Arduino Obstacle-Avoiding Robot: Build Guide

1. Connect the sensor and motor base

With power disconnected, fit the shield to the UNO and connect the left motor to channel A and the right motor to channel B. Secure the sensor so its transducers face the target and cables cannot enter the wheels. Follow the shield's motor-power and VIN Connect guidance before connecting USB and an external supply.

This reference uses UNO Rev3 5 V logic. The standard HC-SR04's Echo is a 5 V signal. For a 3.3 V board such as an ESP32, use an appropriate level-shifting arrangement and a separately checked pin map; do not connect that Echo signal directly to its GPIO.

2. Upload the sketch and check the decision sequence

Save the download in a folder named uno-obstacle-avoider, open it in Arduino IDE, select UNO and the correct port, then verify and upload. Open Serial Monitor at 115200 baud. G starts the demonstration; S stops it. Keep the wheels raised until direction, stopping and sensor behaviour have been checked.

The starting settings are a 25 cm clearance threshold, a 70 ms measurement interval and a 120 ms right turn. These are values to evaluate on your build, not measured stopping distances or universal settings. Use the physical switch to cut power when needed; software commands are not a substitute for that switch.

wait for a start command
measure the echo with a bounded timeout
if the reading is invalid: stop and require a restart
if the obstacle is within the clearance threshold:
  make a short right turn, stop, then measure again
otherwise: drive forward
accept the stop command between control steps

3. Check valid readings and timeout behaviour

The HC-SR04 measures the echo's round-trip time. The code generates a 10 microsecond trigger and estimates centimetres from the pulse duration divided by 58. A missing pulse or a result outside the selected module's nominal 2–400 cm range is treated as invalid, rather than as an empty path.

Use a broad flat target at known distances before trying movement. Then check angled and less reflective targets to observe the limits. If no echo returns, the sketch stops and requires inspection and G to restart. It deliberately does not reverse into space that the front sensor cannot observe.

• Check the labelled pins and common ground if every reading times out.
• Verify both wheel directions with the base raised before floor operation.
• With the motor supply disconnected, inspect the trigger, echo and timeout code if behaviour differs from the expected sequence.
• Use a clear area away from edges; keep people, loose items and pets out of the demonstration space.

4. Tune from observations rather than a guessed safe distance

Begin with low motor commands and ample open space. Measure where the robot actually stops or changes direction relative to the target. Account for the sampling interval, the echo timeout, wheel motion and mechanical response when choosing a clearance threshold.

The turn is a timed demonstration step with one wheel stopped; it is not mapping or path planning. If it repeatedly turns without finding a valid clear path, stop and reposition the build. Record changes in motor commands, turn duration, target material and battery condition.

5. Troubleshoot the input before changing the drive code