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I have a MQ135 gas sensor from keyestudio, and a light sensor from a chinese manufacturer. They are both on their own PCB with resistors, small eeprom and a variable pot.

Turning the variable pot fine tune the calibration of the sensor, but is there anyone who could explain me exactly what is it doing? Does it have an effect on signal amplification? or only adding more or less resistance to the signal output by the light sensor in order to fine tune the reading ?

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If the resistance is higher, your LDR (light sensor) will respond in smaller increments or decrements to the same light changes. Analog inputs have 10 bit (0-1023) resolution, which is fine, but LDRs can be tricky (their sensitivity varies), so a pot is useful for prototyping the resistance you need to wire it up with in your project.

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It's for sensitivity adjustment.

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  • thanks, but I still don't get what is meant by sensitivity... if there is more light for example, while it higher the threshold to which the photoresistor will saturate or will it amplify the output ? – Vincent Teyssier Aug 12 '16 at 18:27

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