Carbon Monoxide detector circuit

[Chris815]

New member here, first post. I'd like some advice on how to build a circuit for detecting carbon monoxide gas. I'm building this project fairly low tech and cheaply as it's mostly for fun with some real life useage for demonstrations.

I've found a sensor online which has a good range of gas detection sensitivity, good enough for me anyway.

Here's a link
http://www.amazon.co.uk/Sensitive-Control-Carbon-Monoxide-Detector/dp/B00HG7HZQW

It has four pins, but I don't know which are the triggers. All of them? How do I connect it up to a simple circuit that, for example, would sound a buzzer as soon as a certain level is detected (can be set on the module) and go off when the under that level.

 

[Arouse1973]

Hi Chris, does it have any markings for the pins on the other side of the PCB. Your going to have a TTL (Digital) output an analog output and +V and 0 V (Common)
Adam
Oh welcome to EP

 

[Chris815]

Thanks Adam, the product listing states there being a signal output indicator and a dual signals output (analog output and TTL output). TTL output signal is low level, allows to connect with SCM directly. Analog output 0~5V.

No idea what an SCM is, I've googled around and found nothing other than electronic companies with those letters in their name haha. No idea what TTL is either!

 

[Arouse1973]

Could SCM be sensitive control module? TTL is digital level which for an output is around 0 to 0.4 Volts for a low level and 2.6 to Vcc (5 Volts) for a high level.
Adam

 

[Chris815]

Googled sensitive control module but coming up with nothing. Guessing it's not as simple as connecting some pins up to a buzzer circuit that sounds when the input is triggered by whichever one or two of the pins when it detects the gas?

 

[Arouse1973]

Look at the words in the link you provided, I think it's what they call the CO module?

 

[Arouse1973]

Googled sensitive control module but coming up with nothing. Guessing it's not as simple as connecting some pins up to a buzzer circuit that sounds when the input is triggered by whichever one or two of the pins when it detects the gas?

I think it could be that simple. What buzzer are you going to use?
Adam

 

[davenn]

its a pity there are no datasheets for the module

 

[Arouse1973]

its a pity there are no datasheets for the module

Yeah it's poor really. You can get one of the sensor on it's own but for the module I couldn't find one.
Adam

 

[Chris815]

Any 5v buzzer will do, I'll have a look for one later. Yeah I found the sensor data sheet too, the LM393 doesn't want to be found.

I've found this though, looks like four pins on the first diagram, but being pretty basic with electronics I may be well off?

http://www.onsemi.com/pub_link/Collateral/LM393-D.PDF

 

[Arouse1973]

That's the IC they are using to generate the TTL level. What I was trying to find was the data sheet for the actual module. However it does tell you the output can sink 20 mA. So you need to find a buzzer that draw this much current or less. Otherwise you are going to need some kind of current buffer on the output.
Adam

 

[Chris815]

Alright. So it should work by hooking up the ground and signal pins in series with a 5v source and a suitable buzzer, the sensor and module together acting as a switch? Or is there a little more to it than that? Electronics aren't usually that simple in my limited experience haha

 

[Arouse1973]

Alright. So it should work by hooking up the ground and signal pins in series with a 5v source and a suitable buzzer, the sensor and module together acting as a switch? Or is there a little more to it than that? Electronics aren't usually that simple in my limited experience haha

Nope that's it, the LM393 has an open collector output so you connect the buzzer - Pin to the sensor and the + Pin to 5 Volts. These sensors normally draw quite a bit off current in the 150-200 mA region, because they have a heating element inside. So make sure your power supply can supply this much current without overheating.
Adam

 

[Arouse1973]

Oh one other thing make sure you get a D.C buzzer and not a transducer. People call them the same, but the transducer types require a varying signal to drive them and won't work with just a constant D.C level.

 

[Chris815]

Great thanks! Yeah didn't mean ground, meant the power pin. Once I've got it I can play around until it works. So I need a 5 volt DC 20mA or less buzzer.

As for power supply, maximum voltage is 5, but it'll still work with less, and I need a higher current/high capacity for because of the load from the heater coil. So would two D cell batteries work? That'll give me 3 volts and enough current since they're designed for high drain applications?

 

[Arouse1973]

Great thanks! Yeah didn't mean ground, meant the power pin. Once I've got it I can play around until it works. So I need a 5 volt DC 20mA or less buzzer.

As for power supply, maximum voltage is 5, but it'll still work with less, and I need a higher current/high capacity for because of the load from the heater coil. So would two D cell batteries work? That'll give me 3 volts and enough current since they're designed for high drain applications?

See what the operating range is for the buzzer, it might work with 3 volts and just be quieter. Give it a try.
Adam

 

[hevans1944]

This image may help with wiring that puppy up:
Visit this page for more information.
And this page too!

 

[dick56]

Check out this URL which is for the part number of the module. It lists that part for the CO sensor also.
http://thaiperfect.com/amazon/?submit=ASIN&cate=Photo&q=B00HG7HZQW

 

[dick56]

Here is the data sheet for the MQ-7 sensor.
https://www.sparkfun.com/datasheets/Sensors/Biometric/MQ-7.pdf

 

[Alec_t]

So would two D cell batteries work?

Not for long with continuous use. According to the datasheet the sensor average power consumption is ~350mW at 5V, so would be ~ 126mW at 3V. If D cell capacity is 20Wh, 2 D cells should run the sensor for ~ 2 x 20 / 0.126 = 317 hours (< 14 days).