Experiment 15: Building an Intrusion Alarm

A couple of years ago I started working with electronics as a hobby. The reason was that it seemed cool to create electronics gadgets and learn about electronics in the process. I had limited training in electronics so I decided to start with simple electronics kits. These kits contain a PCB, electronic components and a simple step by step instruction. So I built a FM radio, an amplifier and some simple LED gadgets but apart from enhancing my soldering skills I didn't learn much about electronics. Then at www.makezine.com I came across the Make:Electronics book by Charles Platt. The book from 2009 but it looked very hands-on and I ordered it. By now I have almost finished the first three chapter and I arrived at experiment 15 which proved to be the most challenging so far.

In experiment 15 I have to build a alarm circuit. After some setbacks I have a working circuit on breadboard.

Two breadboards with on top the magnetic sensor, the breadboard with the noisemaking circuit and the loudspeaker. At the bottom the relay circuit that triggers the noismaking circuit.

A closer look at the relay circuit