RGB driver with microcontroller.

IIRC Elektor magazine has in the past published uC controlled RGB projects.

Pretty much any microcontroller could be programmed to do this task - the solution would be to do the PWM in software, rather than using the on-chip PWM hardware (which, as you noticed, may not exist).

The easiest way I find to do this is by running the PWM in the main loop. The frequency may vary somewhat as other events happen, but on average this will provide adequately fast PWM for visible LED color applications. As an example:

/* Physical outputs to LEDs (syntax is processor/compiler dependent) */ sbit RedLed P1^1; sbit GrnLed P1^2; sbit BluLed P1^3;

void main(void) { unsigned char Red, Grn, Blu, Pwm;

while(TRUE) { /* Do something to acquire values for Red, Grn, and Blu (0..255) */ Red = GetPotentiometer(1); Grn = GetPotentiometer(2); Blu = GetPotentiometer(3);

/* Do PWM processing */ Pwm += 1; /* wraps back to 0 after 255 */ RedLed = (Pwm > Red) ? FALSE : TRUE; GrnLed = (Pwm > Grn) ? FALSE : TRUE; BluLed = (Pwm > Blu) ? FALSE : TRUE;

} // End of main loop }

Note that this method can have a problem. If something happens in the main loop (such as processing a received command) that takes significant processor time (even a few milliseconds), there will be a noticeable perturbation in the brightness of the LEDs. The most reliable way around this is to place the PWM logic in a timer service routine, rather than in the main loop.

The downside of using the timer method is that the timer must trigger fairly rapidly in order to keep the PWM frequency high enough to prevent visible strobing of the LEDs (10 kHz or so), and the additional overhead required by the interrupt service may use up too many processor cycles. This can be mitigated by decreasing the resolution of the PWM from 1/256 to, perhaps,

-- Mark Moulding

if you are controlling all 3 colours then a global brightness control is an unnecessary complication (and probably wont work as expected)

something like an attiny24/44/84 should suffice for both pwm & analog inputs