In this chapter, we use two plastic pumpkins and activate sound and light by using an infrared beam. When those trick-or-treaters come up to your doorway, won’t they be surprised?

Of course, if it’s February and plastic pumpkins are scarce, use these same techniques with some other plastic container shape to create talking dinosaurs, heart-shaped candy boxes, or whatever!

The Big Picture: Project Overview

You can see the finished pumpkin in Figure 9-1.

Here’s the big picture of this pumpkin project:

1. Put together two electronic circuits and fit them into plastic pumpkins with switches, a microphone, and a speaker.

2. Use a microphone to record a sound or message. We like, “Welcome to Sleepy Hollow. We hope you have a good time,” followed by a spooky laugh.

3. One pumpkin transmits an infrared beam to the other. When someone walks between the pumpkins, the recorded message is triggered, along with a flickering red light.

4. To reduce the chance of this IR noise interfering with your gadget, use an IR detector tuned to detect infrared that turns on and off at 38 kHz and ignores infrared not switched at that frequency. The transmitter circuit then sends out infrared that is switched on and off at 38 kHz, and the noise problem is solved.

One complication you’ll deal with along the way is lots of infrared noise floating around. IR is given off by heaters, people, pets, and pretty much any living creature or equipment that gives off heat.

Should you be lucky enough to have an oscilloscope perched on your workbench, you can see that a 38 kHz square wave looks something like the one shown in Figure 9-2. But don’t worry: You don’t have to have an oscilloscope to tune your IR transmitter. We tell you how to tune it in the upcoming section, “Trying It Out.”