Comments: Weather Meter Hookup Guide

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  • If you want to maximize the voltage difference between the 16 possible levels obtained using the technique shown in the weather meter datasheet, the optimum resistor value for the resistor you supply for the voltage divider appears to be about 3511 Ohms, rather than the 10k resistor value shown in the Weather Meter datasheet as an example.

    With the 10k resistor, and a 5V power supply, the minimum difference between voltage values obtained is about 45.4 mV. Using a 3511 Ohm resistor and the same 5V power supply, you can achieve a minimum difference of about 96 mV. You can do almost as well with a more-common 3600 Ohm resistor, which yields a minimum voltage difference of about 95 mV, again assuming a 5V power supply.

    Thus sayeth Excel.

    • How did you go about determining an optimal resistance value to maximize the voltage difference between readings?

  • I have seen some discrepancies between the rainfall measurements of the electronic rain gauge and a manual rain gauge I have next to it. For example, the electronic gauge measured around 44 to 45 mm (I can't remember the exact number) while the manual gauge measured around 65 mm of rain. I did some calculations with pouring in known masses of water, and knowing the surface area of the rain gauge, can calculate how many mm of rain that represents. Then counting the clicks for each of the known masses of water, I was able to determine that each click is actually around 0.3996 mm of rain, not the 0.2794 mm quoted.

    As a verification, if I divide the 44 mm of rain measured the other evening by 0.2794 (to get the number of clicks represented) and multiply that by 0.3996, I get 62.93 mm of rain, which compares favourably with the manual rain gauge. I can share the calculations with anyone that is interested, but I am quite confident that the "magic number" for the rain gauge is 0.3996 mm/click.

  • I found big problems with the rain sensor: even from an average wind, it shakes and registers as if it is raining. On the internet also write about the problems with the rebound, after shifting the rocker arm in the rain, that is, unnecessary triggering. How to solve this?

  • There are two different datasheets for the weather gauge product on the Sparkfun site. This article links to https://www.sparkfun.com/datasheets/Sensors/Weather/Weather%20Sensor%20Assembly..pdf?_ga=2.14578160.633493603.1572019408-434657447.1570326130 .

    One link is in the paragraph that reads:

    As the voltage output will depend on the value of the external resistor used, there is not one common conversion function. For an example of how to calculate this, please reference the datasheet for the meters.

    This datasheet contains at least one error, in the voltage for 315 degrees, which should be 4.33V, not 4.78V.

    The link to this datasheet also appears at the bottom of the hookup guide.

    But a corrected datasheet is linked from the weather meter product page, https://www.sparkfun.com/products/8942 . This page links to: https://cdn.sparkfun.com/assets/8/4/c/d/6/Weather_Sensor_Assembly_Updated.pdf

    The updated datasheet contains the correct voltage value for 315 degrees.

    I haven't compared the two datasheets looking for other errors. Caveat emptor.

  • Hello at Sparkfun, can you please assist me with the power ratings of these products? do they work on 5V?


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