Download Activity 3: Opto Transmitter Student Handout

Wireless Transmission: Your TV Remote
Activity 3: Opto Transmitter Student Handout
Name: ________________________
Date: __________
In this activity you will build an opto (optical) transmitter that uses a 555 timer IC to
pulse an infrared (IR) light emitting diode (LED). You will use this circuit to transmit
different tones to your opto receiver built in Activity 2.
The first thing to do is to identify the parts you will need.
Parts List
R1: 4.7 k Resistor (Yellow, Violet, Red)
R2: 1 k Resistor (Brown, Black, Red)
R3: 100  Resistor (Brown, Black, Brown)
P1: 50 k Potentiometer (variable resistor)
C1: 0.1 F Disc Capacitor (Labeled 104)
C2: 0.01 F Disc Capacitor (Labeled 103)
L1: IR LED
IC1: 555 Timer IC
9 V Battery
Battery Snap
Breadboard
2” Jumper Wires
Tape Measure
You know how to identify the resistors from Activity 1 by using the resistor color code.
The 50 k potentiometer (variable resistor),
or pot, has a rotatable stem and three leads.
Rotating the stem changes the resistance
between the center lead and the leads on the
outside. Pick up a pot and rotate the stem
clockwise and counterclockwise. Write down
three examples of where you might find a pot.
A potentiometer allows you to rotate a dial to
control the electricity through it. For example, a
volume control allows you to rotate a dial to
make sound louder or quieter.
Can you give two examples of where you would find a dial that can be rotated to
control electricity?
Example 1:
Example 2:
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Wireless Transmission: Your TV Remote
The disc capacitors are brown and are not polarized. It does
not matter which way you plug in these capacitors to your
breadboard. They are labeled 103 and 104 as follows:
 0.1 F Disc Capacitor (Labeled 104)
 0.01 F Disc Capacitor (Labeled 103)
The 555 IC looks just like
a 386 IC (but says 555 on
it instead of 386!). It has 8
pins. If you orient the IC
with the notch to the left,
the pin numbers are
counted going counterclockwise around the IC
beginning at the lower left.
The infrared (IR) LED has a smoky clear body as
shown in the picture to the left. One lead is longer
than the other. The longer lead is positive (+) and
the shorter lead is negative (-), just like a visible
light LED.
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Wireless Transmission: Your TV Remote
Overview
The opto transmitter circuit you will build has the following schematic.
The numbers shown inside the rectangle representing IC1 indicate the 555 timer pin
numbers. For example, pins 4 and 8 of the IC are connected to the +9 V power supply
rail and pin 1 is connected to the negative power rail. The black dots emphasize that a
physical connection is made. For example, the black dot at the end of the wire from pin
2 of the IC indicates that the wire is connected to pin 6 as well as C1 and R2.
As you build the circuit on your breadboard, you should look back at this schematic
frequently to relate the schematic drawing to your breadboard circuit.
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Wireless Transmission: Your TV Remote
When you have built the entire circuit, it
should look like the picture to the left.
Generate an outline of the process you
would go through to build this circuit.
Compare the picture of the circuit to the
left to the schematic on the previous
page.
In general, the last element to be
connected in any circuit is the battery.
We will leave the battery connection
until the very end of the building
process.
A good place to start building any circuit
that contains an IC is with the placement
of the IC onto the breadboard.
Then, the other elements can be placed
around the IC.
Building the Opto Transmitter Circuit
The first component to place on your breadboard
is the 555 Timer IC. With the notched end of the IC
toward the top of your breadboard, gently insert
the IC into the breadboard with pins 4 and 5 in row
10.
Using 2” jumper wires, connect pin 1 of the IC to
ground (negative power rail) and pin 8 to the +9 V
power rail.
We also need to connect pin 4 to the +9 V power
rail. You could connect a jumper wire all the way
from pin 4 to the +9 V power rail OR you could
connect a jumper from pin 4 to pin 8!
These connections provide power to the 555 Timer
IC.
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Wireless Transmission: Your TV Remote
Connect C1 (0.1 F labeled 104) between pin 2 of
the IC and ground (negative power supply rail).
Connect C2 (0.01 F labeled 103) between pin 5 of
the IC and hole E12. Then connect a jumper wire
from hole A12 to ground. This effectively connects
C2 from pin 5 to ground.
Connect a jumper wire from pin 2
of the IC to pin 6. This jumper will
criss-cross over the top of the
jumper wire that connects pins 4
and 8.
Connect R1 (4.7 kyellow, violet,
red) between pin 7 of the IC and
the +9 V power supply rail.
Connect the IR LED with the
positive + (longer) lead in hole F1
and the negative – (shorter) lead in hole E1. Bend the IR LED so that it is pointing along
the surface of the table. Connect R3 (100 brown, black, brown) between pin 3 of the
IC and hole C1. Connect a jumper wire from hole J1 to the +9V power supply rail.
Connect R2 (1 k brown, black,
red) between pin 6 of the IC and
hole G16. Connect a wire jumper
from pin 7 of the IC to hole F18.
These connections are for the pot.
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Wireless Transmission: Your TV Remote
Position the pot so that the stem is
pointing toward you with the left
lead in hole J20 as shown in the
picture to the left. The middle lead
will be inserted in hole J18 and the
right lead will be inserted in hole
J16.
Gently push the pot into the
breadboard until the pot is fully
seated as shown in the picture to
the left.
Finally, connect a 9 V battery to a
battery snap and connect the battery to
the power supply rails.
The circuit should now be operating. To
test the circuit, aim the IR LED at the
photo-transistor of the opto receiver that
you built in the last activity. Position the
opto transmitter so that the IR LED is
0.5 inches away from the phototransistor of the opto receiver. You
should hear a tone. As you twist the
stem of the pot, the frequency of the
tone should change. If you do not hear
any sound out of the speaker, you will
need to troubleshoot your opto
transmitter circuit.
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Wireless Transmission: Your TV Remote
If your circuit does not work, immediately disconnect one of the battery snap
leads from the breadboard.
Troubleshooting (Go through this process if your circuit fails to operate)
Troubleshooting is the process of figuring out why a circuit does not work.
1) The most common problem is a wiring error. Check to make sure that every wire
and component lead is going into the hole you think it should go into.
2) The second most common error is a polarity mistake. Check the polarity of the IR
LED.
3) Is the battery dead? Use the voltmeter to measure the voltage across the battery
terminals. Is it 9 V or higher? If not, replace the battery.
4) If all else fails, replace the 555 Timer IC.
The problem with the circuit must be one of the mistakes listed above. You must go
through each step carefully until you find and correct the problem.
Exploration
Turn the stem of the potentiometer and listen carefully to the sound that is produced by
the speaker. Write down below what the sound sounds like as you twist the pot stem.
The sound produced in the opto receiver sounds like _______________________
__________________________________________________________________
As I twist the pot stem, the sound _______________________________________
__________________________________________________________________
What is the maximum distance you can separate the IR LED from the phototransistor
and still get sound?
Answer:
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Wireless Transmission: Your TV Remote
Disassembling the Opto Transmitter Circuit
You will store your opto receiver for use in Activity 4. You will disassemble your opto
transmitter. Remove the potentiometer, resistors, jumper wires, capacitors and IR LED.
Care must be taken when removing an IC from the breadboard. The easiest way to do
this is to use a pair of needle nose pliers to extract the IC as shown in the figure below.
Grip the IC on the ends with
the needle nose pliers. Do not
squeeze the pliers too tightly,
as this can damage the IC.
Hold the breadboard down
with your other hand.
Carefully pull the IC direct out
of the breadboard.
The idea is to avoid bending
the pins of the IC.
Return the circuit components to their proper storage bags as instructed. All of your
small components from the breadboard will go in the Activity 3 bag except the battery
snap. The battery snap and breadboard will go in a bag together. Finally, return the
battery to your instructor.
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