Alcoholmeter - Alcoholmeter with MQ3 sensor

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Lluis Nadal / Mbed 2 deprecated Alcoholmeter

Alcoholmeter with MQ3 sensor

main.cpp@0:05d4673b2832, 2011-04-09 (annotated)

Committer:: lnadal
Date:: Sat Apr 09 14:04:34 2011 +0000
Revision:: 0:05d4673b2832
Child:: 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	0:05d4673b2832	5	*************************************************************************************************************************
lnadal	0:05d4673b2832	6
lnadal	0:05d4673b2832	7	This project was done in 2010-11 school year in Molins de Rei (Barcelona, Spain) in Lluis de Requesens Secondari School.
lnadal	0:05d4673b2832	8
lnadal	0:05d4673b2832	9	Tacher: Lluis Nadal.
lnadal	0:05d4673b2832	10	Students: Agnes Garriga, Manel Tuells.
lnadal	0:05d4673b2832	11
lnadal	0:05d4673b2832	12	**************************************************************************************************************************
lnadal	0:05d4673b2832	13
lnadal	0:05d4673b2832	14	Sensor: MQ-3 alcohol sensor.(http://www.sparkfun.com/; http://www.bricogeek.com/shop/).
lnadal	0:05d4673b2832	15
lnadal	0:05d4673b2832	16	MQ-3 sensor wiring:
lnadal	0:05d4673b2832	17	H1(5V), H2(ground), A(5V), B (R load = 500 Ohm - 1%), R load (mBed pin 20 - ground).
lnadal	0:05d4673b2832	18
lnadal	0:05d4673b2832	19	Analog out (for datalogger or multimeter): mBed pin 18 (1V = 1000 ppm).
lnadal	0:05d4673b2832	20
lnadal	0:05d4673b2832	21
lnadal	0:05d4673b2832	22
lnadal	0:05d4673b2832	23	MQ-3 sensor response is not linear. Calibration was done by passing air (with a fishtank air pump) through a dilute solution of ethanol in water.
lnadal	0:05d4673b2832	24	The resulting air saturated of ethanol vapor and water vapor, was continuously introduced in an open container containing the sensor. Th voltage across a load resistor was measured.
lnadal	0:05d4673b2832	25
lnadal	0:05d4673b2832	26	A 500 Ohm-1% load resistor was selected in order to achieve a measuring range of 3000 ppm.
lnadal	0:05d4673b2832	27
lnadal	0:05d4673b2832	28	After a bit difficult calculations, the sensor response was aproximated in a five degree polynomial:
lnadal	0:05d4673b2832	29
lnadal	0:05d4673b2832	30	X = V(in)
lnadal	0:05d4673b2832	31	ppm = 2.71494E+02X - 3.10999E+02X^2 + 6.85051E+02X^3 - 3.47587E+02X^4 + 7.47499E+01*X^5
lnadal	0:05d4673b2832	32
lnadal	0:05d4673b2832	33
lnadal	0:05d4673b2832	34	For more accurate readins is recommended a minimum heating time of 5 minutes (24 hours is recommended for the manufacturer) but 1 minute give satisfactory results.
lnadal	0:05d4673b2832	35	After heating, the sensor is autozeroed by averaging 5 measures.
lnadal	0:05d4673b2832	36
lnadal	0:05d4673b2832	37	In heating and in autozero operations the sensor must be left away of alcohol vapors!
lnadal	0:05d4673b2832	38
lnadal	0:05d4673b2832	39
lnadal	0:05d4673b2832	40	THIS FREE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND. ENJOY IT.
lnadal	0:05d4673b2832	41
lnadal	0:05d4673b2832	42	*/
lnadal	0:05d4673b2832	43	//**********************************************************************************************
lnadal	0:05d4673b2832	44
lnadal	0:05d4673b2832	45
lnadal	0:05d4673b2832	46	#include "mbed.h"
lnadal	0:05d4673b2832	47	#include "TextLCD.h"
lnadal	0:05d4673b2832	48	#include <sstream>
lnadal	0:05d4673b2832	49	using namespace std;
lnadal	0:05d4673b2832	50
lnadal	0:05d4673b2832	51
lnadal	0:05d4673b2832	52
lnadal	0:05d4673b2832	53
lnadal	0:05d4673b2832	54	float concentration (float x){
lnadal	0:05d4673b2832	55
lnadal	0:05d4673b2832	56	const float A[] = { 2.71494E+02, -3.10999E+02, 6.85051E+02, -3.47587E+02, 7.47499E+01};
lnadal	0:05d4673b2832	57	float result;
lnadal	0:05d4673b2832	58	float B[4];
lnadal	0:05d4673b2832	59	B[0] = x*x;
lnadal	0:05d4673b2832	60	B[1] = B[0]*x;
lnadal	0:05d4673b2832	61	B[2] = B[1]*x;
lnadal	0:05d4673b2832	62	B[3] = B[2]*x;
lnadal	0:05d4673b2832	63
lnadal	0:05d4673b2832	64	result = A[0]x+A[1]B[0]+A[2]B[1]+A[3]B[2]+A[4]*B[3];
lnadal	0:05d4673b2832	65	return result;
lnadal	0:05d4673b2832	66	}
lnadal	0:05d4673b2832	67
lnadal	0:05d4673b2832	68
lnadal	0:05d4673b2832	69
lnadal	0:05d4673b2832	70
lnadal	0:05d4673b2832	71	char messages[5][16] = {"Heating sensor", "64 seconds", "Autozero", "Ready!", "ppm"};
lnadal	0:05d4673b2832	72
lnadal	0:05d4673b2832	73
lnadal	0:05d4673b2832	74	int L;
lnadal	0:05d4673b2832	75	float x;
lnadal	0:05d4673b2832	76	float x0[5];
lnadal	0:05d4673b2832	77	float x_initial;
lnadal	0:05d4673b2832	78
lnadal	0:05d4673b2832	79	TextLCD lcd(p24, p26, p27, p28, p29, p30); // Wiring microcontroller - LCD:
lnadal	0:05d4673b2832	80	// rs(4), e(6), d4(11), d5(12), d6(13), d7(14) (R/W(5) a 0)
lnadal	0:05d4673b2832	81
lnadal	0:05d4673b2832	82	DigitalIn pushbutton = p8; // Pushbutton (normally open). Stops initial heating time when it is pressed. .
lnadal	0:05d4673b2832	83	AnalogOut output(p18); // Analog output to a multimeter or datalogger (1V = 1000 ppm).
lnadal	0:05d4673b2832	84
lnadal	0:05d4673b2832	85
lnadal	0:05d4673b2832	86
lnadal	0:05d4673b2832	87	void text_screen( char message[], int colum, int row) {
lnadal	0:05d4673b2832	88
lnadal	0:05d4673b2832	89	lcd.locate( colum, row);
lnadal	0:05d4673b2832	90	lcd.printf(message);
lnadal	0:05d4673b2832	91
lnadal	0:05d4673b2832	92	}
lnadal	0:05d4673b2832	93
lnadal	0:05d4673b2832	94
lnadal	0:05d4673b2832	95
lnadal	0:05d4673b2832	96	int main() {
lnadal	0:05d4673b2832	97
lnadal	0:05d4673b2832	98	output = 0.0;
lnadal	0:05d4673b2832	99	lcd.cls();
lnadal	0:05d4673b2832	100
lnadal	0:05d4673b2832	101	text_screen(messages[0], 0, 0);
lnadal	0:05d4673b2832	102	text_screen(messages[1], 0, 1);
lnadal	0:05d4673b2832	103	wait(2);
lnadal	0:05d4673b2832	104
lnadal	0:05d4673b2832	105
lnadal	0:05d4673b2832	106
lnadal	0:05d4673b2832	107	for (int j = 0; j<4; j++){
lnadal	0:05d4673b2832	108
lnadal	0:05d4673b2832	109	lcd.cls(); // Heating sensor 4x16 = 64 seconds
lnadal	0:05d4673b2832	110	text_screen(messages[0], 0, 0);
lnadal	0:05d4673b2832	111
lnadal	0:05d4673b2832	112
lnadal	0:05d4673b2832	113	for (int i = 0; i<16; i++){
lnadal	0:05d4673b2832	114	if (pushbutton == 1){ // Pressing pushbutton stops initial heating and enters in measuring mode.
lnadal	0:05d4673b2832	115	break;
lnadal	0:05d4673b2832	116	}
lnadal	0:05d4673b2832	117	lcd.locate(i, 1);
lnadal	0:05d4673b2832	118	lcd.putc(62);
lnadal	0:05d4673b2832	119	wait(1);
lnadal	0:05d4673b2832	120	}
lnadal	0:05d4673b2832	121	}
lnadal	0:05d4673b2832	122
lnadal	0:05d4673b2832	123	lcd.cls();
lnadal	0:05d4673b2832	124	text_screen(messages[2], 0, 0);
lnadal	0:05d4673b2832	125	wait(2);
lnadal	0:05d4673b2832	126
lnadal	0:05d4673b2832	127
lnadal	0:05d4673b2832	128	AnalogIn value(p20); // Reads sensor voltage as a float int the interval (0-1) corresponding to (0 - 3.3V).
lnadal	0:05d4673b2832	129
lnadal	0:05d4673b2832	130
lnadal	0:05d4673b2832	131
lnadal	0:05d4673b2832	132	for (int i=0; i<5; i++){
lnadal	0:05d4673b2832	133
lnadal	0:05d4673b2832	134	x0[i] = value;
lnadal	0:05d4673b2832	135	wait(2);
lnadal	0:05d4673b2832	136
lnadal	0:05d4673b2832	137	}
lnadal	0:05d4673b2832	138	x_initial = (x0[0]+x0[1]+x0[2]+x0[3]+x0[4])/5.0; // Autozero. Average of 5 initial measures.
lnadal	0:05d4673b2832	139
lnadal	0:05d4673b2832	140	lcd.cls();
lnadal	0:05d4673b2832	141	text_screen(messages[3], 0, 0);
lnadal	0:05d4673b2832	142	wait(2);
lnadal	0:05d4673b2832	143
lnadal	0:05d4673b2832	144	while(1) {
lnadal	0:05d4673b2832	145	x = value;
lnadal	0:05d4673b2832	146	x = (x-x_initial)*3.3; // Calculate real voltage.
lnadal	0:05d4673b2832	147
lnadal	0:05d4673b2832	148	if(x<0) x = 0;
lnadal	0:05d4673b2832	149
lnadal	0:05d4673b2832	150	x = concentration(x);
lnadal	0:05d4673b2832	151
lnadal	0:05d4673b2832	152	output = x/3000; // If analog readings do not match digital readings you can adjust this value (1000 ppm = 1V).
lnadal	0:05d4673b2832	153
lnadal	0:05d4673b2832	154	wait(0.1);
lnadal	0:05d4673b2832	155
lnadal	0:05d4673b2832	156	// Float to string conversion.
lnadal	0:05d4673b2832	157	stringstream ss (stringstream::in \| stringstream::out);
lnadal	0:05d4673b2832	158	ss <<x;
lnadal	0:05d4673b2832	159	string reading = ss.str();
lnadal	0:05d4673b2832	160	L = reading.length();
lnadal	0:05d4673b2832	161
lnadal	0:05d4673b2832	162
lnadal	0:05d4673b2832	163	lcd.cls();
lnadal	0:05d4673b2832	164	for (int i=0; i<L; i+=1){
lnadal	0:05d4673b2832	165	lcd.locate(i,0);
lnadal	0:05d4673b2832	166	lcd.putc(reading[i]);
lnadal	0:05d4673b2832	167
lnadal	0:05d4673b2832	168
lnadal	0:05d4673b2832	169
lnadal	0:05d4673b2832	170	text_screen(messages[4], 10, 0);
lnadal	0:05d4673b2832	171	}
lnadal	0:05d4673b2832	172	wait(2);
lnadal	0:05d4673b2832	173	}
lnadal	0:05d4673b2832	174	}

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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@0:05d4673b2832, 2011-04-09 (annotated)

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