4x4 keypad decoder?
Tom Handley email (remove spam text)
Graham, there are several options. The cheapest would be just to use
an 18-pin PIC and make your own encoder. There are plenty of examples
and you can provide a parallel of serial output with an interrupt
signal. I've done this on several occasions. You will need some external
resistors in addition to an R/C, resonator, or crystal oscillator.
If you are using a bus-based design and have 4 lines available and
optionally an interrupt line, the 74C922 4x4 encoder is very simple to
use. You only need two capacitors, one to set the scan rate and the
other to set the bounce delay. It provides a 4-Bit output and includes
an output-enable to tristate the bus. It also provides a data available
signal. It comes in an 18-pin DIP. I've used this chip for years without
problems. Jameco sells them for $6.75 (P/N: 44564). There is also the
74C923 which is a 4x5 (20-key) encoder which works and costs the same.
E-Lab also has a custom 4x4 encoder that I just started using in a
18F452 design. It requires 8 resistors and either a 4MHz resonator or
crystal without the need for external capacitors. It provides either a
4-Bit output or a serial output at either 2400 or 9600 baud. It also
provides an interrupt output. I'm using the serial mode at 9600 with the
interrupt. So far, it has worked as advertized. Jameco sells it for
$6.95 (P/N: 171969).
For more info, see:
At 04:22 21-02-03, Graham North wrote:
>Does anyone know of a 4x4 keypad decoder? I've been 'Googling' but can't
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