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Okay, we have to admit this right upfront: This project is Earl’s absolute favorite in this whole book. Sensitive Sam is a motorized cart. You stick black electrical tape on the floor to create a little path or track for Sam, and Sam uses his sensors to follow the tape around corners and in interesting loops you devise for hours of fun. He also has a little horn you can blow (to warn the cat that he’s coming). What’s not to love?

In this chapter, you discover how to give Sam the “eyes” he needs to sense where he’s going and also how to build a radio remote control device to tell him what you want him to do. Although you’ll find lots of little components and connections going on here, don’t be intimidated; after you get going, we think you’ll find it’s a pretty fun project. (Earl did!)

The Big Picture: Project Overview

You’re probably wondering what this Sam guy looks like and what he’s capable of. Glad you asked. Here’s the low down on Sam, who Has three wheels: This design makes the cart stable. If you use four wheels, you need to include a suspension mechanism to ensure that all wheels stay in contact with the floor at all times. We use one unpowered wheel in front and two independently powered wheels in back. This way, if the motor for one of the wheels in back is shut off, the cart turns in the direction of the motor that was shut off (left or right).

Sports two eyes: These eyes help Sam figure out where to go. Sam’s eyes — phototransistors pointed at the floor — sense infrared (IR) light that is sent out by IR LEDs and then reflected by the floor. By laying down a track of black electrical tape on the floor, you create an area that reflects less of the IR light. We set up the circuit so that when Sam’s eyes hover over reflective floor, the motors turn. If one eye is over the black tape or other nonreflective surface — for example, where a bend comes in the tape track — the motor connected to that eye shuts off, causing the cart to turn and follow the tape. When the eye is back over the reflective floor, the motor turns back on, and the cart goes in a straight line again.

Responds to a remote control: This remote uses radio waves to send its commands to Sensitive Sam. (This is the same technology that a key chain remote control device uses to open the doors on a car.) You can set the switches on the remote control to tell Sam to turn on/off, slow down or speed up, or honk the horn. When you flip a switch and press the transmit button, that effect kicks in.

Sensitive Sam is shown in Figure 13-1 in all his glory.

Here are the types of activities you’ll do in this project:

1. Put together the electronic circuit for the remote control transmitter and then fit the breadboard into a plastic box with switches.

2. Put together the electronic circuit that decodes the radio signal and controls the movement of Sam in response to his sensor eyes.

3. Mount the circuit onto a chassis along with DC motors, wheels, and a few switches.

In the end, you create a cart that follows a track all by itself and responds to your every command. It also has a cute little horn that you can toot.