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Re: gEDA-user: OFF: triac

DJ Delorie wrote: 
I am designing a reflow oven and decided to use a triac to adjust
the power of the heater of the oven. I'm thinking of using an MCU
(ATmega8) to control the triac. However I lack knowledge on how to
drive a triac with an MCU. It must be opto coupled, since the MCU
will be connected to a host computer, thus, can't flow.


Been there, done that.  http://www.delorie.com/house/furnace/

The optos were MOC3011's, the alternacs (like triacs, but can handle
inductive loads too) were digikey Q2015L6-ND's.

MOC301x is ok for use in the US - in countries with 220 or 240VAC you will need MOC302x optos.

Are you trying to just turn the oven on and off, or modulate the power?

If its just on/off, just enable the opto as desired. The oven is a resistive load, so zero crossing is not essential. Few light switches do zero-crossing.

If you are trying to modulate the oven power, you will need to generate an interrupt off the zero crossing, and run a timer from that interrupt.
You (probably want to) enable for the same fraction of both the positive and negative half cycles.

john