Explanation Of Circuit Working

As this project is using MQ-4 gas sensor as mentioned before,fromr its datasheet, it has high sensitivity to propane, butane, isobutene,LPG and natural gas. The sensor can also be used to detect combustible gases, especially methane. This circuit has been tested with LPG gas and was found to work very fine.

         From the schematic circuit, there have 2 LED which is red and green as a indicator of the circuit. The red LED function as a starter or warm up to make an sensor active. The red LED will blink for a few sec before the LED off and the green LED will turn on that show the sensor already activated and ready to detect any various kind of gases. 
      When the sensor would detected gases, the buzzer will sound a few second and the wireless alarm will sound as a warning to people at the building or factory or etc. 
          Here we use 5v dc relay as a switching to make an alarm activated and IC1 LM324 as a amplifier to the circuit. We also used preset resistor 10k to adjust the sensitivity of the sensor and we use 12V adapter as a supply to the circuit


Let watching this video:

As shown above is how the project function when it detect LPG gas.

Doorbell That Being Modified To Fit With The Original Circuit

As being order before we must modified the doorbell so that it can be connected with our sensor circuit. And this is what we have done, we had remove the switch of the transmit ( Tx ) wireless doorbell.
Then we connect the connection wire of the transmitter wireless doorbell to the output of the gas detection sensor.When the sensor detect gas according to the concentration the relay will switch on and the doorbell circuit will sent a signal to the Rx and alarm will on.After a hard work the doorbell had being successfully combines with the real circuit.  

This is the result that we've combined the gas detector circuit and wireless doorbell transmitter(Tx). 

This is the receiver(Rx) from the wireless doorbell. 

.

Type Of Doorbell Used For The Project

Our supervisor had give an order to modified wireless doorbell act as a wireless alarm for the gas sensor. We need to modified this wireless doorbell then connected with gas sensor. Beside our supervisor provide the wireless doorbell. So that we need to do some research to make sure this doorbell can be combine with the original gas sensor circuit.

This is the type of wireless doorbell(real picture)

Circuit Diagram And PCB Layout For The Project

 SCHEMATIC DIAGRAM

PCB TRACK

COMPONENT PLACEMENT

Note : Create a circuit by using Diptrace software to make a PCB track to assemble all the component.