> -----Original Message-----
> From: piclist-bounces@mit.edu [mailto:piclist-bounces@mit.edu] On Behalf
> Of Cristiano Cesaretto
> Sent: 20 February 2012 18:14
> To: Microcontroller discussion list - Public.
> Subject: [PIC] ADC problem with PIC18F2458
>=20
> Hello.
>=20
> I have used a PIC18F2458 to make a joystick controller that features 6
> 12-bit analog axins and 36 buttons.
>=20
> Everything is cool but there is something strange with the 6th analog axi=
s
> (which is AN8 because AN6 and AN7 are not implemented).
> Basically I never read an analog value less than ~85, which corrspond to
> around 100mV.
>=20
> The analog input usually is connected to a potentiometer but I also tried
> to connect it to a ground trace, as near as possible to the USB connector=
..
> but I got the same result.
>=20
> I was wondering what you guys think. Could it be a configuration error?
> The
> other 5 channels work fine.
>=20
> I can post the source code if necessary.

Ensure your ADC acquisition time is large enough.  If you make this too sma=
ll then you get an ADC value that has some dependency on the previously sel=
ected channel.  The minimum acquisition time will depend on your source imp=
edance, and the ADC section of the datasheet shows how to calculate this ti=
me.

Mike

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