On Thu, 4 Dec 1997 07:18:18 +1000 "Paul B. Webster VK2BZC" writes: > > For a "domestic" or amateur theatre application, two channels per >box >seems about right. For more channels one needs to have a three-phase >(don't know how this applies to the US) input which should be >available >in any suitable venue. We put four channels in one single phase box. It can drive four 600 watt 120 VAC loads with a 20 amp inlet. It's also available with a 30 amp inlet. See the Shoebox dimmer at http://www.dovesystems.com . > The question is whether 32 equal time steps is sufficient resolution >for your dimming algorithm. My bet is that it IS. To avoid false >triggering, you wish to avoid the first and last, perhaps first two >and >last two of these "slots". It might also be a good idea to work in >the >approximate 0.5 "tick" remainder in this counting scheme by using a >different base count on alternate interrupts, though this could >generate a minor DC offset. We used the capture/compare register on a 16 MHz 16c74a to get about 32,000 steps per half cycle. I originally tried 256 steps, but near the middle of the control (at 90 degree firing angle), the steps were very visible. Using capture/compare, however, does not seem to allow for PLL. The timer speed is set by the resonator. A table is converting DMX values to timer clicks for the compare. It appears that a PLL would require the table value to be multiplied by a correction factor. I'd rather avoid doing a 16 bit multiply inside the interrupt! Instead, I have two tables, one for 50 Hz and one for 60 Hz. The appropriate table is selected on pwer up. Harold