In this tutorial, we are making a project of a simple motion sensor alarm & light circuit. This circuit is using a PIR or passive infrared sensor module. It will detect any movement of a human, object, or animal at a distance of 5 to 10 meters depending on the sensitivity of the PIR sensor module. After the detection, it will activate an LED and a buzzer for a specific time. Buzzer and the LED activation period are adjusted in the PIR sensor module. This sensor module is readily available and can be purchased from electronic stores or online.
A PIR sensor has a built-in module, it detects the infrared radiation from any object, animal, or human that is in its range. This sensor then converts this detected signal into electrical signals which are later amplified by a FET that is built into the sensor and then sends it to the output pin of the sensor that is further enhanced by the circuit of the PIR sensor module. Now this enhanced signal can be used to activate any appliance such as an alarm or lights/lamp etc for indications.
Hardware Components
The following components are required to make the Motion Sensor Alarm Circuit
| S.no | Component | Value | Qty |
|---|---|---|---|
| 1. | Input Supply DC | 9-12V | 1 |
| 2. | PIR sensor module | – | 1 |
| 3. | Transistor | 2N3904 | 1 |
| 4. | Piezo buzzer | – | 1 |
| 5. | LED | – | 1 |
| 6. | Resistor | 470Ω | 2 |
2N3904 Pinout
For a detailed description of pinout, dimension features, and specifications download the datasheet of 2N3904
Motion Sensor Alarm Circuit
Working Explanation
The operating voltage of this circuit is 9 to 12 volts DC. Check the operating voltage of the PIR sensor module and then operate the circuit with the given voltage. The circuit is simple and has one transistor circuit to activate the buzzer and LED at its output. When the PIR sensor module detects any infrared signal it will send a signal to the circuit and switch on the transistor. This will activate the buzzer and a LED for a preset period. The activation time period depends on the PIR sensor module. A relay can also be used in the place of the LED, its current limiting resistor, and the buzzer. You can connect any AC/DC appliance of your choice and change it to operate them with this circuit.
