Page 62 - Hacking Roomba

Chapter 3 — Building a Roomba Serial Interface Tether 43

Because these sync cables are becoming harder to find as fewer people need them and because
this isn’t as universal as a true RS-232 solution, it’s not the focus of this chapter. However,
instructions are presented in the “Building a USB Serial Tether from a Phone Sync Cable”
sidebar in Chapter 15 if you want to go down that route.

Safety
This project and many others in this book entail building electronic circuits. Doing so exposes
you to heat hot enough to burn your skin, electricity that may zap you or your projects, and
lead that can poison you. It’s easy to be safe, but if you feel unsure about what you’re doing,
stop and read Appendix A. It briefly covers how to solder and how to properly ground yourself.

Parts and Tools

Building electronic circuits is a lot like baking in the kitchen. The recipe is the circuit schematic
and the ingredients are the various electrical components and parts used. Like the cooking
utensils needed in a kitchen, you’ll need a small collection of tools to make your circuit cre-
ation. The following list of tools will be used not just for this project, but for all projects in this
book, and you can use them to build almost any electrical projects you’ll find on the Internet.
If you’re new to hacking, the following list may seem a bit overwhelming. But the component
parts are simple (and cheap) and easy to get from a variety of suppliers. In the Introduction, I
mention several good part suppliers. Jameco (http://jameco.com/) part numbers are used
below simply because they carry both the parts and tools needed and have a friendly web site to
order from.
The next section will show you how the entire project can be broken down into three easily
digestible chunks. These chunks, or sub-circuits, will show up again in subsequent projects in
this book and other circuits that you can discover on the Internet. No circuit is entirely new
and unknown: It’s composed of sub-circuits you will have seen before once you’ve built a few.
Part of the fun of learning new circuits is to see how each one incorporates the bits and pieces
you already know. And like baking, you’ll find that variations to make a circuit your own are
not only possible but recommended.
You will need the following parts for this project:
Mini-DIN 8-pin cable, Jameco part number 10604
10 ft long serial cable with DB-9 female connector, Jameco part number 155521
General-purpose circuit board, Radio Shack part number 276-150

78L05 +5 VDC voltage regulator IC, Jameco part number 51182
MAX232 RS-232C transceiver IC, Jameco part number 24811
220 ohm resistor (red-red-brown color code), Jameco part number 107941
Six 1µF polarized electrolytic capacitors, Jameco part number 94160PS