Programable LED Light bar

[donh69]

I am looking for a way to build a light bar that would allow me to use 36 - 48 Ultra brite LEDs and have programable patterns. I would like to have at minimum: variable speed, flash all, left to right, right to left and back and forth scan . Any ideas?

 

[Exo]

A Pic is probabely the most easy way to achieve programmable patterns.
Building something like this with normal logic would get complex real quick.

 

[laroche73]

patterns & LEDs

What current do your Ultrabright LEDs need? 74HCxxx outputs have a maximum source or sink rating of 25 mA, limited by an overall package dissipation rating of 500 mW (SO package). Six 74HC164's or 74HC595's (8-bit shift registers) in conjunction with a PIC or other small micro would be enough to drive 48 LEDs with intermittent duty. The '595 has a double-buffered output stage, not necessary here since the shift register update rate would be much faster than the human eye could detect changes on the display.

If you wanted to use a minimal number of output drive pins, check out complementary-current drive (p.4). N outputs can drive (N^2 - N) LEDs, 7 for 36, 8 for 48. The disadvantage is that (with some not very flexible exceptions) only one LED can be on at a time without multiplexing, which reduces brightness. Outputs also need to individually be tri-statable, realistically limiting you to using PIC I/O pins.

 

[donh69]

Current ratings on LED

The current rating for the LEDs that I'm looking at is:
D.C. Forward Current If 20mA
Pulse Forward Current Ifp 100mA

 

[Kingpin094]

If you are looking to minimize hardware you might go with something like the UCN5832 from Allegro.
It is a 32-bit latched driver. Each driver has the ability to sink 100mA for a total of 3.2 amps for the
whole chip. It uses a simple SPI 3 wire interface which is very easy to create in software.
I have PIC code to run the chip you decide to go that route.

Here is a link to it.
**broken link removed**