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'[EE:] Detecting a blown lamp'
2005\12\14@105951 by Tim ODriscoll

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Hi Everyone,

I'm making a little PIC-controlled floodlight interface for my house,
and I'd like the PIC to be able to detect if the lamp filament is
working.

The PIC is running off a 7805 from a wall-adapter, and is happily
controlling the floodlight via a triac. The floodlight is running off a
240vAC fused spur and is rated for 500W. I have another floodlight I'd
like to use for a second interface that is 250W, so I'd like to be able
to create a 'generic' broken-filament detector that doesn't rely on
there being a specific wattage of bulb.

I've seen the X-10 Microchip app note where they just use a mega Ohm
resistor to connect a PIC pin up to the mains for the zero-crossing
detect, but I'm not sure on the safety issues of that one.

My other idea was a transistor with it's base connected via a suitably
sized resistor to the 240v live just before the floodlight. The
transistor would drive an optoisolator. I've seen something similar on
piclist.com describing a stalled motor detector, but I've no idea if it
would work with a lamp of variable wattage at 240vAC.

Any thoughts/ideas appreciated.

Cheers,

Tim

2005\12\14@111116 by M Graff

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Tim ODriscoll wrote:
> The PIC is running off a 7805 from a wall-adapter, and is happily
> controlling the floodlight via a triac. The floodlight is running off a
> 240vAC fused spur and is rated for 500W. I have another floodlight I'd
> like to use for a second interface that is 250W, so I'd like to be able
> to create a 'generic' broken-filament detector that doesn't rely on
> there being a specific wattage of bulb.
>
> I've seen the X-10 Microchip app note where they just use a mega Ohm
> resistor to connect a PIC pin up to the mains for the zero-crossing
> detect, but I'm not sure on the safety issues of that one.

The the pic is totally isolated from everything but A/C, that would
work.  There are tricks they are doing there that, if you tie the pic to
(say) a RS-232 port on a PC, will probably cause sparks and/or smoke at
the least.

> My other idea was a transistor with it's base connected via a suitably
> sized resistor to the 240v live just before the floodlight. The
> transistor would drive an optoisolator. I've seen something similar on
> piclist.com describing a stalled motor detector, but I've no idea if it
> would work with a lamp of variable wattage at 240vAC.

You need to detect current flow, not just voltage, right?

How about a very small resistance between the triac's output and the
lamp, and measure the voltage drop across it somehow?  Opto-isolate that
and you'll make it safe.

--Michael

2005\12\14@124655 by John Ward

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hi, the method i've used previously is the current loop/transformer method.

You only need around 25mA for driving a burden resistor which can then be
monitored by a pic a/d port.
The trafo will be quite small, in the region of say 1cm^2

This also makes it electrically isolated.


On 12/14/05, M Graff <spam_OUTexplorer-piclistTakeThisOuTspamflame.org> wrote:
{Quote hidden}

>

2005\12\14@144302 by Tim ODriscoll

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On Wed, 2005-12-14 at 10:11 -0600, M Graff wrote:
> Tim ODriscoll wrote:
> > The PIC is running off a 7805 from a wall-adapter, and is happily
> > controlling the floodlight via a triac. The floodlight is running off a
> > 240vAC fused spur and is rated for 500W. I have another floodlight I'd
> > like to use for a second interface that is 250W, so I'd like to be able
> > to create a 'generic' broken-filament detector that doesn't rely on
> > there being a specific wattage of bulb.
> >
> > I've seen the X-10 Microchip app note where they just use a mega Ohm
> > resistor to connect a PIC pin up to the mains for the zero-crossing
> > detect, but I'm not sure on the safety issues of that one.
>
> The the pic is totally isolated from everything but A/C, that would
> work.  There are tricks they are doing there that, if you tie the pic to
> (say) a RS-232 port on a PC, will probably cause sparks and/or smoke at
> the least.

Trouble is that my floodlight interface is on an rs485 bus, part of
which is an rs232 interface to a PC so I can log everything :-)


> You need to detect current flow, not just voltage, right?

Yes.


> How about a very small resistance between the triac's output and the
> lamp, and measure the voltage drop across it somehow?  Opto-isolate that
> and you'll make it safe.

I've seen 'current-sense' resistors, which are in the milli-Ohms..
They're only rated for a few watts though.. I'm guessing that I need one
which is rated for the same as the floodlight, right? But that's 500W..
Or maybe I'm a little rusty on all that :-)

Cheers,

Tim

2005\12\14@144841 by Tim ODriscoll

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On Wed, 2005-12-14 at 19:46 +0200, John Ward wrote:
> hi, the method i've used previously is the current loop/transformer method.

OK, I admit that I've never heard of that and I don't quite understand
it.. Google isn't helping me much on it either.. Can you elaborate?


> You only need around 25mA for driving a burden resistor which can then be
> monitored by a pic a/d port.

Have you seen this method documented anywhere on the Internet? It sounds
interesting and I'd like to know more..


> The trafo will be quite small, in the region of say 1cm^2

Small is good...


> This also makes it electrically isolated.

Excellent.

Cheers,

Tim

2005\12\14@165012 by Jinx

face picon face
> transistor would drive an optoisolator

I vaguely recall a "blown-fuse indicator" which has an LED +
resistor across the filament. When the filament is OK, next to
nothing will flow through the LED + R (the filament being so
much lower resistance than R). If the filament blows, the LED
will light

2005\12\14@165110 by Andre Abelian

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Tim,

you can do that when the light is off by connecting 10 meg resistor +
diode after your
light bulb where it gets connected to triac to one of pic pin.
make sure your light bulb is connected to HOT wire
software function:
1. turn off the light thru pic
2. check thru resistor logic 1 ?
3.  if it is 1 then the bulb is there 0 means open
4. if 1 turn the light on
5. check thru resistor again if  0 it means it is working if 1 your
triac is open
now you can check if your traic is working too

Andre Abelian




Tim ODriscoll wrote:

{Quote hidden}

2005\12\14@171017 by Mchipguru

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Any reason not to simply look for the light when the lamp is on? You know using an opto detector of some type.
Larry
{Quote hidden}

> --

2005\12\14@182914 by Tim ODriscoll

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Thanks for the suggestions Jinx and Andre..

Hard to choose between the two methods, but I think the opto-coupler in
parallel as per the blown-fuse indicator is the one I'll go for. Reason
being simply that it will consume zero power when the triac's off. Not a
huge concern I know, but what with fossil fuels running out and all,
we've all got to do our bit, eh?

Cheers chaps,

Tim

2005\12\14@183259 by Tim ODriscoll

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On Wed, 2005-12-14 at 17:10 -0500, .....mchipguruKILLspamspam.....charter.net wrote:
> Any reason not to simply look for the light when the lamp is on? You know using an opto detector of some type.

Unfortunately the light is outside on the wall illuminating the
driveway. My control box is inside the roof space, so putting in an ldr
would mean burying my hand up to the shoulder in rock wool insulation to
poke a couple of wires out, then I'd have to get up a ladder on the
outside of the house to mount it all.. So wiring in a new control box is
the nicer option in this instance :-)

Cheers,

Tim.

2005\12\14@184145 by Richard Prosser

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On 15/12/05, Jinx <EraseMEjoecolquittspam_OUTspamTakeThisOuTclear.net.nz> wrote:
> > transistor would drive an optoisolator
>
> I vaguely recall a "blown-fuse indicator" which has an LED +
> resistor across the filament. When the filament is OK, next to
> nothing will flow through the LED + R (the filament being so
> much lower resistance than R). If the filament blows, the LED
> will light
>
> --
Sorry, I can't see this working.
The standard circuit has very low source impedance so the voltage
accross the bulb will be the same whether it's good or bad. The
situation is different in a fusefail detector as normally there is a
load in series as well and its impedance should be much higher than
that of the fuse.
You either need to measure the current when you know it's turned on,
or use an optical setector to figure out if its bright.
RP

2005\12\14@184835 by Kev Pearce \(kevp.com\)

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Tim,

Assuming you have some form of PCB to mount the triac on, make the output
trace nice and wide and straight. Tthen cut two slots each side parallel
with this output trace. Then wrap some very small thin, insulated wire
perpendicular to the trace and using the two slots keep wrapping so you
circle the output trace. This wound wire will pick mains hum and create a
current from it, etc etc

Then feed this into an op amp, convert the ac to dc (possibly before the op
amp) and you'll have a pcb mounted current sensor.

If the light is on current flows, if not none flows...

Nice and simple and isolated from the mains.

I've never tried this but I did think the idea up a while ago when I was
stuck in traffic and wondered how my car's ECU knows when a bulb has blown.
I'm also no expert on mains and current and such stuff, so it might not work
at all but I thought it was an idea that might be worth sharing...

Good luck...


Cheers

Kev/.


{Original Message removed}

2005\12\14@190606 by Jinx

face picon face
> an LED + resistor across the filament

> Sorry, I can't see this working

A good filament is a virtual short across the LED + R

2005\12\14@191431 by Richard Prosser

picon face
On 15/12/05, Kev Pearce (kevp.com) <listsspamspam_OUTkevp.com> wrote:
{Quote hidden}

> {Original Message removed}

2005\12\14@191611 by Richard Prosser

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Only when it's turned off.
I think I'm missing something here .

RP

On 15/12/05, Jinx <@spam@joecolquittKILLspamspamclear.net.nz> wrote:
> > an LED + resistor across the filament
>
> > Sorry, I can't see this working
>
> A good filament is a virtual short across the LED + R
>
> -

2005\12\14@193332 by Jinx

face picon face


> Only when it's turned off.
> I think I'm missing something here .

I don't think you are actually. Whether the filament is there
or not, the terminals still see full PD. The LED + R also see
this PD, and will light whatever the state of the filament. That
wouldn't be the case if the filament was regarded simply as a
piece of wire acting as a short. I did say I "vaguely" recalled
a blown fuse indicator that used an LED, maybe I should
track the ciruit down to see exactly how it was done

2005\12\14@194408 by R. I. Nelson

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part 0 44 bytes
his is a multi-part message in MIME format.
part 1 1302 bytes content-type:text/plain; charset=ISO-8859-1; format=flowed (decoded 7bit)

Tim ODriscoll wrote:

>Hi Everyone,
>
>I'm making a little PIC-controlled floodlight interface for my house,
>and I'd like the PIC to be able to detect if the lamp filament is
>
>
>My other idea was a transistor with it's base connected via a suitably
>sized resistor to the 240v live just before the floodlight. The
>transistor would drive an optoisolator. I've seen something similar on
>piclist.com describing a stalled motor detector, but I've no idea if it
>would work with a lamp of variable wattage at 240vAC.
>
>Any thoughts/ideas appreciated.
>
>Cheers,
>
>Tim
>
>  
>
My memory is sketchy on this but I remember as a kid 50 some years ago.  
We took a neon bulb and soldered 2 pieces of bell wire. ( about 18 or 20
ga.solid copper wire with low voltage insulationused on battery door
bell circuit.  we would take one lead and ground it and the other lead
we would wrap around the hot lead going to the powered device.  (bulb in
this case)When current would flow through the wire the neon light would
light no current the neon was off.  I cannot remeber if we added
resistors or not.

All you would have to dois detect the neon light on or off.  maybe watch
the plasement of the coil too.



part 2 391 bytes content-type:text/x-vcard; charset=utf-8;
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fn:Robert I. Nelson
n:Nelson;Robert I.
org:RIN Designs
adr:;;P.O. BOX 373;RIPON;WI;54971;USA
email;internet:KILLspamrindesignsKILLspamspamcharter.net
tel;work:1-(920)-229-7152
tel;home:1-(920)-748-7443
note;quoted-printable:Custom design and building of small electro mechanical devices.=0D=0A=
       AUTOCAD work ver2002
x-mozilla-html:FALSE
version:2.1
end:vcard



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2005\12\14@195115 by Pierre Desrochers

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Perhaps HEAT could be detected?

R. I. Nelson wrote:

{Quote hidden}

2005\12\14@202506 by Richard Prosser

picon face
> >
> My memory is sketchy on this but I remember as a kid 50 some years ago.
> We took a neon bulb and soldered 2 pieces of bell wire. ( about 18 or 20
> ga.solid copper wire with low voltage insulationused on battery door
> bell circuit.  we would take one lead and ground it and the other lead
> we would wrap around the hot lead going to the powered device.  (bulb in
> this case)When current would flow through the wire the neon light would
> light no current the neon was off.  I cannot remeber if we added
> resistors or not.
>
> All you would have to dois detect the neon light on or off.  maybe watch
> the plasement of the coil too.
>


I've used a similar method to this also - but it detects (AC) voltage
on the wire - not current passing through it. It could be used in this
situation to detect if the light is turned on - then the result
"anded" with the current sensor to check that current is flowing.

RP

2005\12\14@203348 by Peter Todd

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On Wed, Dec 14, 2005 at 07:43:00PM +0000, Tim ODriscoll wrote:

> I've seen 'current-sense' resistors, which are in the milli-Ohms..
> They're only rated for a few watts though.. I'm guessing that I need one
> which is rated for the same as the floodlight, right? But that's 500W..
> Or maybe I'm a little rusty on all that :-)

Nope, think in terms of the power dissipating by the resistor. So for
instance:

120V AC
500W

Through therefore:

Power = Current * Voltage

500W = I * 120V

I = 4.16A

So we've got 4 amps flowing through the AC line right. Now if we add in
that 0.1ohm resistor we can calculate the voltage drop accross it:

V=4.16A*0.1R
V=0.416V

Now think of it this way, the resistor is droping the voltage by
converting electric power to heat. So we can calculate the amoung of
heat it generates doing that using the power equation:

P=IV
P=4.16A*0.416V
P=1.731W

More than your average quarter watt resistor for sure, but a 10W
resistor is totally fine for that purpose.

--
RemoveMEpeteTakeThisOuTspampetertodd.ca http://www.petertodd.ca

2005\12\14@205133 by Jinx

face picon face
part 1 440 bytes content-type:text/plain; (decoded 7bit)

> a blown fuse indicator that used an LED, maybe I should
> track the ciruit down to see exactly how it was done

I think I found the one I was thinking of. It appears to be
suitable only for DC though (in its present form anyway).

A couple of others I found are also for loaded DC

Another suggestion was this simple field detector. A piece
of wire acting as an antenna is wound around the cable


part 2 1877 bytes content-type:image/gif; (decode)


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2005\12\14@213833 by Jinx
face picon face
Remember this ?

----- Original Message -----
From: "Marcel Birthelmer" <spamBeGonemarcelspamBeGonespamcarrietech.com>
To: "Microcontroller discussion list - Public." <TakeThisOuTpiclistEraseMEspamspam_OUTmit.edu>
Sent: Sunday, August 21, 2005 1:08 PM
Subject: [EE]: appliance current sensor

Hello all;
random project time. This is the situation: of the three people I'm
sharing a house with, I'm the only one whose room is not adjoined to
the garage. This means that I can never hear when the washer or
dryer are  done, and so my laundry scheduling is always suboptimal.
Now of course I could just set my watch or whatever, but where's
the fun in that. One additional criterium that will come in is that these
are not my appliances, so I can't open them. Now, I was thinking that
it should be possible to pick up the current draw of those appliances
and then, via a small embedded system or maybe an old computer,
forward this information to the local network or something

----- Original Message -----
From: "Jinx" <RemoveMEjoecolquittspamTakeThisOuTclear.net.nz>
To: "Microcontroller discussion list - Public." <piclistEraseMEspam.....mit.edu>
Sent: Sunday, August 21, 2005 3:25 PM
Subject: Re: [EE] appliance current sensor


{Quote hidden}

2005\12\15@120014 by Tim ODriscoll

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Hi Everyone,

I've found a toroidal current sense pcb-mounted device for a little over
one UK pound. Excellent. It says it's suitable for 50Hz AC voltage and
1A to 10A. It's basically a rectangle with a hole in the middle for the
current-carrying cable, and two pins underneath it for the output.

The datasheet states that there is 50 ohms resistance between the two
pins and the graph implies that I should see 4mV to 5mV for 1A and 7.5mv
for 2A.

That means I should be able to detect what kind of bulb is in the light
too, right? Cool. The two possible bulbs are 250W and 500W, and I live
in the UK, so it's 230vAC.

I've never used the A/D port on a pic before, but I've got a 16f628
earmarked for this, which has one I believe.

How does one connect up this current-sensing coil to a pic a/d pin then?
I'm assuming something nice and simple like I ground one end of the coil
and just wire the other directly into the a/d port, then it's all
software?

Or would that not yield any input?

Cheers,

Tim.

2005\12\15@121701 by Steve Smith

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This might sound a daft idea but it works.

A bridge rectifier in series with the lamp (Ac,Ac) and a led (opto and
resistor, across the +/- in parellel with a 5v zener and a small cap)
basicly when there is lamp that's on the led is also on on the opto the cap
just makes the signal 0 or 1 instead of a square wave princable is
extendable to large lamps by the size of the bridge. Make sure that the
semis can handle the cold current of the lamp its about 10 times the running
current for the first cycle. Should be cheeper that a ct and amplifier.

Just my 2p

Steve

{Original Message removed}

2005\12\15@124345 by Peter

picon face


On Wed, 14 Dec 2005, John Ward wrote:

> hi, the method i've used previously is the current loop/transformer method.
>
> You only need around 25mA for driving a burden resistor which can then be
> monitored by a pic a/d port.
> The trafo will be quite small, in the region of say 1cm^2

If you do not need to sense the failed lamp *immediately* then a
thermistor wired to an a/d input works fine. Could be replaced with a
silicon device (e.g. NPN transistor) near the switching element. This
assumes that the switching element raises by about 10 deg.C in
operation. It is also possible to use a single current metering device
for the entire unit (several loads) as long as the cpu can keep track of
which load is on/off at any one time. Then there is a the simple load
sensing device that consists of an optocoupler shunted by a few (two)
silicon diodes in series with the load.

Peter

2005\12\15@125212 by Peter

picon face


Tim:

         D1..D4 = 50V 3A

L o-------*->|-->|-*----o Lamp phase
          |        |
          |        |
          *-|<--|<-*
          |        |
          *---R1---*  R1 =  50 ohms 0.25W
          |        |
          R2       |  R2 =  50 ohms 0.25W
          |        |
          +--->|---+
             OC LED   Optocoupler LED

The diodes can be a part of an inexpensive rectifier bridge. It will
dissipate at most 5W (at 3A load).

The higher the load, the more interesting it is to use a thermistor type
scheme on the switching element, and sense its temperature.

Peter

2005\12\15@125525 by Peter

picon face


On Wed, 14 Dec 2005 EraseMEmchipguruspamcharter.net wrote:

> Any reason not to simply look for the light when the lamp is on? You
> know using an opto detector of some type. Larry

ambient light

Peter

2005\12\15@125831 by Peter

picon face


On Thu, 15 Dec 2005, Richard Prosser wrote:

> Only when it's turned off.
> I think I'm missing something here .

The original circuit also has a 'leak' resistor in parallel with the
switch so the led sees some current even if the light is off. So much
for 'zero consumption' when the light is off.

Peter

2005\12\15@130010 by Peter

picon face


On Wed, 14 Dec 2005, Pierre Desrochers wrote:

> Perhaps HEAT could be detected?

yes.

Peter

2005\12\15@145409 by olin piclist

face picon face
Peter wrote:
>> Any reason not to simply look for the light when the lamp is on? You
>> know using an opto detector of some type. Larry
>
> ambient light

But why would you be turning on a lamp if there is lots of ambient light?

******************************************************************
Embed Inc, Littleton Massachusetts, (978) 742-9014.  #1 PIC
consultant in 2004 program year.  http://www.embedinc.com/products

2005\12\15@152226 by Wouter van Ooijen

face picon face
> >> Any reason not to simply look for the light when the lamp
> is on? You
> >> know using an opto detector of some type. Larry
> >
> > ambient light
>
> But why would you be turning on a lamp if there is lots of
> ambient light?

And I suppose you could put an LDR near to the lamp, where the light
level from the lamp would be way above the ambient light level. Or you
could detect the difference between lamp off and lamp on.

Wouter van Ooijen

-- -------------------------------------------
Van Ooijen Technische Informatica: http://www.voti.nl
consultancy, development, PICmicro products
docent Hogeschool van Utrecht: http://www.voti.nl/hvu


2005\12\15@175747 by Tim ODriscoll

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Thanks for all the ideas..

I'd like to use the torroidal current sensor, I think.. No huge reason
except that I've not tried any a/d before and I quite like the idea of
being able to detect what kind of bulb is in the lamp. Although if I
can't get it to work, the bridge-rectifier/opto idea would be next.

I think I may have interpreted the data sheet wrong for the torroid I
intend to use, so I've drawn a copy for others' opinions who have
hopefully used something similar. I had inferred from the attached
diagram that there was a resistance of 50 ohms through the actual
device, but in retrospect, I think it may mean I have to supply one
externally.

I'm still not having any luck with Google in finding out how to hook up
one of these things either.. I used to like those 'example circuits' and
'typical applications' at the end of data sheets.. It's probably one of
those things that's so simple everyone already knows so no-one thinks of
writing it down.. Now I know how my Mum feels when she tries something I
find simple like setting the clock on the microwave..

Cheers,

Tim.


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2005\12\15@213706 by Bob Ammerman

picon face
If this thing is (and it appears to be) a 'current transformer' then you
have to be careful!

The 50 ohm resistor is referred to as a 'burden' resistor and is absolutely
required (unless built into the device). Without it the voltage can jump to
surprising values.

Bob Ammerman
RAm Systems




{Original Message removed}

2005\12\16@044222 by Michael Rigby-Jones

picon face


{Quote hidden}

Tim,

Essentialy this device is a transformer, only output voltage is proportional to the current in the primary, as opossed to the voltage accross the primary of a conventional transformer.  The output is an AC signal, most definately NOT suitable for feeding directly into the PIC's AD port.  You will need some signal conditioning first, namely rectification and amplification (and possibly some filtering).

A link to the datasheet for the device would be helpfull.  If the output really is as small as you say (i.e. a few mV) you will have to use a precision rectifier circuit, as a normal diode would never reach conduction as such low voltages.  This would need to be followed by some gain to get the voltage up to a level suitable for the PIC.  If you could find a device with a higher output voltage at the current range you are using, the interface circuit design could be simplified somewhat.

Regards

Mike

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2005\12\16@071659 by Tim ODriscoll

flavicon
face
Mike,

On Fri, 2005-12-16 at 09:42 +0000, Michael Rigby-Jones wrote:
> Essentialy this device is a transformer, only output voltage is
> proportional to the current in the primary, as opossed to the voltage
> accross the primary of a conventional transformer.  The output is an
> AC signal, most definately NOT suitable for feeding directly into the
> PIC's AD port.  You will need some signal conditioning first, namely
> rectification and amplification (and possibly some filtering).

After Bob's reponse I did some more Googling and found Ed Cheung's Home
Automation site where he describes using current transformers and how to
build them. There's also a link on his site to a Google query 'burden
resistor' which throws up a lot more useful info. I've had a jolly good
read up and had surmised exactly what you mention above :-)


> A link to the datasheet for the device would be helpfull.  If the
> output really is as small as you say (i.e. a few mV) you will have to
> use a precision rectifier circuit, as a normal diode would never reach
> conduction as such low voltages.  This would need to be followed by
> some gain to get the voltage up to a level suitable for the PIC.  If
> you could find a device with a higher output voltage at the current
> range you are using, the interface circuit design could be simplified
> somewhat.

The datasheet:
http://www.stokepogesway.net/~tim/datasheets/current_transformer.pdf

I'm starting to think that this is getting a bit overkill, seeing as
Peter's bridge-rectifier/opto seems neater..

Then again, it shouldn't cost too much more for an opamp so maybe it'll
be quite interesting...

Cheers,

Tim.

2005\12\16@085835 by Alan B. Pearce

face picon face
>I'm starting to think that this is getting a
>bit overkill, seeing as Peter's bridge-rectifier/
>opto seems neater..

I know that this arrangement is used to detect the presence of a train in a
block on model railways.

2005\12\16@191241 by Peter

picon face

On Fri, 16 Dec 2005, Alan B. Pearce wrote:

>> I'm starting to think that this is getting a
>> bit overkill, seeing as Peter's bridge-rectifier/
>> opto seems neater..
>
> I know that this arrangement is used to detect the presence of a train in a
> block on model railways.

Yes except it works well mostly for low loads (say <1A). Beyond that it
starts making a lot of heat for a small and unobtrusive circuit it is
supposed to be. A Hall current sensor is not so expensive by the time
you need to measure go/no go 7A and it has to take the inrush of
presumably 40-50Aish gracefully (i.e. even if the filament decides to go
just then). I'd still look into a simple thermistor siliconed to the
insulated side of the triac with extra shrink tubing to increase
insulation (you are using a triac, no?).

Peter

2005\12\17@043959 by Tim ODriscoll

flavicon
face
On Fri, 2005-12-16 at 20:20 +0200, Peter wrote:
> Yes except it works well mostly for low loads (say <1A). Beyond that it
> starts making a lot of heat for a small and unobtrusive circuit it is
> supposed to be. A Hall current sensor is not so expensive by the time
> you need to measure go/no go 7A and it has to take the inrush of
> presumably 40-50Aish gracefully (i.e. even if the filament decides to go
> just then). I'd still look into a simple thermistor siliconed to the
> insulated side of the triac with extra shrink tubing to increase
> insulation (you are using a triac, no?).

I am using a triac, yes. The load that the brightest lamp will cause is
2A. I have another lamp which will pull 1A. I don't know if the triac
heats up much when it's on with these loads though. I have a fairly
large heatsink on it, but I make a point of not touching any part of it
when it's got the 240vAC going through it, so I don't know if it heats
up much.

Although, thinking about it, I might have a temperature probe floating
around somewhere for my multimeter.. I've also got a few ds1820's too..

I'll give that a go..

Cheers Peter,

Tim.

2005\12\17@081302 by Bill & Pookie

picon face
The flood light should heat up nicely.

Bill

----- Original Message -----
From: "Tim ODriscoll" <RemoveMEtimTakeThisOuTspamspamstokepogesway.net>
To: "Microcontroller discussion list - Public." <EraseMEpiclistspamspamspamBeGonemit.edu>
Sent: Saturday, December 17, 2005 1:39 AM
Subject: Re: [EE:] Detecting a blown lamp


{Quote hidden}

> --

2005\12\17@160013 by Peter

picon face


On Sat, 17 Dec 2005, Bill & Pookie wrote:

> The flood light should heat up nicely.

I understand that his light is not next to the controller. Optical light
sensing would not work for the same reason.

Peter

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