encoder y arduino

Incremental Encoders IHands-On Arduino

Hands On Arduino: Encoders

Overview

• Motion Input!

• Encoder Basics!

• Unidirectional Decoding!

• Bi-Directional Decoding!

• Using Pin Change Interrupts!

• Using Assembly Language


How Can We Input Motion?

• We need something that will change when the thing we want to measure moving moves.!

• Generally, something electrical!• Example: Potentiometers

(Resistance Changes)


Types of Motion Input• Position!

• Encoder!• Potentiometer!

• Velocity!• Tachometer!• Rate Gyro!• Estimator!

• Acceleration!• Accelerometer


What is an Encoder?

• A General concept.!

• Implementation depends on the application!

• Used for!• Data Compression!

• Information Security


What does the Encoder Encode?

• Converts a change in position to digital signals.!

• The resolution depends upon the number of pulses in a specified distance!

• If measuring only in one direction, only one “channel” is required.!

• If measuring in both directions, two “channels” are needed: A & B, or I & Q.


Pulse Technology

• Magnetic!

• Switch Contacts!

• Optical Reflective!

• Optical Transmissive


Encoder & Decoder

DecoderEncoder


Absolute Encoders

• Encoders where each position provides a unique “code.”!

• Often based on a Gray code, where the codes for adjacent positions differ by at most 1 bit.!

• No data compression, thus requires n channels.!

• More complicated to work with!

• Exact position is always known.


Absolute Encoders• 8 bit absolute encoder disc!

• each ring corresponds to a different bit.!

• The number of PPR is 28 = 256!

• Requires 8 channels!

• only get 1x decoding!

• know where you are at startup!

• Gray code decoding


Single Direction: Encode

Number of!Pulses per !Revolution!(PPR): N

1x Resolution: 360°/N!2x Resolution: 180°/N

EmitterDetector

T

T

A


Single Direction: Decode

• Count the pulses (1x)!

• Count the transitions (2x)!

• The counting can be done by either:!• polling the channel!

• using the channel to trigger interrupts

An unsigned long (uint32_t) is recommended for the!counter!


Sample Code: Pollingunsigned long count=0; unsigned long timep, time, etime; byte A,Ap; !void setup() { Serial.begin(9600); //connect Channel A to pin 3 pinMode(3, INPUT); //set the initial time timep = micros(); //set the initial value of A Ap = digitalRead(3); }

void loop() { A = digitalRead(3); if (A^Ap)//is there a difference? { count++;//if so, increment. } Ap = A; time = micros(); etime = time -‐ timep; if (etime > 1000000)//every 1 sec { Serial.println(count); timep = time;//reset timer } }


Sample Code: Using Interrupts

unsigned long count=0; unsigned long timep, time, etime; void setup() { Serial.begin(9600); //connect Channel A to pin 3 pinMode(3, INPUT); attachInterrupt(1,transition, CHANGE); //set the initial time timep = micros(); } !void transition() { count++; } !

void loop() { time = micros(); etime = time -‐ timep; if (etime > 1000000)// 1 second { Serial.println(count); timep = time; //reset timer } }


Sample Code: Velocity Estimation

//This displays the number of transitions // per second. unsigned long count=0; unsigned long timep, time, etime; void setup() { Serial.begin(9600); //connect Channel A to pin 3 pinMode(3, INPUT); attachInterrupt(1,transition, CHANGE); //set the initial time timep = micros(); } !void transition() { count++; } !

void loop() { time = micros(); etime = time -‐ timep; if (etime > 1000000)// 1 second { Serial.println(count); count = 0; //reset the counter timep = time; //reset timer } }


Units, Units, Unite!

• Units are essential information for real systems.!

• The units relate to what the relevant quantity is.!

• The encoders have a fixed construction:!• Linear: pulses per inch, pulses per mm!

• Rotary: pulses per revolution.


Units, Units, Unite!

• Example: a rotary encoder on a motor shaft with 512 pulses per revolution.!

• Since one revolution equals 360°, then !• for 1x decoding, each count means the motor has turned

360/512 = 0.7031°.!

• for 2x decoding, there are 512x2 = 1024 transitions per revolution, and each count corresponds to 360/1024 = 0.3516°


Absolute Encoders

• Encoders where each position provides a unique “code.”!

• Often based on a Gray code, where the codes for adjacent positions differ by at most 1 bit.!

• No data compression, thus requires n channels.


BiDirectional Encoding

Emitters Detectors

T

T

T

A

B

1 1

1 1

0 0 1 1 0 0

0 0 1 1 0 0

In-Phase

Quadrature



T

T

A

B

1 1

1 1

0 0 1 1 0 0

0 0 1 10 0

state: 1 2 3 4 1 2 3 4

State A B

1 1 1

2 1 0

3 0 0

4 0 1



A

B

A

B

t

t

t

t

FORWARD:

Reverse

B switches before A

A switches before B


BiDirectional (1x) Decoding

• When B = 1, use the transitions of A to determine whether to increment or decrement the counter.

T

T

A

B

1 1

1 1

0 0 1 1 0 0

0 0 1 10 0

state: 1 2 3 4 1 2 3 4

Edge counter

A-‐rising increment

A-‐falling decrement



T

T

A

B

1 1

1 1

0 0 1 1 0 0

0 0 1 10 0

state: 1 2 3 4 1 2 3 4

B Edge counter

0 A-‐rising decrement

0 A-‐falling increment

1 A-‐falling decrement

1 A-‐rising increment



T

T

A

B

1 1

1 1

0 0 1 1 0 0

0 0 1 10 0

state: 1 2 3 4 1 2 3 4

prior!state

1 2 3 4

present state AB 11 10 00 01

1 11 X dec X inc

2 10 inc X dec X

3 00 X inc x dec

4 01 dec X inc x

X = do nothing.



• switch…case !

• if…else…else!

• Array!

• Pin Position


BD4x: Switch…Caselong count=0; unsigned long timep, time, etime; boolean A,B; byte state, statep; void setup() { Serial.begin(9600); pinMode(2, INPUT);//Channel A pinMode(3, INPUT);//Channel B attachInterrupt(0,Achange,CHANGE); attachInterrupt(1,Bchange,CHANGE); timep = micros(); //set the initial time //read the initial value of A & B A = digitalRead(2); B = digitalRead(3); //set initial state value if ((A==HIGH)&&(B==HIGH)) statep = 1; if ((A==HIGH)&&(B==LOW)) statep = 2; if ((A==LOW)&&(B==LOW)) statep = 3; if ((A==LOW)&&(B==HIGH)) statep = 4; }

void loop() { time = micros(); etime = time -‐ timep; if (etime > 1000000) { Serial.println(count); timep = time; } }


BD4x: Switch…Casevoid Achange() { A = digitalRead(2); B = digitalRead(3); //determine state value if ((A==HIGH)&&(B==HIGH)) state = 1; if ((A==HIGH)&&(B==LOW)) state = 2; if ((A==LOW)&&(B==LOW)) state = 3; if ((A==LOW)&&(B==HIGH)) state = 4; switch (state) { case 1: { if (statep == 2) count-‐-‐; if (statep == 4) count++; break; }

case 2: { if (statep == 1) count++; if (statep == 3) count-‐-‐; break; } case 3: { if (statep == 2) count++; if (statep == 4) count-‐-‐; break; } default: { if (statep == 1) count-‐-‐; if (statep == 3) count++; } } statep = state; }


BD4x: Array

State prior 0 1 2 3

present AB 11 10 00 010 11 X dec X inc1 10 inc X dec X2 00 X inc x dec3 01 dec X inc x

Quadrature Encoder Matrix (Array):

QEM[16] = {0,-‐1,0,1,1,0,-‐1,0,0,1,0,-‐1,-‐1,0,1,0}

Index = 4*state + statep;count = count + QEM[Index];


BD4x: Arrayvoid Achange() { A = digitalRead(2); B = digitalRead(3); //determine state value if ((A==HIGH)&&(B==HIGH)) state = 0; if ((A==HIGH)&&(B==LOW)) state = 1; if ((A==LOW)&&(B==LOW)) state = 2; if ((A==LOW)&&(B==HIGH)) state = 3; index = 4*state + statep; count = count + QEM[index]; statep = state; }

void Bchange() { A = digitalRead(2); B = digitalRead(3); //determine state value if ((A==HIGH)&&(B==HIGH)) state = 0; if ((A==HIGH)&&(B==LOW)) state = 1; if ((A==LOW)&&(B==LOW)) state = 2; if ((A==LOW)&&(B==HIGH)) state = 3; index = 4*state + statep; count = count + QEM[index]; statep = state; }

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