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Done this (many times) as it is somewhat my 'stock in trade' as it
were...i.e. controlling AC motors and heating elements of around 1 kW  by
switching 'off' the incoming AC at a precise point in the phase.

To accomplish this, the zero crossing point need be precisely derived, as
this is the reference from which the phase switching is determined.
The actual switching is handled with a triac (BT139 to BTA 25/26 depending
upon the load requirements) which in turn is driven by a random phase
opto-coupler with triac output (MOC3020)

A good, simple DIY zero crossing circuit I have applied in the past can be
found here:

http://www.dextrel.net/diyzerocrosser.htm

Remember to add a 'snubber'  (resistor and cap) to the triac if the load is
inductive, (should you decide to go this route![?])



On Fri, Jun 14, 2013 at 3:39 PM, Denny Esterline <desterline@gmail.com>wrot=
e:

> My apologies, I somehow completely ignored the turn _OFF_ at any position
> in the cycle requirement. My brain just substituted ON... (Darn brain
> anyway)
>
> -Denny
> --
> http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive
> View/change your membership options at
> http://mailman.mit.edu/mailman/listinfo/piclist
>



--=20
Perry Curling-Hope

Research and Development

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