Although more complicated on the software side, you COULD
multiplex the LEDs so  it would take 7 lines to drive the segments plus
one line to drive each digit (assuming you have high efficiency LEDs so
the PIC can drive seven segments simultaneously, or you'll look at the
thing in the dark).  Also, multiplexing can get a bunch of buttons into
the PIC with fewer wires.
        If you want to take a hardware approach (recalling that the ideal
design has zero parts), you might look at the CD4511.  This is a 7
segment latch decoder driver.  You feed it 4 lines of BCD and strobe a
latch line and it'll hold it.  You can then share the 4 bcd lines and
have individual digit strobe lines.

Harold


Harold Hallikainen
harold@hallikainen.com
Hallikainen & Friends, Inc.
See the FCC Rules at http://hallikainen.com/FccRules and comments filed
in LPFM proceeding at http://hallikainen.com/lpfm

On Fri, 18 Sep 1998 11:38:19 -0700 "Murphy, Patrick (AZ76)"
<PMurphy@SPACE.HONEYWELL.COM> writes:
>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)
>

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