Build a 555 based adjustable timer. The 555 timer IC is a great little device.
http://blog.makezine.com/archive/2009/12/make_electronics_and_the_555_man.html
It can be used in many different applications.

In this Instructable, we use the 555 timer to create a countdown timer. The timer starts with a shake and ends when the LED stops glowing. There's no fancy accelerometer, no Arduino, no coding, just a 555 chip, some miscellanous discrete components and a tilt ball switch. The timer can be adjusted from one to about ten minutes. This particular timer was intended to be used between sets during weight lifting sessions. That is why it is only a one minute timer.

Fail
The final design is really version 1.5. The first version was designed to flip to start and flip to reset.
See the photos. The tilt ball switch proved to be too sensitive for a flip design. The circuit was redesigned to trigger on a shake. Hence the birth of the Shake Timer!

Inspiration/Sources:
A big thanks to these sites for the circuit design.
Adjustable 10 Minute Timer Project
http://www.kpsec.freeuk.com/projects/timer.htm
Bowdens Hobby Circuits
http://www.bowdenshobbycircuits.info/page9.htm#555mono.gif
555 Tutorial
http://williamson-labs.com/555-circuits.htm

Tools:
Drill
Saw
File
Sandpaper
Pliers
Cutters
Hot Glue Gun
Soldering Iron
Exacto Knife
Medium Sandpaper

Parts:
Proto Board - Radio Shack P/N: 276-148
555 IC - Radio Shack P/N: 276-1718
100K Resistor (times two) - Radio Shack P/N: 271-1347
470 LED Resistor - Radio Shack P/N: 271-1317
1Meg Trimmer Pot - similar to DigiKey P/N: 3309P-105-ND
8 Pin DIP Socket - Radio Shack P/N: 276-1995
220uF Capacitor - Radio Shack P/N: 272-1029
0.1uF Capacitor - Radio Shack P/N: 272-1053
Green LED - Radio Shack P/N: 276-022
1N4001 Diode - Radio Shack P/N: 276-1101
9V Battery Clip - Radio Shack P/N: 270-324
9V Battery Holder - Radio Shack P/N: 270-326
9V Battery
Tilt Ball Switch - adafruit
Micro Power Switch - Electronics Goldmine P/N: G16674
Misc wires
2.5 inch diameter mailing tube - recycle bin
Adhesive backed printer paper
Clear adhesive backed shelf paper or clear laminate

 
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Step 1: Build the Circuit

Build the circuit according to the schematic. The schematic is very close to the component layout. When laying out the components make sure the board will fit on the inside of the mailing tube cap. Stuff the proto board and solder it up.

The photos show a modified version 1. A less ugly verion can be put to together when starting from scratch.

When done soldering everything, test the circuit. Temporarily attach the battery, power switch and LED. Shake it. The LED should light up for a period of time and then turn off. Adjust the length of time the LED stays on by adjusting the trimmer pot.
garagemonkeysan (author) says: Mar 12, 2013. 7:26 PM
Thanks for the comment. Yeah, the blinking is a good idea.
Sorry the parts were stuff I had around so I don't know the exact cost.
I'd guess you can duplicate this for around $10. Later! : )
danamark says: Mar 9, 2013. 9:23 AM
Hmm, might be good for a game board timer for a game like Dominate Species for analysis paralysis.

Wished it had a warning light blink or something to show that time was about to run out.

What is a rough estimate cost?
mased007 says: Mar 21, 2011. 6:13 AM
Awesome easy project. Good job.
unknownuser2007 in reply to mased007Mar 21, 2011. 5:43 PM
Thank you! : )
cammel8 says: Dec 17, 2009. 6:46 AM
This is awesome. In my honest opinion 555 tiners are so under rated and so under used on this sight.  I have done alot of projects with them but still have to upload them.

But this is definately cool.  Would work great as a timer for board games too. very well done congrats. 
garagemonkeysan (author) in reply to cammel8Dec 18, 2009. 2:35 PM
 Yes, 555 chips are great. I've used them in several projects. Thanks! : )
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