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I have an LM34 sensor that I've used in the past for "hello world" projects, so I know at least it used to work. A while ago though.

I just recovered it from the bottom of a pile of components to do something with it, but I'm getting very strange behaviours:

  • when I touch it or apply a heat source to it, the output voltage goes down, not up.
  • when I use a 3V button battery or a stack of two (6V), I can touch it, but...
  • when I use a 9V battery it gets really hot (untouchable)
  • assuming the 9V battery issue is because it's drawing too much current, I use resistors, but I still get the output going down issue.
  • Knowing that this worked in the past with a microcontroller, and googling a bit, I found a really simple arduino project that requires no other components, and connects the pins to the 5V and ground. As soon as I do this, it again goes really hot (untouchable).

The issue of it getting really hot somehow makes sense to me, but I'm sure I've used it in this configuration before and I'm seeing articles about it too. Add to it the reversed output voltage, and I'm left completely confused, and just assuming, is it just broken? And did I broke it by connecting it straight into a 9V battery on the first place?

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  • \$\begingroup\$ Have you taken a really good look at the datasheet? I'm thinking that you have made a mistake with the pinout. \$\endgroup\$ Dec 20, 2016 at 1:42
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    \$\begingroup\$ The datasheet says you can connect it to +5V to +20V - i.e. directly, without a resistor - and it will use less than 90μA. So connecting it directly to a 9V battery should be fine. It has low self-heating (0.18°F) so if it gets too hot to touch, something went drastically wrong. I agree with @DwayneReid that you may have made a pinout mistake. Make sure you don't mix up "top view" and "bottom view" in the datasheet diagrams. At this point, the part may be dead. \$\endgroup\$ Dec 20, 2016 at 2:36
  • \$\begingroup\$ what a noob, that was it, I was reading the pinout upside down. Thanks guys. Feel free to write the comment as an answer and I'll mark it accepted. \$\endgroup\$
    – palako
    Dec 20, 2016 at 9:57

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As it was pointed out in the comments to the questions, one must watch out for the pinout, there is a note in the sheet right under the diagram that specifies that the pinout is the bottom view.

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