Tony Nixon wrote:
> 
> Hi all,
> 
> This may be an upcoming PIC project depending on it's feasabillity.
> 
> I was wondering if a small BW video camera could be set up to monitor
> the position of a horizontally moving white vertical line against a dark
> background. I was hoping it may be a simple as using a comparator on the
> video signal to detect where the line is. Then I could use this signal
> to detect the current line position in relation to the frame width.
> 
> Any thoughts?
> 
> I've also finished a Parallax to PIC source code converter. This changes
> Parallax mnemonics to PIC mnemonics and leaves the labels and comments
> etc intact and will be available free on my web site - if and when the
> domain provider gets off thier backside and completes the transfer, (3
> weeks now) >:-[

What about use those Texas Instruments photo cells with 128 pixels?, you
could just locate the white line position on the pixels... another idea
is to use three photo resistors or photo cells, feed the analog signal
into a triangular comparison at analog comparators and voil‡, you would
have a single analog signal which amplitude would represent the position
of the white line. Some table representation:

Left    Center   Right    White-Line  ADC Out 
Cell    Cell     Cell     position    Value
-----   ------   ------  ----------  -------
100%     50%       0      Far left     0%
50%     100%      50%     Center       50%
0%       50%     100%     Far right    100%
25%     100%      75%     75% right    75%
75%     100%      25%     75% left     25%

As you can see, the Right Cell values represent directly the ADC value,
but it needs the triangulation to get that values.

and so on. A simple adc would tell you where the white line is, without
needing to use a video camara.