Operational Amplifier Application: Electronic Security System Design: Part 1 of 2
Operational Amplifier Application:
Electronic Security System Design: Part 1of 2
Theory & Introduction –
Goals For Lab 4 –
In Lab 4 and Lab 5, you will design, build and analyze an electronic security system using a laser
diode, a photo detector, operational amplifiers, resistors, a comparator, a latch, light emitting
diodes and a buzzer.
The main task is to build a circuit that will detect an interruption in a laser
beam and sound an alarm.
You may use an idealized model of the op-amp for your calculations
to simply analysis.
In Lab 4, you will use an op-amp as a current to voltage converter, as a
signal amplifier and as a comparator.
In Lab 5, you will use an op-amp as a buffer.
review Chapter 5 of your textbook regarding the uses of op-amps.
The block diagram of the system is shown in Figure 4.1.
The stages to be build and tested today
are enclosed in the box.
A laser diode, part no. DL3149-055, is employed to send a red light
beam to a photo detector, part no. FDS100.
The photo detector current induced by the light
beam depends on the strength of the beam.
An operational amplifier, or op-amp, will be
connected to the photo detector to convert the current into voltage. Since the output of this first
stage is very small, a second op-amp will be used in an inverting amplifier configuration to
increase the signal level so it can be used in a comparator.
After the voltage is amplified, it will
be sent into a comparator.
In Lab 5, you will build a latch to help isolate the signal from noise, a
buffer to supply the current needed, and a system of LEDs with a buzzer to serve as the alarm.
In the end, whenever the beam is obstructed, the comparator output will be changed.
It will then
be locked by a latch circuit and a buzzer will sound.
Light Emitting Diodes (LEDs) are used to
show the status of the output.
Working with a laser diode in lab requires extra safety procedures.
Never point the laser diode at
Instead, be sure that the laser points directly at the photo detector.
The safety sheet
agreement you signed during the first lab is still in effect.
If you treat the laser as a toy, you will
find yourself removed from the lab and receive a 0 for all work on Labs 4 and 5.
When you are performing the lab, pay special attention to stage 3 and stage 4.
hardware of these stages is very similar, stage 3 converts current to voltage and stage 4 amplifies
the input voltage.
For analysis purposes, the ideal op-amp has two inputs and one output.
The inputs are referred
to as negative and positive.
The output voltage is determined by the input voltages and a
network of resistors, or other elements, attached to the op-amp.