LM335A temperature sensor ADJ voltage too low

Forum 2005-2010 (read only) Hardware Interfacing
1

I'm pretty new to Arduino and seem to be having trouble even getting a simple test project going : (

I have an Arduino Duemilanove, an LM335A temperature sensor, and a 1K Ohm resistor in a breadboard wired like so...

The LM335 is plugged into the board with the ADJ pin in position 3G, the middle pin in position 4G, the right pin in position 5G. So, the + pin is 4G, the GND pin is 5G.

I have a resistor plugged into H4 and I4.

I have a wire connecting the +5V from the Arduino Duemilanove to J4, and the GND connected through a wire to J5.

I have a wire connecting 3F to the analong IN pin 0 on Arduino Deumilanove.

As far as I can tell this is the schematic created:

|----------| 5V+ -------////-------- V+ |----------|
|-Arduino| 1K R | LM335A|
|----------| - GND ---------------------- V- |----------|
| |
Analog PIN0-----------------------------------ADJ

When I plug it into myUSB cable, and use a voltmeter to measure the voltage, I see some screwy things :frowning:

Here is what I measured:

Voltage out of Arduino: 4.86
Voltage on + LM335A pin: 4.86 or 4.85
Voltage on ADJ LM335A pin: 2.13

In Arduino, the sensor value resulting from analogRead on pin 0 returns 475! Suggesting that Arduino thinks the voltage on ADJ is ~2.32

But that's not even the worst part... I could deal with it if the readings were consistently off by a certain amount... but, I would expect the whole thing to at least react to different temperatures.

I put Arduino and the breadboard on a plate and stuck them in the fridge (with the USB cable coming out through the closed fridge door).

The voltage on the ADJ pin went UP! So, apparently, it's warmer in my fridge than it is in the rest of my house!

Any ideas on what I'm doing wrong?

2

Oh also, the LM335A feels VERY hot to the touch after just a few seconds of power.

If I leave my finger on it for more than 2 seconds I would get a painful burn...

3

You are sure you connected the sensor correctly? This sensor does not take much current to operate at all (< 1mA) and should not be hot at all. If the connections are correct then the sensor might be faulty.

4

BV, have you figured out what you did wrong? cuz i am facing the same thing as you. Hope you can help me out. Cheers.

5

I've just got this sensor, and I think you have it wired up incorrectly. In the simple uncalibrated configuration, you should not have anything connected to ADJ.

For the simple uncalibrated circuit, it should go:

Analog PIN0-------------------------.
| |
|----------| 5V+ -------////-------- V+ |----------|
|-Arduino| R1 | LM335A|
|----------| - GND ---------------------- V- |----------|

You just measure the voltage at PIN0 (Vout) and hard code a calibration at a reference temperature:
Tout = Vout * Temp_ref / Vout_ref

The calibrated setup has a pot connected to ADJ, Gnd and PIN0 (wiper at ADJ) (see datasheet).

6

If you did indeed wire it up wrong like in the original post it is hard to see why it got hot as the current would be limited by the 1K resistor. In order for it to get hot you must have wired it up in some other wrong way. you might have fried it already.

7

I figured it out. Thank you for your help. ;D ;D

8

hi, do share the problem and the solution as i'm currently facing a similiar problem too....