5 min precision countdown timer

Thanks! the timer need not be that accurat and need only have min and sec indicators from 5 min down to 30 sec. I want to use discrete componants and i realy want to build it myself. I would like to set the min and sec separatly but two push buttons, one for up and one for down will olso do.

Thanks

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 switches/etc)?

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.

--
Dave M
MasonDG44 at comcast dot net  (Just subsitute the appropriate characters in 
the address)

Never take a laxative and a sleeping pill at the same time!!

A few counter kits that might interest you:

--
Dave M
MasonDG44 at comcast dot net  (Just subsitute the appropriate characters in 
the address)

Never take a laxative and a sleeping pill at the same time!!

If not take a look at the CD4511 datasheet.

Basically you need 3 up/down counters.

The LSD of the seconds is a divide by 10. The MSD of the seconds is a divide by 6. The Minutes is a divide by 5.

--
--
kensmith@rahul.net   forging knowledge

Thanks Dave.

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.

Thanks

Hi Ken. I'm not that good at this game so you will have to explain a little more Thanks

--
I\'ll be happy to help you out, but why do you want to use 5X8 matrix
displays?

It's obvious that you're new to Usenet too:

More below.

FYI, Google Groups is not Usenet; it is but one way of accessing Usenet.

Most folks use a "newsreader" to read the groups.

That means that the vast majority of people don't see what you see on Google.

See how I went back and added a bit of your previous post to this post? That is called **context**. To get context the easy way: (hint: Don't click the Reply link that is in plain sight), click the **show options** link, then click THAT Reply link.

You don't have to re-post **everything** from the previous post; feel free to snip out as much from the automated blockquote as you wish. I only leave enough to show what part I'm referencing ("context"). See above.

Read some threads and observe how others post, then do likewise. . . Rich Grise (pointedly) remarks on context here:

The guidelines for Usenet are here: http://66.102.7.104/search?q=cache:8PaSp2kKbWoJ:

*-top-*-*-message+do-not-*-*-*-original (Worth scanning--especially the parts I've highlighted.)

Thanks John,

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).

Best regards, Spehro Pefhany

--
"it\'s the network..."                          "The Journey is the reward"
speff@interlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com

--
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?

John!

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 Thanks Edward

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 display.

--
--
kensmith@rahul.net   forging knowledge

--
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.