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       Introduction

Project status: CONCEPT - Stay up-to-date with the Mr. Lee CatCam Newsfeed RSS Feed


After the amazing response to the CatCam, I was asked by many people to work on a live camera for the collar. Some approaches have already been done by other people/cats (e.g. Smaka). The struggling stones for a mobile miniature wireless camera system are plenty. Two main constraints are: operation range and operation duration.


       Principle

The principle for a wireless pet camera would look like this:


A battery operated TV camera is mounted on a collar. A video sender puts the image stream on the air. A demodulator receives the RF signal and converts it back to a video signal. The video signal can be displayed on a TV.



Here you can see a proposal for the sender unit. It is operated by 2 rechargeable battery cells. A high efficiency DC/DC converter generates the required system voltage. The unit is conveniently charged over USB. A cheap CMOS camera feeds a FM modulator. The video signal is brought on the air by an antenna.


       General Considerations

In theory everything sounds easy. But in reality there are some issues, especially if the device should be carried by a cat:
  • operation range: The non-ideal cat is wandering away from the house/receiver
  • signal strength: The non-ideal cat is not only walking away from the receiver, it also crawls through grass, hides under bushes, ...
  • power consumption: TV cameras are energy hungry.
  • value: the non-ideal cat may loss the camera
This requires advantaged ideas for the whole system. Key questions are:

Video Transmission:
How can the operation range be expanded ? Can the transmission power be enlarged ? How can the receiver be tuned to receive low level signals ? What is the ideal frequency ?

Power Supply:
How can much energy be stored in the most compact size ? How do I reduce voltage conversion losses ? Can energy management enlarge the runtime ?


       Frequency considerations

The ideal frequency for no direct line of sight, trees, grass, many signal scatters, etc. is as simply as low as possible. This drives other constraints like antenna size (the lower the frequency the larger the antenna) and bandwidth (usually bandwidth is decreasing with frequency). On the other hand we have to check what is available on the market if we donít want to invent the whole system from ground up. Right now the trend for wireless transmission is going to high frequencies. There are 1.2GHz, 2.4GHz and 5.8GHz systems on the market. 1.2GHz systems are already disappearing. 433MHz is spoiled completely by countless wireless devices like door openers, wireless thermometers. 866MHz would be nice, but is not supported well by wireless component suppliers. So far we have to focus on 2.4GHz if we want to have a cheap system.

The 2.4GHz ISM Band is divided in 13 channels:
ChannelFrequency
12.412
22.417
32.422
42.427
52.432
62.437
72.442
82.447
92.452
102.457
112.462
122.467
132.472



       Sender Antenna considerations

Size and construction is defining usability and performance. The best antenna is a directional frequency matched one. But show me the cat what will always look in the direction of the receiver. Or the cat who wants to carry a 1 yard antenna.
A compromise is required between usability and performance. The 2.4GHz frequency allows small antennas. This frequency requires a circular emitting antenna because we probably need to receive scattered signals. The antenna location should be as high as possible.


       Receiver Antenna considerations

For the stationary receiver we can think about a more sophisticated antenna to gain more transmission range then a regular circular antenna is delivering.
Patch Antenna


A directional patch antenna is like a increase in transmission energy. It is a rectangular piece of metal above a metal ground plane. The ground plane acts like a reflector and amplifies the signal by positively overlaying the RF wave. A patch antenna must not point precisely to the sender. A rough adjustment is enough.
BI-Quad Antenna


The same is true for a Bi-Quad antenna which is a metal wire frame above a ground plane. But a Bi-Quad Antenna is more polarized. It has to be tested what kind of antenna is better for our purpose.


       Camera considerations

The TV camera delivers a continous analog signal stream which carries not only the image information but also sync signals.
There are differences regarding the image sensors. The cheap route is to use a CMOS sensor. This is almost like an array of photodiodes. Drawback: lower sensitivity, higher signal noise. More expensive but with higher quality and sensitivity are CCD image sensors. They are more like an array of capacitors charged by photons. A high performance during dusk and dawn are delivered by black and white CCD sensors. The simple reason for this is that one pixel has 3 to 4 times the area compared to a color CCD sensor and that there is no color filter.
The supply voltage and the current draw of the camera must not be neglected. The cheap CMOS camera is usually satisfied with a low voltage and requires not so much power.


       Battery considerations

-will be continued soon-


       Sender considerations

-will be continued soon-


You may want to check out the Order Page if you want to start development by yourself. I order larger quantities of parts for my purposes so you can benefit from much lower prices compared to the regular market prices.


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