Add example for SCD40 FRC

Author: Fototux

SCD40_I2C_FRC_Forced_Recalibration_Example/SCD40_I2C_FRC_Forced_Recalibration_Example.ino

@@ -0,0 +1,216 @@
+/*
+ * Copyright (c) 2020, Sensirion AG
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * * Redistributions of source code must retain the above copyright notice, this
+ *   list of conditions and the following disclaimer.
+ *
+ * * Redistributions in binary form must reproduce the above copyright notice,
+ *   this list of conditions and the following disclaimer in the documentation
+ *   and/or other materials provided with the distribution.
+ *
+ * * Neither the name of Sensirion AG nor the names of its
+ *   contributors may be used to endorse or promote products derived from
+ *   this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
+ * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+ * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+ * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+ * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include <Wire.h>
+
+// SCD40
+const int16_t SCD_ADDRESS = 0x62;
+
+void setup() {
+  float co2, temperature, humidity;
+  uint16_t calibration;
+  uint8_t data[12], counter, repetition;
+  uint8_t ret;
+  
+  Serial.begin(115200);
+  // wait for serial connection from PC
+  // comment the following line if you'd like the output
+  // without waiting for the interface being ready
+  while(!Serial);
+  
+  // init I2C
+  Wire.begin();
+
+  // wait until sensors are ready, > 1000 ms according to datasheet
+  delay(1000);
+  
+  // start scd measurement in periodic mode, will update every 2 s
+  Wire.beginTransmission(SCD_ADDRESS);
+  Wire.write(0x21);
+  Wire.write(0xb1);
+  Wire.endTransmission();
+
+  // wait for first measurement to be finished
+  delay(2000);
+
+  Serial.println("# CO2 values before recalibration");
+
+  // measure 5 times 
+  for(repetition = 0; repetition < 5; repetition++) {
+    // read measurement data: 2 bytes co2, 1 byte CRC,
+    // 2 bytes T, 1 byte CRC, 2 bytes RH, 1 byte CRC,
+    // 2 bytes sensor status, 1 byte CRC
+    // stop reading after 12 bytes (not used)
+    // other data like  ASC not included
+    Wire.requestFrom(SCD_ADDRESS, 12);
+    counter = 0;
+    while (Wire.available()) {
+      data[counter++] = Wire.read();
+    }
+    
+    // floating point conversion according to datasheet
+    co2 = (float)((uint16_t)data[0] << 8 | data[1]);
+    // convert T in degC
+    temperature = -45 + 175 * (float)((uint16_t)data[3] << 8 | data[4]) / 65536;
+    // convert RH in %
+    humidity = 100 * (float)((uint16_t)data[6] << 8 | data[7]) / 65536;
+  
+    Serial.print("# ");
+    Serial.print(co2);
+    Serial.print("\t");
+    Serial.print(temperature);
+    Serial.print("\t");
+    Serial.print(humidity);
+    Serial.println();
+
+    delay(2000);
+  }
+  
+  // wait for another 5 minutes to equilibrate sensor to ambient
+  Serial.println("# Waiting 5 minutes for equilibration");
+  //delay(5 * 60 * 1000);
+
+  // stop scd measurement
+  Wire.beginTransmission(SCD_ADDRESS);
+  Wire.write(0x3f);
+  Wire.write(0x86);
+  ret = Wire.endTransmission();
+  Serial.println(ret);
+
+
+  // wait for sensor
+  //delay(20);
+
+  // assuming an external reference shows 350 ppm
+  calibration = 650;
+  
+  // prepare buffer with data for calibration
+  // calculate CRC for each 2 bytes of data
+  data[0] = (calibration & 0xff00) >> 8;
+  data[1] = calibration & 0x00ff;
+  data[2] = CalcCrc(data);
+  
+  // send command for perform_forced_recalibration
+  Wire.beginTransmission(SCD_ADDRESS);
+  Wire.write(0x36);
+  Wire.write(0x2F);
+  // append data for calibration
+  // 2 bytes calibraion, CRC
+  Wire.write(data[0]);
+  Wire.write(data[1]);
+  Wire.write(data[2]);
+  ret = Wire.endTransmission();
+  Serial.println(ret);
+
+  delay(400);
+  
+  // read data: 2 bytes correction, 1 byte CRC
+  Wire.requestFrom(SCD_ADDRESS, 3);
+  counter = 0;
+  while (Wire.available()) {
+    data[counter++] = Wire.read();
+  }
+
+  if(CalcCrc(data) != data[2])
+    Serial.println("# ERROR: recalibration CRC return value");
+  
+  calibration = ((uint16_t)data[0] << 8 | data[1]);
+  
+  Serial.print("# Value after recalibration\n# ");
+  Serial.println(calibration-32768);
+
+  // output format
+  Serial.println("CO2(ppm)\tTemperature(degC)\tRelativeHumidity(percent)");
+
+  // start scd measurement again in periodic mode, will update every 2 s
+  Wire.beginTransmission(SCD_ADDRESS);
+  Wire.write(0x21);
+  Wire.write(0xb1);
+  Wire.endTransmission();
+
+  // wait for first measurement to be finished
+  delay(4000);
+}
+
+void loop() {
+  float co2, temperature, humidity;
+  uint8_t data[12], counter;
+
+  // send read data command
+  Wire.beginTransmission(SCD_ADDRESS);
+  Wire.write(0xec);
+  Wire.write(0x05);
+  Wire.endTransmission();
+  
+  // read measurement data: 2 bytes co2, 1 byte CRC,
+  // 2 bytes T, 1 byte CRC, 2 bytes RH, 1 byte CRC,
+  // 2 bytes sensor status, 1 byte CRC
+  // stop reading after 12 bytes (not used)
+  // other data like  ASC not included
+  Wire.requestFrom(SCD_ADDRESS, 12);
+  counter = 0;
+  while (Wire.available()) {
+    data[counter++] = Wire.read();
+  }
+  
+  // floating point conversion according to datasheet
+  co2 = (float)((uint16_t)data[0] << 8 | data[1]);
+  // convert T in degC
+  temperature = -45 + 175 * (float)((uint16_t)data[3] << 8 | data[4]) / 65536;
+  // convert RH in %
+  humidity = 100 * (float)((uint16_t)data[6] << 8 | data[7]) / 65536;
+
+  Serial.print(co2);
+  Serial.print("\t");
+  Serial.print(temperature);
+  Serial.print("\t");
+  Serial.print(humidity);
+  Serial.println();
+
+  // wait 2 s for next measurement
+  delay(2000);
+}
+
+// calculate CRC according to datasheet section 5.17
+uint8_t CalcCrc(uint8_t data[2]) {
+  uint8_t crc = 0xFF;
+  for(int i = 0; i < 2; i++) {
+    crc ^= data[i];
+    for(uint8_t bit = 8; bit > 0; --bit) {
+      if(crc & 0x80) {
+        crc = (crc << 1) ^ 0x31u;
+      } else {
+        crc = (crc << 1);
+      }
+    }
+  }
+  return crc;
+}