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[on:]

Hi everyone,

I´m having some trouble with installing the MQ 3 to Arduino. We planned to do an upgrade for a bike and connect it to the alcohol sensor MQ 3. If you have under 1.6 promille a red light should be enlightened, if you have more than 1.6 promille a red light should be on. Now we desperately need a code for this action. Please help...

[Reply #1 on:]

http://nootropicdesign.com/projectlab/2010/09/17/arduino-breathalyzer/

Conclusions

It’s really hard to calibrate this sensor for even an approximate BAC reading. It’s even difficult to correlate readings to looked-up BAC values. There are many environmental factors that affect the resistance within the sensor (humidity, temperature, oxygen concentration), and this is only a $5 device anyway.

[Reply #2 on:]

This is an introduction with all the problems with these gas sensors: http://arduino.cc/playground/Main/MQGasSensors

So you have to do the burn-in time. After that you have to find a good value for the resistor. After that you need a standarized mixture to measure at what analog value the alcohol percentage is. The code is just analogRead() to get the analog value.

If you have done all that, the sensor needs time to heat-up. That could be 2 minutes. This is needed before using it every time.

For analyzing breath, the MQ303A is a much better choice. It doesn't need to be on for 2 minutes before use.