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'[EE]: Lowest possible cost short range RF telemetr'
2000\06\26@164550 by Andrew Seddon

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Would it be possible to use some sort of inductive communications? I
remember seeing it in a product once where the comms were 9600. Admittedly
the coils were about 2cm apart but it could be adapted.

Don`t know much about it myself, prehaps somebody could expand?


Andrew Seddon

2000\06\26@214228 by Dan Michaels

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Russell McMahon wrote:
>I have an application requiring very short range low speed telemetry.
>Low cost is an overwhelmingly significant factor.
>The application is to transfer an occasional on/off signal over a distance
>of around 1 metre.
>Transmitter and receiver orientation cannot be guaranteed. There may be
>object(s) (possibly a person, metalwork etc) in the direct path although
>there will not be solid metal blockage (OK - I'll tell - it's part of an an
>exercise machine.).

Hi Russell,

[OK, last week I fixed your battery charger, this week it'll be
your exercise machine - maybe you oughta hire me as a full-time
consultant - he, he <:-)))].

Funny thing you should mention exercise machine here. You've
probably seen the Polar heart rate monitors. The h.w. inside the
chest belt will signal heart rate to about 200 bpm - and run for
months off a sealed-in lithium battery <-- presumably Li, since
nothing else could fit in that belt. The range is 3 feet or so
- that's about 1M to outlanders.

You can pick up the signal from the Polar belt using a simple coil
and see it on a scope. Each heart beat is signalled by a decaying
5khz tone that lasts for a few msec.

For a receiver, a simple coil-capacitor resonant ckt tuned to 5
Khz, followed by a 2-stage BJT amplifier and rectifier work fine.
Costs about 50 cents US.

The chest belt itself, uses a very simple ckt. BJT operating in
class C, for power savings, picks up/amplifys the heart signal,
which is in the mV range, and bangs a loop coil that resonates
at 5 khz. When not connected to the chest the BJT is off, and
no power is expended. Cost about 50 cents US.

Your constraints would probably be no where near as bad as the
Polar unit. Also, 5 Khz probably isn't even covered by the FCC,
so you won't have to worry about Harold H. jinxing your plans.

The basic amplifier described above will pick up misc garbage,
like emissions from your CRT [although I don't know which ones
specifically]. Also, nearby Polar units interfere with each
other. HOwever, you could send a little coded-pulsetrain to
reject unwanted garbage.

BTW, you can deal with the orientation thing by using 2 or
3 coils, mounted orthogonally w.r.t. each other, and wired
in series - or wired to separate amps for better response.

best regards,
- Dan Michaels
Oricom Technologies
===================

2000\06\26@220141 by Scott Dattalo

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On Mon, 26 Jun 2000, Dan Michaels wrote:

> Funny thing you should mention exercise machine here. You've
> probably seen the Polar heart rate monitors. The h.w. inside the
> chest belt will signal heart rate to about 200 bpm - and run for
> months off a sealed-in lithium battery <-- presumably Li, since

Try years. I just replaced the battery in my (Li CR2032 IIRC, $1.20 at Fry's)
after 5 years of use. I knew it was about time to change my battery when my
respiration rate started exceeding my heart rate. Also, I've never sprinted up a
200' hill and kept my h.r. below 80 bpm!

2000\06\27@143405 by Dan Michaels

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Scott Dattalo wrote:
>On Mon, 26 Jun 2000, Dan Michaels wrote:
>
>> Funny thing you should mention exercise machine here. You've
>> probably seen the Polar heart rate monitors. The h.w. inside the
>> chest belt will signal heart rate to about 200 bpm - and run for
>> months off a sealed-in lithium battery <-- presumably Li, since
>
>Try years. I just replaced the battery in my (Li CR2032 IIRC, $1.20 at Fry's)
>after 5 years of use. I knew it was about time to change my battery when my
>respiration rate started exceeding my heart rate. Also, I've never sprinted
up a
>200' hill and kept my h.r. below 80 bpm!
>

Scott, I suspect the Polar ckt design is so efficient - with say 3
bps each producing a 5 msec long pulse in a class C amp - that the
battery probably will go for years. [I used to use mine on 8-hour
long hikes in the CO mtns - helps an old wheezy body get up those
14ers - anything for a gimmick, huh!].

But was this actually the belt battery or the watch battery you
replaced? If indeed the belt, what did you see inside, viz-aviz
electronics, after you slit it open? Also, how did you reseal it
afterwards?

I believe the watch has 3 tiny pickup coils positioned at R-A
w.r.t. each other to provide orientation non-specificity - but
I never looked inside it either. Don Lancaster mentioned this
device in one of his columns 5-6 years ago, which is where I
got the basic info. Plus, I did download the Polar patent and
looked at it too.

Also, couple of years ago, I built a little pickup amp, tied it
to a PIC datalogger, and tracked my heartrate on many occasions.
On one nearby hike I do a lot for conditioning, I could actually
tell - from looking at the datalog - where I was on the trail by
how hard my heart was pumping. Pretty slick. Who needs GPS!

I don't know if my suggestion helped out Russell, but all in all,
the Polar device is very clever, plus extremely simple and cheap,
electronics.

[what the heck is IIRC ???]

best regards,
- Dan Michaels
Oricom technologies
===================

2000\06\27@151734 by Scott Dattalo

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On Tue, 27 Jun 2000, Dan Michaels wrote:

{Quote hidden}

The sprint referred to a bicycle... I suspect that the long life of the battery
is due in part to it's lack of continuous use. These batteries have very long
shelf lives. So I may've been demonstrating that behavior (I don't use it every
time I ride - seldom during commutes).

>
> But was this actually the belt battery or the watch battery you
> replaced? If indeed the belt, what did you see inside, viz-aviz
> electronics, after you slit it open? Also, how did you reseal it
> afterwards?

There's a quarter-sized (that is 25 cents) lid that's slightly bigger than the
CR2032. An o-ring is present to keep out moisture. When you open the back, you
really can't see much. So I have no idea what the circuit looks like.

> I don't know if my suggestion helped out Russell, but all in all,
> the Polar device is very clever, plus extremely simple and cheap,
> electronics.

and expensive!

>
> [what the heck is IIRC ???]

if I recall correctly

Scott

2000\06\27@171306 by Dan Michaels

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Scott wrote:
..........
>>
>> But was this actually the belt battery or the watch battery you
>> replaced? If indeed the belt, what did you see inside, viz-aviz
>> electronics, after you slit it open? Also, how did you reseal it
>> afterwards?
>
>There's a quarter-sized (that is 25 cents) lid that's slightly bigger than the
>CR2032. An o-ring is present to keep out moisture. When you open the back, you
>really can't see much. So I have no idea what the circuit looks like.
>

OK, so you were actually replacing the battery in the **watch**,
rather than in the belt. The watch should run for a couple of years.
THe belt sucks more juice since it's the xmtr end. However, with
class C operation, you still get long batt life.
===========

>> I don't know if my suggestion helped out Russell, but all in all,
>> the Polar device is very clever, plus extremely simple and cheap,
>> electronics.
>
>and expensive!
>

Yes, the belt-watch setup is expensive to buy, ~$80-100 US, but the
xmtr-link electronics probably costs only $1 US. OTOH, the belt is
very nicely made, and the rest of the watch adds cost. All in all,
probably $10-15 US to manufacture in quantity.

Nice product, plus interesting minimalist engineering design. Good
method, I think, for a very short-range RF link. Add a little
coding to avoid interference, and botta bing. I used a simple
fuzzy logic algorithm to distinquish between pulses picked up from
my computer monitor, and HRM belt signals.

cheers,
- Dan Michaels
==============

2000\06\27@172338 by Scott Dattalo

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On Tue, 27 Jun 2000, Dan Michaels wrote:

> Scott wrote:
> ..........
> >>
> >> But was this actually the belt battery or the watch battery you
> >> replaced? If indeed the belt, what did you see inside, viz-aviz
> >> electronics, after you slit it open? Also, how did you reseal it
> >> afterwards?
> >
> >There's a quarter-sized (that is 25 cents) lid that's slightly bigger than the
> >CR2032. An o-ring is present to keep out moisture. When you open the back, you
> >really can't see much. So I have no idea what the circuit looks like.
> >
>
> OK, so you were actually replacing the battery in the **watch**,
> rather than in the belt. The watch should run for a couple of years.
> THe belt sucks more juice since it's the xmtr end. However, with
> class C operation, you still get long batt life.
> ===========

No, it was the **belt**. I still haven't replaced the battery in the watch.

2000\06\27@191435 by DIAZ SUSANIBAR

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i WANT TO GO OUT FROM  THE LIST. PLEASE THE FORM

2000\06\27@192936 by Peter L. Peres

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Russell McMahon wrote:
>I have an application requiring very short range low speed telemetry.
>Low cost is an overwhelmingly significant factor.

>The application is to transfer an occasional on/off signal over a
distance
>of around 1 metre.

>Transmitter and receiver orientation cannot be guaranteed. There may be
>object(s) (possibly a person, metalwork etc) in the direct path although
>there will not be solid metal blockage (OK - I'll tell - it's part of an
an
>exercise machine.).

Is the ON/OFF signal to sense the heart condition of the user ? <VBG>

Peter

PS: I don't know over 1 meter but closer than that the passive RF tag will
work. At 1 meter you cannot use a simple grid dip type detector because
too many similar things will trigger the system. You also cannot transmit
a lot of power for FCC reasons. Thus whatever you do with a passive tag
you will have to fight with a signal that is 1/d^4 in strength (it could
be 1/d^6 if you use isotropic radiators). In other words, if the user
moves a few cm then the sense signal can move into and out of your
threshold. In other words, you need something really coded or tagged.

The systems used for tracking thieves in supermarkets etc will work at 1
meter but you will need to make sure that the user is near the loop (hide
the loop inside some suitable part of the machine - which must be
dielectric).

For something real easy look at a footswitch or mat switch. Standing left
for x seconds = on, standing right = off. etc.

And last, you could try to implement a hand gesture switch. This is easily
done using a standard PIR device with a special lens that generates the
correct pulse train depending on the direction of waving. This method also
has other applications ;-)

2000\06\27@200104 by Dan Michaels

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>> Scott wrote:
.....
>> OK, so you were actually replacing the battery in the **watch**,
>> rather than in the belt. The watch should run for a couple of years.
>> THe belt sucks more juice since it's the xmtr end. However, with
>> class C operation, you still get long batt life.
>> ===========
>
>No, it was the **belt**. I still haven't replaced the battery in the watch.
>

Oh, bad assumption on my part. My chest belt has no trap door
to the battery. Must be an older [or newer] version/whatever.

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