Re: fading RGB lamps
- From: DJ Delorie <dj@xxxxxxxxxxx>
- Date: 24 Oct 2007 11:16:32 -0400
I've done this with a tiny MCU using pulse dithering. It did exactly
the effect you want, too. You need an MCU, three drive transistors,
and your lamps.
Note: an MCU three PWM modules can do this in hardware, the software
just programs the PWM counts as needed.
What is pulse dithering?
Consider pulse width modulation - for every N clock ticks, the output
is on for the first M of them, and off for the remaining (N-M) of
them. Your period is limited to 1/Nth of the clock frequency, though.
For pulse dithering, you spread the M "on" ticks evenly throughout the
N clock ticks, so your "period" is effectively the same as the clock
frequency. This lets you have more precision in your "brightness"
setting, while using a slower clock speed. Of course, your real
precision is still limited to clock/60Hz.
The algorithm is amazingly simple, and best implemented in an assembler
interrupt routine (due to the use of carry):
int setting;
int count;
interrupt()
{
count += setting;
if (carry)
light_on();
else
light_off();
}
A larger setting will overflow more often, causing the light to be on
more often.
You may even get away without conditionals:
mov #0,bits
add count_red, setting_red
rolc #1,bits
add count_green, setting_green
rolc #1,bits
add count_blue, setting_blue
rolc #1,bits
mov bits, gpio_port
.
- References:
- fading RGB lamps
- From: angel . yves
- fading RGB lamps
- Prev by Date: Re: Someone needs to inform the BBC...
- Next by Date: Re: AC amplitude modulation for inductive loads
- Previous by thread: Re: fading RGB lamps
- Next by thread: Re: fading RGB lamps
- Index(es):
Relevant Pages
|
