Simple circuit controls stepper motors

Posted on May 16, 2012

Stepper motors are useful in many consumer, industrial, and military applications. Some, such as personal-transportation systems, require precise speed control. Stepper-motor controllers can be simple (Figure 1), but they require a variable-frequency square wave for the clock input. The AD9833 low-power DDS (direct-digital-synthesis) IC with an on-chip, 10-bit DAC is ideal for this task, because you need no external components for setting the clock frequency (Figure 2). The device contains a 28-bit accumulator, which allows it to generate signals with 0.1-Hz resolution when you operate it with a 25-MHz MCLK (master clock). In addition, the circuit can easily stop the motor if you program a 0-Hz output frequency.

Figure 3 shows the complete system. The most significant bit of the on-chip DAC switches to the VOUT pin of the AD9833, thus generating the 0-to-VDD square wave that serves as the clock input to the stepper-motor controller. Writing to the frequency-contr

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