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Monday, April 22, 2013

Money Shredding Alarm Clock

A while back I fumbled into Acid Cow's idea for a Money Shredding Alarm Clock.

I figured turning the concept into reality shouldn't be too hard.

All I needed was a few main parts:

SparkFun's ClocKit
A USB Powered Paper Shredder
TIP120 Darlington Transistor
(I also used an Atmel AVR programmer I already had)

Surprisingly the ClocKit managed to use every single pin on the Atmega328 it runs on - leaving me without an obvious control pin for the shredder.

I noticed that two I/O pins were being used for the alarm buzzer - which seemed unnecessary. I reconnected one of the buzzer pins to ground - and the buzzer continued to work fine - freeing up the needed pin to connect the TIP120 to.

About 30 seconds worth of code changes - and my alarm clock was working!

I swapped in a larger 5v / 1 amp power supply after seeing a "reboot" when the shredder fired up (probably voltage sag). Seemed to address the issue.

Tip - check the voltage on wallwarts with a multimeter before connecting them to anything sensitive like a microcontroller. A cheap 5v wallwart might put out closer to 8v unloaded.

The source code is up on Github - but the changes are so minimal - you may just want to start off with Sparkfun's code.

Click here to see a live demo of this project I did on Fox Business news!


  1. Using two pins on a buzzer is often done to increase its apparent voltage. On the first cycle you apply Pin1:VCC, Pin2:GND. On the second cycle you invert that to Pin1:GND, Pin2:VCC. The buzzer will be louder than simply switching one pin on and off.

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  3. This is a really amazing invention! Shredding money will be a waste if you don’t get up after the alarm rings, but I guess that’s what would make you want get up! It’s a actually a good driving force to get up ASAP because you literally have to save your money! I am truly amused by this!

    Ruby Badcoe

  4. Congrats for making a device that makes the user a criminal. It's against the law to destroy US dollars (or any US currency).

    1. Your comments waste space.
      Youtube misses you.

  5. I can see buying this for someone, but not for myself! I love the idea but would hate to lose any money :)

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