Interfacing a Rotary Encoder with an Arduino
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Transcript of Interfacing a Rotary Encoder with an Arduino
Panasonic EVE-KC2F2024B24 pulses per revolution
6mm diameter flattened output shaftoutput type: quadrature (incremental)
minimum life: 15,000 rotationscost: less than $1 (USD)
Arduino Unomicrocontroller board
Interfacing a Rotary Encoder with an Arduino
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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.
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AB
COM
clockwise rotation of knobcounterclockwise rotation of knob
Bpin B = ON
pin B = OFF
Apin A = ON
pin A = OFF
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.
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.
increment rotational counter
decrement rotational counter
Encoder Output and Rotational Direction
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The Guts of a Mechanical Encoder
spring-loaded electrical contacts
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.
A COM B
electrical continuitybetween A and COM
no electrical continuitybetween A and COM
Sensor Wiring (need four 10kΩ resistors and two 0.01F capacitors)
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10kΩ10kΩ10kΩ
10kΩ
the encoder is the part in the red box
this part of the circuit keeps the A, B and COM “switches” from flickering at the beginning or end contact . . . this “debounces” the switches
A Simple Sketch
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volatile int encoderPos = 0; // the value of a volatile variable can change // in the function called by the interruptvoid setup() pinMode(2, INPUT); // encoder pinA is attached to digital pin2 pinMode(3, INPUT); // encoder pinB is attached to digital pin3 attachInterrupt(0, encoder, CHANGE); // interrupt0 maps to pin2 Serial.begin (9600);
void loop() // main body of the sketch employing the interrupt
void encoder() if(digitalRead(2) == digitalRead(3)) // get state of encoder pins A & B encoderPos++; // increment position both are HIGH else encoderPos--; // decrement position if both are LOW Serial.println (encoderPos, DEC); // send encoderPos to serial monitor
• This sketch increments the variable “encoderPos” 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.
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Example ApplicationThis 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.