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Wednesday, February 1, 2012


Một ứng dụng rất hây sử dụng vi điều khiển PIC 16F84A là Cảm biến Gas. 
Sau đây là bài hướng dẫn, mình nghĩ với hướng dẫn chi tiết và có sẵn 
firmware thì các bạn dễ dàng thực hiện thôi.
Kết nối trên testboard



Introduction:
This is a gas detecting circuit capable of sensing many different types of 
gases.  The sensor used is the GH-312 and from the datasheet it is 
capable of sensing gases like smokeliquefied gasbutane and propane
Methanealcohol,hydrogenetc.

Diagram


Parts list
R1                   1K resistor
R2                   1K resistor
P1                    100K potentiometer
C1                   10uF cap
C2                   100nF cap
C3                   100nF cap
C4                   15pF cap
C5                   15pF cap
Xtal                 8Mhz crystal
Led1                3mm red led
Piezo               Piezo
LCD                8X2 LCD
IC1                  16F84A microcontroller
VR1                7805 regulator
GH-312           Gas Sensor
PBC
                                    Top side

 
                                          Buttom side
I've used a 9V battery for this project because the sensor requires a 9V input. 
  The output when the sensor is triggered is always 5V which is perfect for a direct
 connection to any microcontroller.   Although I've used a 9V battery, any 12V 
power supply ( a small wall transformer for example ) will work perfectly since the 
sensor can handle from 9V up to 20V and the microcontroller's voltage is regulated 
by a 7805 regulator.

Testing
The first tests were made with the circuit mounted on a breadboard.   
After initialization the circuit will enter a normal state where it detects no gas. 
The display shows "Sensing...No Gas !".
To test the sensor I used my portable gas soldering iron with the gas coming 
out pointed to the sensor.
The sensor is able to detect the gas and the microcontroller will trigger a
 flashing led warning and sound.
The sound is produced by a small piezo and the display show the message 
"Found Gas". 


Conlusion
It's a pretty cheap and easy to assemble circuit.
Does not require too many parts and the microcontroller is very easy to find
 ( the famous 16F84A from microchip ).
Since it's used a small lcd ( 8x2 ) this project can be portable.
Also this sensor senses several types of gas and it's pretty stable.


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