Introduction: Light Dimmer (PCB Layout)

Hello guys!!

Here I am showing you the PCB layout of the Light dimmer circuit using the most popular timer IC 555.This circuit can also be used to control the speed of DC motor of low power rating. The timer IC can be operated in three modes:

  1. Astable
  2. Monostable
  3. Bistable

The astable mode is used in this circuit.


  1. IC- NE555
  2. Resistor - 1K/0.25W (2nos)
  3. Potentiometer - 10K
  4. Capacitor - 0.01uf,0.1uf
  5. Diode- 1N4148(2nos),1N4007(1nos)
  6. Transistor - BD139(1nos)
  7. Terminal Blocks - (2nos)

Step 1: Circuit Diagram

As I told this circuit is working in the astable mode. By varying the potentiometer R3 the duty cycle of the output pulses can be varied without changing the output frequency. The formula for calculating ON time and OFF time for this circuit is:



Total time period(Ton+Toff) = 0.8(R1+R3)C2

Frequency = 1/Total time period

By using the above calculation the output frequency of this circuit is:

Ton+Toff = 0.8*(1+10)*0.01 = 0.088

Frequency = 1/0.088 = 11.36Khz

So if you want to change the frequency you can change the capacitor value(C2).

Pulse width modulation

Pulse width modulation or PWM is a way of controlling the average voltage value applied to a load by constantly switching it ON and OFF at different duty cycles. Rather than control the brightness of the light by carefully applying less and less voltage to it, we can control it by alternatively switching the voltage fully ON and OFF in such a way that the average ON time produces the same effect as a varying the supply voltage.
In effect, the control voltage applied across the terminals of the light is controlled by the duty cycle of the 555’s output waveform which in turn controls the brightness of the light.

By the PWM technique, we can also control the speed of DC motors. I have also tried this circuit to charge a 4V lead-acid battery and I was able to control the charging current very precisely. So it is an added advantage to this circuit. But make sure that the output frequency is in the Kilohertz range.

Step 2: PCB Layout

The PCB layout and Gerber files are provided here. You can download it from here.

Step 3: Finished Board

After placing the components and soldering them, the board is ready. The potentiometer is fitted on the board itself for handling it easily. The maximum collector current of the output transistor BD139(Q1) is 1.5A. So if you are connecting heavy loads replace the transistor with the appropriate current rating.

Hope you all like this circuit

Thank you!!