Reference

Tabs, keys, settings, parts, simulator coverage and file locations for Circuit Lab 1.0.0.

Tabs

Tab	What it is for
Labs	The course for your board, your progress, the parts on your bench and the board tour
Projects	The 88-project library, your own projects, Import and New project
Datasheet	Your board in plain words: figures, pin map, 3D model and rules
Playground	Common parts wired to your board, for any sketch
Parts	What you own, what you want to build, and the parts to order
Settings	Colours, text size, board, currency and your prices

On a narrow screen the tab bar at the bottom has room for five. Settings then opens from the gear at the top of the Labs tab.

Keyboard

Keys	In a project
Ctrl + Enter	Run or stop the sketch
F5	Run or stop the sketch
Enter	Send the line typed in the serial monitor

In the code editor, Enter keeps the indentation of the line above, and indents one step more after an opening brace {.

Settings

Setting	Choices
Colours	Match my device (the default), Light: drafting paper or Dark: blueprint
Text size	Small, Normal, Large or Extra large, for every screen
Your board	One of the eight boards. The course, the library and the playground follow it.
Currency	A Symbol, and what 1 US dollar equals in it. Select Apply.
Your prices	The parts you have priced yourself; Use estimates again clears them
Keyboard	The shortcuts above

The app does not look up exchange rates. Set the rate yourself.

Parts

The designer has 21 kinds of part. The second column is the real part the parts list suggests.

In the designer	Real part	Pin
LED	LED, 5 mm, with a 220 Ω resistor	Output. PWM dims it.
Push button	Push button, tactile	Input with INPUT_PULLUP; LOW while pressed
Knob (potentiometer)	Potentiometer, 10 kΩ	Analog input
Buzzer	Passive buzzer	Output, played with tone()
Light sensor	Light sensor (LDR) with a 10 kΩ resistor	Analog input; more light reads higher
Slide switch	Slide switch	Input with INPUT_PULLUP; LOW when on
Relay module	Relay module, 1 channel	Output
Temperature sensor	Temperature sensor TMP36	Analog input
Servo motor	Micro servo SG90	Output, with Servo.h, or ESP32Servo.h on ESP32 boards
Distance sensor	Ultrasonic sensor HC-SR04	Two pins: TRIG out, ECHO in, read with pulseIn()
Motion sensor (PIR)	Motion sensor (PIR) HC-SR501	Input; HIGH on motion
Touch sensor	Touch sensor TTP223	Input; HIGH while touched
Tilt switch	Tilt switch	Input with INPUT_PULLUP; LOW when tilted
Door sensor (reed switch)	Reed switch and magnet	Input with INPUT_PULLUP; LOW when the door is shut
Obstacle sensor (IR)	Obstacle sensor (IR)	Input; LOW when something is in front
Soil moisture sensor	Soil moisture sensor	Analog input; drier reads higher
Water level sensor	Water level sensor	Analog input; more water reads higher
Gas sensor	Gas and smoke sensor MQ-2	Analog input; a 5 V module
Sound sensor	Sound sensor module	Analog input
DC motor	DC motor with driver module	Output through the driver module, never straight from a pin. PWM sets the speed.
Laser module	Laser module	Output. Never point it at eyes.

Every project also needs the board and its cable, and a project with parts needs a breadboard and jumper wires. Wiring, worked out for you in the designer, and the build sheet, say where the power and ground wires go.

What the simulator covers

Feature	In the simulator
Digital output and input, pull-ups	Simulated
PWM brightness (analogWrite), on each board's own PWM pins	Simulated
Analog input at each board's own resolution	Simulated
Serial print and serial input	Simulated
tone() on a buzzer	Shown, not played
Servo (attach, write, read) and ultrasonic distance (pulseIn)	Simulated
Relay, slide switch, TMP36 temperature sensor	Simulated
millis, delay and non-blocking timing	Simulated
Wi-Fi and Bluetooth	Real board only
I2C and SPI devices and displays	Real board only
Other libraries, structs, classes, pointers	Real board only
Raspberry Pi 4 / 5 (Linux, Python)	Real board only

The language

The simulator interprets a subset of Arduino C++:

• variables, constants, arrays and { } lists to fill them;
• functions, if, for, while, switch, break, continue and return;
• enum, and String with its common methods;
• simple #define constants. Other lines starting with #, such as #include, are skipped.

struct, class, typedef, namespace and pointers are not supported.

Arduino functions it knows

Kind	Functions
Pins	pinMode, digitalWrite, digitalRead, analogWrite, analogRead, ledcAttach, ledcWrite
Time	delay, delayMicroseconds, millis, micros
Sound and sensors	tone, noTone, pulseIn
Built-in RGB LED	rgbLedWrite, neopixelWrite (ESP32-S3 only)
Maths	map, constrain, min, max, abs, sq, sqrt, pow, sin, cos, round, random
Serial	begin, print, println, write, printf, available, peek, read, readString, readStringUntil, parseInt
String	length, toInt, toFloat, trim, toLowerCase, toUpperCase, concat, equals, equalsIgnoreCase, startsWith, endsWith, indexOf, charAt, substring
Servo	attach, write, read, attached, detach

analogReadResolution, analogSetAttenuation, randomSeed and yield are accepted and do nothing. Calling a function that is neither in this list nor in your sketch stops the run with an error saying it is not available in the simulator.

The constants HIGH, LOW, INPUT, OUTPUT, INPUT_PULLUP, INPUT_PULLDOWN, LED_BUILTIN, PI, DEC, HEX, BIN and OCT are defined, plus each board's pin names, such as A0 or D1, and RGB_BUILTIN on the ESP32-S3.

Export files

For a project called Night light:

Export	File
Program	night-light.ino, or night-light.py for a Raspberry Pi 4 / 5
Circuit diagram	night-light-circuit.svg
Build sheet	night-light-build-sheet.md
Parts to order	night-light-parts.csv
Project file	night-light.circuitlab.json
Parts tab lists	circuit-lab-parts.md and circuit-lab-parts.csv

See Export and import.

Deploy board names

The Deploy dialog shows the name arduino-cli uses for each board (its FQBN). Use the same one in the Arduino IDE or arduino-cli.

Board	arduino-cli board
Arduino Uno R3	arduino:avr:uno
Arduino Nano	arduino:avr:nano, then arduino:avr:nano:cpu=atmega328old if the upload fails
Arduino Mega 2560	arduino:avr:mega
ESP32-S3 DevKitC-1	esp32:esp32:esp32s3
ESP32 DevKit V1	esp32:esp32:esp32doit-devkit-v1
NodeMCU (ESP8266)	esp8266:esp8266:nodemcuv2
Raspberry Pi Pico	rp2040:rp2040:rpipico

The ESP32, ESP8266 and Pico support packages come from extra package indexes, which the app adds for you: Espressif's for the ESP32 boards, the ESP8266 Arduino project's for the NodeMCU, and the arduino-pico project's for the Pico.

Where things are kept

What	Where
Ticks, code edits, your projects, owned parts and settings	On this device only. On the website, in the browser's storage for the site; in the apps, in the app's own data folder.
The deploy add-on on Linux	~/.local/share/circuit_lab/addons
The deploy add-on on Windows	%LOCALAPPDATA%\circuit_lab\addons

Nothing is sent anywhere. Clearing the website's data, or removing the app, removes your work, so export project files you want to keep.

Limits

Item	Value
Serial monitor	Keeps the last 500 lines
Part names	Up to 14 characters
Boards	8; the Raspberry Pi 4 / 5 is not simulated
Kinds of part	21
Library projects	88

Next steps

• Troubleshooting and FAQ
• Run a sketch on the bench
• Boards and the datasheet