⚡ Essential electronics

Imagine a water tank connected to a pipe. The height of the water pushes it downward: that’s voltage. The amount of water flowing through the pipe per second is current. A narrow section of the pipe restricts the flow: that’s resistance. Circuits work the same way, except electrons take the place of water, and the “pipe” needs to form a closed path back to the power source.

How to read this map: Compare the two sides. On the left, the higher the tank, the greater the pressure; the narrow section of the pipe limits the flow. On the right, the battery is the tank, the resistor is the narrow pipe, and the cyan arrow shows that current needs to return to the negative terminal (GND). A loose wire anywhere means an open circuit and zero current.

Why learn this

Every choice of robot component comes down to a question about these three quantities: Does the battery provide enough voltage? Can the driver handle the motor’s current? What resistor protects the LED? Without these basics, you’re buying in the dark and finding out something went wrong by the smell of burning.

Key concepts

A Ohm’s law connects the three quantities: V = R × I. If you know two, you can calculate the third. At the workbench, the calculation you’ll use most often is for the LED resistor: the LED “uses up” a fixed part of the voltage, and the resistor needs to handle the rest, limiting the current to a safe level for the LED and the ESP32 pin.

How to read this map: The top row splits up the voltage (what the pin supplies minus what the LED uses is left for the resistor). The cyan box applies Ohm’s law to find the minimum resistor value. The bottom box checks the current using the value you’ll actually use: 220 Ω, the same one used for the blinking LED in module 1.1.

The calculation in four steps

Why learn this

This is the calculation you’ll repeat most often at the workbench. The same idea (remaining voltage divided by the desired current) comes up in the HC-SR04 voltage divider, when choosing a transistor’s base resistor, and when reading the rover’s battery level.

Key concepts

A breadboard (breadboard) lets you build circuits without soldering, just by inserting wires and components. Inside, each hole is connected to others by hidden metal strips. If you don’t know this map, you can build everything “correctly” in the wrong row. There are two rules: in the middle, the 5 holes in the same column are connected; along the edges, the long + and − lines (the power rails) run along the board.

How to read this map: each colored line represents a metal strip beneath the holes. The green ones show two neighboring columns: they are NOT connected. The amber one shows that the same column on the other side of the gap is a different point. The red (+) and cyan (−) lines are the power rails. On some long boards, the rail is split in the middle: check with a multimeter (topic 4).

Why learn this

Half of the circuits that “don’t work” are correct on paper but one row off. Knowing the internal map helps you find the fault by looking, instead of rewriting the code.

Key concepts

O multimeter is the instrument that turns “I think it’s right” into certainty. A simple digital model can handle everything Trail 1 asks you to do: measure a battery’s voltage , check the value of a resistor and test the continuity of a wire (whether it’s intact or two points are connected).

Three measurements you’ll repeat all the time

Why learn this

When the rover in module 1.6 stops in the middle of the room, the first question is “is the battery OK?” If you can measure it in seconds, you won’t waste the afternoon suspecting the program. Checking continuity before powering up also saves boards from a short you didn’t notice.

Key concepts

A digital signal has only two states: on (HIGH) or off (LOW), like a switch. An analog signal varies continuously, like the voltage from a turning potentiometer or a discharging battery. The ESP32 reads both: digital signals with digitalRead() and the analog one through the ADC with analogRead(). And here's the critical point: on the ESP32, HIGH is 3.3 V, not 5 V.

How to read this map: on the left, the green line only occupies two levels, 0 and 3.3 V. On the right, the cyan line passes through all the values in between, and the ADC gives a proportional number. The red band at the top is the limit: the ESP32 tolerates only about 3.6 V at a pin, so a sensor that outputs 5 V needs a voltage divider (topic 6) or a level shifter.

Why learn this

Many tutorials and modules were made for the Arduino Uno, which runs at 5 V. Connecting one of these directly to the ESP32 is the fastest way to kill a pin, and sometimes the whole board. Knowing what signal each component outputs determines which pin to use, which reading function to call, and whether protection is needed.

Key concepts

Two circuits made from two components show up in almost every robot. A voltage divider uses two resistors in series to deliver a fraction of the voltage: Vsaída = Ventrada × R2 ÷ (R1 + R2). With two equal resistors, the output is half the input. A pull-up is a resistor that “pulls” an input up to 3.3 V while nothing is happening, so the pin never stays undefined.

How to read this map: on the left, follow the voltage from top to bottom: the two equal resistors divide the battery voltage in half, and the green midpoint goes to GPIO 34, always staying below 3.3 V. On the right, the internal resistor connects GPIO 4 to 3.3 V; when you press the button, the pin connects directly to GND and reads 0. The “inverted” logic (pressed = 0) is normal with a pull-up.

Goal: read the voltage of 4 AA batteries through the divider and the state of a button with an internal pull-up, displaying both in the Serial Monitor twice per second. In Wokwi, replace the battery with a potentiometer connected between 3.3 V and GND (the middle output to GPIO 34) and watch the “battery” voltage change.

// Voltage divider + button with pull-up (ESP32, esp32 package 3.x)
// Battery → R1 10k → GPIO 34 → R2 10k → GND   |   Button: GPIO 4 ↔ GND

const int PINO_BATERIA = 34;   // ADC1, input only
const int PINO_BOTAO   = 4;    // has internal pull-up
const float FATOR_DIVISOR = 2.0;  // (R1 + R2) / R2 = (10k + 10k) / 10k

void setup() {
  Serial.begin(115200);
  pinMode(PINO_BOTAO, INPUT_PULLUP);  // released = HIGH, pressed = LOW
  analogReadResolution(12);           // 0 a 4095
  Serial.println("Battery and button reading ready");
}

void loop() {
  int bruto = analogRead(PINO_BATERIA);               // number from 0 to 4095
  int mvPino = analogReadMilliVolts(PINO_BATERIA);    // already in mV, calibrated
  float vBateria = mvPino * FATOR_DIVISOR / 1000.0;  // undoes the divider
  bool apertado = (digitalRead(PINO_BOTAO) == LOW);

  Serial.print("ADC: ");        Serial.print(bruto);
  Serial.print(" | pin: ");    Serial.print(mvPino);   Serial.print(" mV");
  Serial.print(" | battery: "); Serial.print(vBateria, 2); Serial.print(" V");
  Serial.print(" | button: ");   Serial.println(apertado ? "APERTADO" : "solto");
  delay(500);
}

Why learn this

The divider protects the ESP32 from the 5 V ECHO pin on the HC-SR04 (module 1.4) and lets the rover warn you when the battery is running low. The pull-up lets buttons, limit switches, and “collision” sensors give reliable readings without false signals.

Key concepts