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Rain Bird rain sensor does not work with Mini-8

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    Leap Frog Group

    Additional information: I inserted a 4.7 megohm resistor in series with the "open" (wet) rain sensor and the delay LED energized.  When the sensor is "closed" (dry) the delay LED goes out even though the total circuit resistance is approximately 4.7 megohms!  Anyone else would call that an open circuit, especially since the sensor is designed to switch 24VAC at about an amp or so.

    It would appear the Mini-8's test for open circuit is problematic, or I've got a defective unit.  What are the specs for "open circuit"?

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    Brandon Moyer

    You may need to go into the RainSensor settings on the RainMachine and switch it from Normally open to Normally closed (The RainBird default) and see if this helps.

    We also want to make sure its wired correctly as in the diagram above. 

    After double checking both, let me know if you still have trouble. 

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    Leap Frog Group

    Hi Brandon - The sensor is wired correctly per the diagram and as noted it is normally closed (closed when dry, open when wet).  That is how the RainMachine is set as well. 

    I found this post while searching so apparently this is a known issue.  However, unlike the OP's sensor my RainBird sensor is brand new.  I would think that for RainMachine rain sensor purposes any circuit resistance > 1K ohms or so should be "open".

    https://support.rainmachine.com/hc/en-us/community/posts/115006894547-Rain-Sensor-Compatibility 

     

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    Brandon Moyer

    Just incase change RainMachine to normally open, and see if this help, Its possible we may have the settings backwards. 
    If not you may be right and it might just be a resistance issue. According to the Rain Sensor article there are other rain sensors known to work with the mini 8. 

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    Leap Frog Group (Edited )

    No, your software setting is correct - if I open the circuit by removing one of the wires (or as noted, add a 4 to 5 megohm resistor in series with the wet/open sensor) then the Delay LED is lit.  If I short the circuit with a jumper (or when the sensor is dry, and therefore closed) then the Delay LED is not lit.  If you like I can put a potentiometer across the Common / Rain Sensor terminal and tell you exactly what the trip point is - but we know empirically it is > 5 megohms.  I suspect many rain sensor leads will have megohm resistance when wet/open just due to moisture levels, salt air, or whatever.

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    Istvan (Edited )

    Hi, 

    The calculated threshold resistance is around 5.6Meg, 
    Considering your R(sensor) measurement of 4.7Meg, you could just add a 1.5Meg+ resistor in series with your sensor.

    Istvan
    RainMachine Support

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    Leap Frog Group (Edited )

    Thanks - that is exactly what I did.  Is this fixable in firmware or would it require a hardware change?  I'll speculate that the two customers discussing this here https://support.rainmachine.com/hc/en-us/community/posts/115006894547-Rain-Sensor-Compatibility and myself are not the only customers who will be encountering this issue.

    I appreciate the great support!

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    Istvan (Edited )

    Hi,

    This requires a hardware change as it has to do with an on-board comparator trip voltage set by resistors. Thank you for the feedback! 

    Istvan
    RainMachine Support

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    Leap Frog Group

    That would be a good revision for Gen 3 of the Mini-8 (and perhaps the other platforms if they have the same issue).

    Thanks again.

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    Leap Frog Group (Edited )

    @Ian The RainBird sensor conditions are dry/shorted (e.g., less than an ohm in my case) and wet/open (e.g., about 4.7M ohms in my case).  Since the Mini-8 design point for an open circuit is ~5.6M ohms my sensor doesn't show "open enough" when it is wet, even though it is.

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    Ian Coulthard

    So this means this cannot detect a short circuit as no rain but needs 4.7M to do so? Still makes no sense and a bad design.

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    Istvan

    Ian,

    the trip resistance is 5.6Meg. There is a hardware hysteresis that prevents bounce, but other than that, any resistance under ~5.6Meg is detected as "no rain". Having a resistor of 1.5Meg in series with the sensor does one thing: it shifts the range upwards, allowing the usage of sensors which - when disconnected - don't show infinite resistance, but something around a few Megs. So, when the sensor is dry and shorted, the overall resistance of the circuit will be 1.5Meg and the input will read "dry sensor" because it is under the ~5.6Meg threshold. When the sensor is wet, the overall resistance will be 4.7Meg + 1.5Meg > 5.6Meg and the input will see a "wet sensor". 

    Istvan
    RainMachine Support

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