The document describes designing a circuit to control the brightness of LEDs using a rotary encoder and Arduino. It involves connecting a rotary encoder and 4 LEDs to an Arduino board. An Arduino program is written to read the rotary encoder position and adjust the PWM output to the LEDs, varying their brightness as the encoder is turned. The circuit allows increasing or decreasing the brightness of multiple LEDs simultaneously using a single rotary encoder.

1. Embedded Systems and Applications Laboratory Manual 2019
Koneru Lakshmaiah Education Foundation (Deemed to be University), NAAC - “A++”, Guntur, AP | ECE 1
Exp. No.: 2 Date:
Aim:
Design a series of 4 LED brightness controllers using Rotary Encoder.
Objective:
Designing a circuit for controlling the brightness of LED’s by using Rotary encoder.
Hardware Requirements:
S.No. Title of Component Component Image Quantity
1. Arduino Uno 01
2. Rotary encoder KY-040 01
3. 10KΩ resistor/ POT 02
4. 220Ω Resistor 04
5.
Connecting Wires & USB
Cable
As per
Requirement

2. Embedded Systems and Applications Laboratory Manual 2019
Koneru Lakshmaiah Education Foundation (Deemed to be University), NAAC - “A++”, Guntur, AP | ECE 2
Pre Lab Session:
1. Study of Rotary encoder module and Its Description.
2. Study of various Rotary encoder modules.
3. Perform the experiment to light the LED.
4. Study how to vary the brightness of LED

3. Embedded Systems and Applications Laboratory Manual 2019
Koneru Lakshmaiah Education Foundation (Deemed to be University), NAAC - “A++”, Guntur, AP | ECE 3
Description:
The objective of this experiment is to construct a module that varies the brightness of
LED by using Rotary encoder and an Arduino.
Rotary encoder:
With a rotary encoder we have two square wave outputs (A and B) which are 90 degrees
out of phase with each other. The number of pulses or steps generated per complete turn varies.
The Sparkfun Rotary Encoder has 12 steps but others may have more or less. The diagram below
shows how the phases A and B relate to each other when the encoder is turned clockwise or
counter clockwise.
Every time the A signal pulse goes from positive to zero, we read the value of the B pulse. We
see that when the encoder is turned clockwise the B pulse is always positive. When the encoder
is turned counter-clockwise the B pulse is negative. By testing both outputs with a
microcontroller we can determine the direction of turn and by counting the number of A pulses
how far it has turned. Indeed, we could go one stage further and count the frequency of the
pulses to determine how fast it is being turned. We can see that the rotary encoder has a lot of
advantages over a potentiometer.
We will now use the rotary encoder in the simplest of applications, we will use it to control the
brightness of an led by altering a pwm signal. We will use the easiest method to read the
encoder, that is the use of a timer interrupt to check on the values.
We will use the sparkfun encoder as discussed above. The first thing is to determine how fast we
need our timer to operate. If you imagine that at best we could turn the encoder through 180
degrees in 1/10th of a second, that would give us 6 pulses in 1/10th second or 60 pulse per
second. In reality its never likely to be this fast. As we need to detect both high and low values
this gives us a minimum frequency of 120Hz. Lets go for 200Hz just to be sure. (Note: as these
units are mechanical switches, there is the possibility of switch bounce. Using a fairly low
frequency allows us to effectively filter out any switch bounce)
Each time our timer code triggers, we compare the value of our A pulse with its previous value.
If it has gone from positive to zero, we then check the value of the B pulse to see if it is positive

4. Embedded Systems and Applications Laboratory Manual 2019
Koneru Lakshmaiah Education Foundation (Deemed to be University), NAAC - “A++”, Guntur, AP | ECE 4
or zero. Depending on the outcome we can increment of decrement a counter. We then use this
to control the PWM value to increase or decrease the brightness of the LED
Fig:1.1 Rotary encoder
Circuit
 Pin SW on the Rotary Encoder to pin 0 of Arduino.
 Pin clk on the Rotary Encoder to pin 12 of Arduino.
 Pin DT on the Rotary Encoder to pin 11 of Arduino.
 Pin GND on the Rotary Encoder to pin GND of Arduino.
 Connect pin 12 of Rotary encoder to pin GND of Arduino via 10kΩ resistor/pot.
 Connect pin 11 of Rotary encoder to pin GND of Arduino via 10kΩ resistor/pot Connect.
 Connect Pin 3 of Arduino to positive terminal of LED & connect negative terminal of
LED to ground pin of Arduino through 220Ω resistor .
 Connect Pin 5 of Arduino to positive terminal of LED & connect negative terminal of
LED to ground pin of Arduino through 220Ω resistor .
 Connect Pin 6 of Arduino to positive terminal of LED & connect negative terminal of
LED to ground pin of Arduino through 220Ω resistor
 Connect Pin 9 of Arduino to positive terminal of LED & connect negative terminal of
LED to ground pin of Arduino through 220Ω resistor

5. Embedded Systems and Applications Laboratory Manual 2019
Koneru Lakshmaiah Education Foundation (Deemed to be University), NAAC - “A++”, Guntur, AP | ECE 5
Fig 1.2 Circuit setup for interfacing single LED with Arduino UNO and rotary encoder
Procedure:
Step 1: Connect the circuit as shown in Fig 1.4.
Step 2: Complete the programme verification in Arduino Sketch and save the sketch.
Step 3: Connect the Arduino board to PC and upload the verified sketch.
Step 4: Check whether the connected LED’s are glowing or not.
Step 5: If glowing vary the brightness of the LED by rotating the knob of rotary encoder.
Programming Code:
int brightness = 120; // how bright the LED is, start at half brightness
int fadeAmount = 10; // how many points to fade the LED by
unsigned long currentTime;
unsigned long loopTime;
const int pin_A = 12; // pin 12
const int pin_B = 11; // pin 11
unsigned char encoder_A;
unsigned char encoder_B;
unsigned char encoder_A_prev=0 ;
void setup() {
// declare pin 3 to be an output:
// declare pin 5 to be an output:
// declare pin 6 to be an output:
// declare pin 9 to be an output:
pinMode(9, OUTPUT);

6. Embedded Systems and Applications Laboratory Manual 2019
Koneru Lakshmaiah Education Foundation (Deemed to be University), NAAC - “A++”, Guntur, AP | ECE 6
pinMode(3, OUTPUT);
pinMode(5, OUTPUT);
pinMode(6, OUTPUT);
pinMode(pin_A, INPUT);
pinMode(pin_B, INPUT);
currentTime = millis();
loopTime = currentTime;
}
void loop() {
// get the current elapsed time
currentTime = millis();
if(currentTime >= (loopTime + 5)){
// 5ms since last check of encoder = 200Hz
encoder_A = digitalRead(pin_A); // Read encoder pins
encoder_B = digitalRead(pin_B);
if((!encoder_A) && (encoder_A_prev)){
// A has gone from high to low
if(encoder_B) {
// B is high so clockwise
// increase the brightness, dont go over 255
if(brightness + fadeAmount <= 255) brightness += fadeAmount;
}
else {
// B is low so counter-clockwise
// decrease the brightness, dont go below 0
if(brightness - fadeAmount >= 0) brightness -= fadeAmount;
}
}
encoder_A_prev = encoder_A; // Store value of A for next time
// set the brightness of pin 9,3,5,6:
analogWrite(9, brightness);
analogWrite(3, brightness);
analogWrite(5, brightness);
analogWrite(6, brightness);
loopTime = currentTime; // Updates loopTime
}
}

7. Embedded Systems and Applications Laboratory Manual 2019
Koneru Lakshmaiah Education Foundation (Deemed to be University), NAAC - “A++”, Guntur, AP | ECE 7
Output:
Fig 1.3 Circuit with glowing LED’s
Interference Analysis:
The Rotary Encoder ships with LEDs so the end user may increase the brightness to a
level appropriate for the application. The current to each of the 4 LEDs is constant and is set per
the datasheet. A surface mount 220kΩ resistor is provided and a parallel thru-hole resistor may
be added to increase the brightness by lowering the resistance With the surface mount 220kΩ
resistor, the output current is set to about 1mA. Adding a 1kΩ resistor thru-hole will increase the
LED brightness to their highest setting.
Applications
With the help of rotary encoder , we can implement several project related not only
brightness adjustments of LED but can also implement stepper motor, counters, shafting angles
etc,.

8. Embedded Systems and Applications Laboratory Manual 2019
Koneru Lakshmaiah Education Foundation (Deemed to be University), NAAC - “A++”, Guntur, AP | ECE 8
Post Lab Session:
1. Construct a module to on and off a LED by using Rotary encoder
2. Construct a module to vary the brightness of 8 LED’s by using Rotary encoder.
3. Construct a counter module using Rotary encoder

9. Embedded Systems and Applications Laboratory Manual 2019
Koneru Lakshmaiah Education Foundation (Deemed to be University), NAAC - “A++”, Guntur, AP | ECE 9
Viva voice Questions:
Hardware Related Question.
1. What is incremental encoder ?
2. What is absolute encoder ?
3. How do you define the resolution of an encoder ?
4. AC LED - What is it?
5. Light Emitting Diode (LED) - what is it?
6. I have a "5 Volt LED" - what does it mean?
7. LED array - what is it?
8. What is PWM?
9. what is difference between 10k resistor and 10k pot?
10. why 220 resistor is connected along the LED?

10. Embedded Systems and Applications Laboratory Manual 2019
Koneru Lakshmaiah Education Foundation (Deemed to be University), NAAC - “A++”, Guntur, AP | ECE 10
Programming Related Questions
1. Does the pin SW in rotary encoder is input/output ?
2. Does the pin CLK in rotary encoder is input/output ?
3. What is the command for declaring a pin as input ?
4. What is the command for declaring a pin as output ?
5. Explain the command analogRead().
6. Explain the command digitalRead().
7. Differentiate analogRead() and digitalRead().
8. Explain the command analogWrite().
9. Differentiate analogWrite() and digitalWrite().
10. How do you modify the brightness of LED ?
Results
The design of a module that varies the brightness of LED by using Rotary encoder and an
Arduino is done. The Rotary encoder is used to vary the brightness of the LED dynamically. This
experiment can be extended to perform various projects.