Wiki

Component wiki

What each part does, how to choose it and how to wire it, with an example circuit on every page. The same pages are in the app: ⌘K → Component wiki.

Concepts

  • Decoupling capacitorsEvery chip needs a small capacitor right at its supply pin. It supplies the fast current spikes the chip draws, so the rail stays clean.
  • Ground pourA copper area filled around everything else and connected to GND. It gives every part a short return path, shields signals and saves routing.
  • Net labels and power flagsA net label gives a wire a name. Every wire end with the same label is connected, so a schematic stays readable without wires crossing the sheet.
  • Pull-up and pull-down resistorsA resistor to the supply (pull-up) or to ground (pull-down) gives a pin a defined level when nothing else drives it.
  • RatsnestThe thin straight lines on the PCB that show which pads still have to be connected. They come from the schematic and disappear as you route.
  • Track width and equal lengthsHow wide a track must be for its current (IPC-2221), why ground wants a pour, and which pairs, like USB D+ and D-, should have the same length.

Components

  • DC barrel jackThe round power socket for wall adapters (5.5/2.1 mm). Usually centre positive; add reverse-polarity protection because adapters vary.
  • BME280 (breakout)Bosch's temperature, humidity and air-pressure sensor. Hobbyists usually use it on a small breakout board, connected over I²C with four wires.
  • Buck converter and inductorA switching regulator that steps a high voltage (12–24 V) down to 3.3 V efficiently, using an inductor. Needed when an LDO would get too hot.
  • Push buttonA tactile switch closes a contact while pressed. Wired to GND with a pull-up, it reads 1 when released and 0 when pressed.
  • CapacitorA capacitor stores a little charge and releases it fast. Ceramic capacitors steady supply rails, filter signals and set timing.
  • CrystalA quartz crystal sets an accurate clock frequency for a chip, with two small load capacitors to ground. Modules like the ESP32 already have one inside.
  • DiodeA diode lets current flow one way only. Small signal diodes like the 1N4148 stop ghosting in key matrices and protect against coil kickback.
  • Electrolytic capacitorA big, polarised capacitor (hundreds of µF) that buffers the supply where a lot of current is switched, such as LED strips and motors.
  • USB ESD protection (USBLC6-2SC6)A small chip of clamp diodes that absorbs static discharges on the USB data lines and VBUS before they reach your microcontroller.
  • ESP32-C3 moduleEspressif's low-cost Wi-Fi + Bluetooth LE RISC-V module with native USB. The WROOM-02 needs 3.3 V, a few capacitors, an EN delay and a BOOT button.
  • ESP32-C6 moduleEspressif's Wi-Fi 6 + Bluetooth LE + Thread/Zigbee (802.15.4) module. The MINI-1 is small, with native USB on GPIO12/13.
  • ESP32-S3 moduleThe dual-core ESP32 with Wi-Fi, BLE, USB OTG and lots of GPIOs, for cameras, displays and keyboards. WROOM-1 needs the usual 3.3 V, EN and BOOT circuit.
  • Ferrite beadA part that passes DC but blocks high-frequency noise, used with capacitors to give a sensitive chip (analog, radio) a quieter supply.
  • Resettable fuse (PTC)A polyfuse heats up and cuts the current when a short or overload pulls too much, then recovers when it cools. Typical on USB VBUS.
  • Key switch and hot-swap socketMechanical keyboard switches (MX, Choc, Alps) wired in a row/column matrix with one diode per key. Hot-swap sockets let you change switches without soldering.
  • LDO voltage regulatorA linear regulator turns a higher voltage (USB 5 V, a LiPo) into a steady 3.3 V. Simple and quiet; the difference is burnt as heat.
  • LEDA light-emitting diode glows when current flows from anode to cathode. It always needs something that limits the current, usually a resistor.
  • Level shifter (74AHCT1G125)A single buffer that turns a 3.3 V logic signal into a clean 5 V one, typically for WS2812 LED strips driven by an ESP32 or RP2040.
  • LiPo charger and battery connectorThe MCP73831 charges a single lithium-polymer cell from USB, at a current set by one resistor. With a JST PH connector and a power switch the board runs on battery.
  • MOSFETA transistor that works as a switch controlled by voltage. An N-MOSFET switches a load to ground; a P-MOSFET switches the supply side.
  • NPN transistorA bipolar transistor that switches or amplifies with a small base current. MMBT3904 switches LEDs, buzzers and small relays from a GPIO.
  • OLED display (SSD1306, I²C)The common 0.91" (128×32) or 0.96" (128×64) monochrome OLED module with an SSD1306 controller, on four pins: GND, VCC, SCL, SDA.
  • Pin headers and JST connectors2.54 mm headers for breadboard-style wiring, and small JST connectors (SH 1.0 mm for Qwiic/STEMMA QT I²C, PH 2.0 mm for batteries) for cables.
  • Pro Micro and compatible controllersThe classic keyboard controller footprint: 24 pins, 18 GPIOs. ATmega32U4 Pro Micro, RP2040 boards (KB2040, Elite-Pi) and the wireless nice!nano all fit.
  • Raspberry Pi Pico and RP2040 boardsThe Pico is a cheap RP2040 board with 26 usable GPIOs, 3.3 V logic and a simple power scheme; the RP2040-Zero packs the same chip into 23.5 × 18 mm.
  • ResistorA resistor limits current and sets voltages. It is the most common part on any board: LED current, pull-ups, dividers, USB-C configuration.
  • Addressable RGB LED (WS2812B, SK6812)An RGB LED with a tiny controller inside. Chain as many as you like on one data pin; each one takes its colour and passes the rest on.
  • Rotary encoderA knob that turns endlessly and reports steps as two phase-shifted signals (A, B). The EC11 adds a push switch. Common as a volume knob.
  • RP2040 chipRaspberry Pi's dual Cortex-M0+ microcontroller as a bare QFN-56 chip. It needs QSPI flash, a 12 MHz crystal, 3.3 V and a handful of capacitors; the 1.1 V core supply is built in.
  • Schottky diodeA diode with a low forward drop (0.3–0.5 V), used in power paths: reverse polarity protection, OR-ing two supplies, flyback across motors.
  • Screw terminalA terminal block that clamps bare wires with a screw: the easy way to bring power in or take a load (LED strip, motor) off a board.
  • SHT4x temperature and humidity sensorSensirion's tiny I²C sensor for temperature (±0.2 °C typ.) and relative humidity (±1.8 % RH typ.). Needs only 100 nF and the I²C pull-ups.
  • QSPI flash (W25Q)An 8-pin serial flash chip that holds the program of a bare RP2040, or data for any microcontroller. W25Q128JV is 16 MB, W25Q16JV 2 MB with the same pinout.
  • StabilizerA wire-and-slider mechanism that keeps long keys (Shift, Enter, Space) from wobbling. On the PCB it is only holes, with no electrical pins.
  • TRRS jack (split keyboards)A 3.5 mm audio jack used as the link between the two halves of a split keyboard: GND, VCC and one or two data lines over a TRRS cable.
  • USB-C receptacleThe USB-C socket for power and USB 2.0 data. A device needs 5.1 kΩ on each CC pin, or a charger gives it no power at all.
  • Seeed XIAO boardsThumb-sized microcontroller boards (RP2040, ESP32-C6, nRF52840) with USB-C, 11 GPIOs and a 3.3 V output, soldered onto your board as a module.