Part properties and datasheets

Every field under Properties comes from the part's own declaration in the library. A transformer declares turns ratio, primary inductance, coupling and VA rating, and the dialog has four fields. An LED declares a colour, and the dialog has a dropdown of real wavelengths. A resistor declares a value and that's it.

This matters because the alternative — which is what most schematic tools do — collapses every part to one free-text value box. Editing a transformer then means editing the word "Transformer", with nowhere to put the numbers that make it a transformer.

One declaration, four consumers. A property a part declares becomes: a field in this dialog, a parameter the simulator uses, a column on the bill of materials, and something the library build checks. Add it to the part and all four follow.

Field types cover what a datasheet actually gives you: engineering values (10k, 4u7, 100nF), plain numbers, ratios written the way a datasheet writes them (10:1), dropdowns, checkboxes and free text.

Some numbers follow from others, and typing them separately is how a library ends up with a "16 MHz" crystal that resonates at 12. So a property can be derived: type a transformer's turns ratio and the secondary inductance follows from N², as it physically must. Derived fields show their result read-only.

A collapsed Simulation section shows the device model the part uses and every parameter the solver will actually receive, read-only.

Read-only is the point. Every one of those numbers is produced by the properties above, and a second place to type them would be a second source of truth that quietly disagrees with the first. Showing them is what makes a wrong property visible — a transformer whose coupling sat at its default for its whole life did so because nothing ever displayed the value the solver received.

• Manufacturer, MPN and Vendor P/N — leave them blank to let the value resolve a part number automatically, or fill them in to pin a specific one.
• Choose real part… opens a picker of the actual orderable parts matching your value and footprint, and fills all three in from the row you pick.
• Do not populate (DNP) — the part stays on the board and is not fitted. It gets its own line on the BOM rather than being lumped in with fitted parts, because ordering stock nobody is going to solder is a real cost.
• Exclude from BOM — a mounting hole, a part you already own.

A pinned part number wins outright. The whole point of pinning is that the BOM stops guessing, so a parametric match that would "improve" on your choice is a wrong order and doesn't happen. Pinned lines are visibly distinguishable from matches JetCad3 made, because only one of the two carries live stock and pricing.

If the part offers more than one land pattern, Physical → Footprint switches between them by their own labels — "¼W axial, 0.4″ pitch", "0805", and so on. Changing it re-resolves the vendor match, since stock is per package.

Fields takes arbitrary key/value pairs of your own — a tolerance note, an internal part number, an approval reference. They're kept separate from the declared properties on purpose, so a field you name r can never silently become a resistance override.

Datasheet… opens the part's datasheet inside JetCad3. A PDF opens in the viewer — zoom, search, selectable text, and it works offline once you've opened it. A manufacturer landing page opens in the embedded browser instead. Anything that can't be handled, or that a CDN refuses, falls through to your system browser.

That last step is the one that matters: a 403 from a CDN is a completely normal outcome, and "nothing happened when I clicked Datasheet" is the worst possible response to it.