Documentation

Language & Hardware Reference

Concise reference guides for Arduino C/C++ core APIs, hardware timing, sensor interfaces, and circuit components.

Arduino API

Pin modes: INPUT, OUTPUT, INPUT_PULLUP

What pinMode() does electrically, and which mode to use.

Read Guide

digitalWrite() and digitalRead()

Switch outputs and read inputs as HIGH or LOW.

Read Guide

analogRead() and analogWrite()

ADC readings and PWM outputs on each board.

Read Guide

Timing: delay(), millis(), micros()

Blocking and non-blocking ways to measure and wait.

Read Guide

Serial communication

begin, print, println, available, read and printf.

Read Guide

Concepts

Data types and overflow

Why int behaves differently on the Uno and the ESP32.

Read Guide

Voltage dividers

Vout = Vin × R2 / (R1 + R2): sensors, level shifting and potentiometers.

Read Guide

I²C bus basics

Two wires, many devices, each with an address.

Read Guide

What the simulator does and doesn't do

An honest list of what Robotry Labs models.

Read Guide

ESP32

ESP32 DevKit V1 pin guide

Safe pins, input-only pins, strapping pins and ADC2 with Wi-Fi.

Read Guide

ESP32, ESP32-C3 and ESP32-S3 compared

Not every ESP32 has the same pins — check the board before you wire.

Read Guide

Components

Resistor colour code

Read 4-band resistors in seconds.

Read Guide

Safety

Electrical safety for makers

Rules that protect you and your boards.

Read Guide

Circuit Components Reference

Electrical properties, safe operating limits, and wiring guidance for all components supported by Circuit Lab.

LED

output

Light-emitting diode. Current flows from the long leg (anode, +) to the short leg (cathode, −).

Tip: Always put a resistor (220 Ω–1 kΩ) in series, or the LED and the pin can be damaged.

Terminals: Anode (+), Cathode (−)

RGB LED (common cathode)

output

Three LEDs (red, green, blue) in one package sharing a cathode. Mix colours with PWM.

Tip: Each colour needs its own resistor.

Terminals: Red, Common cathode (−), Green, Blue

Resistor

passive

Limits current. Colour bands show the value.

Tip: Resistors have no direction — either way round works.

Terminals: End 1, End 2

Push button

input

Connects its two sides while pressed. The pins on the same side are always connected.

Tip: Use INPUT_PULLUP and wire the button to GND: pressed reads LOW.

Terminals: Side A, Side B

Potentiometer

input

A knob that divides voltage. Outer pins to 5V/3.3V and GND, the middle (wiper) to an analog pin.

Tip: On an ESP32 connect the outer pin to 3.3V, never 5V.

Terminals: Left (to GND), Wiper (signal), Right (to VCC)

Light sensor (LDR)

sensor

Photoresistor: resistance falls as light increases. Use it with a 10 kΩ resistor as a voltage divider.

Tip: LDR from VCC to the analog pin, 10 kΩ from the analog pin to GND.

Terminals: Leg 1, Leg 2

Piezo buzzer (passive)

output

Plays the frequency you send with tone(). A plain HIGH only clicks.

Tip: Connect + to a GPIO and − to GND.

Terminals: +, −

Ultrasonic sensor HC-SR04

sensor

Measures distance with sound: a 10 µs pulse on TRIG, then ECHO stays HIGH for 58 µs per centimetre.

Tip: ECHO outputs 5 V. On an ESP32 use a voltage divider (e.g. 1 kΩ + 2 kΩ) on ECHO.

Terminals: VCC (5 V), TRIG, ECHO, GND

Temperature & humidity (DHT11/DHT22)

sensor

Digital sensor read with the DHT library.

Tip: Bare sensors need a 10 kΩ pull-up on DATA; most breakout boards already have it.

Terminals: VCC, DATA, NC, GND

Servo motor (SG90)

actuator

Turns to an angle from 0° to 180° set by the Servo library.

Tip: Servos draw bursts of current: power bigger ones from a separate 5 V supply with a shared GND.

Terminals: GND (brown), VCC (red), Signal (orange)

DC motor + driver (L298N-style)

actuator

IN1/IN2 set the direction, EN (PWM) sets the speed. The driver supplies the motor current.

Tip: Never connect a motor straight to a GPIO pin — always use a driver.

Terminals: IN1, IN2, EN (PWM), VCC, GND

Relay module (5 V)

actuator

An electrically controlled switch. When triggered it connects COM to NO (otherwise COM to NC).

Tip: Mains voltage is dangerous. In real projects let an adult or professional wire the high-voltage side.

Terminals: VCC, GND, IN, COM, NO, NC

LCD 16×2 (I²C)

display

Character display with an I²C backpack (usually address 0x27).

Tip: Uno: SDA = A4, SCL = A5. ESP32: SDA = GPIO21, SCL = GPIO22.

Terminals: GND, VCC, SDA, SCL

OLED 128×64 (SSD1306)

display

Small graphic display. You can place and wire it; drawing graphics isn't simulated yet.

Tip: Not simulated yet: test OLED sketches on a real board.

Terminals: GND, VCC, SCL, SDA