The part families

The nine categories the parts bin is sorted into, and what lives in each of them.

The editor's part panel files every part under exactly one category. Here is what each one holds and what it is for.

Basics

LED, resistor, capacitor, clock. The four parts a first circuit is made of. The clock is a square wave at a frequency you set, so a circuit with no processor in it still has something moving.

Boards

Eleven of them: Arduino Uno, Nano, Mega 2560 and Leonardo, the bare ATtiny85, Raspberry Pi Pico, ESP32-C3 and ESP32-C6, STM32F411 Black Pill, STM32 Blue Pill and BBC micro:bit V2. Each runs real firmware on our own CPU core. See the boards.

Inputs

Pushbutton, slide switch, joystick, rotary encoder, gamepad, arcade button, 4x4 keypad, potentiometer, slide pot, tilt switch. Everything a person presses, turns or tips. The pushbutton models contact bounce, which is why a debounce lesson here can show the problem rather than describe it, and the encoder chatters for the same reason. See the parts games are made of.

Sensors

LDR, TMP36 temperature sensor, 10 k NTC thermistor, HC-SR04 ultrasonic range finder, PIR motion sensor, reed switch. Each has a slider or a click on the canvas for the thing it is sensing: how bright the room is, what the weather is doing, how far away the wall is, whether anybody is moving, where the magnet is. Most of them are a resistor or a switch in disguise, and what each one really is is worth five minutes.

Two of them are not. The DHT22 and DHT11 hand back forty bits and a checksum down one wire, timed rather than read (signals you time); the MPU6050 is six axes over I2C, and you drag the board itself to tip it (two wires, several chips).

Outputs

Buzzer, piezo speaker, WS2812 addressable LEDs, RGB LED, servo, DC motor, L293D motor driver, 28BYJ-48 stepper, relay. The servo takes a pulse width, not a duty cycle. The DC motor needs a transistor to switch and an H bridge to reverse, because a board pin cannot drive one, and that is the point of having it; see driving a motor.

The stepper and its ULN2003 board are the odd one out: it has no speed, only a position, and the driver for it is a table of four coil patterns and a delay. A stepper is four coils and a table.

Displays

Seven segment, TM1637 four-digit module, SSD1306 OLED over I2C, ILI9341 color TFT over SPI, MAX7219 8x8 matrix, and the 16x2 character LCD twice over: on its own sixteen pins and behind the PCF8574 I2C backpack most kits now ship (both of them). Each decodes its datasheet's own protocol off the pins, and the panel on the canvas repaints from a framebuffer the part hands out. What each one leaves out is on its own page: the ILI9341 takes every library's long init sequence and ignores the parameters, the SSD1306 never stretches the clock and never scrolls, and the character LCD answers no reads at all.

The seven-segment part is eight bare LEDs with a leg each; the TM1637 is a driver, and its two wires look like I2C without being it (why that matters).

Logic

An ideal gate and an ideal inverter as teaching parts, then the real chips: 74HC00, 74HC04, 74HC08, 74HC32, 74HC86, 74HC74 and 74HC595.

The 74HC chips have VCC and GND as real pins and do nothing until they are wired. Unpowered, every output is high impedance, which is the commonest reason a logic circuit looks dead. Propagation delays come from the datasheets and are inertial: a pulse shorter than the delay never reaches the output.

Timers and analog

NE555, op-amp, inductor, signal generator, function generator, oscilloscope, multimeter, NPN transistor, diode.

Four of those are bench instruments rather than components: the function generator, the oscilloscope, the multimeter and the four-channel logic analyzer. You drop them on the canvas and clip their leads onto the circuit like the real things, and between them they cover the questions a circuit will not answer by itself: what is this node doing over time, what is it doing right now, and in what order did those four things happen. See the bench instruments and the logic analyzer.

The plain signal generator beside them is the same waveforms from an ideal output with no front panel, for when you want to drive a node and stop thinking about it.

Clocks, links and remotes

DS3231 real-time clock, HC-05 serial bridge, infrared remote and receiver. The clock keeps time whatever the sketch is doing, and every one of its registers is binary coded decimal (which catches everybody). The HC-05 is modeled as exactly what a circuit can see of it: a UART, with the far end of the link in the serial monitor and no radio anywhere (said plainly). The remote and its receiver send NEC, and the beam between them is drawn as a wire (why).

Power and wiring

VCC at whatever voltage you choose, GND, the full breadboard and the half one. The breadboard is a real 0.1 inch grid, 63 columns wide, with the rails down each side and a 0.3 inch center channel for DIP chips.

The school parts

There is no separate category for them, and that is deliberate: the parts a school kit ships with are filed with everything else. Potentiometer, LDR, servo, motor, ultrasonic, temperature sensor, relay, transistor, RGB LED, LCD1602, keypad and the switches are all in the lists above.

Every part has a project

Every part in the catalog is used by at least one built-in project, and a test fails if one is not. So a part you have never met can always be seen working: open its page from /parts and look at the row underneath.