How to achieve 57 PWM outputs most easily and cheaply

Question

I need to light up 19 RGB LED strips, which it seems would require 19*3=57 PWM outs and 57 transistors. The transistors aren't an issue, but of course the 57 PWM's is. Most micro controllers simply don't have that many.

How can I do this more simply? Is there some kind of device I can get that would let me just pass data to it, perhaps over I2C, and it would control many PWMs? Is there another solution I haven't considered? Maybe whatever is used to control those 8x8 RGB LED dot matrixes?

Any help would be greatly appreciated. Thank you!

Answer 1

Daisy chain 3 of these ICs (datasheet) and control them via SPI. They are designed for driving LEDs.

Adafruit has dev kits if you want to play with it:

http://www.adafruit.com/product/1429

Answer 2

Pretty much any FPGA with a high enough pin count, basic PWM's are very simple in terms of logic design and usage. Add in a soft CPU and you should be able to fit the whole thing into a Xilinx XC6SLX9 in a QFP144 package, i.e. easily hand-solderable.

Answer 3

Actually Cypress PSoC is well suited for this. This PSoC Sensei blog post describes how to achieve 52 hardware 8-bit PWM outputs with a single PSoC3 or PSoC5. The additional ones could be achieved with a $1 PSoC4 acting as a slave over SPI or I2C.

If you haven't heard of PSoC before you might want to take a look; they're 8051 or ARM Cortex M0/M3 cores with some programmable logic beside them. There's also a variant with BLE radio built in.

Not affiliated with Cypress, just a pretty happy customer with their PSoC4 and 5LP devices.