PIR Sensor without Microcontroller | Burglar Alarm

Great to see you all after a long time. Just came up with a simple tutorial on how to use the PIR Sensor without any microcontroller. It will also help you understand the importance of a transistors specifically. We are in the place we hold billions of transistors in our hand (saying about a Smartphone), but it all comes from the single transistor that was demonstrated in 1947. So lets look into it.

In the past, we already learnt about how to use a PIR Sensor with an Arduino. So now we will see how to use a PIR Sensor without any microcontrollers.

Components Required:

• PIR Sensor
• Breadboard
• 9V Battery/Adapter
• 9V Battery Snap Connector
• 7805 Voltage Regulator
• BC547 NPN Transistor
• 1K Ohm Resistor
• 5V Buzzer
• Jumper Wires

What is a transistor?

A transistor is a semiconductor device used to control flow of large current between Emitter and Collector by a small base current. A transistor can used as an amplifier, oscillator or a switch. In our case we will be using it as switch. There are two types of transistors available NPN and PNP Transistors. Depending upon applications, we can use the type of transistor.

An NPN transistor gets triggered by Positive current on base and PNP Transistor gets triggered by a Negative Current in the Base. So if your sensor output is HIGH when there is detection, we will use NPN Transistor.

Some basic digital sensors, output is HIGH in normal condition. But when something detected, the output will be LOW. In this case an PNP Transistor will work. If you note, the name PNP – the middle denotes the Base that is negative, so when you use negative (LOW) applied to base, the transistor passes current between Emitter and Collector.

The Pin details for NPN and PNP Transistor are given below

NPN Transistor

PNP Transistor

As we mentioned, we will be using an NPN Transistor, as the PIR Output a HIGH Signal when motion is detected. So when motion detection, the base of the transistor gets a positive signal, hence the current starts flow from Collector to Emitter. We used a resistor to limit the current flow through the resistor.

Circuit Diagram:

Schematic Diagram:

After making the circuit diagram, In the PIR Sensor there will be two potentiometers available.

Sensitivity Pin – The first one is Sensitivity. How sensitive the Sensor needs to be detected.

Hold the potentiometer facing towards you. The first pin is Sensitivity and Second is Delay Adjustment.

Delay Pin – The Second one is Time Delay. How long the PIR Needs to be turned ON (the Detected State). Make this towards zero position as its minimum time delay will be 3seconds to max 5 minutes. This is very important or else you can’t get the sensor triggered in the middle of the delay. After the delay ends, the sensor backs to its normal position.

PIR Sensor takes some time to warm up. So you may get some issues at starting. Once the time delay and sensitivity is calibrated, it will work normal.