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Motion Sensor Switch for alarm, light or water sprinkler

2014-11-22 08:53  
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The Motion Sensor Switch circuit is a motion sensor controlled automatic water sprinkler but you can easily add an alarm/light function too. Before beginning the construction contact your nearest electronics component vendor and procure a readymade box-type Passive Infrared (PIR) Motion Sensor unit. Such units, packed in a compact enclosure with power input and relay output terminals are widely available.
In prototype, an unbranded (Made in China) PIR Motion sensor with the following specifications are used.

Detection Range:10Meter MaximumSupply Input:12V DC, <500mARelay Output :Common(C),Normally Closed(N/C),Normally Opened(N/O)Relay ON time: 15 Secs (Not Adjustable)

pir motion sensor unit
Now install the PIR module hanging from a 3 metre high mast (to cover 10 metre radius area) and connect its supply and relay terminals to our finished and enclosed circuit, observing right polarity. A 4-core screened cable can be used for this interconnection. Power the circuit from a regulated 12VDC adaptor/solar power box.

Whenever the PIR module detect movement of a live body its relay output toggles and the switching mosfet (T1) in the circuit is switched to on via resistor R1 and related parts. As as result, the EM relay at the output of T1 is activated and the electric sprinkler gets its supply through the relay (RLY1) contacts. This contacts (or spare contacts) can also be used to activate a high-power warning alarm.

Please note that, here T1 is wired as a mini electronic timer. Even after the PIR relay switched off, output relay (RLY1) remains in on state for a short duration decided by the value of timing capacitor C2.

Motion Sensor Switch Circuit Schematic

motion sensor switch circuit schematic
The Electric Sprinkler
electric sprinkler


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