What you're after is a "Presettable Down Counter" with an accurate time
base. But you didn't fully define the project.
You mentioned "precision" in the subject. How much precision do you need
(how many minutes/seconds/milliseconds/etc)? How accurate does the timer
need to be (within seconds/milliseconds/etc)?
How do you wish to preset the time into the timer (potentiometer/thumbwheel
Do you want to build this using discrete components, or can you program a
PIC (a PIC would be marvelously suited for this task)?
Do you specifically want to build this item, or buy off-the-shelf? Look in
the kitchen appliance section of Walmart or Target for cooking timers. They
will perform everything you asked for except for the relay output. However,
you can probably hack the unit and find a point inside that changes state
when the timer expires, and use that to trigger your relay.
MasonDG44 at comcast dot net (Just subsitute the appropriate characters in
Never take a laxative and a sleeping pill at the same time!!
"Bountyhunter" <ja...@fronthosting.com> wrote in message
A few counter kits that might interest you:
I've had a lok around on those sites and seen a couple of
timers/counters, but I'm in Cape Town South Africa and the local
suppleir of those kits informed me that they can order it for me if I
take a minimum of 5. WHAT A LOAD OF CROC!!!!!!! I.m not that good
with electronics that i can figure out and design one on my own but can
read diagrams and put a little thinking like how a decade counter goes
with a 7 seg display ect. When it comes to the 5 x 8 dot matric
display, it a whole new balpark to me.
I'll be happy to help you out, but why do you want to use 5X8 matrix
Professional Circuit Designer
>so you will have to explain a little more
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John Fields wrote:
> I'll be happy to help you out, but why do you want to use 5X8 matrix
> John Fields
> Professional Circuit Designer
The 5 x 8 is something that i've seen in a shop on display an it showed
up brighter than any other display in the shop, also then because of
the price of the that display is a tenth of the price of the same size
seven segment LED display.
They are more of a hassle to drive. Although you *could* make it work
without a micro, it would be even more hassle. Almost invariably they
are internally multiplexed so you have to generate the scan signals,
and you need a few hundred bits of ROM to store the characters (which
could be done with a generous handful of diodes, but it wouldn't be
pretty at all).
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As Spehro noted, if those are multiplexed displays, the job gets to
be much more of a hassle. What more can you find out about them? Are
they just 40 LEDs with 80 leads coming out the back or are there a lot
fewer leads? (Like 13 or 41?) Do you have or can you get their
manufacturer's name and their part number?
Feed: CD4511 datasheet into google to get the data sheet for the CD4511.
From elsewhere in the thread, I have learned that you want to drive a
matrix display. The CD4511 helps the most if you have a 7 segment
This is a 14 pin matrix display. (ELM-2081EWA) If this display is that
big a problem, can I can make my own seven segment LED display with a
couple of super bright LED's? This will give me the same dislpay
brightness as the 5 x 8 matrix display but wil connect the same as an
common cathode seven segment display. As i dont need the timer to time
down for more than 5 min, i can make 3 of these units
>This is a 14 pin matrix display. (ELM-2081EWA) If this display is that
>big a problem, can I can make my own seven segment LED display with a
>couple of super bright LED's? This will give me the same dislpay
>brightness as the 5 x 8 matrix display but wil connect the same as an
>common cathode seven segment display. As i dont need the timer to time
>down for more than 5 min, i can make 3 of these units
You might be able to, but you'd wind up with some ugly characters.
Try it. Lay out a 5X7 array made out of circles (LEDs) and see what
it looks like. Don't forget that the LEDs you assign to a segment
have to stay there no matter what the character is.