# Looking for 3v3 smoke detection sensor

Hi,

I am looking for a smoke sensor to detect a fire. All I could find need 5V. Because I am building a low power project I don’t want to use a level shifter. So i would be very grateful if you could hell me

Kind regards,
Tom

@hl68fx, can you elaborate on what type of sensor you are looking for and any links to the ones you have found? You may be able to use a 5V sensor without a level shifter.

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Hi peekay123,

I am looking for a MQ2 gas sensor like this one: Sensor

The discription says it detects smoke. I could only find these MQ sensor, but any other sensor who detects smoke would be fine too.

@hl68fx, the Grove sensor has an adjustable load resistor (RL) so you can adjust the maximum voltage output/sensitivity of the MQ2 sensor. You can power both the MQ2 heater and Vc (the sensor voltage) with 5V and measure the output of the Grove board using a voltmeter (NOT connected to your Core just yet). Adjust the trimpot to some safe value below 3.3V and then blow some smoke on the sensor to see how it reacts. Adjust the trimpot so the voltage never exceeds 3.3v. Typically, that would be around 4700 ohms or so. Once you are confident that the output voltage will not exceed 3.3v, you can connect it to your Core.

If possible, disconnect the MQ2 sensor entirely and measure the set resistance of the trimpot (RL). Then the formula

Vout = 5 * RL / (RL + RS) where RL is the trimpot resistance and RS is the sensor resistance.

You can solve for RS, giving (if I’m correct!):

``````  Rs = RL * (5 - Vout)
---------------
Vout
``````

You can then get the ppm from the datasheet chart.

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Thank you very much for your answer! That helps me really a lot
I am going to buy this sensor in the next few days and let you know if everything works.

Kind regards,
Tom

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Hi @hl68fx, Does it work with a 3.3v photon?

Hi @FiDel FiDel,

in the end I have bought a cheap smoke detector from a DIY market and connected this to my Photon.
I was using this tutorial: http://www.instructables.com/id/Modify-a-6-EUR-smoke-detector-for-use-with-microco/

I hope it helps you

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