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PICList Thread
'Looking for a AC Current sensor'
1997\03\27@155525 by sdavidson

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face
I went through my old PIC messages and can't find a reference to one, but I
know I have seen one.  I need to sense if a motor is still running (current
through my relays on my PC board.)  Someone must make a PC board mountable
on/off sensor for AC current(1-10amps).  I have seen hall effect switches
mentioned, but can't find a source.  This should be electrical isolated and
will interface to my PIC.

Thanks in advance.

Steve
-------------------------------------
E-mail: spam_OUTsdavidsonTakeThisOuTspamits.bldrdoc.gov
Steven Davidson
Dept. of Comm.  NTIA-ITS.N2
325 Broadway
Boulder, CO  80303
W 303-497-3411  FAX 5995
-------------------------------------

1997\03\27@182200 by Harrison Cooper

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face
Microswitch makes em

{Quote hidden}

1997\03\27@194723 by John Dammeyer

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At 01:37 PM 27/03/1997 PST, you wrote:
>I went through my old PIC messages and can't find a reference to one, but I
>know I have seen one.  I need to sense if a motor is still running (current
>through my relays on my PC board.)  Someone must make a PC board mountable
>on/off sensor for AC current(1-10amps).  I have seen hall effect switches
>mentioned, but can't find a source.  This should be electrical isolated and
>will interface to my PIC.
>

Hall effect might be kind of pricy.  A toroid core with a one layer wrap of
about 30g wire loaded with a diode and a resistor || cap should give you a
high enough voltage to determine if you have current through the primary, (1
turn), going to the motor.

John
Pioneers are the ones, face down in the mud,
with arrows in their backs.
Automation Artisans Inc.      Ph. 1-250-544-4950
PO Box 20002                  Fax 1-250-544-4954
Sidney, BC CANADA V8L 5C9

1997\03\27@201752 by Tony Matthews

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face
sdavidson@ITS.BLDRDOC.GOV wrote:
>
> I went through my old PIC messages and can't find a reference to one, but I
> know I have seen one.  I need to sense if a motor is still running (current
> through my relays on my PC board.)  Someone must make a PC board mountable
> on/off sensor for AC current(1-10amps).  I have seen hall effect switches
> mentioned, but can't find a source.  This should be electrical isolated and
> will interface to my PIC.
>
> Thanks in advance.
>
> Steve
> -------------------------------------
> E-mail: sdavidsonspamspam_OUTits.bldrdoc.gov
> Steven Davidson
> Dept. of Comm.  NTIA-ITS.N2
> 325 Broadway
> Boulder, CO  80303
> W 303-497-3411  FAX 5995
> -------------------------------------
I have'nt tried this but if you put a small coil of wire with a lot of
wraps around the power lead you have a transformer with a 1 turn primary
the pic 16c84 has cmos inputs with protection diodes so you would have a
60 hertz square wave to the pin or not .isolated cheap small.Maybe it'll
work to. Now go back and let the experts tell you how to do it right :}.

1997\03\28@104743 by )

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face
Took a quick look through the Newark Electronics catalog. Found PC mount
sensors from F.W. Bell and Honeywell (pgs. 552-553 of cat. #114). The PC
mount ones are linear output, so you might need a comparator or
something to give you a go/no-go signal. Bell's are the PI series,
Honeywell's are the CSLA1/2 series. There are other non-PC mount type
sensors with a presettable threshold which gives you logic out for above
or below the threshold by Bell, Honeywell and others. These are on the
large size; PC mouse and larger. Some relay manufacturers such as
Guardian make similar (usually relay output) devices.

Hope this is of some help.


Frank Richterkessing
Experimental Methods Engineer
GE Appliances

@spam@FRANK.RICHTERKESSINGKILLspamspamAPPL.GE.COM


{Quote hidden}

1997\03\28@111924 by motodog

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Try Microswitch?

1997\03\28@181339 by Michael S. Hagberg

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face
circuit cellar did an article not long ago thant used ferret beads
and wrapped wire around them to send the signal to an a/d then into
a cpu.  he monitored all the circuits in his house.


michael


'[PICLIST] Current Sensor'
2002\06\16@194710 by Tony Nixon
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picon face
Hi all,

I'm sorry about the delay in the current sensor details. I have been off
work for a week so I could study for my pilots exam. (Of which I passed
:-)))

I should be able to have it ready tonight.

--
Best regards

Tony

mICros
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RemoveMEsalesspamTakeThisOuTbubblesoftonline.com

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2002\06\17@012237 by Pic Dude

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> "so I could study for my pilots exam. (Of which I passed
:-)))"

Woo-hoo!  Congrats!  And welcome to the club.

Cheers,
-Neil.



{Original Message removed}


'[EE:] Current sensor'
2004\02\12@155047 by Dmitriy Fitisov
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Hello everyone,
I think about measuring current in car.
The problem I see - current is big enough and impulses
may go really high and measure voltage drop on resistor I see chalenging.
Another thing I'd like to have -
indication of current direction to or from battery.
Anybody has any thoughts? Current transformator, Hall sensor (??)
anything else?
Thanks.
Dmitriy Fitisov.

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'RE : ] Current sensor'
2004\02\12@160543 by Samuel BOUQUET

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Check out http://www.lem.com or http://www.lemauto.com, leader in current sensor (Hall
effect).

-----Message d'origine-----
De : pic microcontroller discussion list [PICLISTEraseMEspam.....MITVMA.MIT.EDU]
De la part de Dmitriy Fitisov
Envoyé : jeudi 12 février 2004 21:49
À : EraseMEPICLISTspamMITVMA.MIT.EDU
Objet : [EE:] Current sensor


Hello everyone,
I think about measuring current in car.
The problem I see - current is big enough and impulses
may go really high and measure voltage drop on resistor I see
chalenging.  Another thing I'd like to have -  indication of current
direction to or from battery.  Anybody has any thoughts? Current
transformator, Hall sensor (??)  anything else? Thanks. Dmitriy Fitisov.

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'[EE:] Current sensor'
2004\02\12@162413 by Larry Bradley

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Dimitri, I've built a rather complete battery monitoring system for my
sailboat. I used a standard shunt (50 millivolt, 100 amp), amplified the
voltage up to + or - 2 volts, then fed it to a  MAX186 A/D converter, which
is connected to a PIC.

The shunt in my case goes in the -ve battery lead, as this makes life a bit
easier. I used an external A/D that can handle bipolar input voltages. This
one I had on hand - it is an 8 channel, 12 bit converter - I also needed
the 12 bit resolution.

I originally tried a "absolute value" circuit, right out of "The Art of
Electronics", to convert the + or- 2 volts into a positive only voltage,
and a comparator to detect +ve or -ve. This worked fine, but I eventually
went to the external A/D as I had one on hand, and I wanted the higher
resolution.

The shunt I used was from Blue Seas Systems (they have a web site, and any
boating supply place should have their stuff.


At 03:48 PM 2/12/2004 -0500, you wrote:
{Quote hidden}

Larry Bradley
Orleans (Ottawa), Ontario, CANADA

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2004\02\12@163041 by Richard.Prosser

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Dmitriy,

The "traditional" answer to this question is using the bond wire to chassis
(or the live feed wire to the battery) as a current shunt. This works OK
but can be improved by adding temperature compensation. Adding logrithmic
amplifiers (one for each direction) may also be desirable if you are
wanting to cover the whole range.
Are you including cranking current for  example? - or just normal charge &
discharge?.

Embedding a temperature sensor in the bond wire & using it to correct for
wire resistance is probably going to be enough. You will need to figure out
a way of calibrating it however.

An opamp can perform the amplification, filtering  & any level shift
required.

Richard P





Hello everyone,
I think about measuring current in car.
The problem I see - current is big enough and impulses
may go really high and measure voltage drop on resistor I see chalenging.
Another thing I'd like to have -
indication of current direction to or from battery.
Anybody has any thoughts? Current transformator, Hall sensor (??)
anything else?
Thanks.
Dmitriy Fitisov.

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2004\02\12@164114 by David Minkler

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face
Dmitriy,

Measure the voltage drop across the main ground cable between the
battery negative terminal and its point of attachment to the chassis
(I'm assuming negative ground here).  Amplitude will need to be
calibrated but signals are small and direction of current flow is
preserved.  The cable is your sense resistor; it has to be there
anyway.  This was (may still be for all I know) a common technique used
in the old uncalibrated dash displays.

Best regards,

Dave

Dmitriy Fitisov wrote:

{Quote hidden}

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2004\02\12@164734 by David Schmidt

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I believe there are off the shelf hall effect current sensors (pass the wire
through a loop) that will output a conditioned signal.
Just in case you didn't want to buy and add in your own current shunt.

Dave

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2004\02\12@201555 by Dmitriy Fitisov

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Thanks everyone.
Hall effect sensors from http://www.lem.com look nice,
otherwise decided on 50W 0.01 Ohm resistor from Vishay.



{Original Message removed}

2004\02\12@211105 by Jinx

face picon face
Silicon Chip 6/2002. 80A, 3-digit LED, Hall Effect sensor

http://www.siliconchip.com.au/cms/A_30551/article.html

Uses an F84

The code

http://www.siliconchip.com.au/software/jun02/ammeter.zip

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2004\02\12@211933 by Denny Esterline

picon face
Look into the hall effect current sensors from allegro.
http://www.allegromicro.com/sf/0750/

Very low insertion loss, currents to 100A, isolated output, magnitude and
direction information out.

-Denny


> Hello everyone,
>  I think about measuring current in car.
>  The problem I see - current is big enough and impulses
>  may go really high and measure voltage drop on resistor I see
chalenging.
{Quote hidden}

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'[PIC] Allegro Current sensor accuracy ( was: Curre'
2004\09\13@044012 by Ake Hedman
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More on the current sense issue....

Had to check the Allegro datasheet after Chetan Bhargava's post. An (as always ;-) ) I got confused.

In the datasheet a total accuracy of +-2% is stated. The sensitivity is typically 40 mV/A.  So my readings should be  +-8mV off meaning I have a resolution of about +-10.2A.

In the datasheet there is also a noice given as 14mV (0.35A). How should I calculate the effekt of this noice? Can I calculate a running mean of the signal and expect the +-2 accuracy or do I need to add also the 0.35A to the expected error?

Reards
/Ake


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'[EE]: appliance current sensor'
2005\08\20@200656 by Marcel Birthelmer
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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. However, I'm not sure it's such a
good idea for me to be screwing with high-voltage high-current lines. Do
any of you have experience with a similar project?
After some initial investigation I'm guessing a hall sensor would be
best, but I'm not sure which of the wire strands it would wrap around
and so forth.
Any input would be appreciated, both about the actual current sensing as
well as the delivery mechanism from the garage (no cat5 drop; wireless?)
to my room (my computer or otherwise).
For extra credit, Rube Goldberg Machines are also welcome.
- Marcel

2005\08\20@205502 by Jinx

face picon face
> Any input would be appreciated, both about the actual current
> sensing as well as the delivery mechanism from the garage (no
> cat5 drop; wireless?) to my room (my computer or otherwise)

I don't think you'd need to isolate any particular wire to use a Hall
Effect clamp. A washer/drier would be drawing a fairly high current
that could be picked up pretty easily. You can get some pretty cheap
(NZ$10) 433MHz transceivers for comms, or make an FM "bug"
to transmit a beep in the broadcast band that you could pick up
on an ordinary radio

2005\08\20@210250 by Marcel Birthelmer

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face
Jinx wrote:
>>Any input would be appreciated, both about the actual current
>>sensing as well as the delivery mechanism from the garage (no
>>cat5 drop; wireless?) to my room (my computer or otherwise)
>
>
> I don't think you'd need to isolate any particular wire to use a Hall
> Effect clamp. A washer/drier would be drawing a fairly high current
> that could be picked up pretty easily.

Hmm, as I understood you could only apply a current sensor on one
"strand" (either ingoing or outgoing) so that the fields don't cancel
each other out?

You can get some pretty cheap
> (NZ$10) 433MHz transceivers for comms, or make an FM "bug"
> to transmit a beep in the broadcast band that you could pick up
> on an ordinary radio
>

Hmm, interesting idea!

- Marcel

2005\08\20@211655 by Timothy J. Weber

face
flavicon
face
Marcel Birthelmer wrote:
> This means that I can never hear when the washer or dryer are
> done, and so my laundry scheduling is always suboptimal.

Baby monitors are pretty cheap...  I use mine to monitor my washing from
other floors of the house all the time!

Or if you want something more fun, make a low-power RF transmitter bug
and tune into it with an FM radio.
--
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2005\08\20@211954 by Bob Axtell

face picon face
Marcel Birthelmer wrote:

> Jinx wrote:
>
>>> Any input would be appreciated, both about the actual current
>>> sensing as well as the delivery mechanism from the garage (no
>>> cat5 drop; wireless?) to my room (my computer or otherwise)
>>
>>
>>
>> I don't think you'd need to isolate any particular wire to use a Hall
>> Effect clamp. A washer/drier would be drawing a fairly high current
>> that could be picked up pretty easily.
>
>
> Hmm, as I understood you could only apply a current sensor on one
> "strand" (either ingoing or outgoing) so that the fields don't cancel
> each other out?


Have to measure one just conductor- if going across both, they cancel
each other out.

I might add that this is how those  bathroom fault detectors work, i.e.
if one leg doesn't match the other PRECISELY, there is a fault and the
current on both legs is immediately broken.  

{Quote hidden}

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2005\08\20@212909 by Jinx

face picon face
> Hmm, as I understood you could only apply a current sensor on
> one "strand" (either ingoing or outgoing) so that the fields don't
> cancel each other out ?

The sensor is going to be closer to one wire than the other. You'd
be pretty unlucky to get exact cancellation

2005\08\20@214122 by Mike Harrison

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face
On Sat, 20 Aug 2005 17:08:59 -0700, you wrote:

{Quote hidden}

A neat solution is to use a linear GMR sensor - NVE make some. These are more sensitive than hall
devices can easily sense the sort of current you are looking at, without needing to split the 3 core
mains cable - the field is sufficiently assymetrical to get a decent signal if the sensor is clipped
onto the outside of the cable  - you may need to slide it along the cable to get the best signal due
to the core twist. From memory a small amount of gain (10x) plus a data-slicer style comparator will
give you a nice 50/60hz signal when current is flowing and none when off.


': appliance current sensor'
2005\08\20@214301 by Vasile Surducan

face picon face
On 8/21/05, Timothy J. Weber <RemoveMEtjweberTakeThisOuTspamspamlightlink.com> wrote:
> Marcel Birthelmer wrote:
> > This means that I can never hear when the washer or dryer are
> > done, and so my laundry scheduling is always suboptimal.
>
> Baby monitors are pretty cheap...  I use mine to monitor my washing from
> other floors of the house all the time!
>
> Or if you want something more fun, make a low-power RF transmitter bug
> and tune into it with an FM radio.


About 1.5 euro, that's the cost of a small RF transmitter on 80-108MHz FM.
But should be pretty nasty to hear it about one our or so or to hunt
the end of the
washing cycle.

Vasile

'[EE] appliance current sensor'
2005\08\20@214305 by Spehro Pefhany

picon face
At 01:28 PM 8/21/2005 +1200, you wrote:
> > Hmm, as I understood you could only apply a current sensor on
> > one "strand" (either ingoing or outgoing) so that the fields don't
> > cancel each other out ?
>
>The sensor is going to be closer to one wire than the other. You'd
>be pretty unlucky to get exact cancellation

If a high-permeability core goes around both conductors, then the fields
cancel out pretty well.

Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
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2005\08\20@222608 by Jinx

face picon face
> If a high-permeability core goes around both conductors, then
> the fields cancel out pretty well

Is that likely with an appliance lead ?

I just tried a UGN3503 on our washing machine lead and had
no problem picking up a distinctive 30mV 50Hz signal when the
sensor is over the active and the machine is turned on. There is
negligible signal when the machine is turned off. Enough of a
difference to detect, even unamplified, with a PIC comparator
or ADC


2005\08\20@231715 by Spehro Pefhany

picon face
At 02:25 PM 8/21/2005 +1200, you wrote:
> > If a high-permeability core goes around both conductors, then
> > the fields cancel out pretty well
>
>Is that likely with an appliance lead ?
>
>I just tried a UGN3503 on our washing machine lead and had
>no problem picking up a distinctive 30mV 50Hz signal when the
>sensor is over the active and the machine is turned on. There is
>negligible signal when the machine is turned off. Enough of a
>difference to detect, even unamplified, with a PIC comparator
>or ADC

Sure, without something like a toroidal core around the wire(s).

With a clamp-on ammeter I test 0.0A with 15A AC 2-conductors flowing,
regardless of position of the wire inside the core, so the
cancellation seems to be >99.6%.

Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
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2005\08\21@000038 by Jinx

face picon face
> > > If a high-permeability core goes around both conductors,
> > > then the fields cancel out pretty well

> cancellation seems to be >99.6%.

Oh, I see what you mean. I thought you were referring to a shield
in the wire itself

2005\08\21@010920 by Jinx

face picon face
Marcel, our washing machine has a series of LEDs, one for
each part of the program. When the cycle is started, all the
LEDs are on. The last to go off is the red Final Spin. Looking
at this LED might be a better way, on this machine anyway,
than detecting power in the cord, because the amperage is up
and down with each part of the cycle. At times it's very low,
eg when just a valve is open to re-fill, and that may not be
enough to give a big enough comparison to actually finished
and off. A drier won't have those lower power states - it'll
be on (motor at least, with or without heat) or off

2005\08\21@014732 by Marcel Birthelmer

flavicon
face
Jinx wrote:
> Marcel, our washing machine has a series of LEDs, one for
> each part of the program. When the cycle is started, all the
> LEDs are on. The last to go off is the red Final Spin. Looking
> at this LED might be a better way, on this machine anyway,
> than detecting power in the cord, because the amperage is up
> and down with each part of the cycle. At times it's very low,
> eg when just a valve is open to re-fill, and that may not be
> enough to give a big enough comparison to actually finished
> and off. A drier won't have those lower power states - it'll
> be on (motor at least, with or without heat) or off
>

Ours unfortunately has no visual indicators. I can only work with the
environment around the machine. This leaves me with a few parameters to
analyze:
- sound
- current draw
- vibration

So for sound, the baby monitor solution would work. But it's not
something I consider a very elegant solution, really... I'm not just
trying to monitor laundry, I'm trying to learn things about engineering
and, if applicable, electronics as well. I guess a small microphone
connected to an ADC could wait until the machine is entirely quiet and
then signal. That would be subject to environmental noise though. If
both machines are running, it won't work.
For current sensing: the actual current doesn't have to be constant. I
can always slow down the sample rate to the point where any gaps are
skipped or averaged out. The main concern I have here is that I'd have
to isolate one of strands of the wire, and I'm not sure that's such a
good idea.
Vibration testing hadn't actually occured to me until now, but I'm not
sure I can use that. I guess a very precise accelerometer would be able
to detect the shaking from the machine, so maybe that would be another
approach.

Of course, I could just train a monkey to wait for the buzz and then
race to my room to notify me.

- Marcel

2005\08\21@085415 by olin piclist

face picon face
Marcel Birthelmer wrote:
> This means that I can never hear when the washer or dryer are
> done, and so my laundry scheduling is always suboptimal.
>
> ...
>
> 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.

Picking off the current shouldn't be that hard.  My first knee jerk reaction
is to make a small adaptor thingy that has a plug on one end and a socket on
the other.  In other words it can be plugged in line with a standard
appliance.  Now take a ferrite rod and wind a few turns of the hot side on
one end and the return wire on the other.  Make sure the turn directions are
such that the magnetism in the rod adds when current flows thru the
appliance normally.  Now wind maybe 100 turns of magnet wire around the
center of the rod.  Leave 5mm of space between the center windings and
either end winding, and of course keep the insulation on the end windings.

This will give you a nicely isolated 60Hz voltage signal proportional to the
appliance current draw.  For simplicity power the circuit from a small wall
wart which can be part of the overall adapter.

Hopefully you can figure out the rest.  You won't need much analog
electronics to take the current signal and have it drive a PIC A/D input
(just three resistors and a cap if the signal is strong enough).  The PIC
samples the current signal often and the rest is software to decide how low
for how long is considered off.


*****************************************************************
Embed Inc, embedded system specialists in Littleton Massachusetts
(978) 742-9014, http://www.embedinc.com

2005\08\21@104044 by Mark Rages

face picon face
On 8/21/05, Marcel Birthelmer <marcelSTOPspamspamspam_OUTcarrietech.com> wrote:
> Ours unfortunately has no visual indicators. I can only work with the
> environment around the machine. This leaves me with a few parameters to
> analyze:
> - sound
> - current draw
> - vibration
>

There's one you left out -- time.

You could calibrate one of these:
www.acehardware.com/sm-sunbeam-60-minute-timer--pi-1277749.html
to the cycle time.  It's also a portable, wireless solution.

Regards,
Mark
markrages@gmail

--
You think that it is a secret, but it never has been one.
 - fortune cookie

2005\08\21@125532 by Timothy J. Weber

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flavicon
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Marcel Birthelmer wrote:
>
> I guess a small microphone
> connected to an ADC could wait until the machine is entirely quiet and
> then signal. That would be subject to environmental noise though. If
> both machines are running, it won't work.

> Of course, I could just train a monkey to wait for the buzz and then
> race to my room to notify me.

Well, if there's a buzz, what about recognizing that?

This is the most complicated yet plausible method I can come up with
using pieces I'm personally conversant with:

Small condenser mic feeds into a PIC's ADC.  Find out the fundamental
frequency of the buzzer.  Sample at 1-4x Nyquist frequency.  Do an FFT
(may require a dsPIC) and look for energy in that spectral band, OR
count zero crossings and match a window of samples around the zero
crossings to find the fundamental (less computationally intensive and
may work well for a single target sound).  When you've detected that
fundamental for 90-110% of the normal duration of the buzz (and it has
then stopped), send out a packet over a ZigBee wireless connection
(there are several products that will convert TTL serial I/O to ZigBee).
 The other end of that is connected to one of the PICs with USB
support, set up as a HID for simplicity.  The USB then plugs into your
PC and talks to an GUI app there.

Now, ideally, your PC is either set up as a web server (if you have a
broadband Internet connection) so you can poll the state of your laundry
from anywhere in the world (and the rest of us could see it too).  You
could also use a script to FTP it to an external web server though, even
over dialup.

Baby monitors, timers - this seems much simpler and more reliable.  ;)
--
Timothy J. Weber                 http://www.lightlink.com/tjweber
spamBeGonetjweberSTOPspamspamEraseMElightlink.com

2005\08\22@001059 by Chen Xiao Fan

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Great! This will probably one very interesting project for
hobbyist. :)

Who knows what will happen 20 years later? Embedded TCP/IP
seems quite hot some time ago. Everything will has its
own IP address. A person will have lots of IP address
associated with him/her since he/she will carry lots
of gadgets. :)

Seriously the only barrier is now the power source. Wireless
power transfer is not so easy now (only for very low
power).

Regards,
Xiaofan

{Original Message removed}

2005\08\22@002530 by Charles Linquist

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I use an Allegro Hall-effect device to monitor current. Since
it uses magnetic coupling, there is no problem with 110/220VAC.

If you use a 12F675 you can either use the on-board comparator or
an A/D channel to determine whether the appliance is drawing current or
not. You can convert that information to RS-232 by bit-banging a serial
port.

Finally, a Lantronix XPort does a great job of converting serial to
tcp/ip. You can telnet to it, or it can send an email message or serve
up a web page telling you the state of the appliance.

Charles Linquist


Chen Xiao Fan wrote:
{Quote hidden}

> {Original Message removed}

2005\08\22@050626 by Howard Winter

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Jinx,

On Sun, 21 Aug 2005 17:08:42 +1200, Jinx wrote:
>...<
> A drier won't have those lower power states - it'll
> be on (motor at least, with or without heat) or off

Not my dryer - it stops and reverses to stop tangling.  
The off period is a few seconds each time.  (And it's
gas heated, so during those stops there may be just the
control circuits drawing current, or those plus a
solenoid).

Cheers,


Howard Winter
St.Albans, England


2005\08\22@070246 by Howard Winter

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flavicon
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Marcel,

I don't want to spoil the fun by suggesting an off-the-shelf solution, but over here you can get multi-way
socket strips where one (the master) is sensed for current flow, and the others are only switched on when the
master is in use.  They're intended for computer use, where the computer itself plugs into the master and the
monitor, printer, modem, speakers etc. are plugged into the others, so turning off the PC itself turns off the
rest.

So  you could just run a small table-lamp or similar from one of the slave sockets - it will be on while the
machine is running, off when it stops.

Cheers,


Howard Winter
St.Albans, England


2005\08\22@153557 by Peter

picon face

My turn to chip in: I once made an operation sensor for a high power
heater (~15kW). I was not allowed to connect to the circuit in any way.
Including not open boxes to get at the cables etc. So I used a
differential thermistor sensor with an opamp. One thermistor was on the
board and the other was pvc-taped to the high gauge conductor that fed
the heater control unit (3 phase). The heater cable would run hot.
Voila. Inertia was half a minute give or take a little, the cable was
2/3 inches external diameter PVC 5 wires (3ph + gnd). It would heat up
2-3 degrees above ambient with the heater on. That gives more than 2% R
change with any thermistor and is easy to detect.

Another thing I tried was to use a cassette tape playback head and
preamplifier. The head would be brought in contact with the cable. The
output ac would be huge when the load was on. The tape head picks up the
stray field near the cable. The direction and orientation of the head
were important but not that important. The output ratio with/without
load was 1:100 or larger.

Peter

2005\08\25@093719 by Bill & Pookie

picon face
My understanding of the project is to make two devices. The two devices
being a remote device and a local device. The remote device will sense if
each of two appliances are either on or off, and send the information to the
local device for display. If there is a failure in the system, some one will
get yelled at for leaving their cloths in the washer.

Would "not being yelled at" be considered "Mission Critical"?

I think that the sensors for the remote device should be cheep, simple to
interface and fun. With "fun" being important. Different uses for common
objects. The computer could integrate or differentiate the input signal
using a simple algorithm.

////////

Is input one on?

No

Has input one been on in last twenty seconds?

No

Then input one is probably not on.

/////////

It is only necessary for the remote unit to transmit data, and the local
unit to receive this data. As only four states are possible, the data
encoding can be simple. A simple way to do this is to use a form of Morse
code or CW transmition. Yes, dits and dahs.

////////////

The following relationships exist between the elements of the code (dits and
dahs), the characters (letters) and the words:
The DIT is the Basic UNIT of Length.
The DAH is equal in length to three DITS.
The space between the DITS and DAHS within a character (letter) is equal to
one DIT.
The space between characters (letters) in a word is equal to three DITS.
The space between words is equal to seven DITS.
(Source: U.S. Army Technical Manual TM-11459/TO 31-3-16 - Sept. 1957)

///////////


So if a dot is a binary zero and a dash a binary one, the start bit could be
a dash, or three time slots. This time could be divided by two on the
receive side and used to determine weather the next two bits are dashes or
dots, 3 or 1. If less than half the start bit, it is a dot. Else it is a
dash. And no signal for a dash time (3) shows end of data.

With the sensors the effect of ambient noise and drift due to age and
temperature can be somewhat mulled out by taking a reading with no signal
present (appliance off) and using this value as a "floor" for the input.
This calibration can be done upon power up of the remote and/or with a push
button on the remote unit.

As a "fail Safe" feature, the local unit could have a preset timer function
that is set via a push button.

Bill




'[EE] Anybody Used Allegro Current Sensor?'
2006\11\13@211129 by Bob Axtell
face picon face
Part number is ACS750SCA050 .

With 5V in, provides a nom 2.5V output with no current
flowing. The chart indicates high accuracy in either direction
out to 50A. Insertion R is 130uOhm. Looks like all I have to
do is to acquire the 2.5V level when powering up (assuming
no current flow).

The specs are so good I am skeptical. Anybody?

--Bob

2006\11\13@220033 by Marcel Duchamp

picon face
Bob Axtell wrote:
> Part number is ACS750SCA050 .
>
> With 5V in, provides a nom 2.5V output with no current
> flowing. The chart indicates high accuracy in either direction
> out to 50A. Insertion R is 130uOhm. Looks like all I have to
> do is to acquire the 2.5V level when powering up (assuming
> no current flow).
>
> The specs are so good I am skeptical. Anybody?
>
> --Bob

Check the specs over the temp range you would be encountering, Bob.

I've been looking at the Allegro current sensors but the temperature
range spec I've been seeing approaches +/-11% error band.  If that's not
a problem for your application, then they have a lot going for them, low
sense resistance being number one.

One possibility would be to try to temp-compensate them, although it
looks like they already have so you might be facing residual errors
which are usually 2nd or 3rd order.

If you investigate further let us know.

2006\11\13@225527 by alan smith

picon face
Used one in a previous life....seemed to work great.  Have one on a new design..not that part number...20A part...soic8.....and yes...easy..for my design..100mV/amp change, nominal 2.5V center.  For higher temps...believe they make an automotive grade?  But yes...add a cap, a pullup to 5V and you get the change in the voltage.  In my case, I'm looking for a motor stall current so I dont need to carefully monitor.

Marcel Duchamp <KILLspammarcel.duchampspamBeGonespamsbcglobal.net> wrote:  Bob Axtell wrote:
> Part number is ACS750SCA050 .
>
> With 5V in, provides a nom 2.5V output with no current
> flowing. The chart indicates high accuracy in either direction
> out to 50A. Insertion R is 130uOhm. Looks like all I have to
> do is to acquire the 2.5V level when powering up (assuming
> no current flow).
>
> The specs are so good I am skeptical. Anybody?
>
> --Bob

Check the specs over the temp range you would be encountering, Bob.

I've been looking at the Allegro current sensors but the temperature
range spec I've been seeing approaches +/-11% error band. If that's not
a problem for your application, then they have a lot going for them, low
sense resistance being number one.

One possibility would be to try to temp-compensate them, although it
looks like they already have so you might be facing residual errors
which are usually 2nd or 3rd order.

If you investigate further let us know.

2006\11\14@010742 by Steve Smith

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face
Bob:
I have a couple of samples but settled for shunts and op amps its cheaper.

Steve

-----Original Message-----
From: EraseMEpiclist-bouncesspamEraseMEmit.edu [@spam@piclist-bounces@spam@spamspam_OUTmit.edu] On Behalf Of
Bob Axtell
Sent: 14 November 2006 02:12
To: Microcontroller discussion list - Public.
Subject: [EE] Anybody Used Allegro Current Sensor?

Part number is ACS750SCA050 .

With 5V in, provides a nom 2.5V output with no current
flowing. The chart indicates high accuracy in either direction
out to 50A. Insertion R is 130uOhm. Looks like all I have to
do is to acquire the 2.5V level when powering up (assuming
no current flow).

The specs are so good I am skeptical. Anybody?

--Bob

2006\11\14@014546 by Denny Esterline

picon face
> Part number is ACS750SCA050 .
>
> With 5V in, provides a nom 2.5V output with no current
> flowing. The chart indicates high accuracy in either direction
> out to 50A. Insertion R is 130uOhm. Looks like all I have to
> do is to acquire the 2.5V level when powering up (assuming
> no current flow).
>
> The specs are so good I am skeptical. Anybody?
>
> --Bob

The thing that turned me off them was the pinout. No, I didn't expect to put a 50 amp part in a breadboard :-)
The leadframe needs oval holes for the high current connections, puts it outside the limitations of the "prototype" service from all the board houses I checked - board costs easily exceeded the price of a precision shunt resistor and op-amp.

-Denny


2006\11\14@062114 by Bob Axtell

face picon face
Marcel Duchamp wrote:
{Quote hidden}

Take a look at the specs NOW. It would beat +/-11% I am sure. I believe
they are compensating well
with temperature.

The application is not very precise; the client only wants to detect a
FLOW of current, so that anything
over 1 A would be acceptable. And since there can be reverse current
direction, the old method of
measuring across a precise resistor won't work either (because it goes
below ground, requiring a mirror).

I think this is a good choice for only $6 USD. Use a simple PIC10F222 or
a PIC12F675 to make the
measurement.

--Bob


2006\11\14@070857 by Gerhard Fiedler

picon face
Denny Esterline wrote:

> The thing that turned me off them was the pinout. No, I didn't expect to
> put a 50 amp part in a breadboard :-) The leadframe needs oval holes for
> the high current connections, puts it outside the limitations of the
> "prototype" service from all the board houses I checked - board costs
> easily exceeded the price of a precision shunt resistor and op-amp.

I used them (the 50 A parts) with round holes and lots of solder. Seemed to
work well enough.

Gerhard

2006\11\14@074912 by PicDude

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face
Similar situation on my end.  The samples (130A-versions in my case) are on
hold because I've not fouind a good way to run 130A on the PCB to the
terminals of the current sensor.  I also remember not being able to find PCB
screw terminals that can handle that much current.

-Neil.



On Tuesday 14 November 2006 00:08, Steve Smith wrote:
> Bob:
> I have a couple of samples but settled for shunts and op amps its cheaper.
>
> Steve
>
> {Original Message removed}

2006\11\14@111317 by Ariel Rocholl

picon face
What about soldering a cable of the appropiate gauge rather a PCB lane? I
asked for samples to them some time ago and still waiting to get here, but
before receiving them my plan for measuring up to 100A was to use a cable
soldered to the PCB acting as a lane. Otherwise, it is not only the PCB may
not hold the high current, but the power loss will be very high with 100A
and the efficiency of the system will be impacted, something you should be
able to avoid with a hall effect sensor. Otherwise I would bet by a
resistive shunt.

2006/11/14, PicDude <spamBeGonepicdude2spamKILLspamavn-tech.com>:
{Quote hidden}

> > {Original Message removed}

2006\11\14@113634 by PicDude

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Take a look at Zetex ZXCT1009 and ZXCT1010 (from Mouser), which may serve your
needs.  You can put two on them back-to-back to measure bi-directional
current.

Cheers,
-Neil.



On Tuesday 14 November 2006 05:08, Bob Axtell wrote:
{Quote hidden}

2006\11\14@115727 by Alan B. Pearce

face picon face
>Take a look at Zetex ZXCT1009 and ZXCT1010 (from Mouser),
...

Also the LT6100 and LTC6101 from Linear Technology, and HV7800 from Supertex
Inc. This one can be used at mains voltages (up to around 400V IIRC).

>You can put two on them back-to-back to measure bi-directional
>current.

These would all need the same as well for that purpose.

2006\11\14@121049 by William Chops Westfield

face picon face

On Nov 14, 2006, at 3:08 AM, Bob Axtell wrote:

> the client only wants to detect a FLOW of current, so that anything
> over 1 A would be acceptable.

In that case, can't you just use a small coil and a (really cheap)
(digital) hall effect sensor?

BillW

2006\11\14@121612 by Steve Smith

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face
We fit busbar (25mm x 2mm) to the pcb to collect the current and provide
termination points to the world it overcomes the problems of terminals and
gives a stable location to bolt 35mm cables. It also makes like a heatsink
(of sorts)

Steve

{Original Message removed}

2006\11\14@140627 by PicDude

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face
What, pray tell, is this busbar of which you speak?  I had originally looked
at PCB terminals such as Figure D in the top left of this page...
http://www.mouser.com/catalog/628/1219.pdf , since they are a nice interface
to the outside world.  But they only go up to 15 or 20A.

-Neil.



On Tuesday 14 November 2006 11:14, Steve Smith wrote:
> We fit busbar (25mm x 2mm) to the pcb to collect the current and provide
> termination points to the world it overcomes the problems of terminals and
> gives a stable location to bolt 35mm cables. It also makes like a heatsink
> (of sorts)
>
> Steve

2006\11\14@140814 by PicDude

flavicon
face
On Tuesday 14 November 2006 11:10, William Chops Westfield wrote:
> On Nov 14, 2006, at 3:08 AM, Bob Axtell wrote:
> > the client only wants to detect a FLOW of current, so that anything
> > over 1 A would be acceptable.
>
> In that case, can't you just use a small coil and a (really cheap)
> (digital) hall effect sensor?
>
> BillW

Straying off the OP's requirement a bit... In general, using hall effect
sensors in this manner, wouldn't this require calibration of each unit?

-Neil.

2006\11\14@204459 by Bob Axtell

face picon face
William Chops Westfield wrote:
> On Nov 14, 2006, at 3:08 AM, Bob Axtell wrote:
>
>  
>> the client only wants to detect a FLOW of current, so that anything
>> over 1 A would be acceptable.
>>    
>
> In that case, can't you just use a small coil and a (really cheap)
> (digital) hall effect sensor?
>
> BillW
>  
Gee Bill, that is very clever. I had not thought of it. I might try that
for GO/NOGO testing.

--Bob

2006\11\14@222658 by Matt Pobursky

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face
On Tue, 14 Nov 2006 18:05:57 -0700, Bob Axtell wrote:
> William Chops Westfield wrote:
>> On Nov 14, 2006, at 3:08 AM, Bob Axtell wrote:
>>
>>
>>> the client only wants to detect a FLOW of current, so that
>>> anything over 1 A would be acceptable.
>>>
>>>
>> In that case, can't you just use a small coil and a (really
>> cheap) (digital) hall effect sensor?
>>
>> BillW
>>
> Gee Bill, that is very clever. I had not thought of it. I might try
> that for GO/NOGO testing.

We needed a way to test a Hall Effect switch used in a paddle wheel
type flow sensor assembly in production. We didn't want any moving
Rube Goldberg type contraptions so we made a small electromagnet
assembly (steel core coil) and pulsed it to simulate a rotating
magnet. It worked great and was easy to implement.

Lately I've been playing with NVE's GMR sensors. Nice devices, very
sensitive and easy to use.

Matt Pobursky
Maximum Performance Systems

2006\11\15@012459 by Steve Smith

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face
Copper 2mm thick 30mm wide made with a castleated edge to our spec's closest
is commercial product is 18mm centre distribution busbar as made by MG
legrand ABB ect its got pins that are designed to fit circuit breakers in
distribution boards we solder it into PCBs.

Steve

{Original Message removed}


'[EE] 600A current sensor'
2010\02\03@001834 by Bob Blick
face
flavicon
face
I am looking for an isolated current sensor that is isolated and capable
of 600 amps DC. Either something like Allegro's solder-in sensors or a
contactless sensor like those from Amploc. I'd use one of those two
except for the 200A and 300A limits. I'm hoping not to have to do a
current divider, multiple sensors, or any other kludge.

Anyone using or know of something off the shelf that'll work for me?

Thanks,

Bob

--
http://www.fastmail.fm - Accessible with your email software
                         or over the web

2010\02\03@003853 by Sean Breheny

face picon face
Hi Bob,

Take a look at LEM http://www.lem.com

They make a wide range of DC-capable high current level sensors.

See this page specifically:

http://www.lem.com/hq/en/content/view/269/206/

Sean


On Wed, Feb 3, 2010 at 12:18 AM, Bob Blick <.....bobblickspam_OUTspamftml.net> wrote:
{Quote hidden}

>

2010\02\03@005314 by Bob Blick

face
flavicon
face
On Wed, 3 Feb 2010 00:38:45 -0500, "Sean Breheny" said:

> Take a look at LEM http://www.lem.com
>
> They make a wide range of DC-capable high current level sensors.
>
> See this page specifically:
>
> http://www.lem.com/hq/en/content/view/269/206/

Perfect! This is what I want, and $24 in singles is great, considering
the packaging:

http://www.lem.com/hq/en/component/option,com_catalog/task,displaymodel/id,64.71.52.000.0/

Thanks.

Cheerful regards,

Bob


--
http://www.fastmail.fm - Does exactly what it says on the tin


'[EE] i2c current sensors'
2012\05\02@150029 by Chetan Bhargava
picon face
Hi,

Are there any i2c current sensors available? In my application I have
to measure current and voltage of 10 sources up to 15A (DC 5v max).
I can use the ICs from Allegro but then I have to have at least 20 ADC
channels in my microcontroller increasing my pin count to 100.

Thanks

Chetan Bhargav

2012\05\02@155349 by Neil

flavicon
face
Linear LTC4151, and IIRC Maxim has some also.

Cheers,
-Neil



On 5/2/2012 3:00 PM, Chetan Bhargava wrote:
> Hi,
>
> Are there any i2c current sensors available? In my application I have
> to measure current and voltage of 10 sources up to 15A (DC 5v max).
> I can use the ICs from Allegro but then I have to have at least 20 ADC
> channels in my microcontroller increasing my pin count to 100.
>
> Thanks
>
> Chetan Bhargava

2012\05\03@013535 by Chetan Bhargava

picon face
Thanks Neil

On Wed, May 2, 2012 at 12:53 PM, Neil <TakeThisOuTpicdude3.....spamTakeThisOuTnarwani.org> wrote:
> Linear LTC4151, and IIRC Maxim has some also.
>
> Cheers,
> -Neil

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