The library — why reuse beats reinvention

In BWF1 you saw the shape of a product. Now you'll build one from parts that already exist. The secret to fast, reliable product development isn't cleverness — it's reuse.

Forge keeps a library of proven, ready building blocks, organised on four "shelves":

• Subcircuits — reusable circuit blocks. Each is a small, correct wiring for one job: "read a DHT22 sensor," "boost 3.7 V to 5 V," "drive a NeoPixel strip." Forge has 40-plus of them.
• Package layouts — the physical footprint and dimensions of a component or module (how big it is, where its pins and holes are). This is what lets the 3D designer cut the right holes.
• Firmware templates — starter code for a part, so the finished product actually runs.
• Domain designs — whole 3D products you can start from: a lamp, a speaker, a planter, a weather station, a storage tray, and more.

Intermediate product development is mostly composition: pick the right blocks and connect them correctly. This module walks each shelf.

When you describe a product in Forge Design, it doesn't invent circuitry from first principles. It searches the library, finds the subcircuit that matches each job, and wires them together — the right pins, the right power, the right pull-ups.

That has two big benefits:

• It's correct. Each block has already been drawn and checked. You're standing on tested work, not debugging from scratch.
• It's fast. A product becomes "which blocks, connected how" instead of hundreds of tiny decisions.

Your job as the developer shifts up a level: know what blocks exist, and describe your product so the right ones get picked. The clearer you are about what it senses, what it does, and how it's powered, the better Forge's first pass.

The rest of this module builds your fluency shelf by shelf — sensing, power and outputs, the buses that connect them, and the whole-product 3D designs — then finishes with a composite block that bundles several subcircuits into one.