Hexadecimal Keypad

• Hardware Description

• Internal Organization

• The Circuit in Action

• Signal Bouncing

Doug Butterworth Email: epor@psu.edu AIM: Epor55 Phone: 814.217.2466

Hardware Description:

16-Button Numeric Keypad • Rugged black plastic • 4 x 4 Matrix Type • 8-position solder pad • Contact rating: 24VDC @ 20mA • Contact resistance: 200 Ohms

max. • Life test: 1,000,000 life cycles

per key • Size: 3.0"L x 2.8"W x 0.6"H• $7.95 from

Links:Product PageTechnical Documentation(pretty under whelming)

                      

Internal Organization

Output organizationOutput pin # SymbolPin 1 Row 2Pin 2 Row 3Pin 3 Col 1Pin 4 Row 4Pin 5 Col 2Pin 6 Col 3Pin 7 Col 4Pin 8 Row 1

When a button is pushed, the associated row and column pin for that button are connected together.

Circuit Diagram

1 2 3 A Row 1

Hex Keypad: The Movie!

QuickTime™ and aCinepak decompressor

are needed to see this picture.

Uses

• Wired into a keypad encoder.(presentation 19 with Anthony Dotterer)

• Xilinx

• Use your imagination…

Signal Bouncing

Background Theory:• Nearly all mechanical switches generate some

bounce.• After switched, they actually open and close

several times before settling down to their new position.

• Can Last as little as a fraction of a millisecond to as long as 50 ms.

• Only very high quality switches generate little or no bounce.

Signal Bouncing

(Simulated by touching a wire to a alligator clip)

Signal Bouncing On the Keypad

(Wow!)

How to prevent:

• Use an RC network to slow either the rising or falling edge of the event.

• Buy a really good switch!