Author Topic: Davis vs Ambient Weather WS-2902 Humidity readings  (Read 1979 times)

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Offline johnd

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Re: Davis vs Ambient Weather WS-2902 Humidity readings
« Reply #25 on: February 01, 2019, 12:04:34 PM »
Who is it that's saying the conversion to I2C compatibility can be done via firmware alone? That is not my understanding at all.
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Offline galfert

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Re: Davis vs Ambient Weather WS-2902 Humidity readings
« Reply #26 on: February 01, 2019, 12:22:58 PM »
Who is it that's saying the conversion to I2C compatibility can be done via firmware alone? That is not my understanding at all.

Right from the horse's mouth. Sensirion is saying this in the SHT85 documentation. I just posted this a few posts back with excerpt from Sensirion documentation.
https://www.wxforum.net/index.php?topic=36029.msg369625#msg369625

Here is the source document - See attached
Titled: Transitioning from SHT7x to SHT85

« Last Edit: February 01, 2019, 02:06:10 PM by galfert »
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Offline johnd

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Re: Davis vs Ambient Weather WS-2902 Humidity readings
« Reply #27 on: February 01, 2019, 01:11:19 PM »
It needs someone more expert than me in electronics design to comment, but I don't read that as saying that firmware changes alone are adequate, merely that firmware changes are required (ie in addition to potential changes in support components). But maybe I've misinterpreted it.
« Last Edit: February 01, 2019, 01:15:03 PM by johnd »
Prodata Weather Systems
Prodata's FAQ/support site for Davis stations
Includes many details on 6313 Weatherlink console.
UK Davis Premier Dealer - All Davis stations, accessories and spares
Cambridge UK

Sorry, but I don't usually have time to help with individual issues by email unless you are a Prodata customer. Please post your issue in the relevant forum section here & I will comment there if I have anything useful to add.

Offline galfert

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Re: Davis vs Ambient Weather WS-2902 Humidity readings
« Reply #28 on: February 01, 2019, 02:16:13 PM »
I read that documentation to mean that yes firmware alone is all that is required from a technical standpoint and that the there is nothing new and magical about the new sensor in that it uses compatible pins, including voltage requirements. What is different is the protocol (software). It does mention that sometimes it is customary to use a pull up resistor with the new SHT85 but that that it is optional and not required as it is possible to drive the circuit without it. The other mentioned constraint is that the SHT7x and the SHT85 are of a slightly different size dimensions and therefore may require hardware redesign in accommodating the different slightly different shape of the SHT85. But these are minimal size differences of the prepackaged SHT85 and are not an issue if you are redesigning your own module that uses an SHT35 chip with I2C bus...then all you need is the firmware update to support I2C.

I'm not an electronics expert either. So I could be wrong. But that is how I interpret it.

Ecowitt GW1000 | Meteobridge on Raspberry Pi
WU: KFLWINTE111  |  PWSweather: KFLWINTE111
CWOP: FW3708  |  AWEKAS: 14814
Windy: pws-f075acbe
Weather Underground Issue Tracking
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