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555 Timers are very fun to encounter and experiment with.
They can be used as a timer and can be set to a certain frequency. In Part II
of Electronic Project I, we created a circuit that would get an LED to flash.
This time we are going to add a speaker so that we can hear the frequency that
is being emitted.
Components and Cost
Estimate
- 555
Timer Chip ($1.69)
- Resistors
(Included in Radio
Shack's 500-Piece Resistor Assortment - $.03 each)
- (1)
330Ω Resistor ($.03) – Orange Orange Brown
- (1)
1kΩ Resistor ($.03) – Brown Black Red
- (1)
5.1kΩ Resistor ($.03) – Green Brown Red
- (1) 100k
Potentiometer ($1.49)
- (1) .1μF
Capacitor ($1.49)
- (1) 10μF
Capacitor ($1.19)
- (1)
LED (Included in Radio
Shack's 20-LED Assortment - $.15 each)
- (1)
Speaker
·
I did not put an estimate next to this one
because it can vary depending on the quality and how much you are willing to
invest in a speaker. Speakers can be bought or purloined from an old boombox or
stereo that you don't need or want.
The cost estimate comes to $6.10 plus the cost of the
speaker.
Schematic
The schematic above will have the 555 timer emit a certain
frequency through the speaker, depending on how far the potentiometer is
turned.
Instructional Video
I have created a step-by-step instructional video in addition to the written instructions below. It can be viewed here.
Building the 555
Timer with a Speaker
 First we will start by inserting the chip into the
breadboard as shown at left. For a refresher on how to insert chips into board,
see Part V. Next, make power and ground connections to the chip as shown to the
right. It is typically a good habit to have red wire be exclusively power and
black exclusively ground. If problems arise, you can easily pick out where
power and ground is traveling.
 Next, add the
potentiometer and LED to the board (as pictured to the left). These are the
next important components in this circuit. Make sure to place the potentiometer
so that the pins are in different rows; see Part IV for a refresher on how to
plug potentiometers into the board. Using a different color than red or black,
connect pin 2 to pin 6 (I used yellow wire).
 The 1μF capacitor was inserted (as can be seen to the left).
This capacitor is of ceramic type and so it doesn't matter which lead is
connected to ground or the chip. If you have a polarized capacitor, make sure
that the "+" side is toward the chip or that the "–" side is toward ground. In
the image to the right, I added a grey wire to a resistor and connected the
other side of the resistor to the LED.
 Next I added a wire connecting the "ccw" and "w" pins on the
potentiometer (the minuscule wire is circled in orange). I also connected the
middle pin of the potentiometer to pin 7 via a green wire and also through the
5.1kΩ resistor to pin 2 via a purple wire. The 1kΩ is connected to the "cw" pin
of the potentiometer and power.
So what are "ccw", "w", and "cw"? These are
counter-clockwise, wiper, and clockwise respectively. How do you distinguish
pins? The middle pin is always the wiper. The outer pins are defined by the
manufacturer and there is no set way to distinguish them other than by looking
at the part description. The outer pins can be connected in the orientation in
the schematic without regard to which is the counter-clockwise pin and which is
the clockwise pin.
 The final step before trying this out is to add the
capacitor and speaker (shown below). Be sure that the "-" side lead is attached
to the speaker. Make sure also that the speaker is grounded. The left image
shows the pins of the speaker as it connects directly to ground.
Now try plugging power from the 9 volt battery into the
board. If the LED seems to stay lit instead of blinking, that is okay. What the
LED is really doing (in most cases) is blinking so fast that it seems to just
stay lit. You should hear a sound from the speaker. As you turn the
potentiometer, it should change in frequency. Congratulations to those who
accomplished this feat. If yours isn't working right away, there is a basic
checklist that you should walk through before becoming too discouraged. Chances
are it is only a minor issue.
Debugging Checklist
·
Is your battery good?
o If
you used an old battery, try a new one.
·
Make sure that power and ground are connected
directly to the right pins on the chip.
o Pins
4 and 8 should be connected to power.
o Pin
1 should be connected directly to ground.
·
Double check wiring
o Make
certain that not only the components are wired correctly (it is easy to be just
one row off), but also that they are inserted correctly. Capacitors and LEDs
are likely culprits of not being inserted correctly as they are polarized.
·
Is a component broken?
o Does
something smell like it is burning? Is there a black area on a component? If
this is the case, swap out the component and double check the value and the
wiring. Something was not wired correctly to make the component break.
This concludes the Electronic Project I that uses the 555
timer to make simple circuits. Tune in in two weeks when we use operational
amplifiers to make filters for music.
Previous Blogs in Series:
Electronic Projects for Beginners – Components (Part I)
Electronic Projects for Beginners – More Components (Part II)
Electronic Projects for Beginners – Reading Components (Part III)
Electronic Projects for Beginners – Translating the Schematic onto a Breadboard (Part IV)
Electronic Projects for Beginners - Notes Concerning Chips (Part V)
Electronic Project I (Part 1) – 555 Timers
Electronic Project I (Part 2) - 555 Timer with an LED
Electronic Project I (Part 2) - Video
Electronic Project I (Part 3) - Video
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