MG812(Co2) Sensor ppm calculation

[Mahendra Sondagar]

Hello Folks,
This one is my first post here

from few day I'm playing with MG812 Co2 sensor let me tell you that the sensor is quite similar with famous MG811 Co2 sensor but instead of high voltage(6V) it uses** 5V**.
both sensor produced EMF in mV at the output w.r.t Co2 concatenation when Co2 concentration rises output falls.

here is the datasheet for MG812 sensor
0_1473162025895_MG812 CO2 Manual V1.1.pdf

I've taken MG811 as a reference for ppm calculation
here is the link for the firmware from DFrobot
link text

I've use this code with my sensor when i play it my arduino shows, **Under heating/beyond range(400~10,000)
**
that's why I've decides to display it's o\p EMF,
my problem is when i make simple code to to read it's sample voltage then sensor's o\p voltage is not same as suggested in datasheet(250-330mV)

here is my pin config got the Sensor
pin connection

1(Heater1) ---------> +5V
3(Heater2) ----------> GND
2(TE1) ----------> GNG
3(TE2) ----------> Arduino(A0)

here is my o\p on Arduino terminal
MG812 Co2 sensor Interfacing...
Samplse: 23
Volts: 0.11
mV: 112.3046875000

Samplse: 15
Volts: 0.07
mV: 73.2421875000

Samplse: 21
Volts: 0.10
mV: 102.5390625000

Samplse: 16
Volts: 0.08
mV: 78.1250000000

Samplse: 18
Volts: 0.09
mV: 87.8906250000

Samplse: 19
Volts: 0.09
mV: 92.7734375000

Samplse: 15
Volts: 0.07
mV: 73.2421875000

Samplse: 22
Volts: 0.11
mV: 107.4218750000

Samplse: 16
Volts: 0.08
mV: 78.1250000000

Samplse: 19
Volts: 0.09
mV: 92.7734375000

Samplse: 19
Volts: 0.09
mV: 92.7734375000

Samplse: 17
Volts: 0.08
mV: 83.0078125000

Samplse: 20
Volts: 0.10
mV: 97.6562500000

Samplse: 15
Volts: 0.07
mV: 73.2421875000

Guys can any one help me here
I'll appreciate all precious comments and suggestions

[Yveaux]

@Mahendra-Sondagar welcome to the forum!
Did you check with a multimeter if the voltages are the same as the arduino reports?

[Mahendra Sondagar]

yes, Yveaux
I've check through multimeter before

[Yveaux]

@Mahendra-Sondagar then most likely it is an issue with your code to read out the ads. Please share your code it with us.

[Mahendra Sondagar]

@Yveaux
The code is straight foreword it simply reads ADC's channel and convert in to voltage

Insert Code Here
#include <Arduino.h>


void Setup(){
Serial.begin(9600);
Serial.println("MG812 Co2 ppm calculation...");
delay(1000);
}

void loop(){

uint16_t  samplse= analogRead(0);
Serial.print("Samplse: ");
Serial.println(samplse);

float volts=((5.0*samplse)/1024);
Serial.print("Volts: ");
Serial.println(volts);


float mv=(volts*1000);
Serial.print("mV: ");
Serial.println(mv);


delay(2000);
}

[Mahendra Sondagar]

@Yveaux
Have you read datasheet here...
At the o\p side they mention unity gain amplifier with OpAmp

but the thing is that unity gain amplifier always produced same output volts!