Problem in reading analog pins of arduino mega 2560

hello frnds.. I am using arduino mega 2560 board to read ADC count on hyper terminal. In my program.. i m using all 16 (A0 to A15) analog pins of arduino. When i connect A0 pin to +5v it gives 1023 counts... its okk. but when i connect A1 onwords it gives 800 to 900 counts..!!!! Why is it so???? I want full counts on A1 onwords pin... I tried with 4.7K pull up and pull down resistor too.. but output is not coming properly. is there necessity of pull up or pull down resistor???? if yes then plz tell me the which kind of combination it will require???

Post your sketch. Post your schematic. Give your keyboard a shake - the punctuation keys look like they are sticking.

Post your sketch. Post your schematic


Careful AWOL, don't break into song.

Tom...... :)

@tom and @Awol

i have not built any extra ckt…
i am just giving +5v supply to A0 to A15 pin from arduino board itself

Are you allowing sufficient time between analogRead()s on different pins?

Try reading each pin twice and discarding the first reading.


Hi, if you have not ,please read,148850.0.html

Then post us a copy of your sketch you are using to test the analog inputs. A well as a CAD or picture of a hand drawn circuit diagram in jpg, png or pdf format.

Thank you

Tom....... :) PS I agree with Robin2, try giving the reads of the pins a bit of time to load/convert and output the AtoD.