Help With CO2 Sensor

[wifigod]

Hey Guys,

With my ongoing automated mushroom grow chamber project, I want to add the ability to add a CO2 sensor to the setup and have it trigger a fan to blow fresh air in when needed. Normally CO2 sensors I've found have been prohibitively expensive, but recently I stumbled upon this page: http://www.futurlec.com/Gas_Sensors.shtml

On that page they have a $20 CO2 sensor with the following datasheet: http://www.futurlec.com/CO2_Sensor.shtml

My electronics experience as far as circuitry goes is basically nil. I'm getting the general idea of how to hook this up and get some readings, what I don't know is all that I would need to convert the voltages/power levels to the proper levels using the supplied 5v power on the ioBridge. What all would I need and is it possible to interface this relatively easy with the ioBridge's analog input?

Thanks for any insight you can give me!

[fillibar]

The biggest thing you would need is a way to calibrate the readings to what your ioBridge is reporting (after you hook the sensor to it). So if it says 1000... 1000 what... If you have a different method for reading the CO2 (something manual you might have now?) then you can see that 1000 corresponds to X value. Get a few more readings (maybe place it in different rooms not just the mushroom one, or by the CO2 source itself for example) and with the various readings calibrate your ioBridge's results so they match what the other sensor states. Then from that point on you have it set (unless the CO2 sensor itself can loose calibration over time, it happens for most sensors).

[IOBridgeAndy]

The Futurlec and Sparkfun has the same Co2 sensors. But there is a cheaper version
at Link: http://www.seeedstudio.com/depot/electronic-brick-family-sensors-c-48_52.html

To interface it to IOBridge connect the Gnd to Gnd, +5 Volt to +5 V and the signal out to the analog input on the IO bridge.

Warning ... You need calibration (gas) and precision test equipment to calibrate this sensor. Also, it is not recommended to use this sensor as the main (life) protection alert or warning device.

BTW ... to the other users ... the above  website carries alot of sensors that can be attached to the IOBridge (check Electronic Bricks out)
 

[solarguy]

The bare sensor component draws more power then the Bridge can provide.  almost all of these types of gas sensors have an internal heater that draws 150 to 200 milliamps.  The way that they work is that the heater warms up a sensor that changes its resistance relative to the gas density present.  This resistor is used as part of a resistance divider to derive a voltage output.  So if you use an external 5 V power supply that is very clean you can use the sensors and then just connect the resistor divider to the I/O bridge analog input.  Calibration is a whole other issue, have no thoughts on that.

[jbatchelor51]

Calibration to be accurate is not an easy thing to do.  Approximations are possible by using some kitchen chemistry to make CO2 from Baking Soda/Vinegar, but you need to some how purge the system of CO2 to get a 0 concentration.  Maybe make O2 using hydrogen peroxide/piece of uncooked ground beef.  You can bubble the pure 02 into an inverted cup long enough to insure all other gases are gone.  The use a known weight of NaHCO3 to make a known amount of CO2.  You could also use whip cream cans to purge gases out and replace with all Nitrous Oxide, then blend in CO2.  Or a battery and water to make H2 and O2 (cathode/anode respectively if my e-chem serves me correctly)

Not so easy to calibrate....and be careful with the pure O2....it makes things burn really well...Most of these sensors are calibrated by purchasing premixed gas blends.


and in both cases above, don't let the pressure build up.....the chemistry happens until its done no matter what you do.