LED matrix input device, how do they do it?

Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.
Jump to Latest
neutron7

neutron7

Member
Joined 2003
diyti.com
http://cs.nyu.edu/~jhan/ledtouch/index.html

it shows an LED matrix being used as an input device.
i want to make a USB input device using some of these.I have many of them from some LED signs that were thrown out because the cpu boards were toast.

i cant figure out what is actually happening, they say the LED also acts as a light dependant diode, but once the LED is off to measure, where does the light come from to measure?
 

Attachments

  • ledmatrix 003.jpg
    ledmatrix 003.jpg
    82.8 KB · Views: 123
SY

SY

Ex-Moderator
Joined 2002
SYclotron.com
The on-off time of LEDs is quite fast. If you run them at a lower duty cycle, you can use the "off" time to photodetect. I haven't read the Mims paper, but ambient light might work. Even better (I think) would be to scan, i.e., turn the LEDs off one at a time and use the remaining light of the others as illumination.
 
I_Forgot

I_Forgot

Member
Joined 2005
The diodes can operate as emitters and detectors simultaneously. There will be small fluctuations in the voltage across the LED if supplied with a constant current, depending on the amount of light hitting the LED. The light may be from another source, or just light from the LED reflected back to the LED.

Several months ago I saw an article where someone used lit LEDs as an input device to a uC. I think it may have been in Circuit Cellar.

I_F
 
Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.
Top Bottom