Control Surface main
MIDI Control Surface library for Arduino


This example demonstrates the use of MCP23017 I²C port expanders with rotary encoders that send relative Control Change messages, using hardware interrupts so you don't miss any pulses.

Teensy 3.x

This only works on Teensy boards, and maybe on other ARM boards.
I've tested it using a Teensy 3.2 and a Teensy 4.0.

AVR boards (Arduino Uno, Mega, etc.) don't support I²C inside of interrupt service routines, so there's no way to read the state of the MCP23017 inside of an ISR.
The same goes for ESP32 and ESP8266, although there may be ways around this by using alternative I²C drivers or by using FreeRTOS features.


Connect up to 8 encoders to the MCP23017's GPIO pins: the first encoder connects to GPIO A0 and A1, the second encoder connects to GPIO A2 and A3, ..., the eighth encoder connects to GPIO B6 and B7.
Connect the "common" pins of the encoders to ground.
The built-in pull-up resistors of the MCP23017 will be enabled.

Make sure that the reset and address pins are all configured correctly (reset to Vcc; A0, A1 and A2 to ground).

If you need more than one MCP23017 with encoders, you can connect their interrupt pins together. This does result in higher latency, because on average, half of the total number of MCP23017s have to be polled, which is relatively slow, and might lead to missed pulses when using a large number of encoders.


When the position of one of the encoders changes, a relative Control Change message is sent.


Map the Arduino as a Mackie Control Universal in your DAW. The encoders will control the pan (just like the V-Pots on an MCU).

The interrupt pin of the MCP23017 triggers a hardware interrupt on the Arduino. This means that you don't have to manually poll the encoders all the time.

Written by PieterP, 2020-04-06

#include <Wire.h>
// Type for the MCP23017 encoders (translates encoder pulses to position)
using WireType = decltype(Wire); // The type of I²C driver to use
using EncoderPositionType = int32_t; // The type for saving encoder positions
constexpr bool IntSafe = true; // Make it safe to call `update` in an ISR
using MCPEncoderType = MCP23017Encoders<WireType, EncoderPositionType, IntSafe>;
// Type for the MIDI encoders (translates position to MIDI messages)
struct CCMCPEncoder : GenericMIDIRotaryEncoder<MCPEncoderType::MCP23017Encoder,
RelativeCCSender> {
CCMCPEncoder(MCPEncoderType::MCP23017Encoder enc, MIDIAddress address,
int16_t multiplier = 1, uint8_t pulsesPerStep = 4)
: GenericMIDIRotaryEncoder(std::move(enc), address, multiplier,
pulsesPerStep, {}) {}
const uint8_t interrupt_pin = 12;
// Create an object that manages the 8 encoders connected to the MCP23017.
MCPEncoderType enc {Wire, 0x0, interrupt_pin};
// │ │ └─ Interrupt pin
// │ └────── Address offset
// └──────────── I²C interface
// Instantiate 8 MIDI rotary encoders.
CCMCPEncoder ccencoders[] {
enc[0], // The encoder to use
MCU::V_POT_1, // The MIDI address
1, // Encoder speed multiplier
4, // Number of pulses per physical "click" of the encoder
{enc[1], MCU::V_POT_2},
{enc[2], MCU::V_POT_3},
{enc[3], MCU::V_POT_4},
{enc[4], MCU::V_POT_5},
{enc[5], MCU::V_POT_6},
{enc[6], MCU::V_POT_7},
{enc[7], MCU::V_POT_8},
void isr() {
enc.update(); // Read the state of the encoders and update the positions
void setup() {
Wire.begin(); // Must be called before enc.begin()
enc.begin(); // Initialize the MCP23017
attachInterrupt(digitalPinToInterrupt(interrupt_pin), isr, LOW);
void loop() {
// No `enc.update()` here, updating the encoders happens inside of the ISR
constexpr PinStatus_t LOW
The main header file that includes all Control-Surface header files.
Control_Surface_ & Control_Surface
A predefined instance of the Control Surface to use in the Arduino sketches.
void begin()
Initialize the Control_Surface.
void loop()
Update all MIDI elements, send MIDI events and read MIDI input.
An abstract class for rotary encoders that send MIDI events.
GenericMIDIRotaryEncoder(Enc &&encoder, MIDIAddress address, int16_t speedMultiply, uint8_t pulsesPerStep, const Sender &sender)
Construct a new MIDIRotaryEncoder.
A type-safe utility class for saving a MIDI address consisting of a 7-bit address,...
A class for debug MIDI interfaces sending and receiving human-readable MIDI messages over the USB CDC...
constexpr uint8_t V_POT_5
V-Pot 5 (Relative) (Out)
Definition: MCU.hpp:170
constexpr uint8_t V_POT_2
V-Pot 2 (Relative) (Out)
Definition: MCU.hpp:167
constexpr uint8_t V_POT_1
V-Pot 1 (Relative) (Out)
Definition: MCU.hpp:166
constexpr uint8_t V_POT_7
V-Pot 7 (Relative) (Out)
Definition: MCU.hpp:172
constexpr uint8_t V_POT_8
V-Pot 8 (Relative) (Out)
Definition: MCU.hpp:173
constexpr uint8_t V_POT_6
V-Pot 6 (Relative) (Out)
Definition: MCU.hpp:171
constexpr uint8_t V_POT_3
V-Pot 3 (Relative) (Out)
Definition: MCU.hpp:168
constexpr uint8_t V_POT_4
V-Pot 4 (Relative) (Out)
Definition: MCU.hpp:169