Circuit: Stepper Motor Generator

Microcontrollers may dominate today’s stepper motor projects, but there’s a certain charm in driving them with pure CMOS logic. This no-firmware approach strips things down to the fundamentals of digital design, making it perfect for learners and retro enthusiasts alike.

The Circuit

The following straightforward circuit from 2004 turns a clock signal from a square-wave generator into two signals with a 90° phase shift, which is exactly what the stepper motor windings need. The simplicity does mean the frequency is reduced by a factor of four, but that can be easily solved by increasing the input frequency. In a short article, the Elektor Engineering Team explained: “The timing diagram clearly shows that the counter outputs of the 4017 are combined using inverting OR gates to produce two square waves with a phase difference. This creates the correct sequence for powering the windings: the first winding is negative and the second positive, both windings are negative, the first winding is positive and the second negative, and finally both windings are positive.”

Inside the 4017 is a divide-by-10 counter paired with a decoder. When the counter is at zero, output ‘0’ is high. On the next rising edge of the clock, the counter advances to 1 and output ‘1’ goes high. This sequence continues until output ‘4’ becomes active. That output is wired to the reset pin, which instantly drives the counter back to the zero state. To use an oscilloscope to look at this output, you would have to set it up precisely before you would be able to see the pulse. That’s how short it is. The output of an OR gate can only supply several milliamps, which is too little to drive a stepper motor directly. A suitable driver circuit, which goes between the generator and stepper motor, was published in the May 2004 issue of Elektor.

The Original Stepper Motor Generator Project

The original article, “Stepper Motor Generator,’” appeared in Elektor July/August 2004. You can access the article for free during the two-week period following the publication of this post. If you create a circuit of your own, consider sharing your progress on the Elektor Labs platform!

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Editor's Note: This article first appeared in 2004. Given the project’s age, some components or products might not be available, and the key design techniques might seem antiquated. However, we believe the project will inspire you to start new designs in the future.