Hi Patrick,

As one beginner to another let me say I started with even less experience
than you a couple of weeks ago and boy am I surprised at what can be done.
I had almost exactly the same challenge of hooking up 4 x 7 segment LEDs to
a PIC and the same question: Not enough i/o's? Using the circuit in Myke's
book on page 264 doesn't help because even if you could do it - it would
use all the PIC 16F84 i/o lines without leaving any for push buttons.

The Answer: Well, I toyed with using a 40 pin PIC which I bought but never
started with. Instead, I dug out a device I bought and almost forgot about
- it is a 4 digit LCD which has on board intelligence and only requires ONE
i/o line from the PIC. You send it serial commands and it displays whatever
you want. There are only three connections to the device, +5v, GRND and
Data. It cost about $   and you can see it at http://www.elproducts.com

Doing it this way leave me 12 i/o lines for LED's and pushbuttons on a 16F84.

The great thing is that I also got PICBasicPro; a basic compiler that
produces PIC ASM/HEX code and that thing is AMAZING! It makes programming
the PIC a total piece of cake, especially the serial i/o for the display -
its just one line of code like this: SEROUT
1,6,[$F4,tenmins,mins,tensecs,secs] which displays a time code (4 digits)
via pin 1, in mode 6 (N9600), and the $F4 is a configuration byte for
things like whether or not you want leading zeros, colons etc.

To me, it really makes learning PIC ASM a bit redundant unless you are
working on something really critical. The book I found most useful was
"Easy PIC'n" and I use the EPIC plus programmer ($39) hooked up to PC
parallel port.

Hope this helps.
John


At 11:38 AM 9/18/98 -0700, you wrote:
>Hello all,
>
>I am just getting started in the PIC world, and could use some
>help.  Not only am I a beginning PICer, I am also a software
>engineer who is very familiar with embedded controllers but
>couldn't design a circuit to save his life.  I'm familiar with
>components, but I don't know how to make them work together.
>
>Let me tell you where I'm currently at, in order to help you
>help me better.  I have just bought a DT001 and DT101 from
>DonTronics, and Myke Predko's book, "Programming and
>Customizing the Pic Microcontroller".  I'm looking forward to
>building and playing with the platform.  I've already downloaded
>and installed MPLAB 3.4, and I'm starting to get familiar with it
>as well.
>
>The project I have in mind is a device with two 2-digit readouts
>(four 7-segment LEDs), and two sets of 2 pushbutton inputs.  The
>readouts will initially display "20" at powerup.  The buttons are
>used to increment or decrement the corresponding readout by 1.
>The software for this should be a piece of cake.  The hardware,
>although, is a different story (for me, at least).
>
>At first pass, it seems to me that I do not have enough I/O lines
>available on the 16F84 to drive four 7-segment LEDs.  That fact
>dictates some additional circuitry that is beyond my capacity to
>design.  Now it seems I should have bought a DT111 for the
>extra space, but oh well, I'll just use a breadboard for now.
>
>If anyone of you reading this could help me come up with a
>circuit to do what I have in mind, or point out any problems with
>my approach, I would appreciate it very much.
>
>Thank you all for your time.
>
>Patrick Murphy
>murphy@syspac.com  (home)
>pmurphy@az76.honeywell.com  (work)
>
>