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associated with line voltage (60 Hz) would be filtered out but a signal of 25 Hz would
be allowed to pass.
Also, in a digital circuit, a low pass filter is often used to filter an input from a switch.
Figure 6-5. Low pass Filter
A low pass filter may be constructed from one resistor (R) and one capacitor (C). The
cut off frequency is determined according to the formula:
R = 1
2*Pi*C*F
c
F
c
= 1
2*Pi*R*C
6.6 A/D RESOLUTION & ENGINEERING UNITS
Resolution is specified in bits, such as 8, 10 or 12 bits. The 12 bits are really a power
of 2 indicating the number of divisions of full scale the converter can resolve. For
example, a 12 bit converter can resolve (2
12
) = 4096 divisions of full scale. If the
input of the board were +/- 5 volts full scale, each of the 4095 steps would be equal to
0.00244 volts.
Reading from the A/D converter would be thus:
Converter # Volts
4095 4.9976
4094 4.9951
4093 4.9927
2048 0.0
1 − 4.9976
0 − 5.0
21