Instruction manual

of the FET. This causes a change in current from the drain to source. Very little power
is required at the gate to control the larger current flow from source to drain. The
benefits of this type of detector are low radio interference, low noise, specially suited
response. The IR detector is sealed in a metal housing to prevent electromagnetic
interference and to keep them clean.
FIELD OF VIEW
Detectors are available with different fields of view, depending on the
application. The maximum distance and total angle of view are important
specifications needed in choosing a motion detector. The LHI-954 field of
view is shown in Figure 5.
CIRCUIT DESCRIPTION (see page 16)
The IR Section contains only a few components, R1, R2, C1 and
the PIR sensor. As motion is detected, the IR detector will
produce a voltage at the gate of the FET allowing current to flow
from the drain to source, causing the voltage at the input of U1
(pin 13) to change, thus changing the output at pin 14. Resistors
R1 and R2 limit the amount of current flow through the FET.
OPERATIONAL AMPLIFIERS / FILTERS
An amplifier is a device that uses a small amount of power to control a larger amount of power. Just like a small
amount of power on the valve arm of Figure 1 controlled the water pressure in the pipes going to the houses.
The amplifier does not create power (it was already there in the water tower) but it controls the power from a
source.
In electronics, amplifiers are composed of devices called transistors, resistors, and capacitors. The number of
these components used and the way they are assembled determines the characteristics of the amplifier. An
amplifier that can perform many mathematical operations such as adding, subtracting, or multiplying voltages is
called and Operational Amplifier or Op-Amp.
The characteristics of an ideal op-amp are the following:
A. infinite voltage gain (no voltage at all on the input controls, large voltage on the output).
B. infinite bandwidth (no matter how fast the input changes, the output will change just as fast).
C. infinite input impedance (no power required at input to change output).
D. zero output impedance (the output can deliver an infinite amount of power).
Obviously, in the real world these conditions can never be met, but for mathematical purposes they are assumed
in designing electronic circuits with op-amps.
The op-amp has two input terminals, inverting input (--) and non-inverting input (+), and one output terminal.
Figure 6 shows the standard op-amp symbol. The two input terminals are labeled 2 and 3, and the output is 1.
Most op-amps operate with two DC power supplies, +V
CC and --VEE connect to pins 11 and 4 respectively. Since
a single power supply is used in the kit, --V
EE (pin 4) is tied to ground. The op-amp multiplies the difference
between the voltage signals applied at its two input terminals (V3-V2) times the gain of the amplifier (A). A x
(V3-V2) appears at the output terminal as shown in Figure 7.
Figure 4
Figure 5
Figure 6 Figure 7
-6-