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My first instructable! This is something I originally made for a friend who's still using it. It works very nicely at adding a nice ambient light to a dark room. I made this instructable because I decided to make one to stick in the bathroom at my house.
It's a small easy to build circuit that will, as the title says, turn an LED on when it's dark and turn it off when there's light, making it a perfect night light. It runs on a 12v wall adapter, so you won't need to worry about replacing a battery.
It's a small easy to build circuit that will, as the title says, turn an LED on when it's dark and turn it off when there's light, making it a perfect night light. It runs on a 12v wall adapter, so you won't need to worry about replacing a battery.
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Signing UpStep 1What you need
So here's what you need for this project:
[Soldering iron, of course... and solder]
- 100k Resistor
- 1K Resistor
- NPN Switching transistor (2N4401)
- Photo Cell
- 3v LED
- 12v wall adapter (look around... I'm sure you've got one somewhere!)
Optional:
- Small circuit board (makes it easier!)
- SPDT Switch (for complete disconnection)
[Soldering iron, of course... and solder]
- 100k Resistor
- 1K Resistor
- NPN Switching transistor (2N4401)
- Photo Cell
- 3v LED
- 12v wall adapter (look around... I'm sure you've got one somewhere!)
Optional:
- Small circuit board (makes it easier!)
- SPDT Switch (for complete disconnection)
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Issue of 3 leds:
The reason why you are not satisfied with results using 3 leds is because:
a) you should have trippled the resistor values - 3 1k resistors in series and three 100k in series or
b) you should have used "H bridge" to increase the sensitivity.
Alternative voltages:
a) AC Mains & EL wire:
Instead of using a 12v adaptor, you can use a diode bridge with capacitor (see my Instructables).
EL wire can be used effectively with my diode bridge and capacitor power circuit along with your front end sensor circuit.
Or
You can also use an old plone charger, negative of the main circuit touches the outer side of the charging pin, while the positive of the circuit goes inside the pin.
b) DC voltage:
you can also use 9V, 6v or other battery pack variations without changing the main parts of the circuit!
Hope it helps...
reg
ketan
What am I doing wrong here? Any way to increase the sensitivity of the photocell, so that it can turn off the leds with small amounts of light (clear sky during the day)?
Photocell specs:
size: 5.00x4.00mm
resistance on light: 5k-20k ohm
resistance in darkness: 1M ohm
max voltage: 150V (DC)
Peak sensitivity: 560nm
Thanks,
Jeff
thank you!
marC:)
Do you know much much money it will cost me in electricity each month? Not exact, but is it expensive to have on like 7-8 hours a day? Does it use a lot of electricity? Thanks!
Thanks for the instructable!
You can add the light resister to the inverter to make this work.
I want a strip of blue EL wire going around the top of my room that turns on when the lights are off.
I found this one that runs at 12v: http://www.ellumiglow.com/Electric-Optics-EL-Wire-Inverter-p/eo25ei.htm
So now my question is, could I simply remove the 1K resistor all together so that a full 12v from the wall outlet is flowing through then solder the inverter leads into the circuit instead of the LED? Or does their need to be a resistor there still?
?