We'll be using CircuitPython for this project. Are you new to using CircuitPython? No worries, there is a full getting started guide here.

Adafruit suggests using the Mu editor to edit your code and have an interactive REPL in CircuitPython. You can learn about Mu and its installation in this tutorial.

Be sure to load CircuitPython on your board. See this tutorial for the process.

This project requires CircuitPython 3.x or 4.0 alpha 1. CircuitPython 4.0 alpha 2 does not work due to ongoing evolution of the display code.

Like the circuit, the code is also straight-forward.

It works as a simple linear, looping state machine that moves to the next state each time the encoder button is pressed:

  • Mode 0 - adjust the servo angle
  • Mode 1 - sweep the servo repeated between 0 and 180 and back, allowing the time to sweep to be adjusted
  • Mode 2 - adjust the lower bound of the pulse width
  • Mode 3 - adjust the upper bound of the pulse width

To start it initializes hardware and sets up some variables, including a debouncer for the encoder switch. There's nothing special about this and it can be seen in the full listing below.

The main loop is made up of 6 sections.

Housekeeping

We start by grabbing the current time. This is the elapsed time actually, as we just need to measure differences in time, not absolute time of day. We also update the debouncer now.

Download: file
    now = time.monotonic()
    button.update()

Sweep

Next, if the current mode is the sweep mode, the servo angle will need to be updated if the time between steps has passed. If the angle reaches either extreme, the direction of rotation is reversed.

Download: file
    if mode == 1:
        if now >= (last_movement_at + sweep_time / 36):
            last_movement_at = now
            angle += delta
            if (angle > 180) or (angle < 0):
                delta *= -1
                angle += delta

Mode

If the button was just pressed, we change the mode. If we are switching into mode 0 the angle is set to 0. If we are going into mode 1 we set the time it takes to sweep and next time to step the servo. If we are going into mode 2 or 3, the angle is set to the appropriate extreme.

Download: file
    if button.fell:
        servo.angle = 0
        if mode == 0:
            mode = 1
            sweep_time = 1.0
            last_movement_at = now
        elif mode == 1:
            mode = 2
            angle = 0
        elif mode == 2:
            mode = 3
            angle = 180
        elif mode == 3:
            mode = 0
            angle = 0

Adjust

If the encoder switch wasn't just pressed, the encoder is use to adjust the relevant parameter (depending on the current mode).

Download: file
    else:
        current_position, change = get_encoder_change(rotary_encoder, current_position)
        if change != 0:
            if mode == 0:
                angle = min(180, max(0, angle + change * 5))
            elif mode == 1:
                sweep_time = min(5.0, max(1.0, sweep_time + change * 0.1))
            elif mode == 2:
                min_pulse_index = min(10, max(min_pulse_index + change, 0))
                test_servo = servo.Servo(pwm, 
                                         min_pulse=min_pulses[min_pulse_index], 
                                         max_pulse=max_pulses[max_pulse_index])
                test_servo.angle = 0
            elif mode == 3:
                max_pulse_index = min(10, max(max_pulse_index + change, 0))
                test_servo = servo.Servo(pwm, 
                                         min_pulse=min_pulses[min_pulse_index], 
                                         max_pulse=max_pulses[max_pulse_index])
                test_servo.angle = 180

Display

Once any mode change or adjustment has been made, the display is updated as appropriate for the mode.

Download: file
oled.fill(0)
    if mode == 0:
        oled.text("Angle: {0}".format(angle), 0, 0)
    elif mode == 1:
        oled.text("Sweep time: {0}".format(sweep_time), 0, 0)
    elif mode == 2:
        oled.text("Min width: {0}".format(min_pulses[min_pulse_index]), 0, 0)
    elif mode == 3:
        oled.text("Max width: {0}".format(max_pulses[max_pulse_index]), 0, 0)
    oled.show()

Servo

The final step in the loop is to update the angle of the servo.

Download: file
    test_servo.angle = angle

And that's it. Below is the full code. You'll need the debouncer as well which can be found in the library bundle.

Note that this is main.py, not code.py (as is the author's custom when there is more than just one file of Python code) so make sure there is not code.py left over from previous projects.
"""
Servo Tester

Adafruit invests time and resources providing this open source code.
Please support Adafruit and open source hardware by purchasing
products from Adafruit!

Written by Dave Astels for Adafruit Industries
Copyright (c) 2018 Adafruit Industries
Licensed under the MIT license.

All text above must be included in any redistribution.
"""

import time
import board
import busio
import digitalio
import rotaryio
import pulseio
import adafruit_ssd1306
from adafruit_motor import servo
from adafruit_debouncer import Debouncer

#--------------------------------------------------------------------------------
# Initialize Rotary encoder

button_io = digitalio.DigitalInOut(board.D12)
button_io.direction = digitalio.Direction.INPUT
button_io.pull = digitalio.Pull.UP
button = Debouncer(button_io)
rotary_encoder = rotaryio.IncrementalEncoder(board.D10, board.D11)

#--------------------------------------------------------------------------------
# Initialize I2C and OLED

i2c = busio.I2C(board.SCL, board.SDA)

oled = adafruit_ssd1306.SSD1306_I2C(128, 32, i2c)
oled.fill(0)
oled.show()

min_pulses = [ 500,  550,  600,  650,  700,  750,  800,  850,  900,  950, 1000]
max_pulses = [2000, 2050, 2100, 2150, 2200, 2250, 2300, 2350, 2400, 2450, 2500]

min_pulse_index = 10
max_pulse_index = 0

#-------------------------------------------------------------------------------
# Initialize servo

pwm = pulseio.PWMOut(board.D5, frequency=50)
test_servo = servo.Servo(pwm, min_pulse=1000, max_pulse=2000)
test_servo.angle = 0

current_position = None               # current encoder position
change = 0                            # the change in encoder position
angle = 0
mode = 0
sweep_time = 1.0
last_movement_at = 0.0
delta = 5


def get_encoder_change(encoder, pos):
    new_position = encoder.position
    if pos is None:
        return (new_position, 0)
    else:
        return (new_position, new_position - pos)

#--------------------------------------------------------------------------------
# Main loop

while True:
    now = time.monotonic()
    button.update()

    if mode == 1:
        if now >= (last_movement_at + sweep_time / 36):
            last_movement_at = now
            angle += delta
            if (angle > 180) or (angle < 0):
                delta *= -1
                angle += delta

    if button.fell:
        servo.angle = 0
        if mode == 0:
            mode = 1
            sweep_time = 1.0
            last_movement_at = now
        elif mode == 1:
            mode = 2
            angle = 0
        elif mode == 2:
            mode = 3
            angle = 180
        elif mode == 3:
            mode = 0
            angle = 0

    else:
        current_position, change = get_encoder_change(rotary_encoder, current_position)
        if change != 0:
            if mode == 0:
                angle = min(180, max(0, angle + change * 5))
            elif mode == 1:
                sweep_time = min(5.0, max(1.0, sweep_time + change * 0.1))
            elif mode == 2:
                min_pulse_index = min(10, max(min_pulse_index + change, 0))
                test_servo = servo.Servo(pwm,
                                         min_pulse=min_pulses[min_pulse_index],
                                         max_pulse=max_pulses[max_pulse_index])
                angle = 0
            elif mode == 3:
                max_pulse_index = min(10, max(max_pulse_index + change, 0))
                test_servo = servo.Servo(pwm,
                                         min_pulse=min_pulses[min_pulse_index],
                                         max_pulse=max_pulses[max_pulse_index])
                angle = 180

    oled.fill(0)
    if mode == 0:
        oled.text("Angle: {0}".format(angle), 0, 0)
    elif mode == 1:
        oled.text("Sweep time: {0}".format(sweep_time), 0, 0)
    elif mode == 2:
        oled.text("Min width: {0}".format(min_pulses[min_pulse_index]), 0, 0)
    elif mode == 3:
        oled.text("Max width: {0}".format(max_pulses[max_pulse_index]), 0, 0)
    oled.show()

    test_servo.angle = angle

This guide was first published on Nov 16, 2018. It was last updated on Nov 16, 2018.

This page (Code) was last updated on Oct 24, 2020.