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Light switch warning indicator

M

M.Joshi

Jan 1, 1970
0
Hi,

I am trying to design an audible/visual indicator that beeps every
minutes when a light switch is turned on.

The complete circuit has to fit behind a light switch plate and so
transformer cannot be used.

Any ideas or pointers would be really useful.

Thanks
 
D

Dave Plowman (News)

Jan 1, 1970
0
I am trying to design an audible/visual indicator that beeps every 5
minutes when a light switch is turned on.
The complete circuit has to fit behind a light switch plate and so a
transformer cannot be used.

This can't be done unless you have a neutral at the switch position. When
the switch is on there is no potential difference between the terminals
therefore no power source.
 
M

M.Joshi

Jan 1, 1970
0
Dave said:
I am trying to design an audible/visual indicator that beeps every 5
minutes when a light switch is turned on.

The complete circuit has to fit behind a light switch plate and so a
transformer cannot be used.

This can't be done unless you have a neutral at the switch position
When
the switch is on there is no potential difference between th
terminals
therefore no power source.

Any ideas or pointers would be really useful.

--
*I will always cherish the initial misconceptions I had about you

Dave Plowman [email protected] London SW
To e-mail, change noise into sound.


Dave, I was thinking just that after submitting the post! Could th
earth be used instead of neutral for low currents? Is that a goo
idea?

Otherwise, I was considering a coin battery solution where the curren
flowing through a wire is sensed
 
S

Sam Goldwasser

Jan 1, 1970
0
Dave Plowman (News) said:
This can't be done unless you have a neutral at the switch position. When
the switch is on there is no potential difference between the terminals
therefore no power source.

It could be battery or supercap powered.

Or, if the box is grounded, there will be line voltage between the
load side and the box in a correctly wired normal (not 3-way) circuit.

--- sam | Sci.Electronics.Repair FAQ: http://www.repairfaq.org/
Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/
+Lasers | Sam's Laser FAQ: http://www.repairfaq.org/sam/lasersam.htm
| Mirror Sites: http://www.repairfaq.org/REPAIR/F_mirror.html

Important: Anything sent to the email address in the message header above is
ignored unless my full name is included in the subject line. Or, you can
contact me via the Feedback Form in the FAQs.
 
D

Dave Plowman (News)

Jan 1, 1970
0
It could be battery or supercap powered.

Might be difficult to fit all this inside a switch backing box?
Or, if the box is grounded, there will be line voltage between the load
side and the box in a correctly wired normal (not 3-way) circuit.

I hope you're not recommending this? In the UK it would be forbidden - not
least because it unbalances the line and neutral.
 
J

James Sweet

Jan 1, 1970
0
Dave said:
This can't be done unless you have a neutral at the switch position. When
the switch is on there is no potential difference between the terminals
therefore no power source.


There's almost always a neutral in the switch box, occasionally I see an
arrangement with power coming into the light box and a separate switch
drop but it's fairly rare. Also it'd be possible to power the reminder
with a battery in that case, it wouldn't have to draw much power. If the
lamp is incandescent you could even use a rechargeable battery or memory
backup capacitor to power it and "steal" power to charge the battery
when the switch is off.
 
J

James Sweet

Jan 1, 1970
0
Dave said:
It could be battery or supercap powered.


Might be difficult to fit all this inside a switch backing box?

Or, if the box is grounded, there will be line voltage between the load
side and the box in a correctly wired normal (not 3-way) circuit.


I hope you're not recommending this? In the UK it would be forbidden - not
least because it unbalances the line and neutral.
[/QUOTE]


UK electrical boxes are incredibly tiny compared to those in the
US/Canada. Our standard boxes are 2.5" deep but you can get them up to
4" deep in the standard 3.5"x2" size used for single switches and
receptacles.


Connecting between line and ground would not be legal by code, but if
the circuit is designed carefully it would not be a danger either. I'd
lean towards powering it with a battery personally, much safer for the
novice.
 
J

James Sweet

Jan 1, 1970
0
Otherwise, I was considering a coin battery solution where the current
flowing through a wire is sensed.

Don't try to measure current through the wire, it's far easier to
measure voltage across the switch. Zero voltage means the switch is on.
 
D

Dave Plowman (News)

Jan 1, 1970
0
There's almost always a neutral in the switch box, occasionally I see an
arrangement with power coming into the light box and a separate switch
drop but it's fairly rare.

Right. In the UK the latter is the norm. Lighting circuits are radials and
the feed goes from one ceiling lamp to another, with the switch drop from
that lamp. Of course if you have floor outlets for table lamps etc you're
more likely to find a neutral at the switch.
Also it'd be possible to power the reminder with a battery in that
case, it wouldn't have to draw much power. If the lamp is incandescent
you could even use a rechargeable battery or memory backup capacitor to
power it and "steal" power to charge the battery when the switch is off.

Yup - although it might be tight to fit all that within the switch back
box. In the UK, some are so shallow there's just enough room for the cable.
 
S

Sam Goldwasser

Jan 1, 1970
0
Dave Plowman (News) said:
Might be difficult to fit all this inside a switch backing box?


I hope you're not recommending this? In the UK it would be forbidden - not
least because it unbalances the line and neutral.

I did not address the regulatory issues. But, I assumed he was talking
about a few mA of current just to operate a flashing high brightness LED,
the the line balance wouldn't be a practical issue unless it tripped the
RCD/GFCI/whatever.

--- sam | Sci.Electronics.Repair FAQ: http://www.repairfaq.org/
Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/
+Lasers | Sam's Laser FAQ: http://www.repairfaq.org/sam/lasersam.htm
| Mirror Sites: http://www.repairfaq.org/REPAIR/F_mirror.html

Important: Anything sent to the email address in the message header above is
ignored unless my full name is included in the subject line. Or, you can
contact me via the Feedback Form in the FAQs.
 
M

M.Joshi

Jan 1, 1970
0
Dave said:
This can't be done unless you have a neutral at the switch position.
When the switch is on there is no potential difference between the
terminals therefore no power source.

It could be battery or supercap powered.

Might be difficult to fit all this inside a switch backing box?

Or, if the box is grounded, there will be line voltage between th
load
side and the box in a correctly wired normal (not 3-way) circuit.

I hope you're not recommending this? In the UK it would be forbidden
not
least because it unbalances the line and neutral.

--
*Gun Control: Use both hands.

Dave Plowman [email protected] London SW
To e-mail, change noise into sound.



Dave, Could you expand a bit more on what you mean by "unbalances th
line and neutral." please?

Thanks
 
D

Dave Plowman (News)

Jan 1, 1970
0
Dave, Could you expand a bit more on what you mean by "unbalances the
line and neutral." please?

In the UK, neutral is connected to earth at some point - the last possible
one being at the incoming main. After that, they are separate. Use the
earth cable in the house as a return and you are now not drawing equal
current on line and neutral. And RCDs work by looking for a difference in
the current flow between line and neutral, so you don't want to impose a
load which does just that. Of course, if it's only a couple of milliamps
it's unlikely to matter, but in principle it's a bad idea.
 
I

INTERNET SERVICE PROVIDER OWNER ERICH J. SCHULTHEI

Jan 1, 1970
0
M.Joshi said:
Hi,

I am trying to design an audible/visual indicator that beeps every 5
minutes when a light switch is turned on.

The complete circuit has to fit behind a light switch plate and so a
transformer cannot be used.

Any ideas or pointers would be really useful.

Thanks.

now my question is why would you want to design such a sircuit in the
first place? All that beeping is sure to annoy somebody after a while.
 
J

James Sweet

Jan 1, 1970
0
INTERNET said:
now my question is why would you want to design such a sircuit in the
first place? All that beeping is sure to annoy somebody after a while.


Isn't that the idea?
 
D

Dave Plowman (News)

Jan 1, 1970
0
INTERNET SERVICE PROVIDER OWNER ERICH J. SCHULTHEIS
now my question is why would you want to design such a sircuit in the
first place? All that beeping is sure to annoy somebody after a while.

A light remote from the switch so you can't see if it's left on?
 
M

M.Joshi

Jan 1, 1970
0
Dave said:
Dave, Could you expand a bit more on what you mean by "unbalances the
line and neutral." please?

In the UK, neutral is connected to earth at some point - the las
possible
one being at the incoming main. After that, they are separate. Use the
earth cable in the house as a return and you are now not drawing equal
current on line and neutral. And RCDs work by looking for a differenc
in
the current flow between line and neutral, so you don't want to impos
a
load which does just that. Of course, if it's only a couple o
milliamps
it's unlikely to matter, but in principle it's a bad idea.

--
*Cover me. I'm changing lanes.

Dave Plowman [email protected] London SW
To e-mail, change noise into sound.


We currently do not have RCDs installed at the fuse box - they ar
plain wire fuses.

James Sweet mentioned in an earlier post, using a rechargeable batter
or memory backup capacitor to power it and "steal" power to charge th
battery
when the switch is off.

How would this work with no neutral? I am assuming a large wattag
resistor would be required to drop the voltage to a suitable level an
using the earth as a neutral? However, I don't think there will b
enough space behind the switch plate for the resistor
 
R

Ron(UK)

Jan 1, 1970
0
If you just need some kind of indicator to show whether a remote light
is on or off, you can wire a neon lamp (with resistor) across the
switch. In the UK you can buy this ready made as a backplate for a
standard single light switch plate. It`s so you can find the switch in
the dark. When the neon is on, the light is off and vice versa. It`s not
going to beep of course.

Ron
 
D

Dana

Jan 1, 1970
0
Are you building this for a blind person? Just curious.

Hi,

I am trying to design an audible/visual indicator that beeps every 5
minutes when a light switch is turned on.
 
F

Franc Zabkar

Jan 1, 1970
0
This can't be done unless you have a neutral at the switch position. When
the switch is on there is no potential difference between the terminals
therefore no power source.

What about using a dimmer switch set to about 90% duty cycle? The
circuit could grab some power during the 10% off time.

- Franc Zabkar
 
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