Alcoholmeter - Alcoholmeter with MQ3 sensor

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Lluis Nadal / Mbed 2 deprecated Alcoholmeter

Alcoholmeter with MQ3 sensor

main.cpp@2:5bb97fd609cb, 2011-04-09 (annotated)

Committer:: lnadal
Date:: Sat Apr 09 14:18:50 2011 +0000
Revision:: 2:5bb97fd609cb
Parent:: 1:5a58f03abfe9

Who changed what in which revision?

User	Revision	Line number	New contents of line
lnadal	0:05d4673b2832	1	/* Alcoholmeter
lnadal	0:05d4673b2832	2
lnadal	0:05d4673b2832	3	Range: 0-3000 ppm.
lnadal	0:05d4673b2832	4
lnadal	2:5bb97fd609cb	5	*********************************************************************************
lnadal	0:05d4673b2832	6
lnadal	1:5a58f03abfe9	7	This project was done in 2010-11 school year in Molins de Rei (Barcelona, Spain)
lnadal	1:5a58f03abfe9	8	in Lluis de Requesens Secondari School.
lnadal	0:05d4673b2832	9
lnadal	1:5a58f03abfe9	10	Teacher: Lluis Nadal.
lnadal	0:05d4673b2832	11	Students: Agnes Garriga, Manel Tuells.
lnadal	0:05d4673b2832	12
lnadal	2:5bb97fd609cb	13	*********************************************************************************
lnadal	0:05d4673b2832	14
lnadal	2:5bb97fd609cb	15	Sensor: MQ-3 alcohol sensor.(http://www.sparkfun.com/;
lnadal	2:5bb97fd609cb	16	http://www.bricogeek.com/shop/).
lnadal	0:05d4673b2832	17
lnadal	0:05d4673b2832	18	MQ-3 sensor wiring:
lnadal	2:5bb97fd609cb	19	H1(5V), H2(ground), A(5V), B (R load = 500 Ohm - 1%),
lnadal	2:5bb97fd609cb	20	R load (mBed pin 20 - ground).
lnadal	0:05d4673b2832	21
lnadal	0:05d4673b2832	22	Analog out (for datalogger or multimeter): mBed pin 18 (1V = 1000 ppm).
lnadal	0:05d4673b2832	23
lnadal	0:05d4673b2832	24
lnadal	0:05d4673b2832	25
lnadal	2:5bb97fd609cb	26	MQ-3 sensor response is not linear. Calibration was done by passing air
lnadal	2:5bb97fd609cb	27	(with a fishtank air pump)
lnadal	1:5a58f03abfe9	28	through a dilute solution of ethanol in water.
lnadal	2:5bb97fd609cb	29	The resulting air saturated of ethanol vapor and water vapor, was continuously
lnadal	2:5bb97fd609cb	30	introduced in an open container containing the sensor. Th voltage across a
lnadal	2:5bb97fd609cb	31	load resistor was measured.
lnadal	0:05d4673b2832	32
lnadal	2:5bb97fd609cb	33	A 500 Ohm-1% load resistor was selected in order to achieve a measuring range
lnadal	2:5bb97fd609cb	34	of 3000 ppm.
lnadal	0:05d4673b2832	35
lnadal	2:5bb97fd609cb	36	After a bit difficult calculations, the sensor response was aproximated in a
lnadal	2:5bb97fd609cb	37	five degree polynomial:
lnadal	0:05d4673b2832	38
lnadal	0:05d4673b2832	39	X = V(in)
lnadal	0:05d4673b2832	40	ppm = 2.71494E+02X - 3.10999E+02X^2 + 6.85051E+02X^3 - 3.47587E+02X^4 + 7.47499E+01*X^5
lnadal	0:05d4673b2832	41
lnadal	0:05d4673b2832	42
lnadal	2:5bb97fd609cb	43	For more accurate readins is recommended a minimum heating time of 5 minutes
lnadal	2:5bb97fd609cb	44	(the manufacturer recommends 24) but 1 minute give satisfactory results.
lnadal	0:05d4673b2832	45	After heating, the sensor is autozeroed by averaging 5 measures.
lnadal	0:05d4673b2832	46
lnadal	0:05d4673b2832	47	In heating and in autozero operations the sensor must be left away of alcohol vapors!
lnadal	0:05d4673b2832	48
lnadal	0:05d4673b2832	49
lnadal	0:05d4673b2832	50	THIS FREE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND. ENJOY IT.
lnadal	0:05d4673b2832	51
lnadal	0:05d4673b2832	52	*/
lnadal	2:5bb97fd609cb	53	//*******************************************************************************
lnadal	0:05d4673b2832	54
lnadal	0:05d4673b2832	55
lnadal	0:05d4673b2832	56	#include "mbed.h"
lnadal	0:05d4673b2832	57	#include "TextLCD.h"
lnadal	0:05d4673b2832	58	#include <sstream>
lnadal	0:05d4673b2832	59	using namespace std;
lnadal	0:05d4673b2832	60
lnadal	0:05d4673b2832	61
lnadal	0:05d4673b2832	62
lnadal	0:05d4673b2832	63
lnadal	0:05d4673b2832	64	float concentration (float x){
lnadal	0:05d4673b2832	65
lnadal	0:05d4673b2832	66	const float A[] = { 2.71494E+02, -3.10999E+02, 6.85051E+02, -3.47587E+02, 7.47499E+01};
lnadal	0:05d4673b2832	67	float result;
lnadal	0:05d4673b2832	68	float B[4];
lnadal	0:05d4673b2832	69	B[0] = x*x;
lnadal	0:05d4673b2832	70	B[1] = B[0]*x;
lnadal	0:05d4673b2832	71	B[2] = B[1]*x;
lnadal	0:05d4673b2832	72	B[3] = B[2]*x;
lnadal	0:05d4673b2832	73
lnadal	0:05d4673b2832	74	result = A[0]x+A[1]B[0]+A[2]B[1]+A[3]B[2]+A[4]*B[3];
lnadal	0:05d4673b2832	75	return result;
lnadal	0:05d4673b2832	76	}
lnadal	0:05d4673b2832	77
lnadal	0:05d4673b2832	78
lnadal	0:05d4673b2832	79
lnadal	0:05d4673b2832	80
lnadal	0:05d4673b2832	81	char messages[5][16] = {"Heating sensor", "64 seconds", "Autozero", "Ready!", "ppm"};
lnadal	0:05d4673b2832	82
lnadal	0:05d4673b2832	83
lnadal	0:05d4673b2832	84	int L;
lnadal	0:05d4673b2832	85	float x;
lnadal	0:05d4673b2832	86	float x0[5];
lnadal	0:05d4673b2832	87	float x_initial;
lnadal	0:05d4673b2832	88
lnadal	0:05d4673b2832	89	TextLCD lcd(p24, p26, p27, p28, p29, p30); // Wiring microcontroller - LCD:
lnadal	0:05d4673b2832	90	// rs(4), e(6), d4(11), d5(12), d6(13), d7(14) (R/W(5) a 0)
lnadal	0:05d4673b2832	91
lnadal	1:5a58f03abfe9	92	DigitalIn pushbutton = p8; // Pushbutton (normally open). Stops initial heating time when it is pressed.
lnadal	0:05d4673b2832	93	AnalogOut output(p18); // Analog output to a multimeter or datalogger (1V = 1000 ppm).
lnadal	0:05d4673b2832	94
lnadal	0:05d4673b2832	95
lnadal	0:05d4673b2832	96
lnadal	0:05d4673b2832	97	void text_screen( char message[], int colum, int row) {
lnadal	0:05d4673b2832	98
lnadal	0:05d4673b2832	99	lcd.locate( colum, row);
lnadal	0:05d4673b2832	100	lcd.printf(message);
lnadal	0:05d4673b2832	101
lnadal	0:05d4673b2832	102	}
lnadal	0:05d4673b2832	103
lnadal	0:05d4673b2832	104
lnadal	0:05d4673b2832	105
lnadal	0:05d4673b2832	106	int main() {
lnadal	0:05d4673b2832	107
lnadal	0:05d4673b2832	108	output = 0.0;
lnadal	0:05d4673b2832	109	lcd.cls();
lnadal	0:05d4673b2832	110
lnadal	0:05d4673b2832	111	text_screen(messages[0], 0, 0);
lnadal	0:05d4673b2832	112	text_screen(messages[1], 0, 1);
lnadal	0:05d4673b2832	113	wait(2);
lnadal	0:05d4673b2832	114
lnadal	0:05d4673b2832	115
lnadal	0:05d4673b2832	116
lnadal	0:05d4673b2832	117	for (int j = 0; j<4; j++){
lnadal	0:05d4673b2832	118
lnadal	0:05d4673b2832	119	lcd.cls(); // Heating sensor 4x16 = 64 seconds
lnadal	0:05d4673b2832	120	text_screen(messages[0], 0, 0);
lnadal	0:05d4673b2832	121
lnadal	0:05d4673b2832	122
lnadal	0:05d4673b2832	123	for (int i = 0; i<16; i++){
lnadal	0:05d4673b2832	124	if (pushbutton == 1){ // Pressing pushbutton stops initial heating and enters in measuring mode.
lnadal	0:05d4673b2832	125	break;
lnadal	0:05d4673b2832	126	}
lnadal	0:05d4673b2832	127	lcd.locate(i, 1);
lnadal	0:05d4673b2832	128	lcd.putc(62);
lnadal	0:05d4673b2832	129	wait(1);
lnadal	0:05d4673b2832	130	}
lnadal	0:05d4673b2832	131	}
lnadal	0:05d4673b2832	132
lnadal	0:05d4673b2832	133	lcd.cls();
lnadal	0:05d4673b2832	134	text_screen(messages[2], 0, 0);
lnadal	0:05d4673b2832	135	wait(2);
lnadal	0:05d4673b2832	136
lnadal	0:05d4673b2832	137
lnadal	0:05d4673b2832	138	AnalogIn value(p20); // Reads sensor voltage as a float int the interval (0-1) corresponding to (0 - 3.3V).
lnadal	0:05d4673b2832	139
lnadal	0:05d4673b2832	140
lnadal	0:05d4673b2832	141
lnadal	0:05d4673b2832	142	for (int i=0; i<5; i++){
lnadal	0:05d4673b2832	143
lnadal	0:05d4673b2832	144	x0[i] = value;
lnadal	0:05d4673b2832	145	wait(2);
lnadal	0:05d4673b2832	146
lnadal	0:05d4673b2832	147	}
lnadal	0:05d4673b2832	148	x_initial = (x0[0]+x0[1]+x0[2]+x0[3]+x0[4])/5.0; // Autozero. Average of 5 initial measures.
lnadal	0:05d4673b2832	149
lnadal	0:05d4673b2832	150	lcd.cls();
lnadal	0:05d4673b2832	151	text_screen(messages[3], 0, 0);
lnadal	0:05d4673b2832	152	wait(2);
lnadal	0:05d4673b2832	153
lnadal	0:05d4673b2832	154	while(1) {
lnadal	0:05d4673b2832	155	x = value;
lnadal	0:05d4673b2832	156	x = (x-x_initial)*3.3; // Calculate real voltage.
lnadal	0:05d4673b2832	157
lnadal	0:05d4673b2832	158	if(x<0) x = 0;
lnadal	0:05d4673b2832	159
lnadal	0:05d4673b2832	160	x = concentration(x);
lnadal	0:05d4673b2832	161
lnadal	0:05d4673b2832	162	output = x/3000; // If analog readings do not match digital readings you can adjust this value (1000 ppm = 1V).
lnadal	0:05d4673b2832	163
lnadal	0:05d4673b2832	164	wait(0.1);
lnadal	0:05d4673b2832	165
lnadal	0:05d4673b2832	166	// Float to string conversion.
lnadal	0:05d4673b2832	167	stringstream ss (stringstream::in \| stringstream::out);
lnadal	0:05d4673b2832	168	ss <<x;
lnadal	0:05d4673b2832	169	string reading = ss.str();
lnadal	0:05d4673b2832	170	L = reading.length();
lnadal	0:05d4673b2832	171
lnadal	0:05d4673b2832	172
lnadal	0:05d4673b2832	173	lcd.cls();
lnadal	0:05d4673b2832	174	for (int i=0; i<L; i+=1){
lnadal	0:05d4673b2832	175	lcd.locate(i,0);
lnadal	0:05d4673b2832	176	lcd.putc(reading[i]);
lnadal	0:05d4673b2832	177
lnadal	0:05d4673b2832	178
lnadal	0:05d4673b2832	179
lnadal	0:05d4673b2832	180	text_screen(messages[4], 10, 0);
lnadal	0:05d4673b2832	181	}
lnadal	0:05d4673b2832	182	wait(2);
lnadal	0:05d4673b2832	183	}
lnadal	0:05d4673b2832	184	}

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Type:	Program
Mbed OS support:	Mbed 2 deprecated
Created:	09 Apr 2011
Imports:	88
Forks:	0
Commits:	3
Dependents:	0
Dependencies:	2
Followers:	3

main.cpp@2:5bb97fd609cb, 2011-04-09 (annotated)

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