Introduction: 555 PWM Controller

Picture of 555 PWM Controller

The following instructions are intended to guide the assembly of a kit project you may have purchased from me at a Maker Faire or that you put together yourself here: Components & PCB.

The purpose of this project is to learn a bit about hobby electronics, teach yourself some soldering and have useful device in the end. With the addition of 4 AA or AAA batteries or a 4.5-6V power supply you will have a light of which you are are able to control the brightness. If you leave the LED portion of this project out and connect M+ and M- to a DC motor you will be able to control the speed of this motor. You could hack a hand held fan so you can control how fast is spins. It is up to you to decide the fun you will have and the creative gadgets you will make with it.

NOTE (4/20/2014): I am waiting for parts and PCB to come in. I will assemble a few example projects and provide photos and videos. I will also attempt to follow these instructions and make corrections as I find mistakes or insights.

Step 1: Parts

Picture of Parts

Parts are organized by "RefDes"

Reference designators match indicators on the PCB and act as a guide in putting together your 555 PWM Controller.


C stands for Capacitor
Some capacitors are polarized. This is indicated with a "+" symbol on the schematic as well as the PCB. A polarized capacitor will have a stripe running down the negative side. Capacitors will have either a capacitance value or code written on them. For this design there is 1 polarized capacitor [C1] and 2 non-polarized capacitors [C2 & C3]. C1 has the value 100µF as well as the stripe indicating the negative lead. C2 & C3 have the code 104 on them. C2 & C3 are not polarized and it does not matter which direction they are inserted.

R stands for Resistor
Resistors also have codes. These codes are done via colored stripes (for through hole resistors). There are many charts and calculators available to help you determine a resistor's resistance.

The 2 values of resistor we will be using are 10kΩ {Brown, Black, Orange, Brown} and 82Ω {Grey, Red, Black, Brown}.

There is another category of resistor that we are using. We will be using a potentiometer to change the duty cycle of 555 timer's PWM output. We are using a 100KΩ potentiometer here.


D stands for Diode or LED

There are 3 1N4001 diodes [D1, D2 & D3] and 1 LED [D4] light emitting diode used in this project. Diodes like to conduct electricity in 1 direction. This direction is indicated via an arrow on the schematic with a line in front of it. The line on the schematic diode symbol matches a silver stripe on one end of the diode itself as well as a stripe on the PCB.

The LED [D4] we are using in this project has 4 pins. It is a square with one corner cut off. This cut corner helps indicate how to place the LED on the PCB. The cut corner should match the indicator on the PCB.

U stands for Microchip or Integrated Circuit

We are using a 555 timer integrated circuit in this project. There are a few markings that help identify which direction to insert the 555 timer. There may be a dot next to pin 1. There also may be a cut out of the top of the chip. There may be both. The PCB is marked with both. Pin 1 is indicated via a square pad and there is a cut out drawn on the top.

J stands for Jumper or Connector

These will be used to connect power and to an output, if you choose. If you choose to use the output for a motor it is probably a good idea to leave the LED [D4] off as they will compete with each other.

Q stands for Transistor(a Darlington pair in our case)
This is the TIP120 Darlington pair power transistor we are using to drive the LED or motor or whatever. Depending on how much of a load is being used you may need a heat sink. When powering a motor, which can pull over 1 amp sometimes, it is important to use a heat sink. I've found that a medium binder clip on the tab will work in a pinch.

Step 2: Solder Components on Back of the PCB (Optional)

Picture of Solder Components on Back of the PCB (Optional)
If you are interested in using this project to have a variable intensity light continue. If you are interested in driving something like a motor skip this step.
  1. Insert LED [D4] into place
  2. Check to make sure that the corner with the notch taken out of it matches the drawing on the PCB
  3. Tape LED [D4] on to the back of the board (this will help with keeping it in place while you solder)
  4. Flip the PCB so the top is showing
  5. Solder LED [D4] pins from the top side
  6. Flip PCB back to the back side
  7. Insert resistor [R3] into place
  8. Bend the leads of resistor [R3] on the top side of the PCB to help hold it in place
  9. Flip PCB to the top side
  10. Solder resistor [R3] leads from the top side
  11. Clip leads for resistor [R3]

NOTE: R3 is a current limiting resistor and is based on the assumption that the input voltage will be 4.5-6 volts. If you decide to use a different voltage you will need to determine the correct resistor value.

Step 3: Solder Components on Front of the PCB

Picture of Solder Components on Front of the PCB

Use the markings of each component listed in the Parts step help place each component. Use tape or bend the leads to help hold them in place for soldering.

  1. Place and solder the LM555CN chip [U1]
    1. Insert it from the top
    2. Tape it down
    3. Flip the board over
    4. Solder it
  2. Place and solder resistor [R1]
    1. Insert it from the top
    2. Flip the board over
    3. Bend the leads so they hold the resistor in place
    4. Solder it
  3. Place and solder the diodes [D1, D2 & D3]
    1. Insert from the top
    2. Ensure that the markings on the diodes match the markings on the PCB
    3. Flip the board over
    4. Bend the leads so they hold the diodes in place
    5. Solder them
  4. Place and solder the small capacitors [C2 & C3]
    1. Insert from the top
    2. Flip the board over
    3. The leads should already be holding the capacitors in place
      If they are not bend the leads to hold them
    4. Solder them
  5. Place and solder the large capacitor [C1]
    1. Insert from the top
    2. Tape it down
    3. Flip the board over
    4. Solder it
  6. Place and solder the TIP120 power transistor [Q1]
    1. Insert from the top
      Make sure that the tab on Q1 matches the markings on the PCB
    2. Flip the board over
    3. Set the board face down so that Q1 is holding it up at an angle
    4. Solder 1 of the pins
    5. Pick up the board
    6. Using a finger, apply slight pressure on Q1 from the top
    7. Re-apply the soldering iron to the pin you just soldered while using your finger to align Q1 so it sits vertially
      This may take some practice, but you'll get it. Even if you don't it isn't a big deal.
    8. Set board face down again
    9. Solder the rest of the pins
  7. Place and solder the potentiometer [R2]
    1. Insert from the top
    2. Tape it down
    3. Solder mounting pins
    4. Solder other pins
  8. Place and solder power wiring
    1. Power
      1. Insert red wire into VCC
      2. Tape it down
      3. Flip the board
      4. Solder it
    2. Ground
      1. Insert black wire into GND
      2. Tape it down
      3. Flip the board
      4. Solder it
  9. Place and solder output wiring (OPTIONAL)
    1. M-
      1. Insert green wire into M-
      2. Tape it down
      3. Flip the board
      4. Solder it
    2. M+
      1. Insert yellow wire into M+
      2. Tape it down
      3. Flip the board
      4. Solder it
  10. Remove any tape you have used to hold parts down
  11. Connect M- & M+ if you are going to connect them to a motor or other external device
  12. Connect power to a power supply (4 AA batteries will should work if you are using the LED, more for DC motors)
    WARNING: Make sure to get the polarity correct or you may let out the magic smoke.
    1. Red wire to +
    2. Black wire to -
  13. Have fun!

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