Is there a 1-Wire(*) device that can detect the presence of mains? I
suspect that the DS2413 might do it but ideally I'd like it to be
galvanicly isolated so there is no chance of mains getting where it
shouldn't and frying things.

The application is to monitor the various pumps and demands on the
heating system here in conjunction with a scattering of 1-Wire
temperature sensors.

(*) "1-Wire" as in using the same system as the cheap temperature
sensors you can get from Dallas/Maxim.
--
Cheers
Dave.

On Jan 6, 2:57*pm, "Dave Liquorice"
wrote:
Is there a 1-Wire(*) device that can detect the presence of mains? I
suspect that the DS2413 might do it but ideally I'd like it to be
galvanicly isolated so there is no chance of mains getting where it
shouldn't and frying things.

The application is to monitor the various pumps and demands on the
heating system here in conjunction with a scattering of 1-Wire
temperature sensors.

Glue one of the temperature sensors you are already using to a
suitably insulated resistor.

John

Dave Liquorice wrote:

Is there a 1-Wire(*) device that can detect the presence of mains? I
suspect that the DS2413 might do it but ideally I'd like it to be
galvanicly isolated so there is no chance of mains getting where it
shouldn't and frying things.

The application is to monitor the various pumps and demands on the
heating system here in conjunction with a scattering of 1-Wire
temperature sensors.

(*) "1-Wire" as in using the same system as the cheap temperature
sensors you can get from Dallas/Maxim.

Volts or amps?

Only, volts on mains wiring is really hard to detect reliably with a high
resistance isolation as it is so easy to pick up stray voltages.

How about something really simple, like a mains powered relay, an opto-
isolator, or a home brew optoisolator using a photo-device pointing at a
fully sealed mains LED unit?


--
Tim Watts

On Fri, 06 Jan 2012 14:57:53 +0000 (GMT), Dave Liquorice wrote:

DS2413

would a mod of something like
http://www.maxim-ic.com/datasheet/index.mvp/id/3950
be doable
--
(º€¢.¸(¨*€¢.¸ ¸.€¢*¨)¸.€¢Âº)
.€¢Â°€¢. Nik .€¢Â°€¢.
(¸.€¢Âº(¸.€¢Â¨* *¨€¢.¸)º€¢.¸)

On Fri, 6 Jan 2012 07:31:37 -0800 (PST), John Walliker wrote:

Glue one of the temperature sensors you are already using to a
suitably insulated resistor.

But that will mess up the temperature reading. B-)

And not generate a nice clear on/off indication, though that could be
done in the software.

--
Cheers
Dave.

On Fri, 06 Jan 2012 14:57:53 +0000 (GMT), Dave Liquorice wrote:

Is there a 1-Wire(*) device that can detect the presence of mains? I
suspect that the DS2413 might do it but ideally I'd like it to be
galvanicly isolated so there is no chance of mains getting where it
shouldn't and frying things.

The application is to monitor the various pumps and demands on the
heating system here in conjunction with a scattering of 1-Wire
temperature sensors.

(*) "1-Wire" as in using the same system as the cheap temperature
sensors you can get from Dallas/Maxim.

or use a 1 wire a/d onverter and ldr - with a neon on the suppy you are
monitoring - giving electrical isolation and cleanish switching e.g. DS2450
--
(º€¢.¸(¨*€¢.¸ ¸.€¢*¨)¸.€¢Âº)
.€¢Â°€¢. Nik .€¢Â°€¢.
(¸.€¢Âº(¸.€¢Â¨* *¨€¢.¸)º€¢.¸)

On Fri, 06 Jan 2012 14:57:53 +0000, Dave Liquorice wrote:

Is there a 1-Wire(*) device that can detect the presence of mains? I
suspect that the DS2413 might do it but ideally I'd like it to be
galvanicly isolated so there is no chance of mains getting where it
shouldn't and frying things.

The application is to monitor the various pumps and demands on the
heating system here in conjunction with a scattering of 1-Wire
temperature sensors.

(*) "1-Wire" as in using the same system as the cheap temperature
sensors you can get from Dallas/Maxim.


If you aren't doing fast switching use a mains relay (preferably with
gold-plated contacts) feeding a DS2413. It's easier than having to filter
the mains input and gives excellent isolation. You may still have to
debounce the input in software though.

--
Mick (Working in a M$-free zone!)
Web: http://www.nascom.info
Filtering everything posted from googlegroups to kill spam.

On Fri, 06 Jan 2012 17:22:47 +0000, Tim Watts wrote:

Volts or amps?

Only, volts on mains wiring is really hard to detect reliably with a
high resistance isolation as it is so easy to pick up stray voltages.

Presence ie is something switched on? Loads are around 50W for
circulation pumps or oil boiler. I've been half looking at hall
effect switches to feed into a DS2413 1-Wire dual channel PIO device.
But I haven't a clue about the field strengths that hall effect
switches need or those that you'll find around a mains cable carrying
200mA or so.

How about something really simple, like a mains powered relay,

I have a load of relays that could be liberated from the old control
box but that just seems a bit over kill and "old fashioned" but does
solve the isolation side. I can't help feeling that there must be
something from the process control area for this but perhaps they
don't come cheap...

an opto-isolator, or a home brew optoisolator using a photo-device
pointing at a fully sealed mains LED unit?

Mains LED indiactor, opto switch into a DS2413 that's another way.
Might be a fair bit of messing about with heatshrink to make light
tight units though.

--
Cheers
Dave.

On Fri, 06 Jan 2012 21:42:06 +0000, Dave Liquorice wrote:

snip

Presence ie is something switched on? Loads are around 50W for
circulation pumps or oil boiler. I've been half looking at hall effect
switches to feed into a DS2413 1-Wire dual channel PIO device.
But I haven't a clue about the field strengths that hall effect switches
need or those that you'll find around a mains cable carrying 200mA or
so.

How about something really simple, like a mains powered relay,

I have a load of relays that could be liberated from the old control box
but that just seems a bit over kill and "old fashioned" but does solve
the isolation side. I can't help feeling that there must be something
from the process control area for this but perhaps they don't come
cheap...



There are voltage and current sensors available, but you probably don't
want to pay the cost - especially for the current sensors! There are also
little hall effect sensors at a more reasonable price. The problem is
that they give an AC output around zero (and need a negative supply). I
once used a system of connecting an opto-isolator & resistor to watch the
voltage across series diodes (actually a bridge rec with + and -
shorted), but you get a 1.2v or so drop and a pulsating DC signal to deal
with. A relay to watch just the voltage is a lot easier!

--
Mick (Working in a M$-free zone!)
Web: http://www.nascom.info
Filtering everything posted from googlegroups to kill spam.

On Jan 6, 8:08*pm, mick wrote:
On Fri, 06 Jan 2012 14:57:53 +0000, Dave Liquorice wrote:
Is there a 1-Wire(*) device that can detect the presence of mains? I
suspect that the DS2413 might do it but ideally I'd like it to be
galvanicly isolated so there is no chance of mains getting where it
shouldn't and frying things.

The application is to monitor the various pumps and demands on the
heating system here in conjunction with a scattering of 1-Wire
temperature sensors.

(*) "1-Wire" as in using the same system as the cheap temperature
sensors you can get from Dallas/Maxim.

If you aren't doing fast switching use a mains relay (preferably with
gold-plated contacts) feeding a DS2413. It's easier than having to filter
the mains input and gives excellent isolation. You may still have to
debounce the input in software though.

--
Mick * * * * * * * * * * *(Working in a M$-free zone!)
Web:http://www.nascom.info
Filtering everything posted from googlegroups to kill spam.

I retired from electronics 5 years ago, so questions such as this are
of interest. I followed up this DS2413 via Mr Google - now I did
expect to be able to understand quite what this device does, but I'm
obviously already being left far behind as the description was just so
much gobbledegook.

Could some kind person give me an idea of what it does in words on one
syllable plain English please.

Rob

Dave Liquorice wrote:

DS2413

Looks like a very handy device, that...

The only way I can think of doing a reliable non contact volt-detection is
to do something like slip the conductor through a small bit of brass tube
(the detector), then oversleeve that with some plastic, then oversleeve
again with bigger brass tube which is earthed to provide some local
shielding from other stuff - but then you'd probably need to amplify the
signal which leads to a problem of power for the amp circuit.

Unless the DS2413 was sensitive enough to cope directly.

It mentions it has 1M input impedance and a max voltage of 28V on the IO
pins - wonder if a signal diode-tiny capacitor+clamp zener+high-ohms bleed
resistor could clean up the induced mains hum on the pickup (ie turn it into
a DC signal) and still provide enough oomph to the chip???

If it could be made to work reliably, it would be elegantly simple,
intriniscally safe and the pickup assembly could be made split for slipping
onto the conductor with a finishing turn of metal foil sticky tape to
complete the earth shield.

It's a massive conjecture because I've always been crap at analogue stuff...

--
Tim Watts

On 06/01/2012 23:53, robgraham wrote:
On Jan 6, 8:08 pm, wrote:
On Fri, 06 Jan 2012 14:57:53 +0000, Dave Liquorice wrote:
Is there a 1-Wire(*) device that can detect the presence of mains? I
suspect that the DS2413 might do it but ideally I'd like it to be
galvanicly isolated so there is no chance of mains getting where it
shouldn't and frying things.

The application is to monitor the various pumps and demands on the
heating system here in conjunction with a scattering of 1-Wire
temperature sensors.

(*) "1-Wire" as in using the same system as the cheap temperature
sensors you can get from Dallas/Maxim.

If you aren't doing fast switching use a mains relay (preferably with
gold-plated contacts) feeding a DS2413. It's easier than having to filter
the mains input and gives excellent isolation. You may still have to
debounce the input in software though.

--
Mick (Working in a M$-free zone!)
Web:http://www.nascom.info
Filtering everything posted from googlegroups to kill spam.

I retired from electronics 5 years ago, so questions such as this are
of interest. I followed up this DS2413 via Mr Google - now I did
expect to be able to understand quite what this device does, but I'm
obviously already being left far behind as the description was just so
much gobbledegook.

Could some kind person give me an idea of what it does in words on one
syllable plain English please.

Rob

It's a digital i/o device with two pins, either of which can be used as
an input or an output.

The way the outputs are set and inputs read is via serial communication.
Unlike most serial communication, 1-wire devices (they actually use two
wires) have a 0V line and a communications line - the comms line is held
at 5V when not communicating, allowing the device to power itself from
the comms line and store enough power to carry on working during
communications. A number of devices can be daisychained together and
each addressed by its unique 64-bit code, which is set during manufacture.

There's a whole lot more to it, but that's the basics.

SteveW

On Jan 7, 12:02*am, Tim Watts wrote:
Dave Liquorice wrote:
DS2413

Looks like a very handy device, that...

The only way I can think of doing a reliable non contact volt-detection is
to do something like slip the conductor through a small bit of brass tube
(the detector), then oversleeve that with some plastic, then oversleeve
again with bigger brass tube which is earthed to provide some local
shielding from other stuff - but then you'd probably need to amplify the
signal which leads to a problem of power for the amp circuit.

Unless the DS2413 was sensitive enough to cope directly.

It mentions it has 1M input impedance and a max voltage of 28V on the IO
pins - wonder if a signal diode-tiny capacitor+clamp zener+high-ohms bleed
resistor could clean up the induced mains hum on the pickup (ie turn it into
a DC signal) and still provide enough oomph to the chip???

If it could be made to work reliably, it would be elegantly simple,
intriniscally safe and the pickup assembly could be made split for slipping
onto the conductor with a finishing turn of metal foil sticky tape to
complete the earth shield.

It's a massive conjecture because I've always been crap at analogue stuff....

A Y rated capacitor voltage divider driving a fet would be far simpler
and meet more legal requirements.


NT

NT wrote:

On Jan 7, 12:02 am, Tim Watts wrote:
Dave Liquorice wrote:
DS2413

Looks like a very handy device, that...

The only way I can think of doing a reliable non contact volt-detection
is to do something like slip the conductor through a small bit of brass
tube (the detector), then oversleeve that with some plastic, then
oversleeve again with bigger brass tube which is earthed to provide some
local shielding from other stuff - but then you'd probably need to
amplify the signal which leads to a problem of power for the amp circuit.

Unless the DS2413 was sensitive enough to cope directly.

It mentions it has 1M input impedance and a max voltage of 28V on the IO
pins - wonder if a signal diode-tiny capacitor+clamp zener+high-ohms
bleed resistor could clean up the induced mains hum on the pickup (ie
turn it into a DC signal) and still provide enough oomph to the chip???

If it could be made to work reliably, it would be elegantly simple,
intriniscally safe and the pickup assembly could be made split for
slipping onto the conductor with a finishing turn of metal foil sticky
tape to complete the earth shield.

It's a massive conjecture because I've always been crap at analogue
stuff...

A Y rated capacitor voltage divider driving a fet would be far simpler
and meet more legal requirements.


NT

That's effecitvely what I proposed, only the capacitor is formed between the
wire's insulation and the plastic between the sensing electrode and and the
earth shielding.

I was trying to meet the objective of total isolation, hence no direct
contact with the conductor.

Interesting idea with the FET - that could help. Still need to convert the
AC signal to a damped DC one though otherwise the chip is going to have a
hard time deciding if the power is "on".

Cheers

Tim
--
Tim Watts

In article ,
Tim Watts writes:
Dave Liquorice wrote:

DS2413

Looks like a very handy device, that...

The only way I can think of doing a reliable non contact volt-detection is
to do something like slip the conductor through a small bit of brass tube
(the detector), then oversleeve that with some plastic, then oversleeve
again with bigger brass tube which is earthed to provide some local
shielding from other stuff - but then you'd probably need to amplify the
signal which leads to a problem of power for the amp circuit.

Unless the DS2413 was sensitive enough to cope directly.

It mentions it has 1M input impedance and a max voltage of 28V on the IO
pins - wonder if a signal diode-tiny capacitor+clamp zener+high-ohms bleed
resistor could clean up the induced mains hum on the pickup (ie turn it into
a DC signal) and still provide enough oomph to the chip???

Anything capacitive will be horribly subject to transmitting
any noise, usually many orders of magnitude more effectively
than the signal you're actually interested in.

Use an opto-isolator, which mostly give you 4kV isolation and
no differential grounding problems. If you select a part with
darlington output, you can switch it with as little as 1ma
driving the LED side, which you can easily derive from the
mains with a dropper resistor, and some rectification or a
protection diode, and a fuse for safety. If the DS2413 has
an internal pull-up or pull-down, you could connect the
opto isolator directly. Otherwise, you'll need to handle
providing a pull-up or pull-down and micopower from the
1-wire bus.

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]

On Jan 7, 12:57*am, Steve Walker -
family.me.uk wrote:
On 06/01/2012 23:53, robgraham wrote:









On Jan 6, 8:08 pm, *wrote:
On Fri, 06 Jan 2012 14:57:53 +0000, Dave Liquorice wrote:
Is there a 1-Wire(*) device that can detect the presence of mains? I
suspect that the DS2413 might do it but ideally I'd like it to be
galvanicly isolated so there is no chance of mains getting where it
shouldn't and frying things.

The application is to monitor the various pumps and demands on the
heating system here in conjunction with a scattering of 1-Wire
temperature sensors.

(*) "1-Wire" as in using the same system as the cheap temperature
sensors you can get from Dallas/Maxim.

If you aren't doing fast switching use a mains relay (preferably with
gold-plated contacts) feeding a DS2413. It's easier than having to filter
the mains input and gives excellent isolation. You may still have to
debounce the input in software though.

--
Mick * * * * * * * * * * *(Working in a M$-free zone!)
Web:http://www.nascom.info
Filtering everything posted from googlegroups to kill spam.

I retired from electronics 5 years ago, so questions such as this are
of interest. *I followed up this DS2413 via Mr Google - now I did
expect to be able to understand quite what this device does, but I'm
obviously already being left far behind as the description was just so
much gobbledegook.

Could some kind person give me an idea of what it does in words on one
syllable plain English please.

Rob

It's a digital i/o device with two pins, either of which can be used as
an input or an output.

The way the outputs are set and inputs read is via serial communication.
Unlike most serial communication, 1-wire devices (they actually use two
wires) have a 0V line and a communications line - the comms line is held
at 5V when not communicating, allowing the device to power itself from
the comms line and store enough power to carry on working during
communications. A number of devices can be daisychained together and
each addressed by its unique 64-bit code, which is set during manufacture..

There's a whole lot more to it, but that's the basics.

SteveW

Thanks Steve - I should have said I've played with the temperature
sensing versions of this system, but the wording on the Maxim website
for the DS2413 left me absolutely cold. But now that I understand the
basic aim, I'll go back and see if I can understand enough of the
phraseology to see if I could use it too.

Rob

On Sat, 7 Jan 2012 18:40:35 +0000 (UTC), Andrew Gabriel wrote:

Use an opto-isolator, which mostly give you 4kV isolation and
no differential grounding problems.

I was looking for something else and stumbled across the 4N25 opto
isolator that gives 7kV isolation and the blurb wittered about
meeting JEDEC regulations (what ever they are)

And I've just stumbled across a MID400 from Fairchild:

http://www.fairchildsemi.com/pf/MI/MID400.html

Which in the forum thread I found it mentioned in indicates it does
all the messy mains isolation/detection on chip and provides a logic
output. Only external component is a mains rated resistor. Only costs
a few quid as well... B-)

http://www.navitron.org.uk/forum/ind...ic,6127.0.html

This thread also has the idea of using a relay (or opto isolator
transistor) to add/remove a 1-Wire device from the bus and using
software to detect if a given device is present or not.

--
Cheers
Dave.

On Jan 7, 11:12*am, Tim Watts wrote:
NT wrote:
On Jan 7, 12:02 am, Tim Watts wrote:
Dave Liquorice wrote:
DS2413

Looks like a very handy device, that...

The only way I can think of doing a reliable non contact volt-detection
is to do something like slip the conductor through a small bit of brass
tube (the detector), then oversleeve that with some plastic, then
oversleeve again with bigger brass tube which is earthed to provide some
local shielding from other stuff - but then you'd probably need to
amplify the signal which leads to a problem of power for the amp circuit.

Unless the DS2413 was sensitive enough to cope directly.

It mentions it has 1M input impedance and a max voltage of 28V on the IO
pins - wonder if a signal diode-tiny capacitor+clamp zener+high-ohms
bleed resistor could clean up the induced mains hum on the pickup (ie
turn it into a DC signal) and still provide enough oomph to the chip???

If it could be made to work reliably, it would be elegantly simple,
intriniscally safe and the pickup assembly could be made split for
slipping onto the conductor with a finishing turn of metal foil sticky
tape to complete the earth shield.

It's a massive conjecture because I've always been crap at analogue
stuff...
A Y rated capacitor voltage divider driving a fet would be far simpler
and meet more legal requirements.

NT

That's effecitvely what I proposed, only the capacitor is formed between the
wire's insulation and the plastic between the sensing electrode and and the
earth shielding.

I was trying to meet the objective of total isolation, hence no direct
contact with the conductor.

Interesting idea with the FET - that could help. Still need to convert the
AC signal to a damped DC one though otherwise the chip is going to have a
hard time deciding if the power is "on".

Cheers

Tim

Your proposal lacked a Y rated dielectric or any approvals. Converting
50Hz to dc is fairly trivial, if necessary.

NT wrote:


Your proposal lacked a Y rated dielectric or any approvals. Converting
50Hz to dc is fairly trivial, if necessary.

Are you saying that the conductor's insulation is untrustworthy?

--
Tim Watts

In article o.uk,
"Dave Liquorice" writes:
On Sat, 7 Jan 2012 18:40:35 +0000 (UTC), Andrew Gabriel wrote:

Use an opto-isolator, which mostly give you 4kV isolation and
no differential grounding problems.

I was looking for something else and stumbled across the 4N25 opto
isolator that gives 7kV isolation and the blurb wittered about
meeting JEDEC regulations (what ever they are)

4N25 is ancient and has poor gain by today's standards.
I would look at something like TLP523 instead.

JEDEC covers case styles, and in some cases pinouts for
common parts.

And I've just stumbled across a MID400 from Fairchild:

Looks interesting, but I've never used it.

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]

On Jan 7, 11:04*pm, Tim Watts wrote:
NT wrote:
Your proposal lacked a Y rated dielectric or any approvals. Converting
50Hz to dc is fairly trivial, if necessary.

Are you saying that the conductor's insulation is untrustworthy?

I'm saying its required by law to be a class Y dielectric


NT

NT wrote:

On Jan 7, 11:04 pm, Tim Watts wrote:
NT wrote:
Your proposal lacked a Y rated dielectric or any approvals. Converting
50Hz to dc is fairly trivial, if necessary.

Are you saying that the conductor's insulation is untrustworthy?

I'm saying its required by law to be a class Y dielectric



Coming back to common sense, I'd feel happier with applying a detector
sleeve over inulation that iteself meets the voltage requirement, rather
than directly connecting a class Y capacitor. It's not the capacitor that's
the risk, but engineering out other problems like, say, condensation getting
on the PCB where the capacitor is mounted.

If you were manufacturing these, you'd test the prototype and probably apply
coatings or potting to avoid this problem.

For a DIY solution, I'd much rather have a non contact solution as proposed,
or use a relay in a box with space.screw terminals where I can visually
confirm the isolation.

Saying the cap must be class Y is one thing, but it's meaningless unless you
can verify the installation of it.



--
Tim Watts

On Jan 8, 5:42*pm, Tim Watts wrote:
NT wrote:
On Jan 7, 11:04 pm, Tim Watts wrote:
NT wrote:
Your proposal lacked a Y rated dielectric or any approvals. Converting
50Hz to dc is fairly trivial, if necessary.

Are you saying that the conductor's insulation is untrustworthy?

I'm saying its required by law to be a class Y dielectric

Coming back to common sense, I'd feel happier with applying a detector
sleeve over inulation that iteself meets the voltage requirement, rather
than directly connecting a class Y capacitor. It's not the capacitor that's
the risk, but engineering out other problems like, say, condensation getting
on the PCB where the capacitor is mounted.

If you were manufacturing these, you'd test the prototype and probably apply
coatings or potting to avoid this problem.

For a DIY solution, I'd much rather have a non contact solution as proposed,
or use a relay in a box with space.screw terminals where I can visually
confirm the isolation.

Saying the cap must be class Y is one thing, but it's meaningless unless you
can verify the installation of it.

Do you know what a Class Y cap is?


NT

NT wrote:

On Jan 8, 5:42 pm, Tim Watts wrote:
NT wrote:
On Jan 7, 11:04 pm, Tim Watts wrote:
NT wrote:
Your proposal lacked a Y rated dielectric or any approvals.
Converting 50Hz to dc is fairly trivial, if necessary.

Are you saying that the conductor's insulation is untrustworthy?

I'm saying its required by law to be a class Y dielectric

Coming back to common sense, I'd feel happier with applying a detector
sleeve over inulation that iteself meets the voltage requirement, rather
than directly connecting a class Y capacitor. It's not the capacitor
that's the risk, but engineering out other problems like, say,
condensation getting on the PCB where the capacitor is mounted.

If you were manufacturing these, you'd test the prototype and probably
apply coatings or potting to avoid this problem.

For a DIY solution, I'd much rather have a non contact solution as
proposed, or use a relay in a box with space.screw terminals where I can
visually confirm the isolation.

Saying the cap must be class Y is one thing, but it's meaningless unless
you can verify the installation of it.

Do you know what a Class Y cap is?


Yes. What's that got to do with my argument?

--
Tim Watts

On Sun, 8 Jan 2012 00:16:51 +0000 (UTC), Andrew Gabriel wrote:

And I've just stumbled across a MID400 from Fairchild:

Looks interesting, but I've never used it.

The MID400 looks the way to go for this project I think. I've also
noticed the 8 channel 1-Wire IO chip as well, there are at least 4
mains powered devices I want to monitor.

--
Cheers
Dave.

On Sat, 07 Jan 2012 22:29:40 +0000, Dave Liquorice wrote:
And I've just stumbled across a MID400 from Fairchild:

http://www.fairchildsemi.com/pf/MI/MID400.html

Doesn't that just provide a convenient way of detecting that AC is
available, rather than "being used by something"? (it's the latter I'm
interested in, and I thought the OP too...)

On Jan 6, 9:42*pm, "Dave Liquorice"
wrote:
On Fri, 06 Jan 2012 17:22:47 +0000, Tim Watts wrote:
Volts or amps?

Only, volts on mains wiring is really hard to detect reliably with a
high resistance isolation as it is so easy to pick up stray voltages.

Presence ie is something switched on? Loads are around 50W for
circulation pumps or oil boiler. I've been half looking at hall
effect switches to feed into a DS2413 1-Wire dual channel PIO device.
But I haven't a clue about the field strengths that hall effect
switches need or those that you'll find around a mains cable carrying
200mA or so.

How about something really simple, like a mains powered relay,

I have a load of relays that could be liberated from the old control
box but that just seems a bit over kill and "old fashioned" but does
solve the isolation side. I can't help feeling that there must be
something from the process control area for this but perhaps they
don't come cheap...

an opto-isolator, or a home brew optoisolator using a photo-device
pointing at a fully sealed mains LED unit?

Mains LED indiactor, opto switch into a DS2413 that's another way.
Might be a fair bit of messing about with heatshrink to make light
tight units though.

Bog standard opto-isolator with suitable current limit to let 10mA
through the LED. Add a "reverse parallel" diode across the LED to cope
with the AC. Already in a light tight package.

MBQ

On Jan 6, 2:57*pm, "Dave Liquorice"
wrote:
Is there a 1-Wire(*) device that can detect the presence of mains? I
suspect that the DS2413 might do it but ideally I'd like it to be
galvanicly isolated so there is no chance of mains getting where it
shouldn't and frying things.

The application is to monitor the various pumps and demands on the
heating system here in conjunction with a scattering of 1-Wire
temperature sensors.

(*) "1-Wire" as in using the same system as the cheap temperature
sensors you can get from Dallas/Maxim.
--
Cheers
Dave.

A flow switch in line would tell you more about the state of your
pump....

On Thu, 12 Jan 2012 13:45:32 +0000 (UTC), Jules Richardson wrote:

And I've just stumbled across a MID400 from Fairchild:

http://www.fairchildsemi.com/pf/MI/MID400.html

Doesn't that just provide a convenient way of detecting that AC is
available, rather than "being used by something"? (it's the latter I'm
interested in, and I thought the OP too...)

I am the OP and am happy to make the assumption that if there is
mains on the wire directly connected to a pump that the pump is
running...

--
Cheers
Dave.

On Thu, 12 Jan 2012 16:52:45 +0000, Dave Liquorice wrote:
http://www.fairchildsemi.com/pf/MI/MID400.html

Doesn't that just provide a convenient way of detecting that AC is
available, rather than "being used by something"? (it's the latter I'm
interested in, and I thought the OP too...)

I am the OP and am happy to make the assumption that if there is mains
on the wire directly connected to a pump that the pump is running...

Yes, I got hung up on the "monitoring" side of it and missed the "detect
the presence of mains" bit in the first paragraph