Getting Started

Chapter 9 – Digital Meets Analog – ADC and DAC

• Timer/Counter 1 Capture Event

Conversion Timing

he successive approximations are clocked between 50kHz and 200kHz to get the

aximum resolution. You can use higher sampling rate frequencies, but you get

The first conversion

al conversions take 13 clock

Changing Channels

ging channels and voltage
referen lways wait till a conversion
com venient, read the data book

igital eduction

trical noise that affect the

curacy of the ADC. We can put the system to sleep to shut it up and then take

r AD ils in the data book.

The accuracy of the conversion will depend on the quality of the input signal. A
w recommendations:

• Filter out signal components higher than the Nyquist sampling frequency
  (double the frequency of interest) with a low pass filter.


• Sampling time depends on the time needed to charge the sample and hold
  circuit so always use a source with an output impedance of 10 kOhm or
  less.
  Use only slowly varying signals.
  l paths as short as possible.

T

m
lower resolution. The sampling rate is determined by the input clock and by a
prescaler value set in the ADPS bits of the ADCSRA register.
takes 25 clock cycles to initialize the hardware. Norm
cycles and auto triggered conversions take 13.5.

There are some complexities involved in chan
ces that lead to the recommendation that you a
is plete before making a change. If this is incon
and figure it out yourself.

D Noise R

The CPU and I/O peripherals can generate a lot of elec
ac
ou C readings in the quietened environment. Deta

Conditioning the Analog Input Signal

fe

•

• Keep analog signa


• Use the ADC noise canceller function.