Prototype Boards

A prototype board is the half of a tag that is being designed. It carries the sensors and the memory, and nothing else — no processor, no clock, no regulator, no power supply. Those come from a breakout base, which the prototype plugs into.

Base plus prototype together make a working tag that can be programmed, measured against a Joulescope and flown on a bench long before a tag-shaped board is fabricated.

The shared interface

Every prototype board mates the same way: two 1×17 pin headers, J3 and J4, matching the pair on each breakout base. That is the whole interface.

flowchart LR
  subgraph BASE["Breakout base"]
    direction TB
    MCU["Tag processor"]
    RTC["RTC"]
    REG["Regulator"]
    IFACE["Programming + measurement"]
  end
  subgraph PROTO["Prototype board"]
    direction TB
    SENSE["Sensors"]
    MEM["Memory"]
  end
  BASE === |"J3 + J4<br/>2 × 1×17 header"| PROTO

On the prototype side those headers are usually the only footprints that are not a sensor, a memory or a decoupling capacitor. UIUCBreakout has thirteen footprints in total and two of them are the connectors.

Which base, and which tag

A prototype pairs with the breakout base matching its processor family, and together they stand in for a production tag whose sensor set they share exactly.

Prototype	Sensors and memory	Breakout base	Prototypes the tag
IMUTagNandBMP581-breakout	BMM350, BMP581, LSM6DSV, GD5F2GM7RE NAND	tag-breakout-u375-smps-v1	IMUTag
UIUCBreakout	ADXL367, BMP585, AT25FF321A	tag-breakout-l432v2	UIUC tag
steval-daughter-v2	AT25FF321 flash, plus a socket for ST evaluation boards	Either	— generic

The pairing follows the processor family, which in turn follows the battery chemistry: the U375 line runs from a LiPo and the L432 line from a coin cell, and that distinction reaches all the way back into how the base hands its supply to a Joulescope.

The generic carrier

steval-daughter-v2 is the odd one out and deliberately so. Rather than carrying a fixed sensor set, it carries a socket for ST's own evaluation boards, so any sensor ST ships on a STEVAL card can be driven by the project's firmware and measured on the project's bench. It adds a flash chip of its own, since most of those cards have none.

These boards are documented from the top only. Nothing on their undersides needs showing.