The Engineer's Place for News and Discussion®

Electrical Components

The Electrical Components Blog is the place for conversation and discussion about power generation, distribution and protection; connectors and relays; sensors, RFID & passive components; and magnetics and transformers. Here, you'll find everything from application ideas, to news and industry trends, to hot topics and cutting edge innovations.

 Previous in Blog: Electronic Project I (Part 2) – 555 Timer with an LED Next in Blog: Virus Killer?

Subscribe to Discussion:

CR4 allows you to "subscribe" to a discussion
so that you can be notified of new comments to
the discussion via email.

Electronic Project I (Part 3) – 555 Timer with a Speaker

Posted September 02, 2009 12:00 AM by Jaxy

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

1. 555 Timer Chip (\$1.69)
2. 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. (1) 100k Potentiometer (\$1.49)
2. (1) .1μF Capacitor (\$1.49)
3. (1) 10μF Capacitor (\$1.19)
4. (1) LED (Included in Radio Shack's 20-LED Assortment - \$.15 each)
5. (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

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

Interested in this topic? By joining CR4 you can "subscribe" to