A Simple low-cost Home VOCs sensor

Sunyoung Kim
sunyoung.kim@cs.cmu.edu
Human-Computer Interaction Institute
Carnegie Mellon

Eric Paulos
paulos@cs.cmu.edu
Human-Computer Interaction Institute
Carnegie Mellon

This page is to appear at the ACM SIGCHI 2009 WORKSHOP:
"DIY for CHI: Methods, Communities, and Values of Reuse and Customization"
For my bio, click my name, click here.

1. Research Descrption
People spend approximately 90 percent of their time indoors, which makes indoor air quality a major contributing factor towards their health. For non experts, measuring and understanding air quality is difficult without special tools and expensive equipment.
Our goal is to investigate low-cost sensing with DIY strategies to enable everyday citizens to learn about indoor air quality. We are looking at multiple environmental sensors in our research. In this study we demonstrate the use of a low cost($14) VOC sensor.

2. What are VOCs?
Volatile organic compounds (VOCs) are emitted as gases from certain solids or liquids. VOCs include a variety of chemicals, some of which may have short- and long-term adverse health effects. Concentrations of many VOCs are consistently higher indoors (up to ten times higher) than outdoors. VOCs are emitted by a wide array of products numbering in the thousands. Examples include: paints and lacquers, paint strippers, cleaning supplies, pesticides, building materials and furnishings, office equipment such as copiers and printers, correction fluids and carbonless copy paper, graphics and craft materials including glues and adhesives, permanent markers, and photographic solutions.
Organic chemicals are widely used as ingredients in household products. Paints, varnishes, and wax all contain organic solvents, as do many cleaning, disinfecting, cosmetic, degreasing, and hobby products. Fuels are made up of organic chemicals. All of these products can release organic compounds while you are using them, and, to some degree, when they are stored.
(Cited from EPA)

3. Parts for the circuit

TG2620 by Figaro
Arduino Board
Potentiometer
1.2 Kohms Resistor
Breadboard
LED array

4. VOCs sensor: TG2620 ($14)
(1) Description
This sensor is an electrochemical device to detect the gases in air such as Ethanol (C₂H₆O), Hydrogen (H), Iso-butane (CH₃CH(CH₃)₂), Carbon Monoxide (C_O), Methane (CH₄).
The sensor consists of four pins: two of the four pins on the sensor are connected to a heater and the other two are connected to the sensing element. Gas levels are determined by measuring the voltage across a load resistor which is put between the negative pin of the sensing element and ground. This change in resistance can be sent as an analog value to a microprocessor.

(2) Features of TG2620

High sensitivity to VOCs and odorous gases
Low power consumption
High sensitivity to gaseous air contaminants
Small size

(3) Structure

(4) Circuit Diagram

5. Steps (click images to enlarge)

Step 1
You need parts:

a TG 2620 VOCs sensor (data sheet)

a potentiometer

an 1.2 Kohms Resistor

an arduino board (Diecimila)

a breadboard

a capacitor (optional)

an LED array

wires

Step 2
First of all put the VOC sensor onto the breadboard.
The sensor has four pinss. Pin 3 and pin 4 go to Power, and pin 1 to Ground.
Pin 2 is the output. It is connected to Potentiometer and Ground.
Also it is connected to an arduino board, analog pin 0.

Step 3
Insert the 1.2kohms resistor between pin 1 and Power.
This creates a voltage divider necessary to measure the output of the sensor.

Step 4
Insert the LED array.
We used a 10 segment led array. Each pin is connected to a separate arduino digital output line.
We chose a simple sensor output using a series of LEDs to visualize the concentration of VOCs in the air.

Step 5
Insert a capacitor between pin 1 and Ground to stabilize the power signal.

Step 6
Connect Power and Ground from a breadboard to an aurduino board.
Also connect pin 2 to an arduino analog pin 0.

Step 7
Insert a potentiometer between pin 2 and Ground.
We chose a potentiometer to alter the resistance of the load resistor. As an alternative, you can use a fixed register.

Step 8
We are now ready to test the setup.

* Test result video
We burned a paper to test the setup.
The combustion of a piece of paper generated carbon, CO2, some nitrogens and water vapor, and this gaseous air was sensored by the VOCs sensor.
An array LED was lighted responding this gaseous air.

6. Video
This video illustrate the entire steps above.

	Step 1 You need parts: a TG 2620 VOCs sensor (data sheet) a potentiometer an 1.2 Kohms Resistor an arduino board (Diecimila) a breadboard a capacitor (optional) an LED array wires
	Step 2 First of all put the VOC sensor onto the breadboard. The sensor has four pinss. Pin 3 and pin 4 go to Power, and pin 1 to Ground. Pin 2 is the output. It is connected to Potentiometer and Ground. Also it is connected to an arduino board, analog pin 0.
	Step 3 Insert the 1.2kohms resistor between pin 1 and Power. This creates a voltage divider necessary to measure the output of the sensor.
	Step 4 Insert the LED array. We used a 10 segment led array. Each pin is connected to a separate arduino digital output line. We chose a simple sensor output using a series of LEDs to visualize the concentration of VOCs in the air.
	Step 5 Insert a capacitor between pin 1 and Ground to stabilize the power signal.
	Step 6 Connect Power and Ground from a breadboard to an aurduino board. Also connect pin 2 to an arduino analog pin 0.
	Step 7 Insert a potentiometer between pin 2 and Ground. We chose a potentiometer to alter the resistance of the load resistor. As an alternative, you can use a fixed register.
	Step 8 We are now ready to test the setup.
* Test result video We burned a paper to test the setup. The combustion of a piece of paper generated carbon, CO2, some nitrogens and water vapor, and this gaseous air was sensored by the VOCs sensor. An array LED was lighted responding this gaseous air.