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.
• LM358 PinoutDIP-8 / SOIC-8The LM358 is a dual op-amp in an 8-pin package: two independent amplifiers sharing one pair of supply pins. It is the usual choice for single-supply circuits because its inputs work all the way down to ground.
• 555 Timer Pinout (NE555)DIP-8 / SOIC-8The 555 timer in its 8-pin form: two comparators with thresholds at one third and two thirds of the supply, a flip-flop and a discharge transistor. Wire pins 2, 6 and 7 one way for a one-shot pulse, another way for an oscillator.
• 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 headerEvery 40-pin Pi (2, 3, 4, 5, Zero) puts power, ground and each GPIO on the same pins. Physical pin numbers and BCM GPIO numbers are different schemes — mixing them up is the usual cause of a circuit that does nothing.
• Raspberry Pi Pico Pinout40-pin module, 2.54 mm pitch, castellatedThe Pico puts the RP2040 on a 40-pin board: 26 of its 30 GPIO on the edge, three of them with an ADC, plus power pins that let it run from USB, a battery or an external rail.
• 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.
• Arduino Nano Pinout30-pin board, two rows of 15, 0.6 in apartThe Nano is an Uno's ATmega328P on a 30-pin board that plugs into a breadboard or a 0.6 in socket: the same I/O as the Uno, plus two analog-only inputs, A6 and A7.
• 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.