A beloved coworker is returning from Canada soon and in his honor I have created the car horn prank box. Basically, when the red button is pressed, and an LED blinks indicating that there is thirty seconds in which to hide the box somewhere dark. Once the thirty seconds expire, the next time that the box sense light, the car horn honks very loudly. Some fun places to hide the car horn is includes drawers, underneath jackets, in closets, buried in a backpack, or simple left in a room in which the lights have been turned off. The amount of potential mischief that this device can produce makes it a perfect welcome back gift.

Step 1: Materials

You will need:

(x1) Car horn
(x1) Enercell 12V/5Ah Sealed Lead-Acid battery (Radioshack #23-945)
(x1) Arduino Uno (Radioshack #276-128)
(x1) LED holder w/LED (Radioshack #276-068)
(x1) LED holder (Radioshack #276-080)
(x1) 7805 voltage regulator (Radioshack #276-1770)
(x1) TIP31 NPN transistor (Radioshack #276-2017)
(x2) 10K ohm resistor (Radioshack #271-1335)
(x1) 1K ohm resistor (Radioshack #271-1321)
(x1) 220 ohm resistor (Radioshack #271-1313)
(x1) 10uF capacitor (Radioshack #272-1025)
(x1) 1uF capacitor (Radioshack #55047773)
(x1) 1N4004 diode (Radioshack #276-1103)
(x1) Small photocell (Radioshack #276-1657)
(x1) Red pushbutton switch (Radioshack #275-646)
(x1) Aluminum heatsink (Radioshack #276-1368)
(x1) Thermal compound(Radioshack #28-1098)
(x1) 12V automotive relay (Radioshack #275-001)
(x1) Dual PC Board (Radioshack #276-159)
(x2) Pack red and blue quick connects (Radioshack #64-3088)
<p>For the voltage regulator: I'm not sure I can reconcile the photos with the wiring diagram. Specifically, the photos show (and the instructions say) to solder a red wire to the voltage input pin of the 7805, then nut the other end of that wire together with the three red wires with the quick connects. As far as I can tell, the three quick connects go to the battery positive terminal, and the 86 and 30 terminals of the relay. So where does the 10uF capacitor come in? The diagram seems to show it between the ground pin on the 7805 and the red wires that go to the relay... but those wires were directly nutted to the 12V + from the battery (and the voltage in pin on the 7805), right? Can anyone clarify?</p>
<p>must be smaller :D</p>
<p>Where is the template for the L-assembly?</p>
Very nice work! I want to see the result!
Do not do this to me!!! :-)
For how long does the horn honk? and how do you stop it from honking, if it does not stop quickly, on it's own??
About 2 seconds is the sweet spot. The horn takes a brief moment to engage.
I had a neat idea some time ago: <br>Put a battery, a horn, a button and a relay in a box, and wire it so that when the button is pressed the relay activates and feeds the horn and its own coil, so that when the button is released the horn will keep on going as long as the battery lives or someone breaks it open and disconnects the wires. <br>Just put a huge label on it saying &quot;DO NOT PRESS!&quot;, place the box in a frequented area and see who is not able to resist temptation!
This sort would be best done with a klaxon horn.
Anything loud and battery powered does the trick!
VERY WELL PRESENTED! This is by far one of the very best Instructables I've ever read! Instructions are very clear, concise, and lack the usual 'tech speak' or confusing 'slang' often associated with this site. Congratulations! I'm voting for you!
Your ears and possibly your nerves may thank you if you connect a test light at the horn connection during your testing and debugging phase. Then once you feel you have everything operational, remove the test light and connect the horn. Of course if you enjoy scaring yourself, forget what I mentioned, and carry on!
if you enjoy scaring yourself, lol
I believe if you want that UL certification for use on Canadians, you have to include a TASER circuit for when they grab the box and realize it is not their Christmas gift.

About This Instructable




Bio: My name is Randy and I founded the Instructables Design Studio. I'm also the author of the books 'Simple Bots,' and '62 Projects to ... More »
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