Photoresistor

[atwoz]

I have a project in mind. I will use some photoresistors attached to a tv in order to detect changes in the light output. These changes can happen as fast as 10 times per second, something like: dimlight, brightlight, dimlight, brightlight, dimlight..... 10 times.

I was wondering if the photoresistor would be able to change it's resistance that fast or if it has a slow reacion time.

What Picbasic command would be best for this situation? the Pot command perhaps?

Is there a simpler way to monitor the screens activity with external components? ( I'm only interested in a tiny area of the tv)

would some kind of photodiode work?

thanks!

[mackrackit]

A photo diode would work if the external resistance was set for the dim light being off. The more light the more they conduct so the sensitivity can be adjusted. Think of a regular transistor, light is the base.

Look at the count command if you are interested in finding the frequency of change.

[mackrackit]

Another idea. A small solar cell connected via ADC to measure voltage. Might be a speed problem though. But the dim/bright settings would be controlled in the code.

[dhouston]

Look at the Panasonic PNA4603H. There's a datasheet at Digikey.http://rocky.digikey.com/WebLib/Panasonic/Web%20data/PNA4603H.pdf

[Luciano]

Hi,

Here you can see the rise time and fall time of a LDR.
(@10 lux and @1000 lux).
http://docs-europe.electrocomponents.com/webdocs/001a/0900766b8001a9d6.pdf

NORPS-12 CdS Photocell:
http://docs-europe.electrocomponents.com/webdocs/0034/0900766b8003484c.pdf

(The above two links are from the RS Components Ltd web server).

* * *

Use a phototransistor.

Best regards,

Luciano

[atwoz]

THanks for the anwers guys, they were very helpful. I will start looking for an ideal phototransistor.