Setting up a solar powered LED night light?
Newbies with circuits, want to make a solar powered night light for my room. (inc. photoresistor)
I agree that a relay is useless. Everything needs to be very low power (i.e. use MOSFETs). Capacitors might work if you use the new "ultracapacitors", or DLC's, which have huge capacitance and tiny leakage.
Since it's solar powered, you'll have a photocell. You can use this also as the light detector. When the photocell is producing current, charge your battery or ultracapacitor. When photocell voltage drops below some threshold, turn on the LED.
A simple way to go would be to use two or three photocells in series, and run through a diode to your battery/ultracapacitor. THen, run the battery/capacitor positive terminal to the source of a p-channel MOSFET, and run the drain to your LED (with a series resistor to control brightness). Control the gate of the MOSFET with the positive terminal of the photocells.
When the photocell voltage drops a few volts below the battery, the MOSFET will turn on, energizing the LED. When the photocell is .7V more than the battery voltage, the battery will charge.
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