Improved Arduino Rotary Encoder Reading

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Introduction: Improved Arduino Rotary Encoder Reading

Rotary encoders are great input devices for electronics projects - hopefully this Instructable will inspire and help you use one in your next project.

Why write rotary encoder code?

I wanted to use a low cost rotary encoder as an input mechanism for one of my upcoming projects and was initially bewildered by the code options available to take readings from the rotary encoder and determine how many "detents" or cycles the encoder had clicked past and in what direction. I think my main sketch will need to use most of my Arduino's memory so I am avoiding the various available encoder libraries, which seemed to be difficult to make work when I tried a couple of them. They also appear to use far more of the code budget than the sketch-based code approaches discussed from here on.

If you just want to bypass the thinking behind my approach and get straight into the Instructable, feel free to skip ahead to Step 1!

Other Approaches

Several of the main sketch-based (i.e. they don't use a library) approaches are discussed in rt's blog post where they write rotary encoder code that makes the cheapest encoders usable as Arduino inputs. They also have a good example of they logic signal that the encoder produces. rt found that a timer interrupt system worked best for them but I'm concerned that the polling frequency would detract from screen update speed in the main loop of my project sketch. Given that the rotary encoder will be moving for a tiny proportion of the time I want the screen to be updating, this seems a poor match for my application.

I chose to start off using Steve Spence's code here, which was fine on it's own but appeared to really slow down when I incorporated the rest of my sketch code (which involves writing display updates to a small TFT screen). Initially I wondered if it could be because the main loop contains a debounce statement.

I then read Oleg's rotary encoder article on an interrupt service routine version of his previous post, I also thought it might be a good idea to use direct port manipulation to read both pins simultaneously and as soon as the interrupt fires. His code can be used on any input pin if the port manipulation code is rewritten. In contrast, I decided to use only the hardware interrupts on digital pins 2 and 3, so we can set interrupts to only fire on a rising edge of the pin voltage, rather than on pin voltage change, which includes falling edges. This reduces the number of times the ISR is called, distracting from the main loop.

Oleg's code uses a lookup table to reduce compiled code size to a really small size but I couldn't get reliable results which would catch very slow rotation as well as reasonably fast rotation. Bear in mind that hardware debouncing (see Step 2) can help a lot with reliability of readings but I was after a software solution to simplify the hardware build and be as portable to other hardware applications as possible.

This concludes the introduction of my challenge and considerations. In Step 2 we'll take a look at the encoder hardware, terminology and some practical considerations when you want to integrate a rotary encoder into your project.

Step 1: A Bit About Rotary Encoders

Why are rotary encoders so cool?

  1. Unlike a variable resistor/potentiometer they have infinite travel in any direction and because they produce a digital "Gray code" you can scale their readings to whatever range you like.
  2. The dual direction makes them useful for increasing or decreasing a value within a variable or navigating menus.
  3. Finally, many of these rotary encoders come with a centre push button, which can be used to select menu items, reset a counter or do anything you can think of that might suit a momentary push button.

Terms

  1. PPR: pulses per rotation - typically 12, 20 or 24. You might also see specifications for maximum rotation in rpm etc. This is probably determined by the encoder's propensity to "bounce" contacts - see below.
  2. Detent: the little click of the action as it springs to a natural rest point between pulses. There may be one detent per pulse/cycle (not equal to a rotation of the shaft) or two.
  3. Bounce: mechanical contacts inside the encoder literally bounce enough to jump off and back on a contact when rotating, potentially leading to too many readings attributed to that phase of the travel between detents.
  4. Debounce: This can be either done in hardware, perhaps with a low value ceramic capacitor between each pin and Ground, or in software, perhaps with a delay. In either case, the aim is to create a system which ignores bouncing contacts.

Tips

  1. Look out for a threaded section near the base of the shaft and a matching nut if you want to mount your encoder in a panel or enclosure.
  2. Many knobs are available for rotary encoders, with the most easily available coming in 6mm diameter shafts.
  3. Pay attention to whether your encoder shaft uses a flat face or splines to achieve a proper fit with the knob.
  4. The body of the rotary encoder may also come with a raised pin/stub, intended to mate with a small indent/hole in your panel (probably hidden by your knob) and prevent your encoder from rotating when you turn the knob. You might find you want to remove this if you can create enough friction to prevent encoder body rotation using the mounting bolt to screw the encoder in the panel or enclosure.
  5. Make sure you find out where the detent state is for your encoder and adapt your code accordingly. My example uses an encoder whose pins are both disconnected from ground and are pulled high by their respective input pullup resistors. This drives my selection of a RISING interrupt. If both pins were connected to ground when at detent, they would need code which was looking for FALLING pin voltage.

Step 2: The Circuit

The circuit is so simple. You will need:



• An ATMEGA328P based Arduino, such as the Uno, Pro Mini or Nano.
• A mechanical (as opposed to optical) quadrature rotary encoder - this is the most common kind so don't worry too much if it isn't specified. eBay and Aliexpress listings will often mention Arduino in the description and this is a good indicator that one is suitable.
• Hook-up wire/jumper leads.
• Optional: a prototyping breadboard.


First of all, look for a collection of three pins on one side of the encoder. These are the three for measuring rotation with our code. If there are two pins together on another side, these are likely to be for the centre push button. We'll ignore these for now.

Out of the three pins together, the encoder ground pin is connected to Arduino ground pin. Either of the other two pins is connected to digital pin 2 and the remaining on is connected to digital pin 3. If your direction of rotation isn't the way you'd like, just swap the two non-ground pins over.

Pins 2 and 3 are important because on the ATMEGA328P-based Arduinos they are the only pins which have the ability to detect RISING and FALLING pin change interrupts. The MEGA 2560 boards etc. have other hardware interrupt pins which can do this.

Note: In the diagram the ground pin is one of the end pins. In reality, the ground pin is often the centre pin but this is not always the case so read the datasheet or test your encoder to find out which pin is ground.

Another note: ArneTR made a good comment about not having a separately wired connection to the logic positive voltage (e.g. 5V or 3.3V) for the rotary encoder circuit shown. The Arduino can't read the rotary encoder without both a ground signal (which we have connected a wire to) and the logic voltage (sometimes annotated as Vcc or Vdd), so how can the Arduino read the logic from this encoder without a positive voltage wire? The answer is that the ATMEGA328P chip in the Arduino has a special mode you can set on the digital pins (which we are using) where a pin is automatically pulled "high" to the logic voltage by an internal resistor. Look in the code for "pinMode(pinX, INPUT_PULLUP)" to see us telling the Arduino that we want to take advantage of this mode. Once set, we only need to provide the encoder with a ground wire as the sensing wires from the digital pins are already providing the logic voltage.

ONE MORE THING... Githyuk found that a particular branded encoder didn't work with this way of doing things (ie the code below). Please see the comments section for details but in general, trying a different encoder would be a good debugging step when you have exhausted the easier/faster/cheaper steps.

Step 3: The Code

If you are not familiar with programming Arduinos, please get up to speed with this resource from Arduino themselves.

This code is free for your use (as in no cost and to be modified as you please), please attribute where you should.


/*******Interrupt-based Rotary Encoder Sketch*******
by Simon Merrett, based on insight from Oleg Mazurov, Nick Gammon, rt, Steve Spence
*/

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

void 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)
Serial.begin(115200); // start the serial monitor link
}

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
}

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
}

void loop(){
if(oldEncPos != encoderPos) {
Serial.println(encoderPos);
oldEncPos = encoderPos;
}
}

That's it!

Step 4: Conclusion

I hope you find this code useful for your next project which uses a rotary encoder or that it has inspired you to consider a rotary encoder as an input for your next project.

Summary of the Aims

I have tried to write some code which achieves a good balance of:

  • Portability (port manipulation code is the compromise when moving to other chips)
  • Speed (port manipulation really helps)
  • Low compiled code size (port manipulation and bitmath helps)
  • Reliably records slow and fast manual rotation
  • Reduced nugatory interrupt service routine calls (using RISING interrupt and temporarily disabling interrupts)

Caveats and Ideas for Improvement

This code isn't perfect by any means and you might like to change it to use other pins. I tested this code with the sketch which was causing the most delay and least reliable readings with the other approaches discussed - I certainly haven't compared it with timers to see whose code produces fewer nugatory interrupt service routines, takes the least time to execute or filters out the highest percentage of contact bounces. Perhaps someone might like to do a benchmark test against the other approaches out there.

2 People Made This Project!

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145 Discussions

0
joengr
joengr

Question 4 weeks ago

Hey Simon, thanks for the instructable. It is helping me develop the code I need for my hobby. I am able to read the values from the encoder but the one I am using increments/decrements the value every 2 detents. I am using the propwash simulation concentric dual encoder. I am only testing one of them to understand how they work and how to write the code for them. I am planning on using 2-4 of these and would connect to an arduino mega.

I was able to use the digital ones and these have no issues but these ones I was pulling my hair when I wasn't able to make them work.

Is there something in the code I need to review to make them ind/dec every detent? I might be missing something obvious but still.

Thanks for any help you can provide

0
SimonM83
SimonM83

Answer 4 weeks ago

I see those encoders claim two pulses per detent or Type 2. I'm not quite sure what the waveform should look like but you might be able to and to confirm that it matches the logic this code expects to see ( 50% duty square waves that are 90 degrees out of phase). The other thing to check is that you definitely have connected ground to the correct pin and the only other pins are A and B on the encoder. If you get encoder common (ground) connected to one of the microcontroller input pins and microcontroller ground connected to the encoder A or B output, you will often see "lopsided" output.

UPDATE: I have just found this guide to encoders for simulators and it looks like your encoder will only make half the logic state transitions per detent that this code is expecting to see. https://simvim.com/tech_encoder.html#:~:text=Type%202%20%2D%201%2F2%20cycle,times%20between%20two%20fixed%20positions. You could adapt the code to handle this. Perhaps start by noting that the interrupts only fire on RISING edges but can be programmed to do so on CHANGE in either logic direction. You may need to change some of the logic in PinA() and PinB() interrupt service routines but the basic PIND port reads should still work. These will also need adapting to the Mega when you get there.

0
giorgpasq1
giorgpasq1

Question 2 months ago

Hi Simon.
Very nice article!
I have used your code with Arduino UNO and developed my application working very smoothly.
Unfortunately when i moved to Arduino Nano Every (MEGA4809) it cannot complete compiling giving the message:
- 'PIND' was not declared in this scope
I'm not an expert in coding and I can assume there is something wrong in the way interrupt works on the 2 different Arduino.
Any help?
Thanks a lot, I'm a bit desperate...
GP

0
SimonM83
SimonM83

Answer 2 months ago

It's not the interrupts so much (but you will hit issues with that too), more that the instruction to read the whole port is different on the 4809. You could start with https://forum.arduino.cc/index.php?topic=630845.0 to see how the port read could work on the 4809 or replace with digitalRead()s. If you find a successful port to the 4809, please post the code here for others to learn from.

0
SimonM83
SimonM83

Reply 4 weeks ago

Brilliant- congratulations on completing your project and thank you for posting a link here so someone else with the Nano Every can benefit.

1
Trackieman
Trackieman

5 months ago on Introduction

// Need it to work on a STM32 STM32F103 aka Blue Pill? Here you go:-
/********Interrupt-based Rotary Encoder Sketch*******
by Simon Merrett, based on insight from Oleg Mazurov, Nick Gammon, rt, Steve Spence*/

static int pinA = PA0;
static int pinB = PA1;
volatile bool aFlag = 0;
volatile bool bFlag = 0;
volatile uint16_t encoderPos = 0;
volatile uint16_t oldEncPos = 0;
volatile uint16_t reading = 0;

void setup() {
pinMode(pinA, INPUT_PULLUP);
pinMode(pinB, INPUT_PULLUP);
attachInterrupt(digitalPinToInterrupt(pinA), PinA, RISING);
attachInterrupt(digitalPinToInterrupt(pinB), PinB, RISING);
Serial.begin(115200);
}

void PinA(){
noInterrupts();
reading = GPIOA->IDR & 0x3;
if(reading == 0b0000000000000011 && aFlag && encoderPos) {
encoderPos --;
bFlag = 0;
aFlag = 0;
}
else if (reading == 0b0000000000000001) bFlag = 1;
interrupts();
}

void PinB(){
noInterrupts();
reading = GPIOA->IDR & 0x3;
if (reading == 0b0000000000000011 && bFlag) {
encoderPos ++;
bFlag = 0;
aFlag = 0;
}
else if (reading == 0b0000000000000010) aFlag = 1;
interrupts();
}

void loop(){
if(oldEncPos != encoderPos) {
Serial.println(encoderPos);
oldEncPos = encoderPos;
}
}

/*
In this example the rotary encoder connects to PA0, PA1 and GND
It also prevents the count going negative by making sure encoderPos is true.
I've included a screenshot to show it working. If you can't get it to work, check your setup and wiring.

Thank you Simon for your article, it inspired me!
*/

encoder+stm32f103+usb_uart.jpg
0
my_self
my_self

Reply 7 weeks ago

Does not compile for BluePill.
reading = GPIOA->IDR & 0x3; error
Error :
'struct gpio_dev' has no member named 'IDR'.
How to fix?

0
SimonM83
SimonM83

Reply 7 weeks ago

Try searching the error you had. The first result Google threw up for me when I did was that someone was using the wrong/different stm32 core in the arduino ide.

0
my_self
my_self

Reply 7 weeks ago

I had seen that too.
But I need to add the encoder to a sketch (STM32_O_Scope) that only compiles with core "Generic STM32F103C series".
Could that GPIOA->IDR & 0x3; be translated to high-level language?
Thank you very much.


0
SimonM83
SimonM83

Reply 7 weeks ago

I'm sure you could translate it to a high level language but I doubt it would be understood any better by your compiler if you are still using the same core. Why don't you go to the core that applies to your sketch and find out how they do port reads in that core? I'd guess (without checking - you could do that) GPIOA->IDR is just a macro/shorthand for reading the registers that contain the status of a bank of pins.

0
my_self
my_self

Reply 7 weeks ago

With the "generic STM32f103" core this line must read as this:
reading = GPIOB->regs->IDR & 0x3;
However, it only counts up for each direction.
Also, one has to rotate rather fast to see a change.
Do you have any comment?

0
Trackieman
Trackieman

Reply 7 weeks ago

I'm sorry you are having problems getting it to work. I've posted a video that might help. It's a link to my YouTube channel. It's currently NOT a monetized channel. I gain nothing with the video.

0
SimonM83
SimonM83

Reply 4 months ago

Thanks @Trackieman, I've not tested but I'm sure it will be helpful for people.

1
berlingozzo
berlingozzo

4 months ago

Thanks a lot, spent so much time trying to make this rotary encoder work, it finally works with your code!
Do you know if it'd work on a Wemos D1 Mini as it is? I don't think it has interrupt pins. thanks!

0
SimonM83
SimonM83

Reply 4 months ago

Hi, glad it helped! It certainly won't work as-is on a Wemos D1 Mini as significant elements of the code are written for the ATMEGA328P chip in the Arduino Nano/Uno/Pro Mini etc. However, the ESP8266 in the D1 Mini does allow interrupts to be set in the Arduino IDE: https://randomnerdtutorials.com/interrupts-timers-esp8266-arduino-ide-nodemcu/
There are some clues about directly reading pin ports on the ESP8266 here: https://forum.arduino.cc/index.php?topic=423340.0 but it sounds like you'd be able to read fast enough using a pair of digitalRead()s in each ISR (in Arduino IDE) because the ESP8266 is much faster clocking and it looks like the driver code for them to make them work in Arduino has less delay (overhead) than for the ATMEGA328. So it could be quite simple to adapt. Good luck!

0
Ralphxyz
Ralphxyz

6 months ago

No output to Monitor!
Still trying to get this to work!!
At least your code compiles with out errors!

0
djw4250
djw4250

Reply 6 months ago

Thanks Simon. I'm afraid I can't tell what the internal wiring of the encoder is. Using my multimeter I established which encoder pin was the common.
I have connected my encoder pins to UNO pins 2 & 3 and the encoder common is connected to GND on the UNO.
I have studied your sketches that limit the menu length. I'm afraid that I wasn't able to fully understand what I was reading. The idea of interrupts appeals to me but the examples seemed more complex that what I was after. I don't need sub-menus, But I couldn't find an instructable for a simple case like that.

Encoder Basic.JPG
0
SimonM83
SimonM83

Reply 6 months ago

Using your multimeter can you confirm that BOTH the encoder pins connect and disconnect at least once with the common pin when you turn one detent click? You'll have to do this one at a time, unless you have two multimeters.
You could try reading each pin in the loop() next and printing out on your serial monitor what the status is, e.g. Serial.print(digitalRead(encoderPinA)); Serial.print("\t"); Serial.println(digitalRead(encoderPinB)); delay(10);
This will print the logic state of the two encoder pins next to each other on a different line each time, separated by a tab ("\t").
If you vary the delay duration you should be able to catch the logic on each pin if you scroll back up through the serial monitor print. Hopefully you'll see a progression like:
11
10
00
01
or the equivalent for the other direction/wiring/print order.