Author Topic: Convert i2c to sensibus (sensirion) protocol to be read by Davis ISS  (Read 2544 times)

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Offline dendrite

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Re: Convert i2c to sensibus (sensirion) protocol to be read by Davis ISS
« Reply #25 on: July 31, 2018, 06:47:11 PM »
Not much that I can add, but good work. If you could make the 35 easily plug & play I'd pay for it when the pin 35 is released.

Offline jgentry

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Re: Convert i2c to sensibus (sensirion) protocol to be read by Davis ISS
« Reply #26 on: July 31, 2018, 08:39:00 PM »
Not much that I can add, but good work. If you could make the 35 easily plug & play I'd pay for it when the pin 35 is released.

Same here!
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Online mcrossley

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Re: Convert i2c to sensibus (sensirion) protocol to be read by Davis ISS
« Reply #27 on: August 01, 2018, 02:48:23 AM »
My only question would be power consumption? Power management in the ISS must be pretty tight, would this thing require an external power source?
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Online johnd

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Re: Convert i2c to sensibus (sensirion) protocol to be read by Davis ISS
« Reply #28 on: August 01, 2018, 04:07:24 AM »
My only question would be power consumption? Power management in the ISS must be pretty tight, would this thing require an external power source?

Davis imply that a cabled ISS consumes 9mA, but I don't know how much of that might be used by the RS422 connection vs turning on the wireless chips every 2.5 secs or so.
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Offline rdsman

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Re: Convert i2c to sensibus (sensirion) protocol to be read by Davis ISS
« Reply #29 on: August 01, 2018, 08:18:50 AM »
My only question would be power consumption? Power management in the ISS must be pretty tight, would this thing require an external power source?

I don't intend to power it from the ISS.  I'm going to use the VCC signal from the ISS to bring the processor out of Sleep mode, let it do it's thing and then go back to sleep.   Perhaps it could be only solar powered and would fit inside a standard wireless Davis ISS enclosure with the solar panel.

Ray

Offline rdsman

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Re: Convert i2c to sensibus (sensirion) protocol to be read by Davis ISS
« Reply #30 on: August 08, 2018, 04:54:53 PM »
Well, I haven't received my SHT35.  In the mean time I wrote some code that reads the SHT75 in a real similar manner that the ISS does.  It is inserted (in txt format) if anyone is interested.  Just copy and paste it into an
Arduino sketch.

 [ You are not allowed to view attachments ]

It is not a final version by no means, but to be used as a diagnostic tool - goes really great with a logic analyzer!

Ray

Offline rdsman

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Re: Convert i2c to sensibus (sensirion) protocol to be read by Davis ISS
« Reply #31 on: August 21, 2018, 07:02:12 PM »
Thanks to SLOweather, I now have a SHT75 connected to my ISS.  I am capturing the real time data in a piggybacked processor.  I am going to let it run for a while to see if it "chokes".

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« Last Edit: August 21, 2018, 07:07:45 PM by rdsman »
Ray

Offline dendrite

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Re: Convert i2c to sensibus (sensirion) protocol to be read by Davis ISS
« Reply #32 on: August 21, 2018, 09:23:24 PM »
Awesome. Do you have this data online?

Offline galfert

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Re: Convert i2c to sensibus (sensirion) protocol to be read by Davis ISS
« Reply #33 on: August 21, 2018, 11:28:13 PM »
Nice work on the 75 reader. But I'm looking for an update on the 35 which is the next step in your drop 75 insert 35 data design.  Have you gotten data from the 35 yet?
« Last Edit: August 21, 2018, 11:37:23 PM by galfert »
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Offline rdsman

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Re: Convert i2c to sensibus (sensirion) protocol to be read by Davis ISS
« Reply #34 on: August 22, 2018, 03:56:42 AM »
Awesome. Do you have this data online?

No, but this is the Raw data coming from the SHT75, not what the ISS sends to the console.  The actual temperature and humidity values have to be calculated first.  So the next step is to make sure that I can match what the console is displaying in real time.

Nice work on the 75 reader. But I'm looking for an update on the 35 which is the next step in your drop 75 insert 35 data design.  Have you gotten data from the 35 yet?

Yes, I can read the SHT35. 

Ray

Offline rdsman

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Re: Convert i2c to sensibus (sensirion) protocol to be read by Davis ISS
« Reply #35 on: August 22, 2018, 04:25:19 PM »
Quote
The actual temperature and humidity values have to be calculated first.  So the next step is to make sure that I can match what the console is displaying in real time.

The temperature is dead on every time.  The humidity is exactly 1.0% low when I calculate it based on the captured data.  This is an example:

Console shows 46.
RFBee receiver shows 46.4.
Excel spreadsheet gets 46.4.
Arduino shows 45.4.

??????


Ray

Offline galfert

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Re: Convert i2c to sensibus (sensirion) protocol to be read by Davis ISS
« Reply #36 on: August 22, 2018, 04:54:06 PM »
Seem like the Arduino has some sort of -1% offset correction going on. Maybe the scale is different. Like maybe you are reading hex codes it is a difference of whether you start at 0 or if you start counting a 1.
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Offline rdsman

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Re: Convert i2c to sensibus (sensirion) protocol to be read by Davis ISS
« Reply #37 on: August 22, 2018, 06:34:23 PM »
Seem like the Arduino has some sort of -1% offset correction going on. Maybe the scale is different. Like maybe you are reading hex codes it is a difference of whether you start at 0 or if you start counting a 1.

Here is my thinking, the console resolution is 1.0% starting at 1.0%.  Maybe the initialized value of RH is set at 1.0% in the ISS because the console can't display tenths of a percent - even though the ISS transmits in tenths.  It would keep the ISS from transmitting values below 1.0%.   Just a thought for now.....


 
Ray

Offline rdsman

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Re: Convert i2c to sensibus (sensirion) protocol to be read by Davis ISS
« Reply #38 on: August 28, 2018, 04:19:09 PM »
I've made some progress on this project.  While I haven't calculated a percentage of difference between the two, all I can say is most of the time they match each other.  When they differ, is never more than .1 degree in temperature or .1 percent in humidity.

 [ You are not allowed to view attachments ]

Personally, I'd be happy with it the way it is, but I'll see if I can fine tune it.....

I'm amending this to better explain the picture.  The processor is reading the SHT35 and reversing its compensation, calculating what would be expected for the SHT75 and then printing both sets of data out for comparison.
« Last Edit: August 29, 2018, 05:40:50 PM by rdsman »
Ray

Offline jgentry

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Re: Convert i2c to sensibus (sensirion) protocol to be read by Davis ISS
« Reply #39 on: August 28, 2018, 04:25:30 PM »
I've made some progress on this project.  While I haven't calculated a percentage of difference between the two, all I can say is most of the time they match each other.  When they differ, is never more than .1 degree in temperature or .1 percent in humidity.

 [ You are not allowed to view attachments ]

Personally, I'd be happy with it the way it is, but I'll see if I can fine tune it.....

Awesome! Would love to see how it compares when the RH is in the 90% range, especially near or at 100% Might not be able to do this test, but it would be interesting to see how the temps compare when its below 0F
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Offline CW2274

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Re: Convert i2c to sensibus (sensirion) protocol to be read by Davis ISS
« Reply #40 on: August 28, 2018, 06:14:29 PM »
I've made some progress on this project.  While I haven't calculated a percentage of difference between the two, all I can say is most of the time they match each other.  When they differ, is never more than .1 degree in temperature or .1 percent in humidity.

 [ You are not allowed to view attachments ]

Personally, I'd be happy with it the way it is, but I'll see if I can fine tune it.....

Awesome! Would love to see how it compares when the RH is in the 90% range, especially near or at 100%
Yes, very impressive. Don't forget us folks at the other end of the spectrum. ;)

Offline galfert

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Re: Convert i2c to sensibus (sensirion) protocol to be read by Davis ISS
« Reply #41 on: August 28, 2018, 07:17:40 PM »
Very nice results. Will you be sharing your code for the drop 75 and replace with 35 data? I can't wait to see that....but if you are keeping it closed source that's cool too.

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Offline rdsman

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Re: Convert i2c to sensibus (sensirion) protocol to be read by Davis ISS
« Reply #42 on: February 02, 2019, 12:15:11 PM »
I know it has been awhile, but here is the update:

I originally purchased two SHT35-DIS modules.  Along with writing code to emulate the ISS, I also wrote stand alone code for them.  They have been running for months, one with a filter and one without.  I am convinced that they both exhibit the same "wetness" that the other Sensirion sensors do.  I guess that given that the spec sheet states the following:

Quote
The sensor shows best performance when operated within recommended normal temperature and humidity range of 5 C
60 C and 20 %RH 80 %RH, respectively. Long-term exposure to conditions outside normal range, especially at high
humidity, may temporarily offset the RH signal (e.g. +3%RH after 60h kept at >80%RH). After returning into the normal
temperature and humidity range the sensor will slowly come back to calibration state by itself.

The results I got are to be expected.  The above quote applies to the newer SHT85 as well.  Maybe it is just in the packaging, my inexpensive AcuRite doesn't do this!

My results may seem disappointing, but all of my time wasn't wasted.  The same concept could be applied to any other sensor whether it be analog, I2C or other.  I/we just need to come up with a sensor that truly works well outdoors.

Maybe the HYT series is worth looking into.....

 
Ray

Offline galfert

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Re: Convert i2c to sensibus (sensirion) protocol to be read by Davis ISS
« Reply #43 on: February 02, 2019, 01:34:26 PM »
Thank you for the update. So your conclusion is that all the effort of trying to use an SHT35 with the Davis ISS would be for not because the wet bias would still be present. That is odd that your Acurite does not experience this and it has an SHT31. Very mysterious.
 
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Offline CW2274

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Re: Convert i2c to sensibus (sensirion) protocol to be read by Davis ISS
« Reply #44 on: February 02, 2019, 01:57:03 PM »
Quote
The results I got are to be expected.  The above quote applies to the newer SHT85 as well.  Maybe it is just in the packaging, my inexpensive AcuRite doesn't do this!
Firstly, thank you for your work. However, I'm confused.... is not the 85 assembled/shipped completely apart from Davis? I get that the SHT series is supposedly not meant for outdoor use, if so, why does the Acurite (it has a 31, right?) not exhibit the same wet bias?

Offline jerryg

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Re: Convert i2c to sensibus (sensirion) protocol to be read by Davis ISS
« Reply #45 on: February 02, 2019, 02:03:40 PM »
I agree results are disappointing the idea was being able to use a sensor with i2c protocol on the Davis iss but is there any better sensor out there, i guess any one with good specs and no warnings about high humidity problems from the maker of the sensor would be better. I have been using the sht75 for several months and have not had any problems at all compared to the 31 i was using. Down here on the coast of Texas we get a lot of coastal trofs that hang around for several days at a time and the humidity can stay in the 90% range all that time with fog and drizzle and the 75 has not shown any bias at all when the humidity starts to drop. This sensor was used in commercial probes by well known manufacturers so it must be pretty good. I think the question is why do other weather stations use the same sensor and don't seem to have a problem. I just wonder if the owners of those stations just don't realize they may have it. I did not notice the problem until i read about it on the forum and when i really paid attention i saw it, i guess i was blinded by the 100% readings i was getting from the 31 lol. I can not do anything with codes and stuff so i hope those of you who can will keep trying to find an answer to the problem.

Offline rdsman

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Re: Convert i2c to sensibus (sensirion) protocol to be read by Davis ISS
« Reply #46 on: February 02, 2019, 04:09:44 PM »
galfert & CW2274:

I have not taken the Accurite apart to see what is in it.  Will do so soon.  I don't have a SHT85, just noticed what was said on the spec sheet.  Maybe I need to try one just to see.....

jerryg:

I have not tried my SHT75 outside.  The fact that they have been discontinued made it a moot issue in my opinion.



Ray

Offline CW2274

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Re: Convert i2c to sensibus (sensirion) protocol to be read by Davis ISS
« Reply #47 on: February 02, 2019, 04:13:31 PM »
The above quote applies to the newer SHT85 as well.
Certainly not saying you're wrong, but have you actually tried an 85? Like I stated, since Davis has nothing to do with it, perhaps things would be different....
BTW, without giving away any of your potential proprietary knowledge, how difficult would it be for us "commoners" to incorporate an 85 into our ISS's?
Thanks!

Edit: Just saw that you haven't tried the 85. Perhaps it may be worthwhile....
« Last Edit: February 02, 2019, 04:15:22 PM by CW2274 »

Offline rdsman

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Re: Convert i2c to sensibus (sensirion) protocol to be read by Davis ISS
« Reply #48 on: February 02, 2019, 04:49:37 PM »
The Acurite mystery for me is solved.  It uses an old fashioned analog sensor.  Seen in this picture (the white thing standing up).

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The date code on the circuit board in 2014/06/10.  It is newer than my Davis setup!



Ray

Offline ValentineWeather

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Re: Convert i2c to sensibus (sensirion) protocol to be read by Davis ISS
« Reply #49 on: February 02, 2019, 05:07:30 PM »
WOW! Thanks for opening and checking. Had me scratching my head why humidity worked so much better.
Randy