Reference

74HC595 pinout and how it turns 3 microcontroller pins into 8 extra outputs, plus the latch-pulse mistake that trips up almost everyone.

CD4017 pinout, why its outputs aren’t in numeric pin order, and how it pairs with a 555 for the classic LED chaser circuit.

LM741 pinout, why it needs a split supply unlike the LM358, and where offset null and slew rate actually matter.

SSD1306 OLED pinout for both the common I2C and SPI variants, and the driver-chip mismatch that causes most blank-screen problems.

L298N breakout board pinout, wiring, and the onboard 5V jumper mistake that damages a lot of these boards early on.

A labelled reference to the Raspberry Pi Pico and Pico W’s 40-pin GPIO header, including power, ADC, and the four pins that aren’t what they look like.

SG90 micro servo wire colours, pinout, and the power-supply mistake that causes most jittering and reset problems.

2N2222 pinout for the modern TO-92 package, why it’s usually a PN2222A underneath, and what changes on the older metal-can version.

DHT11 and DHT22 pinout, wiring, and the timing quirks of their single-wire protocol that cause most read failures.

LM358 pinout, why its single-supply design differs from a classic split-supply op-amp, and where it trips people up.