Micro Progamming help-CLARIFICATION

[Kim]

Actually, it would count 5s, 10s, 15s, 20s, 25s, 30s, 35s, 40s, 45s,
50s,55s, 1m, 1m5sec,1m10s........1m,55s,
2m.....59m55sec,1h.............................etc



"Ken Smith" <kensmith@green.rahul.net> wrote in message
news:cn955e$ijq$2@blue.rahul.net...

In article <nnTld.8702$Ho4.346078@news20.bellglobal.com>,
Kim <ksleep@sympatico.ca> wrote:
[....]
-Again, I must stress that this is a counter, not a timer. Often
describing
a specialized function is the hardest part of a job. This is a counter,
not
a timer, at all. just consider this a counter that happens to count by
5's,
until it gets to 60, then it places a prefix of 1 ahead of the 5 count,
until it counts to 60 again, then it prefixes the count by 2....and so
on.
So if you drop the idea of seconds, minutes, hours etc, it may be easier
to
understand.

So it counts: 000, 005, 010, 015 ... 055, 100, 101

Right?

You want to make this out of just chips you can buy easily off the shelf.

If you make a counter for each digit, you can connect a BCD to 7 segment
decoder to it and drive a 7 segment LED display or better yet if you find
the right one, a 7 segment LCD.

The bottom digit can be just a simple flip-flop like a 74HC74. It only
has to remember if it is "5" or "0" so there are just 2 states.

The next digit counts up to 5 and the starts over at zero. There are
several counter chips that have a parallel load function that will cause
the counter to load in a value on the next clock. If you use a logic gate
to decode the fact that the digit is 5, you have the signal needed to
cause it to load and also the signal to tell the next stage to count up by
one.

The other digits divide by 10 until we get up to the 24 hours. These
digits can be done with simple decimal counter chips.

23 hours is decoded with logic gates and causes the hour of the day
counters to be reloaded.

Now you have to include some more information. Are these months normal
Jan, Feb etc or can they just be 30 days each?


-I would prefer that the count be held if the batteries were changed, but
if
this is not possible, then forget it.

If you use 74HC parts, you can include a "super cap" in the power circuit.
Even just a normal large value capacitor would give you enough time to
take out one battery and put in another. The "super cap" would give you
hours. If we assume at least 8V from the battery.


------ D3
Vin ---+--!LM7805!----+-------->|---------- To display chips
! ------ !
--- ! +-------->|---+------ To counter chips
--- V D1 ! D2 !
! --- --- \
GND ! --- / 100R
GND ! \
GND !
--- Supercap
---
!
GND

D1 causes the LM7805 to regulate at 5V + one diode drop.

D2 powers the counter normally and prevents the Supercap from trying to
run the display.

D3 just makes the drops equal.

--
--
kensmith@rahul.net forging knowledge

 

[Tim Wescott]

Ken Smith wrote:

In article <10pgck791973p42@corp.supernews.com>,
Tim Wescott <tim@wescottnospamdesign.com> wrote:
[...]

This can all be done with a microprocessor, for much less (precious)
board space than 7400 logic -- although the logic would certainly serve.
Since it's battery powered one would want to see if there were a
microprocessor out there that'd operate over a wide Vdd range and think
of using just two or three cells and no regulator.


Yes but if it is a PIC, someone has to program it.

BTW: A PIC will work over a wide enough range for 3 AA cells to power it.
The issue then is the display current if you want to have the capacitor
hold the count while the batteries are changed.

Yea, I'm assuming programming no matter what.

Assuming 3AA cells and a series schottkey (who's drop I'd have to check
to see if the PIC could handle) a clever programmer could turn off the
display driver in the event of battery loss.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com