At 10:16 AM 9/26/99 -0700, you wrote:
>I'm working a keyless entry system using the PIC16C84 and would
>appreciate anyone's tips and or advice.  I plan for the system to run on
>a 4x3 keypad outside and it will unlock or lock the door on a house when
>the proper code is entered.
>Thanks.
>chris camerlin
>
Hi!
You may try something like this:
use a 16F84 to read the keyboard, there are applications on the AN, let me
see if I
can find one...(2 min wait looking 4 it)...done, I couldn't find it, so:

A0   A1   A2   A3   <---outputs sequenced (see below)
 |    |    |    |
 1----2----3----A-------B0 input
 |    |    |    |
 4----5----6----B-------B1 input    <----typical keypad
 |    |    |    |
 7----8----9----C-------B2 input
 |    |    |    |
 *----0----#----D-------B3 input

you must add pulldown resistors on all tree B inputs

the way of use it is sequencing (high) the inputs A1..A3 (only 1 on at once) and
reading the outputs, if (for example) B1 is high when A2 is selected, then the
digit 6 was pressed.
Now the easiest way to send it to the central is IMHO using RS232, because only
3 wires are necesary (Power, ground and data out), and you also can doit
wireless,
it is more complex and a little more expensive but no wiring needed to the
central.
some time ago I did something like that with RFM modules (encapsulated
transmitters
that works at 400 mhz with ON/OFF modulation at 1200 baud (RX1000/TX1000 model))

each key pressed can be transmitted via RS232 to the central, for extra
security you
can isolate Rs232 with optocoupler and power the keypad with a different
power supply,
so if some kind of short or destruction ocurrs on the pad, it will not
affect the
normal operation of the central.

I have some PDF's of RFM modules and some simple Rs232 routines (without
using prescaler), If you need it, let me know.

did you have the mechanical part solved?.
I hope it will helpful.
   Leandro J. Laporta (LU2AOQ)
   mail: lu2aoq@yahoo.com
   wrk: Arg. Assoc. for Space Technology.
   ham: TCP/IP high speed group HSG