180 leds!

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justDIY

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I need some recommendations for ways to discretely control 180 leds. what I want to build is a circle, circumscribed with 60 RGB leds (180 leds total) .

right now I'm thinking about eight shift registers per color group, that'll give me 64 channels, times three, for a total of 192. I seem to recall seeing a 32 bit shift register from MAXIM or maybe it was someplace else - probably cost more than 8 74hc595's would cost.

I'm thinking I'll make up a circuit board to hold the 24 shift registers, and then use headers / cable harness to wire up the leds. Or I might need to make three circuit boards, with just 8 registers each - it depends how messy the routing becomes.

I'm wondering how to calculate the update rate I can expect shifting out 192 bits of data with a 20mHz pic.

Is there an easier way I'm overlooking? I thought about some sort of multiplexing or matrix building, but the leds kinda prevent that - they'll either be common anode or common cathode depending on the cost from the supplier.
 
The data rate won't be a problem, you can shift data far faster than you require with a much slower device. For a simple multiplexing, how about having 60 outputs from the shift registers, and switch (multiplex) between the three colours?. It's not a minimum output solution, but you're not really looking for that - and it's simple.
 
that sounds like a great plan ... certainly 8 registers is better than 24! Three of the remaining four bits of the 64 bit register could even be used to control which color group was active.
 
justDIY said:
that sounds like a great plan ... certainly 8 registers is better than 24! Three of the remaining four bits of the 64 bit register could even be used to control which color group was active.

I'm a big believer in keeping things simple!
 
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