Name: CHEE KANG TAN
Partner: Kiran Rane
Class & Session: EE 230 A
Instructor: Professor Santosh Pandey
Date & Time: (Thursday) 29th Nov 2012, 4:15pm
FINAL DESIGN PROJECT
A Simple Optical Signaling device that lights LEDs
[2012 Fall]
Introduction
In this final project, the goal is to build a simple optical signaling device that lights a red
LED when the low signal (1k Hz) is transmitted and green LED when the high signal (10k Hz) is
transmitted. In the circuit, it will determine either the red or green LED be lighted from the
signal it receives.
The signal is transmitted via an optical signal, which means the infrared
transmitter LED is sending the information and the infrared red photodiode is receiving it.
The circuit includes the oscillator, amplifier, full wave rectifier, high pass & low pass
filter and peak detector. In the later part of this report, I will discuss more detail about each part
of the circuit design and how it works.
Below is the picture of our actual circuit design.
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Block Diagram
Above is the block diagram of our circuit design for this final project.
It begins with two oscillators. There is one oscillator output 1K and the other one output
10K Hz frequency. The switch will control the output to either oscillator’s output. Then, the
infrared LED (transmitter) will send the output and the infrared red photodiode (detector) will
receive the signal from the transmitter.
Since the signal received from infrared red photodiode in low voltage, we amplify the
signal to get higher voltage by using amplifier. Next, the low and high pass filter will do the
verification for the signal it receives. If the signal is about higher than 6K Hz it is a high pass
signal, if it is about lower than 3K Hz it is a low pass signal. Then, the Full wave rectifier will
convert the signal from A.C to D.C signal and the peak detector will filter the D.C signal to a
better straight line.
Finally, the red LED lights up when it receives 1K Hz signal and Green LED lights up
when it receives 10K Hz signal.
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Circuit Diagram
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Description & Theoretical Calculation of circuit design
This “simple optical signaling device that lights LED” circuit is designed to work as a
simple version of a TV remote control. In this case, the remote is the infrared LED transmit
signal and the TV is the detector that receive signal.
Let’s separate the circuit to two parts; there are receiver part and detector part.
In the receiver part, there are switch controller, oscillator (1K & 10K Hz) and infrared red
LED (transmitter). The switch controller will control the output to connect to either the output of
oscillator 1K Hz or the output of oscillator 10K Hz. In this case, push switch to left is low signal
(1K Hz), to right is high signal (10K Hz) and to the middle is off (not connecting to either
oscillator’s output).
When the infrared red LED (transmitter) is launched, it will transmit the
signal.
In the detector part, there are infrared red photodiode (detector), amplifier, low & high pass
filters, Full wave rectifiers, Peak detector and red & green LEDs. First, the infrared red
photodiode will detect the signal. Second, since the signal it detects is very weak, we decide to
use amplifier to amplify the signal for the next part (signal verification). If the signal is too weak,
it is hard to determine whether it is a high or low pass signal. Third, after amplifier, there is a
separation for low pass filter and high pass filter. The received signal will be filtered according
to the frequency range of the filter. In this case, we chose low pass filter accept frequency lower
than 3K Hz, the high pass filter will work for frequency higher than 6K Hz. Next, the full wave
rectifier will convert the signal from A.C to D.C. Then, the peak detector will filter the signal to
be closer to straight line.
Finally, the red LED will light up for the low signal (1K Hz) and green LED will light up
for high signal (10K Hz)
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Above is the theoretical and description of this circuit design. Now, we will look at the
waveform output from each part of the circuits.
Transmitter part
Oscillators
The Wien Bridge Oscillator is an electronic oscillator that can produce sine waves with a
large range of frequency. In this circuit we use two oscillators to generate two different
frequency output (1K & 10K Hz).
As we know, to build a Wien Bridge oscillator includes two RC networks connected to
the positive terminal to form a frequency selective feedback network and two negative feedback
resistors to amplify the signal.
1
In mathematics explanation, R2 =2R1, f = 2л𝑅𝐶
In this circuit we connected a 1K potential meter series
with R2. It let us more convenient to control the output to the
desire frequency.
For both oscillator (1K & 10K Hz), R2 = 1Kῼ + potential meter,
R1 = 500ῼ.
Oscillator (1K Hz)
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1
1
f = 2л𝑅𝐶 = 2л 𝑥16𝐾 𝑥 0.01𝑢 = 1K Hz
so, R = 16Kῼ, C = 0.01uF
The oscillator 1 output a square wave voltage at 26.9V and frequency at 879.4 Hz.
Oscillator (10K Hz)
1
1
f = 2л𝑅𝐶 = 2л 𝑥160 𝑥 0.1𝑢 = 10K Hz
so, R = 160ῼ, C = 0.1uF
The oscillator 2 output a saw tooth wave voltage at 18.3V and frequency at 8.11K Hz.
When the frequency gets higher, it will change from a square wave to a saw tooth wave form.
The output signal will be sent by the infrared red LED (transmitter).
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After the infrared red photodiode (detector) receive the signal. Below is the signal we got.
Infrared Red Photodiode (1K Hz)
The signal we receive is transmitted wirelessly via an optical signal. So it might has a
little bit noise during the transmit.
It is a square wave, voltage at 17.1V and frequency at 816.19 Hz.
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Infrared Red Photodiode (10K Hz)
It is a saw tooth and square wave, voltage at 17.1V and frequency at 816.19 Hz.
Since the signal from transmitter is a saw tooth wave form. It becomes a “half-square
wave” form signal. But this signal we receive has not noise. I think it is because the signal is in
high frequency.
Next, the circuit will connect to an amplifier that amplifies the signal to a stronger and
stable signal.
Later on, it will be the verification of signals. The Low & High pass filter will determine
the signal it receives is either a low or high frequency signal.
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Low-pass Filter (1K Hz)
Corner frequency:
1
1
fc = 2л𝑅𝐶 = 2л 𝑥15𝐾 𝑥 0.01𝑢 = 1K Hz
so, R = 15Kῼ, C = 0.01uF
We got a sine wave form signal voltage at 3.58V and frequency at 815.79 Hz.
In low pass filter, the input connects with a resistor, then put a capacitor connect to the
output and ground.
Therefore, it will output, only if the signal frequency is lower than 1K Hz.
Actually, in this low pass filter. The signal will also output when it is lower than 3K Hz.
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High-pass Filter (10K Hz)
Corner frequency:
1
1
fc = 2л𝑅𝐶 = 2л 𝑥1.5𝐾 𝑥 0.01𝑢 = 10K Hz so, R = 1.5Kῼ, C = 0.01uF
We got a saw tooth wave form signal voltage at 17.3V and frequency at 8.45K Hz.
In high pass filter, the input connects with a capacitor, then put a resistor connect to the
output and ground.
Therefore, it will output, only if the signal frequency is higher than 10K Hz.
Actually, in this low pass filter. The signal will also output when it is higher than 6K Hz.
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Full wave Rectifier
A full wave rectifier can convert an A.C current to a D.C
current and convert a sine wave form signal to a full wave form.
The circuit diagram at right side is a precision full wave
rectifier we found from lab 9.
Full wave Rectifier (1K Hz)
The input is connected from the output from low pass filter.
From the graph, we got frequency at 815.99 Hz and voltage at 3.9 V.
The rectifier actually did not work that well as we expected, it didn’t convert the signal to
D.C and in full wave form.
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Full wave Rectifier (10K Hz)
The input is connected from the output from high pass filter.
From the graph, we got frequency at 8.53 Hz and voltage at 12.7 V.
The rectifier seems working and converts the A.C current to D.C current. However, there
still has some noises did not get filtered.
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The peak detector will detect the peak voltage of
an incoming waveform. The diode will limit the current
flow in only one direction and the capacitor will charges
up to the peak voltage applied to it.
Peak Detector (1K Hz)
As graph shown, the peak detector filters the signal to a clean straight line.
We get an output of Voltage at 420mV and frequency at 985.96 Hz.
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Peak Detector (10K Hz)
As graph shown, the peak detector filters the signal to a clean straight line.
We get an output of Voltage at 280mV and frequency at 12.83K Hz.
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Discussion & Conclusion
In this lab, we have done the oscillation, transmitting, detection, amplification, filtering,
rectification and peak detection. Each of the circuit works for different tasks to achieve the main
goal of this circuit design.
However, we have some comment and discussion about the improvement of this circuit.
There are something we can do to make the circuit work better in longer distant, more stable
circuit and transmitting a lower noise signal. We could do it by changing the amplifier from the
receiver part to transmitting part, lowering the 10K Hz frequency to 300Hz frequency and
changing a full wave rectifier.
First, we should cancel the amplifier at the receiver part and replace it to the transmitter
part. The original circuit has an amplifier after the infrared red photodiode (receiver) to amplifier
the signal, so that it will be easier to verify whether it is a low or high pass filter. However, the
signal is already big enough to be verified, because the signal it receives is already higher than
15V for both 1K Hz and 10K Hz signals. In addition, the signal at the transmitter part is not high
enough to transmit in long distant. So, we should replace the amplifier to the transmitting to
increase the distant that it can transmit.
Second, we should change the full wave rectifier which can perfectly convert the signal
to a D.C signal. The full wave rectifier in this circuit seems not working sometime (especially in
the 1K Hz frequency). Therefore, change a working full wave rectifier will make the signal be
converted better.
Next, we should change the frequency from 10Hz to 300 Hz. Since, the transmitter can’t
handle frequency higher than 1K Hz efficiently, the signal and waveform it receives will not be a
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stable graph and it will have a lot of noise. Therefore, we should change the frequency by
replacing the resistors and capacitors at the oscilloscope. To get 300 Hz, we should change
Resistor to 5.3Kῼ and Capacitor to 0.1uF.
Finally, I have talked about the problem solving and some ways to make improvement
for this circuit design. I have learned a lot of knowledge about circuit design by doing this final
design project. Actually, it has almost applied most of the circuit we learned in this micro circuit
class.
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