Category Archives: Electronics

Rotary Encoders in Colour on the i2c Bus

24th January 2015 Karl 9 Comments

This is a follow-up to my previous writings on the subject of rotary encoders: Rotary Encoders on the i²c Bus. This time I am using the Sparkfun Rotary Encoder – Illuminated (RGB) (Part: COM-10982), this has the same rotary goodness as the SparkFun 12-step rotary encoder but with the addition of three LED’s to provide a whole host of colours on the rotating shaft.

Test Setup

Again I will be using the MCP23017 port expander to add 16 digital I/O ports to the Arduino via the i²c bus, the rotary encoder part operates in the same manner as before and we can use the internal pull-up resistors to reduce the number of components. The LED’s operate with a common anode and the push button also operates on 5v rather than the usual switching to ground.

For my test setup I have connected the rotary encoder to GPA0 and GPA1, the push button to GPA2 and the Red, Green and Blue LED’s to GPA5, GPA4 and GPA3. Note the 10K pull-down resistor on the push button.

My program on the Arduino changes the colours as you rotate the shaft, you will see seven colours, to see more you would need to use PWM to control the LED’s brightness. With the common anode on the LED’s the logic for switching them is inverted, so HIGH = off, LOW = on. You will need the Adafruit MCP23017 Arduino Library.

#include <Wire.h>
#include "Adafruit_MCP23017.h"  // https://github.com/adafruit/Adafruit-MCP23017-Arduino-Library

// setup the port expander
Adafruit_MCP23017 mcp0;

#define ROT_A 0
#define ROT_B 1
#define ROT_BTN 2
#define ROT_RED 3
#define ROT_GRN 4
#define ROT_BLU 5

// some colours to display
// because of the common anode on the LED's, logic is inverted: 0 = on, 1 = off
//                         R  G  B         
boolean colours[8][3] = { {1, 1, 1},  // off (black)
                          {1, 1, 0},  // blue
                          {1, 0, 1},  // green
                          {1, 0, 0},  
                          {0, 1, 1},  // red
                          {0, 1, 0},  
                          {0, 0, 1},  
                          {0, 0, 0}}; // white                         

int colPointer = 0;
unsigned long currentTime;
unsigned long loopTime;
int rotAprev=0;
const int leds[3] = { ROT_RED, ROT_GRN, ROT_BLU }; 

void setColours(boolean colour[]) {           
    for (int i=0; i<3; i++) {  
       mcp0.digitalWrite(leds[i], colour[i]);    
    }  
    return;
}

void setup() {  

  Serial.begin(9600);
  mcp0.begin(0);                // 0 = i2c address 0x20
   
  mcp0.pinMode(ROT_A, INPUT);     // Rotary switch A
  mcp0.pullUp(ROT_A, HIGH);       // turn on a 100K pullup internally
  
  mcp0.pinMode(ROT_B, INPUT);     // Rotary switch B
  mcp0.pullUp(ROT_B, HIGH);       // turn on a 100K pullup internally
  
  mcp0.pinMode(ROT_BTN, INPUT);   // Push Button
  
  mcp0.pinMode(ROT_RED, OUTPUT);  // Red
  mcp0.pinMode(ROT_GRN, OUTPUT);  // Green
  mcp0.pinMode(ROT_BLU, OUTPUT);  // Blue
  
  mcp0.digitalWrite(ROT_RED, HIGH);  // all colours off
  mcp0.digitalWrite(ROT_GRN, HIGH);  // HIGH = off, LOW = on
  mcp0.digitalWrite(ROT_BLU, HIGH);
  
  currentTime = millis();
  loopTime = currentTime;
  Serial.println("ready");
  setColours(colours[0]);
}


void loop() {
  
  currentTime = millis();
    
  // check every 5 millisecs  
  if(currentTime >= (loopTime + 5)) {
    int rotA = mcp0.digitalRead(ROT_A);
    int rotB = mcp0.digitalRead(ROT_B);  
    
    // turn white if the button is pressed
    if (mcp0.digitalRead(ROT_BTN) == true) {
      setColours(colours[7]);  
    }
    
    // see if there has been any rotation
    if((!rotA) && (rotAprev)) {
      if (rotB) {
        Serial.println("clockwise");
        colPointer++;
      }    
      else {
        Serial.println("counter-clockwise");  
        colPointer--;
      }
      
      // make sure the pointer stays within range
      if (colPointer > 7) {
        colPointer = 0;
      }
      if (colPointer < 0) {
        colPointer = 7;
      }
      
      Serial.print("pointer: ");
      Serial.println(colPointer);
      // set the shaft colour to that in pointer
      setColours(colours[colPointer]);
    }    
    rotAprev = rotA;
    loopTime = currentTime;  // Updates loopTime
   }
}

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#include <Wire.h>

#include "Adafruit_MCP23017.h" // https://github.com/adafruit/Adafruit-MCP23017-Arduino-Library

// setup the port expander

Adafruit_MCP23017 mcp0;

#define ROT_A 0

#define ROT_B 1

#define ROT_BTN 2

#define ROT_RED 3

#define ROT_GRN 4

#define ROT_BLU 5

// some colours to display

// because of the common anode on the LED's, logic is inverted: 0 = on, 1 = off

// R G B

boolean colours[8][3] = { {1, 1, 1}, // off (black)

{1, 1, 0}, // blue

{1, 0, 1}, // green

{1, 0, 0},

{0, 1, 1}, // red

{0, 1, 0},

{0, 0, 1},

{0, 0, 0}}; // white

int colPointer = 0;

unsigned long currentTime;

unsigned long loopTime;

int rotAprev=0;

const int leds[3] = { ROT_RED, ROT_GRN, ROT_BLU };

void setColours(boolean colour[]) {

for (int i=0; i<3; i++) {

mcp0.digitalWrite(leds[i], colour[i]);

}

return;

}

void setup() {

Serial.begin(9600);

mcp0.begin(0); // 0 = i2c address 0x20

mcp0.pinMode(ROT_A, INPUT); // Rotary switch A

mcp0.pullUp(ROT_A, HIGH); // turn on a 100K pullup internally

mcp0.pinMode(ROT_B, INPUT); // Rotary switch B

mcp0.pullUp(ROT_B, HIGH); // turn on a 100K pullup internally

mcp0.pinMode(ROT_BTN, INPUT); // Push Button

mcp0.pinMode(ROT_RED, OUTPUT); // Red

mcp0.pinMode(ROT_GRN, OUTPUT); // Green

mcp0.pinMode(ROT_BLU, OUTPUT); // Blue

mcp0.digitalWrite(ROT_RED, HIGH); // all colours off

mcp0.digitalWrite(ROT_GRN, HIGH); // HIGH = off, LOW = on

mcp0.digitalWrite(ROT_BLU, HIGH);

currentTime = millis();

loopTime = currentTime;

Serial.println("ready");

setColours(colours[0]);

}

void loop() {

currentTime = millis();

// check every 5 millisecs

if(currentTime >= (loopTime + 5)) {

int rotA = mcp0.digitalRead(ROT_A);

int rotB = mcp0.digitalRead(ROT_B);

// turn white if the button is pressed

if (mcp0.digitalRead(ROT_BTN) == true) {

setColours(colours[7]);

}

// see if there has been any rotation

if((!rotA) && (rotAprev)) {

if (rotB) {

Serial.println("clockwise");

colPointer++;

}

else {

Serial.println("counter-clockwise");

colPointer--;

}

// make sure the pointer stays within range

if (colPointer > 7) {

colPointer = 0;

}

if (colPointer < 0) {

colPointer = 7;

}

Serial.print("pointer: ");

Serial.println(colPointer);

// set the shaft colour to that in pointer

setColours(colours[colPointer]);

}

rotAprev = rotA;

loopTime = currentTime; // Updates loopTime

}

Rotary Encoders on the i2c bus

2nd August 2014 Karl 18 Comments

I have been getting to grips with rotary encoders on the Arduino, and to add a little drama I have gotten this working on the i²c bus. Here I will be showing how to set up the necessary hardware and demonstrate a program for the Arduino. I have used a similar setup to control an LED RGB light strip, with three rotary encoders to control the Red, Green and Blue and a fourth for special effects.

The i²c bus

The i²c bus allows connection of multiple devices to the Arduino on just two wires, these can be just about anything from temperature sensors to motor controllers with each device having its own address, up to eight of these can be used using just two wires from the Arduino.

For this project I’ll be using a single MCP23017 port expander, with which I can add sixteen digital I/O pins to the Arduino

The address for the expander is set on pins 15, 16 and 17 (A0, A1 and A2), for a single encoder set all of these to ground. Should you require more expanders the addresses can be set as in the table below, the MCP address is for the Arduino program.

chip address	hardwired address			i²c address	MCP address
chip address	A2	A1	A0	i²c address	MCP address
000	GND	GND	GND	0x20	0
001	GND	GND	3v3	0x21	1
010	GND	3v3	GND	0x22	2
011	GND	3v3	3v3	0x23	3
100	3v3	GND	GND	0x24	4
101	3v3	GND	3v3	0x25	5
110	3v3	3v3	GND	0x26	6
111	3v3	3v3	3v3	0x27	7

Rotary Encoders

The encoders I’m using are the SparkFun 12-step rotary encoder with integrated push-button

Inside they have mechanical contacts that output two square waves when rotated, A and B these are 90^o out of phase with each other so when rotated clockwise output A is ahead of B, and counter-clockwise output B takes the lead, this is a two bit Grey code.

rotary encoder square wave — *rotary switch outputs (source: datasheet)*

So by comparing the two outputs we can determine the direction of rotation.

A Test Circuit

My test setup comprises of two rotary encoders, one Arduino Uno, one MCP23017 port expander, and a couple of resistors. External pull-up resistors are not required on the GPx input ports as the MCP23017 has these internally. Encoder A uses GPA0, GPA1 and GPA2 for the push button. Encoder B is on GPA4, GPA5, and GPA6.

Programming

My program uses the Adafruit MCP23017 and standard wire libraries. The Adafriut library addresses the GPx ports from 0-15, so GPA2 is 2, and GPB2 is 9. I have written this to output the state of rotation to the serial port at 9600 baud.

#include <Wire.h>
#include "Adafruit_MCP23017.h"  // https://github.com/adafruit/Adafruit-MCP23017-Arduino-Library

// setup the port expander
Adafruit_MCP23017 mcp0;

boolean change=false;        // goes true when a change in the encoder state is detected
int butPress = 101;          // stores which button has been pressed
int encSelect[2] = {101, 0}; // stores the last encoder used and direction {encNo, 1=CW or 2=CCW}
unsigned long currentTime;
unsigned long loopTime;

const int encCount0 = 2;  // number of rotary encoders
// encoder pin connections to MCP23017
//    EncNo { Encoder pinA  GPAx, Encoder pinB  GPAy },
const int encPins0[encCount0][2] = {
  {0,1},   // enc:0 AA GPA0,GPA1 - pins 21/22 on MCP23017
  {3,4}    // enc:1 BB GPA3,GPA4 - pins 24/25 on MCP23017
};  

const int butCount0 = 2;  // number of buttons
//             button on encoder: A  B
const int butPins0[butCount0] = { 2, 5 };
// arrays to store the previous value of the encoders and buttons
unsigned char encoders0[encCount0];
unsigned char buttons0[butCount0];

// read the rotary encoder on pins X and Y, output saved in encSelect[encNo, direct]
unsigned char readEnc(Adafruit_MCP23017 mcpX, const int *pin, unsigned char prev, int encNo) {

  unsigned char encA = mcpX.digitalRead(pin[0]);    // Read encoder pins
  unsigned char encB = mcpX.digitalRead(pin[1]);

  if((!encA) && (prev)) { 
    encSelect[0] = encNo;
    if(encB) {
      encSelect[1] = 1;  // clockwise
    }
    else {
      encSelect[1] = 2;  // counter-clockwise
    }
    change=true;
  }
  return encA;
}

// read the button on pin N. Change saved in butPress
unsigned char readBut(Adafruit_MCP23017 mcpX, const int pin, unsigned char prev, int encNo) {

  unsigned char butA = mcpX.digitalRead(pin);    // Read encoder pins
  if (butA != prev) {
    if (butA == HIGH) {
      butPress = encNo;
    }
  }
  return butA;  
}

// setup the encoders as inputs. 
unsigned char encPinsSetup(Adafruit_MCP23017 mcpX, const int *pin) {

  mcpX.pinMode(pin[0], INPUT);  // A
  mcpX.pullUp(pin[0], HIGH);    // turn on a 100K pullup internally
  mcpX.pinMode(pin[1], INPUT);  // B
  mcpX.pullUp(pin[1], HIGH); 
}

// setup the push buttons
void butPinsSetup(Adafruit_MCP23017 mcpX, const int pin) {
  mcpX.pinMode(pin, INPUT);
  mcpX.pullUp(pin, HIGH); 
}

void setup() {  

  mcp0.begin(0);    // 0 = i2c address 0x20

  // setup the pins using loops, saves coding when you have a lot of encoders and buttons
  for (int n = 0; n < encCount0; n++) {
    encPinsSetup(mcp0, encPins0[n]);
    encoders0[n] = 1;  // default state
  }

  // buttons and encoders are in separate arrays to allow for additional buttons
  for (int n = 0; n < butCount0; n++) {
    butPinsSetup(mcp0, butPins0[n]);
    buttons0[n]  = 0;
  }

  Serial.begin(9600); 
  Serial.println("---------------------------------------");  

  currentTime = millis();
  loopTime = currentTime;
}

void loop() {

  // check the encoders and buttons every 5 millis
  currentTime = millis();
  if(currentTime >= (loopTime + 5)){

    for (int n = 0; n < encCount0; n++) {
      encoders0[n] = readEnc(mcp0, encPins0[n], encoders0[n],n);
    }

    for (int n = 0; n < butCount0 ; n++) {
      buttons0[n] = readBut(mcp0, butPins0[n], buttons0[n], n);
    }

    loopTime = currentTime;  // Updates loopTime
  } 
  
  // when an encoder has been rotated
  if (change == true) {

    if (encSelect[0] < 100) {
      Serial.print("Enc: ");
      Serial.print(encSelect[0]);  
      Serial.print(" " );  

      switch (encSelect[1]) {
        case (1): // clockwise
          Serial.println("CW  ");
          break;
        case (2): // counter-clockwise
          Serial.println("CCW  ");
          break;
      }

      // do something when a particular encoder has been rotated.
      if (encSelect[0] == 1) {
         Serial.println("Encoder One has been used");
      }

      // set the selection to 101 now we have finished doing things. Not 0 as there is an encoder 0.
      encSelect[0] = 101;
    }
    // ready for the next change
    change = false; 
  }

  // do things when a when a button has been pressed
  if (butPress < 100) {
    Serial.print("But: ");
    Serial.println(butPress); 

    butPress = 101; 
  }
}

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#include <Wire.h>

#include "Adafruit_MCP23017.h" // https://github.com/adafruit/Adafruit-MCP23017-Arduino-Library

// setup the port expander

Adafruit_MCP23017 mcp0;

boolean change=false; // goes true when a change in the encoder state is detected

int butPress = 101; // stores which button has been pressed

int encSelect[2] = {101, 0}; // stores the last encoder used and direction {encNo, 1=CW or 2=CCW}

unsigned long currentTime;

unsigned long loopTime;

const int encCount0 = 2; // number of rotary encoders

// encoder pin connections to MCP23017

// EncNo { Encoder pinA GPAx, Encoder pinB GPAy },

const int encPins0[encCount0][2] = {

{0,1}, // enc:0 AA GPA0,GPA1 - pins 21/22 on MCP23017

{3,4} // enc:1 BB GPA3,GPA4 - pins 24/25 on MCP23017

};

const int butCount0 = 2; // number of buttons

// button on encoder: A B

const int butPins0[butCount0] = { 2, 5 };

// arrays to store the previous value of the encoders and buttons

unsigned char encoders0[encCount0];

unsigned char buttons0[butCount0];

// read the rotary encoder on pins X and Y, output saved in encSelect[encNo, direct]

unsigned char readEnc(Adafruit_MCP23017 mcpX, const int *pin, unsigned char prev, int encNo) {

unsigned char encA = mcpX.digitalRead(pin[0]); // Read encoder pins

unsigned char encB = mcpX.digitalRead(pin[1]);

if((!encA) && (prev)) {

encSelect[0] = encNo;

if(encB) {

encSelect[1] = 1; // clockwise

}

else {

encSelect[1] = 2; // counter-clockwise

}

change=true;

}

return encA;

}

// read the button on pin N. Change saved in butPress

unsigned char readBut(Adafruit_MCP23017 mcpX, const int pin, unsigned char prev, int encNo) {

unsigned char butA = mcpX.digitalRead(pin); // Read encoder pins

if (butA != prev) {

if (butA == HIGH) {

butPress = encNo;

}

return butA;

}

// setup the encoders as inputs.

unsigned char encPinsSetup(Adafruit_MCP23017 mcpX, const int *pin) {

mcpX.pinMode(pin[0], INPUT); // A

mcpX.pullUp(pin[0], HIGH); // turn on a 100K pullup internally

mcpX.pinMode(pin[1], INPUT); // B

mcpX.pullUp(pin[1], HIGH);

}

// setup the push buttons

void butPinsSetup(Adafruit_MCP23017 mcpX, const int pin) {

mcpX.pinMode(pin, INPUT);

mcpX.pullUp(pin, HIGH);

}

void setup() {

mcp0.begin(0); // 0 = i2c address 0x20

// setup the pins using loops, saves coding when you have a lot of encoders and buttons

for (int n = 0; n < encCount0; n++) {

encPinsSetup(mcp0, encPins0[n]);

encoders0[n] = 1; // default state

}

// buttons and encoders are in separate arrays to allow for additional buttons

for (int n = 0; n < butCount0; n++) {

butPinsSetup(mcp0, butPins0[n]);

buttons0[n] = 0;

}

Serial.begin(9600);

Serial.println("---------------------------------------");

currentTime = millis();

loopTime = currentTime;

}

void loop() {

// check the encoders and buttons every 5 millis

currentTime = millis();

if(currentTime >= (loopTime + 5)){

for (int n = 0; n < encCount0; n++) {

encoders0[n] = readEnc(mcp0, encPins0[n], encoders0[n],n);

}

for (int n = 0; n < butCount0 ; n++) {

buttons0[n] = readBut(mcp0, butPins0[n], buttons0[n], n);

}

loopTime = currentTime; // Updates loopTime

}

// when an encoder has been rotated

if (change == true) {

if (encSelect[0] < 100) {

Serial.print("Enc: ");

Serial.print(encSelect[0]);

Serial.print(" " );

switch (encSelect[1]) {

case (1): // clockwise

Serial.println("CW ");

break;

case (2): // counter-clockwise

Serial.println("CCW ");

break;

}

// do something when a particular encoder has been rotated.

if (encSelect[0] == 1) {

Serial.println("Encoder One has been used");

}

// set the selection to 101 now we have finished doing things. Not 0 as there is an encoder 0.

encSelect[0] = 101;

}

// ready for the next change

change = false;

}

// do things when a when a button has been pressed

if (butPress < 100) {

Serial.print("But: ");

Serial.println(butPress);

butPress = 101;

}

Infra-Red Coin Detector for Arduino

10th October 2013 Karl 2 Comments

For something I’m building I need have the Arduino detect a coin being dropped trough a slot, for this I have built an IR detector, it comprises of an IR LED, IR Photo-Diode, Op-amp and ATtiny85 micro-controller.

The circuit works by having the IR LED flood the Photo-diode so that when an object passes between them the Photo-diode stops letting current through, this is fed into the op-amp to provide a consistent output for the ATtiny85 micro-controller to detect the change in signal to then flash a couple of LED’s and provide a signal to an Arduino.

Here is a program that flashes a couple of LED’s and makes output pin 4 high:

/*
 * coin detector for attiny85 micro-controller
 * detects a change pulse on pin0, makes a couple of LED's on pins 1 and 2 
 * flash and makes pin3 go high for 120ms.
 *
 *  v1.0, October 2013
 *
 * pin change interrupt code taken from; http://www.insidegadgets.com/
 */

#include 

const int ledA = 1;
const int ledB = 2;
const int pinIn = 0;
const int pinOut = 4;
volatile int state = HIGH;
volatile int lastState = state;

#ifndef cbi
#define cbi(sfr, bit) (_SFR_BYTE(sfr) &= ~_BV(bit))
#endif
#ifndef sbi
#define sbi(sfr, bit) (_SFR_BYTE(sfr) |= _BV(bit))
#endif

#define PTIME 30
void pulse(int times) {

  int k = times - 2; 
  // increase x (times - x) for a longer pulse:  p = (PTIME * 2) * x 
  // (30*2)*2 = 120ms
  // (30*2)*3 = 180ms
  digitalWrite(pinOut, HIGH); 
  do {
    digitalWrite(ledA, HIGH);
    digitalWrite(ledB, HIGH);

    delay(PTIME);
    digitalWrite(ledA, LOW);
    digitalWrite(ledB, LOW);
    delay(PTIME);

    if (times < k) {
      digitalWrite(pinOut, LOW);   
    }

  } 
  while (times--);
}

void setup(){
  pinMode(ledA, OUTPUT);
  pinMode(ledB, OUTPUT);
  pinMode(pinOut, OUTPUT);
  pinMode(pinIn,INPUT);

  sbi(GIMSK,PCIE);    // Turn on Pin Change interrupt
  sbi(PCMSK,PCINT0);  // Which pins are affected by the interrupt

  digitalWrite(pinOut, LOW);
  delay(1000);
}

void loop() {

  if (state != lastState) {
    pulse(20); 
    lastState = state;
  }   
  digitalWrite(ledA, HIGH); 
  digitalWrite(ledB, HIGH);     

  system_sleep();
  //delay(5);
}

// From http://interface.khm.de/index.php/lab/experiments/sleep_watchdog_battery/
void system_sleep() {
  cbi(ADCSRA,ADEN); // Switch Analog to Digital converter OFF
  set_sleep_mode(SLEEP_MODE_PWR_DOWN); // Set sleep mode
  sleep_mode(); // System sleeps here
  sbi(ADCSRA,ADEN);  // Switch Analog to Digital converter ON
  state = !state;
}

ISR(PCINT0_vect) {
}

* coin detector for attiny85 micro-controller

* detects a change pulse on pin0, makes a couple of LED's on pins 1 and 2

* flash and makes pin3 go high for 120ms.

* v1.0, October 2013

* pin change interrupt code taken from; http://www.insidegadgets.com/

#include

const int ledA = 1;

const int ledB = 2;

const int pinIn = 0;

const int pinOut = 4;

volatile int state = HIGH;

volatile int lastState = state;

#ifndef cbi

#define cbi(sfr, bit) (_SFR_BYTE(sfr) &= ~_BV(bit))

#endif

#ifndef sbi

#define sbi(sfr, bit) (_SFR_BYTE(sfr) |= _BV(bit))

#endif

#define PTIME 30

void pulse(int times) {

int k = times - 2;

// increase x (times - x) for a longer pulse: p = (PTIME * 2) * x

// (30*2)*2 = 120ms

// (30*2)*3 = 180ms

digitalWrite(pinOut, HIGH);

do {

digitalWrite(ledA, HIGH);

digitalWrite(ledB, HIGH);

delay(PTIME);

digitalWrite(ledA, LOW);

digitalWrite(ledB, LOW);

delay(PTIME);

if (times < k) {

digitalWrite(pinOut, LOW);

}

while (times--);

}

void setup(){

pinMode(ledA, OUTPUT);

pinMode(ledB, OUTPUT);

pinMode(pinOut, OUTPUT);

pinMode(pinIn,INPUT);

sbi(GIMSK,PCIE); // Turn on Pin Change interrupt

sbi(PCMSK,PCINT0); // Which pins are affected by the interrupt

digitalWrite(pinOut, LOW);

delay(1000);

}

void loop() {

if (state != lastState) {

pulse(20);

lastState = state;

}

digitalWrite(ledA, HIGH);

digitalWrite(ledB, HIGH);

system_sleep();

//delay(5);

}

// From http://interface.khm.de/index.php/lab/experiments/sleep_watchdog_battery/

void system_sleep() {

cbi(ADCSRA,ADEN); // Switch Analog to Digital converter OFF

set_sleep_mode(SLEEP_MODE_PWR_DOWN); // Set sleep mode

sleep_mode(); // System sleeps here

sbi(ADCSRA,ADEN); // Switch Analog to Digital converter ON

state = !state;

}

ISR(PCINT0_vect) {

}

Sources:

g7smy.co.uk

Category Archives: Electronics

Rotary Encoders in Colour on the i2c Bus

Test Setup

Links

Rotary Encoders on the i2c bus

The i²c bus

Rotary Encoders

A Test Circuit

Programming

links:

Infra-Red Coin Detector for Arduino

COMPUTERS, ROBOTS AND PHOTOGRAPHY

Test Setup

Links

The i2c bus

Rotary Encoders

A Test Circuit

Programming

links:

COMPUTERS, ROBOTS AND PHOTOGRAPHY

The i²c bus