to but need it for a project):

BLU = RH Vout
WHT = Temp Vout
YLW = Vin 3.3V
GRN = Gnd

Hopefully this helps someone in the future.

Offline belfryboy

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Re: Temp/Hum sensor pinout
« Reply #2 on: February 10, 2018, 03:18:44 PM »
Bear in mind that if you intend to use the Davis sht31 sensor with anything other than the ISS that it does not use the I2C protocol, but the legacy sensibus protocol.

Offline azchrisf

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Re: Temp/Hum sensor pinout
« Reply #3 on: February 11, 2018, 11:45:00 AM »
Correct, it returns voltage based results.
With what little spare time I have these days, I tried plugging it into the Arduino pin for pin correct (A0, A1 for Analog inputs from the sensor), but even with a Sensiron provided sketch I couldn't get any valid data. Strange...

Offline johnd

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Re: Temp/Hum sensor pinout
« Reply #4 on: February 11, 2018, 12:58:32 PM »
Since noone seems to know, I tore a sensor open (did not want to but need it for a project):

BLU = RH Vout
WHT = Temp Vout
YLW = Vin 3.3V
GRN = Gnd

Is this definitely right? I'm happy with yellow and green, but wouldn't the other two wires just be the SDA and SCL of the Sensibus interface? I could well be wrong, but just a little surprised that a digital part is providing separate analogue outputs for T and Hum.
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Offline azchrisf

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Re: Temp/Hum sensor pinout
« Reply #5 on: February 11, 2018, 01:08:14 PM »
Since noone seems to know, I tore a sensor open (did not want to but need it for a project):

BLU = RH Vout
WHT = Temp Vout
YLW = Vin 3.3V
GRN = Gnd

Is this definitely right? I'm happy with yellow and green, but wouldn't the other two wires just be the SDA and SCL of the Sensibus interface? I could well be wrong, but just a little surprised that a digital part is providing separate analogue outputs for T and Hum.
This is an analog part not i2c unless I am missing something...

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Offline johnd

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Re: Temp/Hum sensor pinout
« Reply #6 on: February 11, 2018, 01:18:56 PM »
Quote
This is an analog part not i2c unless I am missing something...

No, SHT31 is a digital part, hence the comments about I2C/Sensibus etc. See:

www.sensirion.com/en/environmental-sensors/humidity-sensors/digital-humidity-sensors-for-various-applications/

Oh, hang on, turns out that it seems to be both digital and analogue somehow. How does that work then? Presumably you have somehow to switch it from one mode to another? Ah, I think they're two separate parts SHT31-DIS (digital) and SHT31-ARP (analogue). So the Davis sourced ones would be just digital I guess.
« Last Edit: February 11, 2018, 01:26:32 PM by johnd »
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Offline dalecoy

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Re: Temp/Hum sensor pinout
« Reply #7 on: February 11, 2018, 05:48:57 PM »

It will be interesting to find out which of those azchrisf actually has.

Offline azchrisf

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Re: Temp/Hum sensor pinout
« Reply #8 on: February 11, 2018, 09:03:07 PM »
It's a standard Davis Sht31. It's been documented in the past that it is an analog variant. Davis never used i2c and still doesn't.
But whatever they are using it certainly doesn't want to communicate over standard analog...maybe some kind of special circuitry is involved - I've traced the pins from the chip to the wires using the Sensiron pinout on the datasheet and even though they are properly connected in every way, I can't get data from the chip.

So I'm going to scrap that idea and just get a SHT35 i2c and make a new ISS unit myself using Arduino after learning a little more. Another member here did it, forget his name.

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« Last Edit: February 12, 2018, 02:04:43 AM by azchrisf »

Offline johnd

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Re: Temp/Hum sensor pinout
« Reply #9 on: February 12, 2018, 03:37:12 AM »
It's a standard Davis Sht31. It's been documented in the past that it is an analog variant. Davis never used i2c and still doesn't.

This is actually all well-known. Davis used analogue T/H sensors up until the end of 2005 (officially) on VP2 stations. Ever since then the VP2 (and the Vue since it was introduced) has used a digital Sensirion T/H part. Belfryboy has also explained about the digital interface - it's Sensibus, which is a relative of the official I2C protocol AIUI, but with enough differences in protocol that the two are not interoperable.

If you were able to find an SHT31-ARP part (the first two letters on the bottom row would be 'AR' if you have a good enough magnifying glass!) then you'd be able to carry on with your original analogue approach, but this wouldn't come from Davis. Does also make me wonder whether the ARP version couldn't be worked up into a replacement part for the analogue sensor in the VP1 and early VP2 stations (and conceivably WMII also), though demand is possibly too low to make it worthwhile.

« Last Edit: February 12, 2018, 03:38:51 AM by johnd »
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Offline azchrisf

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Re: Temp/Hum sensor pinout
« Reply #10 on: February 12, 2018, 03:40:52 AM »
Well then color me stupid and ignorant. <SMH>
I read it was an analog chip and always had been. I have never heard of Sensibus... That explains why I can't get any data from it, and no libraries exist for Sensibus that I know of for Arduino and the Sensiron SHT3x.

Like I said, I'm just going to get the SHT35 and make my own ISS transmitter so I can use the better sensor.
All I have on it is the temp/hum and rain gauge anyways, the UV/Solar and Anenmometer is on seperate transmitters.

Offline belfryboy

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Re: Temp/Hum sensor pinout
« Reply #11 on: February 12, 2018, 04:14:11 AM »
If you use the Arduino sht15 library you will be able to talk to the Davis sensor.

Offline azchrisf

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Re: Temp/Hum sensor pinout
« Reply #12 on: February 12, 2018, 04:27:52 AM »
Hang on a second. Let's stop.
I know this is a SHT3x sensor because it has the round hole in the middle. It is stamped on the chip SHT31. It is not a SHT1x or 2x that has the square hole on the top. My unit was manufacturer last year - and the part # I have in my hands is 7346.070

https://www.scaledinstruments.com/shop/davis-instruments/davis-7346-070-pro2-digital-temperature-humidity-sensor-sensiron-sht31/

UNLESS you are telling me this thing is stamped SHT3x and is actually a SHT15...

Now I am all confused as hell - the only SHT31 variants are the i2c and analog ratiometric voltage. AFAIK Davis doesn't use i2c.
« Last Edit: February 12, 2018, 04:38:03 AM by azchrisf »

Offline johnd

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Re: Temp/Hum sensor pinout
« Reply #13 on: February 12, 2018, 04:58:02 AM »
UNLESS you are telling me this thing is stamped SHT3x and is actually a SHT15...

Now I am all confused as hell - the only SHT31 variants are the i2c and analog ratiometric voltage. AFAIK Davis doesn't use i2c.

It will be a genuine SHT31 I'm sure. Belfryboy is more up on this than me, but AIUI the explanation is that buried somewhere amongst the Sensirion data sheets is the fact that they also make a variant of the DIS SHT31 with Sensibus rather than formal I2C, specifically for backwards compatibility for makers like Davis who've previously used the SHT1x parts with Sensibus. This makes the SHT31 in this special variant a drop-in replacement (other than the slight difference in temperature calibration) for the SHT1x series.
« Last Edit: February 12, 2018, 04:59:34 AM by johnd »
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Offline azchrisf

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Re: Temp/Hum sensor pinout
« Reply #14 on: February 12, 2018, 05:00:48 AM »
Interesting.
I tried using the SHT15 library and a analog + a i2c default sketch and still got no data.

This seems to be a effort in futility - I have alot of work to do coding anyways for the Rain bucket and Temp sensor + transmit the packet out like the ISS does now. So I'll concentrate on that instead unless someone has an idea just for Shi** and Giggles...

Offline belfryboy

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Re: Temp/Hum sensor pinout
« Reply #15 on: February 12, 2018, 05:10:54 AM »
the davis SHT31-LSS uses the same protocol to communicate as the SHT15. They both use Legacy Sensibus. The most commonly available chip is the SHT31-DI  digital i2c, but this is not what Davis use in their sensor. I will try and find a schematic of the test circuit that I use.

 

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