This is an embedded solution using C++, im reading the changes of brightness from a cellphone screen, from very bright (white) to dark (black). 

Using JavaScript and a very [simple script](http://jsfiddle.net/8QSxy/) im changing the background of a webpage from white to black on 100 milliseconds intervals and reading the result on my brightness sensor, as expected the browser is not very precise on timing, some times it does 100ms sometimes less and sometimes more with a huge deviation at times.

```
    var syncinterval = setInterval(function(){
        bytes = "010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101010101";

        bit = bytes[i];
        output_bit(bit);

        i += 1;
        if(i > bytes.length) {
            clearInterval(syncinterval);

            i = 0;
            for (i=0; i < input.length; i++) {
                tbits = input[i].charCodeAt(0).toString(2);
                while (tbits.length < 8) tbits = '0' + tbits;
                bytes += tbits;
            }
            console.log(bytes);

        }
    }, sync_speed);

```

My initial idea, before knowing how the timing was on the browser was to use asynchronous serial communication, with some know "word" to sync the stream of data as RS232 does with his start bit, but on RS232 the clocks are very precise.

![enter image description here](https://i.stack.imgur.com/WGGx7.gif)

I could use a second sensor to read a different part of the screen as a clock, in this case even if the monitor or the browser "decides" to go faster or slower my system will only read when there is a clock signal ([this is a similar application](http://hackaday.com/2011/07/28/microcontroller-communications-using-flashing-lights/) were they swipe the sensors instead of making the screen flicks as i need), but this require a more complex hardware system, i would like not to complicate things before searching for a software solution.

I don't need high speeds, the data im trying to send is just about 8 Bytes as much.