Friday 10 July 2015

PIR Relay Motion Alarm Circuit

The article describes a basic motion activated PIR relay circuit that are available for activating lights only in the existence of a human, hence preserving valuable electric power.

The following is an easy circuit that activates a relay when a living being (a human) is detected by the PIR sensor. Here PIR represents Passive Infrared sensor. It doesn’t generate any infrared radiations to identify the existence of a living being but conversely it detects the infrared radiations released by them.


This circuit employs a HC - SR501 PIR motion sensor that could be the heart of the circuit. In the beginning when the motion is detected by the sensor, it generates a small signal voltage(usually 3.3 volts) that could be given to the base of the transistor BC547 via a current control resistor and therefore, its output goes high and it switches the relay on. This relay could very well be set up to serve with a electrical bulb or a tubelight, night lamp or anything else that actually works on 220VAC.
This circuit is mainly utilized in gardens, so that at night, when we take a stroll in the garden, the circuit switches on a light automatically and it stays lit until we are in the sensor’s vicinity and it gets turned off when we get away from that place and therefore lowering the electricity costs. Here’s a back view of the sensor HC-SR501…


The sensor contains two preset resistors that are available to manage the delay time and sensing range. The delay potentiometer may be modified to choose the time for which light stays on. The sensor when acquired, it features the default mode ‘H’ which implies the circuit switches on the light when motion is detected and it continues to be on for preset time and after the preset time lapses, if the sensor could still identify motion, it may not switch the light off and if it may not detect the motion, it switches off the light. Listed here are the technical information 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)
Certainly one of the drawbacks to PIR motion sensors is that its output goes high even though 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 raises. As a result of low temperature, infrared radiations released by humans travel more distances and therefore leading to unneeded switching of lights. If set up in backyards, you will discover probabilities of activating of light when a car passes by because the radiations provided by hot engine of car fools the sensor.
PARTS LIST:
D1, D2 - 1N4007,
C1- 1000uf, 25V,
Q1 - BC547,
R1 - 10K,
R2 - 1K,
L1 - LED(green)
RY1 - Relay 12V
T1 – Transformer 0-12V.

PIR Motion sensor built unit
PIR Motion sensor built unit
After finishing the development of the circuit, enclose it in an appropriate casing and use a separate casing for the sensor and hook up the sensor to circuit choosing long wires to be able to place sensor at the place you would like such as in a garden and circuit will probably be inside to ensure that the circuit is safeguarded from weather.
And make sure you exercise a separate PCB for relay.
Also, don’t stop thinking about to utilize an appropriate relay with correct current and voltage rating. You can utilize a terminal block which attaches to the relay’s switching contacts, and organize it as demonstrated in image to enable you to modify the electrical device linked to relay contacts
conveniently.


Utilization of this sensors save electricity to great extents. It could actually lessen your electricity bills too!
“PLEASE SAVE THE POWER FOR THE NEXT HOUR!”
If the above design is meant to be utilized with an alarm and a lamp such that both the loads run throughout night but the alarm only throughout day, then the diagram might be altered in the following technique.

PIR alarm with light circuit with day night automatic switching action


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