TVOC on the AirGradient DIY Sensor

Hardware extensions
#1

Some people want to measure chmicals in their house and it is relatively easy to connect the SGP30 TVOC sensor from Sensirion to the AirGradient PCB.

If you are interested to do just that, head over to our blog article:

https://www.airgradient.com/resources/tvoc-on-airgradient-diy-sensor/

1 Like
#2

I’ve got 2 SGP30 sensors on the way!

#3

It would be great to have both SHT30 and SGP30 sensors working in parallel in order to track the humidity and hopefully improve the accuracy of TVOC values.

According to the article “you can theoretically also use both in parallel by connecting one of them to the vailable SCL, SDA breakout pins on the AirGradient DIY board.”

Could you provide more details about this?

Thank you.

#4

@ribeirux
The SHT and SGP sensors are i2c so they run on the same bus with different addresses and thus it should work.
However, I did not explicitly test it so I can not fully confirm it.

#5

I modified (slightly) the firmware to read correctly the data provided by SGP30:

//START
/*
This is the code for the AirGradient DIY Air Quality Sensor with an ESP8266 Microcontroller.

It is a high quality sensor showing PM2.5, CO2, Temperature and Humidity on a small display and can send data over Wifi.

For build instructions please visit DIY Air Quality Sensor

Instructions on using the TVOC sensor (SGP30) instead of the Temperature / Humidity sensor (SHT3x).

The codes needs the following libraries installed:
“WifiManager by tzapu, tablatronix” tested with Version 2.0.3-alpha
“ESP8266 and ESP32 OLED driver for SSD1306 displays by ThingPulse, Fabrice Weinberg” tested with Version 4.1.0
“SGP30” by Rob Tillaart tested with Version 0.1.4

Configuration:
Please set in the code below which sensor you are using and if you want to connect it to WiFi.

If you have any questions please visit our forum at https://forum.airgradient.com/

If you are a school or university contact us for a free trial on the AirGradient platform.

MIT License
*/
#include <AirGradient.h>
#include <WiFiManager.h>
#include <ESP8266WiFi.h>
#include <ESP8266HTTPClient.h>

#include <Wire.h>
#include “SSD1306Wire.h”

#include “SGP30.h”
SGP30 SGP;

AirGradient ag = AirGradient();

SSD1306Wire display(0x3c, SDA, SCL);

WiFiClient client;

// set sensors that you do not use to false
boolean hasPM=true;
boolean hasCO2=true;
boolean hasSHT=true;
boolean hasTVOC=true;

// set to true if you want to connect to wifi. The display will show values only when the sensor has wifi connection
boolean connectWIFI=true;

// change if you want to send the data to another server
String APIROOT = “http://hw.airgradient.com/”;

void setup(){
Serial.begin(9600);

display.init();
display.flipScreenVertically();
showTextRectangle(“Init”, String(ESP.getChipId(),HEX),true);

if (hasTVOC) SGP.begin();
if (hasPM) ag.PMS_Init();
if (hasCO2) ag.CO2_Init();
if (hasSHT) ag.TMP_RH_Init(0x44);

if (connectWIFI) connectToWifi();
delay(2000);
}

void loop(){

if (hasTVOC) SGP.measure(false);

// create payload

String payload = “{“wifi”:” + String(WiFi.RSSI()) + “,”;

if (hasPM) {
int PM2 = ag.getPM2_Raw();
payload=payload+"“pm02”:" + String(PM2);
showTextRectangle(“PM2”,String(PM2),false);
delay(3000);
}

if (hasTVOC) {
if (hasPM) payload=payload+",";
int TVOC = SGP.getTVOC();
payload=payload+"\"tvoc\":" + String(TVOC);
showTextRectangle("TVOC",String(TVOC),false);
delay(3000);

}

if (hasCO2) {
if (hasTVOC) payload=payload+",";
int CO2 = SGP.getCO2();
payload=payload+"“rco2”:" + String(CO2);
showTextRectangle(“CO2”,String(CO2),false);
delay(3000);
}

if (hasSHT) {
if (hasCO2 || hasPM) payload=payload+",";
TMP_RH result = ag.periodicFetchData();
payload=payload+"“atmp”:" + String(result.t) + “,“rhum”:” + String(result.rh);
showTextRectangle(String(result.t),String(result.rh)+"%",false);
delay(3000);
}

payload=payload+"}";

// send payload
if (connectWIFI){
Serial.println(payload);
String POSTURL = APIROOT + “sensors/airgradient:” + String(ESP.getChipId(),HEX) + “/measures”;
Serial.println(POSTURL);
WiFiClient client;
HTTPClient http;
http.begin(client, POSTURL);
http.addHeader(“content-type”, “application/json”);
int httpCode = http.POST(payload);
String response = http.getString();
Serial.println(httpCode);
Serial.println(response);
http.end();
}
}

// DISPLAY
void showTextRectangle(String ln1, String ln2, boolean small) {
display.clear();
display.setTextAlignment(TEXT_ALIGN_LEFT);
if (small) {
display.setFont(ArialMT_Plain_16);
} else {
display.setFont(ArialMT_Plain_24);
}
display.drawString(32, 16, ln1);
display.drawString(32, 36, ln2);
display.display();
}

// Wifi Manager
void connectToWifi(){
WiFiManager wifiManager;
//WiFi.disconnect(); //to delete previous saved hotspot
String HOTSPOT = “AIRGRADIENT-”+String(ESP.getChipId(),HEX);
wifiManager.setTimeout(120);
if(!wifiManager.autoConnect((const char*)HOTSPOT.c_str())) {
Serial.println(“failed to connect and hit timeout”);
delay(3000);
ESP.restart();
delay(5000);
}

}
//END

#6

working:
AirgradientDisplay

#7

Hello,

So I bought a Basic PCB and all the sensors, both SHT31 and the SGP30.
Can I plug it in paralell, the SGP30on top of SHT31, in the same bus?

Can you please elaborate on the “removing the resistors” please?
I only have to do it if I want both SHT and SGP?
Will the SHT work if it’s the only sensor and I take the resistors off?

Thank you.

#8

Can I plug it in paralell, the SGP30on top of SHT31, in the same bus?

Yes but it will probably not work due to the pull up resistors.

Can you please elaborate on the “removing the resistors” please?
I only have to do it if I want both SHT and SGP?

Yes

Will the SHT work if it’s the only sensor and I take the resistors off?

Probably not anymore.

#9

OK thank you for your help.
I have already ordered another SHT so I can try and evaluate the SHT with and without resistors.

I will give feedback after :slight_smile: