Schematik raised $4.6M to help anyone build hardware with AISchematik raised $4.6M pre-seed

Community project

Line-Following Delivery Cart

ESP32
Photo of Line-Following Delivery Cart
Generated with AI

Rigoberto Santiago Garzón

Published October 5, 2026

4
Open in Schematik

This line-following delivery cart is a four-wheel autonomous robot built around an ESP32 microcontroller that navigates marked paths while avoiding obstacles. The cart uses dual TB6612FNG motor drivers to control four independent Faulhaber DC motors, an MCP23017 I2C expander for motor direction control, and an 8-channel multiplexer to manage multiple ultrasonic distance sensors. Power comes from a 2S LiPo battery with a 5V buck converter for the logic circuits.

This guide provides a complete wiring diagram, detailed parts list, and step-by-step assembly instructions for building the chassis, mounting motors and sensors, and integrating the power distribution system. The included ESP32 firmware implements line-following with proportional steering correction, obstacle detection with eight ultrasonic sensors, and automatic stopping when objects are too close. Builders will learn motor control techniques, I2C peripheral expansion, analog multiplexing, and sensor fusion for autonomous navigation.

Wiring diagram

Wiring diagram for Line-Following Delivery Cart

Gather all the parts

QtyComponent
1

TB6612FNG dual motor-driver module (front pair)

A dual motor-driver board that controls the two front 5 V wheel motors from low-power ESP32 signals.

1

TB6612FNG dual motor-driver module (rear pair)

A dual motor-driver board that controls the two rear 5 V wheel motors from low-power ESP32 signals.

1

Faulhaber 5 V DC motor, front left

The front-left 5 V wheel motor that moves the cart.

1

Faulhaber 5 V DC motor, front right

The front-right 5 V wheel motor that moves the cart.

1

Faulhaber 5 V DC motor, rear left

The rear-left 5 V wheel motor that moves the cart.

1

Faulhaber 5 V DC motor, rear right

The rear-right 5 V wheel motor that moves the cart.

1

MCP23017 I2C motor-direction and ultrasonic-trigger module

A small helper board that provides enough output connections for motor direction and for triggering one distance sensor at a time.

1

74HCT4051 8-channel multiplexer module

An eight-way electronic selector that safely lets the ESP32 read one ultrasonic echo signal at a time.

1

10 kΩ resistor for ultrasonic echo voltage divider

10 kΩ

The upper resistor that reduces the 5 V echo signal to a safe ESP32 input voltage.

1

20 kΩ resistor for ultrasonic echo voltage divider

20 kΩ

The lower resistor that completes the voltage divider and safely brings the echo signal down to ground.

1

Batería LiPo 2S 7,4 V 2200 mAh, mínimo 20C

7,4 V 2200 mAh 20C

Una batería recargable que entrega la energía necesaria para los motores y la electrónica del carro.

1

5 V 8 A buck converter (2S LiPo input)

A high-current voltage reducer that turns the battery voltage into a steady 5 V supply for the motors and electronics.

1

DFRobot SEN0142 Fermion MPU-6050 6 DOF Sensor Breakout

DFRobot SEN0142 MPU-6050 breakout with 3-5 V board input, I2C interface, onboard I2C pull-ups, and i2cdevlib Arduino example coverage.

1

TCRT5000 left line-tracking sensor module

A small infrared sensor that sees the dark line beneath the left front of the car.

1

TCRT5000 right line-tracking sensor module

A small infrared sensor that sees the dark line beneath the right front of the car.

1

HC-SR04

Ultrasonic distance measurement sensor

1

HC-SR04

Ultrasonic distance measurement sensor

1

HC-SR04

Ultrasonic distance measurement sensor

1

HC-SR04

Ultrasonic distance measurement sensor

1

HC-SR04

Ultrasonic distance measurement sensor

1

HC-SR04

Ultrasonic distance measurement sensor

1

HC-SR04

Ultrasonic distance measurement sensor

1

HC-SR04

Ultrasonic distance measurement sensor

1

Portafusible con fusible automotriz de 10 A

10 A

Un fusible reemplazable que desconecta la batería si un cable o motor provoca una sobrecorriente.

Assemble it in 6 steps

1. Monta el chasis y la canastilla

Fija los cuatro motores en las cuatro esquinas del chasis. Atornilla la canastilla baja y centrada entre los ejes; deja los ocho sensores de distancia mirando hacia fuera, con el sensor 1 en el frente. Coloca los dos sensores de línea debajo del borde delantero, separados a ambos lados de la línea.

  • La canastilla debe quedar lo más baja posible; una carga alta hace más fácil que el carro vuelque.
  • Deja aproximadamente 8 mm entre cada TCRT5000 y el suelo para que pueda distinguir la cinta negra.
  • No añadas carga a la canastilla hasta probar el carro en el suelo: una carga suelta puede caer sobre las ruedas.

2. Conecta los motores a los dos controladores

Conecta motor_fl a A01 y A02, y motor_fr a B01 y B02 de driver_front. Conecta motor_rl a A01 y A02, y motor_rr a B01 y B02 de driver_rear. Si una rueda gira al revés en la primera prueba, intercambia solamente los dos cables de ese motor.

  • Usa cables gruesos y cortos para los motores; los cables finos se calientan y hacen que el carro pierda fuerza.
  • No conectes los cables de los motores a ningún pin del ESP32: pueden dañarlo.

3. Arma la alimentación protegida

Conecta battery BAT+ al pin IN de fuse_main y fuse_main OUT a buck_5v VIN+. Conecta battery BAT- a buck_5v VIN-. Ajusta primero el buck_5v a 5,0 V con un multímetro. Lleva VOUT+ a VM de ambos controladores, a VCC de los ocho HC-SR04 y a VCC del multiplexor; lleva VOUT- a todas las conexiones GND. Lleva 3V3 del ESP32 a VCC de ambos controladores, VDD del expansor, VIN del MPU-6050 y VCC de ambos TCRT5000.

  • Todas las tierras GND deben estar unidas: así las señales tienen la misma referencia.
  • El fusible va cerca del cable positivo de la batería.
  • Ajusta el regulador antes de conectar el ESP32 o los sensores; más de 5 V puede dañarlos.
  • No uses los controladores TB6612 si un motor Faulhaber supera 1 A al bloquearse; el controlador se puede quemar.

4. Conecta el ESP32, los controladores y el expansor

Conecta GPIO21 a SDA y GPIO22 a SCL de motor_io y del MPU-6050. Conecta RESET de motor_io a 3V3. Conecta GPA0 y GPA1 a AIN1 y AIN2 de los dos controladores; conecta GPA2 y GPA3 a BIN1 y BIN2 de los dos controladores. Conecta STBY de ambos controladores a 3V3. Conecta PWMA de los controladores delantero y trasero a GPIO16 y GPIO18; conecta sus PWMB a GPIO17 y GPIO19.

  • El expansor manda las órdenes de sentido a ambos lados del carro; las cuatro conexiones PWM regulan la velocidad de cada rueda.
  • No intercambies VCC de 3V3 con VM de 5V en los TB6612: VM alimenta motores y VCC alimenta las señales.

5. Conecta los lectores de línea y los sensores de distancia

Conecta AO de line_left a GPIO35 y AO de line_right a GPIO36; conecta sus VCC a 3V3 y sus GND a GND. Conecta S0, S1 y S2 de range_mux a GPIO25, GPIO26 y GPIO27, y EN a GND. Conecta COM del multiplexor al divisor: COM a P1 de echo_r_top, P2 de echo_r_top a P1 de echo_r_bottom y también a GPIO34, y P2 de echo_r_bottom a GND. Conecta ECHO de sonar_1 a X0, sonar_2 a X1 y así hasta sonar_8 a X7. Conecta TRIG de sonar_1 a GPA4, sonar_2 a GPA5, sonar_3 a GPA6, sonar_4 a GPA7, sonar_5 a GPB0, sonar_6 a GPB1, sonar_7 a GPB2 y sonar_8 a GPB3.

  • El par de resistencias baja la señal ECHO de 5 V a un nivel seguro para el ESP32 de 3,3 V.
  • Los ultrasonidos se activan de uno en uno para evitar que uno escuche el eco de otro.
  • No conectes ECHO directamente a GPIO34: la señal de 5 V puede dañar el ESP32.

6. Haz la primera prueba sin carga

Eleva el chasis para que las ruedas no toquen la mesa. Conecta la batería y después el ESP32 por USB. Comprueba que no hay cables calientes ni olor a plástico. Después de desplegar el programa, pon el carro sobre una línea oscura y ajusta los pequeños tornillos de los TCRT5000 hasta que detecten claramente la línea.

  • Prueba primero sin productos en la canastilla y a poca velocidad; después añade peso poco a poco.
  • Mantén dedos, ropa y cables lejos de las ruedas cuando reciban energía.

Review all connections

1. Connections between "battery" and "ESP32"

FunctionbatteryESP32
groundBAT- → 5 V 8 A buck converter (2S LiPo input) VIN-EXT
powerBAT+ → Portafusible con fusible automotriz de 10 A INEXT

2. Connections between "buck_5v" and "ESP32"

Functionbuck_5vESP32
powerVOUT+5V
groundVOUT-GND

3. Connections between "driver_front" and "ESP32"

Functiondriver_frontESP32
powerVM5V
powerVCC3V3
groundGNDGND
digitalAIN1 → MCP23017 I2C motor-direction and ultrasonic-trigger module GPA0EXT
digitalAIN2 → MCP23017 I2C motor-direction and ultrasonic-trigger module GPA1EXT
pwmPWMAGPIO 16
digitalBIN1 → MCP23017 I2C motor-direction and ultrasonic-trigger module GPA2EXT
digitalBIN2 → MCP23017 I2C motor-direction and ultrasonic-trigger module GPA3EXT
pwmPWMBGPIO 17
powerSTBY3V3
powerA01 → Faulhaber 5 V DC motor, front left M+EXT
powerA02 → Faulhaber 5 V DC motor, front left M-EXT
powerB01 → Faulhaber 5 V DC motor, front right M+EXT
powerB02 → Faulhaber 5 V DC motor, front right M-EXT

4. Connections between "driver_rear" and "ESP32"

Functiondriver_rearESP32
powerVM5V
powerVCC3V3
groundGNDGND
digitalAIN1 → MCP23017 I2C motor-direction and ultrasonic-trigger module GPA0EXT
digitalAIN2 → MCP23017 I2C motor-direction and ultrasonic-trigger module GPA1EXT
pwmPWMAGPIO 18
digitalBIN1 → MCP23017 I2C motor-direction and ultrasonic-trigger module GPA2EXT
digitalBIN2 → MCP23017 I2C motor-direction and ultrasonic-trigger module GPA3EXT
pwmPWMBGPIO 19
powerSTBY3V3
powerA01 → Faulhaber 5 V DC motor, rear left M+EXT
powerA02 → Faulhaber 5 V DC motor, rear left M-EXT
powerB01 → Faulhaber 5 V DC motor, rear right M+EXT
powerB02 → Faulhaber 5 V DC motor, rear right M-EXT

5. Connections between "motor_io" and "ESP32"

Functionmotor_ioESP32
powerVDD3V3
groundVSSGND
i2cSDAGPIO 21
i2cSCLGPIO 22
powerRESET3V3

6. Connections between "range_mux" and "ESP32"

Functionrange_muxESP32
powerVCC5V
groundGNDGND
digitalS0GPIO 25
digitalS1GPIO 26
digitalS2GPIO 27
groundENGND
dataCOM → 10 kΩ resistor for ultrasonic echo voltage divider P1EXT

7. Connections between "echo_r_top" and "ESP32"

Functionecho_r_topESP32
analogP2GPIO 34

8. Connections between "echo_r_bottom" and "ESP32"

Functionecho_r_bottomESP32
analogP1 → 10 kΩ resistor for ultrasonic echo voltage divider P2EXT
groundP2GND

9. Connections between "imu" and "ESP32"

FunctionimuESP32
powerVIN3V3
groundGNDGND
i2cSDAGPIO 21
i2cSCLGPIO 22

10. Connections between "line_left" and "ESP32"

Functionline_leftESP32
powerVCC3V3
groundGNDGND
analogAOGPIO 35

11. Connections between "line_right" and "ESP32"

Functionline_rightESP32
powerVCC3V3
groundGNDGND
analogAOGPIO 36

12. Connections between "sonar_1" and "ESP32"

Functionsonar_1ESP32
powerVCC5V
groundGNDGND
digitalTRIG → MCP23017 I2C motor-direction and ultrasonic-trigger module GPA4EXT
digitalECHO → 74HCT4051 8-channel multiplexer module X0EXT

13. Connections between "sonar_2" and "ESP32"

Functionsonar_2ESP32
powerVCC5V
groundGNDGND
digitalTRIG → MCP23017 I2C motor-direction and ultrasonic-trigger module GPA5EXT
digitalECHO → 74HCT4051 8-channel multiplexer module X1EXT

14. Connections between "sonar_3" and "ESP32"

Functionsonar_3ESP32
powerVCC5V
groundGNDGND
digitalTRIG → MCP23017 I2C motor-direction and ultrasonic-trigger module GPA6EXT
digitalECHO → 74HCT4051 8-channel multiplexer module X2EXT

15. Connections between "sonar_4" and "ESP32"

Functionsonar_4ESP32
powerVCC5V
groundGNDGND
digitalTRIG → MCP23017 I2C motor-direction and ultrasonic-trigger module GPA7EXT
digitalECHO → 74HCT4051 8-channel multiplexer module X3EXT

16. Connections between "sonar_5" and "ESP32"

Functionsonar_5ESP32
powerVCC5V
groundGNDGND
digitalTRIG → MCP23017 I2C motor-direction and ultrasonic-trigger module GPB0EXT
digitalECHO → 74HCT4051 8-channel multiplexer module X4EXT

17. Connections between "sonar_6" and "ESP32"

Functionsonar_6ESP32
powerVCC5V
groundGNDGND
digitalTRIG → MCP23017 I2C motor-direction and ultrasonic-trigger module GPB1EXT
digitalECHO → 74HCT4051 8-channel multiplexer module X5EXT

18. Connections between "sonar_7" and "ESP32"

Functionsonar_7ESP32
powerVCC5V
groundGNDGND
digitalTRIG → MCP23017 I2C motor-direction and ultrasonic-trigger module GPB2EXT
digitalECHO → 74HCT4051 8-channel multiplexer module X6EXT

19. Connections between "sonar_8" and "ESP32"

Functionsonar_8ESP32
powerVCC5V
groundGNDGND
digitalTRIG → MCP23017 I2C motor-direction and ultrasonic-trigger module GPB3EXT
digitalECHO → 74HCT4051 8-channel multiplexer module X7EXT

20. Connections between "fuse_main" and "ESP32"

Functionfuse_mainESP32
powerOUT → 5 V 8 A buck converter (2S LiPo input) VIN+EXT

Deploy the firmware

main.cppOpen in Schematik
#include <Arduino.h>
#include <Wire.h>
#include <Adafruit_MCP23X17.h>

constexpr int PWM_FL_PIN = 16;
constexpr int PWM_FR_PIN = 17;
constexpr int PWM_RL_PIN = 18;
constexpr int PWM_RR_PIN = 19;
constexpr int I2C_SDA_PIN = 21;
constexpr int I2C_SCL_PIN = 22;
constexpr int MUX_S0_PIN = 25;
constexpr int MUX_S1_PIN = 26;
constexpr int MUX_S2_PIN = 27;
constexpr int ECHO_PIN = 34;
constexpr int LINE_LEFT_PIN = 35;
constexpr int LINE_RIGHT_PIN = 36;

constexpr uint8_t MCP_ADDRESS = 0x20;
constexpr uint8_t MPU_ADDRESS = 0x68;
constexpr uint8_t DIR_LEFT_1 = 0;
constexpr uint8_t DIR_LEFT_2 = 1;
constexpr uint8_t DIR_RIGHT_1 = 2;
constexpr uint8_t DIR_RIGHT_2 = 3;
constexpr uint8_t TRIGGER_BASE = 4;
constexpr int LINE_THRESHOLD = 2000;
constexpr bool LINE_DARK_HIGH = true;
constexpr uint8_t CRUISE_SPEED = 145;
constexpr uint8_t TURN_SPEED = 85;
constexpr uint16_t STOP_DISTANCE_CM = 22;
constexpr int16_t TILT_LIMIT_RAW = 8000;
constexpr uint32_t SONAR_INTERVAL_MS = 60;

Adafruit_MCP23X17 mcp;
bool mpuPresent = false;
uint16_t distancesCm[8] = {0};
uint8_t nextSonar = 0;
uint32_t lastSonarMs = 0;

void setMotorPwm(uint8_t leftSpeed, uint8_t rightSpeed) {
  ledcWrite(0, leftSpeed);
  ledcWrite(1, rightSpeed);
  ledcWrite(2, leftSpeed);
  ledcWrite(3, rightSpeed);
}

void setDirection(bool forward) {
  mcp.digitalWrite(DIR_LEFT_1, forward ? HIGH : LOW);
  mcp.digitalWrite(DIR_LEFT_2, forward ? LOW : HIGH);
  mcp.digitalWrite(DIR_RIGHT_1, forward ? HIGH : LOW);
  mcp.digitalWrite(DIR_RIGHT_2, forward ? LOW : HIGH);
}

void stopCar() {
  setMotorPwm(0, 0);
}

void selectEcho(uint8_t channel) {
  digitalWrite(MUX_S0_PIN, channel & 0x01);
  digitalWrite(MUX_S1_PIN, (channel >> 1) & 0x01);
  digitalWrite(MUX_S2_PIN, (channel >> 2) & 0x01);
  delayMicroseconds(5);
}

uint16_t readSonarCm(uint8_t channel) {
  selectEcho(channel);
  uint8_t triggerPin = TRIGGER_BASE + channel;
  mcp.digitalWrite(triggerPin, LOW);
  delayMicroseconds(4);
  mcp.digitalWrite(triggerPin, HIGH);
  delayMicroseconds(15);
  mcp.digitalWrite(triggerPin, LOW);
  unsigned long pulse = pulseIn(ECHO_PIN, HIGH, 24000);
  if (pulse == 0) return 0;
  return static_cast<uint16_t>(pulse / 58UL);
}

bool isLine(int raw) {
  return LINE_DARK_HIGH ? raw >= LINE_THRESHOLD : raw < LINE_THRESHOLD;
}

bool isTilted() {
  if (!mpuPresent) return false;
  Wire.beginTransmission(MPU_ADDRESS);
  Wire.write(0x3B);
  if (Wire.endTransmission(false) != 0) return false;
  if (Wire.requestFrom(MPU_ADDRESS, static_cast<uint8_t>(6)) != 6) return false;
  int16_t ax = (Wire.read() << 8) | Wire.read();
  int16_t ay = (Wire.read() << 8) | Wire.read();
  Wire.read();
  Wire.read();
  return abs(ax) > TILT_LIMIT_RAW || abs(ay) > TILT_LIMIT_RAW;
}

void followLine() {
  bool leftOnLine = isLine(analogRead(LINE_LEFT_PIN));
  bool rightOnLine = isLine(analogRead(LINE_RIGHT_PIN));
  setDirection(true);
  if (leftOnLine && !rightOnLine) {
    setMotorPwm(TURN_SPEED, CRUISE_SPEED);
  } else if (!leftOnLine && rightOnLine) {
    setMotorPwm(CRUISE_SPEED, TURN_SPEED);
  } else if (leftOnLine && rightOnLine) {
    setMotorPwm(CRUISE_SPEED, CRUISE_SPEED);
  } else {
    setMotorPwm(0, 0);
  }
}

void setup() {
  Serial.begin(115200);
  Wire.begin(I2C_SDA_PIN, I2C_SCL_PIN);
  analogReadResolution(12);
  pinMode(MUX_S0_PIN, OUTPUT);
  pinMode(MUX_S1_PIN, OUTPUT);
  pinMode(MUX_S2_PIN, OUTPUT);
  pinMode(ECHO_PIN, INPUT);
  pinMode(LINE_LEFT_PIN, INPUT);
  pinMode(LINE_RIGHT_PIN, INPUT);
  ledcSetup(0, 20000, 8);
  ledcSetup(1, 20000, 8);
  ledcSetup(2, 20000, 8);
  ledcSetup(3, 20000, 8);
  ledcAttachPin(PWM_FL_PIN, 0);
  ledcAttachPin(PWM_FR_PIN, 1);
  ledcAttachPin(PWM_RL_PIN, 2);
  ledcAttachPin(PWM_RR_PIN, 3);
  if (!mcp.begin_I2C(MCP_ADDRESS, &Wire)) {
    Serial.println("MCP23017 not found; motors remain stopped.");
    while (true) delay(1000);
  }
  for (uint8_t pin = 0; pin < 12; pin++) {
    mcp.pinMode(pin, OUTPUT);
    mcp.digitalWrite(pin, LOW);
  }
  Wire.beginTransmission(MPU_ADDRESS);
  mpuPresent = (Wire.endTransmission() == 0);
  if (mpuPresent) {
    Wire.beginTransmission(MPU_ADDRESS);
    Wire.write(0x6B);
    Wire.write(0x00);
    Wire.endTransmission();
  }
  stopCar();
}

void loop() {
  uint32_t now = millis();
  if (now - lastSonarMs >= SONAR_INTERVAL_MS) {
    distancesCm[nextSonar] = readSonarCm(nextSonar);
    nextSonar = (nextSonar + 1) % 8;
    lastSonarMs = now;
  }
  bool frontBlocked = distancesCm[0] > 0 && distancesCm[0] <= STOP_DISTANCE_CM;
  if (frontBlocked || isTilted()) {
    stopCar();
  } else {
    followLine();
  }
}

Remix this project

Make it yours in one click

Open a full copy of this project in your own Schematik workspace — diagram, code, parts, and assembly steps included. Swap the sensor, add features, or redesign the whole thing with AI. The author's original stays untouched.

Open in Schematik