AVR-Chat

Stuart,
Check that there´s no ripple en VCC (VCC should be realy stable).

good luck!

--- In AVR-Chat@yahoogroups.com, Stuart Whelan <stuart.whelan@p...> 
wrote:
> Hi folks,
> 
> I am playing with some ADC stuff, but (Damn it Jim,) I am a 
programmer,
> not an electronics whiz.
> 
> I am using Mega8's in PDIP packages, using the internal oscillator
> (running at 8Mhz).
> 
> The chip is setup to use the internal reference 2.56V and a 
prescaler of
> 64 (giving 125.000 kHz ADC clock freq).
> 
> I have .1uf smoothing caps on the right next to the chips between 
VCC
> and GND.
> 
> I have .1uf caps between AVCC and GND, and also between AREF and 
GND.
> Once again right next to the IC.
> 
> The analogue source is 100K linear POTs.
> 
> The pots are 3pin pots with pin 1 connected to GND, pin 3 to AREF 
and
> pin 2 to the ADCn.
> 
> The priority is on smooth and non-fluctuating/steady signal as 
opposed
> to an 'accurate' signal. It is for joystick inputs, and the pots are
> connected to things like throttles and flight yokes, rudder pedals.
> 
> The Mega8 iterates through the 6 ADC channels.
> 
> I have implemented software smoothing within the chip, but the raw
> hardware signal is bouncing around by up to 4 bits.
> 
> My question are these: What else can I do or should I do to get a
> 'smooth signal'?
> 
> - Should I be using an external clock source?
> 
> - Should I be using VCC as my AREF?
> - Should I be using something other than the Int.Ref 2.56v for AREF?
> - What would be regarded as a 'smooth' VCC or AREF? My VCC at the 
moment
> is fluctuating by about 20mV according to the scope.
> 
> Any comments, tips suggestions or advice would be most welcome.
> 
> Kind Regards,
> Stuart Whelan
> 
> Recursion: See Recursion.