Fire is like a double-edged sword. Discovery of fire stands as a milestone in the history of mankind. Fire fighters try their best to fight and extinguish fires when in need. But at the household level, it is observed that if the fire can be extinguished at an early stage, many major accidents can be averted. The aim here is to build a robot that can detect and extinguish fire.
Circuit and working
This fire extinguishing robot is a prototype (Fig. 1) of the actual one. Sensors used here are simple infrared (IR) photodiodes that detect IR rays coming out of the fire. The sensor board mounted on top of the robot’s chassis is circular in shape so that it gives the robot all-round detection view of 360°. Sensors are equally spaced at 45° each. These act as the eyes of the robot.
In the actual robot, use of fire sensors or IR cameras is recommended. But these are too expensive and hence IR photodiodes have been used as a substitute in the prototype.
The pump used here symbolises the fire extinguishing mechanism, and is used as a substitute in the prototype. Also, the body used is not fire-proof. The actual robot must use fire-proof material for proper and better functioning for efficient results.
IR waves. Wavelengths longer than visible and up to 1mm are termed as IR waves. IR radiation can be felt as radiant heat, for example, when you stand in front of a fire.
The light emitted by a burning source comprises IR waves, so by using IR photodiodes as sensors we can detect a fire. This principle has been used in the designing of the sensor board.
DC water pump. A DC water pump is used for the purpose of extinguishing fire. It pumps out water stored in a bottle. The DC water pump is shown in Fig. 2. Any other suitable water pump can also be used.
RF module. A pair of 433MHz RF transmitter-receiver module is used. It allows transmission and reception of serial data without physical connection. The frequency of an RF signal is inversely proportional to the wavelength of the field.
The robot can be made to work in manual as well as in autonomous mode. (Manual mode was tested at EFY Lab.) Different modes of operation are given in Table I. The fire extinguishing robot works in three stages.
Stage 1: Fire detection (autonomous mode). IR photodiodes are connected in reverse bias as shown in the circuit diagram of the sensor module (Fig. 3). Anodes are commonly connected to the ground and cathodes are connected to the 5V via resistors of 1MΩ each.
Voltage across the photodiode is given as input to ADC pins (PA0 through PA7) of ATmega16. When IR waves fall on the IR photodiode, its resistance decreases from 650kΩ to 150kΩ, reducing the voltage across the photodiode, thus changing the input voltage at the ADC pin. By proper quantisation, the presence and absence of the flame can be distinguished.
Similarly, eight IR photodiodes mounted in a circular fashion on the sensor board help detect the fire; the corresponding LED glows if fire is detected. The cone of detection of the IR photodiode is large, thus decreasing the resolution of the system. This problem can be solved by properly shielding IR photodiodes.
Code to detect the presence of fire using the ADC is as follows:
unsigned char v;
if(v>=0 && v <=128) //Stores the digital value of the analog voltage at ADC 0 fire_detected ( ); if(v>128 && v<=255)