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[on:]

I attended some programming classes but I barely remember anything...
I am starting a project which is a big countdown that consists of 25 7segments leds.
It goes from 9999999999999999999999999 to 0. So it would take billions of years to end...
I do not know if is necessary to write code or I just need a diagram.

It should work without a pc connected to it.

What materials will I need? As you can imagine any help would be greatly appreciated

[Reply #1 on:]

4 MAX7219, 4 22K resistors, 4 0.1uC caps, 4 1uF caps, COMMON CATHODE displays - 6 @ 4-digit, 1 @ 1-digit, 7.5 or 9V @ 1A power supply, 1 Uno.
All parts except uno available from taydaelectronics.com
Each MAX7219 will control 2 displays, and 1 will control 1 display.

Search e-bay for 18cm 30cm protoboard if the prototyping boards at tayda are not big enough or you can't string them together.

What will your assembly method be?

[Reply #2 on:]

4 MAX7219, 4 22K resistors, 4 0.1uC caps, 4 1uF caps, COMMON CATHODE displays - 6 @ 4-digit, 1 @ 1-digit, 7.5 or 9V @ 1A power supply, 1 Uno.
All parts except uno available from taydaelectronics.com
Each MAX7219 will control 2 displays, and 1 will control 1 display.

Search e-bay for 18cm 30cm protoboard if the prototyping boards at tayda are not big enough or you can't string them together.

What will your assembly method be?

Since each MAX7219 can control eight digits you might as well go for 32 digits instead of 25.  The software isn't any harder and might actually be easier.

[Reply #3 on:]

It goes from 9999999999999999999999999 to 0. So it would take billions of years to end..

depends on the step size and frequency.
What does the number represent, the national dept?

[Reply #4 on:]

Thank you for your fast response!

It is an art project so visual aspect is quite important. I was thinking in using quite big digits (3-4 inch). I do not know if this has a mayor impact on the structure of the electronic device.
Everything that makes things easier is welcome So if it is better I would go for the 32 digits.
As I mentioned before I am completely new to all this so I appreciate your patience and any advice to keep it as simple as possible.
I found this one: http://www.ebay.es/itm/Protoboard-700-contactos-Breadboard-placa-prototipos-soldadura-Arduino-/170927079955?pt=LH_DefaultDomain_186&hash=item27cc0c4213#ht_2473wt_1190 , is this big enough?

The digit changes every second. That is why it will take so long.

I already know how to make a simple 1 digit countdown, but I can not find the way to make the 25 digits one… any help with diagrams or code is more than welcome

[Reply #5 on:]

This kind of 4" digit?
http://www.kingbrightusa.com/category.asp?catalog%5Fname=LED&category%5Fname=KC1%2DDigit+4%2E0in&Page=1

I'd recommend the Common Anode parts, drive from 12V, connect the cathode segments to TPIC6B595 shift registers to drive them.

This board here can drive 12 digits, use 2 boards and wire up one TPIC6B595 for the 25th digit.
Probably want to wire the anodes together seperately and not source from the board tho. Connect grounds together.
I sell bare boards for $5 each mailed to US locations, all thru hole, easy to assemble. International, a little more for postage.
Complete kit, or assembled tested boards, I'd have to price up.


The actual counting down part is easy.
set up 25 bytes with 9 in each.
once a time period, test if the lowest digit is not 0 and decrement it.
If it is 0, set it to 9 and decrement the next digit.
 if the next one is not 0, decrement it.
  if it is 0, set it 9 and decrement the next digit.
Will have one big long chain checking if a digit is to rollover or not.
Longest chain will from 1000000000000000000000000 to 0999999999999999999999999
And you can add leading 0 blanking too.

[Reply #6 on:]

Looks like a fun project so I'd be willing to write the software for you or help you develop the software if you want to learn how.

[Reply #7 on:]

Complete overkill but you could use bignumber.

http://arduino.cc/forum/index.php/topic,85692.0.html

[Reply #8 on:]

Thank you all for your help

[Reply #9 on:]

I'm thinking you can nicely get two 3" digits with 2 driver chips and SPI signal buffering to the next board.
LED on one side, thru hole parts on the other.

[Reply #10 on:]

Hi!
I just wanted to let you know that the problem is solved.

Thank you all for your help.

[Reply #11 on:]

And what did you do to solve it?