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'220volt lamp matrix'
1999\11\09@082748 by Gabriel Callao

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Hi all,

   I have to make a 220volt lamp matrix of 7x5 lamps=35 lamps. With it, I
will be able to "draw" different letters. If they were leds, I would only
need to control a row (or a column) and do refreshment in every other column
(or row).
   Does anyone know how to control all these lamps using the fewer lines of
a Pic micro, and also fewer triacs ?


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1999\11\09@090459 by Michael Rigby-Jones

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part 0 3452 bytes
<P><FONT COLOR="#0000FF" SIZE=2 FACE="Arial">I suspect you may have some problems multiplexing incandscent lamps due to the high thermal inertia of a lamp filament.&nbsp; A lamp will take a significant amount of time to turn on to full brightness, this will severly limit the speed that they can be switched at.&nbsp; Also thermal stress will cause premature lamp failure.&nbsp; You may be able to overcome both of these by ensuring a continuous low current flows through the lamps, keeping the filaments hot (but not incandescent).&nbsp; However, this will make matrix switching somewhat tricky. </FONT></P>

<P><FONT COLOR="#0000FF" SIZE=2 FACE="Arial">You could avoid multiplexing and use 35 triacs controled by a few shift registers cascaded together.&nbsp; If the light bulbs aren't high power (&lt;60 watts) you could use TO92 cased triacs to save space.</FONT></P>
<UL>
<P><FONT SIZE=1 FACE="Arial">{Original Message removed}

1999\11\09@115906 by wwl

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On Thu, 11 Nov 1999 10:18:53 -0300, you wrote:

>Hi all,
>
>    I have to make a 220volt lamp matrix of 7x5 lamps=35 lamps. With it, I
>will be able to "draw" different letters. If they were leds, I would only
>need to control a row (or a column) and do refreshment in every other column
>(or row).
>    Does anyone know how to control all these lamps using the fewer lines of
>a Pic micro, and also fewer triacs ?
>
>
>__________________________________________________
>Do You Yahoo!?
>Bid and sell for free at http://auctions.yahoo.com
Assuming they aren't very big lamps, you may be able to use
opto-triacs like the very cheap MOC3020 to drive each lamp.
You could wire all the LEDs of the MOC3020's in a 5x7 matrix, and
send a firing pulse to those required to be on early every  mains
half-cycle. You could drive them directly from 12 PIC pins. You could
get this down to 8 pins if you used a HC138 as a row decoder.
You could even do selective dimming with this arrangement - fading-in
the lamps would make them last significantly longer.

1999\11\09@143224 by l.allen

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Gabriel Callao wrote...

> Hi all,
>
>     I have to make a 220volt lamp matrix of 7x5 lamps=35 lamps. With it, I
> will be able to "draw" different letters. If they were leds, I would only
> need to control a row (or a column) and do refreshment in every other column
> (or row).
>     Does anyone know how to control all these lamps using the fewer lines of
> a Pic micro, and also fewer triacs ?
>
I would consider rectifying the 220v AC to DC and then switching in a
matrix using IGBTs.
The High Side switches would be N channel as would the Low Side
switches. The High Side gate drive will float and obtain their power
from small high frequency transformers, the gates being triggered by
opto couplers.
Thats 12 IGBTs and driver ccts.

I am presently in the final design stages of a variable freq 230vac
source and this is the technique I have chosen.

Note that the supply to the lamps will at best be muxed at 5:1 so
brightness may be a problem.

There are some seriously dangerous voltages and high insantaneous
currents present so beware. (Standard warning for newbies who might
not fully understand the dangers involved). Kids... dont try this at
home.
_____________________________

Lance Allen
Technical Officer
Uni of Auckland
Psych Dept
New Zealand

http://www.psych.auckland.ac.nz

_____________________________

1999\11\09@150655 by paulb

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Lance Allen wrote:

> I would consider rectifying the 220v AC to DC and then switching in a
> matrix using IGBTs.

 I was going to suggest Thyristors, but bit my tongue.  Why?  Well, you
must multiplex so that each lamp is pulsed at least 50 times per second.
For the same reason as you always requite a minimum multiplex frequency
of this order.  This means that for five rows, each row is driven for
4 milliseconds.  Note that your rectified DC must also be smoothed so
all rows get the same voltage!

 IGBTs it is!

 Also note - one diode in series with each lamp - this is the secret
to multiplexing incandescent lamps!

> Note that the supply to the lamps will at best be muxed at 5:1 so
> brightness may be a problem.

 Indeed.  Let's look at this.  At full brightness, the lamp has a
certain resistance.  Using rectified DC however, we are driving at 1.4
times the voltage, thus twice the power.  However, it is on at a 1 in 5
duty cycle, so receiving overall 40% full power.  If this is acceptable,
(it may be, to extend lamp life) then go ahead.

 Otherwise consider - using 110V lamps on the 220V supply, using the
PWM control to limit their full brilliance (and along the way,
compensating for actual power line voltage by measuring same).

 Also, you can consider "pre-emptive" filament warming of lamps at
least 1 second *before* they are switched to full brilliance, using
about 10% of full PWM time.  In other words, perform your animation one
second in advance!

 In case it's not obvious, this is a full-fledged PWM application and
also, if the micro "hangs" in mid-multiplex there's going to be
considerable smoke released unless you put in place a few protective
measures.  The WDT at *no* prescale is an obvious one to start, as is
using pull-ups to default to lamp drivers *off*.

> There are some seriously dangerous voltages and high insantaneous
> currents present so beware. (Standard warning for newbies who might
> not fully understand the dangers involved).  Kids... dont try this at
> home.

 Yep.  That's pretty obvious too!  It's a pretty exciting design.
--
 Cheers,
       Paul B.

1999\11\10@074925 by ShadeDemon

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Gabriel Callao wrote:
>     Does anyone know how to control all these lamps using the fewer lines of
> a Pic micro, and also fewer triacs ?
 Using a 5x7 matrix?  Use 5 chained serial latches and
either logic level triacs or high current latches, like the
5895.  If you don't have/use logic level triacs, be careful
of the quadrant you use the triacs in (trigger current
direction vs the AC current direction) because non-logic
level triacs often have 1 of the quadrants needing a much
larger trigger current, like 2-4 times more.  So use the
trigger current direction that is least for both directions
of AC to stay out of the bad quadrant.  Usually means that
you need to take the gate negative to neutral tho, so look
at using a -5V to neutral supply as your logic ground and
sinking the triac gates to that -5V.  Then just use optos on
your input (and any output) if you need to hook up to normal
+5v/gnd referenced outputs..
 Give up on the less triacs though.  Takes 8 times the lamp
and scanning and you end up normally being cheaper to just
use the triacs.  Haven't even found a good way to be able to
scan the triac gates and cut the number of latches yet.
(5895A's are like $4 each, 8 per driver.)  Triacs take too
much gate current for too long to turn on, so if you try and
scan then by the time you hit the last row, you're well into
the cycle and that cuts lamp life noticably.  Not a prob if
its just you, or just for testing, but in a sign, people get
mad if they have to change bulbs much..  Been looking for a
good way to scan them for a long time, and save that other
$25 worth of latching drivers if possible, so I am open to
ideas if you get a brainstorm tho..

1999\11\10@101637 by wwl

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On Wed, 10 Nov 1999 07:56:18 -0500, you wrote:


>  Give up on the less triacs though.  Takes 8 times the lamp
>and scanning and you end up normally being cheaper to just
>use the triacs.  Haven't even found a good way to be able to
>scan the triac gates and cut the number of latches yet.]
Use optocouplers and matrix their LEDs
A high-ish scan rate for the LEDs avoids too much delay into the mains
cycle. This would be no problem to do with  the PIC.
Lamp pre-heat and softstart would be pretty easy to do.

1999\11\10@102511 by Graham North

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How is it possible to do lamp pre-heat and softstart?

I have a similar controller and would like to know how to give the bulbs an
"easier" life.

Graham

       ----------
       From:  Mike Harrison [SMTP:spam_OUTwwlTakeThisOuTspamNETCOMUK.CO.UK]
       Sent:  10 November 1999 16:15
       To:  .....PICLISTKILLspamspam@spam@MITVMA.MIT.EDU
       Subject:  Re: 220volt lamp matrix

       On Wed, 10 Nov 1999 07:56:18 -0500, you wrote:


       >  Give up on the less triacs though.  Takes 8 times the lamp
       >and scanning and you end up normally being cheaper to just
       >use the triacs.  Haven't even found a good way to be able to
       >scan the triac gates and cut the number of latches yet.]
       Use optocouplers and matrix their LEDs
       A high-ish scan rate for the LEDs avoids too much delay into the
mains
       cycle. This would be no problem to do with  the PIC.
       Lamp pre-heat and softstart would be pretty easy to do.

1999\11\10@115725 by wwl

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On Wed, 10 Nov 1999 15:22:51 -0000, you wrote:

>        Use optocouplers and matrix their LEDs
>        A high-ish scan rate for the LEDs avoids too much delay into the
>mains
>        cycle. This would be no problem to do with  the PIC.
>        Lamp pre-heat and softstart would be pretty easy to do.

>How is it possible to do lamp pre-heat and softstart?
You turn the triacs on later in the mains half-cycle, like a lamp
dimmer does.
e.g. at the start of each half-cycle, issue firing pulses to all 'on'
triacs. and for pre-heat, you then fire all the 'off' triacs much
later in the cycle. Of course at this time all the 'on' triacs will
still be latched on, so you can simplify the code by just firing all
of them.

To get even illumination, it may be desirable to scan the matrix
several times quickly whan firing, so each triac sees a burst of short
pulses instead of one long one. Using long pulses may cause uneven
brightness if some rows fire later in the cycle due to the length of
pulses used in previous rows..
It will help if you arrange your matrix such that 7 leds can be on at
a time, so you only have a 5:1 multiplex. You may need 5 external
driver transistors to ensure you get enough current - the PIC may not
be able to source enough to drive all 7 LEDs on 1 pin - depends on the
current requirements of your optos.

Consult your triac data for required firing pulse lengths - a number
of short pulses is roughly equivalent to a single long pulse as it's
about total injected charge (AFAIK).
For the 'On' triacs, you need to make sure you don't fire too soon in
the half-cycle, to ensure the mains voltage is sufficient for the
triac  to latch. A pulse burst as described above will usually ensure
this if it's long enough. Burst firing can also save power on the PIC
side - this can be important if using a transformerless PSU.

1999\11\14@190543 by Gennette Bruce

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This circuit is *VERY* similar to traffic lights on major intersections with
various patterns involving left and right turning lanes, etc.  I suggest a
search in some other electronics lists for how they handle traffic lights -
varying matrix loads, pre heating, pwm, etc.  It's all been done before, so
don't try to re-invent it, ask those who did it.

Bye.

> {Original Message removed}

1999\11\15@090915 by V sml

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If that is the case, then super bright LED should be considered.  This
will shake the requirement.  The traffic light in my
country(Singapore) would be all converted to LED matrix in the next
year.  Don't ask me what are they going to do with the good old
traffic lamps would be replaced.  I don't know.

Ling SM

>This circuit is *VERY* similar to traffic lights on major
intersections with
various patterns involving left and right turning lanes, etc.  I
suggest a
search in some other electronics lists for how they handle traffic
lights -
varying matrix loads, pre heating, pwm, etc.  It's all been done
before, so
don't try to re-invent it, ask those who did it.

>>     I have to make a 220volt lamp matrix of 7x5 lamps=35 lamps.
With it, I
> will be able to "draw" different letters. If they were leds, I would
only
> need to control a row (or a column) and do refreshment in every
other
> column
> (or row).
>     Does anyone know how to control all these lamps using the fewer
lines
> of
> a Pic micro, and also fewer triacs ?

1999\11\15@124139 by M. Adam Davis

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Here they just wait till the light bulbs burn out, and replace them with
the LED unit (compatible with the bulb socket and assembly.)  I believe
the lens was integrated with the bulb, so they don't have to replace
anything but the bulb.  Can't wait until they have super-high brightness
(and cheap) amber and green LEDs...  (They only have red led lights
right now...)

-Adam

V sml wrote:
>
> If that is the case, then super bright LED should be considered.  This
> will shake the requirement.  The traffic light in my
> country(Singapore) would be all converted to LED matrix in the next
> year.  Don't ask me what are they going to do with the good old
> traffic lamps would be replaced.  I don't know.
>

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