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Different result if connecting 9V?

Former Member

I have done the project in Jeremy Blum "Explorign Arduino" related to the three color LED changing with the temperature. It works right when connected with USB, but it is always red if connected to 9V.

Did I do anything wrong? is it normal? how can I solve it?

The sensor is a TMP-36image

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  • Per John's comment, I'm assuming you're using a 9V barrel adapter.

    A couple of points:

    1.     You have to get enough power for the Arduino, the LED, the TMP36, etc.  I never use carbon-zinc batteries or cells (usually labeled "Heavy-Duty").  I prefer Lithium batteries or cells as they can output high current, when needed; but alkaline batteries/cells should be OK.  Check the battery: not just the voltage, but how much current it can output.  Preferably use a new battery.

    2.     The type of problem you're seeing is almost always due to insufficient power.

    3.     Since it's working properly with USB power (original USB 2.0 specifies 5V at 500mA) that should tell you what you need to replicate for total max power.

  • in reply to Former Member

    Hi Brian,

    I have also found that even with batteries it is usually a good idea to have a decoupling capacitor across the power feed.

    John

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