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Author Topic: Carbon Dioxide Wiring Help!  (Read 1904 times)
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I'm trying to wire a carbon dioxide sensor to be read by the Arduino but I'm having some trouble figuring out the wiring diagram.



So far I can see that the two H's have to be connected to +6v and -6v.
Both B's are connected to the "+" side of an op-amp.
Both A's are connected to the output as well as the "-" input.

What op-amp can I use for this sensor? and what is the "mV"? is that just the voltage coming out of A?
also, which output do i connect to the Arduino pin?

Here's the link to the datasheet: http://www.futurlec.com/CO2_Sensor.shtml
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No the two H's have to have 6V between them.  Its a 6V heater, either 6V DC or 6V rms AC.

Its not a good diagram.  I suspect A is signal ground, you measure the EMF developed at B relative to A (the op-amp circuit gives a high input impedance.

I'd try to find a better datasheet for this kind of sensor.  The mV is probably meant to represent a voltmeter

Might this be the same sensor: http://www.parallax.com/Portals/0/Downloads/docs/prod/sens/CO2SensorDatasheetMG811.pdf - that implies you need a very high input impedance CMOS opamp to measure
the signal (input impedance 10^11 ohms or larger).
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The MG811 is also used here: http://middlewaresensing.wordpress.com/2010/08/04/wine-monitoring/

That futurlec CO2 sensor is the MG811.
This sensor needs 6V for the heater, so you need an seperate power supply for it.
There are small circuit boards with this sensor, which have already an amplifier and voltage regulator.
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No the two H's have to have 6V between them.  Its a 6V heater, either 6V DC or 6V rms AC.

Its not a good diagram.  I suspect A is signal ground, you measure the EMF developed at B relative to A (the op-amp circuit gives a high input impedance.

I'd try to find a better datasheet for this kind of sensor.  The mV is probably meant to represent a voltmeter

Might this be the same sensor: http://www.parallax.com/Portals/0/Downloads/docs/prod/sens/CO2SensorDatasheetMG811.pdf - that implies you need a very high input impedance CMOS opamp to measure
the signal (input impedance 10^11 ohms or larger).

Yes that's the same sensor.

also, I do not have the money to buy the pre-made board as it costs $50. I don't know what to do :[
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i found the NDIR principle quite useful...
http://en.wikipedia.org/wiki/NDIR
http://en.wikipedia.org/wiki/Carbon_dioxide_sensor

the sensor boards r quite inexpensive, too...
and they might need less power than that heating thing...
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Yes that's the same sensor.

also, I do not have the money to buy the pre-made board as it costs $50. I don't know what to do :[

I have the Parallax CO2 board with MG811 for use at my workplace, we were characterizing it for possible use in a project.  From my own investigations with it, depending on what you want to do with the sensor the board isn't necessary and might not be worth the extra money.  The main purpose of the Parallax board is the an alarm function, the output is an alarm signal goes high if a manually set CO2 threshold is exceeded (the threshold is set using the board's potentiometer and a voltmeter).  In order to achieve this the board also raises the original sensor signal's voltage from a 250mV to 330mV range to one around 1.8V to 2.4V; but this is only available on test pin vias, not through the premounted headers.  In both cases the lower end of the voltage range means higher levels of CO2.  

As stated earlier, if you don't want the alarm feature and would like a different voltage range (e.g. changed so it's range is closer to 3.3V or 5V and inverted so the higher voltage readings correspond to higher CO2 levels) the Parallax board is probably a waste of money.  In any event, if you want to use this sensor with an Arduino you will need to change the signal's voltage level.  Even using 1.1V as a reference it's difficult to get useful readings from the sensor's direct output and lower voltages are innately more prone to EMI issues.

I hope this helps!
« Last Edit: June 21, 2012, 10:14:01 am by Far-seeker » Logged

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There are small circuit boards with this sensor, which have already an amplifier and voltage regulator.
.

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