My robot doesn't work

Work down this list in order. Most problems are in the first three steps.

1. Power

• Is it switched on? Are the batteries charged? Measure with a multimeter, don’t guess.
• Is the board’s power LED on?
• Does it reset or go weird when motors start? See Powering your robot.

2. Ground

• Are all grounds connected together (battery −, Arduino GND, motor driver GND, sensors)?

3. Wiring

• Compare every wire against the diagram, one by one.
• Breadboard: are parts in the right rows? Is the power rail split in the middle?
• Use continuity mode to check suspicious jumper wires.
• LEDs and other polarised parts the right way round?

4. Code

• Did the upload finish without errors?
• Do the pin numbers in the code match the pins you wired?
• Add Serial.println() messages to see what the code is actually doing.

5. Isolate

• Test one part at a time with the simplest possible program (just blink, just read the sensor, just spin one motor).
• Swap in a known-good part.

6. Ask for help

Share: what you expected, what actually happens, a clear photo of the wiring, and your code. That gets you useful answers fast.

Common symptoms

Symptom	Usually
Nothing happens at all	Power, or no common ground
One motor works, the other doesn’t	Loose motor wire, or wrong driver pin
Robot spins in circles	One motor wired backwards; swap its two wires
Sensor always reads 0 or the maximum	Wrong pin, missing power/GND to the sensor
Works on USB, fails on battery	Batteries flat or too low a voltage
Upload fails	Wrong board/port selected in the IDE; try another USB cable