some concerns about analog input

Forum 2005-2010 (read only) Hardware Troubleshooting
1

hi!

here http://arduino.cc/en/Reference/AnalogRead we say, that the minimum resolution at DEFAULT reference is "5 volts / 1024".
does that mean that 5V and 4.95V r both 1023? or is there no 0V? :o
or is it just easier for computations ("shift right 10" bit is easier than "div 1023")?

why is it, that i get these readings on quite stable voltages (i used a resolution of "aref/1023" -> 0=0V, 1023=5V)? :-?
aref=1.1V 203.4mV 208.8mV 239.3mV 217.2mV 220.1mV 273.6mV
aref=5.0V 190.6mV 197.3mV 228.0mV 205.3mV 210.2mV 259.0mV
it seems like, at aref=5V the readings r 10mV lower than at aref=1.1V?

bye
-arne

2

it just came to me,
that there might be 1024 intervals of width x (x = resolution = 5V/1024):
[0,x[, [x,2x[, [2x,3x[, ..., [5V-x,5V[

is that right now?

-arne