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MQ7-ESP.ino
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331
MQ7-ESP.ino
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/* sensor MQ7. alternate heater 5V/1.4V 60sec/90sec
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// read sensor @ 88sec(of 90-period)
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// Kn.Ny '16
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// This program to be used as CO-alarm in tents wintertime during night. (gasoline or firewood burners)
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// http://www.savvysolutions.info/savvymicrocontrollersolutions/arduino.php?topic=arduino-mq7-CO-gas-sensor
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// http://www.savvysolutions.info/savvymicrocontrollersolutions/index.php?sensor=mq-7-gas-sensors
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// ****************************************************************************************************/
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#define serial
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#define warnlevel 50 //CO ppm warnlevel
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#define continousMeasurement
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#define HeatOnPin D0
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#define Buzzer D5
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#define ADCOffset 3
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#define lotime 90000UL // 90 sek low heating
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#define hitime 60000UL // 60 sek high heating
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#define read_time 148000UL // read 2 sek ahead of end low period
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#define thresholdMeasurement 10 //ToDo
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/*
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struct for rtc memory
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*/
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struct {
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bool burnIn = false; //set to false in productive
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unsigned int minADC = 65535; //save minimal adc value
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byte ringPointer = 0;
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unsigned int adcRingBuf[thresholdMeasurement] = { 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 }; //ring buffer for ten values
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} rtcData;
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// Adjust vRef to be the true supply voltage in mV.
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const float vRef = 4470.0; //mVolt
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const float RL = 10.0; //kOhm
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const float CleanAirRatio = 26.09;
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float Rs = 0.0;
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float R0 = 0.0;
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float ambTemp = 20.0;
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float ambHum = 65.0;
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unsigned int measurement = 0;
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uint32_t calculateCRC32( const uint8_t *data, size_t length ) {
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uint32_t crc = 0xffffffff;
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while ( length-- ) {
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uint8_t c = *data++;
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for ( uint32_t i = 0x80; i > 0; i >>= 1 ) {
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bool bit = crc & 0x80000000;
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if ( c & i ) {
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bit = !bit;
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}
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crc <<= 1;
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if ( bit ) {
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crc ^= 0x04c11db7;
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}
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}
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}
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return crc;
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}
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void updateRTC() {
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//ToDo save rtcData
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//crc32 stuff
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}
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void getRTC() {
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//crc32 stuff
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//ToDo get rtcData
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}
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void saveMeasurement (unsigned int measurement) {
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rtcData.adcRingBuf[rtcData.ringPointer] = measurement;
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rtcData.ringPointer = (rtcData.ringPointer + 1) % thresholdMeasurement;
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}
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float CalcRsFromVRL(float VRL) {
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// VRL = RL voltage in mV.
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// vRef = supply voltage, 5000 mV
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// RL = load resistor in k ohms
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// The equation Rs = (Vc - Vo)*(RL/Vo)
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// is derived from the voltage divider
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// principle: Vo = RL * Vc (Rs + RL)
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//
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// Note. Alternatively you could calc
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// Rs from ADC value using
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// Rs = RL * (1024 - ADC) / ADC
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if ( VRL == 0.0 )
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{
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return vRef * VRL;
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}
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return ((vRef - VRL) * (RL / VRL));
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}
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float CalcRsFromADC(float ADC) {
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if ( ADC == 0 )
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{
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return 10240;
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}
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return (RL * (1024 - ADC) / ADC);
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}
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unsigned int GetCOPpmForRatioRsRo(float RsRo_ratio) {
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/*
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x=Rs/R0; y=ppm
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1,6122158133673148; 50,488950942143966
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0,999928961393748; 100
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0,39070475612941435; 396,4363929567069
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0,22807477512659288; 1000
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0,09483831585572762; 3964,363929567065
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y = 100.607 * (Rs/R0)^-1.54901
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this regression needs to be shifted by the CleanAirRatio.
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R0 = Rs/CleanAirRatio => Rs/R0 => Rs/(Rs_old/CleanAirRatio)
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*/
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float ppm = 0;
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ppm = 100.607 * pow( (RsRo_ratio * CleanAirRatio), -1.54901);
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return (unsigned int) ppm;
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}
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int measurementAnalog() {
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//measure x values and get the mean value
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static unsigned int x = 10;
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unsigned int valueADC = 0;
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for (unsigned int i = 0; i < x; i++) {
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valueADC += analogRead(A0);
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delay(10);
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}
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Serial.println("DEBUG: measurement ADC " + String(valueADC / x));
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return (valueADC / x);
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}
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void burnIn(bool trigger) {
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/*
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if not flag in eeprom set
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then burn in sensor
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*/
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unsigned int measureRow[thresholdMeasurement] = { 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 };
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int counter = 0;
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//set timer with the current milli counter
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unsigned long starttime = millis();
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unsigned long currenttime = millis();
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unsigned long static burnInTime = 172800000; //48 hours * 60 minutes * 60 seconds * 1000 milli
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Serial.println("DEBUG: burnIn");
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if ( !rtcData.burnIn ) {
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digitalWrite(HeatOnPin, HIGH); // => 5V
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while ( currenttime < burnInTime ) {
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delay(1000);
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currenttime = abs(millis() - starttime);
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Serial.print("\r" + String((int)((currenttime / 1000) / 360)) + ":" + String((int)((currenttime / 1000) / 60)) + ":" + String((int)((currenttime / 1000) % 60)) + "..");
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if (trigger) {
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unsigned int tmp = CalcRsFromADC(measurementAnalog());
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measureRow[counter] = tmp;
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counter = ( counter + 1 ) % thresholdMeasurement;
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Serial.println("BurnIn: Current RS from ADC " + String(tmp));
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//ToDo a value which means that the sensor is clean enough.
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//However the resistance drop in first sigth and stabilize then at a specific value, mine approx. 37k Ohm.
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/*if (tmp >= 36.0) {
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Serial.println("BurnIn: Trigger");
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break;
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}*/
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int sum = 0;
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for (int i = 0; i < thresholdMeasurement - 1; i++) {
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sum = sum + abs(measureRow[i] - measureRow[i + 1]);
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}
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Serial.println("DEBUG: Currentsum value " + String(sum));
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if (sum <= 0) {
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Serial.println("BurnIn: Stabilization");
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break;
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}
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}
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}
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//set initial lowest value
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rtcData.minADC = measurementAnalog();
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rtcData.burnIn = true;
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Serial.println("DEBUG BurnIn:\t" + String(currenttime / 1000) + " seconds| rtc.minADC" + String(rtcData.minADC) + " || RS " + String(CalcRsFromADC(rtcData.minADC)));
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}
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}
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/*
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a method to react to changing environmental parameters.
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ToDo: The values are NOT usuable!
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void compensateDriftOld() {
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if (Rs <= 20.0 && Rs > R0) {
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R0 = Rs;
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Serial.println("DEBUG: Drift compensate done. New R0:\t" + String(R0));
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return;
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}
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if ( Rs > 20.0) {
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Serial.println("DEBUG: Sensor needs cleaning!");
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burnIn(false);
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return;
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}
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}
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*/
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/*
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a method to react to changing environmental parameters.
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take the ADC values and calculate the summed up difference.
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renew the R0 if stabilizied ADc values in a row and the old R0 value needs to be smaller
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*/
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void compensateDrift() {
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int sum = 0;
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for (int i = 0; i < thresholdMeasurement - 1 ; i++) {
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sum = sum + (abs(rtcData.adcRingBuf[i] - rtcData.adcRingBuf[i + 1]));
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}
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if (R0 > Rs && sum <= 1) {
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R0 = Rs;
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Serial.println("DEBUG: Drift compensate done. New R0:\t" + String(R0));
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return;
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}
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//check for lowest resistence after heating
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if ( rtcData.adcRingBuf[rtcData.ringPointer] > rtcData.minADC) {
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Serial.println("DEBUG: Sensor needs cleaning!");
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burnIn(false);
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return;
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}
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}
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int measurementCycle() {
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//set timer with the current milli counter
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unsigned long starttime = millis();
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unsigned long currenttime = 0;
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static unsigned long next_time = hitime + lotime; //set complete runtime for one measurement
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unsigned int currentMeasurement, lastMeasurement = 0;
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boolean done_reading = true; //only a simple toggle switch
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//start cleaning sensitive part of sensor
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Serial.println("-------------------------------------------------------------");
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digitalWrite(HeatOnPin, HIGH); // => 5V
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Serial.print("5V:\t on");
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while (currenttime < next_time) {
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//refresh current time
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currenttime = abs(millis() - starttime);
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#ifndef continousMeasurement
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lastMeasurement = currentMeasurement;
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currentMeasurement = measurementAnalog();
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if (thresholdMeasurement > abs(lastMeasurement - currentMeasurement) ) {
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delay(10);
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}
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if (done_reading && currenttime >= hitime) //sensor reach heating time limit
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{
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digitalWrite(HeatOnPin, LOW); // => 1.4V
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Serial.print("\n\r1.4V:\t on\n");
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done_reading = false;
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}
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if (currenttime >= next_time ) {
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break;
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}
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#else
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if (done_reading && currenttime >= hitime) //sensor reach heating time limit
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{
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digitalWrite(HeatOnPin, LOW); // => 1.4V
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Serial.print("\n\r1.4V:\t on\n");
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done_reading = false;
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}
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if (currenttime > read_time) // then do a reading now
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{
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currentMeasurement = measurementAnalog();
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done_reading = true;
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break;
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//add nynquist thereom and sums up multiple measurements
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}
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delay(50);
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#endif
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}
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return currentMeasurement;
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}
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void calibrateCleanAir() {
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Serial.println("DEBUG: calibrate Clean AIR");
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//wait until sensor reach low end resistance
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unsigned int i = 0;
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while ( true ) {
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i++;
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Rs = CalcRsFromADC(measurementCycle());
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Serial.println("Calibrate Clean Air:\t#" + String(i) + "\tRs: \t" + String(Rs));
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/*
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At least three measurements to settle down the sensor
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ToDo : the datasheet mentions that the Rs is between 2k and 20k for 100ppm in air. Therefore the values multiplies with the clean_air_ratio of 26.09
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That leads to a range: 5,2MOhm up to 52,2MOhm which is not in any reach of the real world (17.06.18: current value is ADC 2 up to 3, which is 3403 or 5110 Ohm.
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the resistance get lower with higher CO measurements.
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I guess the maximum value of 20k for 100ppm in air (a cold sensor has Rs = 330k)
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*/
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//if (i >= 3 && Rs <= 20.0) {
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if (i >= 3 && Rs >= 3000.0) {
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//Serial.println ("Rs <= 20.0");
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Serial.println ("Rs >= 3000.0");
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break;
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}
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}
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R0 = Rs;
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Serial.println("R0: \t" + String(R0));
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}
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void ambientMeasurement() {
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}
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float correlateAmbient() {
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return 1.0;
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}
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// the setup routine runs once when you press reset:
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void setup() {
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// initialize serial communication at 115200 bits per second:
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Serial.begin(115200);
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pinMode(HeatOnPin, OUTPUT);
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burnIn(true);
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calibrateCleanAir();
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}
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void loop() {
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float ppm = 0;
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//save adc data
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saveMeasurement(measurementCycle());
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Rs = CalcRsFromADC(rtcData.adcRingBuf[rtcData.ringPointer]);
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Serial.println("Rs: \t" + String(Rs) + " | R0:\t" + String(R0) + " || Ratio:\t" + String(Rs / R0) + "| Ratio:\t" + String(Rs / R0 * CleanAirRatio) );
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ppm = GetCOPpmForRatioRsRo(Rs / R0);
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Serial.println("CO ppm: \t" + String(ppm));
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compensateDrift();
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}
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63
README:md
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63
README:md
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@ -0,0 +1,63 @@
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CO Sensor
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-10.12.17: MQ-7 Sensor, Stecksockel + Platine bestellt
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Aufbau mit wemos D1 mini und Dual Board
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-ggf Temperatur/Luftfeuchte Korrektur
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Brauche Datasheet sowie Berechnung der Kurven
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Low Heat bei bestimmten Umgebungswerten wegen Zerstörungsgefahr durch Wasser
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SHT30 Shield (Pin D1 und D2), genauer und einfach anzusteuern
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-Entscheidung über OLED oder RGB LED
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OLED Display wird ebenfalls über I2C angesteuert (Pin D1 und D2)
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-Lokaler Alarm
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Buzzer Board (Pin D5)
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-globaler Alarm
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mqtt/ESP Now
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-Spannungsversorgung über NPN --geht da 0,7V Drop --> N-MOSFET https://arduinodiy.wordpress.com/2012/05/02/using-mosfets-with-ttl-levels/
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IRLML6344 bestellt
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-Kalibrierung?
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Zwei Möglichkeiten, entweder Clean Air Kalibrierung oder 100ppm Wert + Messgerät
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ESP8266 Speichern der Kalibrierung im RTC
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-Austausch des Sensors?
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Platine enthält Pinlöcher für den Sensor sowie den Sockel
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-Spannungsteiler für Ausgangsspannung MQ7
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Zusätzlicher Ausgang plus Spannungsteiler für 1V (ESP8266)
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560k/150k -> 1.056V --> Kondensator benötigt? http://esp8266-projects.org/2016/08/esp8266-internal-adc-2-the-easy-way-example/
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3k/820 -> 1.073V --> ggf. zu gering
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Spannungsteiler für Wemos Board nicht notwendig -> 150kOhm in Reihe zum eingebauten (110k/220k) Spannungsteiler
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ggf. Kondensator für den Spannungsteiler
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-Regressionsgerade bestimmen
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http://davidegironi.blogspot.de/2017/07/mq-gas-sensor-correlation-function.html
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http://davidegironi.blogspot.de/2017/05/mq-gas-sensor-correlation-function.html
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Achsen sind vertauscht sinnvoller
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beide Skalen logarithmisch
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mittels: https://apps.automeris.io/wpd/ die punkte bestimmen
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power-regresseion berechnen: http://keisan.casio.com/exec/system/14059931777261
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Min/Max bestimmen
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Platine muss angepasst werden
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https://forum.arduino.cc/index.php?topic=294085.0
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http://www.instructables.com/id/Arduino-CO-Monitor-Using-MQ-7-Sensor/
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http://www.savvysolutions.info/savvymicrocontrollersolutions/index.php?sensor=mq-7-gas-sensors
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http://www.savvysolutions.info/savvymicrocontrollersolutions/arduino.php?topic=arduino-mq7-CO-gas-sensor
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Ablauf:
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Init System
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BurnIn Werte prüfen
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Falls nicht vorhanden, BurnIn beginnen
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Umgebungswerte messen
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Prüfen ob Betrieb von Sensor sicher ist ( insbesondere Wasser)
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Preheat nutzen
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Clean Air Kalibrierung durchführen
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BurnIn Werte korrelieren
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Nyquist-Theorem einhalten
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Vergleich mit vorherigen Werten im EEPROM auf Abweichung
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Warnung bei zu großen Abweichungen, Hinweis auf Alterung
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Übergang zum Regelbetrieb
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Messwertreihe vorhalten
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Zu schnelle Wertänderungen lösen Warnung aus
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Zu hoher Wert löst Warnung aus
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Meldung an übergeordnete Instanz bei Warnung
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