Re: image/sensor data routing and saving?

In article <YO->,
says...
> Lots of questions, I hope someone can guide me in the right direction!
>
> I'm looking for some help in designing a system that can take data from an
> image sensor and store it in some sort of MMC/flash memory. It will be
> part of a wearable device for monitoring diet/activity constantly during
> the day.
>
> We're looking into using an image sensor from OmniVision that has built-in
> JPEG compression (e.g. OV03640). We'd like the resolution to be as high as
> possible (2 or 3 Megapixels?) to make later off-line processing results
> more precise, but obviously lower resolutions would be easier to handle in
> terms of power and time, and might not require the compression. Our
> highest frame rate currently only has to be 1 fps (again, saving power and
> processing time), but we'd like the option of lower resolution video for
> future applications.

You will probably end up with smaller frame size, as the requirements for
memory and processing even saving time of larger image , will be a bigger
batery drain. Battery wieght is the biggest part of such a device and
often dictates, what everything else can do.

Remember that at 1fps, a 2 or 3 Megapixel imager (colour as part number
suggests), means even if compressed, means you are likely to have approx
1 MB to save every second.

> How is file formatting usually done with these sorts of devices? Are

It is not the imager just provides a stream of data.

> there dedicated chips for packing data into certain file formats, or do we

Not to my knowledge.

> need a rudimentary OS on a microcontroller? I'm familiar with the simpler

Yes

> family of Microchip PICs (8F and 16F), but there have to be others that are
> more geared towards applications such as this. We want the system to be
> somewhat expandable so that we can include extra sensor data (e.g.
> temperature sensors, accelerometers, ECG monitoring) in the next phase of
> the project. That increases complexity of the system tremendously, since
> we'll have to time stamp data somehow and really multi-task with the
> controller to synchronize the different types of data and get everything on
> the MMC in a timely fashion.

You need to look at low power microcontrollers, possibly also external
RAM to buffer data to be sent to storage device, as imagers tend to
produce a non-stoppable stream of data.

> Any and all suggestions, directions, and corrections are much
> appreciated!

Work out your max battery weight and size to maintain wearable.

Then work out how long the device has to be powered for and what
power density can be achieved.

From this power budget start working out what can be achieved
along with how much data is flying around at what update rates.

--
Paul Carpenter |
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