Interfacing a Senseair K22 Co2 NDIR Sensor via PWM

Forum 2005-2010 (read only) Hardware Interfacing
1

HI All,
I am posting this to interfacing in both forums as unsure about where this really belongs(moderators please feel free to place in correct forum)

I am attempting to interface the above Co2 sensor via PWM input with a pulsein command, I have it hooked up to d14(sanguino) through a 10k resistor on the input and a pullup of 4.7K to +5V

I got the k22 from www.co2meters.com(datasheet is here http://cdn.shopify.com/s/files/1/0019/5952/files/Spec070426-K22-PWM_ed2-2000.pdf?1254409988).

int pin=14;
unsigned long duration;

void setup()
{
pinMode(pin, INPUT);
Serial.begin(115200);
}

void loop()
{
duration = pulseIn(pin, HIGH);
Serial.print(" PPM Co2: ");
Serial.print(duration/20/100,DEC);
Serial.print(" Raw Sensor: ");
Serial.println(duration,DEC);
}

not sure if the readings I am getting make much sense (it does react to my breath very well) so was going to use baking soda and vinegar to rig a saturation test cell :slight_smile:

without breath on sensor:
PPM Co2: 138 Raw Sensor: 277993
PPM Co2: 138 Raw Sensor: 277990
PPM Co2: 138 Raw Sensor: 277994
PPM Co2: 138 Raw Sensor: 277989

with breath on sensor:

PPM Co2: 141 Raw Sensor: 283447
PPM Co2: 412 Raw Sensor: 824556
PPM Co2: 412 Raw Sensor: 824556
PPM Co2: 496 Raw Sensor: 993037
PPM Co2: 496 Raw Sensor: 993039
PPM Co2: 496 Raw Sensor: 993040
PPM Co2: 496 Raw Sensor: 993041
PPM Co2: 496 Raw Sensor: 993040

any suggestions from the forum?
gwen
ie the readings off by 300-350ppm or so
(too low)