The free book · second edition
Build a Car With Your Kid
A no-soldering Arduino robot car you drive from a phone.
A build book for a parent and a child of 12 or older, written for the parent who has never wired anything. Every step says who does it: the kid, the parent, or both. Every stage ends with a test, so a mistake never travels further than one step.
A 261-page colour PDF, or the EPUB. No email, no signup.
- Free
- a colour PDF and an EPUB, no signup
- Ages 12+
- with an adult at the table
- No soldering
- screw terminals and push-on wires
- Android or iPhone
- HC-06 for Android, HM-10 for both
Inside the book
Five parts, from the parts list to your own code
Part 1 is the build. The other four are for after the first drive: why it works, how to find a fault, how to change the program, and how to run it with a group.
- 1Build it together · Chapters 1–13What to buy, and how to help without taking over. Then four stages, each with its own test: the board, the chassis and motors, the motor driver and power, the Bluetooth module, and the first drive. It ends with what to do if it doesn’t move.
- 2Why it works · Chapters 14–20Volts, amps and a shared ground, the board, the motor driver and its H-bridge, how speed is really a fast switch, motors and skid steering, batteries and brown-outs, and how a letter from the phone reaches the car and back.
- 3Find the fault · Chapters 21–25A method for finding faults by halving the problem, worked examples, the Serial Monitor used as a probe, and ten broken cars to diagnose.
- 4Program the car · Chapters 26–32Read the sketch line by line, then the letter commands, the motion code, the speed ladder and the sounds. Find a bug that sat in the car’s code since 2016, then change the car safely to make it yours.
- 5For parents, clubs and teachers · Chapters 33–36What this build does and doesn’t teach, how to run it with six to twelve children, a one-week check, and where to go next.
Pick your module
Android, iPhone, or both
HM-10
Drives from an iPhone (in the free Bluefy browser) and from Android (in Chrome), using a web page: the Troniction remote. If anyone in your house has an iPhone, buy this one.
Checked on a computer and against the datasheet; not yet built into a car.
HC-06
Android only: an iPhone cannot connect to it at all. You drive it from a free Android app, Serial Bluetooth Terminal. It is the module the original car used.
Drove the original car for years; its new wiring is checked on a computer.
Everything else in the car is the same whichever you choose: the same wiring, the same program, the same tests. Where the two differ, the book shows them side by side.
Said plainly
How this book was tested
Built and driven
The reference car, first built in 2021 and rewired in August 2026: the motor wiring and speed control, the power wiring, no soldering anywhere, an HC-06 driven from an Android phone, and the sketch's letters, speeds, horn and tunes.
Checked on a computer
New in this edition, compiled and tested against the datasheets but not yet in the reference car: the module on pins 2 and 3, the HM-10 and its remote, and what the new sketch adds.
Not tested yet
How long it takes, ages 9 to 11, and running it with a group. The book says so where it matters, and nothing untested is written as a step.
With the book
The pages its QR codes open
- The car remote →
For the HM-10: drive from Chrome on Android or Bluefy on an iPhone. Chapters 10 and 11.
- If it doesn’t move →
Run the stage tests in order; the first that fails names the box. Chapter 12.
- Ten broken cars →
Symptoms to diagnose, with hints and answers. Chapter 25.
- The bench pack →
Part 1’s step cards, test boxes and checklists, to print in black and white.
Questions
Straight answers
- Is it really free?
- Yes. Download the PDF or the EPUB: no email, no signup, nothing held back for a paid version.
- How old does my kid need to be?
- 12 or older, with an adult at the table. The child builds; the adult reads each step aloud, checks it against the picture, handles the battery cells and installs the software. Younger children have not been tested with this edition.
- What does it cost to build?
- About $115 of parts at US prices (checked October 2026), bought one by one. Chapter 1 says so before you buy anything, and Chapter 4 walks through every part.
- Does it work with an iPhone?
- With the HM-10 module, yes: you drive it from a web page in the free Bluefy browser. The HC-06 works only with Android phones. The book covers both, side by side.
- Do I need a computer?
- Yes: a Windows or Mac laptop you are allowed to install software on. A Chromebook, a tablet or a locked school or work laptop will not do.
- How long does it take?
- I have not timed a family building from this edition yet, so the book does not promise a time. It is built in four stages, each ending with a test, and every session can stop after a test that passed.
Corrections and updates
Which version you hold, and what changed
The version number is on the copyright page. When I correct or extend the book, the change is listed here with its date.
- 2026-10-01Second edition (version 2.0.0) replaced the first.Five parts instead of one short guide, both Bluetooth modules side by side, the module moved to pins 2 and 3 so the Serial Monitor works while the car is connected, a test at the end of every stage, and a page that says how each part was tested. Same file address, so an old download link now gives you the second edition.
Found a mistake?
Tell me which page, what you did, and what you saw. If your car disagrees with the book, your car is right; the book gets a dated correction.
Opens an email to [email protected].