----- Original Message -----
From: "Royce Simmons" <w2rbn@PRODIGY.NET>
To: <PICLIST@MITVMA.MIT.EDU>
Sent: Wednesday, November 21, 2001 3:33 PM
Subject: Re: [PIC]: Lamp Control


> Greetings All,
>
> I would like to control some 115VAC lamps from a PIC.  There are such a
lot of
> Triacs listed I can't make up my mind what to choose for the job.  I
suppose I
> need an optoisolator to drive the Triac but I don't know which one to
pick.
>
> The load would be 300 watts or less and if there is any zero crossing
software
> kicking around that would be nice to have.  Any and all suggestions on
what
> to do would be most appreciated.

I use the MOC3030 series optocouplers for automatic zero-crossing switching
and the MOC3020 series for phase control (dimmer) uses.
Basically use a triac that is rated a lot more than your current and voltage
and/or use an MOV to protect it from line spikes. Isolated tab versions are
better for safety. Heatsinks may or may not be necessary.
High-valued resistor/zener diode combination can be used on a PIC input to
detect the zero-crossing. Then you start counting from a zero-crossing,
pulse the optocoupler so it switches on the triac. The triac turns off by
itself at the next zero-crossing.
You probably need some inductor in series with the load if you want to be
able to listen to your shortwave radio at the same time because the triac
switching on creates high-frequency noise if there is voltage across it at
the time. This is unnecessary if you are using the zero-crossing turn-on
with a MOC3030.

/\/\/\/*=Martin

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