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+                    GNU GENERAL PUBLIC LICENSE
+                       Version 3, 29 June 2007
+
+ Copyright (C) 2007 Free Software Foundation, Inc. <https://fsf.org/>
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+THE PROGRAM AS PERMITTED ABOVE, BE LIABLE TO YOU FOR DAMAGES, INCLUDING ANY
+GENERAL, SPECIAL, INCIDENTAL OR CONSEQUENTIAL DAMAGES ARISING OUT OF THE
+USE OR INABILITY TO USE THE PROGRAM (INCLUDING BUT NOT LIMITED TO LOSS OF
+DATA OR DATA BEING RENDERED INACCURATE OR LOSSES SUSTAINED BY YOU OR THIRD
+PARTIES OR A FAILURE OF THE PROGRAM TO OPERATE WITH ANY OTHER PROGRAMS),
+EVEN IF SUCH HOLDER OR OTHER PARTY HAS BEEN ADVISED OF THE POSSIBILITY OF
+SUCH DAMAGES.
+
+  17. Interpretation of Sections 15 and 16.
+
+  If the disclaimer of warranty and limitation of liability provided
+above cannot be given local legal effect according to their terms,
+reviewing courts shall apply local law that most closely approximates
+an absolute waiver of all civil liability in connection with the
+Program, unless a warranty or assumption of liability accompanies a
+copy of the Program in return for a fee.
+
+                     END OF TERMS AND CONDITIONS
+
+            How to Apply These Terms to Your New Programs
+
+  If you develop a new program, and you want it to be of the greatest
+possible use to the public, the best way to achieve this is to make it
+free software which everyone can redistribute and change under these terms.
+
+  To do so, attach the following notices to the program.  It is safest
+to attach them to the start of each source file to most effectively
+state the exclusion of warranty; and each file should have at least
+the "copyright" line and a pointer to where the full notice is found.
+
+    <one line to give the program's name and a brief idea of what it does.>
+    Copyright (C) <year>  <name of author>
+
+    This program is free software: you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with this program.  If not, see <https://www.gnu.org/licenses/>.
+
+Also add information on how to contact you by electronic and paper mail.
+
+  If the program does terminal interaction, make it output a short
+notice like this when it starts in an interactive mode:
+
+    <program>  Copyright (C) <year>  <name of author>
+    This program comes with ABSOLUTELY NO WARRANTY; for details type `show w'.
+    This is free software, and you are welcome to redistribute it
+    under certain conditions; type `show c' for details.
+
+The hypothetical commands `show w' and `show c' should show the appropriate
+parts of the General Public License.  Of course, your program's commands
+might be different; for a GUI interface, you would use an "about box".
+
+  You should also get your employer (if you work as a programmer) or school,
+if any, to sign a "copyright disclaimer" for the program, if necessary.
+For more information on this, and how to apply and follow the GNU GPL, see
+<https://www.gnu.org/licenses/>.
+
+  The GNU General Public License does not permit incorporating your program
+into proprietary programs.  If your program is a subroutine library, you
+may consider it more useful to permit linking proprietary applications with
+the library.  If this is what you want to do, use the GNU Lesser General
+Public License instead of this License.  But first, please read
+<https://www.gnu.org/licenses/why-not-lgpl.html>.

README.md

@@ -0,0 +1 @@
+For more information please visit www.bylund-automotive.com.

lambda_sensor.code-workspace

@@ -0,0 +1,12 @@
+{
+	"folders": [
+		{
+			"path": "."
+		},
+		{
+			"name": "lambda_sensor",
+			"path": "lambda_sensor"
+		}
+	],
+	"settings": {}
+}

platformio.ini

@@ -0,0 +1,20 @@
+; PlatformIO Project Configuration File
+;
+;   Build options: build flags, source filter
+;   Upload options: custom upload port, speed and extra flags
+;   Library options: dependencies, extra library storages
+;   Advanced options: extra scripting
+;
+; Please visit documentation for the other options and examples
+; https://docs.platformio.org/page/projectconf.html
+
+[env:uno_wifi_rev2]
+platform = atmelmegaavr
+board = uno_wifi_rev2
+framework = arduino
+lib_deps =
+
+     # RECOMMENDED
+     # Accept new functionality in a backwards compatible manner and patches
+     arduino-libraries/ArduinoBLE @ ^1.2.1
+     https://git.sweproj.com/IHOLL/EasyNextionLibrary.git#master

src/main.cpp

@@ -0,0 +1,495 @@
+/*
+    Example code compatible with the Lambda Shield 2 for Arduino Uno WiFi Rev 2 and smartphone apps.
+    
+    Copyright (C) 2020 Bylund Automotive AB
+    
+    This program is free software: you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+    
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+    
+    You should have received a copy of the GNU General Public License
+    along with this program.  If not, see <http://www.gnu.org/licenses/>.
+    
+    Contact information of author:
+    http://www.bylund-automotive.com/
+    
+    info@bylund-automotive.com
+    
+    Version history:
+    2020-04-13        v1.0.0        First release.
+    2020-05-01        v1.0.1        Bug fixes.
+
+*/
+
+//Define included headers.
+#include <ArduinoBLE.h>
+#include <SPI.h>
+
+//Define BLE service.
+BLEService LambdaService("C664F3C0-81B3-4E7B-A2F6-EA96181A2E71");
+BLEUnsignedCharCharacteristic OxygenLevelChar("C83C027E-F105-4E0D-AA8F-801AC553D5C1", BLERead | BLENotify);
+
+//Define CJ125 registers used.
+#define           CJ125_IDENT_REG_REQUEST             0x4800        /* Identify request, gives revision of the chip. */
+#define           CJ125_DIAG_REG_REQUEST              0x7800        /* Dignostic request, gives the current status. */
+#define           CJ125_INIT_REG1_REQUEST             0x6C00        /* Requests the first init register. */
+#define           CJ125_INIT_REG2_REQUEST             0x7E00        /* Requests the second init register. */
+#define           CJ125_INIT_REG1_MODE_CALIBRATE      0x569D        /* Sets the first init register in calibration mode. */
+#define           CJ125_INIT_REG1_MODE_NORMAL_V8      0x5688        /* Sets the first init register in operation mode. V=8 amplification. */
+#define           CJ125_INIT_REG1_MODE_NORMAL_V17     0x5689        /* Sets the first init register in operation mode. V=17 amplification. */
+#define           CJ125_DIAG_REG_STATUS_OK            0x28FF        /* The response of the diagnostic register when everything is ok. */
+#define           CJ125_DIAG_REG_STATUS_NOPOWER       0x2855        /* The response of the diagnostic register when power is low. */
+#define           CJ125_DIAG_REG_STATUS_NOSENSOR      0x287F        /* The response of the diagnostic register when no sensor is connected. */
+#define           CJ125_INIT_REG1_STATUS_0            0x2888        /* The response of the init register when V=8 amplification is in use. */
+#define           CJ125_INIT_REG1_STATUS_1            0x2889        /* The response of the init register when V=17 amplification is in use. */
+
+//Define pin assignments.
+#define           LED_STATUS_POWER                    7             /* Pin used for power the status LED, indicating we have power. */
+#define           LED_STATUS_HEATER                   6             /* Pin used for the heater status LED, indicating heater activity. */
+#define           CJ125_NSS_PIN                       10            /* Pin used for chip select in SPI communication. */
+#define           HEATER_OUTPUT_PIN                   5             /* Pin used for the PWM output to the heater circuit. */
+#define           UB_ANALOG_INPUT_PIN                 2             /* Analog input for power supply.*/
+#define           UR_ANALOG_INPUT_PIN                 1             /* Analog input for temperature.*/
+#define           UA_ANALOG_INPUT_PIN                 0             /* Analog input for lambda.*/
+
+//Define adjustable parameters.            
+#define           UBAT_MIN                            150           /* Minimum voltage (ADC value) on Ubat to operate */
+#define           hardwareId                          0x01          /* The hardwareId defines which hardware you are using. */
+#define           SERIAL_RATE                         10            /* Serial refresh rate in HZ (1-100)*/            
+
+//Global variables.
+int adcValue_UA = 0;                                                /* ADC value read from the CJ125 UA output pin */ 
+int adcValue_UR = 0;                                                /* ADC value read from the CJ125 UR output pin */
+int adcValue_UB = 0;                                                /* ADC value read from the voltage divider caluclating Ubat */
+int adcValue_UA_Optimal = 0;                                        /* UA ADC value stored when CJ125 is in calibration mode, λ=1 */ 
+int adcValue_UR_Optimal = 0;                                        /* UR ADC value stored when CJ125 is in calibration mode, optimal temperature */
+int HeaterOutput = 0;                                               /* Current PWM output value (0-255) of the heater output pin */
+int CJ125_Status = 0;                                               /* Latest stored DIAG registry response from the CJ125 */
+int HeaterStatus = 0;                                               /* Defines the heater status for the GUI front-end */
+
+
+//PID regulation variables.
+int dState;                                                         /* Last position input. */
+int iState;                                                         /* Integrator state. */
+const int iMax = 250;                                               /* Maximum allowable integrator state. */
+const int iMin = -250;                                              /* Minimum allowable integrator state. */
+const float pGain = 120;                                            /* Proportional gain. Default = 120*/
+const float iGain = 0.8;                                            /* Integral gain. Default = 0.8*/
+const float dGain = 10;                                             /* Derivative gain. Default = 10*/
+int serial_counter = 0;
+//Lambda Conversion Lookup Table. (ADC 39-791).
+const PROGMEM float Lambda_Conversion[753] {
+  0.750, 0.751, 0.752, 0.752, 0.753, 0.754, 0.755, 0.755, 0.756, 0.757, 0.758, 0.758, 0.759, 0.760, 0.761, 0.761, 0.762, 0.763, 0.764, 0.764,
+  0.765, 0.766, 0.766, 0.767, 0.768, 0.769, 0.769, 0.770, 0.771, 0.772, 0.772, 0.773, 0.774, 0.774, 0.775, 0.776, 0.777, 0.777, 0.778, 0.779,
+  0.780, 0.780, 0.781, 0.782, 0.782, 0.783, 0.784, 0.785, 0.785, 0.786, 0.787, 0.787, 0.788, 0.789, 0.790, 0.790, 0.791, 0.792, 0.793, 0.793,
+  0.794, 0.795, 0.796, 0.796, 0.797, 0.798, 0.799, 0.799, 0.800, 0.801, 0.802, 0.802, 0.803, 0.804, 0.805, 0.805, 0.806, 0.807, 0.808, 0.808,
+  0.809, 0.810, 0.811, 0.811, 0.812, 0.813, 0.814, 0.815, 0.815, 0.816, 0.817, 0.818, 0.819, 0.820, 0.820, 0.821, 0.822, 0.823, 0.824, 0.825,
+  0.825, 0.826, 0.827, 0.828, 0.829, 0.830, 0.830, 0.831, 0.832, 0.833, 0.834, 0.835, 0.836, 0.837, 0.837, 0.838, 0.839, 0.840, 0.841, 0.842,
+  0.843, 0.844, 0.845, 0.846, 0.846, 0.847, 0.848, 0.849, 0.850, 0.851, 0.852, 0.853, 0.854, 0.855, 0.855, 0.856, 0.857, 0.858, 0.859, 0.860,
+  0.861, 0.862, 0.863, 0.864, 0.865, 0.865, 0.866, 0.867, 0.868, 0.869, 0.870, 0.871, 0.872, 0.873, 0.874, 0.875, 0.876, 0.877, 0.878, 0.878,
+  0.879, 0.880, 0.881, 0.882, 0.883, 0.884, 0.885, 0.886, 0.887, 0.888, 0.889, 0.890, 0.891, 0.892, 0.893, 0.894, 0.895, 0.896, 0.897, 0.898,
+  0.899, 0.900, 0.901, 0.902, 0.903, 0.904, 0.905, 0.906, 0.907, 0.908, 0.909, 0.910, 0.911, 0.912, 0.913, 0.915, 0.916, 0.917, 0.918, 0.919,
+  0.920, 0.921, 0.922, 0.923, 0.924, 0.925, 0.926, 0.927, 0.928, 0.929, 0.931, 0.932, 0.933, 0.934, 0.935, 0.936, 0.937, 0.938, 0.939, 0.940,
+  0.941, 0.942, 0.944, 0.945, 0.946, 0.947, 0.948, 0.949, 0.950, 0.951, 0.952, 0.953, 0.954, 0.955, 0.957, 0.958, 0.959, 0.960, 0.961, 0.962,
+  0.963, 0.965, 0.966, 0.967, 0.969, 0.970, 0.971, 0.973, 0.974, 0.976, 0.977, 0.979, 0.980, 0.982, 0.983, 0.985, 0.986, 0.987, 0.989, 0.990,
+  0.991, 0.992, 0.994, 0.995, 0.996, 0.998, 0.999, 1.001, 1.003, 1.005, 1.008, 1.010, 1.012, 1.015, 1.017, 1.019, 1.022, 1.024, 1.026, 1.028,
+  1.030, 1.032, 1.035, 1.037, 1.039, 1.041, 1.043, 1.045, 1.048, 1.050, 1.052, 1.055, 1.057, 1.060, 1.062, 1.064, 1.067, 1.069, 1.072, 1.075,
+  1.077, 1.080, 1.082, 1.085, 1.087, 1.090, 1.092, 1.095, 1.098, 1.100, 1.102, 1.105, 1.107, 1.110, 1.112, 1.115, 1.117, 1.120, 1.122, 1.124,
+  1.127, 1.129, 1.132, 1.135, 1.137, 1.140, 1.142, 1.145, 1.148, 1.151, 1.153, 1.156, 1.159, 1.162, 1.165, 1.167, 1.170, 1.173, 1.176, 1.179,
+  1.182, 1.185, 1.188, 1.191, 1.194, 1.197, 1.200, 1.203, 1.206, 1.209, 1.212, 1.215, 1.218, 1.221, 1.224, 1.227, 1.230, 1.234, 1.237, 1.240,
+  1.243, 1.246, 1.250, 1.253, 1.256, 1.259, 1.262, 1.266, 1.269, 1.272, 1.276, 1.279, 1.282, 1.286, 1.289, 1.292, 1.296, 1.299, 1.303, 1.306,
+  1.310, 1.313, 1.317, 1.320, 1.324, 1.327, 1.331, 1.334, 1.338, 1.342, 1.345, 1.349, 1.352, 1.356, 1.360, 1.364, 1.367, 1.371, 1.375, 1.379,
+  1.382, 1.386, 1.390, 1.394, 1.398, 1.401, 1.405, 1.409, 1.413, 1.417, 1.421, 1.425, 1.429, 1.433, 1.437, 1.441, 1.445, 1.449, 1.453, 1.457,
+  1.462, 1.466, 1.470, 1.474, 1.478, 1.483, 1.487, 1.491, 1.495, 1.500, 1.504, 1.508, 1.513, 1.517, 1.522, 1.526, 1.531, 1.535, 1.540, 1.544,
+  1.549, 1.554, 1.558, 1.563, 1.568, 1.572, 1.577, 1.582, 1.587, 1.592, 1.597, 1.601, 1.606, 1.611, 1.616, 1.621, 1.627, 1.632, 1.637, 1.642,
+  1.647, 1.652, 1.658, 1.663, 1.668, 1.674, 1.679, 1.684, 1.690, 1.695, 1.701, 1.707, 1.712, 1.718, 1.724, 1.729, 1.735, 1.741, 1.747, 1.753,
+  1.759, 1.764, 1.770, 1.776, 1.783, 1.789, 1.795, 1.801, 1.807, 1.813, 1.820, 1.826, 1.832, 1.839, 1.845, 1.852, 1.858, 1.865, 1.872, 1.878,
+  1.885, 1.892, 1.898, 1.905, 1.912, 1.919, 1.926, 1.933, 1.940, 1.947, 1.954, 1.961, 1.968, 1.975, 1.983, 1.990, 1.997, 2.005, 2.012, 2.020,
+  2.027, 2.035, 2.042, 2.050, 2.058, 2.065, 2.073, 2.081, 2.089, 2.097, 2.105, 2.113, 2.121, 2.129, 2.137, 2.145, 2.154, 2.162, 2.171, 2.179,
+  2.188, 2.196, 2.205, 2.214, 2.222, 2.231, 2.240, 2.249, 2.258, 2.268, 2.277, 2.286, 2.295, 2.305, 2.314, 2.324, 2.333, 2.343, 2.353, 2.363,
+  2.373, 2.383, 2.393, 2.403, 2.413, 2.424, 2.434, 2.444, 2.455, 2.466, 2.476, 2.487, 2.498, 2.509, 2.520, 2.532, 2.543, 2.554, 2.566, 2.577,
+  2.589, 2.601, 2.613, 2.625, 2.637, 2.649, 2.662, 2.674, 2.687, 2.699, 2.712, 2.725, 2.738, 2.751, 2.764, 2.778, 2.791, 2.805, 2.819, 2.833,
+  2.847, 2.861, 2.875, 2.890, 2.904, 2.919, 2.934, 2.949, 2.964, 2.979, 2.995, 3.010, 3.026, 3.042, 3.058, 3.074, 3.091, 3.107, 3.124, 3.141,
+  3.158, 3.175, 3.192, 3.209, 3.227, 3.245, 3.263, 3.281, 3.299, 3.318, 3.337, 3.355, 3.374, 3.394, 3.413, 3.433, 3.452, 3.472, 3.492, 3.513,
+  3.533, 3.554, 3.575, 3.597, 3.618, 3.640, 3.662, 3.684, 3.707, 3.730, 3.753, 3.776, 3.800, 3.824, 3.849, 3.873, 3.898, 3.924, 3.950, 3.976,
+  4.002, 4.029, 4.056, 4.084, 4.112, 4.140, 4.169, 4.198, 4.228, 4.258, 4.288, 4.319, 4.350, 4.382, 4.414, 4.447, 4.480, 4.514, 4.548, 4.583,
+  4.618, 4.654, 4.690, 4.726, 4.764, 4.801, 4.840, 4.879, 4.918, 4.958, 4.999, 5.040, 5.082, 5.124, 5.167, 5.211, 5.255, 5.299, 5.345, 5.391,
+  5.438, 5.485, 5.533, 5.582, 5.632, 5.683 ,5.735, 5.788, 5.841, 5.896, 5.953, 6.010, 6.069, 6.129, 6.190, 6.253, 6.318, 6.384, 6.452, 6.521,
+  6.592, 6.665, 6.740, 6.817, 6.896, 6.976, 7.059, 7.144, 7.231, 7.320, 7.412, 7.506, 7.602, 7.701, 7.803, 7.906, 8.013, 8.122, 8.234, 8.349,
+  8.466, 8.587, 8.710, 8.837, 8.966, 9.099, 9.235, 9.374, 9.516, 9.662, 9.811, 9.963, 10.119 };
+//Function for transfering SPI data to the CJ125.
+uint16_t COM_SPI(uint16_t TX_data) {
+
+  //Set chip select pin low, chip in use.
+  digitalWrite(CJ125_NSS_PIN, LOW);
+
+  //Transmit and receive.
+  byte highByte = SPI.transfer(TX_data >> 8);
+  byte lowByte = SPI.transfer(TX_data & 0xff);
+
+  //Set chip select pin high, chip not in use.
+  digitalWrite(CJ125_NSS_PIN, HIGH);
+
+  //Assemble response in to a 16bit integer and return the value.
+  uint16_t Response = (highByte << 8) + lowByte;
+  return Response;
+  
+}
+
+//Temperature regulating software (PID).
+int CalculateHeaterOutput(int input) {
+  
+  //Calculate error term.
+  int error = adcValue_UR_Optimal - input;
+  
+  //Set current position.
+  int position = input;
+  
+  //Calculate proportional term.
+  float pTerm = -pGain * error;
+  
+  //Calculate the integral state with appropriate limiting.
+  iState += error;
+  
+  if (iState > iMax) iState = iMax;
+  if (iState < iMin) iState = iMin;
+  
+  //Calculate the integral term.
+  float iTerm = -iGain * iState;
+  
+  //Calculate the derivative term.
+  float dTerm = -dGain * (dState - position);
+  dState = position;
+  
+  //Calculate regulation (PI).
+  int RegulationOutput = pTerm + iTerm + dTerm;
+  
+  //Set maximum heater output (full power).
+  if (RegulationOutput > 255) RegulationOutput = 255;
+  
+  //Set minimum heater value (cooling).
+  if (RegulationOutput < 0.0) RegulationOutput = 0;
+
+  //Return calculated PWM output.
+  return RegulationOutput;
+  
+}
+
+//Function to read inputs and update values.
+void UpdateInputs() {
+
+  //Update analog inputs.
+  adcValue_UA = analogRead(UA_ANALOG_INPUT_PIN);
+  adcValue_UR = analogRead(UR_ANALOG_INPUT_PIN);
+  adcValue_UB = analogRead(UB_ANALOG_INPUT_PIN);
+
+  //Do not display values above oxygen content in air.
+  if (adcValue_UA > 854) adcValue_UA = 854;
+
+  //Update CJ125 status.
+  CJ125_Status = COM_SPI(CJ125_DIAG_REG_REQUEST);
+  
+}
+
+//Function to transfer current values to app.
+void UpdateBLEOutput() {
+
+  //Only update if app is connected.
+  if (BLE.connected()) {
+
+    //Calculate checksum.
+    uint16_t checksum = HeaterStatus + hardwareId + CJ125_Status + adcValue_UA + adcValue_UR + adcValue_UB;
+
+    //Assembled data.
+    String txString = (String)HeaterStatus;
+    txString += ",";
+    txString += (String)hardwareId;
+    txString += ",";
+    txString += (String)CJ125_Status;
+    txString += ",";
+    txString += (String)adcValue_UA;
+    txString += ",";
+    txString += (String)adcValue_UR;
+    txString += ",";
+    txString += (String)adcValue_UB;
+    txString += ",";
+    txString += (String)checksum;
+    txString += "\n";
+
+    //Update character.
+    for (int i = 0; i < txString.length(); i++) {
+      OxygenLevelChar.writeValue(txString.charAt(i));
+    }
+    
+  } else {
+    
+    //Poll for BLE radio events and handle them.
+    BLE.poll();
+    
+  }
+  
+}
+float Lookup_Lambda(int Input_ADC) {
+  
+    //Declare and set default return value.
+    float LAMBDA_VALUE = 0;
+
+    //Validate ADC range for lookup table.
+    if (Input_ADC >= 39 && Input_ADC <= 791) {
+      LAMBDA_VALUE = pgm_read_float_near(Lambda_Conversion + (Input_ADC-39));
+    }
+    
+    if (Input_ADC > 791) {
+      LAMBDA_VALUE = 10.119;
+    }
+
+    if (Input_ADC < 39) {
+      LAMBDA_VALUE = 0.750;
+    }
+    
+    //Return value.
+    return LAMBDA_VALUE;
+    
+}
+
+//Function to transfer current values to front end.
+void UpdateSerialOutput() {
+  
+  //Calculate checksum.
+  uint16_t checksum = HeaterStatus + hardwareId + CJ125_Status + adcValue_UA + adcValue_UR + adcValue_UB;
+
+  //Assembled data.
+  String txString = (String)HeaterStatus;
+  txString += ",";
+  txString += (String)hardwareId;
+  txString += ",";
+  txString += (String)CJ125_Status;
+  txString += ",";
+  txString += (String)adcValue_UA;
+  txString += ",";
+  txString += (String)adcValue_UR;
+  txString += ",";
+  txString += (String)adcValue_UB;
+  txString += ",";
+  txString += (String)checksum;
+  
+  //Output values.
+  Serial.println(txString);
+  
+}
+
+//Function to update user interfaces and output.
+void UpdateUI() {
+  
+  //Local variables.
+  const float AirFuelRatioOctane = 14.70;
+  
+  //Sensor is not active.
+  if (HeaterStatus == 0) {
+    
+    //Output LED's.
+    digitalWrite(LED_STATUS_POWER, LOW);  
+    digitalWrite(LED_STATUS_HEATER, LOW);  
+
+    //Output serial data.
+    UpdateSerialOutput();
+
+    //Output logo to display.
+
+
+  }
+  
+  //Sensor is heating up.
+  if (HeaterStatus == 1) {
+     
+    //Output LED's.
+    digitalWrite(LED_STATUS_POWER, HIGH);  
+    digitalWrite(LED_STATUS_HEATER, HIGH);  
+
+    //Output serial data.
+    UpdateSerialOutput();
+
+    
+    //Delay for flashing LED's.
+    delay(500);
+
+ 
+    //Output LED's.
+    digitalWrite(LED_STATUS_HEATER, LOW);
+    
+    //Delay for flashing LED's.
+    delay(500);
+    
+  }
+    //Sensor is measuring.
+  if (HeaterStatus == 2) {
+
+    //Output LED's.
+    digitalWrite(LED_STATUS_POWER, HIGH);  
+    digitalWrite(LED_STATUS_HEATER, HIGH);
+    
+    //Output serial data.
+    UpdateSerialOutput();
+
+    //Output display data.
+
+      Serial1.print(Lookup_Lambda(adcValue_UA) * AirFuelRatioOctane, 2);
+      Serial1.print(Lookup_Lambda(adcValue_UA), 2);
+
+  }
+}
+
+
+void setup() {
+  
+  //Set up serial communication.
+  Serial.begin(9600);
+  Serial1.begin(115200);
+  //Set up SPI.
+  SPI.begin();  /* Note, SPI will disable the bult in LED*/
+  SPI.setClockDivider(SPI_CLOCK_DIV128);
+  SPI.setBitOrder(MSBFIRST);
+  SPI.setDataMode(SPI_MODE1);
+  
+  //Initialize BLE.
+  BLE.begin();
+  BLE.setDeviceName("Arduino");
+  BLE.setLocalName("Lambda Sensor");
+  BLE.setAdvertisedService(LambdaService);
+  LambdaService.addCharacteristic(OxygenLevelChar);
+  BLE.addService(LambdaService);
+  BLE.advertise();
+
+  //Set up digital output pins.
+  pinMode(CJ125_NSS_PIN, OUTPUT);  
+  pinMode(LED_STATUS_POWER, OUTPUT);
+  pinMode(LED_STATUS_HEATER, OUTPUT);
+  pinMode(HEATER_OUTPUT_PIN, OUTPUT);
+
+}
+
+void loop() {
+
+  //Update Analog Values.
+  UpdateInputs();
+
+  //Update front ends.
+  UpdateBLEOutput();
+  
+  //Turn off heating.
+  if (adcValue_UB < UBAT_MIN || CJ125_Status != CJ125_DIAG_REG_STATUS_OK) {
+
+    //Update heater status to off.
+    HeaterStatus = 0;
+    analogWrite(HEATER_OUTPUT_PIN, 0);
+
+    //Output LED's.
+    digitalWrite(LED_STATUS_POWER, LOW);  
+    digitalWrite(LED_STATUS_HEATER, LOW);
+
+  }
+  
+  //Heat sensor.
+  if (adcValue_UR >= 250 && adcValue_UB >= UBAT_MIN && CJ125_Status == CJ125_DIAG_REG_STATUS_OK) {
+    
+    //Output LED's.
+    digitalWrite(LED_STATUS_POWER, HIGH);  
+    digitalWrite(LED_STATUS_HEATER, LOW); 
+
+    //Set CJ125 in calibration mode.
+    COM_SPI(CJ125_INIT_REG1_MODE_CALIBRATE);
+  
+    //Let values settle.
+    delay(500);
+  
+    //Store optimal values before leaving calibration mode.
+    adcValue_UA_Optimal = analogRead(UA_ANALOG_INPUT_PIN);
+    adcValue_UR_Optimal = analogRead(UR_ANALOG_INPUT_PIN);
+    
+    //Set CJ125 in normal operation mode.
+    //COM_SPI(CJ125_INIT_REG1_MODE_NORMAL_V8);  /* V=0 */
+    COM_SPI(CJ125_INIT_REG1_MODE_NORMAL_V17);  /* V=1 */
+
+    /* Heat up sensor. This is described in detail in the datasheet of the LSU 4.9 sensor with a 
+     * condensation phase and a ramp up face before going in to PID control. */
+
+    //Update heater status to heating.
+    HeaterStatus = 1;
+    
+    //Calculate supply voltage.
+    float SupplyVoltage = (((float)adcValue_UB / 1023 * 5) / 10000) * 110000;
+    
+    //Condensation phase, 2V for 5s.
+    int CondensationPWM = (2 / SupplyVoltage) * 255;
+    analogWrite(HEATER_OUTPUT_PIN, CondensationPWM);
+    
+    int t = 0;
+    while (t < 500 && adcValue_UB > UBAT_MIN) {
+    
+      //Update Values.
+      UpdateInputs();
+    
+      //Update frontends.
+      UpdateBLEOutput();
+
+      //Increment.
+      t += 1;
+      delay(10);
+      
+    }
+    if ( (100 / SERIAL_RATE) ==  serial_counter) {
+
+    //Reset counter.
+    serial_counter = 0;
+
+    //Update frontends.
+    UpdateUI();
+
+    }
+    //Ramp up phase, +0.4V / s until 100% PWM from 8.5V.
+    float UHeater = 8.5;
+    while (UHeater < 13.0 && adcValue_UB > UBAT_MIN && adcValue_UR > adcValue_UR_Optimal) {
+  
+      //Update Values.
+      UpdateInputs();
+  
+      //Update frontends.
+      UpdateBLEOutput();
+      
+      //Set heater output during ramp up.
+      CondensationPWM = (UHeater / SupplyVoltage) * 255;
+        
+      if (CondensationPWM > 255) CondensationPWM = 255; /*If supply voltage is less than 13V, maximum is 100% duty cycle*/
+  
+      analogWrite(HEATER_OUTPUT_PIN, CondensationPWM);
+  
+      //Increment Voltage.
+      UHeater += 0.004;
+      delay(10);
+      
+    }
+    
+  }
+
+  //Adjust PWM output by calculated PID regulation.
+  if (adcValue_UR < 250 && adcValue_UB >= UBAT_MIN && CJ125_Status == CJ125_DIAG_REG_STATUS_OK) {
+    
+    //Calculate and set new heater output.
+    HeaterOutput = CalculateHeaterOutput(adcValue_UR);
+    analogWrite(HEATER_OUTPUT_PIN, HeaterOutput);
+
+    //Output LED's.
+    digitalWrite(LED_STATUS_POWER, HIGH);  
+    digitalWrite(LED_STATUS_HEATER, HIGH);
+
+    HeaterStatus = 2;
+    
+  }
+  serial_counter++;
+}

test/README

@@ -0,0 +1,11 @@
+
+This directory is intended for PlatformIO Unit Testing and project tests.
+
+Unit Testing is a software testing method by which individual units of
+source code, sets of one or more MCU program modules together with associated
+control data, usage procedures, and operating procedures, are tested to
+determine whether they are fit for use. Unit testing finds problems early
+in the development cycle.
+
+More information about PlatformIO Unit Testing:
+- https://docs.platformio.org/page/plus/unit-testing.html