Arduino Line Follower Robot: Build & Calibrate

1. Check the power plan and connect the reference hardware

Disconnect power before assembly. Fit the shield to the UNO, connect the left motor to channel A and the right motor to channel B, and secure the array ahead of the wheels. Use the manufacturer's mounting guidance; begin with the array parallel to the surface and adjust its height while reading sensor values.

The motor supply must meet the motors' requirements and the shield's electrical and thermal limits. Follow the shield documentation for the VIN Connect arrangement when motor and controller power are separate. Have the power plan checked before connecting USB and a motor supply. Motor outputs must not be connected to controller GPIO pins.

2. Upload the reference sketch with the wheels raised

Download the sketch into a folder named uno-line-follower and open it in Arduino IDE. Select Arduino UNO and the correct port, then verify and upload. No additional library is used. Open Serial Monitor at 115200 baud; startup applies the shield brakes and waits for calibration.

The sketch defines forward direction separately for the two motors because their mounting orientations can differ. Check FORWARD_LEVEL with the wheels raised and a clear line pattern under the sensors before floor testing. BASE_PWM and TURN_PWM are starting settings, not a measured speed or a value guaranteed to move every motor.

sample a light surface and a dark surface
refuse start if either sample is missing or contrast is too low
repeat while started:
  read left, centre and right sensors
  if no line or ambiguous pattern: stop and wait for restart
  if line is left: reduce the left motor command
  if line is right: reduce the right motor command
  otherwise: drive both sides forward

3. Calibrate on your actual surface

With the wheels raised, place every sensor over the light surface and send W in Serial Monitor. Then place every sensor over the dark surface and send B. Read the three values printed after each sample. The code compares each measurement with its own light and dark references, rather than assuming one universal threshold.

The initial MIN_CONTRAST setting is 80 UNO ADC counts. Inspect the readings before changing it: weak contrast can come from mounting height, unsuitable materials, ambient light or incorrect wiring. If either sample is missing or any sensor lacks the configured contrast, G will not start the motors.

• Check each sensor sees distinctly different readings over both surfaces.
• Place the centre sensor over the line with the outer sensors over the lighter floor.
• Send G only after checking motor direction with the wheels raised.
• Send S to stop; keep the physical switch accessible throughout the demonstration.

4. Test a short line before attempting a course

Start on a clear floor-level track, not near a table edge or stairs. After a straight section works, add a gentle curve and observe the readings and wheel response. This simple controller does not implement PID or junction navigation. When no sensor sees the line, or the two outer sensors both see dark, it stops and requires repositioning and G to restart.

Change one setting or mechanical adjustment at a time and repeat the same track section. Record the surface, sensor height, power arrangement and code settings. Tune for repeatable tracking before trying to increase the motor command.

5. Troubleshoot sensing, steering and power separately