The post discuses the pinout details of the standard passive infrared (PIR) sensor RE200B and also explains how to make a a PIR motion detector circuit using a single transistor and relay, which can detect the IR radiation from human body and activate the attached relay.
What is a PIR
PIR is the acronym for Passive Infra Red. The term "passive indicates that the sensor does not actively take part in the process, meaning it does not itself emit the referred infra red signals, rather passively detects infrared radiations emanating from warm blooded animal in the vicinity.
The detected radiations are converted into an electrical charge proportional to the detected level of the radiation. This charge is then further enhanced by the built-in FET and fed to the output pin of the device which becomes applicable to an external circuit for further amplification and for triggering the alarm stages.
The image shows a typical PIR sensor pin out diagram. It's quite simple to understand the pinouts and one may easily configure them into a working circuit with the help of the following points:
As indicated in the following diagram, PIN#3 of the sensor should be connected to the ground or the negative rail of the supply.
Pin#1 which corresponds to the "drain" terminal of the dvice should be connected to the positive supply, which must be ideally a 5V DC.
And pin#2 which corresponds to the "source" lead of the sensor must be connected to ground via a 47K or 100K resistor. This pin also becomes the output pin out of the device and the detected infrared signal is carried forward to an amplifier from pin#2 of the sensor.
Making a Practical PIR Sensor Based Motion Detector Circuit
In the above section we learned the datasheet and the pinouts of a standard PIR sensor now lets' move on and study a simple application for the same:
The circuit diagram of a PIR motion detector unit is shown above. A practical implementation of the explained pin-out details can be witnessed here.
In the presence of a human IR radiation, the sensor detects the radiations and instantly converts it into minute electrical pulses, enough to trigger the transistor into conduction, making its colector go low.
The IC 741 has been set up as a comparator where its pin#3 is assigned as the reference input while pin#2 as the sensing input.
The moment the collector of the transistor goes low, the potential at pin#2 of the 741 IC becomes lower than the potential at pin#3. This instantly makes the output of the IC high, triggering the relay driver stage consisting of the another BC547 transistor and a relay.
The relay activates and switches ON the connected alarm device.
The capacitor 100uF/25V makes sure that the relay remains ON even after the PIR is deactivated possibly due the exit of the radiation source.
The PIR device should be suitably enclosed inside a frensel lens cover so that its efficiency is adequately enhanced.
PIR Circuit using a Single Transistor
The following post explains a simple PIR motion detector relay circuit which can be used for activating lights only in the presence of a human, thus saving precious electric power.
Written and Tested By: SSkopparthy
How the Circuit Works
Here is a simple circuit that activates a relay when a living being (a human) is detected by the PIR sensor. Here PIR stands for Passive Infrared sensor. It doesn’t produce any infrared radiations to detect the presence of a living being but on the other hand it detects the infrared radiations released by them.
This circuit uses a HC - SR501 PIR motion sensor which is the heart of the circuit. Initially when the motion is detected by the sensor, it produces a small signal voltage(usually 3.3 volts) which is fed to the base of the transistor BC547 through a current control resistor and hence, its output goes high and it switches the relay on.
This relay can be configured to be used with a electrical bulb or a tubelight, night lamp or anything else that works on 220VAC.
This circuit is mostly used in gardens, so that at night, when we go for a walk in the garden, the circuit switches on a light automatically and it remains lit until we are in the sensor’s vicinity and it gets turned off when we move away from that place and hence reducing the electricity costs.
Here’s a back view of the sensor HC-SR501…
PIR Sensor Front View:
The sensor consists of two preset resistors which can be used to control the delay time and sensing range.
The delay potentiometer can be adjusted to decide the time for which light remains on.
The sensor when purchased, it comes with the default mode ‘H’ which means that the circuit switches on the light when motion is detected and it remains on for preset time and after the preset time lapses, if the sensor could still detect motion, it does not switch the light off and if it could not detect the motion, it switches off the light.
Here are the technical details of the sensor HC-SR501
- Working voltage range: 4.5VDC to 12VDC.
- Current Drain: <60uA
- Voltage output: 3.3V TTL
- Detection distance: 3 to 7 metres(can be adjusted)
- Delay time: 5 to 200 seconds(can be adjusted)
One of the disadvantages of PIR motion sensors is that its output goes high even when a rat or a dog or some other animal moves in front of it and it switches on light unnecessarily.
In cold countries, the sensor’s sensing range increases. Due to low temperature, infrared radiations released by humans travel more distances and hence causing unnecessary switching of lights.
If installed in backyards, there are chances of activating of light when a car passes by because the radiations emitted by hot engine of car fools the sensor.
D1, D2 - 1N4007,
C1- 1000uf, 25V,
Q1 - BC547,
R1 - 10K,
R2 - 1K,
L1 - LED(green)
RY1 - Relay 12V
T1 – Transformer 0-12V.
After completing the construction of the circuit, enclose it in a suitable casing and use a separate casing for the sensor and connect the sensor to circuit using long wires so that you can place sensor at the place you wish like in a garden and circuit will be inside so that the circuit is protected from weather.
And remember to use a separate PCB for relay.
Also, don’t forget to use a suitable relay with correct current and voltage rating. You can use a terminal block which connects to the relay’s switching contacts, and arrange it as shown in image so that you can change the electrical device connected to relay contacts easily.
Usage of this sensors save electricity to great extents. It could reduce your electricity bills too!
“PLEASE SAVE THE POWER FOR THE NEXT HOUR!”
If the above PIR motion detector design is intended to be used with an alarm and a lamp such that both the loads operate during night but the alarm only during day, then the diagram may be modified in the following manner. The idea was suggested by Mr. Manjunath