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When monitoring air quality, in addition to displaying the current value at a certain moment, we want to know the changes over a period of time. The CO2 monitoring project shared today provides an idea of how to display both a single value and a curve graph. Overall, the project is quite simple, and the hardware used is also common, which can be completely replaced with other sensors.
☞ Hardware Composition
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ESP32 Board
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3.5-inchTFT Touch
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SGP30 Air Quality Sensor
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3D Printed Shell
☞ Why CO2 Measurement Needs Historical Levels
For a parameter that is very easily changed and has a wide range, checking the value at a certain moment is not very meaningful. For example, the CO2 level may reach a very high concentration at this moment, but the next moment it may return to normal in a certain area. Typically, temperature and humidity in the air are measured by checking the current values, but CO2 concentration measurement is different; it is measured using a sensor to obtain levels within a certain space, and there are too many influencing factors: wind, human breathing, temperature, humidity, etc. Therefore, recording historical values is important for judging CO2 levels and changes.
☞ Core Component – Sensor
The SGP30 sensor used in the project, is the first metal oxide gas sensor that integrates multiple sensing elements on a single chip, providing detailed information on air quality, such as the content of carbon dioxide (CO2) and volatile organic compounds (VOCs). Only CO2 measurement is used here.
For convenience, a sensor module used in the project not only includes SGP30, but also integrates the DHT11 module for measuring temperature and humidity. Additionally, there is a buzzer on the board for alerts.
The most important thing is that it can be used with a 3.5-inch LCD device and just plug it in.
☞ Code
The programming environment for ESP32 uses Arduino IDE, which is simple and convenient. It will display the values measured by the sensor and plot the curve with historical values on the 3.5-inch LCD display. The main code is as follows:
#include "SPI.h"
#include "TFT_eSPI.h"
#include <Wire.h>
#include "Adafruit_SGP30.h"
#include "DHT.h"
#define BUZZER_ON digitalWrite(BUZZPIN, HIGH)
#define BUZZER_OFF digitalWrite(BUZZPIN, LOW)
#define LDO_1V8_ON digitalWrite(LDO_PWR_EN_PIN, HIGH)
#define LDO_1V8_OFF digitalWrite(LDO_PWR_EN_PIN, LOW)
#define DHTPIN 18 // Digital pin connected to the DHT sensor
#define DHTTYPE DHT11 // DHT11
#define BUZZPIN 5
#define LDO_PWR_EN_PIN 19 //AP2112K enable pin
#define I2C_SDA 26
#define I2C_SCL 27
TFT_eSPI tft = TFT_eSPI();
DHT dht(DHTPIN, DHTTYPE);
Adafruit_SGP30 sgp;
int list_1[50] = {0};
int list_1_length = 20;
int list_2[50] = {0};
int list_2_length = 20;
int interval = 3000;
void setup(){ Serial.begin(115200);
Serial.println("Environment Test!");
dht.begin();
pinMode(BUZZPIN, OUTPUT);
pinMode(LDO_PWR_EN_PIN, OUTPUT);
BUZZER_ON;
LDO_1V8_ON;
delay(1000);
BUZZER_OFF;
Wire.begin(I2C_SDA, I2C_SCL);
Serial.println("SGP30 test");
if (!sgp.begin()) { Serial.println("Sensor not found :("); while (1) ; }
//Draw frame tft.init(); tft.fillScreen(TFT_BLACK); tft.setTextColor(TFT_WHITE); tft.setTextSize(2); tft.setCursor(10, 40); tft.println("Makerfabs line chart");
delay(1000); tft.fillScreen(TFT_BLACK); draw_line_chart_window("TVOC Line Chart ( Unit : ppb ) ", (String) "Interval : " + interval + " ms", list_1_length, 0, 1200, TFT_WHITE); draw_line_chart_window2("ECO2 Line Chart ( Unit : ppm ) ", (String) "Interval : " + interval + " ms", list_2_length, 0, 5000, TFT_WHITE);}
void loop(){ draw_line_chart(list_1, list_1_length, 0, 1200, TFT_WHITE); draw_line_chart2(list_2, list_2_length, 0, 5000, TFT_WHITE); delay(interval);
int tvoc = 0; int eco2 = 0; weather_read(&tvoc, &eco2);
draw_line_chart(list_1, list_1_length, 0, 1200, TFT_BLACK); draw_line_chart2(list_2, list_2_length, 0, 5000, TFT_BLACK); add_list(list_1, list_1_length, tvoc); add_list(list_2, list_2_length, eco2);}The complete code can be downloaded from GitHub:
github.com/Makerfabs/Project_Touch-Screen Camera/tree/master/example
If you can’t download it, you can reply “CO2 measurement” on “Darwin said” on WeChat to get the code.
☞ Actual Measurement
CO2 concentration changes quite rapidly at times, for example, breathing on the sensor will immediately increase the value. Of course, if you want to detect changes in concentration over a period of time, you need to place the sensor in an appropriate position.
Although this project is designed to monitor CO2 concentration levels, it can be adjusted according to your needs to monitor TVOC, temperature, or humidity. As shown in the figure, it collects two values and plots them in lines on the display.
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