Honestly, how many people have been in this scenario (leave a yes or no in the comments) : It is 2:30 in the morning and you wake up with a need to do something whatever that may be (bathroom, forgotten homework assignment, project due in 5 or 6 hours, etc.) it takes you 5-10 minutes to find the light switch (give or take...)
My mother likes a night light for the bathroom but she didn't want one that stayed on all night so I needed one that could detect a person. Many thoughts popped up into my head on what sensors to use. I could us esuch as the Linescan Imaging Sensor Daughterboard by Parallax but that was overkill and too expensive. A cheaper solution would be to use a few ir leds with ir phototransistor but still too complicated. I also thought of the Ping Sensor from Parallax but too hard to program with my beginner standards in C and, it used too much power. (I'm more of a Spin and Assembly language person.) I finally looked through my sensors box and found...(...drumroll please...) ...Parallax's Passive Infared Motion Sensor! It was fairly inespensive ($9.99), it could work in the dark, and, I have had experience in programming these!
Step 1: Get the Required Materials.
1 of everything except where noted.
PIR Motion Sensor from Parallax
LED ( Preferably Ultra Bright White. I bought mine along with other colors at Ebay from this seller: http://myworld.ebay.com/led.shop*2010/?_trksid=p4340.l2559
They will compile your own personal mix of colors if you want them to...they will charge more but it is a personalized order. I also found this order of only white LEDs but very cheap.
Many jumper wires
Optoisolator/ optocoupler/ relay
Resistor. Define the value yourself.