LEDs as sensors!

This project uses very simple off-the-shelf high-brightness red LEDs.

The theory is that each and every LED (even the standard ones) act as capacitors when it's connected backwards, and the speed at which it discharges depends by the light it "sees".
Therefore, timing the discharge one can calculate how much light was there in the first place. A quicker way is to simply calculate the voltage drop provided by the LED when it's disconnected, which is what I am doing.

The two bright LEDs are alternating between forward bias (emitting), reverse bias (charging) and high impedance (discharging).
The ADC is triggered shortly after putting them into hi-Z mode, and uses a 1.5 V reference generated by an LM317.

MCU: ATmega8 running at 8 MHz internal oscillator); binary size: 534 bytes.

Category:

Science & Technology

Tags:

• electronics
• atmel
• avr
• atmega8
• lm317
• leds
• photovoltaic
• capacitors
• touch
• control

[66Ralphy99]

Thanks for that - wanna make a touch remote controller for Winamp, for when I am in the shower (will be sealed in a box, with windows for the leds to make it water resistant). Gonna use a picaxe, then hack a cheap usb numeric keypad (unsolder keys & replace dem with relays) to give an input for next or last track or volume up or down. Coool!

[100roberthenry]

will this be affected by daylight...and darkness?...

[100roberthenry]

hi im looking to just fade 1 led up and down by this type of sensor...any ideas..i want to be able to fade a led up and down with my foot?... :)

[CARLHALEY1964]

can you do the same with Flexi Force Sensors

[kiriakoskakos]

Type PRIZE before youtube and hit enter

[GustavoFire]

00:54 OVNIS!

[herecomesurman]

can you please give us the schematic diagram of this project and it's components? thank you in advance!

[eduardo17cova]

my friend could you tell me how to do this proyect please

[msplace08]

very nice, good job!

[extremisto47]

I have few Soviet transistrors in metal. If remove a part of its body they became a fototransistors. Sensitivity depends of its amplification characteristics.