alcohol sensor

Forum 2005-2010 (read only) Hardware Interfacing
1

Just purchased a few alcohol sensors from Seeed studio

http://www.seeedstudio.com/depot/alcohol-sensor-mq303a-p-549.html?cPath=6

looking to make my own breathalyzer, then test it out :wink:

anyone done anything with these sensors? will these even work? any pointers?

2

  1. READ THE DATASHEET
    http://www.seeedstudio.com/depot/images/product/MQ303A.pdf

  2. Wire up the circuit in the datasheet

  • choose appropiate resistors to get your required sensor range (1.1V, 3.3V, 5.0V)
  1. DO NOT POWER THIS THING DIRECLY FROM THE ARDUINO
  • there is a heater inside the tester that takes 120 mA the arduino
    can not power it directly from a pin, but you can have a transistor
    to turn it on or off via the Arduino and external powersupply.

after that it's just a simple matter of reading the analog pin

David

3

Oh, and a tutorial, translated with google from portogisian to english:
http://translate.google.com/translate?js=y&prev=_t&hl=no&ie=UTF-8&layout=1&eotf=1&u=http%3A%2F%2Flusorobotica.com%2Findex.php%2Ftopic%2C111.0.html&sl=pt&tl=en

David

4

I'd like to offer my services for the calibration phase of your project.
:smiley:

5
  1. DO NOT POWER THIS THING DIRECLY FROM THE ARDUINO
  • there is a heater inside the tester that takes 120 mA the arduino
    can not power it directly from a pin, but you can have a transistor
    to turn it on or off via the Arduino and external powersupply

David

i have the same problem but i have no idea of how to use a transistor, where can i read some about this?

THANKS

6

just google "transistor tutorial"
aruino specific
http://todbot.com/blog/bionicarduino/

read those pdf files (4 of them)
in this one http://todbot.com.s3.amazonaws.com/bionicarduino/bionic_arduino_class3.pdf
a transistor is driving a small dc motor (5v) so this hookup is what you use (see page 11-14 on the tutorial)

David

EDIT: make sure that the ground pin of sensor is to arduino ground also. Regulated 5V to transistor from a powersupply or from >5V to a voltage regulator (5V) to transistor.

7

after looking at the spec sheet i am a little confused.

The heater requires 0.9V and has an internal resistance of 4.5 Ohms. It also lists the heater current at 120 mA.

I plan on using 4xAA batteries so assuming my voltage for all four in series is approximatley 5.5 volts

should I size the acompaning resister in a voltage divider layout to be around 20 OHms to get the 0.9 Volts at the heater?

This will however give me a total current of about 220 mA.

will this harm the sensor?

8

here is all you need
http://sensorworkshop.blogspot.com/

But it seems heater voltage is not the same there
so you need a resistor/pot between your voltage and pin to tune your voltage down to 0.9V

Are there only 3 pins on your sensor?

9

my sensor has only three pins.

one GND, one for powering the Heater, and one for the sensing resistance.

The part number is MQ303A. It is not the same one pictured on the blog, but similar. Thanks for the link.

I will try it out tonight.

I bought two just in case I break one :slight_smile: