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Homebrew Davis Solar sensor

For discussion of DIY weather equipment - sensors, accessories, improvements to existing kit etc
EA1EF
Posts: 3
Joined: Fri Nov 29, 2013 10:57 am
Weather Station: Davis
Operating System: w7
Location: Reinosa

Re: Homebrew Davis Solar sensor

Postby EA1EF » Fri Nov 29, 2013 12:00 pm

Sorry if it´s offtopic but y have a question that can be very interesting for homebuilt (any) sensor for Davis Vantage Pro2 system.

I study in deepth different theories for implement third party sensors on Davis Vantage Pro stations because the only official option isn´t cheap (the Envoy8x + datalogger + PC + wireless kit for third party sensors).

I thing that SOLAR RADIATION IMPUT OF ISS davis Vantage Pro Pro2 are the best for this pourpose because it has the best precission with theorical 1077 steps ( 1800wm2 / 1,67uV steps) very close to therorical 10 bit signal 0-1024 steps. This 10 bit precission can alow precission for many type of sensor signals cheating the console,

The idea is Cheat the console with a "electrically compatible" third party sensor connected to Solar sensor ISS imput, the Davis vantage Pro system will processed this signal as Solar Radiation but isn´t true, i will get the processed signal in remote server and recalculate to the true signal unit to obtain real gauge. I thing that temperature compensation are internal in sensor and does no affect to third party sensors could connect here. The processed and filtered signal in console to 10 minutes media in console are so good for this pourpose, and no problem timming 50s-1minute or 5 minutes for low signals.

My sensor I thing is "electrically compatible":

IMPUT
Operating voltage from 2.7V to 5.5V ( 2.3mA-3.3V 3.1mA-5V) (original sensor 1mA typical)
~50mS power up initialization (

OUTPUT
Analogic Voltage 10bit 0-1024 (imput voltage scaled, if 3v imput 0-3v ouput 10bit signal)

TEST the THEORY: (fail)
I fail to test this teory with a simpliest test: in ISS Solar radiation IMPUT RJ-11 I bridge the imput YELLOW wire supply signal 3VDC to analogic 0-3VDC GEEN wire output signal, and bridge the Red and Black Ground wires.

And activate sensor in weatherlink ( in console didn´t configure anything), no reads in console and no reads in wheaterlink

Would read equivalent 3VDC imput maximun scale 1800w/m2 but none read seems.

any idea that are wrong? in nest weeks I try whit the distance sensor but i thing anything are bad in my theory.

sorry bad Inglish, thanks for attention.

edit. a will try the bridge voltage sensor with a resistor for lower than 3v voltage signal because newe info about maximun mA current in ISS sensors supply are:

The input IS linear...
The minimum display value for UV index is 0.5 at 0.070 volts.
The step voltage (from say 1.0 to 1.1 UV index) is 0.0143 volts per step.
The MAX input for 16.0 UV index is 2.395 volts.

The short circuit current from the ISS is 28 mA.
With a 2.67 mA load, the ISS voltage is 2.723 volts
With a 1.383 mA load, the ISS voltage is 2.858 volts
Open ckt. ISS voltage is 3.003 volts.
The ISS samples the UV sensor every 50 seconds for 2 seconds (the 3 volts IS switched NOT constant).
PM me if you would like a copy of the spreadsheet.
Bill
Last edited by EA1EF on Sat Nov 30, 2013 10:57 am, edited 3 times in total.

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mcrossley
Posts: 5192
Joined: Thu Jan 07, 2010 9:44 pm
Weather Station: Davis VP2
Operating System: Stretch Lite rPi
Location: Wilmslow, Cheshire, UK
Contact:

Re: Homebrew Davis Solar sensor

Postby mcrossley » Fri Nov 29, 2013 12:47 pm

This sounds quite feasible and workable.

How long did you leave your sensor connected? The ISS goes into a sort of 'sleep' mode if there is no solar signal detected in order to save battery power at night. Instead of sampling the solar sensor 50 seconds it falls back to every 10 minutes (iirc), once it detects a voltage coming back, then it switches into the normal 50 second sampling routine.

EDIT: Actually I'm not sure about that - I think it only applies to the UV sensor.

The solar sampling time is quite short, nominally 120ms (varies between 110-135ms), but your 50ms power up should be fine.

I have the following notes about the input to the ISS...

Input line is diode clamped to 0V and 3.3V, there is a 'switched' 100k pull-up to 3.3V, 'protected' with a 100R resistor. (Requires a rail to rail op-amp in sensor)

EA1EF
Posts: 3
Joined: Fri Nov 29, 2013 10:57 am
Weather Station: Davis
Operating System: w7
Location: Reinosa

Re: Homebrew Davis Solar sensor

Postby EA1EF » Fri Nov 29, 2013 4:31 pm

ok i continue investigating, new info about this are:

The input IS linear...
The minimum display value for UV index is 0.5 at 0.070 volts.
The step voltage (from say 1.0 to 1.1 UV index) is 0.0143 volts per step.
The MAX input for 16.0 UV index is 2.395 volts.

The short circuit current from the ISS is 28 mA.
With a 2.67 mA load, the ISS voltage is 2.723 volts
With a 1.383 mA load, the ISS voltage is 2.858 volts
Open ckt. ISS voltage is 3.003 volts.
The ISS samples the UV sensor every 50 seconds for 2 seconds (the 3 volts IS switched NOT constant).
PM me if you would like a copy of the spreadsheet.
(Bill)

whit this info probably the comsuption of sensor supply are important date to see final results, i thing

EA1EF
Posts: 3
Joined: Fri Nov 29, 2013 10:57 am
Weather Station: Davis
Operating System: w7
Location: Reinosa

Re: Homebrew Davis Solar sensor

Postby EA1EF » Sun Nov 09, 2014 7:46 pm

the big and esay problem to solved are the davis timming for this sensors

davis only take sourced a few milliseconds for Radiation sensor (about 0,4 seg) and take the read in first 0,2 sec aprox)

in UV sensor take sourced about 1,5 seg and read about first 0'4 sec.

easier way to solve are keel allways sourced the sensor from a stabilized source on the PCB (just on end thansistor pin)

regards

pomonabill221
Posts: 1
Joined: Sun May 15, 2011 2:03 am
Weather Station: Davis Vantage Pro 2
Operating System: Windows XP SP3
Location: Pomona, ca.

Re: Homebrew Davis Solar sensor

Postby pomonabill221 » Thu May 14, 2015 7:20 pm

mcrossley wrote:Here is the interface info...

ISS Solar Input
===============
0V = 0 W/m2
~1.67V = 1000 W/m2
2.977V ~ 1780 W/m2
step per W/m2 = 1.67mV

Input line is diode clamped to 0V and 3.3V, there is a 'switched' 100k pullup to 3.3V, 'protected' with a 100R resistor.
(Requires a rail to rail op-amp)

Samples every 50 seconds for 120ms (power on) - varies between 110-135ms

2 - Yellow - +V
3 - Green - signal
4 - Red - Ground
5 - Black - Ground


ISS UV Input
============
0V = 0 UVI
zero offset = 70mV = 0 UVI
2.395V = 16 UVI
3V = 16 UVI
step per 0.1 UVI = 14.3mV

Input line is diode clamped to 0V and 3.3V, there is a 'switched' 100k pullup to 3.3V, 'protected' with a 100R resistor.
(Requires a rail to rail op-amp)

Samples every 50 seconds for 2 seconds (power on)
Samples every 5 minutes when dark (?)

2 - Yellow - +V
3 - Green - signal
4 - Red - Ground
5 - Black - Ground



hHmmm... this looks like the data I posted! Where did you get this info?

User avatar
mcrossley
Posts: 5192
Joined: Thu Jan 07, 2010 9:44 pm
Weather Station: Davis VP2
Operating System: Stretch Lite rPi
Location: Wilmslow, Cheshire, UK
Contact:

Re: Homebrew Davis Solar sensor

Postby mcrossley » Fri May 15, 2015 8:46 am

pomonabill221 wrote:hHmmm... this looks like the data I posted! Where did you get this info?


I quite probably is, I didn't derive it myself, but I'm afraid I have long lost the original reference, I had that saved in a .txt file, but it was from the WX forum. I found it to be accurate though, so if you originally derived it - thanks!


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