Debugging Techniques for PROS

Print any value to the Brain's 240×272px LCD while the robot runs. Perfect for checking sensor reads, variable values, and task state between matches.

COPY// Clear screen + print multiple values
pros::lcd::initialize();    // in initialize()

// Anywhere in your code:
pros::lcd::set_text(1, "IMU: " + std::to_string(chassis.imu.get_heading()));
pros::lcd::set_text(2, "Motor temp: " + std::to_string(left_motors[0].get_temperature()));
pros::lcd::set_text(3, "Intake on: " + std::to_string(intakeOn));

• Lines 1–8 are available. Line 1 = top of screen.
• Tip: Print once per 50ms in a task loop — more frequent clears the screen too fast to read.
• Tip: Print the thing you're least sure about, not all variables at once.

PROS routes printf() over USB to your VS Code terminal. Run pros terminal in the integrated terminal while the robot is connected.

COPY// Print formatted output to terminal
printf("[auton] segment 2 start — heading: %.2f\n", chassis.imu.get_heading());
printf("[intake] speed=%d temp=%.1f\n", intake.get_actual_velocity(), intake.get_temperature());

// Structured log: timestamp + label + value
printf("[%dms] motor_temp %.1f\n", pros::millis(), left_motors[0].get_temperature());

• Use \n at the end of every printf — it flushes the buffer.
• Pattern: Use bracket labels [subsystem] so you can grep the output.
• Won't work at competition — remove or wrap prints in a #define DEBUG flag before competing.

COPY// Debug wrapper — removes all prints in release build
#define DEBUG 1
#ifdef DEBUG
  #define LOG(fmt, ...) printf(fmt, ##__VA_ARGS__)
#else
  #define LOG(fmt, ...)
#endif
// Use LOG() instead of printf() everywhere
LOG("[auton] turn complete — actual: %.2f\n", chassis.imu.get_heading());

When you can't read the Brain screen (robot is far away, or screen is obstructed), use the V5 Brain's built-in status LED or an indicator LED on a 3-wire port to show state.

COPY// Flash an LED N times to indicate state
pros::adi::DigitalOut led('A');

void ledFlash(int n) {
  for (int i = 0; i < n; i++) {
    led.set_value(1); pros::delay(150);
    led.set_value(0); pros::delay(150);
  }
  pros::delay(400); // gap between sequences
}

// Flash 1 = step 1 reached, flash 2 = step 2, etc.
ledFlash(1); chassis.pid_drive_set(24, 110); chassis.pid_wait();
ledFlash(2); chassis.pid_turn_set(90, 90); chassis.pid_wait();

Write data to a CSV on the Brain's microSD card. Insert a microSD into the Brain, then read the file on your laptop after the run.

COPY#include <fstream>

void startLog() {
  std::ofstream log("/usd/run_log.csv", std::ios::app);
  log << "time,heading,left_vel,right_vel,temp\n";
  log.close();
}

void logRow() {
  std::ofstream log("/usd/run_log.csv", std::ios::app);
  log << pros::millis() << ","
      << chassis.imu.get_heading() << ","
      << chassis.left_motors[0].get_actual_velocity() << ","
      << chassis.right_motors[0].get_actual_velocity() << ","
      << chassis.left_motors[0].get_temperature() << "\n";
  log.close();
}
// Call logRow() every 50ms in a task for a full run record

• Open run_log.csv in Excel or Google Sheets — graph motor velocities to spot stalls.
• Each run appends. Delete the file between sessions to start fresh.

PROS ships a terminal dashboard that shows motor ports, temperatures, currents, and sensor values updated live. Run it while connected via USB.

COPY# In VS Code integrated terminal
pros terminal
# Separate window for motor dashboard
pros monitor

• Shows every port: motor RPM, temperature, current draw, connected status.
• Useful for spotting which motor is overheating or which port is dead during a test run.
• Use alongside printf terminal output — open two terminal panes side by side.