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Keyboard
Program, Data, Commands to software can be given from keyboard
Key Switch
- Key board – set of key switches
- |||r to typewriter
When a key is pressed:
- Key switch is activated
- An electronic circuit determines the pressed key
- Std 8 bit code is generated & sent to computer
Encoding: Detecting which key is pressed & generating corresponding code
Serial Keyboard
- Sends data bit by bit in serial fashion
- Computer converts data into parallel byte
Types of Keys
- Function Keys
- Numeric Keys
- Cursor Control & Editing Keys
- Alphanumeric Keys
Keyboard Function
Functions by Keyboard electronics
- Sensing a key depression
- Encoding
- Sending code to computer
Scanning Technique (Standard Technique)
Rows: used as input to matrix.
Keyboard electronics sends signal to matrix through rows
Columns: used as output from matrix
Lines are sensed by electronic circuits
Types of Key switches
- Mechanical Key Switch
- Membrane Key Switch
- Capacitive Key Switch
Mechanical Key switch Keyboard
Mechanical Key Switch
Working:
- Key is fixed on a plunger
- On pressing it, connection is made between two points in keyboard matrix
- Activates signal which is sensed by key board matrix
- On releasing the key, plunger comes back to its original position due to spring action
- Connection is also removed
*Keyboard is bulky & has wear & tear problem
*Servicing Easier
Capacitive Key switch keyboard
- Key activation affects capacitance between two conducting plates
- Plates placed with small gap by Mylar sheet.
- On key press, the plunger pushes the plates reducing the gap
- Changes capacitance between sheets
- Keyboard electronics senses capacitance change & identifies the key
- Small in size & more durable
- Not easily serviceable
Membrane Key switch Keyboard
- No. of membrane switches present & no springs
- On key press, electric circuit is closed by two metallic contacts
- On releasing the key circuit is broken
- Less moving parts – silent keyboard
