This code can also be used to control simple relays to turn a bigger light on or off. You can upload the example code with the Arduino IDE. Also adjust the time-delay potentiometer to the lowest value. Turn it counterclockwise as far as it will go.
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We will understand for what purpose PIR sensor is used? Its basic trigger operations, pin connection details, technical specifications and finally we will be looking at some real life applications.
We will begin by understanding the actual PIR sensor unit which are installed inside standard PIR modules and learn its internal characteristics, pinout details and internal working details.
What is a PIR Sensor? PIR is an electronic sensor which detects the changes in the infrared light across certain distance and gives out an electrical signal at its output in response to a detected IR signal. It can detect any infrared emitting object such as human beings or animals if it is the range of the sensor, or moves away from the range, or moves within the range of the sensor. The PIR sensor module can be divided in to two parts an infrared sensitive crystal and the processing circuit.
Illustration of PIR sensitive crystal: The dark portion of the metal where the IR sensitive crystal is housed, the sensitive crystal can detect the level of infrared in the surroundings. It actually houses two pyroelectic sensors for detecting moving objects.
If one of the sensitive crystals detects change in infrared increment or decrement than the other sensitive crystal, the output gets triggered. A dome shaped plastic structure is normally placed over this sensitive crystal which acts as lens to focus the infrared light on the sensors. How PIR Works The sensing operation of a pyroelectric infrared sensor is based on the property or characteristic which becomes responsible for altering the polarization of its material in response to temperature changes.
These sensors employ a dual or a pair of sensing elements for sensing the IR signals in two steps, which ensures a foolproof detection by cancelling the unwanted temperature variations within the existing EMI stage.
This two-step sensing process improves the overall stability of the sensor and helps to detect IR signals only from human presence. On the left we can see a pair of IR sensing elements connected in series. The upper end of this series is connected with the gate of an in-built FET which acts as a small IR signal amplifier. When a moving IR signal is detected by the pair of sensing elements, it generates a corresponding pair of hi and low logic signals as discussed above: These pulses are appropriately amplified by the FET and replicated at its output pin for further processing by an attached circuitry.
The associated EMI stages along with the capacitor provide extra filtration to the process, in order to produce a clean set of pulses at the indicated output pin of the PIR.
The output and Vss pins negative pin of the PIR is connected with an external pull down resistor, the Vdd pin is supplied with a 5V supply. A stationery black body generates the required equivalent infrared radiation for the PIR sensor through a chopper mechanism. The chopper plate alternately cuts the IR signals imitating a moving IR target.
This chopped IR signal hits the PIR sensor generating the specified pulses across its output pin, which is suitably amplified through an opamp for analysis on a scope.
The Ideal Test Conditions for the above set up can be seen below: Balancing the Sensing Element output Since a dual sensing mechanism is employed in PIRs, it becomes necessary to ensure that the processing through the pair of lenses is correctly balanced.
This enhances the performance of the PIR many folds and allows the end user to get well defined optimized, amplified output from the module. The circuit inside standard modules consist of IC BISS which is specifically designed for motion detection applications.
Two knobs are provided, one for adjusting the sensitivity of the module and another knob is for adjusting the time length for how long the output should stay HIGH after the module is triggered. This is time period can be adjusted from 5 seconds to 5 minute. Sensitivity Range: The angle of the detection area is around degree cone. A knob is given to adjust the sensitivity; we can vary from 3 meter to 7 meters perpendicular to senor.
The sensitivity reduces as we move either sides of the sensor. Quiescent current: The Quiescent current is the current consumed from the supply, when the sensor is not detecting any motion or when it is in idle. It consumes less than 50 uA, which makes the sensor battery friendly. These two modes can be access by changing the jumper position given in the module. Repeat Trigger Mode: When the PIR sensor is set in repeat trigger mode, when a human is detected the output turns HIGH the timer counts for 5 seconds, but when another human is detected with in those 5 seconds the timer reset to zero and counts another 5 seconds after 2nd human is detected.
Block Time: The block time is the time interval where the sensor is disabled or will not detect motion. The block time for HC- SR is 3 seconds by default. This occurs after the delay time which was set by timer knob the output goes LOW for 3 seconds; during this interval no motion will be detected. After the 3 seconds LOW the sensor will be ready to detect motion again. It measures 32 mm x 24 mm.
Lens Size: The white dome structure which encloses the pyroelectric sensor is called Fresnel lenses, which increase the detection range and it looks opaque. It measures 23 mm in diameter.
PIR Sensor Datasheet, Pinout Specifications, Working
Editing a Biss0001 PIR circuit + connection to 18m2
Voltage Regulator 3V DC voltage regulator 7. Protection Diode To protect the module from high current. Fresnel lense :The lens is just a piece of plastic. It has three sections A, B and C. The Fresnel lens condenses light, providing a larger range of IR to the sensor. The lens costs only a few cents and can change the breadth, range, sensing pattern, very easily.