Symptom index
What is it doing?
Find what it is doing in the list below. Every symptom here is one a real person typed on a forum — not a category invented to look tidy.
First, find the box
A Bluetooth project is four things in a row — your phone, the module, the Arduino, and the thing it drives. The signal only ever moves one way along that line, so almost every problem is one box misbehaving. Work out which, and the fix is usually small.
| Box | When it is the problem, you see |
|---|---|
| Phone | Won't pair. Never appears in the list. Pairs and drops. |
| Module | Garbage characters. Total silence. The module gets warm. |
| Arduino | The module is clearly fine, but the sketch does nothing, or the wrong thing. |
| The thing | All of that works, the letter arrives — and the motor sits there. |
- PhoneIt never appears in my phone's Bluetooth listRead the fix →
- ModuleIt pairs, then drops after a few secondsRead the fix →
- ModuleThe Serial Monitor shows ⸮⸮⸮Read the fix →
- ArduinoUploading a sketch hangs foreverRead the fix →
- ModuleAT commands return ERROR, or nothing at allRead the fix →
- PhoneIt works on Android but my iPhone can't see itChapter 10
- ModuleHalf the AT commands in the tutorial don't exist on my moduleChapter 24
- ModuleThe module got hot, and now it's deadRead the fix →
- ModuleDo I need those two resistors, or not?Read the fix →
- PhoneIt asks for a pairing code and 1234 does not workRead the fix →
- ArduinoIt says connected, but the Arduino does nothingRead the fix →
- ArduinoThe command arrives split in half, or twice overRead the fix →
- ModuleIt works on USB but not on a batteryChapter 15
- ModuleIt works on the bench but not across the roomChapter 36
- The thingThe letter arrives, but the motors do nothingChapter 9
- ArduinoWhich pins do I use on a Nano, a Mega, an ESP32?Chapter 26
- ModuleWhich module should I even buy?Read the fix →
- ModuleShould I just use an ESP32 instead?Read the fix →
- PhoneWhat app do I use to test it?Chapter 4
- PhoneI want to drive it from a web pageChapter 30
- PhoneMIT App Inventor will not connectChapter 29
- ModuleI need two Arduinos to talk to each otherChapter 32
12 of 22 have a free write-up so far — the rest are answered in the book, and more are published every week.
Every one of these, in one place
Arduino Bluetooth — Make It Connect ends with a fix encyclopedia: symptom, cause, the test that tells you which, and the fix. $15.