src/co2-sensor.c

   1 /* ****************************************************************
   2  *
   3  * Copyright 2017 Samsung Electronics All Rights Reserved.
   4  *
   5  * Licensed under the Apache License, Version 2.0 (the "License");
   6  * you may not use this file except in compliance with the License.
   7  * You may obtain a copy of the License at
   8  *
   9  *      http://www.apache.org/licenses/LICENSE-2.0
  10  *
  11  * Unless required by applicable law or agreed to in writing, software
  12  * distributed under the License is distributed on an "AS IS" BASIS,
  13  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  14  * See the License for the specific language governing permissions and
  15  * limitations under the License.
  16  *
  17  ******************************************************************/
  18
  19 #include <peripheral_io.h>
  20 #include <math.h>
  21 #include "adc-mcp3008.h"
  22 #include "log.h"
  23
  24 #define CO2_SENSOR_VOLTAGE_GAIN (8.5)
  25
  26 #define CO2_SENSOR_REF_VOLTAGE (5)
  27 #define CO2_SENSOR_VALUE_MAX (1024)
  28
  29 //#define USE_EXAMPLE_CODE
  30
  31 #ifdef USE_EXAMPLE_CODE
  32 /* CAUTION !!  These data are EXAMPLE Data, NOT REAL data */
  33 #define CO2_SENSOR_DEFAULT_VALUE_ZP (690) // 400ppm
  34 #define CO2_SENSOR_DEFAULT_VALUE_1000 (600)
  35 #endif /* USE_EXAMPLE_CODE */
  36
  37 static const double log400 = 2.602;
  38
  39 static bool initialized = false;
  40 static double co2_zp_volt = -1;
  41 static double slope_value = 10000; // A real slope value should be a negative value.
  42
  43 void co2_sensor_close(void)
  44 {
  45         adc_mcp3008_fini();
  46         initialized = false;
  47 }
  48
  49 int co2_sensor_read(int ch_num, unsigned int *out_value)
  50 {
  51         unsigned int read_value = 0;
  52         int ret = 0;
  53
  54         if (!initialized) {
  55                 ret = adc_mcp3008_init();
  56                 retv_if(ret != 0, -1);
  57                 initialized = true;
  58         }
  59
  60         ret = adc_mcp3008_read(ch_num, &read_value);
  61         retv_if(ret != 0, -1);
  62
  63         *out_value = read_value;
  64
  65         return 0;
  66 }
  67
  68 static inline double __value_to_volt(unsigned int value)
  69 {
  70         return (double)value * CO2_SENSOR_REF_VOLTAGE / CO2_SENSOR_VALUE_MAX / CO2_SENSOR_VOLTAGE_GAIN;
  71 }
  72
  73 static double __calc_slope(double zp_volt, double sec_volt, double x_axis_diff)
  74 {
  75         return (zp_volt - sec_volt) / (x_axis_diff);
  76 }
  77
  78 /* To use to calibrate ppm value*/
  79 int co2_sensor_set_calibration_values(unsigned int zero_point_v,
  80                 unsigned int second_point_ppm, unsigned int second_point_v)
  81 {
  82         double sec_volt = -1;
  83         double x_axis_diff = -1;
  84
  85         retvm_if(zero_point_v <= second_point_v, -1, "%u - %u", zero_point_v, second_point_v);
  86         retv_if(second_point_ppm <= 400, -1);
  87
  88         co2_zp_volt = __value_to_volt(zero_point_v);
  89         sec_volt = __value_to_volt(second_point_v);
  90         x_axis_diff = log400 - log10(second_point_ppm);
  91         slope_value = __calc_slope(co2_zp_volt, sec_volt, x_axis_diff);
  92
  93         return 0;
  94 }
  95
  96 double co2_sensor_value_to_voltage(unsigned int value)
  97 {
  98         retv_if(value > 1023, -100000000.0); // out of value range
  99
 100         return __value_to_volt(value);
 101 }
 102
 103 /* Not implemented !!! */
 104 unsigned int co2_sensor_voltage_to_ppm(double voltage)
 105 {
 106         double ppm = 0;
 107         /* Make this function yourself */
 108         /* Please ref. 'Theory' section in https://sandboxelectronics.com/?p=147#Theory */
 109
 110         /* Example */
 111 #ifdef USE_EXAMPLE_CODE
 112         if (slope_value > 0)
 113                 co2_sensor_set_calibration_values(CO2_SENSOR_DEFAULT_VALUE_ZP,
 114                                 1000, CO2_SENSOR_DEFAULT_VALUE_1000);
 115
 116         if (voltage >= co2_zp_volt)
 117                 return 400;
 118
 119         ppm = pow(10, (voltage - co2_zp_volt)/slope_value + log400);
 120 //      if (ppm > 10000)
 121 //              ppm = 10000;
 122 #endif /* USE_EXAMPLE_CODE */
 123
 124         return (unsigned int)ppm;
 125 }
 126
 127 unsigned int co2_sensor_value_to_ppm(unsigned int value)
 128 {
 129         /* You can use this function after implementing co2_sensor_voltage_to_ppm() function */
 130         return co2_sensor_voltage_to_ppm(co2_sensor_value_to_voltage(value));
 131 }
 132