Check out the parts list here.

What You Need For Your 555 Timer Circuits With Flashing LED

  • 555 Timer IC
  • 10VDC Power Supply
  • 10uF Electrolytic Capacitor (16V or higher)
  • 1 kΩ Resistor
  • 470 Ω Resistor
  • 9 kΩ Potentiometer (or any variable resistor)
  • LED (whatever color you like!)
  • Red and Black Wires (solid core – 22 AWG)
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How To Hook It Up

For those who want a quick explanation, just hook up the pins of the 555 timer illustrated in the basic schematic below. Match up the numbers of the pins with the numbered leads of the circuit elements as shown in this diagram. You will find a more detailed explanation and image of the finished breadboard below. You can also reference the LM555 datasheet for better explanations of the pin-outs.

The Schematic Of The Circuit

The semi-circular notch on the IC chip indicates the top of the chip. The pins are numbered from 1 to 8 in a counter-clockwise fashion starting with 1 at the top left (as shown).

555 Timer Circuit Schematic

The Fundamentals

You want to hook up this circuit exactly as shown and with the exact same components I used because I have experienced problems quickly if you stray from the specified components. You can make it work with other resistor and capacitor values, but you may need to do some calculations to see whether it will work. You will need to calculate your time constant (T = RC) to determine how your capacitor will charge and discharge to get the appropriate frequency of flashing. In the video, I explain that your time constant equals your total resistance multiplied by your total capacitance. Resistances add in series and in parallel you have:

Resistors In Parallel Equation

Where this equation gives you your total resistance. The resistor connected to the LED does not affect your time constant, but it is only there to keep your LED from frying!

Capacitors actually add in the exact opposite manner to resistors. Capacitance just add in parallel, and you can use the same equation above to add capacitance in series.

The 555 timer actually produces a square wave, like a serial clock used in digital logic, where a series of transistors inside the IC chip produce a sequence of on and off voltages at a certain frequency. Thus, 555 timer circuits are frequently used in digital logic.

Pin 1 on the timer chip is the ground (GND) pin that is connected to the common ground on your power supply. Pin 8 is where your power is supplied, and in our case it is 10VDC. The rest of the pins deal with the way that your voltage signals are timed, and this is impacted by your resistors and capacitors. Here is an illustration of what each pin is responsible for:

Pin Configuration
When you have everything properly hooked up, your 555 timer circuit should resemble something like the one shown below. If you are having issues, please remember to start by building it exactly the same way that is shown in this tutorial. Once you have gotten your circuit to work, you can experiment with changing the values of the resistors and capacitors, but 555 timers are finicky. If you change something and it stops working, you need to first draw out your schematic, make the appropriate calculations, and then see why your LED is not coming on or is not flashing. If you are getting frustrated with it, remember that these chips can burn out, so grab your DMM and test your pins for continuity! You want to test your pins for continuity on a 555 timer chip that you know works (like a shiny brand new one), and then write down what pins are connected to each other internally with very low impedance. Remember that this IC chip consists of several transistors on the inside.

Finished 555 Circuit
As mentioned in the video, 555 timer circuits are used for a variety of tasks. They play a big role in timing circuits in general, but they are also used for many other projects. Projects that you would normally think require a microcontroller can sometimes take advantage of only a 555 timer and some simple electronics components. What projects can you think of that you would like to build with them?

For more tutorials on circuits design, continue by clicking here.