The Pinouts Book is a free digital book created for designers and engineers as a quick reference for remembering the different pinout functions in your electronics projects.

The book covers 130 commonly used components (view list), such as connectors, single board computers, dev boards, memory cards, microcontroller chips, and more.

If you need more technical information, each page has a link at the top (e.g. pinouts.org/XXX), and these redirect to official datasheets / specifications.