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Arduinio Weather Station Grapher

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rossw:

--- Quote from: WooferHound on March 12, 2021, 06:23:31 am ---Suspected that the voltage output from a solar panel would not accurately follow the actual light level.

--- End quote ---

But it CAN.


--- Quote ---I feel that the readings I'm getting follow actual levels really good until it gets close to Full Sunlight and then it compresses and flattens out a little bit.

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Quite a lot looking at your graph!


--- Quote ---The small solar panel being used to sense the light is 6 volts and measured only 60 ma short circuit. I don't think it is even big enough to charge a Powerbank in the first place. The voltage divider uses 1200 ohms across it so it's not loaded much at all.

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I would load it up WAY more. I mean *WAY* more.
At 6V with 1200R that's only 5mA and you won't be getting anything LIKE a representative curve.

I would like you to try with a 22 ohm to the panel + and then 82 ohm to ground. Take the junction of the 22 and 82 to your arduino input.
That should give you 58mA draw at full voltage, and reduce the voltage to the arduino to just 4.7V (safe, with a little headroom for overshoot)

What you SHOULD see on a cloudless day is a section of a sine-wave. Despite you thinking the sun comes up and is basically the same brightness all day, it really isn't - at least, not with a fixed detector!

rossw:
Here's an example - the last 24 hours at my location.

The green curve is the calculated intensity at this time of day and this day of year, based on my lat/lon, for an arbitary horizontal-plane.

The red curve is the 5-minute peak value observed (which would normally be right at the edge of the blue area, but we have had high cloud all morning, and at midday a lot more cloud has moved in - the high peaks are cloud-edge-effect and the lows are where we've been in deeper shade)

The blue area is the average intensity over the whole 5 minute sample period.

As you can see, it "should" follow a near-perfect section of a sinewave - the amount of the sinewave depends on the time of year and your latitude.

These are measured using a large-area PIN diode and a "perfect short circuit" using the earlier-mentioned transimpedance amplifier.

WooferHound:

--- Quote from: rossw on March 12, 2021, 02:46:39 pm ---
I would like you to try with a 22 ohm to the panel + and then 82 ohm to ground. Take the junction of the 22 and 82 to your arduino input.
That should give you 58mA draw at full voltage, and reduce the voltage to the arduino to just 4.7V (safe, with a little headroom for overshoot)


--- End quote ---

OK I changed those resisters in the Divider Network.
Didn't have the exact values, so I added 50% to each value where I'm using 33 ohm and 120 ohm to divide it.

It does look wildly better with more definition in the brighter samples.
Was worried that putting a load on the panel would reduce Low Light Sensitivity, but that is not really important anyway.

Want to start averaging several samples together instead of taking the sample and immediately plotting the pixel, but I still am not good enough with the programming. Having trouble declaring variables properly, I think it has something to do with Scope of the variable. Really need to learn how to declare a 2 Dimensional Array but keep getting syntax errors.

But still Having fun . . .

Here is a 2 hour section of todays cloud cover with the changes made to the resistors.

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