Question about LED matrix and a light pen.

T&E Engineer

I would like to come up with another use for my 7 x (5 * 4 = 20) LED matrix.

I was thinking of designing a light pen to draw over the LEDs for·something such as a tic tac toe or drawing screen. However, I believe light pen's (photo transistors - comes with the BOE-BOT) require·a·LED display to be turned on for it to sense so this·idea may not work. I think their primary use is with CRT screens. I saw Beau's design project for the SX video module using an SX18 that made me believe this idea won't work unless the display is turned on first.

Thoughts...comments.

Thanks,

Timothy Gilmore

Beau Schwabe

Timothy,

If you can come up with a scheme in software to "flicker" your LED 's in a scan pattern, say when a "trigger" is pressed
on the light pen it might work. Ideally the scan pattern "flicker" would be fast enough that you could not see it, but the
photo detector ( light pen) could.


Additional thought!!!

Since you have FULL control of the scan, you can use it to your advantage to get a MUCH quicker pen position.
A simple X Y scan should do it.....

For example turn on ALL of the LED's in the first column and then the second, the third, etc. until you are done.
Do the same thing for your rows. By making note of which row and column the phototransistor responded, you
can easily pinpoint the correct position without needing to scan through each LED one by one.

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Beau Schwabe

IC Layout Engineer
Parallax, Inc.

Post Edited (Beau Schwabe (Parallax)) : 12/15/2005 3:42:34 AM GMT

Paul Baker

My thoughts exactly Beau, though you could cut the scan short once the detection occurs eliminating the need to flicker the remaining rows or columns, so if the pen is over LED(1,3) only the first column would be flickered and the 1st-3rd rows.

BTW very cool idea Timothy, its neat to see your incremental improvements to your project.

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
·1+1=10

Post Edited (Paul Baker) : 12/15/2005 4:33:01 PM GMT

T&E Engineer

Thanks for the great sugestions and complement Paul and Beau.

I will look into this when I get some time soon.

Thanks again!

Timothy Gilmore