AVR-Chat

--- In AVR-Chat@yahoogroups.com, David VanHorn <dvanhorn@c...> wrote:
> At 06:57 PM 6/22/2004 +0000, p_anglum wrote:
> 
> >I'm using a Tiny 15 to convert a 0-10 volt input to PWM output.
> >I use a voltage divider (10K - 10K) to scale the 0-10 down to 0-5 
> >before applying it to PB3(ADC3).
> >
> >Everything seems to work except at the lowest range of input 
voltage 
> >the A/D seems to always read some small voltage.  In fact, with my 
0-
> >10V input removed and only the voltage divider on the input to to 
> >ADC3 I read about .9 volts on ADC3.  It appears the source of the 
> >voltage is the ADC3 pin itself.  Any ideas?
> >(All voltage measurements were made in refernce to pin4 - GND on 
the 
> >Tiny15)
> 
> You may have too high an input impedance. 
> Also, what's your reference voltage? On the Tiny-26's, the 
2.5V "precision" reference comes out at 2.7V.

I meant to say I'm using the Vcc (5V) as my reference.  It works 
great at the high end.  At 10 volts (5 volts after the voltage 
divider) the output goes to 100%.  But on the low end I can't get it 
below approx 20% - which makes sense since the input is a almost 1 
volt (.9V).  Also, if I ground  ADC3 to pin 4 the output duty cycle 
does go to 0%.  I'm also reading only the 8 MSB.