Sanity check - analog input co2 sensor

Forum 2005-2010 (read only) Hardware Interfacing
1

I'm connecting a CO2 sensor to an analog pin. Im not so good at reading schematics so I was hoping somebody could say yea that looks right before I toast this sensor or arduino.

heres my nifty fritzing. what a cool program!!

I dont plan on using the alarm so i left that part of the circuit out.

and heres a link to the datasheet.
http://sundaecorp.com/co2meters/Documentation/Datasheets/DS22-LO-01%20-%20K22%20LO.pdf

http://www.co2meter.com/collections/co2-sensors/products/k-22-lo-co2-sensor-module

thanks for looking.

2

Fritzing aint right, sorry.

Why does fritzing show a chip? iTs a circuit board like the arduino. And you have the analog out shorted to ground anyway.

3

ok thanks.
So then can you tell me what this means?
It looks tome like it goes from pin 4 to ground to a resistor to arduino.

what am I reading wrong?

Fritzing shows a chip because its just a place holder for 4 pins.

I saw those caps but I thought they were just showing what was already on the PCB.
Why is it to the left (on the other side) of the connection to arduino. how would I connect it? Or is it paralell vs in line?

4

ah. i see my fritz didnt match my own words.
hows this one?

5

Breadboard columns are all the same node. So your resistor is shorted out by the column. (In other word, you don't want to wire it this way.)

6

ok. im not using a breadboard. how about this?
If this is correct I dont see how it matches the diagram? Bu this is howmy other sensors are connected.

7

what is the ground between pin 4 and the resistor in their diagram referring to?

8

ah. ok. according to some reading they usually put an amount in uF for the cap size. Wonder why they didnt. I see they recommend a 220uF between pin 1 and 2 as well.
Why would a capacitor between ground and the sensor be for? voltage fluctuations?

9

ok . because of this:

Capacitors can also eliminate ripples. If a line carrying DC voltage has ripples or spikes in it, a big capacitor can even out the voltage by absorbing the peaks and filling in the valleys.

thanks. Ill go try wiring it up now.

10

Hello,

This is Andrew Robinson from CO2Meter.

Just a few comments to get you up and running properly:

  • You can really get away without any caps on this circuit. The analog output will be read just fine by the ADC, but if you have noise problems down the line I would add a small valued (.1uFish) cap to the analog output.
  • The 220uF cap is already installed on the sensor, it's used for decoupling. The CO2 sensor operates with a pulsed IR lamp that has a nasty current spike, to give predictable behavior it is decoupled on board.
  • The 10kOhm resistor on the signal line is just for current limiting. If you were so inclined, you could omit it too. The schematic is definitely for a more robust implementation, for hooking it up to an Arduino you just need some bits of wire.
  • We have an app-note on communicating with these sensors via I2C on the Arduino platform, instead of using the analog output, if you're feeling ambitious. You'll get a more precise reading out of it, and I've always considered digital readings a little more kosher when available.

Let me know if you have any further questions!

11

always cool when the manufactor chimes in. Thanks