Introduction: ROBOCOP

An Arduino is an open-source microcontroller development board. In plain English, you can use the Arduino to read sensors and control things like motors and lights. This allows you to upload programs to this board which can then interact with things in the real world. With this, you can make devices which respond and react to the world at large.

ROBOCOP is one such project made using Arduino. It can protect one's house from thieves, fire and LPG leak.

It is controlled using HC-05 Bluetooth Module and the most common Smartphone.

Step 1: Parts Required

  • Arduino UNO
  • Bluetooth Module HC-05
  • Jump Wires ( For Connections )
  • PIR Motion Sensor
  • NTC Thermistor
  • MQ-2 Gas Sensor
  • Servo Motor
  • Arduino IDE ( Software to upload the code )

I have used 3 arduino for more clarity and perfect timings of arduino. This can also be done using a single arduino.

Step 2: Connection Part 1

1. Connections on first arduino

    • To this arduino the thermistor is connected, which is used to get the temperature of the surroundings.
    • I have used a NTC Thermistor. For a NTC Thermistor, as the temperature increases, the resistance offered decrease.

    • For this I use AREF pin as my analog reference for more accuracy in readings.

    • Connect A0 to one leg of a 10kΩ(mentioned as 22K in picture it is wrong, Sorry) resistor and one leg of Thermistor.

    • Other leg of the resistor to the 3.3V of Arduino.

    • Also connect 3.3V of arduino to AREF of arduino

    • Connect the other leg of Thermistor to the Negative OR GND of Arduino.

    • Instead you can also refer the picture .

Step 3: Connection Part 2

2. Connection on Second Arduino

  • To this Arduino the PIR Motion Sensor is connected
  • Connect the OUTPUT pin of PIR to the 9 pin of Arduino.
  • Connect VCC of PIR to +5V of arduino
  • Connect GND of PIR to GND of arduino
  • Instead you can refer the picture

Step 4: Connection Part 3

3. Connection on Third Arduino

  • To this arduino the Servo Motor is connected
  • Connect the OUTPUT pin of Servo to 6 pin of Arduino
  • Connect VCC of Servo to the +5V pin of Arduino
  • Connect GND of Servo to the GND of Arduino
  • Also to this same arduino the Gas Sensor is connected.
  • Connect the three pins on one side of MQ-02 to +5V of Arduino
  • Connect the middle leg on other side of MQ-02 to GND of Arduino.
  • Connect the other two legs to GND through a 22KΩ and also to A0 pin of Arduino
  • Instead you can refer the picture

Step 5: Connection Part 4

Take a breadboard.

Connect RX and TX of bluetooth module to two rows of breadboard.

Connect RX of Bluetooth to TX of each Arduino.

Connect TX of Bluetooth to RX of each Arduino.

Connect VCC of HC-05 to +5V of any arduino

Connect GND of HC-05 to GND of any arduino.

Instead you can refer the picture

At last verify the connections once again and wire the LEDs as indicators according to pin declared in the program.

Step 6: About the Sensors


The PIR sensor itself has two slots in it, each slot is made of a special material that is sensitive to IR. The lens used here is not really doing much and so we see that the two slots can 'see' out past some distance (basically the sensitivity of the sensor). When the sensor is idle, both slots detect the same amount of IR, the ambient amount radiated from the room or walls or outdoors. When a warm body like a human or animal passes by, it first intercepts one half of the PIR sensor, which causes a positive differential change between the two halves. When the warm body leaves the sensing area, the reverse happens, whereby the sensor generates a negative differential change. These change pulses are what is detected. ( See picture for reference )


A thermistor is a type of resistor whose resistance is dependent on temperature, more so than in standard resistors. The word is a portmanteau of thermal and resistor. Thermistors are widely used as inrush current limiter, temperature sensors (Negative Temperature Coefficient or NTC type typically), self-resetting overcurrent protectors, and self-regulating heating elements (Positive Temperature Coefficient or PTC type typically).
Thermistors are of two opposite fundamental types: With NTC thermistors, resistance decreases as temperature rises. An NTC is commonly used as a temperature sensor, or in series with a circuit as an inrush current limiter.With PTC thermistors, resistance increases as temperature rises. PTC thermistors are commonly installed in series with a circuit, and used to protect against overcurrent conditions, as resettable fuses.

Temperature can be estimated by using the formula, T=B/ln(R/r∞)


From home appliances such as air conditioners to electric chimneys and safety systems at industries monitoring of gases is very crucial. Gas sensors are very important part of such systems. Small like a nose, gas sensors spontaneously react to the gas present, thus keeping the system updated about any alterations that occur in the concentration of molecules at gaseous state. Gas sensors are available in wide specifications depending on the sensitivity levels, type of gas to be sensed, physical dimensions and numerous other factors. This Insight covers a methane gas sensor that can sense gases such as ammonia which might get produced from methane. When a gas interacts with this sensor, it is first ionized into its constituents and is then adsorbed by the sensing element. This adsorption creates a potential difference on the element which is conveyed to the processor unit through output pins in form of current.

Step 7: App Creation

This app can easily be created using MIT App Inventor 2.

Follow the pics to do the app by yourself or download it from the given link.

Step 8: Program for Arduino 1

Download the code and Upload it.

Step 9: Program for Arduino 2

Download the code and Upload it.


Step 10: Program for Arduino 3

Download the code and Upload it.

Step 11: The Final Touch and Working Proof

We have installed the protector in a small model house for testing. We have also tested and ROBOCOP is working superb.

Pls...... Vote If you like this and sorry for grammatical errors (if any)

And if you find anything fault with this, Pls..........Pls...........Do comment or mail me.

Thanks for reading my project.

Note:- Here, I have used 3 arduino for accuracy and perfectness in time. If I try coding them in a single one the time of execution and time of producing results are delayed. If you wish you can use a single arduino and produce the same output. If you are doing so try and cut-short the programs so that you can minimize the time of execution.

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