Obstacle-Avoiding Rover

Pan and zoom to explore the wiring. Remix the project to edit it in your own workspace.

1. 01

   Prepare the chassis and motor driver

   Mount the Pico, L298N module, battery holder, and the two motors securely. Keep the motor wires away from the ultrasonic sensor face. Remove the ENA and ENB jumpers from the L298N so the Pico can control motor speed with PWM.

   • Tip: Fit a caster wheel at the front or rear of the two-wheel chassis.
   • Tip: Do not power the circuit while making or changing connections.

   • ⚠ The L298N gets warm during use; leave airflow around its heatsink.
   • ⚠ Confirm each motor's stall current is within the L298N module's real thermal capability.
2. 02

   Wire both motors to the L298N

   Connect the left motor's two leads to OUT1 and OUT2. Connect the right motor's two leads to OUT3 and OUT4. If a motor runs opposite to the intended direction during testing, swap only that motor's two output leads.

   • Tip: Use short, secure motor wires to reduce electrical noise.

   • ⚠ Never connect a motor directly to a Pico GPIO pin.
3. 03

   Make the battery and regulated 5 V power wiring

   Connect battery BAT+ to the L298N VS motor-supply input and to buck VIN. Connect battery BAT− to L298N GND and buck GND. Before connecting loads, adjust and measure the buck VOUT as exactly 5.0 V. Then connect buck VOUT to Pico VSYS and HC-SR04 VCC; connect their grounds to the same common ground.

   • Tip: Add an inline power switch or unplug the battery when the rover is not in use.
   • Tip: The Pico is fed at VSYS with regulated 5 V, not through a GPIO pin.

   • ⚠ Verify the buck output with a multimeter before connecting the Pico or sensor: more than 5.5 V can damage them.
   • ⚠ All grounds—battery, buck, L298N, Pico, and HC-SR04—must be connected together.
   • ⚠ Use a proper 2S LiPo charger/balancer appropriate for your battery; do not charge it through this circuit.
4. 04

   Wire Pico control signals to the L298N

   Connect Pico GP2 to IN1, GP3 to IN2, GP4 to ENA, GP6 to IN3, GP7 to IN4, and GP8 to ENB on the L298N. Keep ENA and ENB jumpers removed.

   • Tip: Use the Pico's labeled GP pin numbers, not physical header-pin positions.
   • Tip: The L298N inputs accept the Pico's 3.3 V logic levels.

   • ⚠ Do not connect the L298N 5 V pin to a Pico GPIO.
5. 05

   Wire and protect the HC-SR04 signal

   Connect HC-SR04 TRIG to Pico GP10, VCC to regulated 5 V, and GND to common ground. Create a voltage divider for ECHO: HC-SR04 ECHO → 10 kΩ resistor → junction → Pico GP11; from that same junction connect a 20 kΩ resistor to common ground. This reduces the 5 V ECHO signal to about 3.3 V.

   • Tip: Mount the two ultrasonic transducers facing straight forward and clear of the chassis.
   • Tip: Keep the divider junction insulated so it cannot short to adjacent wiring.

   • ⚠ Never connect a standard 5 V HC-SR04 ECHO pin directly to Pico GP11; Pico GPIO pins are 3.3 V-only.
6. 06

   Perform a safe first power-on

   Lift the drive wheels off the ground, connect the battery, and use Schematik's Deploy button to flash the rover firmware. The rover drives forward when it sees clear space. At 25 cm or closer it stops, reverses briefly, then pivots right before continuing.

   • Tip: If the rover drives backward instead of forward, swap both leads of both motors or reverse the relevant direction logic.
   • Tip: If it pivots the wrong way, swap one motor's leads or change the turn direction in firmware.

   • ⚠ Keep hands, hair, and loose wires away from the wheels during powered testing.
   • ⚠ Disconnect battery power before altering any wiring.

#include <Arduino.h>
// HC-SR04 signal paths pass through a 3.3V/5V level shifter.

// Forward declarations
void motor(int a, int b, int en, int value);
void drive(int left, int right);
unsigned int distanceCm();

const int LEFT_IN1 = 2, LEFT_IN2 = 3, LEFT_EN = 4;
const int RIGHT_IN1 = 6, RIGHT_IN2 = 7, RIGHT_EN = 8;
const int TRIG_PIN = 10, ECHO_PIN = 11;
const int CRUISE_SPEED = 190, TURN_SPEED = 175;
const unsigned int OBSTACLE_CM = 25;

void motor(int a, int b, int en, int value) {
  value = constrain(value, -255, 255);
  digitalWrite(a, value > 0 ? HIGH : LOW);
  digitalWrite(b, value < 0 ? HIGH : LOW);
  analogWrite(en, abs(value));
}
void drive(int left, int right) { motor(LEFT_IN1, LEFT_IN2, LEFT_EN, left); motor(RIGHT_IN1, RIGHT_IN2, RIGHT_EN, right); }
unsigned int distanceCm() {
  digitalWrite(TRIG_PIN, LOW); delayMicroseconds(3);
  digitalWrite(TRIG_PIN, HIGH); delayMicroseconds(10); digitalWrite(TRIG_PIN, LOW);
  unsigned long us = pulseIn(ECHO_PIN, HIGH, 30000UL);
  return us ? us / 58UL : 0;
}
void setup() {
  pinMode(LEFT_IN1, OUTPUT); pinMode(LEFT_IN2, OUTPUT); pinMode(LEFT_EN, OUTPUT);
  pinMode(RIGHT_IN1, OUTPUT); pinMode(RIGHT_IN2, OUTPUT); pinMode(RIGHT_EN, OUTPUT);
  pinMode(TRIG_PIN, OUTPUT); pinMode(ECHO_PIN, INPUT);
  drive(0, 0);
}
void loop() {
  unsigned int cm = distanceCm();
  if (cm && cm <= OBSTACLE_CM) {
    drive(0, 0); delay(120); drive(-CRUISE_SPEED, -CRUISE_SPEED); delay(300);
    drive(TURN_SPEED, -TURN_SPEED); delay(480); drive(0, 0); delay(80);
  } else drive(CRUISE_SPEED, CRUISE_SPEED);
  delay(90);
}

“Deploy to device” opens this project in Schematik, where you can flash it to your board over USB.