Author Topic: Convert i2c to sensibus (sensirion) protocol to be read by Davis ISS  (Read 1770 times)

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Offline Skyliner

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Hi

This is my first post (sorry for my english  :roll:) and I want to know if it's possible that a sensirion sht35 with i2c digital interface to communicate with the Davis ISS which reads only sensibus protocol. I have thought in an Integrated Circuit between sht35 and Davis ISS to convert the protocol but I have found no documentation about it. Actually I have a SHT75 working with the Davis.

SHT35 is great with very accurate readings, high time response and it's working with an orange pi pc. You can see in realtime at:

http://meteoarchena.es/sht35.php

Greetings from Spain


Offline jgentry

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Re: Convert i2c to sensibus (sensirion) protocol to be read by Davis ISS
« Reply #1 on: July 17, 2018, 08:50:06 PM »
Don’t think so but I’m not an electronics expert.

Do you have the SHT-31 sensor too? If so, how does it compare to the SHT-35 in terms of humidity?  There are some of us who believes that the SHT-31 humidity sensor does not operate within specs and has a wet bias in mid range humidities and a dry bias on the high end.

Here is a thread discussing the SHT-31

https://www.wxforum.net/index.php?topic=34658.0
Davis Vantage Pro2. SHT-75. WU: KXALJEMI2 & KALTHORS2. CWOP/APRS: C6353 & E6358

  

Offline CW2274

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Re: Convert i2c to sensibus (sensirion) protocol to be read by Davis ISS
« Reply #2 on: July 17, 2018, 09:25:43 PM »
Forum member "ct" where are you.....?

Offline jgentry

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Re: Convert i2c to sensibus (sensirion) protocol to be read by Davis ISS
« Reply #3 on: July 17, 2018, 10:17:41 PM »
Forum member "ct" where are you.....?

Are you referring to ctwx?
Davis Vantage Pro2. SHT-75. WU: KXALJEMI2 & KALTHORS2. CWOP/APRS: C6353 & E6358

  

Offline CW2274

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Re: Convert i2c to sensibus (sensirion) protocol to be read by Davis ISS
« Reply #4 on: July 17, 2018, 10:32:45 PM »
Forum member "ct" where are you.....?

Are you referring to ctwx?
I don't believe so.
The person I'm referring to has the capability to use (and I think does) the SHT35 with a VP2, or with something. He gets the i2c thingy so other sensors could potentially be used.
I sent him a pm, but he doesn't post much.

Offline jgentry

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Re: Convert i2c to sensibus (sensirion) protocol to be read by Davis ISS
« Reply #5 on: July 17, 2018, 10:41:05 PM »
Forum member "ct" where are you.....?

Are you referring to ctwx?
I don't believe so.
The person I'm referring to has the capability to use (and I think does) the SHT35 with a VP2, or with something. He gets the i2c thingy so other sensors could potentially be used.
I sent him a pm, but he doesn't post much.

Ok.  Hope he gets your message. Would love to have some options.  Thanks for contacting him.
Davis Vantage Pro2. SHT-75. WU: KXALJEMI2 & KALTHORS2. CWOP/APRS: C6353 & E6358

  

Offline ct

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Re: Convert i2c to sensibus (sensirion) protocol to be read by Davis ISS
« Reply #6 on: July 17, 2018, 10:59:39 PM »
I use an i2c SHT35 with a custom built controller.   No idea how you can use a SHT35 with a Davis ISS.

I also have an SHT31 inside a Davis FARS about 2 metres away from the SHT35.

The SHT35 last reached 100% humidity on 28 June 2018 5:45AM.  At the same time the SHT31 was at 96%.

The SHT35 has been in operation for about 15 months, the SHT31 a little longer.

I could probably produce a few graphs comparing the 2 sensors.

Offline CW2274

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Re: Convert i2c to sensibus (sensirion) protocol to be read by Davis ISS
« Reply #7 on: July 17, 2018, 11:05:14 PM »
No idea how you can use a SHT35 with a Davis ISS.
Damn, I was afraid you'd say that.  ](*,)
Thank you for replying.

Offline openvista

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Re: Convert i2c to sensibus (sensirion) protocol to be read by Davis ISS
« Reply #8 on: July 17, 2018, 11:37:45 PM »
My understanding is that SHT31s are 35s that didn't make the cut. The 35s are the best of the lot. Given that, the 31s could vary widely in quality depending on the strictness/enforcement of quality control at Sensirion.

My wild guess would be that 35s wouldn't be problematic at first (see Randy's struggles in the other thread with two new 31s). But, over time, they very well could develop the same problems as the 31s since they are the same sensor. If someone has different information, I'd be glad to entertain it.
Davis Vantage Pro2 FARS | https://marquetteweather.com | EW7933

Offline CW2274

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Re: Convert i2c to sensibus (sensirion) protocol to be read by Davis ISS
« Reply #9 on: July 18, 2018, 12:19:57 AM »
It wasn't so much about making the 35 work, but having the newer protocol that would allow for different sensor options for the ISS.

Offline dendrite

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Re: Convert i2c to sensibus (sensirion) protocol to be read by Davis ISS
« Reply #10 on: July 18, 2018, 08:23:40 AM »
I've been using the 75s for the faster response times. For most of the temp range, the 75 isn't too far off from the 31...toward -20C you start getting bigger disparities.

I'm not sure if it's been mentioned, but the SHT75 is being discontinued in favor of a pin type SHT35 available at the end of this year.

https://www.sensirion.com/en/environmental-sensors/humidity-sensors/pintype-digital-humidity-sensors/

The 75 is plug and play with a Davis ISS. Apparently the new one will be based on the SHT35-DIS so it'll probably be I2C.

Offline Skyliner

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Re: Convert i2c to sensibus (sensirion) protocol to be read by Davis ISS
« Reply #11 on: July 18, 2018, 08:31:07 AM »
Ok... it's been a long time since I've posted this...thanks to the response email service of wxforum  :grin:

Well… Firstly I had a SHT11 that came with Davis Station in 2011. The max humidity I got was about 96-97%. Since that moment I thought that that value was not very accurate in foggy nights.

I've purchased a SHT75 with better humidity specs and I found that in high humidities was just the same about 96% for the max. So... when I saw that SHT31 by Davis was in the market I've got it and put it on my Davis station…. just disappointed with the results… 96% in max values too and in the middle range a 2% lower of humidity compared to the SHT75.

I've then purchased a SHT31 and SHT35 from Closed Cube and with an Orange Pi PC (similar to the Raspberry but cheaper) I put it both into Davis Station with a cat 5 cable. The SHT31 with i2c protocol was similar in middle ranges to SHT35 and SHT75 (put as main sensor on station) but in high humidities the values was of 96-97% again. Only the SHT35 reached values of 99%.

Also the variation time was better. I think just like it is said in the link above (thanks for it jgentry  ;)) the size of the filter cap could affect the variation time. The SHT35 with SF2 Cap filter from Closed Cube is just closed to the sensor leaving no air chamber between, not like the Davis sensors where there is a big air chamber that needs more time for renewing the air.

After I've purchased and saw the results of Davis SHT31 I wrote to Davis asking if SHT35 was coming soon and they said to me that it wasn't in their plans. I'm a big disappointed why Davis for just 8$ of difference between SHT31 and SHT35 mount in their units the cheapest one. I think Davis is there to improve and install high-end sensors (just a difference of 8$...for God's sake !!)

Actually I've put +0.1ºC and +1% offsets to SHT75 in Davis console and is giving similar values in SHT75 and SHT35 http://meteoarchena.es with the Davis SHT75 and http://meteoarchena.es/sht35.php with the i2c SHT35. Observe that max/min values are quite similar but in high humidities and in response time SHT35 makes the difference.


The 75 is plug and play with a Davis ISS. Apparently the new one will be based on the SHT35-DIS so it'll probably be I2C.


Yes... I'm afraid of that… the sht35 from Closedcube is cheap and handy for mounting with pre-soldered headers
« Last Edit: July 18, 2018, 08:32:58 AM by Skyliner »

Offline hwcorder

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Re: Convert i2c to sensibus (sensirion) protocol to be read by Davis ISS
« Reply #12 on: July 18, 2018, 10:23:22 AM »
I've been using the 75s for the faster response times. For most of the temp range, the 75 isn't too far off from the 31...toward -20C you start getting bigger disparities.

I'm not sure if it's been mentioned, but the SHT75 is being discontinued in favor of a pin type SHT35 available at the end of this year.

https://www.sensirion.com/en/environmental-sensors/humidity-sensors/pintype-digital-humidity-sensors/

The 75 is plug and play with a Davis ISS. Apparently the new one will be based on the SHT35-DIS so it'll probably be I2C.

I contacted senserion support and they confirmed the new pin version of the 35 will be I2C.  Sounds like I may be stockpiling the SHT75's and storing them to switch out every 12-18 months.  Hopefully by the time I run out there will be better options out there.

Anybody out there think they could make an ISS transmitter that would be compatible with I2C?  I'm sure there are many on this forum including me that would jump all over that.
« Last Edit: July 18, 2018, 10:30:59 AM by hwcorder »


Offline mcrossley

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Re: Convert i2c to sensibus (sensirion) protocol to be read by Davis ISS
« Reply #14 on: July 18, 2018, 11:36:10 AM »
Anybody out there think they could make an ISS transmitter that would be compatible with I2C?  I'm sure there are many on this forum including me that would jump all over that.
Should be fairly straight forward. I have an Arduino based board that emulates an ISS and re-transmits temp/hum/rain/wind sp/wind dir/solar/UV
You'd just need to add an IC2 library to talk to the sensor and inject the values.
The library for the VP2 radio emulation was written by kobuki on this board, I modded my version slightly from an older version of his.
Mark

Offline rdsman

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Re: Convert i2c to sensibus (sensirion) protocol to be read by Davis ISS
« Reply #15 on: July 18, 2018, 12:26:38 PM »
If you had a SHT35 module that fits in the VP2 and an inline protocol converter.........

Just my 2 cents!

Ray

Offline ValentineWeather

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Re: Convert i2c to sensibus (sensirion) protocol to be read by Davis ISS
« Reply #16 on: July 18, 2018, 01:04:11 PM »
I'm all onboard for new controller if we can get away from the Davis protocol: and change to better temp/hum sensor.  My dislike for 31 has grown especially when it runs high humidity when accuracy is critical during high heat and humidity outbreaks common many areas. 

Would have to be pretty much p&p and compatible with the existing sensor array. I would be willing to run cat5 or whatever it took doesn't need wireless for temp/hum.   
Randy

Offline rdsman

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Re: Convert i2c to sensibus (sensirion) protocol to be read by Davis ISS
« Reply #17 on: July 24, 2018, 12:11:25 PM »
First off, I have a VUE not a VP2.  It is the older style Vue with a plug-in Temp/Humidity sensor.  The sensor is the SHT-11.  This style of sensor
is no longer available.  If anyone has one that they are willing to part with (working or not) please PM me.  (I really just need the cable.)

By attaching an IDC connector to the ribbon cable, I scoped out the following:

Pin 1 Data (Red Stripe)
Pin 2 Clock
Pin 3 Ground
Pin 4 VCC - Goes High only during a measurement.

Here is a capture of the raw temperature data:

 [ You are not allowed to view attachments ]

Here is a capture of the raw humidity data:

 [ You are not allowed to view attachments ]

I have a SHT-75 coming, so first I will write some code that emulates the Vue read cycles.  I will then get the SHT-35 and try to emulate the SHT-75 with it.

PS:  I'm not in a hurry!

Ray

Offline SLOweather

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Re: Convert i2c to sensibus (sensirion) protocol to be read by Davis ISS
« Reply #18 on: July 24, 2018, 01:07:21 PM »
First off, I have a VUE not a VP2.  It is the older style Vue with a plug-in Temp/Humidity sensor.  The sensor is the SHT-11.  This style of sensor
is no longer available.  If anyone has one that they are willing to part with (working or not) please PM me.  (I really just need the cable.)


The cable is just a plain ol' 4 conductor phone cable and modular connector...

Offline rdsman

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Re: Convert i2c to sensibus (sensirion) protocol to be read by Davis ISS
« Reply #19 on: July 24, 2018, 01:14:16 PM »
Quote

The cable is just a plain ol' 4 conductor phone cable and modular connector...


Not on the Vue.  The cable is a six conductor ribbon cable.  One end is soldered to the sensor board and the other end has a weird molded plug on it.

Ray

Offline SLOweather

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Re: Convert i2c to sensibus (sensirion) protocol to be read by Davis ISS
« Reply #20 on: July 24, 2018, 01:58:00 PM »
Not on the Vue.  The cable is a six conductor ribbon cable.  One end is soldered to the sensor board and the other end has a weird molded plug on it.

OK. Sorry. Like this?


Offline rdsman

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Re: Convert i2c to sensibus (sensirion) protocol to be read by Davis ISS
« Reply #21 on: July 24, 2018, 02:16:32 PM »
Quote
OK. Sorry. Like this?

Yes, that's it.  Would you like to get rid of it?

Ray

Offline SLOweather

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Re: Convert i2c to sensibus (sensirion) protocol to be read by Davis ISS
« Reply #22 on: July 24, 2018, 02:57:45 PM »
Sure. PM me your postal address.

Quote
OK. Sorry. Like this?

Yes, that's it.  Would you like to get rid of it?

Offline rdsman

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Re: Convert i2c to sensibus (sensirion) protocol to be read by Davis ISS
« Reply #23 on: July 24, 2018, 03:26:38 PM »
Sure. PM me your postal address.

Quote
OK. Sorry. Like this?

Yes, that's it.  Would you like to get rid of it?

I just sent you a PM.  You just don't know how much this will help me out!  I want to do this project, but not destroy my Vue in the process.  My only other option was going to be to use my RFBee as a repeater and do a
drop and insert.  In other words when the SHT-75 data came along, substitute that data with the SHT-35 data formatted correctly.

I really only need the cable, you could just cut the sensor off if you like.

Thanks so much!

« Last Edit: July 24, 2018, 03:39:29 PM by rdsman »
Ray

Offline rdsman

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Re: Convert i2c to sensibus (sensirion) protocol to be read by Davis ISS
« Reply #24 on: July 31, 2018, 04:56:20 PM »
Well, I now have an ISS emulator up and running.  It reads from the SHT75 using the same timing as the Davis ISS.

 [ You are not allowed to view attachments ]

Next step is to write a SHT75 emulator, with the final goal of reading a SHT35 (or any other sensor) and presenting the data to the ISS in SHT75 format.

Any comments?

Ray

 

anything