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Author Topic: Help with CO2 sensor hookup  (Read 3934 times)
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Don't remotely claim to understand what I am doing, but I bought this CO2 sensor:

...yet, did not realize it first needs 6V for the heater, but also the current requirements of 200mA.  Could someone help with how I would wire this to an arduino or should I start looking for a different 5V sensor???

Symbol  Parameter Name  Technical   Remarks
VH  Heating Voltage  6.0± 0.1 V  AC  or  DC
RH  Heating Resistor  30.0± 5%[ch937]  Room Temperature
IH  Heating Current  @200mA  
PH  Heating Power  @1200mW  
Tao  Operating Temperature  -20—50  
Tas  Storage Temperature  -20—70  
?  E??M F  Output  30—50mV  350—10000ppmCO2
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My first post so no links smiley-sad  Here is the datashet URL

http://www.futurlec.com/CO2_Sensor.shtml
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I wonder whether it really needs 2% regulation on the heater supply:  that seems a bit extreme.  I'd expect something more like 5%,  or even 10%,  in that application.

You can get that 2%,  though,  by using an LM317,  with a trimpot in the voltage-setting path.  A google search will turn up a datasheet,  and examples of how to do it.

Since the output is down in the hundreds of mV range,  you don't need to worry about the fact that the heater runs off 6V.   You can still use it with a 5V Arduino.

Ran
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I believe the 6V +- 0.1V is the maximum heater voltage not the
recommended operating voltage.

I have used the e2v line of sensors. For example the MiCS-5521CO sensor
specs a maximum heating voltage of 5V +- 0.1V. Under the operating
conditions table the typical heating voltage as listed as 2.5V.

(* jcl *)
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Thanks to the both of you for your guidance.  I am still awaiting the sensor to arrive before I really get to start playing with it.  Will try to post pictures when I do.
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Okay still need a bit of help.  Heater definately works, but I am having trouble understanding how to read the output...since it is in mV, how do wire A and B to an analog input?
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I'm very new to the electronics scene here, but this particular part is of interest to me, as I'm planning on incorporating it into my project as well.  To me, it appears A is connected to GND while B gives a mV level charge.

I could be reading that chart wrong, totally possible here, but it looks like  at 300 PPM (normal outdoor air level) it has a voltage of 325 mV and at 2000 PPM (as high as I need it) it will read 286mV, a difference of only 39 mV!!  With the arduino's 4.88 mV resolution, that's only ~ 8 steps total.  My thinking is correct here, right?  Not sure if this will work for you, it's not enough for me.

I'm working on other aspects of my project at the moment, but at the moment I think that either a higher resolution A/D converter (ADS1286PB??) or an op-amp would work to take this output to something more useful.  I know this post is a bit old, but then if you've figured out how to use it, I want to hear it!
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If you want an accuracy in the 0.5% to 1% range you can use the
ATmega ADC and condition the sensor with an instrumentation amplifier.
Analog Devices makes a number of pre-trimmed devices. If you get a x100 device
you will at a 3.9V span.

I would look at http://www.e2v.com and http://www.appliedsensor.com
The datasheets and app-notes are a lot more detailed.

(* jcl *)

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Quote
I'm working on other aspects of my project at the moment, but at the moment I think that either a higher resolution A/D converter (ADS1286PB??) or an op-amp would work to take this output to something more useful.  I know this post is a bit old, but then if you've figured out how to use it, I want to hear it!  
Back to top    

You have two choices:

1. Use external op-amp to increase the measurement range to use more of the normal 0-5vdc range of the Arduino analog input pin.

2. Use the analogReference(INTERNAL) command to make the Arduino measurement range around 0- 1.1vdc. This would give you around one step per millivolt resolution.  http://arduino.cc/en/Reference/AnalogReference

Lefty
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jluciani ~ not sure what you mean by .5% - 1%, are you referring to CO2 concentration, I'm trying to differentiate with a resolution of 50 ppm minumum, which is .005%!  I'm designing a CO2 controller that will be used in a greenhouse to take the ambient CO2 from 300PPM to 2000PPM, so I'm looking at a fairly narrow range.  I'm also thinking I'll need at least one full step of resolution in between the trigger level and releasing the trigger, and as one of the goals here is to maintain as stable of an environment as possible, I want this to be as small as possible.

If I get what you mean by '100x' 'instrumental amplifier', that's what I was leaning towards; I ordered a 10 pack of TL062 the other day for the pH probe I'm also going to try and cobble together.  I have an inkling of how to use these, but no experience with them yet.

I briefly looked into those two sites, but instantly I was turned off by appliedsensor's front page "We'll use our intellectual property, proprietary software tools" ... yeah, no.  smiley-wink   I'm trying to make this as open source as possible; that phrase just turns me off.  e2v looks a little more promising... even though some of their documentation says for IR11BR it measures between 0% and 100%, in the
more generic datasheet that covered the whole product range stated the IR11BD and IR21DB sensed 0-3000PPM,0-2.0% vol, and 0-5.0% vol... that might need a little further investigation, but for now, I think the sensor from Futurlec (MG811) will work fine.

retrolefty ~ "Use the analogReference(INTERNAL) command to make the Arduino measurement range around 0- 1.1vdc. This would give you around one step per millivolt resolution.  http://arduino.cc/en/Reference/AnalogReference"

Thank you!!!  If my math is correct, with a difference of 1700PPM being represented by a change of 39mV, a 1mV resolution would equal around 45 PPM per step.  Still a little higher than I would like, but hey, this will work!
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The 0.5% - 1% refers to the accuracy of the voltage reading. There will
be other errors in using the sensor. A 10bit ADC has a maximum accuracy of
apx 0.1-0.2%. There will probably be other errors in your system (especially
when you try to calibrate smiley-wink

Not sure why you need to use software from Applied Sensors. I downloaded the
app notes and datasheets which where PDF files. The couple times I have
called them they where pleasant to deal with.

An instrumentation amplifier (IA) is a special configuration of op-amps. The devices that you can purchase from Analog Devices have been laser trimmed to reduce
offset, gain and common-mode voltage rejection. It will be a lot less expensive to purchase an IA than to build your own using precision resistors and op-amps.

(* jcl *)
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jcl,

I also have the Futurlec MG811 CO2 Sensor
I would like to attach to an Arduino (ATMEGA328).

My plan is to be able to blow on the sensor and have LED's light-up,  more CO2 would make more LED's light up.
- or -
A certain amount of CO2 will make LED's flash differently.
- or possibly -
a timed rate of CO2 will make LED's flash differently.

I have been trying to follow along but I am new to all this.
You speak of math, %'s, PPM's, mV's. vol's . . .
I'm looking all this up, to try and understand.

I found another thread with people having the same problem.
Apparently the sensor was burned out trying to get it to work.

I found the instrumentation amplifier(s) but I can't figure out which one to get?
Any chance on a specific one?
Is this all I need?

Any help would be appreciated.
Thanks,
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I found this on another post from Riddick . . .

"both suggests that u use an amplifier in order to raise the input resistance and the sensitvity...
maybe a MAX9939 or a TLV4120 or a CS3302 is a good choice"
http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1272008003/5

This is different from your suggestion?
http://www.analog.com/en/amplifiers-and-comparators/instrumentation-amplifiers/products/index.html

Attempts burned out a CO2 Sensor here:
http://blowitallaway.com/?p=734
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the TLC271 (OpAmp) seems to be a good choice, 2...

if u dont like to make a complicated circuit, u might like these:
http://www.mb-systemtechnik.de/produkte_co2_messung_co2_sensor_modul.htm
http://www.senseair.se/oem.php
but they r more expensive, IIRC...

-arne
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-Arne

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Since I have a the Futurlec MG811 CO2 Sensor I should try and use it. (plan A)
I could use the Senseair as plan B (backup).

I will order what ever you think is easiest to use with Arduino and the Futurlec MG811 CO2 Sensor?

jcl, might chime in as well on this . . .

If I could be guided through it would be great.
Pick a something and I will order. . .
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