Transcript Engineering 1040: Mechanisms & Electric Circuits Fall 2011

Engineering 1040: Mechanisms & Electric Circuits
Winter 2015
Interfacing Light-Emitting Diodes (LEDs)
&
Push Buttons to Microcontrollers
Light-Emitting Diodes (1)
Source: Wikipedia (http://en.wikipedia.org/wiki/Light-emitting_diode)
Light-Emitting Diodes (2)
• An LED is a diode
• Its emitter comprises of a semiconductor die. It has a cathode and
an anode.
• Usually a diode allows an electric current to pass only in one
direction.
• When an LED is connected to a circuit its forward current should
not exceed a maximum allowable limit.
• We can limit this current by using current limiting resistors.
Technical Specifications of the LED
Forward Current vs Forward Voltage of the LED
Methods of interfacing LEDs to a
microcontroller
Method 1
Method 2
What is the value of R?
Interfacing push buttons to the
microcontroller
• Switches are used to make, break or change connections in an
electrical circuit.
• Push button switches are usually spring loaded so it returns the
moving element to the original position when the pushing force is
removed.
• There two types of push buttons.
Normally Open
Switch
Normally Closed
Switch
Interfacing Push Buttons
“Normally Open“ Push Button
“Normally Closed" Push Button
Switch Bounce
LED 3
Pin D0
Reset
Pin 1
(MCLR)
LED 2
Pin D1
Bootload
Pin 33
(B5)
Set pin D0 as Output Port (LED)
Set Pin B5 as Input Port (switch)
Set all pins of PORT D0 as zero
Set sw equals to 0010000 in binary
PORTB & 0x20 = PORTB AND 0b00100000
Port B
0x10
Result
2016
0
0
2016
2016
2016
0
2016
0
0
0
0
When the button is released pin B5 is set to HIGH,
PORTB=0b00100000 or 0x20
When the button is pressed pin B5 is set to LOW,
PORTB=0b00000000 or 0x00
LED is OFF
sw = 1
LED is ON
sw = 0
• Before the button is pressed pin B5 is HIGH
PORTB=0b00100000 or 0x20
• Then sw becomes, sw=0x20 & 0x20 = 0x20;
• Since sw= 0x20, the condition is TRUE so the
code will remain in the while loop .
• When the button is pressed pin B0 is LOW.
PORTB=0 or PORTB=0x0
• Then sw becomes, sw=0x00 & 0x20 = 0;
• Since sw=0, the condition is FALSE so the code
will exit the while loop .
• Sets the pin D1 to HIGH
• When pin D1 is HIGH it lights the LED
• Sets a delay for button debounce
LED is ON
sw = 0
LED is ON
• Now the button is pressed
• So pin B5 is LOW
PORTB=0b00000000 or 0x00
• Then sw becomes, sw=0x00 & 0x20 = 0;
• Since sw= 0, the condition is TRUE so the
code will remain in the while loop .
• When the button is released pin B0 is HIGH.
PORTB=0b00100000 or PORTB=0x20
• Then sw becomes, sw=0x20 & 0x20 = 0x20;
• Since sw= 0x20, the condition is FALSE so the
code will exit the while loop .
sw = 1
• Sets a delay for button debounce
LED is ON
LED is ON
sw = 1
sw = 0
LED is OFF
• NOW the button is released pin B5 is HIGH
PORTB=0b00100000 or 0x20
• Then sw becomes, sw=0x20 & 0x20 = 0x20;
• Since sw= 0x20, the condition is TRUE so the
code will remain in the while loop .
• When the button is pressed pin B0 is LOW.
PORTB=0 or PORTB=0x0
• Then sw becomes, sw=0x00 & 0x20 = 0;
• Since sw=0, the condition is FALSE so the code
will exit the while loop .
• Sets the pin D1 to LOW
• When pin D1 is LOW the LED stops to light
• Sets a delay for button debounce
LED is OFF
• Now the button is pressed
• So pin B5 is LOW
PORTB=0b00000000 or 0x00
• Then sw becomes, sw=0x00 & 0x20 = 0;
• Since sw= 0, the condition is TRUE so the
code will remain in the while loop .
• When the button is released pin B0 is HIGH.
PORTB=0b00100000 or PORTB=0x20
• Then sw becomes, sw=0x20 & 0x20 = 0x20 ;
• Since sw= 0x20, the condition is FALSE so the
code will exit the while loop .
sw = 0
sw = 1
LED is OFF
• Sets a delay for button debounce