@Phil1977, your setup is looking very promising. It will be interesting to know what kind of bit-density you can squeeze onto that wheel.
I'm now wondering about how the "charging" light should best be applied. I think that a high intensity light for a short amount of time, is greatly preferable to a lower intensity light for a longer time. But there is a latency to the charging process! When the LED turns on it takes a while for the phosphor to respond and this is actually visible - the LED goes to full brightness instantly, but the glow from the phosphor takes a little time to increase. And then the same happens in reverse, when the LED goes off, the phosphor's natural decay is very obvious.
Following is a graph of my light sensor's output frequency (y-axis) over time (seconds, x-axis). The phosphor was charged up for 1 second from a 30 mA 395 nm LED basically at point blank, and aimed at the same side of the phosphor that faces the sensor...
![Optical Delay Dynamic RAM (ODDRAM!)](https://www.eevblog.com/forum/index.php?action=dlattach;topic=435781.0;attach=2344693;image)
This tells me a few things:
- My LED sucks. So I've ordered some hopefully more capable COB LEDs (3 Watts allegedly)
- The TSL235R is an awesome sensor. Apart from it being unobtainable these days.
- I'm going to have to complete a full ring revolution in something like 15 seconds. Including sensing and refreshing the bits.
- The half-life isn't constant! It increases as it gets dimmer. Hmm.