How To: Not Stumble in the Dark
By Jakob Griffith on May 2nd, 2009 at 6:41PM
Most people have an overhead ceiling fan that also has lights. I find mine rather convenient as if I want some light, I reach up and pull the knob. If I want some more air circulation, I reach up and pull the other knob. Simple when your room is lit, but what about in the dark? Say after waking up from being too hot, you reach up and pull the knob only to find you grabbed the light instead of the fan and are now blinded!
In this guide, I’ll show you a quick and dirty circuit to make sure you never pull the wrong knob again!
The basic idea is to be able to see which knob is which in the dark. I first thought of perhaps glow in the dark paint, but the glow fades out after just 30 minutes. The plus is that it’s simple and works right off the bat. I figured I would be a bit more geeky and wire up an LED, but here is the cool part, making it only come on when it’s dark!
The circuit is simple enough, you’ll need an LED of any color, a resistor of about 10kohm, a photoresistor, a transistor, and a battery of about 1,500 or more mAh 3 to 9 volt. All these you can easily find in old broken electronic devices and only take a second to de-solder. I wouldn’t even bother going to an electronic shop.
Wire them up according to the below photo (Do note, your transistor might have the legs in a different order, read up on PNP and NPN and EBC legs first!)
And you’re done! Here it is with lights on and off:
To find out how long your LED will last, take your battery’s mAh and divide it by your LED’s draw. 1,500 divided by 20 will last you 75 hours, theoretically.
If you have any questions or want some additional help, please comment or contact me personally.
