Pinout reference

Pin functions for the parts that get looked up most — including the boot-strap pins and voltage limits that quietly break a build.

• LM741 Op-Amp PinoutDIP-8 / SOIC-8The LM741 is the classic general-purpose operational amplifier. Eight pins: two inputs, one output, two supplies, two offset-null pins and one no-connect.
• ESP8266 PinoutESP-12E module / NodeMCU dev boardThe ESP8266 exposes eleven usable GPIO. Several carry boot-strapping duties, so which pins are safe to use is the thing most people are actually looking up.
• ATtiny85 PinoutDIP-8 / SOIC-8Eight-pin AVR with six usable I/O. Pin 1 is RESET and doubles as an I/O only if you burn a fuse that makes the chip hard to reprogram.
• Raspberry Pi GPIO Pinout40-pin 2.54 mm headerThe 40-pin header is identical across Pi 2, 3, 4, 5 and Zero. Physical pin numbers and BCM GPIO numbers are different schemes — mixing them up is the usual cause of a circuit that does nothing.
• Arduino Uno PinoutATmega328P, Uno R3 form factorFourteen digital pins, six analog, and a handful with second jobs — PWM, interrupts, SPI and I²C — which is what the pinout is usually consulted for.
• ESP32 PinoutESP32-WROOM-32 module / DevKitCThe ESP32 has far more I/O than the ESP8266, but several pins are input-only, several are tied to the internal flash, and a few decide boot mode.