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230 10.15 Schematic of microcontroller and stepper motor IC

components. The UCN-5804 does most of the grunt work of con-
trolling a stepper motor. This simplifies our microcontroller pro-
gram and overall circuit while enhancing the hardware, a good
combination.
The schematic for a stepper motor controller using a dedicated IC
is shown in Fig. 10.15, and a photograph of the circuit is shown in
Fig. 10.16. The UCN-5804 is powered by a 5V direct current (DC)
power supply. While internally powered by 5 V, it can control stepper
motor voltages up to 35 V.

Notice in the schematic that there are two resistors labeled “rx”
and “ry” that do not show any resistance value. Depending upon
the stepper motor, these resistors may or may not be necessary.
Their purpose is to limit current through the stepper motor to 1.25 A
(if necessary).
Let’s look at our 5V stepper motor. It has a coil resistance of 13
ohms. The current draw of this motor will be 5 V/13 ohms 0.385
A, or 382 milliamperes (mA), well below the 1.25-A maximum rat-
ing of the UCN-5804. So in this case resistors rx and ry are not
needed and may be eliminated from the schematic.
Team LRN
Chapter ten