Published March 31, 2023 © MIT

Human Breathalyzer to monitor ketosis

It is a tool to monitor the presence of acetone in our breath. It uses gas sensor MQ-135, 1.3inch OLED display, DHT22 & Arduino Uno.

IntermediateFull instructions provided2 hours2,738

Things used in this project

Hardware components

MQ-135 Gas Sensor Module

Any MQ-135 gas sensor will work.

DFRobot DHT22 Temperature and Humidity Sensor

It is basically DHT-22 Module

Arduino UNO

Adafruit Monochrome 1.3" 128x64 OLED graphic display

1.3-inch SH1106 i2c Monochrome OLED display 128x64 (4pins)

Software apps and online services

Arduino IDE

Story

Human Breathalyzer for Non-Invasive Monitoring of Ketones:

Acetone is a volatile organic compound that is produced as a byproduct of the metabolism of fats in the liver. When the body is in a state of ketosis, such as during fasting, low-carbohydrate diets, or certain medical conditions like diabetes, the production of acetone increases, and it can be detected in the breath.

Measuring acetone in breath can provide a non-invasive way to monitor the levels of ketones in the body. This can be useful for people with diabetes who are following a low-carbohydrate or ketogenic diet, as well as for athletes who are trying to optimize their performance by improving their metabolic efficiency. In addition, monitoring acetone in breath can also be used to track weight loss progress, as higher levels of acetone may indicate that the body is burning more fat for energy.

However, it's important to note that while acetone in breath can be a useful biomarker, it should always be interpreted in the context of other health markers and symptoms and should not be used as a standalone diagnostic tool.

Here, just to test a basic prototype we are using gas sensor MQ-135 and temperature & humidity sensor DHT-22 which has been interfaced with Arduino Uno R3.

Interfacing Sensors with Arduino Uno:

Gas sensor MQ-135 has four pins VCC, GND, D0 & A0. VCC is connected to the 5v pin of Arduino uno, GND is interfaced with GND pin and similarly A0 of sensor is attached to the analog pin A0 of Arduino with a load resistor of 10kohm. Here pin D0 is unused.

For DHT-22, the data pin of sensor has been connected to digital pin 2 of Arduino Uno whereas Positive pin has been interfaced to 5v and negative to GND.

To display the result SH1106 1.3-inch monochrome i2c screen is being used and has four pins VCC, GND, SCL &SDA. VCC is connected to 5v and GND to ground pin in Arduino Uno. SCL is connected to analog pin A5 of Arduino Uno and SDA to A4 respectively.

Note:The sensors are not placed in the controlled environment so the pollutants may impact the efficacy of device. MQ-135 sensor is not only sensitive to Acetone, so the calibrations has been made in the code. 10k ohm resistor is being used as load resistor.

Working model

To make the connections clearer schematic illustration of circuit interface has been provided below.

Code

Code with calibration for MQ-135 to measure amount of acetone in breath.

#include <Adafruit_Sensor.h>
#include <DHT.h>
#include <Adafruit_SH1106.h>
#include <Wire.h>

#define DHTPIN 2
#define DHTTYPE DHT22
DHT dht(DHTPIN, DHTTYPE);

#define MQ_PIN A0
#define RL_VALUE 10.0
#define RO_CLEAN_AIR_FACTOR 3.08

float readMQ();
float getResistance(float sensor_volt);

#define OLED_RESET 4
Adafruit_SH1106 display(OLED_RESET);

void setup() {
  Serial.begin(9600);
  display.begin(SH1106_SWITCHCAPVCC, 0x3C);
  dht.begin();
//display.setRotation(2); (in case you want to rotate display.)
  display.clearDisplay();
  display.setTextSize(1);
  display.setTextColor(WHITE);
  display.setCursor(0, 0);
  display.println("Initializing");
  display.println("Breathalyzer...");
  display.display();
  delay(2000);
}

void loop() {
  float h = dht.readHumidity();
  float t = dht.readTemperature();
  float sensor_volt = analogRead(MQ_PIN) / 1024.0 * 5.0;
  float rs = getResistance(sensor_volt);
  float ratio = rs / RO_CLEAN_AIR_FACTOR;
  float ppm = pow(ratio, -1.179) * 4.385;
  float mgL = ppm * 1.995;
    display.clearDisplay();
  display.setCursor(0, 0);
  display.println("Human Breathalyzer");
  display.drawLine(0, 12, 127, 12, WHITE);
  display.setCursor(0, 15);
  display.print("Acetone (ppm): ");
  display.print(ppm, 2);
  display.setCursor(0, 30);
  display.print("Acetone (mg/l): ");
  display.print(mgL, 2);
  display.setCursor(0, 45);
  display.print("Temp: ");
  display.print(t, 1);
  display.print(" C");
  display.setCursor(0, 55);
  display.print("Humidity: ");
  display.print(h, 1);
  display.print(" %");
  display.display();
  delay(2000);
  display.clearDisplay();
  display.setCursor(0, 0);
  display.println("Blow into sensor");
  display.display();
  delay(2000);
}

float readMQ() {
  int i;
  float rs=0;
  for (i=0;i<10;i++) {
    rs += getResistance(analogRead(MQ_PIN) / 1024.0 * 5.0 );
    delay(100);
  }
  rs = rs/10.0;
  return rs;
}

float getResistance(float sensor_volt) {
  return RL_VALUE * (5.0 - sensor_volt) / sensor_volt;
}