1. Interfacing to External Devices Explore Digital Interfaces techniques Introduce some complex optical devices and how to interface them Describe methods for switching devices on and off

2. Interfacing Digital Input Signals • General requirements of all digital input signals: • The voltage input level should only be the legal allowed voltage. • They should not be corrupted by glitches • They should switch cleanly and fast.

3. Forms of Signal Degradation

4. Simple Interfacing for Digital Signals

5. Switch Debouncing • Switch debouncing happens when mechanical contacts switch and thus from the force of the switching they bounce for a few milliseconds.

6. Actual switch Bounce Signal

7. Hardware Methods for Debouncing

8. Software method of Debouncing 1

9. Software method of Debouncing 2

10. Interfacing Keypads 1

11. Interfacing Keypads 2

12. Keypad Scanning Algorithm

13. Optical Devices: Single 7-segment Display

14. Optical Devices: Multiplexed 7-segment Display

15. Optical Devices: Example Circuit

16. Optical Devices: Opto-Isolator

17. Object Sensors

18. Shaft Encoders Angular Speed S = output frequency / number of holes revolutions per second This setup does not give indication of direction

19. Incremental Quadrature Shaft Encoder

20. Absolute Shaft Encoders

21. Inductive Load Switching

22. Examples of Inductive Loads

23. Mechanical Relays

24. The use of H-Bridge 1

25. The use of H-Bridge 2

26. The use of H-Bridge 3

27. The use of H-Bridge 4

28. Semiconductor H-Bridge 1

29. Semiconductor H-Bridge 2 http://www.dprg.org/tutorials/1998-04a/