Electronic Project I (Part 2) – 555 Timer with an LED

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. Adding an LED will allow you to see the frequency. The higher the frequency, the faster the LED will blink and the lower the frequency, the slower the LED will blink.

Components and Cost Estimate

1. 555 Timer Chip ($1.69)
2. Resistors (Included in Radio Shack's 500-Piece Resistor Assortment - $.03 each)

• (1) 6.8KΩ Resistor ($.03) – Blue Grey Red

1. (1) 10k Potentiometer ($1.49)
2. (1) .01μF Capacitor ($1.49)
3. (1) 10μF Capacitor ($1.19)
4. (1) LED (Included in Radio Shack's 20-LED Assortment - $.15 each)

The cost estimate comes to $6.04.

Schematic

The schematic at left will have the LED blink fast or slow depending on how far and in which direction 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 Blinking LED

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.

Add the LED from pin 3 on the chip to ground. Insert the potentiometer anywhere on the board. Then wire pin 2 to pin 6 (orange wire).

The 10μF capacitor can then be connected from pin 2 or pin 6 (because they are both connected with orange wires) to ground. I used pin 2 because that side of the chip is closest to ground. Connect the .01μF capacitor from pin 5 to ground.

Connect the potentiometer to pin 6 and pin 7 (above left). Pin 6 should be should be connected to the middle pin on the potentiometer and pin 7 should be connected to one of the outer pins. The final step is to add the resistor to the circuit (below).

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. As you turn the potentiometer, the light should blink at different speeds. 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?
• 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.
• Pins 4 and 8 should be connected to power.
• Pin 1 should be connected directly to ground.
• Double check wiring
• 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?
• 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.

Tune in tomorrow to learn how to use the 555 timer to produce sound through a speaker. Most of the components you will need tomorrow, you already have in your possession from making this circuit.

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) - Video