1. EE 22442 - Embedded Systems Fall 2015
Chapter Eight:
The human and physical interfaces
EE Embedded Systems Fall 2015
Belal H. Sababha, Ph.D.
Assistant Professor of Electrical & Computer Engineering
Computer Engineering Department
King Abdullah II Faculty of Engineering
Princess Sumaya University for Technology
Amman, 11941, Jordan
Phone: ext. 222
Web:

2. Introduction In this chapter we will learn about:
Human interfacing needs and some simple means of meeting these.
Some simple example sensors.
Some ways of interfacing between sensor signals and the microcontroller.
Some simple example actuators.
Some ways of interfacing between the microcontroller and the actuator.

3. Human physical interfaces

4. Human physical interfaces 2

5. The keypad

6. Reading a Keypad

7. LED displays

8. Multiplexing of digits

10. //Live Demo: Display a counter from 0 to 9 on a Single 7 Segment incremented every 1 sec
unsigned char tick=0;
unsigned char i;
unsigned char mysevenseg[10]={0x3F, 0x06, 0x5B, 0x4F, 0x66, 0x6D, 0x7D, 0x07, 0x7F, 0x6F};
interrupt(){ // TMR0 overflow interrupt occurs every 32ms
tick++; //increment tick evey 32ms
if(tick==33){ // this condition is true every almost 1 second
i++; // counter incremented every 1 second
if(i==10) i=0;
tick=0; }
INTCON = INTCON & 0xFB; // clear the interrupt flag
void main() {
TRISD = 0x00; //PORTD connected to the 7 segment
OPTION_REG = 0x07; // Osc clock/4, prescale of 256
TMR0 = 0;
INTCON = 0xA0; // Global Interrupt Enable and Local Enable the TMR0 Overflow Interrupt
while(1){
PORTD=mysevenseg[i];

11. unsigned char tick, i, qq, rr;
unsigned char sevenseg[10]={0xBF, 0x06, 0x5B, 0x4F, 0x66, 0x6D, 0x7D, 0x07, 0x7F, 0x67};
interrupt(){ //TMR0 interrupt increments tick every 32 ms
tick++;
if(tick==33){
i++; //increment counter every 1 second
if(i==100) i=0;
qq=i/10; // split i into two separate digits
rr=i%10;
tick=0;
}//if
INTCON = INTCON & 0xFB; //clear T0IF flag
}//interrupt
void main() {
TRISD= 0x00;
PORTD=0x00;
ADCON1= 0x06; //PORTA is Digital
TRISA = 0x00; // PORTA output, PORTA is used to enable the required 7 segment display to do time multiplexing
OPTION_REG= 0x07; //osc clock select, with prescaler of 256
TMR0=0x00;
INTCON = 0xA0; //Global Interrupt Enable, Local TMR0 Overflow Interrupt Enable
while(1){
if(TMR0&0x40){
PORTA=0x02; // enable the 10’s seven segment
PORTD=sevenseg[qq];
else{
PORTA=0x01;// enable the 1’s seven segment
PORTD=sevenseg[rr];
}//else
}//while
}//main
//Live Demo: Display a counter from 0 to 99 on a multiple 7 Segments incremented every 1 sec

12. Some simple sensors The microswitch Light-dependent resistors
Optical object sensing
Ultrasonic object sensor
Hall effect sensor
Temperature Sensor

13. The microswitch

14. Light-dependent resistors (LDR)

15. Optical object sensing
Infrared reflective sensor
Infrared reflective sensor
1.6V 0.1mA

17. Optical object sensing
Rangefinder IR sensor
Measuring range: cm
Current consumption: 30mA typical
Includes 10" 3-wire cable
Supply voltage: V

18. Ultrasonic object sensor
e.g XL-MaxSonar®-EZ™ Sensor Line
Component Overview
Resolution of 1 cm
10Hz reading rate
Read from all 3 sensor outputs: Analog Voltage, Serial, Pulse Width
Virtually no dead zone, objects closer than 20 cm range as 20 cm
Maximum Range of 765 cm (300 inches) or 1068 cm (420 inches)
Operates from V
Low 3.4mA current requirement
Small, light weight module
Designed for easy integration into your project or product
Operational Temperature from -40˚C to +70˚C (-40˚F to +160˚F)
Real-time automatic calibration (voltage, humidity, ambient noise)
Firmware filtering for better noise tolerance and clutter rejection
200,000+ Hours Mean Time Between Failure
Retail Price Range: $29.95-$54.95

19. Hall effect sensor

20. Temperature Sensor Microchip - MCP9700/9700A Typical Applications
• Hard Disk Drives and Other PC Peripherals
• Entertainment Systems
• Home Appliance
• Office Equipment
• Battery Packs and Portable Equipment
• General Purpose Temperature Monitoring

22. Ensuring legal logic levels and input protection

23. Switch debouncing Reading Switches Polling
Use interrupt to read switches

24. Actuators: motors and servos
Brushed DC Motors
Brushless DC Motors
Stepper Motors
Servo Motors

25. Motors
Brushed DC Motor
Brushless DC Motor
Stepper Motor

26. Servo Motors
Angular positioning: the ‘servo’

27. Interfacing to actuators
Simple DC switching
Reversible switching: the H-bridge

28. Simple DC switching

29. Reversible switching: the H-bridge