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Project Notes

#232 555 PWM LED Dimmer

Test a PWM LED dimmer circuit using a 555 timer.

The Build


This circuit uses a 555 Timer-based PWM circuit to dim a LED strip.

Steering diodes in the 555 timing circuit allow adjustment of the duty cycle with little change to the ~1kHz frequency.

The 555 Timer signal is used to switch the LED strip with a low-side n-channel MOSFET.

I’m using a 1m (60 LED) stretch of a 12V LED strip, and the maximum current draw is 133mA. Since this is quite low power, I’m using a 2N7000 MOSFET which is rated for 200mA continuous/500mA pulsed.


At maximum duty cycle (almost 100%), LED current measures 133mA and the voltage drop over the FET drain-source is 0.71 V.

The minimum duty cycle of ~1.25% does not completely turn off the LEDs. At this point the LED current measures 3.2mA and the voltage drop over the FET drain-source is 4.45 V.


At midpoint of the pot, duty cycle is ~50%:


LED Strip Specifications

I’m using this (very) cheap 3014 Led Strip Light. According to the seller specs:

Attribute Specification
Length 5m
LED Density 60 LED/m
Color cold white
View angle 120°
Working Voltage 12V DC
Power consumption 20W, 4W/m, ~67mW/LED
Working Temperature -40 to 70°
Luminous Flux 880-1080 Lumens/Meter
Size L500cm (5M) x W0.5cm x T0.20cm
lifespan >100,000 hours



The Schematic

The Build

Credits and References

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This page is a web-friendly rendering of my project notes shared in the LEAP GitHub repository.

LEAP is just my personal collection of projects. Two main themes have emerged in recent years, sometimes combined:

  • electronics - usually involving an Arduino or other microprocessor in one way or another. Some are full-blown projects, while many are trivial breadboard experiments, intended to learn and explore something interesting
  • scale modelling - I caught the bug after deciding to build a Harrier during covid to demonstrate an electronic jet engine simulation. Let the fun begin..
To be honest, I haven't quite figured out if these two interests belong in the same GitHub repo or not. But for now - they are all here!

Projects are often inspired by things found wild on the net, or ideas from the many great electronics and scale modelling podcasts and YouTube channels. Feel free to borrow liberally, and if you spot any issues do let me know (or send a PR!). See the individual projects for credits where due.