Tutorial — Practice 6: Stepper motor

Learn by programming: follow each step, write your own code, then validate with the lab questions and exam. Adapt pins and routines to your board when needed.

What you will build

Drive a stepper motor with full-step sequence, ULN2003 driver, and direction control.

1
RC0–RC3 outputs to ULN2003

Set PORTC bits 0–3 as outputs. Each line drives a stepper coil via ULN2003 (higher current than the PIC). RA0 as input to reverse direction.
```
								        CLRF    TRISC
        BSF     TRISA, 0
        CLRF    LATC
							
```
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2
Full-step sequence table

Typical unipolar sequence: `0x01, 0x02, 0x04, 0x08` (one coil at a time). Store the table in flash with `DB` and read with TBLRD* or index in RAM. Apply the pattern to LATC.
```
								secuencia:
        DB      0x01, 0x02, 0x04, 0x08

aplicar_fase:
        ; fase = 0..3 -> LATC = secuencia[fase]
        RETURN
							
```
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3
Advance phase and control direction

Variable `fase` (0–3). Each step: increment or decrement per `sentido` (toggle with RA0). Link to `aplicar_fase` and a delay between steps—that delay sets RPM.
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4
Delay between steps with Timer

Avoid long busy-wait if you also use interrupts. Simple option: calibrated `retardo_paso` loop; better: Timer0 overflow every N ms. Tune speed until rotation is smooth without excessive vibration.
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5
Test CW/CCW rotation in Proteus

Verify sequence on LEDs or virtual motor. Press RA0: direction should reverse without losing steps. Document schematic and phase table in the report.
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Before you code — pre-lab

Pre-laboratory — reference research

Pre-lab research for Practice 6 (Stepper motor, UNEXPO).

Q 1 What is a stepper motor and how does it rotate?

A stepper converts electrical pulses into discrete angular steps. Each step turns the shaft a fixed angle (e.g. 5.625°/step on small geared motors).

Coils are energized in sequence (full or half step). The PIC cannot drive coil current directly — a driver (ULN2003) sits between PIC and coils.

Q 2 Full step and half step sequences

Full step: one coil on at a time — 4 states per cycle, more torque, less resolution.

Half step: two coils at intermediate states — double steps per revolution, smoother motion.

Example unipolar sequence (coils A–D):
`1000 → 0100 → 0010 → 0001 → 1000`

Store the sequence in a table and advance an index each step.

Q 3 Role of the ULN2003

The ULN2003 is a Darlington array with protection diodes. It amplifies PIC outputs (~20 mA) to motor coil current (~hundreds of mA). ULN2003 inputs come from the PIC; outputs drive unipolar stepper coil commons.

Review the motor and ULN2003 driver datasheet from the schematic.

Design your solution

Write your pseudocode

Include: sequence table, phase index, timer delay, direction/speed buttons and ULN2003 driver.

0 characters (minimum 80)

My pseudocode draft

My flowchart draft

Reference pseudocode

START
    Config 4 outputs → ULN2003
    Config Timer0 for step delay
    phase ← 0, direction ← CW
    table ← {1000, 0100, 0010, 0001}
REPEAT FOREVER
    IF step_button THEN advance_phase()
    IF dir_button THEN direction ← toggle
    write table[phase] to motor port
    wait timer_delay
END REPEAT

Reference flowchart

Practice 6 stepper motor flowchart — Phase sequence, step delay and direction control.

Build and adapt the code

Practica · UNEXPO

Lab Practice 6

Control a stepper motor with coil energization sequences. May combine PWM or timed digital outputs.

Typical elements

Driver (ULN2003 or similar)
4 PIC outputs to coils
Buttons for direction and speed
Timer for step delay

Reference source code

After building — post-lab

Post-laboratory — reference research

Post-lab analysis after controlling the motor in simulation or hardware.

Q 1 How do you control stepper motor speed?

Speed depends on time between steps. Use a Timer or software delay between sequence changes. Shorter delay → more steps per second → higher angular speed. Too short and the motor misses steps.

Q 2 How do you reverse rotation direction?

Reverse the order of the energization sequence: decrement the phase index instead of incrementing, or walk the table backwards. A button can toggle a `direction` variable.

Document the exact bit pattern sent to each coil.

Check what you learned

Tutorial hub · Exercises

Tutor IA

Tutorial — Practice 6: Stepper motor

RC0–RC3 outputs to ULN2003

Full-step sequence table

Advance phase and control direction

Delay between steps with Timer

Test CW/CCW rotation in Proteus