Micromouse Construction Tutorial Part 3: Sensors & Testing

A circuit is a closed path for electricity flow, requiring a power source (battery) and a load (motor). Without a load, connecting a battery directly creates a dangerous short circuit that generates heat and sparks. Wires carry electricity and are insulated to prevent current from flowing to unintended metal parts. Switches interrupt circuits to turn robots on/off by making or breaking electrical connections. Terminal blocks connect multiple wires securely while maintaining electrical continuity. Color-coded wires (red to red, black to black) prevent dangerous incorrect connections. Soldering melts metal to permanently join wire tips for secure connections.

This section covers essential soldering fundamentals including kit components (soldering iron, stand, pump, wire, sample circuit), stand assembly techniques, safety precautions (200-300°C temperatures require avoiding contact with metal tip), soldering iron readiness testing, wire preparation, and proper cleaning techniques using a damp sponge. These foundational skills are critical for beginners before attempting circuit assembly.

Soldering is the most important skill for electronics repair. To master it, read books, watch videos, and practice regularly (30 minutes daily). Electronic boards come in types: double-sided (traces on both surfaces), single-sided (traces on bottom with jumpers), and multi-layer (up to 10 layers in sandwich structure). Different components require different iron power—large capacitors need 60W+ irons. Safety is critical: soldering smoke contains lead, so always use a fan. Component removal requires locating the component, applying solder to melt joints, and using a desoldering pump immediately while solder is molten. The sucker cover protects the tip. For integrated circuits, use low-melting-point solder (70°C) which remains liquid longer.

Successful electronics soldering requires using proper solder (60/40 tin-lead with integrated flux from electronics stores, not plumbing solder), maintaining a clean and properly heated soldering iron tip, and applying heat for only 4-6 seconds per joint to prevent damaging circuit board pads; the soldering process involves applying fresh solder to joints, heating until the solder melts, and using a solder pump or copper mesh tip to remove excess solder, while avoiding blowing on hot solder joints which causes cold solder joints that fail electrically.

Breadboards allow circuit testing without soldering, with positive and negative terminals for power connections. LEDs emit light when electricity passes through them, available in various colors. Resistors reduce current flow to protect components. Jumper wires connect components in circuits, with different types (male-to-male, male-to-female, female-to-female). Potentiometers are variable resistors that control current flow, similar to volume controls. Piezoelectric buzzers produce sounds for robot alerts. Switches control circuit connections. Arduino Nano is a smaller version of Arduino Uno, suitable for smaller robots. Power systems require multiple batteries (typically 4 for Arduino, which operates at 5V) because motors and sensors draw significant current.

An infrared proximity sensor detects obstacles using an emitter and receiver pair. The emitter sends infrared light that reflects off objects and is detected by the receiver. Unlike ultrasonic sensors that measure distance, this sensor provides binary digital output indicating only presence or absence of an obstacle. The detection range is adjustable via a multi-turn screw, with specifications of 3cm minimum and 80cm maximum. The sensor requires 5V power (brown positive, blue negative) and a signal wire (black). Installation options include embedding into walls or mounting on surfaces. An LED indicator provides visual feedback when an obstacle is detected.

Infrared obstacle sensors operate on a simple emitter-receiver principle where infrared rays are emitted and reflected back when encountering obstacles. Key technical specifications include an operating temperature range of -10°C to +50°C and a detection distance of 2 cm to 40 cm with 2 cm resolution. The sensor produces a digital output signal (HIGH/LOW) indicating presence or absence of obstacles. Compared to ultrasonic sensors, IR sensors are more cost-effective for short-range applications while maintaining good precision, though they may be affected by ambient light conditions.

An infrared sensor consists of a transmitter and receiver that work together to detect objects or measure distance. The transmitter emits infrared light that is invisible to the human eye, and the receiver detects the reflected light when it bounces off objects. This sensor is commonly used in remote controls for televisions and other electronic devices, as well as in proximity detection systems and obstacle avoidance applications. The sensor can detect objects without physical contact and is effective in various lighting conditions.

The infrared obstacle sensor works by emitting an infrared signal and detecting when the signal bounces off an obstacle and returns to the receiver. When the sensor detects an obstacle, it sends a signal to the Arduino, indicating that an obstacle has been found. If no signal returns, it means there is no obstacle or the obstacle is too far away.

IR sensors detect walls by emitting infrared light and measuring reflected intensity. Closer objects reflect more light, enabling distance sensing. Key advantages include easy implementation, compact size, contactless operation, and analog distance measurement. Limitations include ambient light sensitivity, non-linear response requiring calibration, sensor variation, and material-dependent behavior. The emitter circuit uses an IR LED (880nm, 1.3V, 100mA max), MOSFET switching, bypass capacitors for voltage stabilization, and current-limiting resistors calculated via Ohm's Law (R ≈ 51Ω for 40mA at 3.3V). A pull-down resistor ensures proper transistor deactivation.

A basic sensor reading program requires: (1) declaring variables for sensor pins (e.g., pin_ldr1, pin_ldr2), (2) creating variables to store readings (e.g., lectura_ldr1, lectura_ldr2), (3) activating serial communication in Setup for data display, (4) reading sensors in the main loop and storing values, (5) displaying data on screen. The ESP32 can be programmed using the Arduino environment by adding the board manager URL in preferences.

Arduino programs follow a standard structure: setup() configures pins and initializes serial communication, while loop() contains the main logic. For digital reading, pinMode sets the pin as INPUT, and digitalRead checks the sensor state. For analog reading, analogRead reads the 0-1023 value. Conditional statements like if-else implement decision-making based on sensor readings.

Students create a function to read sensor data by configuring a variable to store sensor values. They use the 'digitalRead' function to read values from slot 0. The sensor outputs 0 when no motion is detected and 1023 when motion is detected. Students use the print function to display variable values in the terminal. They create conditional logic using 'if' blocks to compare the motion variable to a threshold value (1023). If the condition is true (motion detected), one action is executed; if false (no motion), another action is executed. This demonstrates basic programming logic: if-else statements for decision-making.

A typical sensor reading program structure includes: (1) setup() function with Serial.begin() and pinMode() calls, (2) loop() function that reads sensors and displays data, (3) variable declarations for storing readings, and (4) Serial.println() for output. The code should be organized logically, with initialization in setup() and ongoing operations in loop(). This structure ensures the Arduino runs correctly and provides useful output for monitoring.

A basic Arduino program for reading a digital sensor involves initializing serial communication using Serial.begin(), declaring a variable to store the sensor status, and reading the sensor value using digitalRead(). The sensor pin is configured as an INPUT in the setup function. The program then reads the sensor value and processes it in the main loop.