Quick answer: the Arduino Stepper library controls motor timing, but it is not a power driver – every stepper needs external motor-control hardware matched to its coil topology, supply and current. Sort out the driver before you touch example code.
Topology comes first
The Stepper library supports unipolar or bipolar motors, but the coil arrangement decides how you wire and drive the motor, not the library. Because the library alone is not a power stage, the interface between your board and the coils is where the real engineering lives.
Driver and current budgeting
The TI ULN2003A illustrates the kind of part used for inductive switching: it contains seven NPN Darlington pairs with common-cathode clamp diodes intended for driving inductive loads. A subtle but important detail is that the 500 mA collector-current figure is a single-output rating – it is not a promise that every channel can run at that current simultaneously.
| Check | What to verify | Why it matters |
|---|---|---|
| Motor topology | Unipolar or bipolar coil arrangement | Determines the drive scheme |
| Driver part | The exact driver datasheet for your board | Ratings differ between similar part numbers |
| Current budget | Per-channel vs simultaneous limits | Single-output ratings do not sum freely |
| Coil documentation | Winding sequence from the motor’s own data | Guessing pin order risks miswiring |
An ordered verification process
- Identify the motor’s coil topology from its own documentation before wiring anything.
- Select a driver rated for that topology and note both its per-channel and simultaneous current limits.
- Match the driver’s supply to the motor’s requirements, keeping the driver within its own thermal limits.
- Never connect motor coils directly to GPIO pins – always go through the driver stage.
- Confirm the step sequence matches your coil arrangement before running example firmware.
- Recheck against the driver’s actual datasheet rather than assuming pin-for-pin equivalence between similar parts.
One point deserves emphasis: ratings and pinouts belong to the exact part number you have. A datasheet for one multi-channel driver is not a substitute for the datasheet of another, so match the part you actually hold.
Reader questions
Can I drive a small stepper straight from Arduino pins?
No. The library requires external motor-control hardware; the pins cannot supply coil current.
Does the Stepper library set my motor current?
No. It controls step timing. Current limiting is a property of the driver and supply you choose.
How do I choose a supply for the motor and driver?
Match the supply to the motor’s requirements and keep the driver within its own thermal limits; the two ratings are related but not the same.
How do I know my coil wiring is right?
Use the motor’s own documentation. The library supports both topologies, so a wrong assumption about the coils produces wrong motion, not an error message.
Documentation
- Arduino Stepper library official README
- Texas Instruments ULN200x/ULQ200x Darlington array datasheet, SLRS027T
Documentation note: the cited sources support the library scope and the cited driver’s ratings. Your motor’s model, pin order, torque and speed come from its own documentation, so verify those before wiring.
