Download File

FINAL DESIGN PROJECT
ZHANG ZHONG
The goal of this final project to build a simple optical signaling device that lights a
red LED when one button is pushed and green LED when another button is pushed. The
twist is that the signal determining either the red or green light must be transmitted
wirelessly -- in this case via an optical signal. The transmitting circuit consists of 2 parts
and the receiving circuit consists 3 parts. The whole processes like the graph below.
In the transmitting circuit, we firstly need to produce an Oscillator can
generate a high frequency signal and a low frequency signal by choosing
different resistor ratios. We connected the output of the Wien Bridge Oscillator
directly to a signal diode which is looks like a LED with the function to transmit
signal. The two frequencies we generated are around 1.5KHZ and 10KHZ.
As for the receiving circuit, firstly we need to amplify the signal we get by
using a diode with 1M ohm resistor and an op-amp so as to be able to catch the
signal comes from the Wien Bridge Oscillator. After the signal is being captured
by the detector, the circuit secondly needs to separate the higher frequency the
lower frequency to go through the bandpass filters to filter out the useless
frequency. How to separate these frequencies? We set a range for the high
Bandpass Filter which only can allow frequencies in range of 1.7k to 60k to pass
and the low pass frequency which is for the frequencies which are lower than
1.7k. In order to set the range for filters, capacitors and resistors ratio is very
important to calculate by using f=1/2*2pi*R*C. In practical, the most barriers are
the lab kit just has couples of different values in terms of the Capacitors and
Resisters. As a result, we need to calculate and choose carefully about the
relative C and R. Next step, the circuit needs to convert these two frequency
signals which are A.C signals to D.C signals so as to able to light up LEDs. Rectifier
circuit is used to convert signals from A.C to D.C which was covered during the
lab section this semester. We did some researches from previous lab section to
build this circuit. In this whole project, there are several things need to pay
special attention on: make sure all parts are being grounded, to not make the
circuit in a big mess that connect all the power supply for op-amps is a good idea
to reduce the use of banana connectors.
The whole circuit likes this
This is the circuit that we built for the project. A lot of students made the
circuit in two breadboards but we thought it is kind of hard for others to
recognize those different parts. So we divide it the whole project into three
breadboards for easier recognizing.
1. Wien Bridge Oscillator:
As shown in the above image on the breadboard down bottom, a Wien
bridge oscillator in the whole circuit as an input resources to produce a high
frequency and a low frequency. In order to produce two different signals, we
designed only one oscillator to produce two frequencies which are controlled by
switch. That is what the real circuit looks like in the above circuit image. By
changing to different resistance, we generated two frequencies by a single
oscillator. We measured two outputs by oscilloscope to record the graph shown
below.
The lower frequency produced by Wien Bridge Oscillator
The higher frequency produced by Wien Bridge Oscillator
2. The Detector Circuit:
On the bottom right in the circuit image, a detector is used to capture the
signal from the IC LED. To keep the voltage down, we put a 1Mohm resistor
between the non-inverting terminal of op-amp and the output terminal of
op-amp. For more clear and strong signal, we build the IC LED and the diode of
detector almost at same position in the same breadboard to make sure that the
signal we captured can be used for next several steps.
3.
Band pass filter:
Shown in 3 and 5 in the circuit image, the low pass filter is allow to pass
a low frequency such as our 1.5kHz frequency and the high pass filter is use to let
the 10kHz to pass through. The range for the high pass filter is about 1.7kHz to
60kHz and the range for the low pass is below 1.7k which is perfectly fit our
signal from oscillator.
4. Full wave Rectifier:
The function of rectifier to convert the input A.C signal to a D.C output signal.
It turns the negative wave to the positive side to make it a full wave. In project
we built two rectifier circuits for both high and low frequencies. When both
signals are converted to D.C signal, we connected the output to RED or Green
LED and by switched the resistors from oscillator part to light each LED up.
Here are the data for the value of capacitor and resistors that we used in
each circuit to be able to produce signal or set a pass range.
These are the pictures of circuit when we light the Red light up by
connected the power supply of op-amps. After switch to different resistance, the
green one lights up.