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Author Topic: Why did I melt my LM35DZ?  (Read 585 times)
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Dear all

I am new to Arduinos, having just bought a kit last week.  My kit came with an LM35DZ temperature sensor and I connected it directly to ground, 5V and pin A0, as shown on many internet tutorials.  I used the simple AnalogReadSerial sketch to read a value off A0, as I only wanted to show the sensor was working.  The serial monitor showed the board was transmitting and when I touched the sensor to try and change the reading I realised it was extremely hot (hot enough to burn my finger).

I then tried connecting a 220ohm resistor in the 5V line to the sensor.  The serial monitor showed no change in the value even when touching the (now cold) sensor.

I presume I have destroyed the sensor but what did I do wrong?  I definitely correctly identified the sensor pins.

Thanks in advance
Ian
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Brunsbüttel, SH, F.Rep.GERM
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hi!

can u show us a picture?
and the sketch?

i use many LM35 and they never get hot...

i say:
1.
either the polarity is wrong (5V/GND swapped)
2.
or u configured the A0 pin as output...

have fun...
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-Arne

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You should always double check every connection before you apply power - the alternative is expensive.
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Thank you for the replies.  The sketch I used was as follows (AnalogReadSerial from the Learning site)

Code:
/*
  AnalogReadSerial
  Reads an analog input on pin 0, prints the result to the serial monitor.
  Attach the center pin of a potentiometer to pin A0, and the outside pins to +5V and ground.
 
 This example code is in the public domain.
 */

// the setup routine runs once when you press reset:
void setup() {
  // initialize serial communication at 9600 bits per second:
  Serial.begin(9600);
}

// the loop routine runs over and over again forever:
void loop() {
  // read the input on analog pin 0:
  int sensorValue = analogRead(A0);
  // print out the value you read:
  Serial.println(sensorValue);
  delay(1);        // delay in between reads for stability
}

I connected it in accordance with the LM35DZ datasheet http://www.ti.com/lit/ds/symlink/lm35.pdf - I don't have a picture to hand but it was simply +Vs to 5V, GND to GND, Vout to A0.

A Google Image search for "lm35dz arduino" shows a lot of pictures where the ground and 5V are the opposite way around to that shown on the datasheet.  I assume the orientation of the ground and +Vs pins is switched depending on the manufacturer and I got it the wrong way around?

Ian

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Quote
I connected it directly to ground, 5V

Next time, put a small resistor to its +Vs pin, in case of wrong connection. Anything less than 1k will work. After that, you can take it out if you wish.
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Quote
A Google Image search for "lm35dz arduino" shows a lot of pictures where the ground and 5V are the opposite way around to that shown on the datasheet.
Er no.
This implies that you miss read the data sheet. On page 2 you will see the view is from the bottom. I looked at a few images from google and they all looked right to me.
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Er no.
This implies that you miss read the data sheet. On page 2 you will see the view is from the bottom. I looked at a few images from google and they all looked right to me.
I can't argue with that.  Don't I feel silly....

Thanks everyone
Ian
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