9 PWM channels

[Andrew Cowan]

I'm working on another RGB LED project, and I require three sets of LEDs, so 9 PWM channels in total.

I don't really want lots of PICAXE chips, so I'm looking for an expansion chip (serial, SPI or I2c - I don't mind).

Has anyone had any experience with any output expansion chips (supporting PWM) that they would recommend? I know Dippy has created such a system - is that available for sale?

Thanks

Andrew

 

[Dippy]

Hi Andrew,

I'm sure I've seen mention of such a thing on this Forum within the last 6 months.
I'd be surprised if such a thing didn't exist as RGB is popular.
Have you searched Farnell?


My code was not PICAXE BASIC unfortunately.
Basically, I had a DO loop of length 100 so that RGB values were in percents.
Then load the separate RGB values into 3 variables.
Run the loop. Decrement the variables on each loop.
Have a conditional to test variable >0. If so have an output. If not deassert.
This is like a home-made PWM.
I didn't use the PIC PWM as it was a dedicated chip.

My own code added multiplexing and ADCing (overheat thermistor) and reading the USART buffer.
This allowed the PIC (18F25K20) to control 8x RGB+W channels.
4 'PWM' channels plus 8 lines for MOSFET control.
And serial control like an LCD firmware chip. (Address,%R,%G,%B,%W)
And reducing power in overheat condition and reporting back to Host.

I'm sure with a fast x-Y decoder you could multiplex even more.

The bit I was pleased about most was my serial read+process without flicker.
I interleaved the processing so that it was 'hidden' time-wise amonst the muliplexing. No gaps, no flicker.... feeling good...

I think each individual RGBW ran at about 3kHz , so fairly stable. But you could see the strobe effect if you really waggled your eyes. (Far less flickery than most car rear red sidelights!!).

I don't even know where it is now. I only did it as an exercise.

To try and do the same thing with an X2 PICAXE may be possible but I think you could only do one if you wanted it fairly flicker-free.

 

[Andrew Cowan]

I've made PWM controllers before with that method (PIC, not PICAXE) - although I haven't used serial on raw PICs before.

http://www.nxp.com/#/ps/ps=[i=48878]|pp=[t=pfp,i=48878] has a great range of I2C controlled multi channel LED drivers - I just need to pick one now!

Andrew

 

[Andrew Cowan]

http://uk.farnell.com/nxp/pca9685pw/ic-led-driver-rgba-28-tssop/dp/1854074?Ntt=PCA9685 Seems to be the best solution - and very reasonable at £1.33 (if you buy 10). I'll add some next time I place a Farnell order.

 

[techElder]

More detail on Andrew's post:

NXP I²C general purpose I/O
NXP I²C LED display control
NXP RTCs with I2C interface
NXP I²C temperature/voltage monitors

I've made PWM controllers before with that method (PIC, not PICAXE) - although I haven't used serial on raw PICs before.

http://www.nxp.com/#/ps/ps=[i=48878]|pp=[t=pfp,i=48878] has a great range of I2C controlled multi channel LED drivers - I just need to pick one now!

Andrew

 

[Simmicht]

Sparkfun has this cool widget, it is called BlinkM
http://www.sparkfun.com/products/8579

 

[geoff07]

These are neat. Red, Blue, Green in one blob for GBP 1.35 one off:

http://www.coolcomponents.co.uk/catalog/product_info.php?products_id=223

http://www.coolcomponents.co.uk/catalog/resources/YSL-R596CR3G4B5C-C10.pdf

 

[sniper887]

TLC59108 or TLC59116. They work similarly to the NXP chips and have, respectively, 8 or 16 channels of PWM.

 

[Hemi345]

There are these LEDs from Sparkfun. I believe they've been mentioned on this forum before.

https://www.sparkfun.com/products/12986

 

[JimPerry]

TLC59108 are available free from TI as samples - they are surface mount though I've got a few if you want them PM your address