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.

```    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.

```    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.

```    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
```

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

```    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.

```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.

`    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.

Written by Dave Astels for Adafruit Industries

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

import time
import board
import busio
import digitalio
import rotaryio
import pulseio

#--------------------------------------------------------------------------------
# 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.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.