Sorry to keep asking questions, but I'm trying to kill several birds
with one stone. I want to sense proximity to a receiver so that I can
transmit telemetry data (hence the reason I asked about RFID tags), and
also to charge the battery inductively. I wonder if anyone has any tips
on the latter? The battery is very low capacity (20mA 3V) Vanadium
Pentoxide Lithium.
Thanks in anticipation,
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_OUTkirtleyTakeThisOuTcua.edu http://engineering.cua.edu/biomedical
Chris Kirtley wrote:
>Dear all,
>
>Sorry to keep asking questions, but I'm trying to kill several birds
>with one stone. I want to sense proximity to a receiver so that I can
>transmit telemetry data (hence the reason I asked about RFID tags), and
>also to charge the battery inductively. I wonder if anyone has any tips
>on the latter? The battery is very low capacity (20mA 3V) Vanadium
>Pentoxide Lithium.
>
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.
> Chris Kirtley wrote:
> >Dear all,
> >
> >Sorry to keep asking questions, but I'm trying to kill several birds
> >with one stone. I want to sense proximity to a receiver so that I can
> >transmit telemetry data (hence the reason I asked about RFID tags), and
> >also to charge the battery inductively. I wonder if anyone has any tips
> >on the latter? The battery is very low capacity (20mA 3V) Vanadium
> >Pentoxide Lithium.
> >
Dan Michaels replied:
> 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.
>
Trevor Baylis (The Inventor of the Clockwork Radio). I believe he went
walking in the Namibian Desert and used the power to keep his mobile fone
charged.
wearables.about.com/gadgets/wearables/ has a bunch of wearable
computer links; Bet you can find a Piezo charger on there. http://testarne.www.media.mit.edu/people/testarne/TR328/main-tr328.html,
for example, is a good place to look for some theoretical info.
IIRC someone had a Piezo powered "Computer in a shoe" some time back,
used for some casino scam or another; ("Takes all kinds" and we seem to
have an ample supply...)
For inductive charging, you're talking a transformer basically - The one
side can be driven with an AC field, to charge, when you detect a load
(Impedance change) you know you're possibly connected, rectify in the
receiving unit to give power to recharge the battery (Possibly have to
charge that battery over some time IIRC, so maybe connection should be
separate from recharge?) Signalling through a transformer isn't too
hard to do, differential drive of the windings is a good idea
probably... Don't want to blow the receive drivers when charging, of
course, so think over inductive kickback, etc., carefully. (Higher
frequency AC coupled to the Power side through caps would do this, it's
been used before.) I know some industrial fuelling systems use an
inductor around the gas nozzle to authorize fuel on a per-vehicle
per-tank basis, been too long since I looked at one though.
Probably can drive the coils with a PIC for that small of a battery...
Might think of a coil pair that self-center (i.e. have a small thimble
sized depression in the shoe that a matching projection on the other
cable fits against) to mate things together.
I might do something in a power / comms cycle like,
10mS Charge (proportional to even number of charge sine waves <G>)
1mS idle (or smaller)
4mS Send (from Power side to shoe)
1mS idle
4mS Receive (from Shoe to Power Side)
and use a "Ping / Pong" protocol (say 400Hz to 10kHz for Power Send,
really depends on your coils and I'm not an RF expert nor do I know how
tiny your coils will be! <G>)
> Dear all,
>
> Sorry to keep asking questions, but I'm trying to kill several birds
> with one stone. I want to sense proximity to a receiver so that I can
> transmit telemetry data (hence the reason I asked about RFID tags), and
> also to charge the battery inductively. I wonder if anyone has any tips
> on the latter? The battery is very low capacity (20mA 3V) Vanadium
> Pentoxide Lithium.
>
> Thanks in anticipation,
>
> 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: kirtleyKILLspamcua.edu
> http://engineering.cua.edu/biomedical
>
> Clinical Gait Analysis: http://guardian.curtin.edu.au/cga
> Send subscribe/unsubscribe to .....listprocKILLspam.....info.curtin.edu.au
Chris Kirtley wrote:
>Dear Dan,
>
>No - nobody has done this. Just lots of speculation. The one guy who has
>done something (Trevor Bayliss) in England, used a mechanical generator
>(like those hand-grip torches).
>
>If you work it out (as I have done) there simply is nowhere near enough
>energy (several orders of magnitude) in piezo-electric methods.
>
Hi Chris,
You may be right concerning producing enough power to run a transmitter.
However, still worth investigating some of the stuff various people
are doing in the area of "wearable computers". MIT Media Lab, etc
- those guys/gals have done all kinds of stuff like this. One article
talks about generating 17W during a brisk walk:
>For inductive charging, you're talking a transformer basically - The one
>side can be driven with an AC field, to charge, when you detect a load
>(Impedance change) you know you're possibly connected, rectify in the
>receiving unit to give power to recharge the battery (Possibly have to
>charge that battery over some time IIRC, so maybe connection should be
>separate from recharge?)
Chris,
I've been reading this thread and it seemed to be covered well enough by
others but possibly if you can describe your environment slightly more fully
I may be able to offer some advice. I have been involved with development of
inductive power transfer and bidirectional signalling. Usually the distances
involved are as small as possible - typically mm to cm range but larger
distances can be accommodated in special circumstances - see below.
You were talking about a required detection range of several feet and this
is indeed hard in the general case with inductive methods BUT it may well be
possible to develop a special case which has adequate flexibility. By using
a large flat loop which the user walks over you could position them anywhere
within the loop.
I am not sure whether your user consciously comes to the download point or
whether the data transfer happens with the user unawares during other
operations.
If a loop as above was positioned across the width of a corridor you could
probably arrange data transfer as they walked along the corridor depending
on data rate and amount of data to be sent. Alternatively, if the user is
intended to cooperate, the system could detect their presence and ensure
that they were stable and suitably instructed before commencing download. I
have seen systems in use which use a loop perhaps 2 metres across and
perhaps 10 metres long which induce power into units within the confines of
the loop.
Can you comment further on the human interaction and general environment
aspects.
Chris Kirtley wrote:
>Dear Dan,
>
>No - nobody has done this. Just lots of speculation. The one guy who has
>done something (Trevor Bayliss) in England, used a mechanical generator
>(like those hand-grip torches).
>
>If you work it out (as I have done) there simply is nowhere near enough
>energy (several orders of magnitude) in piezo-electric methods.
>
Hi,
I've been lurking on this thread, and i understand that you (Dr. Kirtley)
are knowledgeable about gait and walking. Therefore I do not understand
how you have come to the conclusion that there is nowhere near enough
energy in piezo-electric methods.
I am not knowledgeable about walking but my calculations (which may be way
off) amount to about 80kgf x 0.05m per second for a 80kg man who is
hiking or walking (not running). Which is about 9.81 Ws. Assuming that the
total efficiency of the converter (piezo is 20% or better) is 0.1 and that
10% of the available energy is tapped (f.ex. by a sport shoe's heel that
compresses about 5mm out of the 5 cm foot raise - correct me if I'm
wrong), then you will have 0.01 of 9.81 W. Which is 0.0981W. Or about
1.9mA @5V. If you charge a battery with this you will have at least 10mAh
after 10 hours.
Maybe this is too little for your project, but some of the assumptions
made above are way exaggerated (downwards). FYI an Israeli man has
patented some method to generate electricity from walking using polymer
piezo materials a few months ago. I have no idea how to search for the
patent.
> Hi,
>
> I've been lurking on this thread, and i understand that you (Dr. Kirtley)
> are knowledgeable about gait and walking. Therefore I do not understand
> how you have come to the conclusion that there is nowhere near enough
> energy in piezo-electric methods.
>
> I am not knowledgeable about walking but my calculations (which may be way
> off) amount to about 80kgf x 0.05m per second for a 80kg man who is
> hiking or walking (not running). Which is about 9.81 Ws. Assuming that the
> total efficiency of the converter (piezo is 20% or better) is 0.1 and that
> 10% of the available energy is tapped (f.ex. by a sport shoe's heel that
> compresses about 5mm out of the 5 cm foot raise - correct me if I'm
> wrong), then you will have 0.01 of 9.81 W. Which is 0.0981W. Or about
> 1.9mA @5V. If you charge a battery with this you will have at least 10mAh
> after 10 hours.
>
> Maybe this is too little for your project, but some of the assumptions
> made above are way exaggerated (downwards). FYI an Israeli man has
> patented some method to generate electricity from walking using polymer
> piezo materials a few months ago. I have no idea how to search for the
> patent.
Really! I know of prior art. Your estimates of power generation from walking
take most of the factors into account, however you're a little too conservative.
I've seen optimistic estimates for 2.5Watts. The actual power is probably
between our extremes (and closer to your estimate).
With respect, there's a lot of speculation about power generation from
walking, but there's nothing out there that works.
Even Bayliss mechanical method seems to be giving disappointing results.
I'd love to be corrected, but I get a bit fed up with everyone telling
me that it's possible when it ain't!
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: KILLspamkirtleyKILLspamcua.edu http://engineering.cua.edu/biomedical
> I'd love to be corrected, but I get a bit fed up with everyone telling
> me that it's possible when it ain't!
I'm way outside of my experience boundaries here, but I suspect the failures for
the other methods are because they lack the proper material and/or apparatus
suitable for the energy conversion. I had the opportunity to experiment with a
material that was quite suited for the job. Even if I knew it's properties, I
wouldn't be at liberty to discuss them. I can only mention their existance since
that is "public knowledge" (if of course, you're associated with the right
public - or republic, whichever the case may be). Suffice it to say, that there
are materials that are flexible and capable of converting mechanical energy to
electrical energy (with the coercing assistance of clever electronics). Piezo
materials are an example, but orders of magnitude too stiff. I'm sure you may
have examples of others that are much more flexible, but their conversion
efficiencies are much too low.
Chris wrote:
>Dear Peter,
>
>With respect, there's a lot of speculation about power generation from
>walking, but there's nothing out there that works.
>
>Even Bayliss mechanical method seems to be giving disappointing results.
>
>I'd love to be corrected, but I get a bit fed up with everyone telling
>me that it's possible when it ain't!
>
Chris, did those MIT guys I mentioned previously misspeak?
Did you check their stuff?
Original msg included below:
===========================
Hi Chris,
You may be right concerning producing enough power to run a transmitter.
However, still worth investigating some of the stuff various people
are doing in the area of "wearable computers". MIT Media Lab, etc
- those guys/gals have done all kinds of stuff like this. One article
talks about generating 17W during a brisk walk:
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: kirtleyEraseME.....cua.edu http://engineering.cua.edu/biomedical
>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.
The trainers with the flashy light thingies in the sole do this as I understand a thread on this list a wee while back.
I'll stick my neck out here and say that if someone paid me to do it I could
*** certainly *** produce a device that generated electrical power from
walking.
I have thought about this a fair bit when I was doing a moderate amount of
walking some while ago. Not a normal mode of longer distance locomotion for
me usually (regrettably).
The trouble with Piezo, as Scott has noted, is that the short distances
involved mean that the forces involved must be multiplied in some manner to
undesirably high levels. This can be achieved by having a very high
deceleration somewhere in the system but this is generally not desirable
when
this is a by-product of walking. Ideally you want to deliver the power as
continually as possible across the working "stroke". Users may :-) object to
platform shoes which telescope to the ground at all times as you walk, so
you are limited to doing something in the deceleration phase as the foot
strikes the ground. A degree of "sponginess" may be acceptable but if this
gets too noticeable the user will quite rightly object.
If I wanted to do this quickly and simply to achieve "some" power I would
probably first look at a mechanical sprung system using rare-earth magnets
and a fairly conventional alternator arrangement. This could be built to be
quite thin and would certainly be able to be built into a shoe heel. A shoe
sole would be harder.
End result could probably feel like an xxx-air-sole but the "air" feeling
would be the alternator magnetics. I would imagine that a fair proportion of
a watt could be achieved "easily"
Consider the effort taken to "pump" the hand operated alternator torches
that one cam buy and translate this into more intermittent but higher force
pulses.
While you would not do this, imagine strapping such a torch on a frame on
you shoe so that the lever was operated as you walked.
- Would it work? - of course.
- Would you feel the forces involved? - hardly, if mounted correctly.
- Could this be translated into a much more professional system? - yes.
From: Dr. Chris Kirtley <RemoveMEkirtleyTakeThisOuTspamCUA.EDU>
>With respect, there's a lot of speculation about power generation from
>walking, but there's nothing out there that works.
>
>Even Bayliss mechanical method seems to be giving disappointing results.
>
>I'd love to be corrected, but I get a bit fed up with everyone telling
>me that it's possible when it ain't!
Is one of the objections to using pedestrian action to recharge batteries a case of the gait of your research subjects is not a normal human gait (as in a crippled person)? I have not seen any mention of this as being a problem in the thread.
To follow on Russell's idea of pumping, would it not be possible to have a generator made out of a small computer processor type fan spun with a pump action a bit like a child's top? I am thinking of the sort of top that was available perhaps 40 years ago with a handle that you pumped down on to make the top spin, a bit like the push screwdrivers you used to be able to get.
If nothing else this list certainly explores some way out ideas for trying to achieve the impossible.
Well, you could likely kill two birds with one stone. If I understand you
correctly, you need the device in the shoe to know when it is within reange of a
receiver, and also to be charged through some sort of non-contact (possibly
inductive) setup.
All you need to do is wind a coil around your device, tuned to a given
frequency, rectify it and charge your batteries any time you are within the
chargin coil. You can use a few discrete components to tell you when you are
being charged, and therefore are within range of the receiver. No need to go to
RFID or other systems.
If you can get your subjects to stand on foot-print marks on the floor, it
becomes even easier (or tell them to put their shoes there for the evening).
Not only that, but you could also use the same coil for bi-directional
communication.
The shoe stand is always sending out a weak magnetic field at a given
frequency. When the shoe is placed on it, the shoe can detect the field. (the
stand could also detect the shoe, but that won't be necessary here)
When the shoe detects the field, it sends a commend to the stand to enter
communication mode. Since they are in very close proximity, very low power may
be used to send information back and forth on a master-slave protocol of some
sort.
When done, it tells the stand to charge it (probably for a pre-determined amount
of time), and goes to sleep until the charging is done (either because the shoes
were removed, or the charging cycle has ended.) If it isn't charged enough, and
it's still on the stand, it can request more energy.
Chances are good that your subjects remove their shoes for several hours a day,
and can remember to put them on a stand overnight. If not, the entire cycle
except charging could be carried out in a hallway witha larger coil as the walk
past it, etc.
Benefits of this would include low radiation magnetic fields, no wasted power on
the portable device reading for RFID or another tag, very low poer for
transmission, etc.
>
> Dear all,
>
> Sorry to keep asking questions, but I'm trying to kill several birds
> with one stone. I want to sense proximity to a receiver so that I can
> transmit telemetry data (hence the reason I asked about RFID tags), and
> also to charge the battery inductively. I wonder if anyone has any tips
> on the latter? The battery is very low capacity (20mA 3V) Vanadium
> Pentoxide Lithium.
>
> Thanks in anticipation,
>
> 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: kirtleySTOPspamspam_OUTcua.edu
> http://engineering.cua.edu/biomedical
>
> Clinical Gait Analysis: http://guardian.curtin.edu.au/cga
> Send subscribe/unsubscribe to spamBeGonelistprocSTOPspamEraseMEinfo.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
> Benefits of this would include low radiation magnetic fields, no wasted power on
> the portable device reading for RFID or another tag, very low poer for
> transmission, etc.
Not to mention if your subjects/patients have any broken bones, they can
stand in the field for a few hours a day and heal faster... 8-)
Dale
(whose mother used an EM field to heal a broken leg back in the early
'80s)
---
The most exciting phrase to hear in science, the one that heralds new
discoveries, is not "Eureka!" (I found it!) but "That's funny ..."
-- Isaac Asimov
Hi Chris,
Err, Umm, how about putting the charger/transmitter in a pad
that goes under a rug by the toilet? pretty much everyone
stops by once in awhile, and the distance is controlled and
pretty short, and plenty of time.
> Dear all,
>
> Sorry to keep asking questions, but I'm trying to kill several birds
> with one stone. I want to sense proximity to a receiver so that I can
> transmit telemetry data (hence the reason I asked about RFID tags), and
> also to charge the battery inductively. I wonder if anyone has any tips
> on the latter? The battery is very low capacity (20mA 3V) Vanadium
> Pentoxide Lithium.
>
> Thanks in anticipation,
>
> 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@spam_OUTcua.edu
> http://engineering.cua.edu/biomedical
>
> Clinical Gait Analysis: http://guardian.curtin.edu.au/cga
> Send subscribe/unsubscribe to spamBeGonelistprocKILLspaminfo.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
>
>
>
>
-- http://www.piclist.com hint: PICList Posts must start with ONE topic:
"[PIC]:","[SX]:","[AVR]:" =uP ONLY! "[EE]:","[OT]:" =Other "[BUY]:","[AD]:" =Ads
Alice Campbell wrote:
>
> Hi Chris,
> Err, Umm, how about putting the charger/transmitter in a pad
> that goes under a rug by the toilet? pretty much everyone
> stops by once in awhile, and the distance is controlled and
> pretty short, and plenty of time.
>
> alice
Hee hee! Just make sure you don't use high voltages in the
design! ;o)
(Sorry to make fun of a great idea Alice!)
-Roman
I've taken a flashing LED shoe apart and it contained a lithium battery ,
and the LED legs were used for the switch.
John
*************************************************************** .....John.Walshespam_OUTinpactmicro.com
John Walshe @Inpact wrote:
>
> I've taken a flashing LED shoe apart and it contained a lithium battery ,
> and the LED legs were used for the switch.
> John
That's cheatin! So the Doc was right... ;o)
-Roman
I hope all the walking energy generator fans will now shut up!
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: TakeThisOuTkirtley.....TakeThisOuTcua.edu http://engineering.cua.edu/biomedical
At 11:18 AM 10/31/2000 -0500, you wrote:
>Thanks, John.
>
>I hope all the walking energy generator fans will now shut up!
>
Shoot, you only asked for 3v at 20 mA = 60mW - a long way from
the virtual 17W at MIT - I can do 60 mW with my eyelids in
REM sleep -[oops, sorry Chris, I always drove the profs nuts
in college too - he, he].
At 04:03 PM 10/27/00 +0100, John Walshe @Inpact wrote:
>I've taken a flashing LED shoe apart and it contained a lithium battery ,
>and the LED legs were used for the switch.
>John
I was shocked to find, in a pair of nikes, mercury switches!
I don't particularly like the lithium battery either.
The thought of a nail through either item into the foot....
On a related note, I recently bought some piezo disks, and one of them
connected to a high-brightness LED *does* result in noticable (but not
by any means "bright") flashes each time the disk is tapped or stressed.
>
> I hope all the walking energy generator fans will now shut up!
>
I dont get this comment?
Dont you want people exploring ideas along these lines?.....
I object to being told to SHUT UP because my engineering thoughts are not
to your satisfaction.
BTW I have stored charge from piezo kynar plates flexed for 1 minute that
ran a led for 5 sec.. not a bad start from a crude bench experiment.
Lance Allen
Embedded Systems Lab
CSE
Electronic and Electrical Engineering
School of Engineering
University of Auckland
New Zealand
>On a related note, I recently bought some piezo disks, and one of them
>connected to a high-brightness LED *does* result in noticable (but not
>by any means "bright") flashes each time the disk is tapped or stressed.
>
>BillW
Now that you've gone my way, connect a SMD rectifier bridge to the disk,
and connect a small NiCd button cell at the output of it. Discharge the
cell and then whack/walk/crush/whatever the disk using some popular
activity (If you drive a car place it in your rear pant's pocket). At the
end of the day take out the NiCd and discharge to measure charge. I did
try to put one in a sports shoe's (split) sole and it did charge the
battery but due to insulation problems and comfort I gave up early. This
was about 2 years ago... A proper lab with plastic injection and
manufacture capability (as in injected shoe soles) ought to be able to do
much better. The energy comes from flexing the sole, not pressure in this
case. FYI. Now I'll just shut up ;-)
Alright... alright! I'm sorry I said "shut up". I'd actually like to
hear more from people who actually had a go at this - I was just getting
tired of people suggesting it was easy.
Have you measured the voltage and current that you get when you flex the
material (I presume it is PvDF)? That's really what we need to know.
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: RemoveMEkirtleyspamBeGonecua.edu http://engineering.cua.edu/biomedical
Sheesh. I didn't expect this much response to an off-the-cuff comment.
The Piezo disks in question are standard ceramic element on a brass disk
that you see in audio "beeper" sort of applications. About an inch in
diameter overall, a bit less than 3/4 inch for the ceramic area. They're
NOT the kynar film type (hmm. I've got some samples of that SOMEWHERE...)
I bought 24 from an ebay seller for about $3, for "beeping" applications.
I hooked one up to my scope. with a 27 ohm resistor load, a "thwack" with a
fingername gives me a nice exponentially decaying sine wave with about .5V
peak voltage and about 1ms duration. "open circuit" voltage under similar
stimulation is about 40V with a rather messier and longer duration waveform.
While you could probably easilly use something like this to make an LED
flasher for your shoes that would last ... longer than the shoes, the fact
that a small lithium coin cell can provide "enough" power to do this as well
is pretty damning from an overall product perspective, IMHO.
>Have you measured the voltage and current that you get when you flex the
>material (I presume it is PvDF)? That's really what we need to know.
Did not. All I had was a CRO and the flexing material produces waveforms
that need to be integrated to make sense of them. I think that using a
NiCd button cell with known efficiency at constant temperature (+/- 5 deg
C) makes a good integrator. I did not go all the way with this because the
implementation difficulties doomed the project. My button cell was a VARTA
AG50 if I'm not mistaken (50 mAh ?). Using very inconclusive measurements
~1 hour of walking (in house) gave more than 10 mAh. This used two stacked
piezo disks (2" dia) meant for alarm system bleepers. One of the disks was
damaged after use (cracked) due to incorrect mounting. The rectifier was
Shottky diodes (two doubles making a bridge). The thing was definitely
unconfortable (try to imagine walking with a piece of solid stuck in the
middle of your shoesole). FYI the piezo disks mentioned produce more than
12V peaks into 1Meg (standard scope probe) when gently flexed with fingers
(no more than 500 grams x 2.5 cm moment ~= 0.125 Nm - the deflexion must
have been under 2mm). It is hard to get specs for these, but perusing the
datasheets of some ceramics manufacturers will likely yield more data. Ok,
so each deflexion yields about 200uW with one disk. 5 deflexions will be 1
mW. The storage system has an efficiency of 50% overall. Take it from
there ;-)
You must not forget that ceramics can pack a very high energy density per
volume. Think of the size of kW rated ultrasonic transducers, or how hard
it is to duplicate a plain piezo gas lighter using electronics and a
transformer !
good lucks,
Peter
-- http://www.piclist.com hint: PICList Posts must start with ONE topic:
"[PIC]:","[SX]:","[AVR]:" =uP ONLY! "[EE]:","[OT]:" =Other "[BUY]:","[AD]:" =Ads
cua.edu
