├── LICENSE
├── README.md
├── arduino_sample
└── arduino_sample.ino
├── library.properties
└── src
├── MQ2.cpp
└── MQ2.h
/LICENSE:
--------------------------------------------------------------------------------
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/README.md:
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1 | MQ-2 sensor library
2 | ===================
3 |
4 | This is a simple library to use with the MQ-2 sensor in arduino.
5 |
6 | Based on this page: Sandbox electronics
7 |
8 | The following page it's also useful if you want to know how to calibrate the sensor (it's for MQ-6 sensor but it works as the MQ-2 does):
9 | http://www.savvymicrocontrollersolutions.com/index.php?sensor=mq-6-gas-sensors
10 |
11 | Usage
12 | ======
13 | To intall the library to use it with the Arduino IDE, download it as zip and unzip it into your 'libraries' folder and restart the Arduino IDE.
14 |
15 | To know how to use this library view the [sample](/arduino_sample/arduino_sample.ino).
16 |
17 | Examples
18 | =========
19 | Setup:
20 |
21 | #include <MQ2.h>
22 |
23 | int pin = A0;
24 |
25 | MQ2 mq2(pin);
26 |
27 | void setup(){
28 | mq2.begin();
29 | }
30 |
31 |
32 | Read all data:
33 |
34 | float* values = mq2.read(true); //true to print the values in the Serial
35 |
36 |
37 | Read specific data:
38 |
39 | float lpg = mq2.readLPG();
40 |
41 | float co = mq2.readCO();
42 |
43 | float smoke = mq2.readSmoke();
44 |
45 |
46 | License
47 | =========
48 | Copyright 2015 labay11
49 |
50 | Licensed under the Apache License, Version 2.0 (the "License");
51 | you may not use this file except in compliance with the License.
52 | You may obtain a copy of the License at
53 |
54 | http://www.apache.org/licenses/LICENSE-2.0
55 |
56 | Unless required by applicable law or agreed to in writing, software
57 | distributed under the License is distributed on an "AS IS" BASIS,
58 | WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
59 | See the License for the specific language governing permissions and
60 | limitations under the License.
61 |
--------------------------------------------------------------------------------
/arduino_sample/arduino_sample.ino:
--------------------------------------------------------------------------------
1 | #include
2 |
3 | //change this with the pin that you use
4 | int pin = A0;
5 | float lpg, co, smoke;
6 |
7 | MQ2 mq2(pin);
8 |
9 | void setup(){
10 | Serial.begin(9600);
11 |
12 | // calibrate the device
13 | mq2.begin();
14 | }
15 |
16 | void loop(){
17 |
18 | /*
19 | * read the values from the sensor, it returns
20 | * an array which contains 3 values.
21 | * 0 : LPG in ppm
22 | * 1 : CO in ppm
23 | * 2 : SMOKE in ppm
24 | */
25 | float* values= mq2.read(true); //set it false if you don't want to print the values to the Serial
26 |
27 | // lpg = values[0];
28 | lpg = mq2.readLPG();
29 | // co = values[1];
30 | co = mq2.readCO();
31 | // smoke = values[2];
32 | smoke = mq2.readSmoke();
33 |
34 | delay(1000);
35 | }
36 |
37 |
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/library.properties:
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1 | name=MQ2-sensor
2 | version=1
3 | author=Adria Labay
4 | maintainer=Adria Labay
5 | sentence=Simple library to read and interpret data from the MQ2 snesor.
6 | paragraph=Based on this page: Sandbox electronics. The following page it's also useful if you want to know how to calibrate the sensor (it's for MQ-6 sensor but it works as the MQ-2 does): http://www.savvymicrocontrollersolutions.com/index.php?sensor=mq-6-gas-sensors.
7 | category=Sensors
8 | url=https://github.com/labay11/MQ-2-sensor-library
9 |
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/src/MQ2.cpp:
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1 | #include "Arduino.h"
2 | #include "MQ2.h"
3 |
4 | MQ2::MQ2(int pin) {
5 | _pin = pin;
6 | Ro = -1.0;
7 | }
8 |
9 | void MQ2::begin(){
10 | Ro = MQCalibration();
11 | Serial.print("Ro: ");
12 | Serial.print(Ro);
13 | Serial.println(" kohm");
14 | }
15 |
16 | void MQ2::close(){
17 | Ro = -1.0;
18 | values[0] = 0.0;
19 | values[1] = 0.0;
20 | values[2] = 0.0;
21 | }
22 |
23 | bool MQ2::checkCalibration() {
24 | if (Ro < 0.0) {
25 | Serial.println("Device not calibrated, call MQ2::begin before reading any value.");
26 | return false;
27 | }
28 |
29 | return true;
30 | }
31 |
32 | float* MQ2::read(bool print){
33 | if (!checkCalibration()) return NULL;
34 |
35 | values[0] = MQGetPercentage(LPGCurve);
36 | values[1] = MQGetPercentage(COCurve);
37 | values[2] = MQGetPercentage(SmokeCurve);
38 |
39 | lastReadTime = millis();
40 |
41 | if (print){
42 | Serial.print(lastReadTime);
43 | Serial.print("ms - LPG:");
44 | Serial.print(values[0], 5);
45 | Serial.print("ppm\t");
46 | Serial.print("CO:");
47 | Serial.print(values[1], 5);
48 | Serial.print("ppm\t");
49 | Serial.print("SMOKE:");
50 | Serial.print(values[2], 5);
51 | Serial.print("ppm\n");
52 | }
53 |
54 | return values;
55 | }
56 |
57 | float MQ2::readLPG(){
58 | if (!checkCalibration()) return 0.0;
59 |
60 | if (millis() < (lastReadTime + READ_DELAY) && values[0] > 0)
61 | return values[0];
62 | else
63 | return (values[0] = MQGetPercentage(LPGCurve));
64 | }
65 |
66 | float MQ2::readCO(){
67 | if (!checkCalibration()) return 0.0;
68 |
69 | if (millis() < (lastReadTime + READ_DELAY) && values[1] > 0)
70 | return values[1];
71 | else
72 | return (values[1] = MQGetPercentage(COCurve));
73 | }
74 |
75 | float MQ2::readSmoke(){
76 | if (!checkCalibration()) return 0.0;
77 |
78 | if (millis() < (lastReadTime + READ_DELAY) && values[2] > 0)
79 | return values[2];
80 | else
81 | return (values[2] = MQGetPercentage(SmokeCurve));
82 | }
83 |
84 | float MQ2::MQResistanceCalculation(int raw_adc) {
85 | float flt_adc = (float) raw_adc;
86 | return RL_VALUE * (1023.0 - flt_adc) / flt_adc;
87 | }
88 |
89 | float MQ2::MQCalibration() {
90 | float val = 0.0;
91 |
92 | // take multiple samples
93 | for (int i = 0; i < CALIBARAION_SAMPLE_TIMES; i++) {
94 | val += MQResistanceCalculation(analogRead(_pin));
95 | delay(CALIBRATION_SAMPLE_INTERVAL);
96 | }
97 |
98 | //calculate the average value
99 | val = val / ((float) CALIBARAION_SAMPLE_TIMES);
100 |
101 | //divided by RO_CLEAN_AIR_FACTOR yields the Ro according to the chart in the datasheet
102 | val = val / RO_CLEAN_AIR_FACTOR;
103 |
104 | return val;
105 | }
106 |
107 | float MQ2::MQRead() {
108 | float rs = 0.0;
109 |
110 | for (int i = 0; i < READ_SAMPLE_TIMES; i++) {
111 | rs += MQResistanceCalculation(analogRead(_pin));
112 | delay(READ_SAMPLE_INTERVAL);
113 | }
114 |
115 | return rs / ((float) READ_SAMPLE_TIMES); // return the average
116 | }
117 |
118 | float MQ2::MQGetPercentage(float *pcurve) {
119 | float rs_ro_ratio = MQRead() / Ro;
120 | return pow(10.0, ((log(rs_ro_ratio) - pcurve[1]) / pcurve[2]) + pcurve[0]);
121 | }
122 |
--------------------------------------------------------------------------------
/src/MQ2.h:
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1 | # ifndef MQ2_h
2 | # define MQ2_h
3 |
4 | # if ARDUINO >= 100
5 | # include "Arduino.h"
6 | # else
7 | # include "WProgram.h"
8 | # endif
9 |
10 | // define the load resistance on the board, in kilo ohms
11 | # define RL_VALUE 5.0
12 | // given constant
13 | # define RO_CLEAN_AIR_FACTOR 9.83
14 |
15 | // reads 10 times the sensor every 50ms and takes the average
16 | // NOTE: it is encouraged to take more samples during the calibration
17 | # define CALIBARAION_SAMPLE_TIMES 10
18 | # define CALIBRATION_SAMPLE_INTERVAL 50
19 |
20 | // reads 5 times the sensor every 50ms and takes the average
21 | # define READ_SAMPLE_TIMES 5
22 | # define READ_SAMPLE_INTERVAL 50
23 |
24 | // 10s, time elapsed before new data can be read.
25 | # define READ_DELAY 10000
26 |
27 | class MQ2 {
28 | public:
29 | /*
30 | * Creates the sensor by giving the pin where it is attached.
31 | */
32 | MQ2(int pin);
33 |
34 | /*
35 | * Initialises the sensor before getting any data.
36 | * This step is necessary as it needs to be calibrated based on
37 | * current air and temperature conditions.
38 | */
39 | void begin();
40 |
41 | /*
42 | * Stops the sensor, calibration and any read data is deleted.
43 | *
44 | * Pin information is kept, so just call `begin()` again
45 | * to read new values, no need to create a new object.
46 | */
47 | void close();
48 |
49 | /*
50 | * Reads the LPG, CO and smoke data from the sensor and returns and
51 | * array with the values in this order.
52 | *
53 | * The read procedure takes `READ_SAMPLE_TIMES` samples from the sensor
54 | * every `READ_SAMPLE_INTERVAL` ms and returns the average.
55 | *
56 | * NOTE: do not modify the values of the returned array in place or deallocate it,
57 | * that could have unexpected consequences. Time to PANIC.
58 | */
59 | float* read(bool print);
60 |
61 | /*
62 | * Same as before but only return the data from the specified gas.
63 | *
64 | * If the time elapsed since the last measurement is smaller than
65 | * `READ_DELAY`, the same prior value will be returned.
66 | */
67 | float readLPG();
68 | float readCO();
69 | float readSmoke();
70 |
71 | private:
72 | int _pin;
73 |
74 | float LPGCurve[3] = {2.3, 0.21, -0.47};
75 | float COCurve[3] = {2.3, 0.72, -0.34};
76 | float SmokeCurve[3] = {2.3, 0.53, -0.44};
77 | float Ro = -1.0;
78 |
79 | float values[3]; // array with the measured values in the order: lpg, CO and smoke
80 |
81 | float MQRead();
82 | float MQGetPercentage(float *pcurve);
83 | float MQCalibration();
84 | float MQResistanceCalculation(int raw_adc);
85 | bool checkCalibration();
86 |
87 | int lastReadTime = 0;
88 | };
89 |
90 | # endif
91 |
--------------------------------------------------------------------------------