SMD led strip as light sensor

Is it possible to use SMD led strip as a strip of led light sensors?

As more and more of the leds in the strip get covered by e.g. a towel, the voltage drops. This way it would be possible to compute the number of leds in the strip that are covered.

Is it possible to use SMD led strip as a strip of led light sensors?

No.

As more and more of the leds in the strip get covered by e.g. a towel, the voltage drops.

I don't believe you. How are you measuring the voltage and where?

Grumpy mike

Try it.

I have a short strip, around 10 LEDs, and just tried measuring the voltage on my Fluke DMM and all 8 LEDs gave 0.04v in bright light.

Covering some LEDs, did appear to reduce the voltage.

But as you can see, it's only around 5mV per led.

And it's also dependant on level of light.

Hi,

http://playground.arduino.cc/Learning/LEDSensor

Tom...... :)

Tom I see your :-

TomGeorge: http://playground.arduino.cc/Learning/LEDSensor

and raise you my http://www.thebox.myzen.co.uk/Workshop/LED_Sensing.html I wrote this about 5 years ago.

I still say no.

Thanks for your responses

Grumpy_Mike: Could you very briefly describe why it doesn't work? In my case each led in the strip will be either completely covered (zero light) or completely uncovered (max light).

Most of the LED strips I have see that expose the LEDs in the way you need are designed to run off 12V and have built in resistors. Therefore if you were to use it like you said then it would only be in multiples of three that coverage would activate a totally separate LED circuit. Covering say two out of three LEDs would not necessarily drop the voltage by two thirds of an LED contribution.

Mike wasn't your conclusion that this was not totally reliable?

I guess for some art installations that just want to give some form of input to people, it may be usable, as long as the limitations are known.

BTW. Did you do any temperature testing, I have a suspicion that perhaps the output voltage may also be temperature dependant

No never did any temprature testing.
My page was about using the LEDs as leaky capacitors, the more light the more they leak. You can also use them the other way round as photo voltaic generators. Anotherr problem with just wiring a bunch in parallel like this is that then then tend to charge each other. The whole thing is a mess and I don’t think it will work. Hence my original answer.

Thanks Mike

I did a bit more testing on my strip of white LED's (there are actually 12 LEDS in my strip, I didn't count them last time), and the amount of voltage produced as photovoltaic looks to be so small that its right down in there with the mains noise.

I guess you could integrate out the mains noise,but I agree it looks like its more trouble that its worth.