Keyboard Types Mechanical key switches Membrane type: with advantage that they can be made very thin and sealed Capacitive Type: When a key is pressed the capacitance between the plates varies. Hall effect: No mechanical contact. It take advantage of the deflection of a moving charge by a magnetic field. Keyboard Circuit connection and Interfacing Detect a key press De-bounce the key press Encode the valid key to produce a standard code for pressed key The above three tasks can be performed with hardware, software or a combination depending on the application Keyboard interfacing Figure show the interfacing of the keypad using 8255. The rows of the keypad are connected to say PORT-A and columns connected to PORT-B. PA is in