Searching \ for '[OT]: Inductive coupling' in subject line. ()
Make payments with PayPal - it's fast, free and secure! Help us get a faster server
FAQ page: www.piclist.com/techref/index.htm?key=inductive+coupling
Search entire site for: 'Inductive coupling'.

Exact match. Not showing close matches.
PICList Thread
'[OT]: Inductive coupling'
2000\10\20@214050 by Dr. Chris Kirtley

flavicon
face
Dear all,

I still didn't get any replies about inductive coupling. Forget the bit
about battery charging, if you like :-) - perhaps if I phrase it
differently - how would you transmit an on-off switch signal a few feet
without using RF? (no infra-red etc. please!).

Chris
--
Dr. Chris Kirtley MD PhD
Associate Professor
HomeCare Technologies for the 21st Century (Whitaker Foundation)
NIDRR Rehabilitation Engineering Research Center on TeleRehabilitation
Dept. of Biomedical Engineering, Pangborn 105B
Catholic University of America
620 Michigan Ave NE
Washington, DC 20064
Tel. 202-319-6247,  fax 202-319-4287
Email: spam_OUTkirtleyTakeThisOuTspamcua.edu
http://engineering.cua.edu/biomedical

Clinical Gait Analysis: http://guardian.curtin.edu.au/cga
Send subscribe/unsubscribe to .....listprocKILLspamspam@spam@info.curtin.edu.au

--
http://www.piclist.com hint: The list server can filter out subtopics
(like ads or off topics) for you. See http://www.piclist.com/#topics




2000\10\20@214933 by Mark Willis

flavicon
face
Here are the 3 posts I've received / Sent on this;  I cc'ed you so (I
hope!) you'll get this:

Dan Michaels wrote:
> Alternatively, use a piezo in the sole of the shoe that flexes
> and produces voltage during walking to keep the battery charged.
> I think this has been done already by someone.
>
> - danM

Chris Carr wrote:
{Quote hidden}

Mark Willis wrote:
{Quote hidden}

 Mark

Dr. Chris Kirtley wrote:
{Quote hidden}

--
http://www.piclist.com hint: The list server can filter out subtopics
(like ads or off topics) for you. See http://www.piclist.com/#topics




2000\10\21@054933 by Andy Howard

picon face
----- Original Message -----
From: "Dr. Chris Kirtley" <EraseMEkirtleyspam_OUTspamTakeThisOuTCUA.EDU>
To: <PICLISTspamspam_OUTMITVMA.MIT.EDU>
Sent: Saturday, October 21, 2000 2:37 AM
Subject: [OT]: Inductive coupling


> Dear all,
>
> I still didn't get any replies about inductive coupling. Forget the bit
> about battery charging, if you like :-) - perhaps if I phrase it
> differently - how would you transmit an on-off switch signal a few feet
> without using RF? (no infra-red etc. please!).

I've lost track of the thread here, was this to detect if you're in range of
the base unit?

I don't know if you can get transducers small enough for your application,
but ultrasonic might be worth investigating.

Or for no battery power drain, bar-code the shoe and use a surplus POS
scanner.




.

--
http://www.piclist.com hint: The PICList is archived three different
ways.  See http://www.piclist.com/#archives for details.




2000\10\21@132309 by victor faria

flavicon
face
how about the clapper?:)

----- Original Message -----
From: "Dr. Chris Kirtley" <@spam@kirtleyKILLspamspamCUA.EDU>
To: <KILLspamPICLISTKILLspamspamMITVMA.MIT.EDU>
Sent: Friday, October 20, 2000 9:37 PM
Subject: [OT]: Inductive coupling


{Quote hidden}

--
http://www.piclist.com hint: The PICList is archived three different
ways.  See http://www.piclist.com/#archives for details.




2000\10\21@141614 by Chris Carr

flavicon
face
Inductive Coupling to transfer power is used in the real world. I believe
that it is used to charge some electric vehicles like forklift trucks,
pallet handlers etc
I have had a quick look at likely sources but not come up with any reference
sites. I believe that the system is also proposed for electric cars. If I
remember correctly the efficiency is not good, particularly when compared to
plugging in a cable. However, you do not have to remember to unplug the
cable before driving off !!!

Regarding Signalling an On/Off instruction.

Precisely what do you mean by "a few feet", I'm sure we have all been caught
out be imprecise phrases such as this :-)    The speaker means 50 feet, the
listener assumes he means 2 feet. The result being a cock-up

Inductive Coupling is one method, but has very limited range, If you want to
rule out RF such as 433MHz then how about using 40kHz Ultrasonic Transducers

Regards
Chris

{Quote hidden}

--
http://www.piclist.com hint: The PICList is archived three different
ways.  See http://www.piclist.com/#archives for details.




2000\10\21@185405 by Dr. Chris Kirtley
flavicon
face
Dear Chris,

I suppose by "a few feet" I mean at least one and preferably 5-10.

The problem with ultrasound is that the transducers are quite thick - I
have to keep the thickness down to about 3-4 mm.

I have a telemetry transmitter on there already, which is working fine,
but I need to tell it when to transmit. If it is out of range the data
will be lost (not to mention wasting power). So it needs to know that it
is within range. At the moment I simply press a switch, but it would be
nice to automate this. I don't want to incorporate an RF receiver
because that would require be a big increase in size and power -
basically it's not an option. I was wondering about an RFID tag, and I
still think that's probably the best option. Do you know what sort of
range you can get with them?

Chris
--
Dr. Chris Kirtley MD PhD
Associate Professor
HomeCare Technologies for the 21st Century (Whitaker Foundation)
NIDRR Rehabilitation Engineering Research Center on TeleRehabilitation
Dept. of Biomedical Engineering, Pangborn 105B
Catholic University of America
620 Michigan Ave NE
Washington, DC 20064
Tel. 202-319-6247,  fax 202-319-4287
Email: kirtleyEraseMEspam.....cua.edu
http://engineering.cua.edu/biomedical

Clinical Gait Analysis: http://guardian.curtin.edu.au/cga
Send subscribe/unsubscribe to EraseMElistprocspaminfo.curtin.edu.au

--
http://www.piclist.com hint: The PICList is archived three different
ways.  See http://www.piclist.com/#archives for details.




2000\10\21@220023 by Donald L Burdette

picon face
Chris -

I notice you're an MD.  I hope this isn't an in-body or life support
application, because if so you'll have many regulatory/approval hoops to
jump through.  I wouldn't even want to touch the job if you paid me, and
I do this stuff for a living.

Assuming it's not for implantation or life support, you're still asking
for a lot.  You want data transmission over several feet without using
hardwire, rf, or light.  Since no one has yet been able to harness
gravitational fields for data transmission, that leaves magnet and
electric ( but not E-M) fields.

Motorola has been working on a new ID tag technology they call
Bi-Statics, which uses electric fields to communicate, as well as to
power up the tag, which consists (I think) of a tiny chip mounted  to two
capacitive plates which are side by side instead of face to face.  They
are being very tight-lipped about technical data.  We tried to get specs
so we could build a reader, and they won't even talk to us except to say
"call back later".

I do, however have some experience in magnetically coupled RFID devices
at 125 kHz and 13.56 MHz, as well as a power-plus-data system operating
at 70 kHz.  Transmission of data over several feet is possible.
Unfortunately, magnetic antennas tend to be pretty directional.  Is this
OK?    Also, I'd never even attempt this in a system like RFID where the
data is in an unpowered tag, and the reader has to send enough power to
energize the tag, then the tag sends data back by applying a tiny
modulation of the RF field generated by the reader.  I might attempt this
if the data were in a powered system that could generate a field that can
be sensed by the receiver.  Is that what you have?

As far as trying to charge the battery, it can be done, but requires
fairly close proximity of the two coils--say 1 or 2 inches max.  Forget
about getting to several feet.

If you're still interested, give me some more information and I'll
respond.  The kind of info that's important is:  size limitations, cost
limitations, approvals required, hobby or commercial, power available at
each side, reliability requirements,

By the way, I do have the M'Chip RFID developer's kit, and have played
with it.  It's not bad, but it's probably not for your application.  It's
really aimed at a skilled developer who wants to develop his own system.
If you have specific questions, ask away.

Don

--
http://www.piclist.com hint: The PICList is archived three different
ways.  See http://www.piclist.com/#archives for details.




2000\10\21@230817 by Dr. Chris Kirtley

flavicon
face
Dear Don,

Thanks for your patience!

size limitations - that's the most important. It has to fit in a shoe,
so I'm aiming for about an inch square or so and very thin - about 3-4
mm. It has to fit inside an insole. My circuit (PIC, EEPROM, telemetry
transmitter) fits this criteria at the moment, but as I say I am using a
switch to tell it when it is within range. I'd like this to be
automatic.

cost - < $100

limitations - it has to be inside the shoe - well, I'm starting to think
about mounting it under the instep, which might permit infra-red

approvals required - let's not worry about that for the moment :-)

hobby or commercial - well, university research - somewhere in between

power available at each side - plenty at the receiver (it's a PC - the
reciver - a Linx LC - goes into the RS232), about 10 mA max at the
transmitter

reliability requirements - I'm flexible at the moment, but clearly this
would have to be good in the long run

Note that I am not trying to send the data this way - I already have a
conventional RF transmitter. I just need something to tell it that it's
in range of the receiver.

So, are you saying that an RFID tag wouldn't cover much distance?

Chris
--
Dr. Chris Kirtley MD PhD
Associate Professor
HomeCare Technologies for the 21st Century (Whitaker Foundation)
NIDRR Rehabilitation Engineering Research Center on TeleRehabilitation
Dept. of Biomedical Engineering, Pangborn 105B
Catholic University of America
620 Michigan Ave NE
Washington, DC 20064
Tel. 202-319-6247,  fax 202-319-4287
Email: RemoveMEkirtleyEraseMEspamEraseMEcua.edu
http://engineering.cua.edu/biomedical

Clinical Gait Analysis: http://guardian.curtin.edu.au/cga
Send subscribe/unsubscribe to RemoveMElistprocspam_OUTspamKILLspaminfo.curtin.edu.au

--
http://www.piclist.com hint: The PICList is archived three different
ways.  See http://www.piclist.com/#archives for details.




2000\10\22@014507 by staff

flavicon
face
Dr. Chris Kirtley wrote:
{Quote hidden}

Hi Chris,

       I saw soemthing on TV about the RFID tags in cattle ears,
they scan them as the cows go through the gates from a metre or two. :o)
Maybe search for some farming or ag uses??
-Roman

--
http://www.piclist.com#nomail Going offline? Don't AutoReply us!
use RemoveMElistservTakeThisOuTspamspammitvma.mit.edu?body=SET%20PICList%20DIGEST




2000\10\22@042018 by Graham

flavicon
face
>
>Note that I am not trying to send the data this way - I already have a
>conventional RF transmitter.
>

could you change it for a transceiver...???.(NORDIC)...then you can have
half duplex comms , size should be similar/same (based on assumption that
you are using another 433 module)..


Graham

-Need *high IP3* AND good N/F ?? try this- http://www.rfham.com

--
http://www.piclist.com#nomail Going offline? Don't AutoReply us!
use EraseMElistservspamspamspamBeGonemitvma.mit.edu?body=SET%20PICList%20DIGEST




2000\10\22@092817 by steve

flavicon
face
Sorry - I haven't been following the thread but has anyone suggested
a conversation with a pacemaker clinic. It's twenty years since I was
involved with medical electronics but I recall that recharging and
gathering data from pacemakers using inductive loops was the hot
topic at the time.

Steve.

======================================================
Steve Baldwin                Electronic Product Design
TLA Microsystems Ltd         Microcontroller Specialists
PO Box 15-680, New Lynn      http://www.tla.co.nz
Auckland, New Zealand        ph  +64 9 820-2221
email: RemoveMEstevebKILLspamspamtla.co.nz      fax +64 9 820-1929
======================================================

--
http://www.piclist.com#nomail Going offline? Don't AutoReply us!
use listservSTOPspamspamspam_OUTmitvma.mit.edu?body=SET%20PICList%20DIGEST




2000\10\22@112911 by Dr. Chris Kirtley

flavicon
face
Dear Andy/Russell/Roman/Graham,

I thought those anti-shoplifting tags that you describe WERE RFID tags?
Are they different? How do they work? It sounds like exactly what I
want.

I think it's clear that I need to seperate the two functions of receiver
proximity detection and battery charging - the latter is obviously going
to need a very short range inductive link. I'd still like to know about
this as well, by the way - how many turns for each coil and what
frequencycurrent etc to use.

AS far as the data link is concerned, can I stress again that this is
not the major telemetry channel - that goes via a conventional RF
transmitter. All I need is someting to tell me that I am withink range.
I could arrange for coils in the carpet (the device is in the person's
shoe) but I'd rather have it based on the base-station PC if possible.
What about tramsmitting something via the AC power lines in the house -
would that work?

Chris
--
Dr. Chris Kirtley MD PhD
Associate Professor
HomeCare Technologies for the 21st Century (Whitaker Foundation)
NIDRR Rehabilitation Engineering Research Center on TeleRehabilitation
Dept. of Biomedical Engineering, Pangborn 105B
Catholic University of America
620 Michigan Ave NE
Washington, DC 20064
Tel. 202-319-6247,  fax 202-319-4287
Email: spamBeGonekirtleySTOPspamspamEraseMEcua.edu
http://engineering.cua.edu/biomedical

Clinical Gait Analysis: http://guardian.curtin.edu.au/cga
Send subscribe/unsubscribe to KILLspamlistprocspamBeGonespaminfo.curtin.edu.au

--
http://www.piclist.com#nomail Going offline? Don't AutoReply us!
use EraseMElistservspamEraseMEmitvma.mit.edu?body=SET%20PICList%20DIGEST




2000\10\22@133939 by Chris Carr

flavicon
face
The Anti-Shoplifting tags are simply a tuned circuit. The frequency they are
tuned to is the same as that emitted from the coils placed at the shop exit.
When you leave with an intact tag the tuned circuit sucks the energy from
the transmitter coils as it basically acts as a short circuit at the tuned
frequency. This increase in energy demand triggers off the alarm.

The tuned circuit is nullified by placing it in a strong field so the
current flowing round the tuned circuit is so high it fuses. Crude but it's
cheap and it works.

To summarise, the presence of a tag can be detected but as all tags are
identical, you cannot identify which tag it is.

It is possible to have an identifiable tag which is both powered by and
modulates the magnetic field but I believe that these are very close
proximity devices.

One possibility is to modify a hearing aid. These often have an inductive
pickup facility. String a wire round a room to form an inductive loop and
couple it to a suitable audio source (your sound card?). Just a thought.

Regards
Chris
{Original Message removed}

2000\10\22@161948 by Dr. Chris Kirtley

flavicon
face
Dear Chris,

That's interesting - up till your explanation I'd been under the
misapprehension that the anti-shoplifing tags were the same as RFID
tags. Now I see that they are not. Actually, it looks like these (the
anti-shoplifing type) are really what I am looking for. How do I get
hold of some, together with the associated driving coils etc.?

Chris
--
Dr. Chris Kirtley MD PhD
Associate Professor
HomeCare Technologies for the 21st Century (Whitaker Foundation)
NIDRR Rehabilitation Engineering Research Center on TeleRehabilitation
Dept. of Biomedical Engineering, Pangborn 105B
Catholic University of America
620 Michigan Ave NE
Washington, DC 20064
Tel. 202-319-6247,  fax 202-319-4287
Email: @spam@kirtley@spam@spamspam_OUTcua.edu
http://engineering.cua.edu/biomedical

Clinical Gait Analysis: http://guardian.curtin.edu.au/cga
Send subscribe/unsubscribe to spamBeGonelistprocspamKILLspaminfo.curtin.edu.au

--
http://www.piclist.com#nomail Going offline? Don't AutoReply us!
use .....listservspam_OUTspammitvma.mit.edu?body=SET%20PICList%20DIGEST




2000\10\22@225554 by Donald L Burdette

picon face
Chris -

That (and a previous message) clears up a lot.

This looks like an application begging to be run at 13.56 MHz.  That
particular frequency had been devoted to high-power transmitters
(anti-theft sensors at the exit of retail stores) and other devices (rf
excited flourescent light bulbs, for instance).  It's also convenient
because your pickup coil in the shoe could be a few turns (or maybe even
one turn) with 1 to several square inches area, while your transmit coil
from the PC side could be quite large.  As soon as the shoe is within
range of the antenna, it starts sending data.

Here's how I'd do it:

The shoe has a small loop antenna as described above, with a parallel
capacitor to make a resonant LC circuit at 13.56 MHz.  The cap value will
be in the range of 50-250 pF, depending on your antenna.  A simple diode
rectifier (amplitude detector) going into a comparator  would tell you
when there's a field present.  The whole thing could cost $0.50 to $1.00
US, and run on 10-20 uA.

The PC has a large loop (single turn) antenna excited constantly or in
short pulses that occur frequently.  You have to be kind of careful with
this because the antenna voltage is 100+ volts.  Some commercial units
use up to 500 volts.  This unit would be more expensive.  Depending on
how you build it, the electronics could be anywhere from a few dollars to
a few tens of dollars, and the mechanicals could be several times that.
The transmit frequency has to be crystal controlled to meet FCC
regulations for this band, which dictate precise frequency control.

With this setup, I'd think you could get max ranges of 2-3 feet.

If you want better range or discrimination, you modulate the transmit
field either with a constant tone or with actual data.  Your receiver
then detects the tone (fairly simple) or the data (more complicated, but
very doable in a PIC), and only when it detects the correct modulation
does it turn on the RF transmitter.  I wouldn't swear to it, but you may
be able to get ranges of 5-10 feet this way.

A technically clever person with basic electronic knowledge (calculation
of RC filters, configuration of op-amp and comparator circuits) could get
a system running without too much difficulty, but to optimize it well
would require either extensive trial and error, or some more advanced
skills.  I would read Microchip's RFID literature, but I wouldn't bother
with their developer's kit.  The lit is available on the web, I think.

One of the drawbacks of magnetic coupling like this is that the antenna
coils are kind of directional.  They want to be kind of near parallel
planes and co-axial.  Range drops off rapidly as you get off-axis, and as
you get beyond +-30 degrees off parallel.  That's why I think placing the
transmit coil on the floor is good.  When the shoe is within the loop
(less than 1 radius from the center) and within 6-12 inches of co-planar,
even a crude system should work well.  As you get more optimized, you
could operate within 2-3 radii of the center or even more.

If you want to get the transmit antenna off the floor, you run into
parallelism and directionality problems.  Perhaps mounting the antenna at
45 degrees with the axis pointing at the location you expect the shoe to
travel through (doorway?) might work, or mounting it in the ceiling may
work if you get your range high enough.

Hope this helps.

Don

{Quote hidden}

--
http://www.piclist.com#nomail Going offline? Don't AutoReply us!
use TakeThisOuTlistserv.....spamTakeThisOuTmitvma.mit.edu?body=SET%20PICList%20DIGEST




2000\10\23@071100 by Phil Tipping

flavicon
face
On 21 Oct 00, at 18:50, Dr. Chris Kirtley wrote:

> I suppose by "a few feet" I mean at least one and preferably 5-10.

If you have 3 to 6 volts available at the device check out Microchip's
HCS412 secure transponder. When used as a powered tag, it can
be made to wake up at about 1m range. Normally, it would then
send it's serial number or do an IFF check via RF (see the data
sheet 41099a.pdf at
http://www.microchip.com/10/lit/pline/security/encoders/index.htm)
but you could use this wake up to turn on your pic and initiate
sending your data over your link. I have played with the device
using the Keeloq evaluation kit and it works well. With a larger
antenna (on the fixed station end particularly) you may get even
more range. The 412 can even tell you when the battery is getting
low by setting one bit in the data it outputs so you may be able to
forget about re-charging on the fly. You will be able to fit the few
components into the space you have available.
{Quote hidden}

Phil

--
http://www.piclist.com hint: To leave the PICList
RemoveMEpiclist-unsubscribe-requestspamspamBeGonemitvma.mit.edu




2000\10\23@081631 by Alan B. Pearce

face picon face
how much data do you need to transfer, or to be more exact, how long does it take? If you have stored up data over some hours say, and then need to transfer it in a burst, can you get a situation where the subject sits in a chair, or can be located in some other way, so the transponder can be at a (relatively) known point. What I envisage is a chair which has a loop in the floor say a couple of feet diameter that the shoe is going to be in proximity of to pick up the signal to tell it to transmit.

Another possibility I thought of while writing the above is contact anyone doing hearing aids and sound loops for buildings. I was involved in doing this for a church, and started out with a 100 meter reel of three core figure 8 wire. I used 1.5mm cross section, and taped it to the floor in a square around the outside of the pews. The DC resistance of this was very close to 8 ohms, so I connected it to the output of a 100 watt audio amplifier, and using a sense coil arrangement that they use for testing these things, got acceptable magnetic field about three times the "diameter" ( if a square loop has such a thing) of the loop. As you are going one direction with your signal this sort of technology may be what you require.

--
http://www.piclist.com hint: To leave the PICList
spamBeGonepiclist-unsubscribe-request@spam@spamspam_OUTmitvma.mit.edu




2000\10\23@100437 by M. Adam Davis

flavicon
face
RFID tags have as long a range as you are willing to make an antenna (and how
sensitive your receiver is, I suppose).

One of microchip's RFID publications (available as PDF on their web site) has
the formula you need - put in feet from RFID tag, and it will give you coil size
in diameter.

I'm not sure what is going on in your case, though.  Is the person carrying the
RFID tag, or is the RFID tag stationary, and the device the person is carrying
detects its presence?

At any rate, the size of the coil is exponentially related to the distance from
the tag.  A coil about 6" in diameter will successfully scan a tag within 6-10
inches.

-Adam

"Dr. Chris Kirtley" wrote:
{Quote hidden}

--
http://www.piclist.com hint: To leave the PICList
RemoveMEpiclist-unsubscribe-requestEraseMEspamspam_OUTmitvma.mit.edu




2000\10\23@144437 by Chris Carr

flavicon
face
Chris Kirtley wrote :
> Dear Chris,
>
> That's interesting - up till your explanation I'd been under the
> misapprehension that the anti-shoplifing tags were the same as RFID
> tags. Now I see that they are not. Actually, it looks like these (the
> anti-shoplifing type) are really what I am looking for. How do I get
> hold of some, together with the associated driving coils etc.?
>
Try the Search Engines for Anti-Theft Tagging or Security Tagging and look
for Antenna
Heres one URL to give you an idea of what to expect
http://www.thenetworlduk.net/Ideal/product/taggingproducts.asp

Your main problem may be getting tags in reasonable quantities. i.e. less
than 1000 or even 10000. I would suggest grovel mode at your local Mall
might be the best option, or manufacture your own tags, Double sided sticky
tape, aluminium cooking foil and a sharp knife plus an example to copy.

But I thought the idea was for the Inductive Link to kick off the TX on the
moving body. If the tag is on the body, its not going to help surely

Regards
Chris

--
http://www.piclist.com hint: To leave the PICList
@spam@piclist-unsubscribe-requestRemoveMEspamEraseMEmitvma.mit.edu




2000\10\23@192243 by John Mullan

picon face
Don,

I'm not sure if this is the kind of info you can supply.......

In the hobby robot I am working on, I would like to incorporate an
inductively coupled charger that it can park itself near when it needs a
boost.  Do you have any info for this?

John Mullan

----Original Message-----
  >From:       Donald L Burdette <EraseMEdlburdettespam@spam@JUNO.COM>
  >To:         @spam@PICLISTspam_OUTspam.....MITVMA.MIT.EDU
  >Cc:
  >Bcc:
  >Subject:            Re: [OT]: Inductive coupling
  >Type:       IPM.Note
  >Date:       Saturday, October 21, 2000 10:03 PM
  >
  >Chris -
  >As far as trying to charge the battery, it can be done, but requires
  >fairly close proximity of the two coils--say 1 or 2 inches max.  Forget
  >about getting to several feet.
  >
  >If you're still interested, give me some more information and I'll
  >respond.
  >
  >Don
  >
  >--
  >http://www.piclist.com hint: The PICList is archived three different
  >ways.  See http://www.piclist.com/#archives for details.
  >
  >
  >
  >

--
http://www.piclist.com hint: To leave the PICList
spamBeGonepiclist-unsubscribe-requestEraseMEspammitvma.mit.edu




2000\10\23@194133 by David VanHorn

flavicon
face
At 07:20 PM 10/23/00 -0400, John Mullan wrote:
>Don,
>
>I'm not sure if this is the kind of info you can supply.......
>
>In the hobby robot I am working on, I would like to incorporate an
>inductively coupled charger that it can park itself near when it needs a
>boost.  Do you have any info for this?

There's nothing really special about this. It's just a loosely coupled
transformer. Of course it's inefficient as hell, but wall power is cheap(ish).

Higher frequencies are better, 100kHz should be convenient.

There are a few things you can do, like sensing a load, and only applying
the power when there's someone there to catch it.

Build a prototype and try!

I did one, years ago, as a charger for an underwater metal detector. The
whole thing had nothing to break the seal, and no exposed metal contacts.
Reed switches and a magnetic "wand" allowed you to adjust everything.

--
http://www.piclist.com hint: To leave the PICList
piclist-unsubscribe-requestspamBeGonespammitvma.mit.edu




2000\10\23@215422 by Dan Michaels

flavicon
face
At 06:33 PM 10/23/2000 -0500, you wrote:
>At 07:20 PM 10/23/00 -0400, John Mullan wrote:
>>Don,
>>
>>I'm not sure if this is the kind of info you can supply.......
>>
>>In the hobby robot I am working on, I would like to incorporate an
>>inductively coupled charger that it can park itself near when it needs a
>>boost.  Do you have any info for this?
>


A guy named Grey Walter built one of these many years ago - before
anyone still alive here today was born. A little mobile robot with
a 2-celled brain, that ran from light when the battery was fully
charged and sought out light when the battery was low. Just came
up and plugged itself in a socket. Since a PIC has more than 2
brain cells, it should be able to do better than a 1940's flip-flop.

I found 953 links to GW on google.com:

http://www.ias.uwe.ac.uk/gwonline.html

- danM
======

--
http://www.piclist.com hint: To leave the PICList
RemoveMEpiclist-unsubscribe-request@spam@spamspamBeGonemitvma.mit.edu




2000\10\24@234054 by Donald L Burdette

picon face
John -

As Dave VanHorn pointed out, there's nothing really special about this.

Of course, "nothing really special" is a relative assessment, so here
goes.

Higher frequencies are generally better, but only because the magnetic
core and windings can be made smaller and lighter.  Frequencies up to 50
or 100 kHz are attainable by the hobbyist without expensive materials.
To make things really simple, I'd shoot for 30-50 kHz, as it keeps it
inaudible and easy to build.

What you want to build is a transformer.  Imagine a standard filament
transformer with the coils wound side by side instead of one over the
other.  Now saw it in half between the two coils.  Put one half in your
robot, and the other in your base station.  When you put them back
together (or close enough) they once again act like a transformer.

Here are some gotchas to mind:

First, if you go above 400-600 Hz, you can't use iron transformer cores
any more.  The iron actually absorbs energy from each cycle, and so the
faster you cycle, the more power gets absorbed.  Ferrite materials can
run down to those frequencies, but generally work better at higher
frequencies.  Ferrites for power magnetics have the same problems as
iron, but to a much lesser degree, which allows them to run at higher
frequencies.  Practical frequency limits vary based on material, but can
run from 50-500 kHz.

One half of the transformer without the other half attached will draw
very high current compared to the intact transformer.  That's because
you've broken the magnetic path through the core, reducing the inductance
of the primary.  You MUST limit the current going into the primary or it
will be destroyed.  As you bring the secondary closer and closer, it
looks more like the original transformer.  Keep in mind that gaps of
0.001" are significant, and 1/8" is huge.  This is the biggest problem
you face--aligning the two core halves and getting them close enough.

To transfer the kind of power you need to run a robot, you will need a
core (two halves).   Assuming you're looking for one-off, if you can find
an old power supply with a big two-piece ferrite-core inductor or
transformer in it, you have your core, or you can try to find a new one.
AFAIK, places like Digi-Key don't stock these things.  You're going to
have to experiment with turns ratio (don't assume V1/V2 = T2/T1, which is
the standard transformer equation).  Put as many turns of suitable wire
as will fit on the secondary, then play with the primary.

The second hurdle is to build an oscillator that can drive power into the
primary, but can withstand a shorted output (the primary looks like a
short circuit when the secondary is not there).  Don't figure on getting
more than 10% of your input power to the secondary unless you mate the
cores almost perfectly.   And don't plan on getting a lot of power
through it.  Going crude like this, figure no more than 10% of what a
similar sized filament transformer could handle.  You may have to
experiment quite a bit to even reach that.

There, now I've scared you off.  Sorry.  ;-)

If you're still interested, feel free to keep asking questions.



Or you could forget the cores altogether, and just make two coils of wire
and try to lay them as close as possible to each other (so they're almost
the same coil).  For this, you want as high a frequency as you can manage
- say 100 or 125 kHz.  Make your coils big, like 4" diameter at least.
I'd start with maybe 30 turns of #20 or #22 wire on a 4" form for the
primary, 60T for secondary.  Lay them one on top of the other and see how
much power you can transmit.

When you make your rectifier circuit on the secondary, don't forget to
use high-speed diodes.  Schottky's are good for that, or get some with a
reverse recovery time of 0.2uS (200nS) or less.

If you get into this and want to optimize it, there's a 'valley fill
circuit' which helps the power transfer effeciency.  It's essentially a
crude power factor correction circuit.  Search the web or ask me for the
info.




Don








Don

--
http://www.piclist.com hint: PICList Posts must start with ONE topic:
"[PIC]:","[SX]:","[AVR]:" =uP ONLY! "[EE]:","[OT]:" =Other "[BUY]:","[AD]:" =Ads




2000\10\25@023058 by Thys Van Tonder

flavicon
face
You can have a look on the Siemens Matsushita website. I came across some
articles on inductive coupling and Planar cores
You can link there via http://www.siemens.de (I hope)


Thys

{Original Message removed}


'[OT]: Inductive coupling'
2000\11\07@171028 by Jilles Oldenbeuving
flavicon
face
I know i'm a little bit late, but i was on holiday...

As to what Chris is saying: electric toothbrushes use inductive charging so
that you don't have any electrical contacts... and they do it easy too... once
opened u such a thing and only a few components....

Regards,

Jilles Oldenbeuving
.....jilles@spam@spamEraseMErendo.dekooi.nl
-----Oorspronkelijk bericht-----
Van: Chris Carr <.....nyedRemoveMEspamBTINTERNET.COM>
Aan: .....PICLISTSTOPspamspam@spam@MITVMA.MIT.EDU <PICLISTEraseMEspam@spam@MITVMA.MIT.EDU>
Datum: zaterdag 21 oktober 2000 19:15
Onderwerp: Re: [OT]: Inductive coupling


{Quote hidden}

--
http://www.piclist.com hint: To leave the PICList
piclist-unsubscribe-requestspam_OUTspam@spam@mitvma.mit.edu




2000\11\08@101614 by Dr. Chris Kirtley

flavicon
face
Dear Jilles,

Yes - I know about the toothbrushes. I used to have one, but can't seem
to find it to pull apart... no wonder my teeth are falling out too! :-)

Chris
--
Dr. Chris Kirtley MD PhD
Associate Professor
HomeCare Technologies for the 21st Century (Whitaker Foundation)
NIDRR Rehabilitation Engineering Research Center on TeleRehabilitation
Dept. of Biomedical Engineering, Pangborn 105B
Catholic University of America
620 Michigan Ave NE
Washington, DC 20064
Tel. 202-319-6247,  fax 202-319-4287
Email: spamBeGonekirtley@spam@spamcua.edu
http://engineering.cua.edu/biomedical

Clinical Gait Analysis: http://guardian.curtin.edu.au/cga
Send subscribe/unsubscribe to RemoveMElistprocEraseMEspamKILLspaminfo.curtin.edu.au

--
http://www.piclist.com hint: PICList Posts must start with ONE topic:
"[PIC]:","[SX]:","[AVR]:" =uP ONLY! "[EE]:","[OT]:" =Other "[BUY]:","[AD]:" =Ads





'[OT]: Inductive coupling'
2002\01\02@172611 by Jinx
face picon face
> on 10/22/2000 Chris Carr wrote :

> The Anti-shoplifting tags are simply a tuned circuit. The frequency
> they are tuned to is the same as that emitted from the coils placed
> at the shop exit. When you leave with an intact tag the tuned circuit
> sucks the energy from the transmitter coils as it basically acts as
> a short circuit at the tuned frequency. This increase in energy
> demand triggers off the alarm.

"In July 2001, legislators in Colorado passed House Bill 01-1221
into law, thus making it illegal for any resident of Colorado to wear
aluminium underpants. Shoplifters had been using them to foil
electronic alarm systems. The law allows exceptions for those who
can prove they wear aluminium underpants for "personal" reasons"

--
http://www.piclist.com hint: PICList Posts must start with ONE topic:
[PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads


2002\01\02@183239 by Bob Barr

flavicon
face
On Thu, 3 Jan 2002 11:25:32 +1300, Jinx wrote:

>
>"In July 2001, legislators in Colorado passed House Bill 01-1221
>into law, thus making it illegal for any resident of Colorado to wear
>aluminium underpants. Shoplifters had been using them to foil
>electronic alarm systems. The law allows exceptions for those who
>can prove they wear aluminium underpants for "personal" reasons"

"personal reasons"????
I'd sure hate to have to explain *that* to a judge.

--
http://www.piclist.com hint: PICList Posts must start with ONE topic:
[PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads


2002\01\02@190216 by Jinx

face picon face
>can prove they wear aluminium underpants for "personal" reasons"

"personal reasons"????

I'd sure hate to have to explain *that* to a judge.

If you're one of the 11 people in Colorado who isn't a shoplifter
or pervert, or an out-of-state aluminium underpants wearer
you've got nothing to worry about. Cue Dukes Of Hazzard banjo
chase music as Coloradans head for the state line, underpants
flying out the car windows and bouncing off the Troopers wind-
screen

How long before it gets made federal law and you can expect to
be grilled by The Men In Black.

Actually they would be quite good for grilling - whip your fancy
new aluminium dacks off, wrap them around a piece of fish and
a couple of spuds, chuck it on the barbie. "Hmmm, what's that
seasoning ?" "Hey, there's a hair in mine !"

The question begs to be asked - how do tell if someone is
wearing aluminium underpants ?

Do they have a T-shirt ?

Shorts (tick)
Briefs (cross)
Neither (cross)
Fabric  (cross)
Rubber (cross)
Metal (tick)

Or maybe they are so hopelessly perverse they can't help
accessorising and wear the anti-alien-scan aluminium hat too

Imagine the confusion - popping into Radio Shack and asking
if they have any "aluminium boxes for an alarm project".

"Boxers ? Alarm ? You realise you're on video sir ?"
"No, no, no, boxes"

--
http://www.piclist.com hint: PICList Posts must start with ONE topic:
[PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads


2002\01\02@194853 by Russell McMahon

picon face
I don't know where these utterly ludicrous ideas originated!

To be at all effective you must use materials which provide magnetic
shielding. Non ferrous materials (here Aluminium (to be confused with
Aluminum)) do not, of course, work for this purpose. At the minimum one
should wear soft iron sheet headgear and preferably a mu-metal cap should be
employed - especially if near field radiation (in either direction) is of
concern. Recent private correspondence suggests that use of steel from
WW1-vintage German capital ships scuttled at Scapa Flow may be of additional
utility if low radiation count is an ancillary consideration. This material
is much used in space probes and the Aurora-brigade should probably ponder
possible correlations with the use of personal EM shielding headgear.



     Russell McMahon
_____________________________


{Original Message removed}

2002\01\02@200020 by David VanHorn

flavicon
face
At 10:03 AM 1/3/02 +1300, Russell McMahon wrote:
>I don't know where these utterly ludicrous ideas originated!
>
>To be at all effective you must use materials which provide magnetic
>shielding. Non ferrous materials (here Aluminium (to be confused with
>Aluminum)) do not, of course, work for this purpose.

The systems work in around 10 MHz for the inductive tags, and upwards of a
GHz for the diode mixers. Aluminum foil is an effective shield
here.  Copper works well too.

>  At the minimum one
>should wear soft iron sheet headgear and preferably a mu-metal cap should be
>employed - especially if near field radiation (in either direction) is of
>concern.

Better for DC-1MHz sorts of fields.

--
http://www.piclist.com hint: PICList Posts must start with ONE topic:
[PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads


2002\01\03@032343 by Alexandre Domingos F. Souza

flavicon
face
>"In July 2001, legislators in Colorado passed House Bill 01-1221
>into law, thus making it illegal for any resident of Colorado to wear
>aluminium underpants. Shoplifters had been using them to foil
>electronic alarm systems. The law allows exceptions for those who
>can prove they wear aluminium underpants for "personal" reasons"

       Hmmm...how they can be sure I'm not wearing aluminium underpants? Will they look at it? ;oD


---8<---Corte aqui---8<----

Alexandre Souza
spamBeGonetaitospam_OUTspamRemoveMEterra.com.br
http://planeta.terra.com.br/lazer/pinball/

---8<---Corte aqui---8<----

--
http://www.piclist.com hint: The list server can filter out subtopics
(like ads or off topics) for you. See http://www.piclist.com/#topics


2002\01\03@032847 by Alexandre Domingos F. Souza

flavicon
face
>"personal reasons"????
>I'd sure hate to have to explain *that* to a judge.

       "dear Judge, I'm wearing aluminium underpants, because I'm afraid that celular emissions and microwave can turn me powerless in "the fun area", so I use these ugly, but utile underpants"...Go figure! ;oD


---8<---Corte aqui---8<----

Alexandre Souza
.....taitospamRemoveMEterra.com.br
http://planeta.terra.com.br/lazer/pinball/

---8<---Corte aqui---8<----

--
http://www.piclist.com hint: The list server can filter out subtopics
(like ads or off topics) for you. See http://www.piclist.com/#topics


2002\01\03@041319 by Jinx

face picon face
>can prove they wear aluminium underpants for "personal" reasons"

> Hmmm...how they can be sure I'm not wearing aluminium
> underpants? Will they look at it? ;oD

Yes. But you may have to buy them dinner afterwards

I wonder if aluminium undies swish like corduroy ? Perhaps
they'll use a swish detector, strange men with parabolic
microphones lurking in shopping mall alcoves

--
http://www.piclist.com hint: The list server can filter out subtopics
(like ads or off topics) for you. See http://www.piclist.com/#topics


2002\01\04@154735 by Jinx

face picon face
> > >can prove they wear aluminium underpants for "personal"
> > >reasons"
> >
> > "personal reasons"????

Here's a reason to wear them - and perhaps a use for those
left-over Gameboy cameras too

<mindboggled>

"An entrepreneur in Egypt has patented female chastity
briefs which, when lowered for more than 5 minutes,
automatically dial the husband's cellphone"

</mindboggled>

About as bad an omen for a long-term partnership as a pre-nup

--
http://www.piclist.com hint: The PICList is archived three different
ways.  See http://www.piclist.com/#archives for details.


2002\01\05@042827 by Alexandre Domingos F. Souza

flavicon
face
><mindboggled>
>"An entrepreneur in Egypt has patented female chastity
>briefs which, when lowered for more than 5 minutes,
>automatically dial the husband's cellphone"
></mindboggled>

       Lots of things can be done in 5 minutes ;o)


---8<---Corte aqui---8<----

Alexandre Souza
taitospam@spam@terra.com.br
http://planeta.terra.com.br/lazer/pinball/

---8<---Corte aqui---8<----

--
http://www.piclist.com#nomail Going offline? Don't AutoReply us!
email EraseMElistservRemoveMEspamSTOPspammitvma.mit.edu with SET PICList DIGEST in the body


2002\01\05@045309 by Jinx

face picon face
> ><mindboggled>
> >"An entrepreneur in Egypt has patented female chastity
> >briefs which, when lowered for more than 5 minutes,
> >automatically dial the husband's cellphone"
> ></mindboggled>
>
>         Lots of things can be done in 5 minutes ;o)

By you perhaps  8 :P

--
http://www.piclist.com#nomail Going offline? Don't AutoReply us!
email RemoveMElistservKILLspamspamTakeThisOuTmitvma.mit.edu with SET PICList DIGEST in the body


2002\01\05@123721 by Bob Barr

flavicon
face
On Sat, 5 Jan 2002 07:10:19 -0200, "Alexandre Domingos F. Souza"
wrote:

>><mindboggled>
>>"An entrepreneur in Egypt has patented female chastity
>>briefs which, when lowered for more than 5 minutes,
>>automatically dial the husband's cellphone"
>></mindboggled>
>
>        Lots of things can be done in 5 minutes ;o)
>

As long as we're already in [OT]:

And in a lot longer time without ever lowering the panties. :=)

--
http://www.piclist.com#nomail Going offline? Don't AutoReply us!
email spamBeGonelistservspam@spam@mitvma.mit.edu with SET PICList DIGEST in the body


2002\01\05@142004 by Alexandre Domingos F. Souza

flavicon
face
>>         Lots of things can be done in 5 minutes ;o)
>By you perhaps  8 :P

       For sure ;o) Not so pleasurefull, but the completeness of the "real objective" of the act can be achieved. :o)


---8<---Corte aqui---8<----

Alexandre Souza
RemoveMEtaitospam_OUTspamterra.com.br
http://planeta.terra.com.br/lazer/pinball/

---8<---Corte aqui---8<----

--
http://www.piclist.com#nomail Going offline? Don't AutoReply us!
email listservspamspammitvma.mit.edu with SET PICList DIGEST in the body


2002\01\05@142419 by Mark Newland

flavicon
face
But how long to reset the briefs?  Lower them for 4 minutes, back up for
1 second, and repeat...

Bob Barr wrote:

{Quote hidden}

--
http://www.piclist.com#nomail Going offline? Don't AutoReply us!
email listservspam_OUTspammitvma.mit.edu with SET PICList DIGEST in the body


2002\01\05@180625 by Jinx

face picon face
> But how long to reset the briefs?  Lower them for 4 minutes,
> back up for 1 second, and repeat...

And you need a floppy to close the session

--
http://www.piclist.com#nomail Going offline? Don't AutoReply us!
email RemoveMElistservKILLspamspam@spam@mitvma.mit.edu with SET PICList DIGEST in the body


2002\01\05@180631 by Jinx

face picon face
>>>  Lots of things can be done in 5 minutes ;o)
>>By you perhaps  8 :P

> For sure ;o) Not so pleasurefull, but the completeness of
> the "real objective" of the act can be achieved. :o)

Glad to hear you've got your eye on what really matters and
you get back to your PICs ASAP

--
http://www.piclist.com#nomail Going offline? Don't AutoReply us!
email listservspamBeGonespam.....mitvma.mit.edu with SET PICList DIGEST in the body


2002\01\06@002726 by Dale Botkin

flavicon
face
Mark Newland <KILLspamapespam.....ESKIMO.COM> said:

> But how long to reset the briefs?  Lower them for 4 minutes, back up for
> 1 second, and repeat...
>

I've been resisting the temptation to jump in on this topic as it drifts
closer and closer to the bounds of propriety, but...  I just have to say I
don't think I'd want to be minding a timer at such a critical moment.

8-)

Dale

--
http://www.piclist.com hint: To leave the PICList
spam_OUTpiclist-unsubscribe-requestspamKILLspammitvma.mit.edu


More... (looser matching)
- Last day of these posts
- In 2002 , 2003 only
- Today
- New search...