Make Electronics

Experiment 15: Intrusion Alarm Revisited

144 Chapter 3

attach them, and don’t allow the iron to remain in contact with anything for

more than 10 seconds. It will quickly melt insulation, and may even damage

the internal parts of the switches.

In projects that are more complex than this one, it would be good practice

to link the top panel with the circuit board more neatly. Multicolored ribbon

cable is ideal for this purpose, with plug-and-socket connectors that attach to

the board. For this introductory project, I didn’t bother. The wires just straggle

around, as shown in Figure 3-111.

To/From

Sensor

Switches

In Closing

12V DC

S1

S2

To Circuit
Board

Power to

Circuit

Board

Normally Closed

Normally Open

(push to test)

Off

On

680 ohms

Figure 3-110. The components can be wired together like this to
replicate the circuit shown in The red and green circles are LEDs.
Small, solid black circles indicate wire-to-wire solder joints.

Figure 3-111. The circuit board has been installed in the

base of the project box, and the power input jack has been

screwed into the end of the box. Twisted wire-pairs have

been connected on a point-to-point basis, without much

concern over neatness, as this is a relatively small project.

The white insulation at the top-right corner of the front

panel is heat-shrink tube that encloses a solder joint and the

680 Ω load resistor. Soldering wires to the pushbutton switch

requires care and precision, as the contacts are closely

spaced.