How to Use a 555 Timer IC

The 555 timer has been a favorite since the 1970s.

When building an electronic project that needs a timer or oscillator, the 555 IC is a common choice. This chip has been a hobbyist favorite since the 1970s, containing the basics for many different analog timing applications. To use it, first study the 555's data sheet and determine if its specifications fit your needs. To build a circuit with the 555, you'll need a prototype breadboard, a few capacitors and resistors, some connecting wire and a DC power supply.

Things You'll Need

• 555 timer IC
• 555 timer data sheet
• Prototype breadboard
• Resistor assortment
• Capacitor assortment
• Assorted pieces of 22-gauge solid jumper wire
• Oscilloscope
• 9-volt DC power supply

Instructions

1. Examine the 555 timer's data sheet. Note that, as with many eight-pin ICs, pin eight takes positive power and pin one takes ground. A timing capacitor goes between pin two and ground. It has a pulse output at pin three. You connect timing resistors at pins six and seven.

2. Look over the sample applications on pages seven through 10 on the data sheet. Choose the sample circuit that most closely fits the needs of your project.

3. Select the timing resistors and capacitor to suit your timing requirements. Page eight of the data sheet has formulas for determining these component values based on the frequency or time interval you need.

4. Insert the 555 IC into the prototype board so its pins straddle the IC channel that runs down the middle. Jumper positive power to pin eight and ground to pin one. Insert the capacitor so one of its leads connects to pin six, and the other connects to ground. Insert the timing resistors according to the sample circuit you chose in step two. Insert a long jumper wire at pin three to use as the output. If your circuit calls for an input trigger, insert another long wire to connect to pin two. Wire the power supply to the breadboard.

5. Turn your oscilloscope on. Connect its input probe to the long jumper coming from the 555's output. Connect its grounding clip to the minus side of the power supply or other circuit ground. Plug the power supply in and turn it on. You should observe a timing pulse on the oscilloscope screen.

Tips & Warnings

• When you've finished with your project, try other sample circuits listed on the data sheet. Its simple, flexible design encourages experimentation.

References

• National Semiconductor: 555 Timer Datasheet
• Williamson Labs: 555 Timer Tutorial