555 Timer Oscillator Tutorial

You can build a 555 oscillator in under an hour.

The versatile 555 integrated circuit (IC) lets you create many kinds of time-based circuits by adding a few simple components. Its flexibility follows a building-block approach, containing basic timer functions you can connect in different ways. Begin with a simple LED-flashing oscillator circuit. After you get it working, see what happens when you change the values of the timing resistors and capacitor. Once you get the hang of this circuit, look up other 555 projects that exploit its various features and try them. This circuit takes under an hour to put together.

Things You'll Need

• 555 Timer Integrated Circuit
• 1K ohm resistor (R1)
• 1K ohm resistor (R3)
• 470K ohm resistor (R2)
• 9-volt Battery
• 9-volt Battery clip
• Prototype breadboard
• Assorted short pieces of #22 insulated solid jumper wire
• 5mm light-emitting diode (LED)
• 1-microfarad 50V capacitor (C1)

Instructions

1. Press the 555 timer IC into the prototype breadboard so that its pins straddle the slot meant for integrated circuits. Make sure you orient the IC so the notch or dimple faces to your left, so pin 1 is the first pin at the IC's lower left.

2. Insert a short piece of #22 jumper wire into the breadboard, connecting pins 6 and 2 of the IC together. Use another piece of wire to connect pins 4 and 8 together.

3. Identify the capacitor and resistors. The resistors are small cylinders with color-coded stripes. The capacitor will have the microfarad value printed on its plastic body.

4. Insert the capacitor C1 into the breadboard so its positive lead, if it has one, connects to the 555's pin 2. Insert its other lead so it connects to pin 1. Insert one lead of the 470K timing resistor R2 so it connects to pin 2 of the IC. Insert its other lead so it connects to pin 7. Insert one lead of a 1K resistor so it connects to pin 7, and insert the other lead to connect to pin 8. This is the other timing resistor, R1. Insert one lead of the other 1K resistor R3 so it connects to the 555's output at pin 3. Insert the other lead so R3 connects into a free column nearby on the breadboard. Insert the LED's anode pin into the same column so it connects with the resistor. Insert its cathode pin so it connects to pin 1 of the 555.

5. Insert the positive (red) lead from the 9-volt battery clip so it connects to the 555's pin 8. Insert the battery clip's negative (black) lead so it connects to pin 1.

6. Connect a fresh 9-volt battery into the clip. The LED should begin to flash on and off.

Tips & Warnings

• If you have trouble finding a 1 microfarad, 50-volt capacitor, you can use a capacitor with nearly any voltage greater than 20V.

References

• 555 Timer Circuits: Flashing LED Circuit
• National Semiconductor: 555 Timer Datasheet