RGB/ PWM controllers

[beny1949]

everyone,

I am looking for a controller for a clock project i am doing that will allow me to get most colours and shades from an RGB LED. does anyone know an i2c or stand alone chip that will allow me to do this with a minimum of outputs?

the highest amount of outputs i can commit to the LED's is 3, or ideally it would go on the i2c bus.

I have seen a few controllers that fit the bill, but are not the easiest to mount, due to the size of the pads.

So, to summerise; i want a pwm controller, ideally on the i2c bus. This can either be through hole, or surface mount providing that its possible to solder without any speciast equipment.

Thanks very mucn,
Ben

 

 

[premelec]

I use DACs TI TLC5620 4ch 8 bit or TLC5628 8 bit 8ch - PICAXE sets DAC output voltage which drives base of transistor - emitter to resistor to ground to determine current - collector to LED and + V - makes a stable constant current drive with easy to use parts [DIP].

 

[hotcarrier]

premelec---would it be possible for you to post the software you used to drive the TI TLC5620?

 

[inglewoodpete]

It can be done with 4 pins: a PWM pin + 3 x colour drivers. Is that too many?

The circuit is fairly simple. Common anode LED example: the 3 colours are multiplexed on 3 pins. Each pin has a resistor to the base of a small signal NPN transistor. All emitters connect to 0v. Each collector connects to a resistor which in turn connect to each of the 3 cathodes of the multi colour LED. The common anode connection of the 3-colour LED connects to the PWM pin of the PICAXE, which supplies a 'chopped' supply rail to control the brightness of each colour.

 

[manuka]

It may be worth contacting (via me) my Kiwi mate Andrew &quot;Brightspark&quot;, as he's just finished a lengthy corporate artwork contract that emulates the rainbow colours of the NZ paua (&quot;PA-WA&quotabolone sea shell. All done with zillions of LEDs &amp; chained 08Ms + beefy PSUs. Apparently cost was incidental to achieving the desired effect, &amp; even Google's offerings would be impressed <A href='http://images.google.co.nz/images?hl=en&amp;q=paua&amp;ie=UTF-8&amp;oe=UTF-8&amp;um=1&amp;sa=N&amp;tab=wi ' Target=_Blank>External Web Link</a>...

 

[premelec]

My code won't copy - paste... basically I make the data up in w0 [symbol dataout] and then shift it out... on 08M 8x8 DAC

symbol dataout = w0
symbol clk = 1
symbol outpin = 2
symbol load = 4
symbol channel = b3
symbol range = b4

dataout = channel * 2 + range * 256 + value

for b8 = 1 to 12 'data bit string
pin1 = bit11 : pulsout clk 1
dataout = dataout * 2 'shift one bit
next b8

pulsout load,1 'set new value in DAC channel

Hope this helps... look at the TI data sheets to make it clearer...

 

[beny1949]

thanks very much guys, will definately use this in my project.

hopefully i will be able to post it on the picaxe projects site! when its up and running

Ben