falohun-2016-ijca-908473.pdf — page 3

International Journal of Computer Applications (0975 – 8887) 
Volume 135 – No.7, February 2016 
32 
failing to meet the deadline produces false output and does 
endanger the human lives.” 
3. DESIGN ANALYSIS 
3.1 Circuit Diagram 
The schematic diagram in Figures 3a and 3b diagrammatically 
depicts the gas detection system (i.e. from the power stage, 
detection and alarm stage).  
The amount of supplied power into the circuit is dependent on 
the combined power usage on each component in the circuit. 
From the right-most part of Figure 3 is written 12V, 300mA 
i.e. the calculated average power that was sufficient to power 
the whole circuit. And this power was generated from an AC-
DC adapter which can step down, rectify and stabilize 
outputs. 
The adapter gets connected to the circuit board via a polarized 
adapter jack port which is not fixed on the board but screwed 
to the casing that houses the whole circuit. From the supplied 
12V, 300mA, is connected the U1, 78L05 a three (3) pin 
voltage regulator which is supplied with any DC < 35V and 
will always give the DC output of 5V. 
This DC output of 5V is where other components tap from. 
First, is the gas sensor (MQ-9), then the 555Timer, and most 
importantly, the alarm systems (the four (4) red led and 
buzzer) and other components as the resistors and capacitors. 
 
Figure 3a: Circuit diagram for the gas detector with 
audible alarm system with ISIS Professional 
 
Figure 3b: Close Circuit diagram for the gas detector with 
audible alarm system. 
 
3.2 Principle of operation 
The gas detector alarm system is designed with the intention 
to ensure that the event of gas is intelligently detected, 
promptly notified and interactively managed. It is built around 
a timer to accept input from the gas sensor, MQ-9, and 
activate a buzzer and set of led that alerts in the event of gas. 
The sensor used is the MQ-9 and from the datasheet, it 
specializes in gas detection equipment for carbon monoxide 
and CH4, LPG family and any other relevant industry or car 
assemblage. 
3.3 Sensor 
For detecting the event of gas which is associated with fire is 
monitored using a gas sensor.  
It advantage is that it has; 
 
Good sensitivity to CO/Combustible gas  
 
High sensitivity to Methane, Propane and CO  
 
Long life and low cost  
 
Simple drive circuit 
The  enveloped  MQ-9  has  6  pins, 4  of  which  are  used  to 
fetch  signals, and  other  2  for providing heating current. The 
sensor works with voltages between 5V and 12V AC or DC. 
A 5V supply voltage was used for this design. Once powered, 
the output of the sensor is normally HIGH but goes LOW 
when gas is sensed.  
 
 
 
Figure 3c:The MQ-9 gas sensor. 
4. IMPLEMENTATION AND TESTING 
4.1 Construction 
The physical realization of the project is very vital. This is 
where the fantasy of the whole idea meets reality. Here the 
paper work is transformed into a finished hardware.  
Notables on the Design; 
1. 
Set of pore holes for proper ventilation and proper 
communication between the circuit and the external 
environment. 
2. 
When the circuit is ON, a green led comes ON, and 
red when gas is sensed. 
3. 
 A protruded sensor for proper contact in detecting 
gas. 
4. 
The packaged container fit the size of the circuit