living with the lab Interfacing a Rotary Encoder

living with the lab Interfacing a Rotary Encoder with an Arduino Rotary encoders are used keep track of the rotational position of a knob, like a volume knob on a stereo, or the rotational position of a motor shaft. Panasonic EVE-KC 2 F 2024 B 24 pulses per revolution 6 mm diameter flattened output shaft output type: quadrature (incremental) minimum life: 15, 000 rotations cost: less than $1 (USD) Arduino Uno microcontroller board

living with the lab Encoder Output and Rotational Direction counterclockwise rotation of knob pin A = ON A pin A = OFF pin B = ON B A B COM pin B = OFF increment rotational counter When switch A goes OFF and B is ON, then rotation must be clockwise. When switch A goes OFF and B is OFF, then rotation must be counterclockwise. When switch A goes ON and B is OFF, then rotation must be clockwise. When switch A goes ON and B is ON, then rotation must be counterclockwise. decrement rotational counter 2

living with the lab The Guts of a Mechanical Encoder As the encoder knob is turned, the spring-loaded contacts pass over metal segments that connect to the A, B and COM pins. Electrical continuity occurs when a contact touches metal, but no continuity occurs when a contact touches the black plastic. One of the three contacts is always touching COM. electrical continuity between A and COM no electrical continuity between A and COM spring-loaded electrical contacts A COM B 3

living with the lab Sensor Wiring (need four 10 kΩ resistors and two 0. 01 F capacitors) 10 kΩ this part of the circuit keeps the A, B and COM “switches” from flickering at the beginning or end contact. . . this “debounces” the switches 10 kΩ the encoder is the part in the red box 4

living with the lab A Simple Sketch • • • This sketch increments the variable “encoder. Pos” when the encoder knob is turned clockwise and decrements the variable when the knob is turned counterclockwise. The sketch uses an “interrupt” to avoid missing any changes in the position of the knob. The Arduino Uno has two interrupts attached to digital pins 2 and 3; we only use pin 2 as an interrupt here. volatile int encoder. Pos = 0; void setup() { pin. Mode(2, INPUT); pin. Mode(3, INPUT); attach. Interrupt(0, encoder, CHANGE); Serial. begin (9600); } void loop(){ } void encoder() { if(digital. Read(2) == digital. Read(3)) {encoder. Pos++; } else {encoder. Pos--; } Serial. println (encoder. Pos, DEC); } // the value of a volatile variable can change // in the function called by the interrupt // encoder pin. A is attached to digital pin 2 // encoder pin. B is attached to digital pin 3 // interrupt 0 maps to pin 2 // main body of the sketch employing the interrupt // get state of encoder pins A & B // increment position both are HIGH // decrement position if both are LOW // send encoder. Pos to serial monitor 5

living with the lab Example Application This implementation shows a knob mounted to the rotary encoder. This hardware includes two LEDS that come on and off as the encoder passes over the contacts. The hardware can be used with the sketch on the previous slide to demonstrate how the encoder works. 6