Circuit Design Principles
These pages set out how a Scadys board is designed so that a prototype can be assembled by hand, probed, isolated block by block, programmed and repaired. Every Scadys prototype is built in-house, on a hot plate and with hot air, and is brought up on the bench by one engineer. A board that ignores these principles still works when it is perfect. It is very hard to bring up when it is not, and a first prototype never is.
| Principle | Covers |
|---|---|
| Test points | Which nets get a test point or a through-hole ring, which face they sit on, and which nets are probed at component pads instead. |
| Isolating circuit blocks with DNP parts | Fitting fallback circuits but leaving them disconnected, select links, and current-measurement links. |
| Part sizes for hand assembly | The 0603 rule, the packages that are excluded, paste printing and orientation checks on small parts. |
| Double-sided boards | What goes on each face, the reflow order, and what a populated face does to stencilling and rework. |
| Bed-of-nails interfaces | The assembler's test and programming jig, and what it needs from the board. |
| Programming interfaces and connectors | The 6-pin ESP-PROG connector, programmer power, USB sockets on maker versions and companion-module access. |
| Thermal relief on through-hole pads | Making hand-soldered through-hole pads on a copper pour solderable with an iron. |
These principles are written for the prototype. A production board may remove parts that only serve bring-up, such as a current-measurement resistor, and each page says where that applies.