Using PWM in MaixPy

2024-05-14

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Introduction

To use PWM in MaixPy (v4), first set the pin function to PWM using pinmap.

Each PWM corresponds to a specific pin, as shown in the pin diagram of MaixCAM:

We recommend using PWM6 and PWM7.

For MaixCAM, since WiFi uses all pins of SDIO1, PWM4~9 can only be used alternatively with WiFi.

TODO: Provide a method to disable WiFi (requires disabling the WiFi driver in the system, which is quite complex)

Using PWM to Control a Servo in MaixPy

Here we take controlling a servo as an example, using PWM7 and the A19 pin of MaixCAM:

from maix import pwm, time, pinmap

SERVO_PERIOD = 50     # 50Hz 20ms
SERVO_MIN_DUTY = 2.5  # 2.5% -> 0.5ms
SERVO_MAX_DUTY = 12.5  # 12.5% -> 2.5ms

# Use PWM7
pwm_id = 7
# !! set pinmap to use PWM7
pinmap.set_pin_function("A19", "PWM7")

def angle_to_duty(percent):
    return (SERVO_MAX_DUTY - SERVO_MIN_DUTY) * percent / 100.0 + SERVO_MIN_DUTY

out = pwm.PWM(pwm_id, freq=SERVO_PERIOD, duty=angle_to_duty(0), enable=True)

for i in range(100):
    out.duty(angle_to_duty(i))
    time.sleep_ms(100)

for i in range(100):
    out.duty(angle_to_duty(100 - i))
    time.sleep_ms(100)

This code controls the servo to rotate from the minimum angle to the maximum angle and then back to the minimum angle.

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