first what youll notice my grammer isnt the best :)
ok what youll need: 1 transister/mosfet that can handle the current for the water gun motor, this is the one i used - http://www.sparkfun.com/products/10213 - then a diode, i used this one - http://www.sparkfun.com/products/8589 - then a 10k ohm resistor, then a PIR, i didnt use this one but it should work - http://www.sparkfun.com/products/8630 - then a bread board, i used this one - http://www.sparkfun.com/products/7916 - then some jumpers these are what i used - http://www.sparkfun.com/products/124 - then an arduino, i used a uno - and a water gun, which was for me, a pretty hard thing to find around the house, but i got one from a pesticede battery operated sprayer (it had never been used). and i made the sprayer tip using some tubing, a .22 air gun pellet and a tack ( im pretty creative:). last a battery and battery holder that will work for your sprayer motor. oh and also keep in mind this instructable was done by me, a 14 year old who just got into elctonics in the last few months, plus this is my first instructable :).
Step 1: The Code
first, upload the code. go to the bottom of this page - http://www.ladyada.net/learn/sensors/pir.html - copy and then paste it in the arduino ide, then change the LED pin to digital pin 3, then save the code in the ide, then upload the code to your arduino.
Step 2: Wiring Up the PIR
follow this wiring diagram for the PIR. yellow jumper is out or signal, black is ground, and red is positive
Step 3: The Circuit
now build this circuit on a bread board, but know that you wont get it to work the first time. and its very picky on how you put the jumpers, especially around the mosfet/transistor.
Step 4: The Box
now, i built a box from some 1/4 luan plywood and some VERY heavy duty super glue called "2p-10" made by fast cap. but im not going to tell you exactly how to built it because it depends on how you want to rig it all up and how big your water tank is.
Step 5: The End
now youre done!!!! and i'll add that you can also hook it up to a automatic airsoft gun's motor and then in instead of a water gun youll have a full-auto airsoft turret!!! so untill next time have fun and comments are greatly appreciated