make projects

Homemade Alarm Made From Two Audio Jacks

Homemade Alarm Made From Two Audio Jacks

A homemade alarm system made from two “normally closed” audio jacks is the focus of our most recent Weekend Project, the Alarm Bag. The alarm system, built into an enclosure (above), can be installed into any bag (in our project, a messenger bag is used) or even modified to act as a door or window alarm. The 2-jack design means the alarm will activate whenever the second audio jack (the trigger) is removed.

How-To: Variable DC Power Supply

How-To: Variable DC Power Supply

Hobbyist electronics projects need robust, reliable power supplies for prototyping and testing. I learned how to build this circuit from the Basic Analog Circuits class at ITP taught by Eric Rosenthal, but took it several steps further in building a solid enclosure and integrating a voltage meter. Now it lives on my desk, ready to power most small projects I’m working on, ranging from 0 – 24 volts and up to two amps. You can learn all about how to make one yourself using this Make: Projects tutorial.