Rotary encoders with centre-push buttons are cool input hardware for projects, especially if you want to be able to scroll through menus and select options. Hopefully this Instructable will give you the confidence to try a basic menu system out and combine it with a rotary encoder to give a professional feel to your next project!
Why menus and rotary encoders need code
I wanted to have a menu in an upcoming project and use a rotary encoder with a centre push button as my input hardware. This is really similar to the LCD controllers for RAMPS and Arduino MEGA 3D printers. The rotary encoder will allow me to scroll through the menu options, i.e. navigate the menu, select sub-menus and also change values within sub-menus/settings – very versatile for one hardware interface! A microcontroller is needed to manage all of this and microcontrollers need instructions, AKA code!
Other options
The problem I had with existing Arduino menu libraries and menu code is that for simple menus they were overly complicated. Another drawback of many alternatives was that the code was designed for LCD screens and momentary push buttons, not rotary encoders and adaptable to other display outputs. These menus were geared around selecting between a small number of modes and incrementing values relatively slowly. We know that rotary encoders are a great hardware input option because they afford relatively fast input value changes while retaining fine control at slow speed. I wanted to write code which would allow unambiguous top level menu navigation but also allow you to quickly scroll through a large range of values within each sub-menu/setting, exploiting the strengths of the rotary encoder.
The approach
I decided to follow some advice to use if() statements for a simple menu structure and keep it sketch-based. The resultant code builds on my previous Instructable which sought to reliably read the rotation pulses and direction. Please check it out for background.
In this sketch, we add the reading of the centre push button on the rotary encoder shaft, using code that Nick Gammon developed to record button state changes with debouncing and without relying on the Arduino’s delay() function that prevents the microcontroller from executing other code and would potentially introduce noticeable delay in our sketch, e.g. slow display refresh rates. Button state change code is much more useful than just reading digital logic high or low when using a button to select something once, like a menu option, as it can help you prevent unintentional multiple selections for each button press.
Let’s take a look at what you need to set up to use this example code in Step 1.
Step 1: Preparation
If you haven’t yet, please see my other Instructable on rotary encoder reading to find out how to set up your hardware and Arduino IDE software.
If you haven’t yet, please see my other Instructable on rotary encoder reading to find out how to set up your hardware and Arduino IDE software.
Hardware
The additional hardware connections you need to make use of centre push button are shown in the pictures. I used Fritzing to draw the diagram but it didn’t have a rotary encoder component which represented the most likely pin layout, so just use that diagram in conjunction with the notes and look at the photo of the rotary encoder to see what you are more likely to be looking for in terms of rotary encoder pin layout.
One of the two pins on one side of the rotary encoder (as opposed to the side with three pins) needs to be connected to ground and another to a digital pin on the Arduino. I have used D4 for the example sketch. If you choose a different pin, don’t forget to change the value of buttonPin in the sketch.
Next comes the code in Step 2.
Step 2: Code
This is the code. By looking at the structure and the comments I hope you will find it easy to adapt for your specific needs!
/*******Interrupt-based Rotary Encoder Menu Sketch*******
* by Simon Merrett, based on insight from Oleg Mazurov, Nick Gammon, rt and Steve Spence, and code from Nick Gammon
* 3,638 bytes with debugging on UNO, 1,604 bytes without debugging
*/
// Rotary encoder declarations
static int pinA = 2; // Our first hardware interrupt pin is digital pin 2
static int pinB = 3; // Our second hardware interrupt pin is digital pin 3
volatile byte aFlag = 0; // let's us know when we're expecting a rising edge on pinA to signal that the encoder has arrived at a detent
volatile byte bFlag = 0; // let's us know when we're expecting a rising edge on pinB to signal that the encoder has arrived at a detent (opposite direction to when aFlag is set)
volatile byte encoderPos = 0; //this variable stores our current value of encoder position. Change to int or uin16_t instead of byte if you want to record a larger range than 0-255
volatile byte oldEncPos = 0; //stores the last encoder position value so we can compare to the current reading and see if it has changed (so we know when to print to the serial monitor)
volatile byte reading = 0; //somewhere to store the direct values we read from our interrupt pins before checking to see if we have moved a whole detent
// Button reading, including debounce without delay function declarations
const byte buttonPin = 4; // this is the Arduino pin we are connecting the push button to
byte oldButtonState = HIGH; // assume switch open because of pull-up resistor
const unsigned long debounceTime = 10; // milliseconds
unsigned long buttonPressTime; // when the switch last changed state
boolean buttonPressed = 0; // a flag variable
// Menu and submenu/setting declarations
byte Mode = 0; // This is which menu mode we are in at any given time (top level or one of the submenus)
const byte modeMax = 3; // This is the number of submenus/settings you want
byte setting1 = 0; // a variable which holds the value we set
byte setting2 = 0; // a variable which holds the value we set
byte setting3 = 0; // a variable which holds the value we set
/* Note: you may wish to change settingN etc to int, float or boolean to suit your application.
Remember to change "void setAdmin(byte name,*BYTE* setting)" to match and probably add some
"modeMax"-type overflow code in the "if(Mode == N && buttonPressed)" section*/
void setup() {
//Rotary encoder section of setup
pinMode(pinA, INPUT_PULLUP); // set pinA as an input, pulled HIGH to the logic voltage (5V or 3.3V for most cases)
pinMode(pinB, INPUT_PULLUP); // set pinB as an input, pulled HIGH to the logic voltage (5V or 3.3V for most cases)
attachInterrupt(0,PinA,RISING); // set an interrupt on PinA, looking for a rising edge signal and executing the "PinA" Interrupt Service Routine (below)
attachInterrupt(1,PinB,RISING); // set an interrupt on PinB, looking for a rising edge signal and executing the "PinB" Interrupt Service Routine (below)
// button section of setup
pinMode (buttonPin, INPUT_PULLUP); // setup the button pin
// DEBUGGING section of setup
Serial.begin(9600); // DEBUGGING: opens serial port, sets data rate to 9600 bps
}
void loop() {
rotaryMenu();
// carry out other loop code here
}
void rotaryMenu() { //This handles the bulk of the menu functions without needing to install/include/compile a menu library
//DEBUGGING: Rotary encoder update display if turned
if(oldEncPos != encoderPos) { // DEBUGGING
Serial.println(encoderPos);// DEBUGGING. Sometimes the serial monitor may show a value just outside modeMax due to this function. The menu shouldn't be affected.
oldEncPos = encoderPos;// DEBUGGING
}// DEBUGGING
// Button reading with non-delay() debounce - thank you Nick Gammon!
byte buttonState = digitalRead (buttonPin);
if (buttonState != oldButtonState){
if (millis () - buttonPressTime >= debounceTime){ // debounce
buttonPressTime = millis (); // when we closed the switch
oldButtonState = buttonState; // remember for next time
if (buttonState == LOW){
Serial.println ("Button closed"); // DEBUGGING: print that button has been closed
buttonPressed = 1;
}
else {
Serial.println ("Button opened"); // DEBUGGING: print that button has been opened
buttonPressed = 0;
}
} // end if debounce time up
} // end of state change
//Main menu section
if (Mode == 0) {
if (encoderPos > (modeMax+10)) encoderPos = modeMax; // check we haven't gone out of bounds below 0 and correct if we have
else if (encoderPos > modeMax) encoderPos = 0; // check we haven't gone out of bounds above modeMax and correct if we have
if (buttonPressed){
Mode = encoderPos; // set the Mode to the current value of input if button has been pressed
Serial.print("Mode selected: "); //DEBUGGING: print which mode has been selected
Serial.println(Mode); //DEBUGGING: print which mode has been selected
buttonPressed = 0; // reset the button status so one press results in one action
if (Mode == 1) {
Serial.println("Mode 1"); //DEBUGGING: print which mode has been selected
encoderPos = setting1; // start adjusting Vout from last set point
}
if (Mode == 2) {
Serial.println("Mode 2"); //DEBUGGING: print which mode has been selected
encoderPos = setting2; // start adjusting Imax from last set point
}
if (Mode == 3) {
Serial.println("Mode 3"); //DEBUGGING: print which mode has been selected
encoderPos = setting3; // start adjusting Vmin from last set point
}
}
}
if (Mode == 1 && buttonPressed) {
setting1 = encoderPos; // record whatever value your encoder has been turned to, to setting 3
setAdmin(1,setting1);
//code to do other things with setting1 here, perhaps update display
}
if (Mode == 2 && buttonPressed) {
setting2 = encoderPos; // record whatever value your encoder has been turned to, to setting 2
setAdmin(2,setting2);
//code to do other things with setting2 here, perhaps update display
}
if (Mode == 3 && buttonPressed){
setting3 = encoderPos; // record whatever value your encoder has been turned to, to setting 3
setAdmin(3,setting3);
//code to do other things with setting3 here, perhaps update display
}
}
// Carry out common activities each time a setting is changed
void setAdmin(byte name, byte setting){
Serial.print("Setting "); //DEBUGGING
Serial.print(name); //DEBUGGING
Serial.print(" = "); //DEBUGGING
Serial.println(setting);//DEBUGGING
encoderPos = 0; // reorientate the menu index - optional as we have overflow check code elsewhere
buttonPressed = 0; // reset the button status so one press results in one action
Mode = 0; // go back to top level of menu, now that we've set values
Serial.println("Main Menu"); //DEBUGGING
}
//Rotary encoder interrupt service routine for one encoder pin
void PinA(){
cli(); //stop interrupts happening before we read pin values
reading = PIND & 0xC; // read all eight pin values then strip away all but pinA and pinB's values
if(reading == B00001100 && aFlag) { //check that we have both pins at detent (HIGH) and that we are expecting detent on this pin's rising edge
encoderPos --; //decrement the encoder's position count
bFlag = 0; //reset flags for the next turn
aFlag = 0; //reset flags for the next turn
}
else if (reading == B00000100) bFlag = 1; //signal that we're expecting pinB to signal the transition to detent from free rotation
sei(); //restart interrupts
}
//Rotary encoder interrupt service routine for the other encoder pin
void PinB(){
cli(); //stop interrupts happening before we read pin values
reading = PIND & 0xC; //read all eight pin values then strip away all but pinA and pinB's values
if (reading == B00001100 && bFlag) { //check that we have both pins at detent (HIGH) and that we are expecting detent on this pin's rising edge
encoderPos ++; //increment the encoder's position count
bFlag = 0; //reset flags for the next turn
aFlag = 0; //reset flags for the next turn
}
else if (reading == B00001000) aFlag = 1; //signal that we're expecting pinA to signal the transition to detent from free rotation
sei(); //restart interrupts
}
// end of sketch!
I have used “DEBUGGING” at the start of every comment on any line which isn’t critical for the menu to do its thing. If you are happy with the menu’s function, you might want to comment out or delete these lines for smaller compiled sketch size.
Be aware that a key part of menu navigation is feedback to the user while they are scrolling through the option and settings. Therefore if you choose not to include the DEBUGGING lines, you should probably use another visual indicator (e.g. LCD text display, LEDs) that encoder inputs are navigating the menu and changing settings.
If I comment out the DEBUGGING lines (noting that some visual feedback would still be needed for menu navigation) the compiled code is around 1,650 bytes for the Arduino Uno, hopefully leaving plenty of room on your ATMEGA328P for the more exciting parts of your sketch!
Go to Step 3 to find out how the menu system works.
Step 3: Operation and Conclusion
Operation
If you open the serial monitor in Arduino after uploading this sketch, and start to turn the encoder shaft, you should see the top level menu rotating through the number of sub-menus/options you have (limited using the modeMax variable). If you press the centre-push button you will see that the mode/sub-menu you have scrolled to is selected and now you have free reign to scroll through 0-255 values in that sub-menu. Now, if you press the centre-push button you will set that value to setting1 or setting2 or setting3 etc. The Arduino automatically and instantaneously returns you to the top level menu once this has happened.
While powered up, the Arduino remembers what you set each setting to and if you go back to the sub-menu for a setting you have already set a value to, it will start your encoder adjustments from the last value you chose!
Conclusion
I set out to write some sketch-based code that would allow rotary encoders to navigate a basic menu for Arduinos. I also tried to make it readable so that, unlike some alternatives, someone could see the menu structure and know what changes to the code they would need to make to tailor the menu to their needs.
This code is basic and generic, specifically to demonstrate the functionality while being easily adaptable to your own application. It uses the serial monitor as a basic debugging tool which also removes the need for a separate display if you want to see how the code works. I hope you find it useful and are inspired to edit, adapt and improve it!
Please share anything you do with it in the comments!
