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I have done my project on alcohol detection for drivers, but I don't know the minimum and maximum distances between the alcohol sensor and the driver. What are the maximum and minimum distances?

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MQ-3 Alcohol Sensor is base the amount ethanol molecules that is present near the electrodes. Therefore minimum and maximum distance had no or little bearing.

To give a little insight in to how the MQ3 sensor works.

The sensing element as shown in the picture below is a cuboid structure made out of an Alumina (Yellow) tube covered with Tin Dioxide (Light Brown). The electrode which is made out of Aurum is shown in Black.

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The pin out and a drive circuit for the sensor are shown below.

MQ3 Sensor pin out

MQ3 Circuit

The above circuit activate the heating element.

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As a result electrons begin to move because Tin Oxide ceramics has become a semi-conductor.

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Now when air with alcohol elements enter the cuboid structure the circuit generate additional current because the ethanol burns into Acetic acid.

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Therefore the minimum or maximum distance has no bearing, but the presence of alcohol will have significant effect on the sensor. For more detail information review the references.

References:

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