I need some Ambient light sensing, what to use?

I need to add some light sensing to my clock so I can dim the max7221 when its dark. What should I use? LED + opamp into an analog in pin? Photoresistor?
Would a photodiode give me an analog information? like more than just "there is some light"

Photoresistor setup as a voltage divider to one of the analog pins, some messing with you should be able to get it to behave how you want.

I was going to do the same thing, but settled on simply dimming it during certain hours of the day. (Just in case you haven't considered that approach.)

hook one end of the photoresistor into VCC or the 3.3 line, and the other end into the analog pin?

Yea I'm dimming mine during certain hours but still needs tweaking.

Nope :slight_smile:

You have to hook it up as a voltage divider to an anlog in on the Arduino board. Like this:

http://webzone.k3.mah.se/projects/arduino-workshop/projects/arduino_meets_processing/instructions/ldr.html

Then use Analog Read to get a value representing the amount of light hitting the LDR, then use that number to dim the max7221