At 08:40 PM 4/12/02 -0400, you wrote:
>I knew you were going to ask that...  :)
>Basically I want to build:
>
>http://www.elwire.com/faq/seq/seq5/index.html
>
>But I don't have a schematic nor the thing itself to examine.  EL wire
>glows then you put a 120v current thru it; 4-8khz is the brightest, but
>60hz will produce some light.  What you normally do it get a "driver"
>(battery to 120vac / someKhz, they vary) and connect the EL wire to it.
>  The aforementioned circuit uses a little PIC to switch the connected
>driver's output to one of five EL wires using triacs.a
>
>I looked up the triac specs ("L201E3" into google) and it seems more or
>less identical to the one I'm using.  It looks like the triacs are being
>driven directly by the PIC pins thru 470 ohm resistors.  So I wired up
>what I think is the equivalent circuit (I have EL wire and a driver, not
>the same as theirs, but its 120vac at 1Khz) and a triac and no go.
>
>In their circuit I don't understand what the diode is for (polarity
>protection for the DC to power the pic?).

Yes, that's all. It's just in series with the input to the regulator.


>It looks so simple yet I can't get the equivalent to work at all and I'm
>running out of time and getting kind of frantic about it (10 days before
>an art exhibition happens) ...

One problem right off- the triacs spec'd on that web page are guaranteed
to trigger at 3mA in ALL 4 QUADRANTS. It looks like the circuit uses the
"tough" 4th quadrant (gate +ve MT2 -ve). The Motorola/Onsemi "sensitive gate"
triacs need 3.3 times as much current to trigger (10mA) in that quadrant
and 5mA in the other quadrants. You could reduce the gate resistor and
consider changing it so the gate gets -ve drive. The +5 would then be
the common for the high voltage supply and you'd supply a negative voltage
to power the unit. Low would be ON, high OFF. This is the preferred way
to drive a triac, as it avoid Q4. I haven't looked at this in a lot of detail,
so be  careful. That would reduce the current requirements to only 5mA,
and you could simply use 240R resistors rather than the 470R. The PIC
should be able to drive the 10mA too, but you might have to fiddle with
the  resistor value to get it close enough to right, and there are issues
with triac gates under some conditions.

This way of using a triac is a little odd, but I think I see what they
are doing.

>Anyone?  Anyone?
>
>Should I just order a bunch of optoisolator triac drivers (MC3010) and
>be done with it?

You'd still have to pay attention to the drive current. If the isolation
is worth something to you , the extra cost might be worth it, otherwise
there isn't much advantage that I can see.

Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
speff@interlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com
9/11 United we Stand

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