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#432 ULN2003A Stepper Driver Modules

Investigating the common ULN2003A modules provided for unipolar stepper motor control - this one is identified as X113647



Unipolar stepper motors are commonly used with microcontrollers. One the one hand they are simple to drive - no polarity reversal required. But on the other hand, the current/power requirements of the motors usually exceed the capability of the microcontroller (e.g. Arduino) board to supply directly.

The most common solution for this is to employ the ULN2003A Darlington transistor array chip. It can be dropped on a breadboard with no additional components in a moment, but it is also common to find ULN2003A modules offered with some additional features, such as:

  • LEDs for activity indication on each stepper coil connection
  • bypass capacitor on the motor power line

While ULN2003A modules can literally be used for any purpose, they are typically aimed at stepper motor use, as they connect up only 4 of the Darlinton pairs, and include a 5-pin connector commonly used with stepper motor drives.

The X113647 Driver Board

There are any number of versionss of the ULN2003A module. I have one identfiied as X113647 and is commonly supplied with the 28BYJ-48 stepper motor.

In addition to LEDs and a smotthing capacitor, this module includes a jumper that disconnects the positive motor supply from the connector to the motor - though I can’t think of a really good reason why this might be useful.


When used with the 28BYJ-48, the connections are as follows:

Controller-side Stepper-side 28BYJ-48
IN1 OUT1 Blue
IN2 OUT2 Pink
IN3 OUT3 Yellow
IN4 OUT4 Orange
- COM: 5-12V Red




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.