Motion Sensor -.pdf

MQ2 & MQ3

MQ2

MQ-2 Smoke Sensor  The MQ-2 Gas Sensor module detects gas leakage in

home and industry.  The MQ series of gas sensors use a small heater inside with an electrochemical sensor.  They are sensitive to a range of gasses and are used indoors at room temperature.  The output is an analog signal and can be read with an analog input of the Arduino

MQ-2 Smoke Sensor  The MQ-2 smoke sensor is sensitive to smoke and to the

following flammable gases:  LPG  Butane  Propane  Methane  Alcohol  Hydrogen  The resistance of the sensor is different depending on the type of the gas.  The smoke sensor has a built-in potentiometer that allows you to adjust the sensor sensitivity according to how accurate you want to detect gas.

MQ-2 Smoke Sensor

Features  Features

1. Wide detecting scope 2. High sensitivity and fast response 3. Long life and stable 4. Simple drive circuit  Due to its fast response time and high sensitivity, measurements can be taken as soon as possible.  The sensor sensitivity can be adjusted by using the potentiometer.

Application  Domestic gas leakage detector  Industrial Combustible gas detector  Portable gas detector

MQ-2 Smoke Sensor

How does it Work?  The MQ2 has an electrochemical sensor, which changes its 

  



resistance for different concentrations of varied gasses. The sensor is connected in series with a variable resistor to form a voltage divider circuit and the variable resistor is used to change sensitivity. When one of the above gaseous elements comes in contact with the sensor after heating, the sensor’s resistance change. The change in the resistance changes the voltage across the sensor, and this voltage can be read by a microcontroller. The voltage value can be used to find the resistance of the sensor by knowing the reference voltage and the other resistor’s resistance. The sensor has different sensitivity for different types of gasses. The sensitivity characteristic curve is shown below for the different type of gasses.

Where, 1. Ro is the resistance of the sensor in clean air 2. Rs is the resistance of sensor when exposed to gasses

How does it Work?  The voltage that the sensor outputs changes

accordingly to the smoke/gas level that exists in the atmosphere.  The sensor outputs a voltage that is proportional to the concentration of smoke/gas.  In other words, the relationship between voltage and gas concentration is the following:  The greater the gas concentration , the greater the output voltage  The lower the gas concentration , the lower the output voltage

Procedure to Calculate the Concentration of a Particular Type of Gas  To find the concentration of gas, two values has to be measured 





 



using a microcontroller with ADC such as Arduino, 1. Ro – The resistance of the sensor when measured in clean air, 2. Rs – The resistance of the sensor when it is exposed to any of the mentioned gasses To find Ro, connect the sensor to one of the Analog pins of Arduino, note 100 values, and select the median value. This will reduce if any dynamic errors present in the values. The sensor is connected in the series with a variable resistor (Potentiometer on the sensor board). So, to find the resistance of the sensor (Ro or Rs), the resistance of the variable resistor (R1) is required. In most of the MQ2 sensor modules, any one end of the potentiometer and the middle pin of potentiometer will be connected between Sig or Vout Pin and Ground. Find the resistance of R1 using a multimeter and note it down.

Procedure to Calculate the Concentration of a Particular Type of Gas  The voltage across the sensor Vs (Vs is Vo in Clean Air) is calculated by using the



   



following formula: Vs=VRef – ADC_Value * (VRefH-VRefL)/(2R) Where, VRefH is the higher Reference voltage of the ADC, in Arduino, it is usually 5V or 3.3V VRefL is the lower reference voltage of the ADC, in Arduino, it is usually 0V R is the resolution of the ADC, in most of the Arduino boards, it is 10 Bits Once the voltage across the sensor and value of R1 is known, the resistance of the sensor can be calculated by using the formula Ro=R1 Vo/ (VRef-Vo) Where Vo is the voltage across the sensor in clean Air Similarly, the Resistance of the sensor when exposed to gas can be calculated by repeating the above steps and using the formula Rs=R1 Vs / (VRef-Vs) Where Vs is the voltage across the sensor in the Air contaminated with LPG molecules Note:The value of R1 is only for finding the value of Rs and Ro. For finding the concentration of gas, R1 is not required as the concentration is dependent on the Rs/Ro ratio. R1 is not required for finding just the ratio.

Procedure to Calculate the Concentration of a Particular Type of Gas  Finding the Concentration of a Gas

The concentration of a gas can be calculated by measuring the sensor’s Ro and Rs values and using the following formula  Concentration = Xo (Y/ Yo) Φ Where Φ is the slope, which can be found using the Sensitivity Characteristic curve and the following formula Φ = Log (Y2/Y1) / Log(X2/X1) Where (X2, Y2) and (X1, Y1) are any two points on a section (lines between indicated points on the curve) of the curve. Since the curve has different slopes at different concentrations the (X2, Y2) and (X1, Y1) values should be taken from the corresponding sections  The Xo and Yo values are Initial Concentration and Rs/Ro ratio on a section of the curve (lines between marked points), these values are the starting points of each section (each line between marked points has different slopes) Y is the Rs/Ro Ratio for the current concentration of the gas

MQ3

MQ-3 Alcohol Sensor  The alcohol sensor we will use is the MQ-3 sensor.

This is a sensor that is not only sensitive to alcohol, particularly ethanol, which is the type of alcohol which is found in wine, beer, and liquor.  This type of sensor circuit can be used as a breathalyzer to check a person's blood alcohol level.  Just as we exhale carbon dioxide when we breathe out, we also will breathe out some alcohol if we have alcohol in our blood.  Any alcometer device can measure this alcohol content.

MQ-3  The more ethanol in your blood, the more there is in

the air on exhalation.  This alcohol content gives a good indication for if a person is drunk and how drunk they are.  The amount of alcohol exhaled into the air is proportional to the amount of alcohol which will be found in a person's blood.  Alcometers use a built-in formula to estimate blood alcohol content from exhaled air alcohol content.

MQ-3  For different countries, the level of alcohol in the blood     

that defines a person as over the limit for driving varies. The range ranges from 0.01 to 0.10. Most countries have a limit of about 0.05. For example, Greece, Greenalnd, and Iceland all have limits of 0.05. Canada has a higher limit set at 0.08. In the United States, it is also 0.08. In India, the permissible blood alcohol content (BAC) is set at 0.03% per 100ml blood. That works out to 30mg of alcohol per 100 ml of blood.

Features  Features  It has good sensitivity to alcohol in wide range, and

has advantages such as long lifespan, low cost and simple drive circuit &etc.  Main Applications  It is widely used in domestic alcohol gas alarm, industrial alcohol gas alarm and portable alcohol detector.