Using Rain/Freeze Sensor with OpenSprinkler

Rain/freeze sensors are useful for detecting rain or freeze conditions, and delays or stops watering accordingly. There are many types of rain sensors on the market. Recently I tried out this Orbit 57069 rain/freeze sensor. It’s very easy to connect to OpenSprinkler, and works quite well. The rain delay time can be easily adjusted by setting the water evaporation speed.

So how does this rain sensor work? It’s pretty simple. The sensor has two wires, which are normally connected to each other inside through a switch. The top of the sensor has a small chamber, which contains a string of sponge pads (see below). When it rains, the water will drip into the chamber and gets absorbed by the sponge pads. The pads will then expand and press against each other as well as the top of the chamber. When it expands to a certain point, the switch inside the sensor will be pressed down, disconnecting the two wires. The height of the chamber can be adjusted to control when the sensor is activated – in other words, the amount of rain that will activate the sensor. There are five options: 1/8, 1/4, 1/2, 3/4, and 1 inch.

Down below the chamber is an evaporation window. The size of the window controls how fast the absorbed water evaporates, thereby controlling the rain delay time. After the rain stops, the sponge pads will gradually shrink, and at some point the switch is released, thus the two wires are connected again. This is a very clever design because it’s purely mechanical, requires no power itself, and is easy to adjust. The downside is that you cannot set the delay time precisely – obviously the local humidity and temperature will affect the evaporation speed.

Once you figure out how it works, it’s very easy to connect it to OpenSprinkler. The diagram above shows the connection (Not sure where the ‘common wire’ is? Check out this diagram). Simply put, the sensor acts as a normally-closed switch placed on the common wire. When the sensor detects rain or freezing condition, it disconnects the common wire from the sprinkler valves. As is, it can work with almost any kind of sprinkler timer, without modifying the timer itself.

The sensor should be installed on the roof or next to the gutter. You need to run a wire from the sensor to your sprinkler timer. The sensor itself comes with a relatively long wire, so that shouldn’t be a problem. If you want, you can even get a wireless version at a slightly higher cost.

That’s it – if you need automatic rain delay control, this is an easy, inexpensive option you may consider.

13 thoughts on “Using Rain/Freeze Sensor with OpenSprinkler

  • February 26, 2012 at 5:18 am
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    This mod would presumably disable the ability to manually control zones, for example if you ran the simple web-based system after it had rained.
    I wonder if we could utilise a spare I/O pin and make this software controllable. I can think of some situations where we might like to override the rain sensor.

    • February 26, 2012 at 10:26 am
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      Geoff, yes that’s a good point. Digital pin 3 in the pinouts can be used for this purpose. I should consider this in future design to have a terminal block dedicated for rain sensor.

  • December 18, 2013 at 11:53 am
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    What’s the wiring for the 2.0 controller with the dedicated rain sensor input? Just both wires into that port instead of going to station1?

    Thanks.

    • December 20, 2013 at 1:30 am
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      Just connect the two wires from the rain sensor to the terminal — it’s non-polar so it doesn’t matter which way you connect. Then in software you can configure how the rain sensor input will be used.

  • July 3, 2014 at 12:26 pm
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    I replaced an old sprinkler timer with an Orbit #57896. The watering is working fine. I also am attempting to connect an Orbit #57069 “Automatic rain/freeze sensor. The statement on the sensor box side says: “This will not work with open circuit timers”. Inside the timer there are two connection tabs that say “sensor” and are connected by a metal loop wire. How do I connect the rain sensor to the timer? The original wires of the old sensor come out of the ground and were attached to the old rain sensor. I don’t know from where they originated. From the sprinkler valve control perhaps?
    Help in connecting them together, if possible !!

    Charles

    • July 7, 2014 at 12:49 am
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      I don’t know what ‘open circuit timers’ mean. You should be able to connect your new sensor directly to the rain sensor port on your sprinkler timer.

  • July 15, 2015 at 7:12 am
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    I was wondering how the freeze detection works on the Orbit #57069 given it is wholly mechanical? Is there perhaps a dedicated bi-metallic strip employed somewhere or something? (the instructions online claim freeze detection triggers at a specific temperature which is not adjustable so it seems like there is separate dedicated sensor). I ask because I am finding the #57069 model expensive in the UK when compared to identical ‘looking’ slightly earlier models (or rebranded metric versions) but these of course don’t mention freeze detection at all.

    • July 15, 2015 at 10:19 am
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      I am pretty sure it’s all mechanical, although I haven’t figured out how the freeze detection works. Perhaps it’s some kind of mechanical sensor deep inside, with sealed water, and expands to close a switch when it freezes?

  • July 15, 2015 at 7:36 am
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    Further I notice a description on anazon states the freeze sensor is ‘digital’ which makes me wonder if it’s a simple mechanically operated switch or if it actually uses the typical 24v ac supply and therefore won’t work with opensprinkler dc?

    • July 15, 2015 at 10:20 am
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      Where in the description that says the freeze sensor is digital?

  • April 13, 2017 at 7:08 am
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    I realize this is an old post, but did anyone ever confirm whether the freeze function actually exists, and
    if so, does it have an extra lead to power the circuit?

    • May 29, 2017 at 10:43 pm
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      Yes: many rain sensors have built-in freeze sensing capability. These are mechanical sensors that do not need power.

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