The Trinket / Gemma M0 can use the default Servo library. The Arduino Code for 'Knob' is a good place to start.
The following pins on each controller can be used for driving servos with the default Servo Library:
- Trinket M0 - Use PWM pins D0, D2, D3, D4 (pin D1 cannot be used)
- Gemma M0 - Use PWM pins D0, D2 (pin D1 cannot be used)
Trinket & Gemma with ATtiny85
To control servos with the tiny microcontroller on the Trinket, we'll need a Servo library. The default Arduino Servo library is really only good for Uno/Leonardo/Due and similar beefy processors that can drive servos 'standalone'. Sadly, the Attiny85 can't quite do that as it does not have 16bit timers.
So instead we'll use a simpler servo library. Luckily, we wrote one that's perfect! Download the Adafruit_SoftServo library from https://github.com/adafruit/Adafruit_SoftServo by clicking the button below
Please ensure your Arduino IDE is augmented to support Trinket per the Introducing Trinket Guide.
The code below may be copied-and-pasted into a new project window in the Arduino IDE.
// SPDX-FileCopyrightText: 2018 Mikey Sklar for Adafruit Industries
//
// SPDX-License-Identifier: MIT
/*******************************************************************
SoftServo sketch for Adafruit Trinket. Turn the potentiometer knob
to set the corresponding position on the servo
(0 = zero degrees, full = 180 degrees)
Required library is the Adafruit_SoftServo library
available at https://github.com/adafruit/Adafruit_SoftServo
The standard Arduino IDE servo library will not work with 8 bit
AVR microcontrollers like Trinket and Gemma due to differences
in available timer hardware and programming. We simply refresh
by piggy-backing on the timer0 millis() counter
Required hardware includes an Adafruit Trinket microcontroller
a servo motor, and a potentiometer (nominally 1Kohm to 100Kohm
As written, this is specifically for the Trinket although it should
be Gemma or other boards (Arduino Uno, etc.) with proper pin mappings
Trinket: USB+ Gnd Pin #0 Pin #2 A1
Connection: Servo+ - Servo1 Potentiometer wiper
*******************************************************************/
#include <Adafruit_SoftServo.h> // SoftwareServo (works on non PWM pins)
#define SERVO1PIN 0 // Servo control line (orange) on Trinket Pin #0
#define POTPIN 1 // Potentiometer sweep (center) on Trinket Pin #2 (Analog 1)
Adafruit_SoftServo myServo1, myServo2; //create TWO servo objects
void setup() {
// Set up the interrupt that will refresh the servo for us automagically
OCR0A = 0xAF; // any number is OK
TIMSK |= _BV(OCIE0A); // Turn on the compare interrupt (below!)
myServo1.attach(SERVO1PIN); // Attach the servo to pin 0 on Trinket
myServo1.write(90); // Tell servo to go to position per quirk
delay(15); // Wait 15ms for the servo to reach the position
}
void loop() {
int potValue; // variable to read potentiometer
int servoPos; // variable to convert voltage on pot to servo position
potValue=analogRead(POTPIN); // Read voltage on potentiometer
servoPos = map(potValue, 0, 1023, 0, 179); // scale it to use it with the servo (value between 0 and 180)
myServo1.write(servoPos); // tell servo to go to position
delay(15); // waits 15ms for the servo to reach the position
}
// We'll take advantage of the built in millis() timer that goes off
// to keep track of time, and refresh the servo every 20 milliseconds
// The SIGNAL(TIMER0_COMPA_vect) function is the interrupt that will be
// Called by the microcontroller every 2 milliseconds
volatile uint8_t counter = 0;
SIGNAL(TIMER0_COMPA_vect) {
// this gets called every 2 milliseconds
counter += 2;
// every 20 milliseconds, refresh the servos!
if (counter >= 20) {
counter = 0;
myServo1.refresh();
}
}
From the Tools→Board menu, select Adafruit Trinket 8 MHz (or Gemma). Connect the USB cable between the computer and Trinket, press the reset button on the board, then quickly click the upload button (right arrow icon) in the Arduino IDE.
If you get an error message (or a huge list of them), it’s usually one of the following:
- Is the Arduino IDE properly configured for Trinket use? Try compiling and uploading a simple sketch (like the Blink example, set for pin #1).
- Is the Adafruit_SoftServo library properly installed? It must be correctly named and in the right location (the Arduino libraries folder - see All About Installing Arduino Libraries for a guide).
- If the code compiles but does not upload, press the reset button and try the upload again.
The code compiles to 1678 bytes of 5310 maximum.
Now you can try twisting the potentiometer to watch the servo spin!
Page last edited January 21, 2025
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