Strange behavior ADC7 ATMega328P

acjacques · Joined: 24 Feb 2019 Posts: 13 Location: Rio de Janeiro

When testing the AD channels on a NANO board ATMega328p I am receiving strange values from the AD channel #7 at pin 22 just between the 5V pin and the AD #6. Trying with a potentiometer I receive values ranging from about 18 up to 940 and not from 0 to 1023 as expected extreme sides. It seems also noisy.

All other channels works fine with the same code.

'===================================
Config Adc = Single , Prescaler = Auto , Reference = Avcc

Dim W As Word
Dim Z As String * 10

Do
W = Getadc(7) 'select the ADC channel on getadc(#)
Z = Str(w)
Z = Format(z , "0000")
Z = "AD7=" + Z
Print Z
Loop
'===================================
There are any special configuration to have this channel working properly ?

(BASCOM-AVR version : 2.0.8.1 )

albertsm · Joined: 09 Apr 2004 Posts: 5922 Location: Holland

there is no special config.
just make sure you connect to the right pin. and also, check if the input you offer is not too high for the AD converter.
keep wires very short and possible add a small cap to ground on the input pin.

notice that the DIP version of the chip does not have these channels.