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[on:]

I was wondering if it was at all possible to create an led matrix in the shape of a triangle using normal multiplexing. I'm fairly new to arduino and I have had no problem making an 8x6 matrix with a 4017 Decade counter and 74hc595 shift register. But for my project I don't need a rectangle, I simply need a triangle shape that I can program
        O
      OOO
    OOOOO
  OOOOOOO
OOOOOOOOO <--something like that

Just so that I don't have to waste more LEDs filling in the unused blank spots

Would I just build it like normal and program it like, (B0,B000,B00000,B0000000,B000000000); or would that not work

Any input/help is greatly appreciated! Thanks

[Reply #1 on:]

yea it should be the same, you have 25 led's though so your basicilly adding a whole shift register and byte of code to drive the 1 extra LED, maybe just use a transistor for that top one and its own pin

[Reply #2 on:]

Beautiful! That's a good idea instead of adding another chip. Thanks for the quick reply too btw:)

[Reply #3 on:]

let me ask you, are you planning on addressing each individual LED to make animations, or are you just making a scroll effect like on a beer pong table or pinball machine

if its the latter you can greatly simplify it

[Reply #4 on:]

I'm going to be making up individual frames in an excel sheet that I made up and then have the program cycle through the frames to make up an animation, if you got any ideas on how to make things more simple, I'm all ears... Or I guess on a computer, all eyes!

[Reply #5 on:]

Maybe take one half of the triangle and wire it upside down. That way you can make full use of the multiplex, no wasted columns on any of the rows or vice versa. It would add a bit of complication to your code, but you could still deal with it in a way that it wouldn't affect how you make each frame in your spreadsheet.

Maybe there's a smarter, less complicated way to do it... But basically my point is you could fine something to keep from wasting those unused pins...

[Reply #6 on:]

Or just use a MAX7219 ($1.25) & set it up in no-decode mode for 4 digits.
4 SPI writes & have nice quick animations.

[Reply #7 on:]

Or just use a MAX7219 ($1.25)

Where do you get them for that price. At Farnell they are ten times that price.

[Reply #8 on:]

eBay http://www.ebay.co.uk/itm/10pcs-Original-MAX7219CNG-DIP-24-MAX7219-MAXIM-LED-Display-Drive-NEW-m-/390357314467?pt=UK_BOI_Electrical_Components_Supplies_ET&hash=item5ae31beba3

http://www.ebay.co.uk/itm/10PCS-MAX7219CNG-DIP-24-MAX7219-MAXIM-LED-Display-Drive-/250905632143?pt=LH_DefaultDomain_0&hash=item3a6b241d8f

[Reply #9 on:]

Amazon: $4.02 + shipping

[Reply #10 on:]

Amazon: $4.02 + shipping

Expensive. The second link I supplied was for 10 chips, less than $6 and free shipping.

[Reply #11 on:]

http://www.taydaelectronics.com/catalogsearch/result/?q=max7219

Ordered:
8 x MAX7219 $1.25 each
20 5.5mm/2.1mm panel mount power connectors
10 each of 9 resistor values
Shipping $1.80 to Boston, MA area

Am using 4 now to drive 4 8x8 matrix displays

[Reply #12 on:]

I am building a large 7-segment display.  There are four digits and they are approx 9" by 6".  Each segment is illuminated by 3 three color LEDs.  I hope to display my house number as well as time/temperature and seasonal messages ("HoHo" at Christmas, etc.).  To control each segment individually required 7 segments x 4 digits x 3 colors = 84 signals.

I decided the simplest way to do this was to use an MM5450 LED Display driver.  DIP packages from Digi-Key are less than $5.  Jameco has it for less than $4.  SMS packages are even cheaper but my soldering skills don't allow their use.  Since each 5450 provides 34 outputs, I could have used 3 for the display but instead I used one 5450 per digit.  This allowed me to construct each digit individually.

The interface to the Arduino is very straightforward with just 3 signals: clock, data and digit enable.  The modular design may make maintenance of the message board simpler.  My experience has been that electronics like this when exposed to the variations of Ohio weather tend to occassionally need repair.

I think a big advantage to using a chip specifically designed for LED driving is that current limiting resistors are not required.  In looking on-line, I see that some hobbyists use the 5450 but that it is not widespread.  Here's one interesting application (it's in Spanish):


He uses current limiting resistors but I don't think they are necessary.

My display is still a work in progress (I hope to finish the first digit tonight) so maybe there are problems that I haven't met yet. 

It seems to me that the 5450 would work well in your multiplexing application.