I bought a 3-pack of the MQ-135 and I let the sensor burn-in for 24 hours. I consistently get a value of 500-530. I introduce smoke to it and the value never changes. Not sure if all the sensors are defective, but from what I've read online, I should get 100-150 value in clean air and it'll go up from there if detecting anything.
I'm leaning towards something other than the MQ-135 and really would like to buy a highly sensitive one. Maybe one that can detect 2nd hand smoke from a ways away.
Any ideas for alternative sensors? I'm willing to pay more than a few bucks for this if it's good.
The MQ series of sensors is priced so cheaply for a good reason: they are very finicky, require extensive burn-in and and careful calibration to be at all useful. You should not believe any values you read on line.
Since they all detect several gases, they can only report that something in the environment has changed.
An air particle sensor like this one might work for you, otherwise buy a commercial smoke alarm with digital output.
First I strongly agree with jremington's post. There is a reason any of the MQ sensors are so inexpensive (cheap). Next as to smoke detection you want to give this NFPA (National Fire Prevention Act) page a read. You choose the sensor based on the technology and your intended application.
By the actual documentation for the device, you also need to do the calibration for the gas you want to detect. Their suggestions is to use ammonia if you want to detect ammonia. To use alcohol if you want to detect alcohol.
There is nothing in the official document about "smoke" detection. What gas is in your smoke that you wish to detect?
Thank you all for the quick responses! Appreciate it.
I'll look into the links provided.
I want to detect near-by 2nd hand smoke from cigarettes. I assume lots of stuff in that, just don't know what would be the easiest to detect reliably or if multiple sensors combined will help determine, yes, it is in fact 2nd hand smoke.