Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!sun-barr!newstop!exodus!oobleck.Eng.Sun.COM!bender From: bender@oobleck.Eng.Sun.COM (Michael Bender) Newsgroups: sci.electronics Subject: Re: Light Dimmer Message-ID: <3450@exodus.Eng.Sun.COM> Date: 27 Nov 90 01:50:51 GMT References: <2570007@hppad.HP.COM> Sender: news@exodus.Eng.Sun.COM Organization: Sun Microsystems, Mt. View, Ca. Lines: 28 In article <2570007@hppad.HP.COM> lindner@hppad.HP.COM (Steffen Lindner) writes: >I would appreciate it if any of you could help me with the following: > >Background Information: >I am trying to built a digitally controlled light dimmer. This system should >control about 24 individual channels. Each channel consists of one or more >lights (incandescent). The maximum load on each channel is about 3A. The >dimmer must allow a minimum of 16 brightness settings (more would be better). >The system uses a microcontroller for I/O and triggering the TRIACs. All >seems well except that I have not been able to come up with a simple, cost >effective solution to reduce (eliminate) noise. A few years ago I built an 8-channel digitally-controlled dimmer. I used an 8749 for the CPU, and Intel 8254 (right number??) counter/timer chips to actually control the firing of the Triacs. A zero-cross detector would feed the CT chips' reset (clear?) input, a higher-frequency clock would actually clock the CT chips, and the 8749 would load values into the CT registers, which determined the duty cycle of the Triac-controlled load. It worked quite well. The CT chips would be used in auto-reload mode, so that every time they got a reset (clear??) from the zero-cross detector, they would start counting again; after a programmed number of counts, they would trigger the Triac and it would turn on for the remainder of the cycle. mike -- Won't look like rain, Won't look like snow, | DOD #000007 Won't look like fog, That's all we know! | AMA #511250 We just can't tell you anymore, We've never made oobleck before! | MSC #298726