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This tutorial will show you how to breadboard a basic analog circuit that will allow you to adjust the flashing speed of two LEDs.

We will follow the schematic provide on Eric Rosenthal's Basic Analog Circuits class at ITP NYU.

Let's go!

Step 1: Components

The components needed for the job are:

  • 1 - LM555 chip - data sheet - animation
  • 2 - 100 resistors
  • 1 - 2.2k resistor
  • 1 - 4.7k resistor
  • 1 - 20K potentiometer
  • 1 - 47uf capacitor
  • 2 - LED's (you pick the colors)
  • 1 - Breadboard
  • 1 - 9v battery & connector

Step 2: Tools (not Needed If You're Using Jumper Wires)

To make custom length wires, tools we will need are:

  • 1 - Wire stripper pliers
  • 1 - Wire clippers
  • 1 - Needle nose pliers
  • Some wires

Step 3: LM555

Look closely at the LM555 chip and you can see a small circular indentation on the top surface. This circle indicates pin #1 on the chip.

Let's orient the chip so that the circle is on the top left corner and place it in the center of the breadboard.

Have a gander at the LM555 data sheet. It's always a good practice to look through the datasheet of any chips you're working with. It's like reading the construction manual of an Ikea furniture piece before you assembles everything together.

General Description
The LM555 is a highly stable device for generating accurate time delays or oscillation. Additional terminals are provided for triggering or resetting if desired. In the time delay mode of operation, the time is precisely controlled by one external resistor and capacitor. For astable operation as an oscillator, the free running frequency and duty cycle are accurately controlled with two external resistors and one capacitor. The circuit may be triggered and reset on falling waveforms, and the output circuit can source or sink up to 200mA or drive TTL circuits.

Step 4: Pin #1

We'll start with pin #1 and grounds it.

Step 5: Pin #2

Pin #2 is directly beneath Pin #1. Notice that the numbering of the pins goes from the top left, down, cuts across to the right and then goes up.

We connect pin #2 to pin #6.

Step 6: Pin #3

We'll connect the 100 resistor to pin #3. The LED's negative pin connects to the resistor and the positive pin goes to power.

Repeat with the other LED.

Step 7: Pin #6 (We'll Skip Pin #4 & #5 for Now)

  1. Place your 20K potentiometer on the breadboard.
  2. Connect the potentiometer's ground pin to the LM555's pin #6.
  3. Connect the potentiometer's ADC pin to ground.
  4. Connect the 47uf capacitor's positive pin to the LM555's pin #6 and grounds the negative pin.

Step 8: Pin #7

  1. Connect the 2.2k resistor to:
    1. LM555's pin #7
    2. 20K potentiometer's power pin
  2. Connect the 4.7k resistor to power.

Step 9: Pin #8

Complete your board by:

  1. Connect pin #4 to pin #8.
  2. Pin #8 to power.

Step 10: Connect Power to Play - FINISH

Now that your circuit is complete, connect power and you can turn your potentiometer to adjust the flashing speed of the LED.

Cheers!

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