IR controlled solenoid valveI would like to develop a motion activated sprinkler to deter birds (cranes and other smaller birds) and small animals from eating the fish in my pond. I am using the approach of controlling a solenoid valve via a PIR motion sensor. However, this means the thing will activate even if humans walk past it.

Is there any method to trigger it only for motion by small animals (say less than 2.5 ft height)? I'm open to suggestions on entirely different sensors/methods.

Based on some pet friendly intrusion alarm websites, it looks like there may be PIR sensors that can be tuned to differentiate between animals less than 50 pounds vs more. I just can't seem to find the existence of such sensors.

  • \$\begingroup\$ Photo of the physical setup please. There's probably an alternative like IR trip wires or narrow FOV pyroelectric sensors at different heights to discriminate things. You could just try turning your PIR sensor 90 degrees so that it only detects vertical movement (most PIR motion sensors have two sensor elements arranged horizontally and compares the heat change between the two to detect motion). \$\endgroup\$
    – DKNguyen
    Jun 16, 2020 at 19:32
  • 1
    \$\begingroup\$ Machine vision and object recognition - using a $10 webcam. \$\endgroup\$
    – rdtsc
    Jun 16, 2020 at 19:45
  • \$\begingroup\$ You could also just try tilting your PIR sensors downward...wherevere they are pointing at. \$\endgroup\$
    – DKNguyen
    Jun 16, 2020 at 19:47
  • \$\begingroup\$ @DKNguyen, how would it help if I tilt it downwards? Wouldn't it still trigger if a human walked past it? \$\endgroup\$ Jun 16, 2020 at 19:57
  • \$\begingroup\$ @SamuraiJack Sure, if the human walked under it. But you would have to get a lot closer and lower. It's really hard to know what you can do without knowing the physical setup. \$\endgroup\$
    – DKNguyen
    Jun 16, 2020 at 19:59

1 Answer 1


Search Mouser for PIR sensors and look at the datasheets for what is available in terms of analog/digital outputs, detection ranges, and field of view.

Some ideas you can try out:

Differential FOV PIR:

  • Use two rather narrow FOV sensors. Aim one at the pond surface and aim the other in the same direction but above the pond surface.
  • Use a narrow FOV sensor and a wide FOV sensor. Aim the narrow FOV at the pond and aim the wide FOV sensor straight up. Since the FOV is wide and the sprinkler is low it should be able to capture tall things around it, including behind it. The result would be that as long as a human is nearby the sprinkler just never turns on.

In either case, you set things up so that the sprinkler turns on only when the sensor, and only the sensor, aimed directly at the pond detects something.

PIR + Proximity Sensor PIR sensors have a pretty wide FOV, even the narrow FOV ones so the above methods might not pan out. But you could use a PIR sensor with a proximity sensor (such as near-IR) which is available in very narrow FOVs and aim it up to distinguish whether something tall is in the way. The sun could cause issues though for such a upward pointing sensor.

Thresholding: Get a sensor with analog output and a MCU or comparator circuitry and find a threshold of non-zero movement to delineate between large warm bodies and small warm bodies moving around. The problem is PIR sensors give stronger readings the warmer a body is, the larger it is, the faster it is moving, and the closer it is so these are all variables. For example, setting it so the typical warm bird body moving around and bird-like speeds and typical distance could still allow a human moving slowly and far enough away from the sensor to trigger it.

  • \$\begingroup\$ Thanks! I understand most of this. About using narrow FOV sensor and wide one - Will this require a MCU? Is there any easier/analog way to set it up so the solenoid releases the water only when the narrow one detects motion and wide one does not? \$\endgroup\$ Jun 16, 2020 at 20:45
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    \$\begingroup\$ @SamuraiJack If they are digital output you shouldn't need anything more than a logic gate or two. Or you can use a PICAXE which has dev software that allows placing blocks so no that you don't need to program if you don't want to, but I am not sure if you can put them in sleep for battery conservation. \$\endgroup\$
    – DKNguyen
    Jun 16, 2020 at 20:46
  • \$\begingroup\$ @SamuraiJack You can do "anything" without a microcontroller BUIT eg Arduinos are astoundingly easy to learn to use, low cost (China sourced) and you'll never regret having made their acquaintance. \$\endgroup\$
    – Russell McMahon
    Oct 30, 2020 at 10:36

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