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[on:]

Hi everyone.

I tried to read value from an LM335 temperature sensor, i used this tutorial http://learn.adafruit.com/tmp36-temperature-sensor/using-a-temp-sensor.
In my room the temperature is 20.2C but the arduino serial monitor  display wrong data like these:

Sensor value Analog Pin 0: 755.00
Calculated Volt: 3.69
Calculated Milli Volt: 368.65
Calculated Cersius: 95.50
Calculated Fahrenheit:: 203.90
----------------------------------
Sensor value Analog Pin 0: 757.00
Calculated Volt: 3.70
Calculated Milli Volt: 369.63
Calculated Cersius: 96.48
Calculated Fahrenheit:: 205.66
----------------------------------
Sensor value Analog Pin 0: 756.00
Calculated Volt: 3.69
Calculated Milli Volt: 369.14
Calculated Cersius: 95.99
Calculated Fahrenheit:: 204.78
----------------------------------
Sensor value Analog Pin 0: 756.00
Calculated Volt: 3.69
Calculated Milli Volt: 369.14
Calculated Cersius: 95.99
Calculated Fahrenheit:: 204.78
----------------------------------
Sensor value Analog Pin 0: 756.00
Calculated Volt: 3.69
Calculated Milli Volt: 369.14
Calculated Cersius: 95.99
Calculated Fahrenheit:: 204.78
----------------------------------
Sensor value Analog Pin 0: 761.00
Calculated Volt: 3.72
Calculated Milli Volt: 371.58
Calculated Cersius: 98.43
Calculated Fahrenheit:: 209.18
----------------------------------
Sensor value Analog Pin 0: 757.00
Calculated Volt: 3.70
Calculated Milli Volt: 369.63
Calculated Cersius: 96.48
Calculated Fahrenheit:: 205.66
----------------------------------
Sensor value Analog Pin 0: 761.00
Calculated Volt: 3.72
Calculated Milli Volt: 371.58
Calculated Cersius: 98.43
Calculated Fahrenheit:: 209.18
----------------------------------
Sensor value Analog Pin 0: 756.00
Calculated Volt: 3.69
Calculated Milli Volt: 369.14
Calculated Cersius: 95.99
Calculated Fahrenheit:: 204.78
----------------------------------

I used  this code

Code:

// ------------------
    void loop() {
// ------------------

  // Take sample_count temperature readings.  Will calc the average.
 

    sensor = analogRead(sensorPin);
    Serial.print("Sensor value Analog Pin 0: ");
    Serial.println(sensor);
    volt = (5.0 * sensor) / 1024.0;
    Serial.print("Calculated Volt: ");
    Serial.println(volt);
    milivolt = volt * 100;
    Serial.print("Calculated Milli Volt: ");
    Serial.println(milivolt);
    c = milivolt - 273.15;
    Serial.print("Calculated Cersius: ");
    Serial.println(c);
    f = (c * 9/5) + 32;
    Serial.print("Calculated Fahrenheit:: ");
    Serial.println(f);
    Serial.println("----------------------------------");
    delay(1000);
  }

These code i found here on arduino forum :
 

[Reply #1 on:]

well, millivolt should be volt/1000.0, not volt * 100.0.

[Reply #2 on:]

well, millivolt should be volt/1000.0, not volt * 100.0.

Hmmm, millivolt = volt * 1000, because 1 Volt is 1000mV.

The page you linked to uses a completely different sensor, I was a bit surprised that you measured anything at all with this wiring. Did you consult the datasheet of your sensor?

[Reply #3 on:]

Oops, he still needs 1000 vs 100, though.

[Reply #4 on:]

Agree on the use of 100 from above. Also make sure you have wired it up properly, although usually you get no reading rather than a wrong one.

volt = (5.0 * sensor) / 1024.0;

The assumption here is that you have 5 volts. If you are powering the Arduino from a USB port this is probably not the case - it is worth checking with a voltmeter. Remember that you are getting 0-1023 for the full range of the voltage. If you have 4.5 volts you will be 10% out. Sometimes my USB port is as low as 4.2 volts.

At the location in my signature below I have a library that tries to calibrate itself by working out what the voltage actually is, using the internal Arduino voltage reference. I know this library works so it is worth using it to check your hardware setup using it.

Edit: Look at the circuit here: https://github.com/hgdeoro/py-arduino-proxy/wiki/Example%3A-Testing-LM335

[Reply #5 on:]

Yes the LM335 and the LM36 are two very different sensors requiring a different way of wiring them up and a different way of converting the reading into a temperature. Apart from that it is fine.