Introduction :

Sensors allow you to sense motion, almost always used to detect whether a human has moved in or out of thesensors range.

They are small, inexpensive, low-power, easy to use and don't wear out.

For that reason they arecommonly found in appliances and gadgets used in homes or businesses.

They are often referred to as PIR, "PassiveInfrared", "Pyroelectric", or "IR motion" sensors.

Everything emits some low level radiation, and the hotter something is, the more radiation is emitted

. The sensor in a motion detector is actually split in two halves. The reason for that is that we are looking to detect motion (change) not average IR levels. The two halves are wired up so that they cancel each other out. If one half sees more or less IR radiation than the other, the output will swing high or low.

The PIR sensor itself has two slots in it, each slot is made of a special material that is sensitive to IR. The lens used here is not really doing much and so we see that the two slots can 'see' out past some distance (basically the sensitivity of the sensor).

When the sensor is idle, both slots detect the same amount of IR, the ambient amount radiated from the room or walls or outdoors.

When a warm body like a human or animal passes by, it first intercepts one half of the PIR sensor, which causes a positive differential change between the two halves. When the warm body leaves the sensing area, the reverse happens, whereby the sensor generates a negative differential change. These change pulses are what is detected.

Features :

• Voltage: 5V – 20V
• Power Consumption: 65mA
• TTL output: 3.3V, 0V
• Delay time: Adjustable
• Lock time: 0.2 sec
• Trigger methods: L – disable repeat trigger, H enable repeat trigger
• Sensing range: less than 120 degree, within 7 meters
• Temperature: – 15 ~ +70
• Dimension: 32*24 mm, distance between screw 28mm, M2, Lens dimension in diameter: 23mm