Page 171 - Making PIC Microcontroller Instruments and Controllers

CONDITIONING THE INPUT SIGNAL

General

Filst, we need to get a handle on the signals coming into our insEuments. This chapter
cove$ the techniques used to collect and condition ihe ilput signals so they can be con-
nected !o the microcontroller.
Beforc we can do useful work, we need to detect and manage the signal wo are inter-
ested in. In our particular case, there is the added requirement that the signal either be
an electrical signal or be such that it can easily be conve ed into an electrical signal.
Though a Bourdon tube prcssue gauge might rcad the pressue just fine for most engi-
neerirg applications, we need a pressure sensor that provides us with an elecldcal signal
we can feed into an electrical instrumgnt. We are not so much concemed with the mag-
ninrde of the signal as we are wifh knowing it is iII a range we can read, manipulate,
ard bring into our microcontrollers. A linear signal response is most desirablo, but we
can take care of the nonlinearity of a signal in oul controller with software if that
becomes necessary.
In the engircering laboratory and amateur engineer's workshop, the electrical signals
we encounter will most likely be somewhgre between 0 aDd 120 volts ac and between
0 and 24 volts dc. No matter what the conditions. extleme caution and care should be
exercised when dealing with any kind of electrical signal. Electricity can be lethal if not
handled with care. When you aie dealing with the higher cur€nts and voltages, seek
the help of an experienced electriciar if you feel the least bit uncomfo(able wiih under-
taking that part of the task. Be informed that certain work must meet the rcquiements
of the National Electrical Code in most judsdictions, so help from an experienced
person (electrician) can save you a lot of time and headaches.
Let's take a look at the ac signah nrst, and ihen we will look at dc signals.