Arduino temperature sensor counting back - arduino

Question

I am trying to get my new velleman vma320 to work with my arduino.
It doensn't work at all, the temperature goes down its heated up. I've tried everything. Can somebody help me? Here is my code...
int SensorPin = A0;
void setup() {
Serial.begin(9600);
}
void loop() {
//reading
int sensorvalue = analogRead(SensorPin);
Serial.print("value: ");
Serial.print(sensorvalue);
//voltage
float voltage = sensorvalue * 5.0;
voltage /= 1024.0;
Serial.print(", volts: ");
Serial.print(voltage);
//temperature
float temperature = (voltage - 0.5) * 100 ;
Serial.print(" degrees C");
Serial.println(temperature);
}
Is it something I have done wrong? Or is it just the sensor? I tried it with two sensors.
If you can help me that would be awesome.
Thanks in advance,
Jens Van den Eede.

Answer 1

So, this is the working code for a thermister velleman vma320. According to the way it's wired, voltage will go down as the temperature goes up, and it's not linear.
#include <math.h>
double Thermistor(int RawADC) {
double Temp;
Temp =log(10000.0/(1024.0/RawADC-1)); // for pull-up configuration
Temp = 1 / (0.001129148 + (0.000234125 + (0.0000000876741 * Temp * Temp ))* Temp );
Temp = Temp - 273.15; // Convert Kelvin to Celcius
return Temp;
}
void setup() {
Serial.begin(9600);
}
void loop() {
Serial.println(int(Thermistor(analogRead(A0))));
delay(1000);
}

Answer 2

Please note the above code only provides accurate temperatures if you are supplying the VMA320 with 3.3VDC (from VCC, not 5V).
Also add "Temp = (Temp * 9.0)/ 5.0 + 32.0;" above "return Temp;" if you wish to convert to °F