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I am using an Arduino Uno board for sensing analog input. I have connected the board only through a USB cable to my laptop, but the board does not sense analog input,

Is it necessary to use an external power supply ?

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    What sketch are you using? What do you mean it "doesn't sense"? What sensor are you using? You don't have to use an external power supply for the ADC to work. – Jason Stewart Mar 11 '16 at 3:54
  • I am using "Analog Input" sketch from Examples, where A0 is used as analog in. I have connected 10k pot, to +5, and gnd, center pin to A0 input, 'does not sense' mean there is no effect on LED connected at pin 13 when pot is set to different positions, Later the board seems to have burnt when pot was set to minimum level (zero volt input to A0) – user2064616 Mar 12 '16 at 3:09
  • Setting the pot to minimum would not burn out the board, if the connections are as you say they are. An external power supply should not be needed, USB should supply enough power. When you say the board has burnt out, does power LED still work? Does the Arduino still respond to the IDE, if you try to upload "Blink" for example? If Blink still works then the board is probably not burnt out. – Greenonline Mar 16 '16 at 7:50
  • I think "burnt" = you blew the polyfuse. This means that you made the wrong connections to the potentiometer, connecting the cursor to either 5V or ground. If the led is always on then you probably connected ground to the cursor (and so the delay between turn on and off is around 1ms), while if the led blinksat about 0.5 Hz you connected +5v to the cursor (and so the period is always 2*1024ms). Double check the potentiometer pinout with a multimeter, then triple-check it and, if you are really sure it is right, check it again... – frarugi87 Mar 16 '16 at 9:02

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