Use a PIC16C74.  Lots of I/O pins, A/D no problem.  My battery check ckt is
nice and simple.  For 9V batteries, I use a 2N2222A transistor.  Connect a
digital I/O pin to the base via a 100K resistor.  this is your on/off so
the ckt does not draw current when not needed.  Connect a 2.2k resistor b/w
emitter and ground.  A 9.1K goes b/w collector and Vbat+.  The analog
voltage at the emitter (with a high applied to the base) will convert to
your battery voltage in tenths of volts if your Vref is +5V.

I recommend the abort key be instant, without delay (safety).  with a
PIC16C74, each LED could have its own I/O pin, with pins for future
enhancements readily available.

----------
> From: Dr. Ed Edmondson, Jr. Ph.D. <Dreaejrphd@AOL.COM>
> To: PICLIST@MITVMA.MIT.EDU
> Subject: PIC_k You Brains
> Date: Thursday, October 08, 1998 9:52 PM
>
> I am really glad to see that all you picsters are so easily amused :-)).
> Technical people with a good sense of humor are hard to find.
>
> What I need to do is just PIC your brains a little.  I have all the
hardware,
> software and books to learn what to do with these PIC devices.  What I
need is
> a little bit of direction.  I am wanting to build a model rocket launcher
for
> a friend who has an asthmatic son.  I have seen some simple designs but
tend
> to lean towards the flair for bells and whistles.  So what I will have a
very
> I/O intensive little PIC.
>
> I want to use 10 LED's for the launch sequence (10, 9, 8, 7, ....2, 1,
L).
> These LED's will count down in sequence with the last LED "L" flashing at
> about 1-2 Hz at launch.  I want to use a piezo alarm to sound a launch
warning
> for the last 4 counts (LED's 4, 3, 2, 1, L).  Then there would be a dual
> RED/GREEN LED for the Fuze continuity check and a button for this test
(maybe
> it could be automated).  Then we have a flashing (1-2 Hz) red LED to
indicate
> the countdown has been halted due to emergency and a button to activate
this
> feature.  There is also a flashing yellow LED (1-2 Hz) to indicate a
temporary
> hold on the countdown sequence and the button to hold and restart the
> countdown.  Two buttons for on and off and a green LED to indicate power
"ON."
>
> I also want a master reset button (Must be held in for 5 -10 seconds) to
reset
> the whole system to a known state and disable the launch circuit.  I am
> planning on using a key switch for the master interlock on the launch
circuit.
> This and maybe using a SSR to isolate the launch and Fuzing circuit will
> enhance the safety issue.  I want the unit to also go "To Sleep" after 5
or 10
> minutes of inactivity.  Pressing any key would reawaken the system in the
> state it was in prior to "Sleep."
>
> Finally it would be great to have some form of battery condition
indicators.
> Maybe a small LCD voltmeter to measure battery voltage or current.  Maybe
a
> battery gas gauge like Benchmarq sells for high priced power tools.
Maybe use
> the display for a clock too?  Want to be able to use alkaline or
rechargeable
> batteries to power the thing.  It would be great if it could be charged
from
> an auto cigarette lighter!!
>
> What I need is suggestions on  what PIC  might really fit the bill here.
> There is a lot of I/O, a watch dog timer, maybe an A/D, should be able to
> drive LED's, an SSR, a piezo audio indicator, determine battery condition
and
> charge state.  And much more.
>
> With all these bells and whistles this asthmatic young teen could have
the
> ABSOLUTE neatest model rocket launcher at the contests.  This is his only
form
> of recreation due to his exacerbated condition.
>
> What I will get out of this journey, in addition to his smiles, is the
> knowledge earned from getting this thing designed and built.  I have
MPLAB on
> a Compaq Presario 1610 and a PIC Start Plus Programmer.  I have all the
PIC
> books written by anyone I could find.  I have a free source for the PIC
chips.
> What I need is direction and suggestions along the way.
>
> Want to help??  The only real concern is SAFETY to prevent an accidental
> launch which might cause an injury.  This can be avoided with some old
> fashioned design criteria and common sense.  I have until December 24th
to get
> this done.  Any direction and comments would be greatly appreciated by
the
> recipient and myself.
>
> Ed