how to make a shadow sensor

Forum 2005-2010 (read only) Hardware Interfacing
1

I have photosensor, and been able to breadboard and using some tutorials ,
I make the arduino light the Led when Light, but How can I make it the other way, the dimm up the Led when shadow is over the photosensor
any help is very welcome

2

I assume your photosensor is an LDR (Light Dependent Resistor) and that it is hooked up as a voltage divider to an anlagog input.

You read the amount of light with analogRead() which in turn returns a number in the 0 - 1023 range.

You set a threshold in that range that you decide is "shadow" and then start to make the LED shine brigther with analogWrite().

3

And if you then put the LED next to the light sensor you will have made a relaxation oscillator.

If you don't see the LED flash then introduce a small delay in the loop();

4

thank you all.
I have cadmium sulfide photoshell n LDR (Light Dependent Resistor)
the sketch for the electronics and ardruino is from Massimo Banzi,
works great, when I put my finger on the LDR the led Fades
how ever I want the other way, when shadow or light is block from LDR I want the led to go On.
my current info is like this.

tannk you in advance.

goes like this

for the LDR connection goes like this

ground---Resistor 10k--connection to pin 0 analog----LDR-- --5v

for LED goes like this

groudn---LED ----pwm 9
running this

#define LED 9;
int val = 0;
void setup () {
pinMode(LED, OUTPUT);
}
void loop () {
val = analogRead(0);
analogWrite(LED, val/4);
delay(10);
}

5

If the code you posted works the way you want, one simple solution would be to replace

analogWrite(LED, val/4);

with

analogWrite(LED, 255-(val/4));

val/4 will always be a value between 0-255, so doing a 255 - (val/4) will result in an "inverted" value. 0 becomes 255, 255 becomes 0, 50 becomes 205, etc.

Good luck in your Arduino endeavours! :smiley: