At 07:00 PM 9/13/2003 -0500, you wrote:
>So, a big question I have now is, how many individual LEDs can you
>multiplex so that the display is bright enough?  What is the minimum
>number of components needed to drive 100's multiplexed LEDs?  I would
>like to design an 8x1 character display to start with.  For 5x7
>characters, I would need ((5 + 1) * 8 - 1) * 7 = 329 LEDs, or 47 columns
>of 7 LEDs each .  Can I use 5 4017 chips chained end to end to count
>from 1 to 50 to select the columns and light a whole column at a time or
>light each LED in each column in turn?

Most of the monochrome ones I've seen use CA display, and have 5 high
power anode drivers and a bunch (maybe 128) cathode sinks.

You can drive them with a higher multiplex ratio than 5:1, of course,
but you start to get into trade-offs with brightness vs. how hard you
are pushing the LEDs (maximum ambient temperature, reliability etc.).

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

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