Pi Servo pHAT (v2) Hookup Guide

Contributors: QCPete, santaimpersonator

Python Examples

The example code for this product is located in the GitHub repository for the Python package; it is also hosted with the ReadtheDocs documentation:

• Example 1: Full Sweep for 90 Degree Servo
• Example 2: Full Sweep for 180 Degree Servo
• Example 3: Get Servo Position for 180 Degree Servo
• Example 4: Change PWM Frequency for 180 Degree Servo

To run the examples, simple download or copy the code into a file. Then, open/save the example file (if needed) and execute the code in your favorite Python IDE. For example, with the default Python IDLE click Run > Run Module or use the F5 key. To terminate the example use the Ctrl + C key combination.

Example 1

We will only cover the first example; however, we will also be breaking down how the code works and explaining how it functions.

Import Dependencies

The first part of the code, imports the required dependencies to operate.

language:python
import pi_servo_hat
import time

Initialize Constructor

This line instantiates an object for the device.

language:python
test = pi_servo_hat.PiServoHat()

Soft Restart

This line soft resets the PCA9685 chip, clears the MODE1 register, and returns the PWM frequency to the default 50 Hz.

language:python
test.restart()

Test Run

This section of the code moves the servo arm to 0° by outputting a 1 ms PWM signal, pausing for a second, then it moves the arm to 90° by outputting a 2 ms PWM signal, and holds the position for a second.

language:python
# Moves servo position to 0 degrees (1ms), Channel 0
test.move_servo_position(0, 0)

# Pause 1 sec
time.sleep(1)

# Moves servo position to 90 degrees (2ms), Channel 0
test.move_servo_position(0, 90)

# Pause 1 sec
time.sleep(1)

Sweep

The final section of the code repeatedly sweeps the servo arm from 0° to 90° and then back. The code iterates with ~1° increments and prints the input position.

language:python
while True:
    for i in range(0, 90):
        print(i)
        test.move_servo_position(0, i)
        time.sleep(.001)
    for i in range(90, 0, -1):
        print(i)
        test.move_servo_position(0, i)
        time.sleep(.001)