5kHz receiver

[vic]

Hi,

I have one of these common heart monitor watches with a belt that straps
around the chest. According to the manual the belts emits one pulse per
heartbeat on a 5kHz carrier. I'd like to be able to pick up this signal
to do some more advanced analysis than what the watch allows, however I
lack experience in the RF field.

So, could you give me some tips on how to design the antenna and the RF
amplifier circuit?

[Martin Brown]

On 24/04/2012 08:43, vic wrote:
> Hi,
>
> I have one of these common heart monitor watches with a belt that straps
> around the chest. According to the manual the belts emits one pulse per
> heartbeat on a 5kHz carrier. I'd like to be able to pick up this signal
> to do some more advanced analysis than what the watch allows, however I
> lack experience in the RF field.

5kHz is audio band so a largish pancake coil of wire and a hifi amp
should see it. (or maybe even cheaper a crystal earpiece on the loop )

> So, could you give me some tips on how to design the antenna and the RF
> amplifier circuit?

Low noise preamp followed by a PLL detector probably needed to pick
signal from noise. Are you sure it is on a 5kHz carrier?
Seems an awfully low frequency.

--
Regards,
Martin Brown

[pault]

Sparkfun sell a reciever
http://www.sparkfun.com/products/8661

but it should be possible to build one
very cheaply

[vic]

Thanks for the link, I didn't know it existed. It costs almost twice the
price of my watch though, and it's from another brand so I'm not certain
it would be compatible.

[vic]

On 24/04/2012 09:53, Martin Brown wrote:
> 5kHz is audio band so a largish pancake coil of wire and a hifi amp
> should see it. (or maybe even cheaper a crystal earpiece on the loop )

Would any tuning be necessary, or a simple coil would suffice ?

> Low noise preamp followed by a PLL detector probably needed to pick
> signal from noise.

Do you think an LM567 could be a good choice for a PLL detector down the
chain?

> Are you sure it is on a 5kHz carrier?
> Seems an awfully low frequency.

I was surprised as well, but I checked several sources and they are
consistent. I guess this might have something to do with power
consumption since the belt is supposed to be able to operate on a CR2032
battery for 1 year.

[Martin Brown]

On 24/04/2012 09:46, vic wrote:
> On 24/04/2012 09:53, Martin Brown wrote:
>> 5kHz is audio band so a largish pancake coil of wire and a hifi amp
>> should see it. (or maybe even cheaper a crystal earpiece on the loop )
>
> Would any tuning be necessary, or a simple coil would suffice ?

I'd try it without and at close range first.
Tuning would involve fairly large capacitors or a huge coil.

>
>> Low noise preamp followed by a PLL detector probably needed to pick
>> signal from noise.
>
> Do you think an LM567 could be a good choice for a PLL detector down the
> chain?

567 is a bit long in the tooth now. CMOS 4046 would need less power.

>> Are you sure it is on a 5kHz carrier?
>> Seems an awfully low frequency.
>
> I was surprised as well, but I checked several sources and they are
> consistent. I guess this might have something to do with power
> consumption since the belt is supposed to be able to operate on a CR2032
> battery for 1 year.

How odd.

--
Regards,
Martin Brown

[pault]

5khz is in the VLF band (also in the human hearable audio band)

This looks like a suitable VLF receiver circuit:

(Magnetic Pickup) at
http://www.spiro.fisica.unipd.it/~mbarbisa/espfis/VLFwhistle.htm#Magnetic

you probably dont need the second op amp and should feed the output
into
a tone decoder pll like the lm567

an even simpler circuit on the same page might work too
(Super-Tiny VLF Receiver)
http://www.spiro.fisica.unipd.it/~mbarbisa/espfis/VLFwhistle.htm#Super-Tiny

see http://www.scary-terry.com/more_stuff/tonedet/tonedet.htm
for an example lm567 circuit

[hamilton]

Why is the brand a secret ??

This discussion would go a lot faster with that secret information.

hamilton

[Robert Macy]

On Apr 24, 4:18 am, pault <pau...@gmail.com> wrote:
> 5khz is in the VLF band (also in the human hearable audio band)
>
> This looks like a suitable VLF receiver circuit:
>

> (Magnetic Pickup) athttp://www.spiro.fisica.unipd.it/~mbarbisa/espfis/VLFwhistle.htm#Magn...

>
> you probably dont need the second op amp and should feed the output
> into
> a tone decoder pll like the lm567
>
> an even simpler circuit on the same page might work too

> (Super-Tiny VLF Receiver)http://www.spiro.fisica.unipd.it/~mbarbisa/espfis/VLFwhistle.htm#Supe...
>
> seehttp://www.scary-terry.com/more_stuff/tonedet/tonedet.htm

> for an example lm567 circuit

Thank you for these URLs!
I didn't see any mention of Chernov Radiation being a source of VLF.

It is my understanding that as a cosmic particles enter our atmosphere
they slows down, thus giving off energy, called Chernov Radiation. I
understand that the effect is greatly enhanced by using a tank of
water to slow the particles down and using photon multiplier tubes to
'view' the light trail these particles give off. Japan has a cave
lined with some 1,000+ multiplier tubes [at $20,000 each that's
impressive!]

Further by calculating the information from the light trails it is
possible to determine energy/origin essentially making a form of
telescope that can look deep into space. Note: the cave setup in Japan
went through an unexplained failure mechanism where by they lost
almost ALL tubes, going off like a popcorn string. They had to drain,
replace, only to lose them again.

There was a Professor in New Mexico who contended that by measuring
VLF, you could surmise the Chernov Radiation of these particles as
they went through the atmosphere, thereby making a much cheaper form
of telescope. I designed the magnetic VLF receiver with noise floors
50X less than earth's field's noise floor and I got to add the concept
of placing many such VLF receivers spaced every so far along the US,
for 1000's of miles, essentially a phased array antenna. The end
result would be creating an extremely wide lense telescope capable of
looking deeper into space than man has ever looked in his history.

[mike]

Can you tap the demodulated signal out of the watch?

[miso]

I have one of those Polars. They are coded, so I think you would save
yourself a lot of work just getting the sparkfun board.

I guess if you are using a treadmill, you could use such a monitor. I
only use mine outdoors. The real advantage to a Polar monitor is zone
conditioning. You set up the watch such that it tracks your heart rate,
and then you try to stay in a zone. The watch can also estimate the
calories burned. It also yells at you if you haven't exercised in a while.

[vic]

On 24/04/2012 15:59, hamilton wrote:
> This discussion would go a lot faster with that secret information.

Sorry. The brand is Géonaute, and the model Kalenji 100.

[pault]

theres the Kalenji cardio connect
http://www.decathlon.co.uk/kalenji-cardio-connect-id_8160570.html

[pault]

The Stanford University VLF Group ( http://vlf.stanford.edu/ ) may
be involved in that area of research

theres an interesting vlf page here ( http://www.vlf.it/ )
and a yahoo discussion group ( http://tech.groups.yahoo.com/group/VLF_Group/
)

[Robert Macy]

> The Stanford University VLF Group (http://vlf.stanford.edu/) may

> be involved in that area of research
>

> theres an interesting vlf page here (http://www.vlf.it/ )

> and a yahoo discussion group (http://tech.groups.yahoo.com/group/VLF_Group/
> )

Thanks for the URLs!