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'[PIC] [EE]: Using DC to control AC.'
2002\08\12@001549 by Tony Harris

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hi,

I'm trying to figure out how to use my PIC to control an AC voltage.

For example:

I have a fountain that las low voltage AC lights, and a set of low voltage
AC pumps (say 3 lights and 3 pumps, all run off of 12V AC, max all three
lights and all three pumps would be on.  The pumps are rated at 3.6A).  I
want to create a program to turn on and off lights and the pumps at my will.

Obviously, my PIC circuit is a DC circuit.

So, can anyone suggest what I might be able to do in order to control this
AC voltage?  I don't need to funnel a lot of power, 60 watts (actually 43.2,
but increasing a bit for safety) per "switch".

So, the AC side would be 12V AC, the DC would be 5V DC for the PIC and
either the LCD or perhaps LED's to indicate what is on and off.

Any resources, sites, small samples would be most appreciated.

-Tony

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2002\08\12@005034 by kben

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Hi Tony,
Try the data sheet for the MOC3011, I had a PIC controlling several
60 watt bulbs with an opto-isolator and triac.
support.tandy.com/support_supplies/doc66/66249.pdf
I believe figure 8 was the circuit I used.
I am sure some of the EE's will chime in.
I am a programmer not an EE :)

Good luck,
Kevin

{Quote hidden}

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2002\08\12@005257 by Dave Gomez

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How about using relays, they are electrically isolated on each side, or
opto-isolators, rated for ac on one side.


Dave gomez

On 8/11/02 9:07 PM, "Tony Harris" <spam_OUTtonyTakeThisOuTspamELROYNET.COM> wrote:

{Quote hidden}

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2002\08\12@010111 by adam

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Good call...

...be careful about polarity, though (if you go the opto-isolater
route)...

> -----Original Message-----
> From: .....adam-requestKILLspamspam@spam@viratech.com [adam-requestspamKILLspamviratech.com] On
> Behalf Of Dave Gomez
> Sent: Sunday, August 11, 2002 11:51 PM
> To: .....PICLISTKILLspamspam.....MITVMA.MIT.EDU
> Subject: Re: [PIC] [EE]: Using DC to control AC.
>
> How about using relays, they are electrically isolated on each side,
or
{Quote hidden}

three
> > lights and all three pumps would be on.  The pumps are rated at
3.6A).
> I
> > want to create a program to turn on and off lights and the pumps at
my
> will.
> >
> > Obviously, my PIC circuit is a DC circuit.
> >
> > So, can anyone suggest what I might be able to do in order to
control
> this
> > AC voltage?  I don't need to funnel a lot of power, 60 watts
(actually
> 43.2,
> > but increasing a bit for safety) per "switch".
> >
> > So, the AC side would be 12V AC, the DC would be 5V DC for the PIC
and
{Quote hidden}

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2002\08\12@034145 by john

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Hi,

If you dont mind spending a bit of money, there is a product made by the
company called Opto 22 called a solid state switch. 3-24 v dc in, controls up
to 240V ac at a selectable current rating ( device dependent). These are
triacs which have an opto coupler built in, so there is less contact noise
etc.

On the other hand, a nice automotive style relay with spade terminals and a
good old 2n2222 should work fine.

Regards
John

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2002\08\12@074456 by fred jones

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If they still carry it, go to RadioShack and buy an MOC3010 optoisolator.
It has a triac output.  It doesn't handle the current you need but you use
that to switch a larger triac that will handle your needs.

Back about 20 years ago when I was in school I wanted to build a light
controller to sequence incandent light bulbs.  I asked several of my
teachers and I got either, I don't know, or use relays.  I knew neither of
those were good answers.  I happened to be browsing the blue "276" series at
RadioShack when I saw the MOC3010 and it had a schematic on the back of the
package showing how to connect it up to a triac.  It works great, you can
switch 110 volt 60watt light bulbs on and off with a 5V signal and nothing
to wear out.
Good luck,
Fred


{Quote hidden}

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2002\08\12@074700 by Tony Harris

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To all that have replied:  Thank you for your ideas.  I had considered
"standard" relays, but I would like a "quieter" solution, I'm thinking of
the opto isolator, or the SSR from the company opto-22.

Kevin B.: I too come from the same type of background - and am trying to
learn some of the intracacies of circuit design :)

It looks like the MOC3011 would be a good device.  I see in figure 8 the
Triac connected to the chip.  do you happen to remember which one you used?
I would like to take a look into this option a bit more.

John W.: Have you used these SSR's from opto-22 in the past?  what kind of
cost are they?  are they loud, quiet, what?  Would I need to use a triac
with them, or would it be a complete solution?

Thanks in advance!

-Tony


{Original Message removed}

2002\08\12@091406 by Tony Harris

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New question:

I have been looking up triacs, and I see there are MANY to choose from.

Most of the ones I have found are rated at 400V, xA, ymA.  I assume as long
as on the mA side I remain below what my MOC30xx can handle, I'm pretty much
good to go.

But, I have noticed there is an option for isolated and non-isolated.

Can someone tell me what the difference is and which one would be more
appropriate?  I'm still trying to find more info on the difference between
those key types of triacs, but I haven't yet - most docs have just talked
about the basic principal of triacs.

-Tony
{Original Message removed}

2002\08\12@093040 by Russell McMahon

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> Most of the ones I have found are rated at 400V, xA, ymA.  I assume as
long
> as on the mA side I remain below what my MOC30xx can handle, I'm pretty
much
> good to go.

The TRIAC should be rated at a current handling capacity well above your
load. For your application, most will be.

As you say, gate current should be less than the MOCxxxx can handle. This
will generally be the case. You will need to do a little design from the
datasheet to size the gate resistor.

> But, I have noticed there is an option for isolated and non-isolated.
>
> Can someone tell me what the difference is and which one would be more
> appropriate?  I'm still trying to find more info on the difference between
> those key types of triacs, but I haven't yet - most docs have just talked
> about the basic principal of triacs.

Isolation in this concept is a mechanical and not an electronic principle.
"Isolated" just means that the metal tab is not electrically connected to
any part of the TRIAC's circuitry. It is an excellent idea to use isolated
devices for experimenting and when the design is not critical. It stops you
accidentally connecting things to your circuit accidentally. An isolated
TRIAC will almost always have a slightly higher thermal resistance from
internal die to case so it will nit be able to be operated at quite as high
a power level but this will not bother you here.

I recommend an isolated TRIAC for your purpose if price is not extremely
different. 9Usually only slightly dearer).

If there are "snubberless" versions these are also worthwhile for beginners.

Note that you MAY need a modest heatsink on the TRIAC depending on current
level.- consult data sheet for specs.

If driving lightbulbs do note that inrush current at turn on is many times
the operating current. Not a problem usually unless you are switching quite
rapidly but wit time for bulb to call OR if TRIAC is rated close to on
current.




       RM

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2002\08\12@094303 by john

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Hi, I have used the 25A/45A 250V SSR's and they work well.
They cost a bit,  $20/25 for you ?
The lower rating ones are possibly alot cheaper

they come with 4 stud terminals .. you put 5V on the 2 input studs and it
will switch the output for you across the 2 output studs( think of it as a
switch, you use it in the same fashion).
They are triacs, with opto-couplers, and therefor would not make an audible
click on or off. Electrically, they are zero-crossing and thereby eliminating
the associated turn on spike when switching on a voltage say mid cycle.
There is also alot of talk about switching AC signals just past the
zero-crossing point.. and i dont care to get involved with that issue :)

If youre up to the task, a simple MOC3020 or similar ( zero-crossing or non
zero-crossing version maybe) opto linked with 2 resistors to a BT 139 triac
.. and bobs your uncle ... not quit the $25 cost of the SSR from opto 22 ...
but then again .. it is nicely housed in a block of resin with heatsink,
mounting holes  and screw down tags.... just perfect for that York enclosure
your going to put on the wall with the Pic etc ? .......

Regards

John

On Monday 12 August 2002 01:49 pm, you wrote:
{Quote hidden}

> {Original Message removed}

2002\08\12@105049 by Dale Botkin

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On Sun, 11 Aug 2002, Tony Harris wrote:

> I'm trying to figure out how to use my PIC to control an AC voltage.

Been through this exact same exercise.  See:

http://www.botkin.org/dale/yardlites/yardlites.html

I use two MOSFETs to switch the low-voltage AC side, derive the PIC DC
power from the AC as well.  Works like a charm.  I'm currently looking at
adding two more MOSFETs in parallel to reduce the heat, but then I'm
switching over 100W.  I've had this in use for about a month or so now,
works perfectly.  Big tip of the hat to Dave Dilatush for the idea.

Dale

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2002\08\12@110548 by Alan B. Pearce

face picon face
>But, I have noticed there is an option for isolated and non-isolated.

>Can someone tell me what the difference is and which one would be more
>appropriate?  I'm still trying to find more info on the difference between

Without looking at the data sheet for the devices concerned, I suspect the
difference is if the tab of the TO-220 package is isolated from the chip or
not. If not then you will probably need electrical isolation from the
heatsink. If it is isolated, then you MAY get away with not isolating the
package from the heatsink, but I would still expect to see a warning inside
the case that the heatsink could be electrically live.

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2002\08\12@114312 by Herbert Graf

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{Quote hidden}

       Look up triacs and opto-couplers, they are perfect for this sort of
application. TTYL

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2002\08\12@121050 by Dale Botkin

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On Mon, 12 Aug 2002, Herbert Graf wrote:

>         Look up triacs and opto-couplers, they are perfect for this sort of
> application. TTYL

For the low voltage stuff, I'd go with the MOSFETs instead.  I have found
it to be a perfect solution.  Very little power wasted, parts are pretty
cheap, you can use logic level MOSFETs to avoid needing driver transistors
and such.

Here's the old thread:
http://www.piclist.com/techref/postbot.asp?by=thread&id=Switching+low%2Dvoltage+AC&tgt=_top&key=%22Switching+low+voltage+AC+%22&from=

My original post:
http://www.piclist.com/techref/postbot.asp?by=time&id=piclist\2002\02\18\114448a&tgt=_top

First mention of using MOSFETs:
http://www.piclist.com/techref/postbot.asp?by=time&id=piclist\2002\02\18\180632a&tgt=_top


Dale

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2002\08\12@122449 by Harold M Hallikainen

picon face
       As others have suggested, you can use an opto isolator to drive a triac.
This is what we do in our Shoebox series of dimmers
(http://www.dovesystems.com/BuildPage.php?page=shoebox). These are used
in applications similar to yours by Atlantic Fountains (see
http://www.atlanticfountains.com/). For small quantity stuff, it's
probably a lot simpler (and safer) to just use a solid state relay. An
SSR has the same circuitry, but it's all put together for you. There are
some inexpensive SIP SSRs (for example, see
http://www.crydom.com/assets/ssrpcb/cx.pdf and
http://www.digikey.com/scripts/us/dksus.dll?Detail?Ref=65203&Row=122195).


Harold


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2002\08\12@145510 by Mike Singer

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Maybe I'm too late with my message,
I was at Black Sea coast for some days.
Are you sure 12V lights and motors are really AC?
If no, why not feed them with DC?
There were threads on DC/DC converters.

1. Feed your project with unstabilized 12DC.
2. Add 12V DC to 12V DC PIC-regulated converter.
   (approx $5 components)
3. Split project into channels. Feed each channel with
   PIC-regulated converter.
4. Get lamps brightness and fountain pumps power
   be correlated with music using PIC ADC.
5. Use different lamp colors, place, if possible, a lamp
   inside a water jet.
6. Add motors to rotate water jets, and so on.

Do this one step at a time. You may stop at each
step, with the result not worse then with former AC project.

Sorry, If I've missed something.

Mike.

Tony Harris wrote:
> I'm trying to figure out how to use my PIC to control an AC voltage.
>
> For example:
>
> I have a fountain that has low voltage AC lights, and a set of low
voltage
> AC pumps (say 3 lights and 3 pumps, all run off of 12V AC, max all
three
> lights and all three pumps would be on.  The pumps are rated at 3.6A).
I
> want to create a program to turn on and off lights and the pumps
> at my will.
>
> Obviously, my PIC circuit is a DC circuit.
>
> So, can anyone suggest what I might be able to do in order to control
this
> AC voltage?  I don't need to funnel a lot of power, 60 watts
> (actually 43.2,
> but increasing a bit for safety) per "switch".
>
> So, the AC side would be 12V AC, the DC would be 5V DC for the PIC and
> either the LCD or perhaps LED's to indicate what is on and off.
>
> Any resources, sites, small samples would be most appreciated.

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2002\08\12@211807 by kben

picon face
Hi Tony, the opto-isolator I used was
Digikey part # MOC3011M-ND
I sent ann email to the PICList at the time
and Bob Blick said that the triac was a non-critical
part. Bob suggested using a triac from Radioshack.
I think I order the triac from Digikey. T2800 rings
a bell, but I could not find it at Digikey ?
Just a reminder, I was strickly switching 120V 60W
light bulbs, your needs maybe different than mine.

Good Luck,
Kevin

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