Page 176 - Making PIC Microcontroller Instruments and Controllers

116 coxD|rr6t{|llc tHE tI{PUt glGl{AL

into floating inputs siould have a pull-up resistor ( 10 to l00k ohtns) at the pin to tie the
pin high. Opto isolato$ can be used to isolate the noisy signal electrically ftom the PIC
If you have an isolator available, use it
when necessary.
The dia$ams in Figures 11.3 through 11.6 show various techniques that may be

5 VOLTS

gre Opto isotatton ot inco.ing 12-vott signal.

ANYSUITABLE
BUFFERWITH
CI\,IOS OR TTL
5.VOLT OUTPUT
LOGIC INPUT

X3ffi $voltTTl-level signals.

ANYSUITABLE
HEX HIGH TO LOW BUFFERWITH
LEVELSHIFTER CI\,IOS OR TTL
LIKETHE 74HS4O5O OUTPUT

1s-VOLT
LOGIC INPUT