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'[EE]: Incandescent bulb detection...'
2007\04\06@174905 by John Walker

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Hi all! Long time lurker, first time poster.

I am working on a project where I want to use a PIC pin to detect that
an incandescent light bulb (120VAC 25W) has been inserted into a
standard light socket. I want to do this by using the fact that when a
bulb is in the socket its filament will act as a sort of switch across
the socket contacts. There are two ways I can think of doing this:

1) I could use a DPDT relay connected across the socket and energize the
relay when I scan the socket. (Seems dangerous to me)

2) I could use the technique discussed in the Microchip App. note
concerning AC interfacing. The problem with this is that I want to be
able to detect the bulb without having to turn it on. I could flow low
current through it but that would change the component values and cause
problems when the bulb is actually turned on with full current.

I'm sure there are several other ways to accomplish this and could use
your recommendations. To recap, I want to detect when a bulb is in a
socket using the filament as a switch. I will use a PIC pin to monitor
this and will use another PIC pin to turn the light on/off. The light
will be an incandescent type operating at 120VAC and be rated at 25W.

Thanks in advance.


2007\04\06@180947 by Jack Smith

picon face

> I'm sure there are several other ways to accomplish this and could use
> your recommendations. To recap, I want to detect when a bulb is in a
> socket using the filament as a switch. I will use a PIC pin to monitor
> this and will use another PIC pin to turn the light on/off. The light
> will be an incandescent type operating at 120VAC and be rated at 25W.
>
> Thanks in advance.
>
>
>  
One could use the PIC to generate a high frequency square wave using the
PCM module. Then couple this to the AC line via a small value blocking
cap and measure the injected signal level with a diode detector and the
PIC's ADC. Presumably the injected high frequency voltage will differ
whether the bulb is in place or not. Might need to isolate the bulb from
the rest of the house wiring with an RF choke, however, as otherwise the
total impedance of the wiring plus other devices will vary as loads are
added, switches thrown, etc.

A variant on this would be to inject a high frequency current into the
line via a current transformer and measure it.

Appropriate caution needed when selecting components that connect to the
line, of course.

Jack

2007\04\06@182812 by Recon

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John Walker wrote:

>Hi all! Long time lurker, first time poster.
>
><SNIP>
>  
>

>I'm sure there are several other ways to accomplish this and could use
>your recommendations. To recap, I want to detect when a bulb is in a
>socket using the filament as a switch. I will use a PIC pin to monitor
>this and will use another PIC pin to turn the light on/off. The light
>will be an incandescent type operating at 120VAC and be rated at 25W.
>
>Thanks in advance.
>
>  
>
If  the light is wired correctly in the USA the Neutral or white wire
should have the same electrical potential as ground (earth).

Put a small SPDT relay in series with the blub.  Throught the N.C.
contact run a wire from PIC PIN to the other side of the bulb socket
that the PHASE wire would connect to.  Test it for ground allowing for
the resistance of the bulb filament.

If for some reason the bulb is energised the relay will close and keep
120V from going to the PIC PIN.

Recon

2007\04\06@183056 by William Jacobs

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John,
I think I would try somthing like this.

main---------switch---------light bulb---------main
 !                          !
 !                          !
 !---------resistor------diode----to pic

The resistor is a pull up resistor.  The light bulb will drive the
output to 0
You will need to scale the output to "Pic" range
bill


John Walker wrote:

{Quote hidden}

2007\04\06@183952 by Jesse Lackey

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face
On a related note ... I'm curious if anyone has any ideas on how to
detect an incandescent vs. CF (or LED) bulbs.  The relevant difference
being that most CF (no idea about LED) can't be dimmed.  Really not sure
how this could be done!  Anybody ever do this?  Can it be done reliably
with CF bulbs from different manufacturers?

J

John Walker wrote:
{Quote hidden}

2007\04\06@201732 by Carl Denk

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face
On the current "This Old House" on PBS  TV, they had a CF that they said
was dimable.

Along the lines of this thread, I have in the distant list of things to
do: Load management to minimize the electrical demand. Without running
extra wire, I'd like to be able to detect when a load (sump pump,
freezer, furnace, etc.) is calling for power. I Have a panel next to the
main breaker panel, could run wires to that panel and then to the load.
A PIC or PLC could then open or close the circuit, to minimize the
amperage at the main.

Jesse Lackey wrote:
{Quote hidden}

2007\04\06@211106 by rlistas

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Hi,

Could you please say which Microchip App is that ?

I´m trying to solve a problem that is very similar
to your problem.

I need to know when ANY kind of load is connected
to the power line, so I turn on an external power
inverter. (12DC to 127AC)

A very small inverter 1W, connected to the line was my
first idea. When it senses a drain of more current, it turns on the
big generator.

Any suggestion is welcome.

Thanks !


Rubens




>2) I could use the technique discussed in the Microchip App. note
>concerning AC interfacing. The problem with this is that I want to be
>able to detect the bulb without having to turn it on. I could flow low
>current through it but that would change the component values and cause
>problems when the bulb is actually turned on with full current.

2007\04\07@004922 by Robert Rolf

picon face
I would suggest looking at the phase angle between voltage and current.
An incandescent bulb is almost purely resistive whereas CF lamps will
have some phase shift due to their inductive power convertors (assuming imperfect
power factor convertors, if they even bother to use them).

LEDs will have a 'dead band' where they draw no current as voltage rises,
until biased on.

If you switch the LOW side of the circuit, then 120VAC will appear on the
switch only when the bulb filament is intact. Use a standard 120VAC detect
optocoupler circuit to see the signal (capacitive voltage divider)
and provide your needed isolation to the PIC.

Robert

Jesse Lackey wrote:

{Quote hidden}

2007\04\07@041600 by Peter P.

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To detect an incandescent bulb, whether on or off, you can look at the voltage
across the open switch .or. the current through the switch. Iow, for dc, a
double comparator should work. One side measures the voltage across the switch
and the other current by measuring a voltage across a shunt. So both of these
are voltages and they are in parallel. So one measurement is enough:

Measure the voltage across the switch, whether open or closed (assuming the
switch voltage drop when conducting does not make this measurement difficult).

So for AC, putting an optocoupler across a triac should do the job (with the
additional caveat that the oc must sense 'on' with voltages from 1.3 to 300 V
across it - this is not your average optocoupler but there are ways to fix that).

The detection of the type of bulb installed by looking at the wires is nearly
impossible. Incandescent can be distinguished from everything else by looking at
the wires only (using two currents, even across a halogen transformer), but
after that there is no way to tell arc lamps, electronic ballasts, leds direct
driven, leds switcher driven. It's a jungle.

Peter P.


2007\04\07@124850 by Tom Wehn

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Hi all! Long time lurker, first time poster.

I am working on a project where I want to use a PIC pin to detect that
an incandescent light bulb (120VAC 25W) has been inserted into a
standard light socket--

>From one lurker to another!

Could you install a low voltage transformer (120:25) in series with the lamp
and wire the appropriate resistor across the switch. It shouldn't be to hard
to clip the voltage from the transformer to a useable level with the
detection voltage running through it and still handle the 120 line.

Tom

2007\04\07@131733 by Brooke Clarke

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face
Hi John & PIClist:
bulb detection...
-----------------

By using an impedance measurement looking toward the lamp and the rest of the
house isolated with chokes good at the test frequency.  Instead of using a
random frequency for the measurement, choose a frequency that will detect not
only incandescent bulbs but also CF and LED bulbs in either the on or off
state.  A similar technique is used for testing batteries.


Hi Carl:
House load monitoring
---------------------

Some years ago I connected a current transformer on one of the branch circuits
 by removing the wire from the breaker and threading it though the hole in the
current transformer.  Do not use a clamp on type transformer, they have a much
lower dynamic range because of the residual air gap when closed and so can not
see the small loads.

The current on one breaker is 20 amp max so that's the size of current
transformer needed.  Since you know what loads are on each breaker you can
choose which ones you want to watch and only put transformers on them.

I soldered a resistor across the output winding then ran wire to a Radio Shack
Color computer that had an AC voltmeter input card.  On the screen there was a
plot, similar to what's used with seismometers, so instead of only having one
screen width you can have say 24 screen widths all displayed at once.

After a day when you look at the screen it's amazing what you can see.  For
example the first thing you notice is the refrigerator which is a constantly
cycling load.  If someone gets up during the night and opens the refrigerator
door you see the light come one, or if they turn on a room light you will see
that.  In the morning or evening where there's a lot of things being turned on
and off in parallel it's hard to separate then, unless they have a unique
current, then when you see a step of that size you know what it is.

If I was going to do this now using one of the Onset Computer U12 data loggers
(most if not all PIC based and very cleaver) would be the way to go.
http://www.pacificsites.com/~brooke/Hobo.html  <- 16C56, TLC549, 8 bit A/D, 4
ea. 24LC65, 2032 coin cell (old)
http://www.pacificsites.com/~brooke/GPend.shtml <- 16F690, 24LC512, single LED
2-way interface, 2032 coin cell, XL330 3-axis accelerometer

Have Fun,

Brooke Clarke


--
w/Java http://www.PRC68.com
w/o Java www.pacificsites.com/~brooke/PRC68COM.shtml
http://www.precisionclock.com

2007\04\07@182257 by Peter P.

picon face
To illustrate (detects incandescent bulb good/bad):

L mains
o
|
+----------------+
|                |
|                |
|              FUSE
|                |
R1               |
100K            LOAD
1W             (BULB)
|                |
+--C1 0.1u--+    |
|           |    |
+--Z1 5-12V-+    |
|           |    |
OC           v    |
LED         to N  |
|                |
D FET            |
G-+--R2 1K--+----+
S |         |    |
| TVS 5V  R3 1M TRIAC
| |         |    | \
+-+---------+----+  +--gate
|
o
N mains

A small bipolar can be used instead of the FET. The led outputs pulses which can
be used as after-zero-crossing pulses (quadrant 1) if and only if the bulb is in
and whole. The power supply can be shared for several channels.

Peter P.


2007\04\09@071718 by John Walker

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Rubens,

Here is the URL of the App. Note

http://ww1.microchip.com/downloads/en/AppNotes/00521c.pdf



>> Hi,

>> Could you please say which Microchip App is that ?

2007\04\11@161208 by Peter P.

picon face
Peter P. <plpeter2006 <at> yahoo.com> writes:


 |                |
 D FET            |
 G-+--R2 1K--+----+
 S |         |    |
 |

Of course R2 is 1M not 1k. Funny how nobody caught it.

Peter P.


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