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#573 555 PWM Motor Control

Testing small DC motor control with a 555 time PWM signal


Here’s a quick demo..



Pulse-width Modulation (PWM) is a common method for controlling the speed of DC motors.

The PWM duty cycle controls the nett power being provided to the motor, but by maintaining a constant “on” voltage, the torque is not greatly affected by speed.

The PWM frequency is not so important, however there will be a “sweet spot” for a particular motor:

  • too high, and low speed control can be affected (not enough power delivered in each “on” cycle to move the motor)
  • too low, and vibration and “chugging” can be a problem
  • need to avoid resonant frequencies of the mechanical assembly

A 555 timer makes a simple controller. Here I’ve used a “diode-steered” variable duty cycle configuration, with PWM duty cycle controlled with a 100kΩ variable resistor.

The motor I’m testing with is a small DC motor, with a fly-back diode to dissipate the voltage spike as the motor load is switched.




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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.