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PICList Thread
'AC power control with 12C671'
1998\12\10@145226 by Toby Stensland

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I would like to control how much power is delivered to some Christmas lights, using a PIC12C671.  Initially, I was going to detect AC zero crossings, wait for my desired phase delay, then fire an SCR (phase control, repeat every half cycle).  The only problem with this is that I am a PIC newbie and would rather find a method with simpler programming.

My question is are there simpler ways to control the power to my christmas lights with a PIC?  The reason I ask, is that in our lab there is a very simple device to vary the power delivered to a AC motor (universal vacuum type motor).  It consists only of a potentiometer (100k, to select voltage), a red disc capacitor marked V130LA10A, a orange capacitor inductor looking thing marked .22-200 DC, a small resistor looking thing (diode maybe?), and a triac (SK3659 or MAC15-8).  I don't know how this works, but whatever it does, must not require the timing that I would need for phase-control.


Toby Stensland
spam_OUTtobyTakeThisOuTspamstensland.com                   http://www.stensland.com

1998\12\10@145848 by paulb

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Toby Stensland wrote, without linefeeds:

> in our lab there is a very simple device to vary the power delivered
> to a AC motor (universal vacuum type motor).  It consists only of a
> potentiometer (100k, to select voltage), a red disc capacitor marked
> V130LA10A,

 MOV = Metal Oxide Varistor = surge supressor.

> a orange capacitor ... marked .22-200 DC, a small resistor looking
> thing (diode maybe?),

 Likely a Diac - trigger device with threshold somewhere in the 8 to
30V range.

> and a triac (SK3659 or MAC15-8).

 Standard light dimmer circuit.
--
 Cheers,
       Paul B.

1998\12\10@154245 by Richard A. Smith

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On Thu, 10 Dec 1998 12:37:21 -0700, Toby Stensland wrote:

>My question is are there simpler ways to control the power to my christmas ligh
ts with a PIC?  The reason I ask, is that in our
lab there is a very simple device to vary the power delivered to a AC motor (uni
versal vacuum type motor).  It consists only of a
potentiometer (100k, to select voltage), a red disc capacitor marked V130LA10A,
a orange capacitor inductor looking thing
marked .22-200 DC, a small resistor looking thing (diode maybe?), and a triac (S
K3659 or MAC15-8).  I don't know how this
works, but whatever it does, must not require the timing that I would need for p
hase-control.

That's basically an analog version of what you want to do with the PIC.  You wil
l probally find that the capacitor is tied to the gate
of the triac and charges through the pot.  When the cap reaches Vg of the triac,
it discharges and turns on the triac.  Repeat
cycle.

I don't know if it will be any eaiser code wise but you might look into zero cro
ssing power control.  Basically instead of turning the
ac on at a particular phase point you turn the AC off for x cycles and then on f
or x cycles.  Also has the advantage that it does
not generate any EMI since all the switching is done at the zero cross.



--
Richard A. Smith                         Bitworks, Inc.
.....rsmithKILLspamspam@spam@bitworks.com               501.521.3908
Sr. Design Engineer        http://www.bitworks.com

1998\12\10@155915 by Michael J. Ghormley

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Toby Stensland wrote:

<snip>
> It consists only of a potentiometer (100k, to select voltage), a red disc capa
citor marked V130LA10A,<snip>

The V130LA10A is a MOV (Metal Oxide Varistor).  It is a transient voltage surge
supressor and is
usually used across an AC power line.  It has a nominal breakdown voltage of 130
AC (RMS) or 175VDC.
It handles about 38 joules of energy.  The 10A at the end is supposed to be an a
mperage rating, but I
could never make it fit the specs.  Anyway, a 10A handles approximately half the
current of a 20A, etc.

Michael

*************************************************************************
When the way of the Tao is forgotten, kindness and ethics must be taught.
Men must learn to pretend to be wise and good.  --  Lao Tzu
*************************************************************************

1998\12\10@155925 by Zonn

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On Thu, 10 Dec 1998 12:37:21 -0700, Toby Stensland <tobyspamKILLspamSTENSLAND.COM> wrote:

>I would like to control how much power is delivered to some Christmas lights, using a PIC12C671.  Initially, I was going to detect AC zero crossings, wait for my desired phase delay, then fire an SCR (phase control, repeat every half cycle).  The only problem with this is that I am a PIC newbie and would rather find a method with simpler programming.
>
>My question is are there simpler ways to control the power to my christmas lights with a PIC?  The reason I ask, is that in our lab there is a very simple device to vary the power delivered to a AC motor (universal vacuum type motor).  It consists only of a potentiometer (100k, to select voltage), a red disc capacitor marked V130LA10A, a orange capacitor inductor looking thing marked .22-200 DC, a small resistor looking thing (diode maybe?), and a triac (SK3659 or MAC15-8).  I don't know how this works, but whatever it does, must not require the timing that I would need for phase-control.

Nope, sorry to disappoint.  But it DOES use the timing you would need for your
project.

The diode thing is really a DIAC which is really kind of a voltage controlled
switch.  Above a certain voltage it turns on.  It's also bi-directional.  The
DIAC will behave the same regardless of which way you supply the voltage.

The circuit is setup so that as the voltage from the AC rises, it eventually
hits a point where the DIAC is triggered on.  This in turn fires the TRIAC for
the rest of the cycle, after which point the Triac turns itself off, and the
whole thing starts over on the opposite edge of the cycle.

The variable resistor is used to change the voltage across the DIAC so that a
higher or lower line voltage is needed to trigger the DIAC.  This in turn cause
the DIAC to trigger later to earlier in the cycle, for a dimmer to brighter
light.  So the timing is all built in, using the level of the AC cycle as the
trigger point/timing -- everything happens 120 times a second.

Capacitors and inductors are thrown in to keep the whole unit from acting too
much like a wide band AM noise generator.  (Just try using an AM radio near one
of these things!)

-Zonn

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1998\12\11@010507 by Harold Hallikainen

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On Fri, 11 Dec 1998 06:55:13 +1000 "Paul B. Webster VK2BZC"
<.....paulbKILLspamspam.....midcoast.com.au> writes:

>
>  Standard light dimmer circuit.


       The standard light dimmer circuit, of course, is doing phase
control timing using an RC network.  Although it'd be terribly nonlinear
and probably vary unit to unit, it seems that one could "remote" a
hardware store light dimmer by using an opto coupler that has a CDS
opto-resistor as the output device.  Substitute it for the pot in the
timing circuit, then vary the LED current (possibly using the PWM output
of a PIC).
       In our light dimmer products (at http://www.dovesystems.com), we
use the PIC to drive an opto triac at the appropriate point in the AC
cycle (using the capture compare register to generate an interrupt at the
appropriate time), or have a PIC do DMX to analog conversion, then drive
analog comparators that are comparing the analog with a negative going
ramp synced with the AC line.


Harold




Harold Hallikainen
EraseMEharoldspam_OUTspamTakeThisOuThallikainen.com
Hallikainen & Friends, Inc.
See the FCC Rules at http://hallikainen.com/FccRules and comments filed
in LPFM proceeding at http://hallikainen.com/lpfm


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