Skip to content
Create a gist now

Instantly share code, notes, and snippets.

Mayhew Labs Encoder ring code
TODO: Isolate the read_encoder() output and make sure that's correct before attempting to anything with it. Then you're working with -1 for one direction, 1 for the other direction, and 0 for sitting still.
Copyright (c) 2011 Mayhew Labs.
Written by Mark Mayhew
This example shows 3 sequences that are possible on the ring of LEDs around the encoder based on rotation of an encoder. The 3 sequences are
selected by entering 1, 2, or 3 in the serial command prompt. The serial window shows the current rotary encoder count. As the encoder is turned,
the serial display shows a raw count of the rotary encoder's value and the LEDs show a scaled version of the value. If the button on the rotary
encoder is pushed, the bottom LED will come on. Each section of code below discusses the process required to do this.
A note on setting the output sequence:
Think of each LED as a single bit in a 16-bit long binary string. If a bit is 1, the LED is on, if a bit is 0, the LED is off.
By making a string of ones and zeros, we choose which LEDs to have on and off, and then send this string to the shift register to display it.
For example 1000000000000001 binary (0x8001 in hex) will have the fist and last LEDs on, the rest off.
Reading the rotary encoder is performed with Oleg's example code:a
//These are the pins that will talk to the shift register through SPI
#define SDI 11 //Data
#define CLK 12 //Clock
#define LE 13 //Latch
//These are the rotary encoder pins A, B, and switch
#define ENC_A 8
#define ENC_B 9
#define ENC_SW 10
#define ENC_PORT PINB //The port that the rotary encoder is on (see
// Global variables
int scaledCounter = 0; //The LED output is based on a scaled veryson of the rotary encoder counter
int sequenceNumber = 1; //The output sequence for the LEDs
int incomingByte = 0; //Serial input to select LED output sequence
/*This is a 2 dimensional array with 3 LED sequences. The outer array is the sequence;
the inner arrays are the values to output at each step of each sequence. The output values
are 16 bit hex values (hex math is actually easier here!). An LED will be on if its
corresponding binary bit is a one, for example: 0x7 = 0000000000000111 and the first 3 LEDs
will be on.
The data type must be 'unsigned int' if the sequence uses the bottom LED since it's value is 0x8000 (out of range for signed int).
unsigned int sequence[3][16] = {{0x0,0x1,0x2,0x4,0x8,0x10,0x20,0x40,0x80,0x100,0x200,0x400,0x800,0x1000,0x2000,0x4000},
void setup()
//Set SPI pins to output
pinMode(SDI, OUTPUT);
pinMode(CLK, OUTPUT);
//Set encoder pins to input, turn internal pull-ups on
pinMode(ENC_A, INPUT);
digitalWrite(ENC_A, HIGH);
pinMode(ENC_B, INPUT);
digitalWrite(ENC_B, HIGH);
pinMode(ENC_SW, INPUT);
digitalWrite(ENC_SW, HIGH);
//Set serial rate, prompt for desired sequence
void loop()
//Local Variables
static uint8_t counter = 0; //this variable will be changed by encoder input
int8_t tmpdata;
//Call read_encoder() function
tmpdata = read_encoder();
//if the encoder has moved
//Print out the counter value
//Serial.print("Counter value: ");
//Serial.println(counter, DEC);
//Set the new counter value of the encoder
counter += tmpdata * 4;
//Scale the counter value for referencing the LED sequence
//***NOTE: Change the map() function to suit the limits of your rotary encoder application.
// The first two numbers are the lower, upper limit of the rotary encoder, the
// second two numbers 0 and 15 are limits of LED sequence arrays. This is done
// so that the LEDs can use a different scaling than the encoder value.
scaledCounter = map(counter,0,255,0,15);
//Send the LED output to the shift register
shiftOut(SDI,CLK,MSBFIRST,(sequence[sequenceNumber][scaledCounter] >> 8)); //High byte first
shiftOut(SDI,CLK,MSBFIRST,sequence[sequenceNumber][scaledCounter]); //Low byte second
//If the encoder switch is pushed, this will turn on the bottom LED. The bottom LED is turned
//on by 'OR-ing' the current display with 0x8000 (1000000000000000 in binary)
if (!digitalRead(ENC_SW))
shiftOut(SDI,CLK,MSBFIRST,((sequence[sequenceNumber][scaledCounter]|0x8000) >> 8));
* read_encoder() function as provided by Oleg: *
* *
* *
* Returns change in encoder state (-1,0,1) *
************************************************************************ */
int8_t read_encoder()
int8_t enc_states[] = {0,-1,1,0,1,0,0,-1,-1,0,0,1,0,1,-1,0};
static uint8_t old_AB = 0;
old_AB <<= 2; //remember previous state
old_AB |= ( ENC_PORT & 0x03 ); //add current state
return ( enc_states[( old_AB & 0x0f )]);
Sign up for free to join this conversation on GitHub. Already have an account? Sign in to comment
Something went wrong with that request. Please try again.