Photocell programming

Projects Programming
1

Hello, I am using a photocell to open my blinds automatically at dusk.
I currently use a < 70 reading to trigger the blind motors (please note....the motors aren't really blind :slight_smile:
I would like to trigger the motors only at dawn and not at dusk.
How would I program that?
I am thinking a statement that says if the readings are increasing (going from dark to light) then trigger.
Here is a small portion of my code (flag is the state of the blinds, 0 = closed, 1 = open

flag = EEPROM.read(100);
if (photocellReading < 70 && flag == 0)

OPEN();

Thanks for anyone's help

2

You could study the Arduino State Change example to learn how to detect dawn, rather than dusk (rising intensity, rather than falling). Basically, you compare readings taken a few minutes apart.

3

You may have to find a way to block other rising signals, like passing car headlights, street lights turning on, etc...

4

Thanks Jremington, hopefully that will get me on the right track.

5

Or add a real time clock , temperature might another indicator ?

6

You will definitely need some hysteresis, and perhaps some time averaging to avoid false triggering
from shadows, lights going past, etc.