I recently saw a tiny camera at a local computer fair, at a very
reasonable price. It's roughly a 1cm cube, with a 5cm wire for a
transmitting antenna. It is listed as being able to transmit video up
to 100M to a base unit, which comes with it in the box.

The lady on the stall told me that most people who are buying them
seem to be remote controlled model aircraft buffs. Well, I got to
thinking, occasionally one of our cats go missing - this thing is so
small,light and cheap, (smaller than the ID box the cats currently
wear on their collars) why not attach one to their collars? Might have
a fighting chance of 'seeing' which tree they're caught up in then!

So, I have 2 questions:

1. 
Cats' safety.
Is there any strong evidence that the radio transmission might be
likely to be harmful to the animal? They'd be wearing the collar-cam
when they were let out - maybe for a couple of hours each day.

2. 
Getting power to the camera.
The camera is supplied with a connector for a pp3 style 9v battery -
the oblong ones very roughly about 1cm x 2cm x 5cm, with the snap-on
connector clip on the smallest side. These would be too big for a cat
to lug around - can anybody think up a more suitable power supply
arrangement, preferably rechargeable? I have a very misty preliminary
idea; a plastic tube forming part of the collar, containing hearing
aid - style cells stacked up to provide ~ 9v (say, a stack of 8 x 1.2v
cells. NiMH maybe? Maybe It'd have to be 2 stacks of 8, with each
stack of 8 having the cells in series then the two stacks in
parralell, to get sufficient capacity. I don't know, haven't done the
maths - misty preliminary idea, as I say.) Quite likely there's a much
better idea for providing sufficient power in a 'cat-friendly' manner.


cutaway view of collar acting as battery pack


--------------------------------------wall of plastic tube
 |""""""| |""""""| |""""""| |""""""|
 |      | |      | |      | |      |   wire
-|      |-|      |-|      |-|      |------------to camera +
 |-    +| |-    +| |-    +| |-    +|
 |      | |      | |      | |      |
 |      | |      | |      | |      |
 |      | |      | |      | |      |
 |      | |      | |  |   | |      |     ___wall of plastic tube
 |______| |______| |__|___| |______|    /
----------------------|--------------- '
OOOOOOOOOOOOOOOOOOOOOO|OOOOOOOOOOOOOOO neck padding on inside 
                      |                   of collar
                      |
                      \---'button' NiMH (?) cells
                          'hearing-aid' style



As a benchmark for the power supply capacity required, an arrangement
that matched the capacity of a standard zinc-carbon pp3 9volt battery
should suffice?

---

Request for Question Clarification by sycophant-ga on 31 Jan 2003 00:43 PST

Do you have a link to this camera specifically? I can address the
issues generally , but the specifics may be difficult without knowing
details of the camera in question.

Specificaly, the questions re power are going to be very hard without
details.

I'd love to help you on this, let me know.

Regards,
sycophant-ga

---

Clarification of Question by gan-ga on 31 Jan 2003 03:07 PST

Hi sycophant-ga, thanks for your interest in my question. 

Yes I do appreciate that without knowing fuller details of the camera,
you would not be able to do precise calculations regarding the power
supply. Unfortunately, I neglected to make a note of details of the
camera, and the fair isn't on again until next wednesday.

All the same, I do know that a standard pp3 type battery will power
the camera for several hours, which should suffice - so, the search
would be for a cell arrangement that would equal or surpass a standard
zinc-carbon pp3 in terms of mAH capacity and current supply rating,
and provide a similar voltage, around 9v.

A 9v zinc carbon pp3 has a capacity rating of 420 mAH (I looked at a
Varta example at:
http://trade-info.varta.com/salesmaterial/general-catalog/020255VINTVR8.pdf
).

Current draw by the camera? Sorry - no info on this, as I said.

A generalised answer would be fine really, if you can give some ideas
as to what kind of cells there are available, & maybe think about how
these could be incorporated into a safe collar. I remember once having
a night fishing float which ws powered by a lithium battery, that
battery was about 2mm wide and 1cm long - maybe something like those
could be arranged like a bandiolier around the outside of a collar
(gunslinger cat :-/), although I'm not sure lithium cells would be the
right technology - aren't those for long term, very low current
applications? I guess I need short term, rechargeable, ?current cells.
Whether NiMH, NiCd, or whatever, cells small enough would be available
I don't know..

I guess I'm hoping to hire imagination as much as hard facts on this
one.

Oh.. Charging any type of cell arrangement won't pose a problem, I'll
be able to build a charger to suit.

"Recreate the abilities of a zinc-carbon pp3 in the shape of a cat's
collar"

---

Request for Question Clarification by sycophant-ga on 31 Jan 2003 11:03 PST

Okay, I have a few little experiments to carry out first... "Here
kitty kitty kitty..."

But I should have a few options for you in the not-to-distant future.
You are in the UK, right?

Regards,
sycophant-ga

---

Clarification of Question by gan-ga on 31 Jan 2003 17:33 PST

Hi again sycophant-ga,

Thanks for having a look at this, Yes, UK here.

Hi Gan,

I'll do this in back-to-front order - start with question two -
Battery options.

As I am sure you are aware, there are a huge range of cells on the
market, however most of the small ones (watch and hearing-aid type)
are not rechargeable, and offer a very low current making them
somewhat ineffective in running something like a small camera.

Looking at the link you posted, it seems a 9V battery weighs it at
around 50g - which, based on some very unscientific testing, does not
seem too much for a cat to carry on it's collar, in so far as it does
not seem to affect it's ability to move (or scratch) however, in the
case of my test subject, some cats may not really enjoy the
experience. But based on your reply to Missy's comment below I will
assume that your cat is more open to such ideas than mine.

If you think your cat can deal with the size and approximate weight of
a standard 9V cell, then perhaps a rechargeable one would suit? I have
found the following at RadioShack (I could not find a UK retailer with
a good online catalogue of batteries):

NiCad 9V Cell - 8.4V, 120 mAh
http://www.radioshack.com/product.asp?catalog%5Fname=CTLG&product%5Fid=23%2D448

NiMH 9V Cell - 8.4V, 150mAh
http://www.radioshack.com/product.asp?catalog%5Fname=CTLG&product%5Fid=23%2D529

Both of these cells have much lower current ratings than the Varta
battery you mentioned, although as we don't know the draw of the
camera, it's hard to know whether this is going to last the four hours
you need or not.

Also generally available are NiCad portable phone batteries, which,
link the one in this link, seem to be just button cells, wired in
series and plastic wrapped. However, it seems very difficult to find
those basic button cells on their one. One option may be to buy some
of these batteries (typically 3.6V) and dismantle them and reassemble
them on a collar. The one I have linked two seems to get 3.6V from two
cells, so they should rate at 1.8V each - five of these button cells
should give you 9V. The dimensions are not listed, but my personal
experience with them leads me to believe fit could be fitted to a
collar without too much difficulty.
http://www.radioshack.com/product.asp?catalog%5Fname=CTLG&product%5Fid=960%2D0521

I believe that a 9V cell, attached length ways to a collar should not
get in the way too much although might be a little large when combined
with the camera. The only way to know for sure is going to be to test
it with the cat involved.

Otherwise, I think the base cells from NiCad portable phone batteries
are your best bet for creating a power source in the shape of a cat's
collar.

Another, less practical but more environmentally friendly, option is
solar power, two of these panels should power the camera, although a
rectifier maybe needed to drop the voltage to a usable level, and with
a larger harness (rather than a collar) they could be strapped to the
cat :)
http://www.radioshack.com/product.asp?catalog%5Fname=CTLG&product%5Fid=980%2D0879

Now, as for the RF emissions, from your description of the device I
assume that it operates in the UHF range, as a 2.4GHz transmitter
generally requires a much more substantial antenna than a wire. I
would estimate that the power of such a transmitter would be less than
50mW, in fact based on looking at the products on this page
(http://www.21best.com/21_best/electronic/security/video/transmitter/for_sale_450.html)
it is probably closer to 20mW.

This power level is so small that it is unlikely to be any more
dangerous to an animal or person than simply living in the
transmission area of a UHF-based TV station. And even then, I have
been able to find no real information about any dangers associated
with UHF transmissions. Most of the RF transmissions that people are
concerned about are in the microwave range, where direct exposure can
be a danger.



Some other thoughts on the issue:

You may find some problems with the range, 100m is likely to be in a
clear line-of-sight, while UHF signals will pass trough solid objects,
the do attenuate quickly, and something as simple as going under a
building or being on the other side of an earth mound may affect your
ability to received your cat-cam signal.

Also, you mentioned the magnet within the cat's current collar set up.
You may find that it interferes with the camera's image. While CCD and
CMOS cameras are quite resilient to magnetic fields, a strong source
nearby could still have some affect. This is probably worth testing
before hand, if you are able.

I hope this helps, your project sounds very noble, and I am sure
entertaining as well. Let me know if I can help more on this issue,
and also let us know how it turns out :) I am sure we'd all love such
a collar for our own cats.

Regards,
sycophant-ga

Very interesting answer, thanks. The sugar cube camera you linked to
is very similar to the one I saw, minus casing & antenna. (The
transmitter must be contained in a very small area!). As for a battery
pack, well, the same stall that sells the camera also sells a huge
range of replacement mobile and dect 'phone batteries - sure I'll be
able to find one I could strip down for suitable cells. Good idea!
'Why didn't I think of that' =grin=

Glad to hear you think the transmissions will not pose a hazard; I'll
check the cam before I buy to check it's not operating in the
microwave range.

I did wonder if the magnet-thing would cause a problem. That's one for
experimentation I guess.

Wow, gan, you're brave.

My cats would *eat* me if I tried to put a collar on either of them,
much less one with a camera on it!  Let us know how it all works out!

--Missy

Hi Missy,

This little guy is very good about collars and stuff like that. In the
picture below you can see the automatic cat-flap operator (which came
supplied with the catflap and is just a magnet in a plastic case - I
wondered if I hadn't bought a dogflap by mistake) hanging from his
collar - If I remove that, and add a small square magnet to the bottom
of the camera, the whole camera/catflap operator assembly will still
be smaller than the catflap operator you can see in the picture!

http://www.beginnerprogrammer.com/googleanswers/louie.jpg

Now the other cat might well be a different story.. look out for next
question, 'where to get tetanus jab' ;-)