Getting Code Onto Trinket

Before we start disassembling or building the circuit, it's a good idea to get code uploaded to the micro-controller first. If you don't write / understand code, don't to worry! You don't need to be a programmer to be able to upload prewritten code :-) 

We'll walk you through the whole process. 

First, visit the Trinket tutorial page by clicking the button below. Follow the instructions to download & setup the Arduino IDE and install drivers.

Make sure you are able to get sketches compiled and uploaded, especially the blink example in the tutorial. Once you are comfortable with using the Trinket, you can continue!

Install Adafruit TiCoServo Library

Next, we need to add support for the micro servo. The Adafruit TiCoServo library is used to manage servo pulses. You'll need to install the library either manually or using the Library Manager in the Arduino IDE.

Search for TiCoServo to locate it and Install!

You'll need to install the Adafruit package to the additional boards manager in order to install the Adafruit TiCoServo library. Visit the Adafruit Arduino IDE setup tutorial to install the profile!

Uploading Code to Board

Now that we have the Adafruit boards & NeoPixel library installed, we can get our code ready to upload onto the board. Select all of the code listed below in the black box and copy it to your clip board. Then, in Arduino IDE, paste it in the sketch window (making sure to overwrite anything currently there). Next, goto the Tools menu > Board and select Adafruit Trinket (if you're using the 3V Adafruit Trinket version use Trinket 8Mhz. If you're using the 5V Trinket, select Trinket 16Mhz). Now you can click on the "check mark" icon to verify the code. If it's all good, we can continue to upload the code to the board.

Connect USB Data Cable to Trinket

Be sure to use a micro USB cable that can transfer data - A USB cable that ONLY charges devices will simply not work. Plug it into the microUSB port on the Adafruit Trinket board and the USB port on your computer (try to avoid connecting to a USB hub). As soon as you plug it in, you'll see a red LED blink on the Adaruit Trinket - This let's you know the board is ready to accept code. While the LED is blinking, click on the Upload button (It's a right arrow icon, next to the check mark). The Arduino IDE will notify you if the upload is successful and completed.

We've had issues with uploading code to the Trinket on a Mac with El Capitan – If you're running this setup be sure to use a USB 2.0 Hub. The issue is due to USB 3.0 ports on Mac hardware.
// SPDX-FileCopyrightText: 2018 Limor Fried for Adafruit Industries
// SPDX-License-Identifier: MIT

// Trinket Servo Monster sketch
// Hardware: Adafruit Trinket (3V or 5V), micro servo, LED + resistor
// Libraries: uses Adafruit_TiCoServo library to manage servo pulses,
// even though NeoPixels are NOT being used here.

#if !defined(__AVR_ATtiny85__)
 #error "This code is for ATtiny boards"
#include <Adafruit_TiCoServo.h>
#include <avr/power.h>

// Servo parameters.  Pin MUST be 1 or 4 on a Trinket.  Servo position
// is specified in raw timer/counter ticks (1 tick = 0.128 milliseconds).
// Servo pulse timing is typically 1-2 ms, but can vary slightly among
// servos, so you may need to tweak these limits to match your reality.
#define SERVO_PIN  4 // Pins 1 or 4 are supported on Trinket
#define SERVO_MIN  4 // ~1 ms pulse
#define SERVO_MAX 26 // ~2 ms pulse

#define LED_PIN    0 // "Eye" LED is connected here

Adafruit_TiCoServo servo;

void setup(void) {
#if (F_CPU == 16000000L)
  // 16 MHz Trinket requires setting prescale for correct timing.
  // This MUST be done BEFORE servo.attach()!
  pinMode(LED_PIN, OUTPUT);
  digitalWrite(LED_PIN, HIGH);

uint32_t lastLookTime = 0; // Time of last head-turn

void loop(void) {

  unsigned long t = millis(); // Current time

  // If more than 1/2 second has passed since last head turn...
  if((t - lastLookTime) > 500) {
    if(random(10) == 0) { // There's a 1-in-10 chance...
      // ...of randomly moving the head in a new direction:
      servo.write(random(SERVO_MIN, SERVO_MAX));
      lastLookTime = t;   // Save the head-turn time for future reference

  // Unrelated to head-turn check,
  if(random(10) == 0) { // there's a 1-in-10 chance...
    // ...of an "eye blink":
    digitalWrite(LED_PIN, LOW);  // The LED turns OFF
    delay(random(50, 250));      // for just a short random moment
    digitalWrite(LED_PIN, HIGH); // then back ON

  delay(100); // Repeat loop() about 10 times/second

This guide was first published on Jul 18, 2017. It was last updated on Jul 18, 2017.

This page (Software) was last updated on Jul 15, 2017.

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