Non-Contact Battery Charging and Comms

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Are there any parts out there that provide for non-contact power and  
communications for electronic devices?

I'm working on a product that'll consume low power (around 200mW), but  
that would benefit greatly if it could be mated to a computer via some  
super-low-range non-contact power source.  The model of what I'm thinking  
of is an inductive loop that transmits using some means (FSK?) and  
receives by sensing variations in the load of the loop.

There's a standard out there (Qi) that covers the power part, but I'm not  
finding anything that covers the power and talking back and forth.

--  

Tim Wescott
Wescott Design Services
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Re: Non-Contact Battery Charging and Comms
On Mon, 17 Mar 2014 15:47:06 -0500, Tim Wescott wrote:

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Oops -- comms can be pretty slow: 100k-baud would be nice, but 10k would  
be acceptable.

--  

Tim Wescott
Wescott Design Services
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Re: Non-Contact Battery Charging and Comms
Tim Wescott wrote:
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That's a bit much for modulating the power transfer signal directly.
Since it most likely has to pass EMC I'd look into data transfer on an
ISM band. Not necessarily 13.56MHz because that could be plastered in
some heavy industry area and the band is kind of narrow anyhow. 27.12MHz
is better, or just use 2.45GHz since there's lots of chips available.

For non-contact power it is customary to stay below 150kHz in order to
dodge some EMC regulation bullets. How much distance must be allowed
vertically and laterally? Electric toothbrushes often use ferrite rod
cores. I'd also stay away from 60kHz and 120kHz, to avoid complaints
about atomic clocks suddenly quitting or disturbing home automation systems.

--  
Regards, Joerg

http://www.analogconsultants.com/

Re: Non-Contact Battery Charging and Comms
On Mon, 17 Mar 2014 14:19:06 -0700, Joerg wrote:

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Vertical and lateral distance is negotiable at the moment.  The customer  
was thinking of having something that plugs into the side of the unit (I  
think he's seen those tooth brushes).

It doesn't seem to be a problem that has bazzilions of pre-packaged  
solutions out there, which does take one aback.

--  

Tim Wescott
Wescott Design Services
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Re: Non-Contact Battery Charging and Comms
Tim Wescott wrote:
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"Plugs into the side" is good news, meaning the distance and offset is
well controllable. You'll also have to ask them about any efficiency
rules they must fulfill, EPA and whatnot. I remember when I was happily
roaring into a switcher design and casually asked the client whether
there'd be any power factor requirement. "Oh, darn, yes!" ... whew.


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The power transfer doesn't have any canned solutions, there is not
enough market and the requirements are too widely scattered. Plus most
of the stuff is cut-throat cost-sensitive so any ICs would not stand a
chance anyhow. It's generally all done in discretes.

If it has to be low loss think in the direction of resonant power
transfer when designing it. Resonance is your friend with wireless power
transfer. Unfortunately it's usually only practical to have one side
(power source side) resonant.

On the data side you should be able to use standard stuff unless it
absolutely must be transferred via the same set of coils. On a resonant
transfer scheme that could get you deep into an analog hellhole. But
those can be fun, like a mountain biker seeing a scary downhill section :-)

--  
Regards, Joerg

http://www.analogconsultants.com/

Re: Non-Contact Battery Charging and Comms
On Mon, 17 Mar 2014 15:20:35 -0700, Joerg wrote:

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There is a standard out there that's getting adopted for smart phones and  
other similar sized bits of kit.  It's the "Qi" standard that I  
mentioned.  But making a compliant device would, I think, cost a lot more  
than it would be worth to the customer.

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The customer suggested communicating over the power connection.  I think  
it's probably not a good idea, however much fun it may be to try.

When I hit things like this I often have to discipline myself not to go  
there -- it's tempting to do things the fun way, forgetting that it's on  
the customer's dime and may not be the most cost effective way to proceed.

--  
Tim Wescott
Control system and signal processing consulting
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Re: Non-Contact Battery Charging and Comms
Tim Wescott wrote:
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It probably depends how onerous the standard and licensing is. Also, if
you need fast datacom I believe that's not covered and then you have a
custom situation at hand anyways. Might not be worth to bother with a
standard then because nothing they'd ever wanted to plug in would be
compatible with your data solution.


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Yeah, I am sometimes tempted as well. But if there is any other method,
such as a 2nd coil and core for data, that's way easier. Just keep in
mind radio cert rules if you go ISM. In many jurisdictions that is
considered "intentional radiator" and then the EMC test takes longer and
costs more.

--  
Regards, Joerg

http://www.analogconsultants.com/

Re: Non-Contact Battery Charging and Comms
On Mon, 17 Mar 2014 16:52:07 -0500, Tim Wescott

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If it 'plugs in', what advantage is there to contact-free transfer?

RL

Re: Non-Contact Battery Charging and Comms
legg wrote:
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a. No soiling up of contacts
b. No corrosion
c. No safety reg infringements
d. Resistance to harsh cleaning agents
e. Can be simply hosed off
f. Much less field failures
g. Cosmetic (same color everywhere)
.....

And so on.

--  
Regards, Joerg

http://www.analogconsultants.com/

Re: Non-Contact Battery Charging and Comms
On Tue, 18 Mar 2014 11:04:27 -0700, Joerg wrote:

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Joerg said it as well as I could.

It's to be used on shipboard.  It probably won't be immersed in salt  
water in its daily life, but it needs to resist being splashed with it on  
a regular basis.

--  
Tim Wescott
Control system and signal processing consulting
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Re: Non-Contact Battery Charging and Comms
On Tue, 18 Mar 2014 16:13:43 -0500, Tim Wescott

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Must be an interesting computer packaging exercise, in that case.

RL

Re: Non-Contact Battery Charging and Comms
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Goofy idea: Wad of white LEDs on the PC, solar cell on the portable
device.  Modulate the LEDs from 90% to 100% with the data; pick up the
varying solar cell output on the portable device to get the data back.

Plus you get "free" extra battery charging if the user leaves the
portable device in a sunny spot.

Probably needs too much surface area on the portable device, and I don't
know what the bandwidth of your average solar cell (photodiode) is.

Matt Roberds


Re: Non-Contact Battery Charging and Comms
On Tue, 18 Mar 2014 05:14:13 +0000, mroberds wrote:

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Way inefficient, but it just sparked the idea of using optical comms,  
which may well work -- I'll have to try it on for speed.

--  

Tim Wescott
Wescott Design Services
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Re: Non-Contact Battery Charging and Comms
Tim Wescott wrote:
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IR can transmit through certain kinds of plastic, meaning you could
still have a hermetic seal.

--  
Regards, Joerg

http://www.analogconsultants.com/

Re: Non-Contact Battery Charging and Comms
On Tue, 18 Mar 2014 17:42:01 -0700, Joerg wrote:

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Yup.  I wonder how hard it would be to find optically black epoxy that's  
IR-transparent?  It can't be that hard - it's what they enclose some of  
the IR LEDs and phototransistors in.

--  

Tim Wescott
Wescott Design Services
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Re: Non-Contact Battery Charging and Comms
Tim Wescott wrote:
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You mean the resin base? For example here:

http://catalog.ides.com/Datasheet.aspx?I34%794&E21%9221

--  
Regards, Joerg

http://www.analogconsultants.com/

Re: Non-Contact Battery Charging and Comms
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I did say it was goofy.  :)

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Wiki says IrDA has specs up to 1 Gbit now, but I don't know if you can
actually do that.  When it was on a lot of laptops and printers I think
it was in the dialup modem/ISDN speed range, like up to a few hundred
kbits or so.  You don't *have* to use IrDA but there may be pre-existing
code and hardware (especially on the PC side) for it.

Matt Roberds


Re: Non-Contact Battery Charging and Comms
wrote:

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We should discuss. I've designed 200 W and 2kW WPT systems. If your client  
has the expected volume in Production, we could knock their socks off.

If you're after 'prepackaged' solution, also contact me.

The 'worst' was 1.25W transferred over 4 inches with incredible design  
restrictions for the sizes of the source AND receiver.


Most important question is 'what is the size of the receiver?'

Re: Non-Contact Battery Charging and Comms


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Tim,

few months ago i was consulted for a design of a docking station where i  
plan to use silvertel modules. AFAIK Qi specs did not assume that data  
transmitted are for other purpose than power management.  
Besides i dont understand "inductive loop that transmits using some means  
(FSK?) and receives by sensing variations in the load of the loop" What  
does that mean ?

Better to use BLE modules for data trans ...

HBV

Re: Non-Contact Battery Charging and Comms
Habib Bouaziz-Viallet wrote:

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You can modulate the data onto the power path and use the same magnetic
link. But north of 10kbaud that gets dicey. Because if you have to
spectrally go above 150kHz the conducted emissions cert can become
tricky. Well, at least if it all has to be cheap.

Even below 150kHz it's not easy, one can quickly disturb home automation
systems using PLC and als atomic clocks. For example, if stuff spills
into the 60kHz WWVB or 77.5kHz DCF in Europe.

[...]

--  
Regards, Joerg

http://www.analogconsultants.com/

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