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 /* CAUTION !!  These data are EXAMPLE Data, NOT REAL data */
  30 #define CO2_SENSOR_DEFAULT_VALUE_ZP (690) // 400ppm
  31 #define CO2_SENSOR_DEFAULT_VALUE_1000 (644)
  32
  33 #define USE_EXAMPLE_CODE
  34
  35 static const double log400 = 2.602;
  36
  37 static bool initialized = false;
  38 static double co2_zp_volt = -1;
  39 static double slope_value = -1;
  40
  41 void co2_sensor_close(void)
  42 {
  43         adc_mcp3008_fini();
  44         initialized = false;
  45 }
  46
  47 int co2_sensor_read(int ch_num, unsigned int *out_value)
  48 {
  49         unsigned int read_value = 0;
  50         int ret = 0;
  51
  52         if (!initialized) {
  53                 ret = adc_mcp3008_init();
  54                 retv_if(ret != 0, -1);
  55                 initialized = true;
  56         }
  57
  58         ret = adc_mcp3008_read(ch_num, &read_value);
  59         retv_if(ret != 0, -1);
  60
  61         *out_value = read_value;
  62
  63         return 0;
  64 }
  65
  66 static inline double __value_to_volt(unsigned int value)
  67 {
  68         return (double)value
  69                 * (double)(CO2_SENSOR_REF_VOLTAGE / CO2_SENSOR_VALUE_MAX)
  70                 / 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         retv_if(zero_point_v <= second_point_v, -1);
  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 - log(second_point_ppm);
  91
  92         slope_value = __calc_slope(co2_zp_volt, sec_volt, x_axis_diff);
  93
  94         return 0;
  95 }
  96
  97 double co2_sensor_value_to_voltage(unsigned int value)
  98 {
  99         retv_if(value > 1023, -100000000.0); // out of value range
 100
 101         return __value_to_volt(value);
 102 }
 103
 104 /* Not implemented !!! */
 105 unsigned int co2_sensor_voltage_to_ppm(double voltage)
 106 {
 107         double ppm = 0;
 108         /* Make this function yourself */
 109         /* Please ref. 'Theory' section in https://sandboxelectronics.com/?p=147#Theory */
 110
 111         /* Example */
 112 #ifdef USE_EXAMPLE_CODE
 113         if (slope_value < 0)
 114                 co2_sensor_set_calibration_values(CO2_SENSOR_DEFAULT_VALUE_ZP,
 115                         CO2_SENSOR_DEFAULT_VALUE_1000, 1000);
 116
 117         if (voltage >= co2_zp_volt)
 118                 return 400;
 119
 120         ppm = pow(10, (voltage - co2_zp_volt)/slope_value + log400);
 121 #endif
 122
 123         return (unsigned int)ppm;
 124 }
 125
 126 unsigned int co2_sensor_value_to_ppm(unsigned int value)
 127 {
 128         /* You can use this function after implementing co2_sensor_voltage_to_ppm() function */
 129         return co2_sensor_voltage_to_ppm(co2_sensor_value_to_voltage(value));
 130 }
 131