Physical prototyping lab2-analog_digital

Implement the light effect as seen in
KIT, the Knight Rider car from the 80's
TV series with David Hasselhoff.
The sequence should be activated
when a user presses a button
HOMEWORK: KNIGHT RIDER
1

HOMEWORK: SOLVING IT
Besides wiring the breadboard, you
had to write the program needed to
make it work.
The “clever” solution makes use of
arrays, we iterate through them using a
FOR loop.
2

PHYSICAL PROTOTYPING
© 2011 K3 Creative Commons v3.0 SA-NC
Lab 2: Analog & Digital
With the Arduino prototyping board

for(counter=0; counter<end; counter++){}
1)The FOR loop is a software construct that will execute a
block of code a number of times.
2)The code will be looped until a certain condition is met
3)FOR loops are constructed with an initialization value, a
condition statement, and a counting statement
4)We use them to iterate a certain action a determined
amount of times
counter initialization
FOR LOOP
condition counter
increment / decrement
4

ARRAYS
1) ARRAYS are sets of indexed values arranged in order in
the processor's memory
2) All the elements in an array have an unique identifier
3) The different “positions” in the array are addressed through
numerical index values between squared brackets
4) Array constructors include the type, and the size of the
array (the number of elements they consist of)
5) The elements of an empty array are NULL (nothing)
6) It is possible to initialize an array with a specific set of
values:
E.g. int theList[] = {1, 3, 'e', 19};
5

WHAT IS “ANALOG”?
The real world is NOT digital.
Temperature fluctuation, for example,
involves a range of values and generally
does not changes abruptly over time.
Using analog sensors we measure
environmental parameters like
temperature, light intensity, etc.
These are a set
of analog values
6

Are sensors which transform environmental parameters
into a multi-level voltage value (between 0 and 5 volts)
There are many types of sensors that provide us with
analog voltage values:
LDR (or CDS): light dependent resistors aka light
sensors
NTC and PTC: temperature dependent resistors
aka temperature sensors
Potentiometers and sliders: angle and position
dependent resistors
ANALOG SENSORS
7

READING ANALOG VALUES
 Microprocessors cannot handle analog values as humans
do. They need to be translated into digital data, something
the microchip can understand.
 Sensors transform real world data like the temperature into a
voltage value between 0 and 5 volts. These values are
different from the HIGH (1) and LOW (0) that characterize
digital signals, because they can take any value between 0
and 5 volts.
E.g: 0.3 volts, 3.27 volts, 4.99 volts are possible values.
 The readings resolution depends on the capabilities of the
processor/microcontroller you are using.
Arduino can distinguish 1024 different levels between 0
and 5 volts.
8

 Are devices which change resistance (and thus the voltage) when
you twist or slide them.
 Arduino can measure the voltage which flows through them.
 We can use this data to control other things, like LED’s.
 We call potentiometer those that rotate around one of their axis
 We call sliders those that move linearly along one of their axis
POTENTIOMETERS vs SLIDERS
A circuit using a
potentiometer
A circuit using a
slider
9

CONNECTING THE POTENTIOMETER
Potentiometers are useful for improvising quick interfaces.
The recommended resistive value is 10 Kilo Ohms. (10K)
On the Arduino board there are 6 Analog Input pins, they are
numbered from 0 to 5.
Analog inputs are not declared in the setup of the programs,
unlike the Digital Inputs.
We will use this easy circuit to control the oscillation speed of the
basic Blink-LED example
10

analogRead(pin number);
 Returns the value from a specific analog
port
 Values from 0 to 1023
 0v = 0
 5v = 1023
READING THE SENSOR
11

int potPin = 2; // select the input pin for the potentiometer
int ledPin = 13; // select the pin for the LED
int val = 0; // variable to store the value coming from the
// sensor
void setup() {
pinMode(ledPin, OUTPUT); // declare the ledPin as an OUTPUT
}
void loop() {
val = analogRead(potPin); // read the value from the sensor
digitalWrite(ledPin, HIGH); // turn the ledPin on
delay(val); // stop the program for some time
digitalWrite(ledPin, LOW); // turn the ledPin off
delay(val); // stop the program for some time
}
EXAMPLES ► ANALOG ►
ANALOG INPUT

LDR
Light dependent resistor
 We call the resistor a “pull up” resistor
 It is usually 10K
 You can use exactly the same code as in the previous example
13

FADING LEDS
1) LEDs are Light Emmitting Diodes, and can only be turned on
or off.
2) However, it is possible to fake their level of intensity through
the use of a mathematical trick called PWM (Pulse Width
Modulation) which will be explained later.
3) In essence, what you need to know for making the next
experiment, is that there is a function called analogWrite(pin,
intensity) that will write an analog value to one of the PWM-
labelled pins on your prototyping boards.
4) PWM runs in parallel to the rest of Arduino, which means
it will not stop any of the other processes which are running.
5) Hook up one LED with it's correspondent resistor to
e.g. pin 10, and execute the following example.
14

EXAMPLES ► ANALOG ► FADING LED
int value = 0; // variable to keep the actual value
int ledpin = 9; // light connected to digital pin 9
void setup() { // nothing for setup
}
void loop() {
for(value = 0; value <= 255; value+=5) // fade in (from min to max)
{
analogWrite(ledpin, value);
delay(30); // waits for 30 milliseconds
}
for(value = 255; value >=0; value-=5) // fade out (from max to min)
{
analogWrite(ledpin, value);
delay(30);
}
}

SERIAL COMMUNICATION
USING THE SERIAL LIBRARY
Serial.xxxx
Serial defines a method to use the serial port
Serial.begin(baud);
Placed in setup to initiate serial communication ”baud” is baudrate
(”communication-speed”)
Serial.print();
Writes (sends) something to the serial port
Serial.println();
Writes (sends) with cr and lf
16

PROGRAMMING SUMMARY
Commonly used Arduino methods:
int analogRead(pin);
reads an analog value from an analog pin number
analogWrite(pin, value);
writes a time-dependant signal through the use of the
so-called PWM pins
Serial.println(data);
sends data back to the computer to be seen through the
serial monitor
Serial.begin(baud);
opens the serial communication at baud speed
17

Physical prototyping lab2-analog_digital

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