MH-Z-CO2-Sensors/MHZ.cpp

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/* MHZ library
By Tobias Schürg
*/
#include "MHZ.h"
MHZ:: MHZ(uint8_t rxpin, uint8_t txpin, uint8_t pwmpin, uint8_t type)
: co2Serial(rxpin, txpin)
{
_rxpin = rxpin;
_txpin = txpin;
_pwmpin = pwmpin;
_type = type;
co2Serial.begin(9600);
}
void MHZ::setDebug(boolean enable) {
debug = enable;
if (debug) {
Serial.println("MHZ: debug mode ENABLED");
} else {
Serial.println("MHZ: debug mode DISABLED");
}
}
int retryCount = 0;
int MHZ::readCO2UART() {
if (debug) Serial.println("-- read CO2 uart ---");
byte cmd[9] = {0xFF, 0x01, 0x86, 0x00, 0x00, 0x00, 0x00, 0x00, 0x79};
byte response[9]; // for answer
if (debug) Serial.print(" >> Sending CO2 request");
co2Serial.write(cmd, 9); //request PPM CO2
// clear the buffer
memset(response, 0, 9);
int waited = 0;
while (co2Serial.available() == 0) {
if (debug) Serial.print(".");
delay(100); // wait a short moment to avoid false reading
if(waited++ > 10) {
if (debug) Serial.println("No response after 10 seconds");
co2Serial.flush();
return STATUS_NO_RESPONSE;
}
}
if (debug) Serial.println();
// The serial stream can get out of sync. The response starts with 0xff, try to resync.
// TODO: I think this might be wrong any only happens during initialization?
boolean skip = false;
while (co2Serial.available() > 0 && (unsigned char)co2Serial.peek() != 0xFF)
{
if (!skip) {
Serial.print("MHZ: - skipping unexpected readings:");
skip = true;
}
Serial.print(" ");
Serial.print(co2Serial.peek(), HEX);
co2Serial.read();
}
if (skip) Serial.println();
if (co2Serial.available() > 0) {
int count = co2Serial.readBytes(response, 9);
if (count <9) {
co2Serial.flush();
return STATUS_INCOMPLETE;
}
} else {
co2Serial.flush();
return STATUS_INCOMPLETE;
}
if (debug) {
// print out the response in hexa
Serial.print(" << ");
for (int i = 0; i < 9; i++) {
Serial.print(response[i], HEX);
Serial.print(" ");
}
Serial.println("");
}
// checksum
byte check = getCheckSum(response);
if (response[8] != check) {
Serial.println("MHZ: Checksum not OK!");
Serial.print("MHZ: Received: ");
Serial.println(response[8], HEX);
Serial.print("MHZ: Should be: ");
Serial.println(check, HEX);
temperature = STATUS_CHECKSUM_MISMATCH;
co2Serial.flush();
return STATUS_CHECKSUM_MISMATCH;
}
int ppm_uart = 256 * (int)response[2] + response[3];
temperature = response[4] - 44; // - 40;
byte status = response[5];
if (debug) {
Serial.print(" # PPM UART: ");
Serial.println(ppm_uart);
Serial.print(" # Temperature? ");
Serial.println(temperature);
}
// Is always 0 for version 14a and 19b
// Version a?: status != 0x40
if (debug || status != 0) {
Serial.print(" ! Status maybe not OK ! ");
Serial.println(status, HEX);
} else if (debug) {
Serial.print(" Status OK: ");
Serial.println(status, HEX);
}
// co2Serial.flush();
return ppm_uart;
}
uint8_t MHZ::getLastTemperature() {
return temperature;
}
byte MHZ::getCheckSum(byte *packet) {
if (debug) Serial.println(" getCheckSum()");
byte i;
unsigned char checksum = 0;
for (i = 1; i < 8; i++) {
checksum += packet[i];
}
checksum = 0xff - checksum;
checksum += 1;
return checksum;
}
int MHZ::readCO2PWM() {
if (debug) Serial.print("-- reading CO2 from pwm ");
unsigned long th, tl, ppm_pwm = 0;
do {
if (debug) Serial.print(".");
th = pulseIn(_pwmpin, HIGH, 1004000) / 1000;
tl = 1004 - th;
ppm_pwm = 5000 * (th - 2) / (th + tl - 4);
} while (th == 0);
if (debug) {
Serial.print("\n # PPM PWM: ");
Serial.println(ppm_pwm);
}
return ppm_pwm;
}