Is there any way to make this circuit stay on during the day and off during the night? I want the opposite of a night light, a day light.
Electrical – Opposite of night light, on in day off at night
led
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In the second 'for' loop, i is immediately not <1, so the loop never executes.
for(int i =7; i<1; i--)
should say
for(int i =7; i>=0; i--)
You need the LED to be lit when the photoresistor is high resistance. So replace the photoresistor with a fixed resistor R3, to supply the base current to turn the transistor on.
Then you need the LED to turn off when the light shines, and the photoresistor is low resistance. So connect the photoresistor from base to ground.
Now, when its resistance is low enough, it will drain the current from R2 to ground, and hold the base voltage below 0.6V turning the transistor off.
Say, at 3kilohms we aim to get the base voltage down to 0.3V. Then 0.3V/3k = I = 0.1ma. Then R3 must drop the remaining voltage 4.7V at 0.1ma, so R3 should be 47k.
Now the transistor will start to turn on when the photocell resistance exceeds 6 kilohms. If that's still too bright, increase R2.
Answer in a schematic
Best Answer
When the photo cell reaches 0.6V = Vbe, the LED starts to dim towards off.
This is 4.4V/2.2k= 2 mA
To reverse the direction of control with 2mA , replace the cell with 0.6V /2mA = 300 Ohms assuming threshold was OK before. Increase for more sensitivity on a cloudy day.
Then replace 2.2 K with photo sensor.