> > I'm starting to think I'll stick with relays instead. You know
> > where you are with a switch

Y don't buy no ugly truck!!!! :-)

The failure to work is a temporary problem.
You are doing something wrong.
It's not something major (but might as well be until you find what it is).
Once you've found it you'll be very very very glad to have added triacs to
your arsenal of possible solutions.

Basically, triacs driven by MOCxxx zero crossing opto couplers work. That's
what they are designed to do. Somewhere along the line you've failed to
design the circuit to meet their needs. Once you do they'll work as
intended.

Lets try designing the input circuit.
MOC3041 datasheet http://www.isocom.com/datasheets/db91048.pdf

MINIMUM design drive current to trigger is 15 mA
DESIGN LED froward current in MOC3041 is 1.4V
(Both these values may be lower in practice but you MUST design to datasheet
guaranteed limiting values (or else).

Your series indicator LED is red so we'll allow it a 1.2v drop for now.

You want 15 mA MINIMUM input.
You show this from =%v.
If that is a hard supply feed, well and good.
If it is eg a PIC pin it will drop well below 5v at 15 mA.

So available drive is (5-1.4-1.2) = 3.2v
Available drive current is 3.2/200 =  16 mA.

IF the drive is solid 5v and IF the series LED is 1.2V drop max at 15 mA
then you have just enough drive (IF your 200 ohm resistor (+/- 5%) is not
+5%).

ie the input drive is JUST marginally adequate to meet design specs,
probably :-).
ie this probably ISN'T the probl;em, but for now add a bit more drive to be
sure.

For now

1.    Drive from a hard 5V supply.
2.    Ensure that the series LED lights when you apply 5V drive.
3.    Change R1 to 150 ohms (or even 120 ohms).(Abs max LED rating is 50 mA
so you have substantial safety margin)

Note that IF this part had worked reliably at 10 mA they would have sold it
as a MOC3042, so it will be somewhere in the 10 to 15 mA range that it
actually triggers reliably.


Now read what other people said about R2 and have fun.



        Russell McMahon

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