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Most vending machine sensors use passive infrared (PIR) sensors, which unlike optical sensors that use an LED transmitted and infrared receiver, emits nothing. Rather than radiating, the PIR responds to infrared energy emitted by any nearby objects. Any object with a temperature above zero degrees Celsius emits infrared energy, through black-body radiation. Invisible to the human eye, the magnitude of this radiation varies with temperature, which is exactly what makes the PIR function the way it does. <br />
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Most vending machine sensors use passive infrared (PIR) sensors, which unlike optical sensors that use an LED transmitter and infrared receiver, emit nothing. Rather than radiating, the PIR responds to infrared energy emitted by any nearby objects. Any object with a temperature above zero degrees Celsius emits infrared energy, through black-body radiation. Invisible to the human eye, the magnitude of this radiation varies with temperature, which is exactly what makes the PIR function the way it does. <br />
     
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