Introduction
You might think about purchasing an HC-SR501 Passive Infrared (PIR) sensor if you want to create a trail camera, a house burglar alarm, or perhaps you want to activate animated Halloween decorations when trick-or-treaters knock on your door.
You may use the PIR sensor to determine when an animal or human enters or exits the sensor's field of view. The majority of contemporary security systems, automated light switches, garage door openers, and similar devices that need to respond to motion use this sensor.
Let's first examine the PIR sensor's operation before delving into the details.
How does that PIR Sensor work?
At temperatures higher than absolute zero (0 Kelvin / -273.15 °C), everything, including the human body, emits heat energy in the form of infrared radiation. A thing emits more radiation the hotter it is. Since this radiation emits at infrared wavelengths, it cannot be seen by the human eye. The PIR sensor is made particularly to pick up on infrared radiation at certain intensities.
There are two major components of a PIR sensor:
- The image above shows a pyroelectric sensor, which is a circular piece of metal with a rectangular crystal in the middle.
- Fresnel lenses are specialized lenses that focus infrared signals on pyroelectric sensors.
pyroelectric Sensor
A pyroelectric sensor is a window with two rectangular slots constructed of a substance that enables infrared radiation to flow through (usually coated silicon). Two independent infrared sensor electrodes, one providing the positive output and the other the negative output, are located behind the window.
The wiring of the two electrodes makes them cancel each other out. This is so that we can detect changes in IR levels rather than just ambient IR levels. Because of this, we obtain the output when one side detects more or less IR radiation than the other.
Fresnel Lens
You could think that the Fresnel lens being employed here is ineffective. In actuality, this is what broadens the PIR sensor's viewing area and range. It is incredibly helpful for creating PIRs that are compact but powerful because of its lightweight, narrow design.
A Fresnel lens is made of plastic that has had a number of concentric grooves etched into it. Individual refracting surfaces, these curves focus parallel light rays at a focal point. Because of this, a Fresnel lens, despite being smaller in size, may concentrate light similarly to an optical lens.
The lens is really divided into numerous facet sections, each of which is a distinct Fresnel lens, to extend the PIR sensor's range and field of vision.
A variety of detection areas/zones are created by the various faceting and sub-lenses and are interspersed with one another. Because each lens center in the image above is pointing to a different side of the PIR sensing element, the centers of the lenses appear to be "inconsistent" in the image above.
Parts in the PIR sensor
The HC-SR501 PIR sensor is a fantastic option for the majority of our Arduino projects that call for determining whether someone has entered or left the area. It is inexpensive, low power, simple to interface with, and very well-liked by enthusiasts.
The PIR sensor itself is quite simple and functional right out of the box. Simply apply ground and 5V to 12V of power. When motion is detected, the sensor output is HIGH; when it is not, it is LOW (no motion detected).
You can use this output to program the microcontroller to respond to the motion by turning on/off lights, turning on a fan, turning on a Halloween prop, or even capturing a photo of an intruder.
BISS0001 IC
The passive infrared (PIR) controller IC, designated BISS0001, is the brain of the module. The BISS0001 is one of the most reliable PIR controllers on the market because of the noise immunity it offers.
This chip emits a digital output pulse after performing some minor processing on the Pyroelectric sensor's output.
power
The module has a built-in 3.3V precision voltage regulator, allowing it to run on any DC voltage between 4.5 and 12 volts, however, 5 volts is the most popular.
A protection diode, sometimes referred to as a safety diode, is included inside the module to guard it against reverse voltage and current. As a result, your module won't be harmed even if you unintentionally connect the power with the wrong polarity.
Sensitivity adjustment
On the back of the PIR sensor is a potentiometer for sensitivity adjustment.
The maximum detection range is set by this potentiometer. Sensitivity can be changed between a range of roughly 3 and 7 meters (9 to 21 feet). The topology of your room, however, may have an impact on the actual range you receive. The sensitivity and hence the range are increased by turning the pot counterclockwise, and vice versa.
Time-delay adjustment
On the PIR sensor's rear, there is an additional potentiometer for adjusting the Time-Delay.
How long the output will remain HIGH following motion detection is controlled by this potentiometer. It can be altered between 1 second and around 3 minutes. The delay is adjusted by rotating the potentiometer; clockwise rotation lengthens the delay and counterclockwise rotation shortens it.
A jumper is the trigger choice
The sensor's response to motion detection can be controlled by one of two trigger modes.
Single Trigger Mode: The sensor's response to motion detection can be controlled by one of two trigger modes.
Multiple Trigger Mode: Numerous triggers will be set off by the continual movements.
You can select between two modes using the board's berg jumper (some modules have a solder bridge jumper):
L-The single trigger mode will be configured if you choose L. When motion is detected, the output in this mode turns HIGH and stays HIGH for the duration of the Time-Delay potentiometer. Until the output changes back to LOW at the conclusion of the time delay, further detection is halted. The output will become HIGH once again if there is still motion. The following image shows how thoroughly Motion #3 is disregarded.
H-The multiple trigger mode will be set by selecting H. When motion is detected, the output in this mode turns HIGH and stays HIGH for the duration of the Time-Delay potentiometer. Every time motion is detected, the time delay is reset since, unlike single trigger mode, additional detection is not prohibited. After the motion has stopped, the output doesn't go back to LOW right away. Thus, the multiple trigger mode is thus named.
Optional Components
Two extra components can be soldered onto the HC-SR501 module's solder pads. These are typically designated as "RT" and "RL." Be aware that on some boards, the label may be hidden by a Fresnel lens on the component's opposite side.
Thermistor, also known as a temperature-sensitive resistor, connection. By including this, the HC-SR501 can operate in very cold conditions. Additionally, this somewhat improves the detector's accuracy.
This connector is for a photoresistor or light-dependent resistor (LDR). This addition enables the HC-SR501 to function in the dark. Building motion-sensitive lighting systems can benefit from this.
These extra parts can be connected to the module directly using solder or extended to far-off locations using cables and connectors.
PIR Sensor Pinouts
There is a 3-pin connector on the HC-SR501. The pinout can be found in the following image since the Fresnel lens obscures the marks.
VCC - The sensor's power source is VCC. Although 5V is frequently used, you can connect an input voltage of any value between 5 and 12V to this pin.
OUT - The 3.3V TTL logic output is on the pin. When motion is detected, it goes HIGH, and when it is not, it goes LOW (no motion detected).
GND - is the ground pin
Specifications of PIR Sensor
- Voltage 4.8 V – 20 V
- Current (idle) <50 µA
- Logic output 3.3 V / 0 V
- Delay time 0.3 s – 200 s, custom up to 10 min
- Lock time 2.5 s (default)
- Trigger repeat : L = disable, H = enable
- Sensing range <120 °, within 7 m
- Temperature – 15 ~ +70 °C
- Dimension 32 x 24 mm
- screw-screw 28 mm, M2
- Lens diameter: 23 mm
PIR Sensor Layout
Application of PIR sensor
- Intruder alarms.
- Automatic ticket gates.
- Entryway lighting.
- Security lighting.
- Automated sink/toilet flusher.
- Hand dryers.
- Automatic doors.
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