Editing: BHI385_Molecule v12

Field: Description

# BHI385 + BMM350 Combo Molecule — Hardware Reference

16×16 mm combo breakout carrying a Bosch BHI385 smart-sensor hub (9-DOF fusion engine) and a BMM350 magnetometer on the BHI's internal auxiliary I²C bus. This is the target board for `fw_arm`'s **BHI385 combo** sensor (sensor_id `0x31` in the wire protocol).

- **Source:** [adom-inc/bosch-molecules/Molecule_BHI385-BMM350_bosch_v1](https://github.com/adom-inc/bosch-molecules/tree/main/Molecule_BHI385-BMM350_bosch_v1) — imported 2026-04-17
- **KiCad project:** `Molecule_BHI385-BMM350_bosch_v1.kicad_pro`
- **Wiki page:** [molecules/bhi385-molecule-v12-607000](https://wiki-ufypy5dpx93o.adom.cloud/wiki/molecules/bhi385-molecule-v12-607000)
- **Board:** 17 contacts, silk revision `V1: 2025-09-10`, silkscreen title `BHI385+BMM350`
- **ICs:** U1 = BHI385 (Bosch LGA-20, 2.5 × 3.0 × 0.95 mm), U2 = BMM350 (Bosch BGA-9 WLCSP)

> **Mechanical/electrical twin of the BHI360 combo.** Netlist, component placement, silk, and all strap options are identical. The only real differences: the U1 part number is BHI385 (not BHI360), the date stamp is `2025-09-10` (not `2025-09-03`), and the demo firmware expects this board at I²C address **0x29** (not 0x28) — which you achieve via the *opposite* strap bridge. See **[../molecule_bhi360_bmm350/README.md](../molecule_bhi360_bmm350/README.md)** for the full component table, aux-bus wiring, power architecture, and bring-up flow — all of those apply identically. This file documents only the BHI385-specific differences.

## What's different vs the BHI360 combo

### Silkscreen title + date stamp

- BHI360 molecule: `BHI360+BMM350`, `V1: 2025-09-03`
- **BHI385 molecule:** `BHI385+BMM350`, `V1: 2025-09-10`

If two unlabeled boards sit side-by-side on the bench, that is the easiest way to tell them apart without pulling out a loupe.

### Target I²C address: 0x29

Demo firmware (`fw_arm`) expects this molecule at **0x29**. The address strap works the same way, but you bridge the *other* option:

| Strap | HSDO tied to | I²C address |
|---|---|---|
| Bridge MC12 ↔ MC3 (silk `0x28`) | +VDDIO (HIGH — via R5) | 0x28 *(this would be the BHI360 sibling)* |
| **Bridge MC11 ↔ MC3 (silk `0x29`)** | GND (LOW) | **0x29** ← *required for this molecule* |

Schematic annotation on the board: *"HSDO (I2C ADD Select). Jumper to GND (LOW): 0x29. Jumper to VDDIO (HIGH): 0x28. Reset Active-LOW."*

### Firmware blob

Upload uses **`Bosch_Shuttle3_BHI385_bsxsam_lite.fw`** (vendored as `firmware/sensors/bhi385_sdk/Bosch_Shuttle3_BHI385_bsxsam_lite.fw.h`) — the BHI385 BSX-SAM-Lite fusion firmware. This is a different blob than the BHI360's `Bosch_Shuttle3_BHI360_BMM350C.fw`; do not cross-load.

## Wiring to the Arm RM2 I²C bus

Identical to the BHI360 combo, with the address-strap swap:

```
Combo MP3 (VDD)  ──── +1.8 V rail
Combo MP2 (VDDIO)──── RM2 +3V3
Combo MP1 (GND)  ──── RM2 GND
Combo MC4 (HSDA) ──── RM2 GPIO4 (I²C0 SDA, shared bus)
Combo MC5 (HSCL) ──── RM2 GPIO5 (I²C0 SCL, shared bus)
Combo MC2 (HIRQ) ──── (optional)
Combo MC1 (RST)  ──── (optional; if driven, pull high through 10 kΩ)
```

**Solder-bridge MC11 ↔ MC3** (strap to GND / silk `0x29`). **Do not** bridge MC12 — that is the BHI360's strap.

## BHI360 / BHI385 coexistence check

Both molecules share I²C lines on the arm bus with:
- BMI270 @ 0x68, BMA400 @ 0x14, BMA580 @ 0x18, standalone BMM350 @ 0x15
- This BHI385 @ 0x29 and the sibling BHI360 @ 0x28

No collisions. But if **either** BHI combo's address strap is mis-set, you'll either (a) see a duplicate at 0x28 or 0x29, or (b) find the BHI385 missing while the BHI360 scans fine. Verify both straps under magnification before powering the bus.

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