Pinouts
73 boards and packages.
Single-board computer
BeagleBone Black P8 Header
The GPIO side of the BeagleBone Black. Most of it is already spoken for by the on-board eMMC and HDMI, which is the first thing to work out before wiring a cape.
3.3 VBeagleBone Black P9 Header
The power, serial, I2C, SPI and analog side of the BeagleBone Black. The seven ADC channels take 1.8 V at most.
3.3 V / 1.8 V ADCMilk-V Duo (CV1800B)
A five dollar board that boots Linux on a RISC-V core, in the Raspberry Pi Pico footprint. USB-C at the top, pin 1 top-left.
3.3 V GPIO, 1.8 V ADCRadxa ROCK 5B
RK3588S octa-core board with a Raspberry-Pi-shaped 40-pin header. The holes line up; almost nothing else does.
3.3 V GPIO, 1.8 V ADCRaspberry Pi 26-pin GPIO Header
The original Model A and Model B header. Pins 1 to 26 match the 40-pin layout, with three that moved between board revisions.
3.3 VRaspberry Pi 40-pin GPIO Header
The J8 header shared by every 40-pin Raspberry Pi, from the Model B+ through the Pi 5. Names are BCM numbers, which is what libgpiod, pigpio and the Python GPIO libraries expect.
3.3 V
Dev board
Adafruit Feather (standard footprint)
Not one board: the footprint every Feather and FeatherWing shares, from the 32u4 to the RP2040 and ESP32-S3. USB at the top.
3.3 V, mandated by the specificationArduino Mega 2560 (main headers)
ATmega2560 with 54 digital pins, 16 analog inputs and four hardware serial ports. These are the Uno-compatible side headers; D22 to D53 live on the separate double-row header at the end of the board.
5 VArduino Nano v3
The same ATmega328P as the Uno on a 18 x 45 mm breadboard-friendly footprint, plus two extra analog-only inputs. Orientation below has the USB connector at the top.
5 VArduino Uno R3
The ATmega328P reference board. 5 V logic throughout, which is exactly why it still gets used for anything driving relays, LED strips or older 5 V peripherals.
5 VArduino Uno R4 Minima
The Uno shape and 5 V logic, with a 48 MHz Renesas RA4M1 underneath: a real DAC, an op-amp, CAN, and 14-bit ADC.
5 VESP-01 / ESP-01S (ESP8266)
The cheapest way to put WiFi on something, and the most awkward. Two usable GPIO, both strapping pins, and no on-board regulator. Orientation below has the antenna on the right.
3.3 V, not 5 V tolerantESP32 DevKit V1 (30-pin)
The common 30-pin ESP32-WROOM-32 board. Plenty of GPIO, but four are input only, five are strapping pins and half the ADC stops working the moment WiFi comes up.
3.3 VESP32-CAM (AI-Thinker)
ESP32 with an OV2640 camera and a microSD slot for the price of a sandwich. Almost every exposed pin is already spoken for, and there is no USB. Orientation below has the camera facing up.
3.3 VESP32-S3-DevKitC-1
Espressif's reference board for the S3: dual-core Xtensa at 240 MHz, native USB, and 45 GPIOs on two 22-pin headers. Three of them may not be yours.
3.3 VNXP FRDM-K64F
120 MHz Cortex-M4F with Ethernet, an accelerometer, a microSD slot and an on-board debugger, in the Arduino Uno R3 footprint, but it is a 3.3 V board.
3.3 V, not 5 V tolerantPro Micro (ATmega32U4)
ATmega32U4 with native USB, so it can be a keyboard or a mouse without a helper chip. The board in most custom keyboard builds. USB at the top.
5 V at 16 MHz, or 3.3 V at 8 MHzRaspberry Pi Pico (RP2040)
RP2040 board with 26 exposed GPIO, three ADC channels and the PIO blocks that make it unusually good at bit-banged protocols. Pin 1 is the top-left castellation with the USB connector facing up.
3.3 VRaspberry Pi Pico 2 (RP2350)
Pin-compatible successor to the Pico, with twice the RAM, a choice of Arm or RISC-V cores, and the security hardware the first one lacked. Same 40-pin layout, USB at the top.
3.3 VSeeed XIAO ESP32C3
A thumbnail-sized RISC-V board with WiFi, BLE and a battery charger. The 14-pin XIAO footprint is shared across the whole family, so a SAMD21, RP2040 or nRF52840 drops into the same socket. USB-C at the top.
3.3 VSTM32F103C8T6 Blue Pill
72 MHz Cortex-M3 with real SWD debugging for about the price of a Nano. Orientation below has the USB connector at the top.
3.3 VSTM32F411CEU6 Black Pill
100 MHz Cortex-M4F with USB-C that actually enumerates, the board most people move to after a Blue Pill. Pin 1 is top-left with USB-C up.
3.3 VTeensy 4.0
600 MHz Cortex-M7 on a board the size of a postage stamp. Nothing else in the hobby space is close on raw speed. USB at the top.
3.3 V, not 5 V tolerantTeensy 4.1
A 600 MHz Cortex-M7 on a board the size of a stick of gum, with Ethernet pads, an SD socket and more serial ports than most people can use.
3.3 V, not 5 V tolerantWEMOS D1 mini (ESP8266)
ESP8266 WiFi board in a 34 x 25 mm footprint. Only one ADC and a handful of usable GPIO, several of which are boot strapping pins, the constraint that defines most D1 mini projects.
3.3 V
Microcontroller
AT89S52 (8051)
The 8051 that is still buyable and still in every embedded syllabus. Four 8-bit ports, in-system programmable, DIP-40.
4.0-5.5 VATmega328P (PDIP-28)
The chip inside the Uno and Nano, on its own in a 28-pin DIP. Useful when you want the Arduino toolchain on a bare board. The mapping between port pins and Arduino numbers is the part nobody remembers.
1.8-5.5 VATtiny85 (PDIP-8)
8 KB AVR in an 8-pin package with five usable I/O. Every pin does three or four jobs, so the whole design problem is deciding what each one gives up.
1.8-5.5 VCH32V003 RISC-V Microcontroller
A 48 MHz RISC-V part that costs about ten cents, runs from 2.7 to 5.5 V and needs one capacitor to start. Programmed over a single wire.
2.7-5.5 VMOS 6502
The 8-bit CPU behind the Apple II, C64, NES and BBC Micro, and still the usual first homebrew computer build.
5 VPIC16F877A
The PIC that taught a generation of engineering students. 33 I/O, eight ADC channels and a DIP-40 you can still breadboard.
2.0-5.5 VZilog Z80
8-bit CPU of the ZX Spectrum, MSX and CP/M era, with a scattered data bus that catches everyone wiring one by hand.
5 V
Integrated circuit
24LC256 I2C EEPROM
32 KB of non-volatile storage on two wires. The same pinout covers the whole 24Cxx family from 1 Kbit to 512 Kbit.
1.7-5.5 V74HC00 Quad NAND Gate
Four 2-input NAND gates, the cheapest way to build any logic function at all.
2-6 V (HC)74HC04 Hex Inverter
Six plain inverters. The cheapest logic chip there is, and the wrong one if your input edge is slow.
2-6 V (HC)74HC08 Quad AND Gate
Four 2-input AND gates. Same pin arrangement as the 74HC00, so the two get mixed up constantly.
2-6 V (HC)74HC138 3-to-8 Decoder
Three address lines in, one of eight outputs low. The standard way to generate chip selects in a homebrew computer.
2-6 V (HC)74HC14 Hex Schmitt Inverter
Six inverters with hysteresis. The part that turns a mushy signal into a clean edge, debounces a switch with one resistor and one cap, and makes an oscillator out of nothing.
2-6 V (HC)74HC165 Shift Register (parallel in)
Eight inputs into three microcontroller pins. The mirror image of the 74HC595, and the part you want for a bank of buttons.
2-6 V (HC)74HC245 Octal Bus Transceiver
Eight bidirectional buffers with a direction pin and a tri-state enable. What you put between a CPU bus and anything you do not fully trust.
2-6 V (HC)74HC32 Quad OR Gate
Four 2-input OR gates, in the same pin arrangement as the 74HC00 and 74HC08.
2-6 V (HC)74HC4067 16-Channel Analog Multiplexer
Turns one ADC pin into sixteen. An analog switch, not a buffer, so it passes signals both ways and brings its own resistance along.
2-6 V74HC595 Shift Register
8-bit serial-in, parallel-out shift register with a separate output latch. Three microcontroller pins buy you eight outputs, and chaining Q7S into the next chip's DS extends that indefinitely.
2-6 V (HC)74HC74 Dual D Flip-Flop
Two edge-triggered D flip-flops with preset and clear. One bit of memory, a divide-by-two, or a proper synchronizer for an async input.
2-6 V (HC)74HC86 Quad XOR Gate
Four 2-input XOR gates: a controlled inverter, a one-bit comparator and the core of every adder and CRC.
2-6 V (HC)ADS1115 16-Bit ADC
Four single-ended or two differential channels at 16 bits over I2C, with a gain stage and its own reference. What you add when the microcontroller's ADC is not good enough.
2-5.5 VBME280 Humidity, Pressure and Temperature Sensor
Three environmental measurements in a grain of rice, over I2C or SPI. Accurate enough on pressure to tell which floor of a building you are on.
1.71-3.6 VCD4017 Decade Counter
Ten outputs, one high at a time, advancing on each clock. Pair it with a 555 and you have a chaser with no code at all.
3-18 V (CMOS)CD4051 8-Channel Analog Mux
One analog pin becomes eight. Bidirectional, so it multiplexes sensors into an ADC or fans a signal back out.
3-18 V (CD4051), 2-10 V (74HC4051)DHT22 / AM2302 Humidity and Temperature Sensor
Humidity and temperature on one wire, in a plastic grille you can read in about ten lines of code. Slow, cheap and everywhere.
3.3-5.5 VDS1307 Real-Time Clock
The cheap I2C clock chip. Keeps time on a coin cell for years and drifts minutes a month, because the crystal is bare and uncompensated.
4.5-5.5 VDS18B20 Temperature Sensor
1-Wire digital thermometer. Dozens share a single microcontroller pin, each with its own 64-bit address. Flat face toward you, pins down.
3.0-5.5 VHC-SR04 Ultrasonic Rangefinder
Ping-and-listen distance sensor, 2 cm to 4 m. Four pins, 5 V only, and an echo pin that will happily feed 5 V into a 3.3 V board.
5 VHX711 Load Cell Amplifier
A 24-bit ADC built for bridge sensors, with the gain and the reference already inside. What turns four strain gauge wires into a weight.
2.6-5.5 VICL7660 Charge Pump Inverter
Turns +5 V into -5 V with two capacitors and no inductor. The cheapest way to get a negative rail for an op-amp on a single-supply board.
1.5-10 VINA219 Current and Power Monitor
Measures current and voltage on a rail up to 26 V and reports both over I2C, while running from 3.3 V itself. The part behind most USB power meters.
3-5.5 V supply, senses up to 26 VL293D Motor Driver
Quad half-bridge with built-in flyback diodes: two DC motors bidirectionally, or one bipolar stepper. Old, inefficient and still the part in every starter kit.
4.5-7 V logic / ≤36 V motorLM324 Quad Op-Amp
Four LM358s in a DIP-14, and a completely different pin arrangement from the dual. Note the supply pins are not at the corners.
3-32 V single or +/-1.5-16 V splitLM339 Quad Comparator
Four open-collector comparators. Same package as the LM324 quad op-amp, but a different pinout.
2-36 V single or +/-1-18 V splitLM358 Dual Op-Amp
The default jellybean op-amp: two channels, runs from a single supply, and cannot reach either rail.
3-32 V single or +/-1.5-16 V splitLM393 Dual Comparator
Two comparators in the same DIP-8 arrangement as the LM358 op-amp, with open-collector outputs. The two look identical on a board and are not interchangeable.
2-36 V single or +/-1-18 V splitMAX485 RS-485 Transceiver
Half-duplex RS-485 driver and receiver, the usual way to get Modbus or a long serial run off a microcontroller.
5 V (MAX3485 is the 3.3 V part)MAX6675 Thermocouple Converter
Reads a type-K thermocouple to 1024 C and hands back a 12-bit number over SPI, with cold-junction compensation already done.
3-5.5 VMAX7219 LED Display Driver
Drives eight 7-segment digits or an 8x8 matrix over three wires, with its own BCD decoder, brightness control and scanning. No refresh code at all.
4.0-5.5 VMCP23017 I2C I/O Expander
Sixteen real GPIOs over two wires, with direction, pull-ups and interrupts per pin. The PCF8574 grown up and given a register map.
1.8-5.5 VMOS 6522 VIA
Two 8-bit ports, two timers, a shift register and interrupt handling. The chip that turns a bare 6502 into a computer with I/O.
5 VMOS 6551 ACIA
Serial port for a 6502 system: a full UART with its own baud rate generator, so one crystal gives you every standard rate.
5 VNE555 Timer
The timer that refuses to die. Monostable, astable or Schmitt comparator depending on how you wire the three resistor-divider taps. Pin 1 is bottom-left of the notch.
4.5-16 VPCA9685 16-Channel 12-Bit PWM Driver
Sixteen independent 12-bit PWM channels over I2C, each with its own start and stop point. The chip under every servo and LED driver breakout.
2.3-5.5 VPCF8574 I2C I/O Expander
Eight more pins over two wires, and the chip on every I2C LCD backpack. Quasi-bidirectional outputs, which is the catch.
2.5-6 VTP4056 Li-Ion Charger
A complete single-cell lithium charger in eight pins. One resistor sets the current, and nothing else is needed, which is why it is on every USB charging module sold.
4-8 V in, 4.2 V outULN2003 Darlington Array
Seven open-collector Darlington sinks with built-in clamp diodes, for relays, solenoids and 28BYJ-48 steppers.
Inputs 5 V TTL, outputs to 50 VWS2812B Addressable LED
RGB LED with the controller on the die. Four pins, one data wire, and more ways to go wrong than any other four-pin part.
5 V data, 0.7 x VDD threshold