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. 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. 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.
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.
The following rough Gif simulation shows how a PIR sensor responds to a moving human and develops a couple of short sharp pulses across its output leads for the required processing or triggering an appropriately configured relay stage. The following figure shows the internal layout or the configuration inside a standard PIR sensor. 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 following image shows a standard PIR sensor test set up. 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.
Ir sensor specification pdf printer
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. The sensing elements are tested and appropriately configured by evaluating the respective single signal output voltage SSOV through the following formula:.
The main technical specifications and dimension parameters of a PIR sensor can be learned from the following details:. 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.
When the module detects a motion of infrared the output goes HIGH at 3. This is time period can be adjusted from 5 seconds to 5 minute. 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.
PIR Sensor Datasheet, Pinout Specifications, Working
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. 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. The block time is the time interval where the sensor is disabled or will not detect motion.
The block time for HC-. 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. 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. For enthusiasts who intend to build the complete PIR module along with the sensor and a full fledged amplifier, the following standard schematic can be employed and used for any relevant PIR sensor based application triggering.
Have further doubts or questions? Please feel free to put them forth through the below given comment box.
If you have any circuit related query, you may interact through comments, I'll be most happy to help! Your email:. All attempts with two separate sensors have been unreliable. Any ideas? Glad you liked it. It looks feasible.
My aim is to keep track of how many people are in a room, so if the last person leaves the room light will go off. I measured the output 2 of the chip. I get the high low signal now direction of travel the other. Need to do a bit more playing to see if it is reliable. Hi Thanks for helping. The circuit is really simple and easy to make. But a 6v lead acid battery is big and bulky for the cabinet. Will the circuit and 5v buzzer will work. You can experiment with the uF capacitor to modify the delay interval.
Hii i mean to say when pir detect any intruder, as soon as the output goes high it will trigger the delay on circuit which in turn triggers the alarm after sec.
This delay interval is necessary because when the owner comes back it gives him sufficient time to turn off the circuit.
And for alarm interval. The pir delay knob is adjusted anywhere between min Do you like the idea. Hii Once again thank, you have discussed the functionality of pir sensor in a very simple manner and its very easy to understand.
Bro i just come through an idea make an very cost effective pir sensor alarm and this time without using an arduino so it will be very cheap. Could you please help me by providing a complete diagram for this security ststem. Thanks Avi, I can surely help you with the design, but I could not understand the role of the second timer?
Infra Red Obstacle Detector
Hey swagatam. I have a pir sensor that is giving output without any detection and it is repeating after a period of time without any detection.
May it be collected? If possible how? I am looking for info regarding those add on functions especially about the thermistor. I tried to put one 10k NTC thermistor into mine because here in our country, the temperature always hovers on high 30 to 35 degree celsius and my module seems to have difficulty detecting movements.
However I dont see any difference.
Maybe because I dont know what type or value of thermistor that must be used or technical know how on the thermal compensation function of this module. I hope you could investigate it in the future. Great site by the way, more power! Pls give me some details about bjddt-p photo sensor.
Like working principle and adjustment. Thanks in advance.
Hi Naresh, It will be difficult for me to explain the setting up procedure without practically checking it, I think you should contact the manufacturer or the dealer to learn the exact details…. Rest assured, comments once submitted will reach the Admin without fail.
Your email address will not be published. Notify me via e-mail if anyone answers my comment. Contents hide. Comments This is brilliant thank you. Have taken the lens of , but more experimenting is needed. Thanks for all this usefull info , it helped me work out where to start. Hi sir, Pls give me some details about bjddt-p photo sensor.