Hardware Specification

Actual Badge (Prototype / v0.1)

The badge is the product’s primary hardware artifact. Everything else is infrastructure for it.

Functional Requirements

Requirement Target Notes
Battery life ≥ 7 days continuous operation Single charge, normal duty cycle
GPS accuracy ≤ 15m from known property boundary Under open sky; degraded in dense tree cover
BLE detection range ≥ 5m reliable, ≥ 10m line-of-sight Equipment tag detection
BLE detection rate > 85% over 100 test events at 5m Exit gate metric
Upload reliability > 95% of scheduled batch uploads succeed Under normal cellular coverage
Operating temperature -10°C to 55°C Field conditions in Southeast US
Weather resistance IP54 minimum Rain and dust exposure expected
Display Worker ID + shift start time readable in sunlight E-ink; no backlight required
Form factor Wearable; lanyard or badge clip compatible Not to exceed credit card footprint by > 2x

Component Stack

MCU — Primary candidates

Option A: Nordic nRF52840

  • Architecture: ARM Cortex-M4F, 64 MHz
  • RAM: 256 KB, Flash: 1 MB
  • BLE: 5.0 (scanner + peripheral in simultaneous roles)
  • Power: Deep sleep ~1.5 µA; BLE advertising ~4 mA; active ~5 mA
  • SDK: Zephyr RTOS (recommended) or Nordic nRF5 SDK
  • Reason to prefer: Best-in-class BLE power profile; Zephyr has strong community and Blues Wireless examples

Option B: Espressif ESP32-C3

  • Architecture: RISC-V single-core, 160 MHz
  • RAM: 400 KB, Flash: 4 MB (module dependent)
  • BLE: 5.0
  • Power: Deep sleep ~5 µA; active ~80 mA (higher than nRF; manage with duty cycle)
  • SDK: ESP-IDF or Arduino framework
  • Reason to prefer: Lower cost, faster firmware prototyping, large community
  • Reason to prefer nRF instead: Better power efficiency for 7-day target

Selection note: MCU is finalized during Phase 2 by the firmware engineer. The firmware architecture document covers both paths. The hardware spec will be updated to reflect the final selection after the first 72-hour battery test.

Cellular + GPS Module — Blues Wireless Notecard

Model: NOTE-WBEX (LTE-M/NB-IoT + GPS, worldwide)

  • Connectivity: LTE-M (Cat-M1) and NB-IoT on global bands
  • GPS: u-blox SARA-R4 integrated (same module)
  • Interface to MCU: I2C or UART (I2C preferred for simplicity)
  • API: JSON over I2C/UART — no AT commands; human-readable request/response
  • Data routing: Notehub (Blues cloud router) → HTTPS webhook to ingest API
  • Power: Active ~400 mA (cellular transmit peak); idle ~7 mA; sleep ~8 µA
  • Operating temp: -40°C to 85°C

Notehub routing configuration: Events from the Notecard are routed through Blues Notehub to a configurable HTTPS endpoint. The ingest API URL and API key are provisioned in Notehub at device registration time. The MCU sends events to the Notecard as JSON; the Notecard batches and uploads them to Notehub; Notehub forwards to the ingest API.

Why Blues Notecard:

  • Eliminates the need to manage SIM cards, APN configuration, or cellular provider relationships
  • GPS is collocated with cellular in one module — no separate GPS chip required
  • JSON-native API dramatically reduces firmware complexity
  • Blues Developer Relations is reachable and responsive (community forum + Discord)
  • Dataplan included in hardware cost at low volumes; bulk plan available at scale

Single-source risk: See [docs/roles/10-hardware-ops-supply-chain.md] for mitigation strategy and alternative modem candidates.

BLE Scanner (on MCU)

The MCU BLE radio operates in scanner role to detect equipment tag advertisements.

  • Scan interval: 200ms (configurable to balance power vs. detection latency)
  • Scan window: 50ms per interval
  • Detection criterion: RSSI > -70 dBm (configurable; corresponds to ~5m range in open air)
  • Tag identification: by Bluetooth MAC address or UUID (protocol TBD by firmware engineer; MAC preferred for simplicity at prototype)
  • Event generated: ble_proximity event when a known tag MAC/UUID is detected above threshold

Accelerometer

Purpose: Motion state classification (moving vs. stationary). Used to:

  • Tag GPS events with motion context
  • Suppress spurious GPS pings during stationary periods (power optimization)
  • Detect shift-end condition (extended stationary period at end of day)

Candidate: Bosch BMA400 or STMicroelectronics LIS2DH12

  • Both support hardware low-power wake-on-motion interrupt
  • SPI or I2C interface
  • Current draw in low-power mode: < 5 µA

E-ink Display

Purpose: Worker-facing status without requiring a phone or backlit screen.

Displays:

  • Worker ID (assigned at shift start)
  • Shift start time
  • Badge status: charging / active / offline (no cellular)

Candidate: Waveshare 2.13” e-ink HAT (212 × 104, black/white) or equivalent

  • SPI interface
  • Refresh rate: ~2 seconds (acceptable for shift-start assignment; not used for real-time data)
  • Power: ~26 mW active; ~0 µW holding static image

Power

Battery target: Lithium polymer (LiPo), 2000–3000 mAh Charging: USB-C, 5V charging circuit Power management: Hardware duty cycling on MCU + Notecard sleep modes

Rough power budget (for 7-day target at 2000 mAh):

Mode Current draw Duty cycle Avg contribution
MCU active (GPS + BLE scan) ~10 mA 20% 2.0 mA
Notecard cellular upload ~400 mA 0.5% (2 min/30 min) 2.0 mA
Notecard idle ~7 mA 79.5% 5.6 mA
MCU sleep ~2 µA 0% (not used for main loop) ~0 mA
Estimated average     ~9.6 mA

At 2000 mAh ÷ 9.6 mA = ~208 hours ≈ 8.7 days of operation.

This is a first-order estimate. Actual will be lower due to GPS cold starts, startup current spikes, and accelerometer overhead. Firmware engineer validates against the 7-day exit gate.

Enclosure

Version at prototype: 3D-printed PLA or PETG

  • IP54 rating is the target (see Industrial Designer role doc)
  • Dimensions: TBD by Industrial Designer during Phase 2 optional engagement
  • Mounting: Lanyard attachment point + belt clip hole
  • At prototype: enclosure is functional but not production-grade

Note: Do not engage the Industrial Designer until the firmware exit gate is met. The enclosure design should follow a working firmware, not precede it.

Equipment Tag (BLE Beacon)

The equipment tag is a passive BLE beacon attached to a truck, trailer, or mower. It is not made by Actual. It advertises over BLE on a standard profile.

Requirements

Requirement Target
BLE version 5.0
Advertisement interval ≤ 200ms (ensures fast detection by badge scanner)
RSSI at 1m ≥ -50 dBm
Battery life ≥ 12 months
Weather resistance IP65 minimum (outdoor equipment exposure)
Mounting Adhesive + optional screw mount
Form factor < 50mm × 50mm × 15mm

Candidate Devices

Option A: Ruuvi Tag (RuuviTag Pro)

  • IP67, weatherproof, CR2477 battery (~12-18 months)
  • Open-source firmware; configurable advertisement interval
  • Available in bulk from Ruuvi.com

Option B: Nordic Semiconductor Thingy:53 (repurposed)

  • Development kit option only; not a production recommendation

Option C: Generic iBeacon / Eddystone beacon (various manufacturers)

  • Search: “IP65 BLE beacon industrial” on Alibaba or Mouser
  • Verify: advertisement interval, battery life, temperature rating before ordering
  • Risk: firmware is not field-upgradeable on generic beacons

Recommended for prototype: Ruuvi Tag. Known quality, IP67, field-proven. Switch to a lower-cost generic at scale once detection is validated.

Tag-to-Equipment Assignment

Each tag has a MAC address. The MAC address is recorded at provisioning and mapped to a piece of equipment (e.g., truck-001, trailer-003, mower-005) in the device registry in PostgreSQL.

When a badge detects a tag MAC, the cloud system resolves the MAC to equipment ID. The engineer does not hard-code equipment names in firmware — firmware reports the MAC address; the cloud resolves identity.

Hardware BOM (Prototype Estimate)

Component Unit cost (est.) Qty per badge kit Notes
Blues Notecard NOTE-WBEX $49.00 1 Retail; bulk pricing available
Blues Notecarrier (breakout board) $12.00 1 Dev use; custom PCB replaces this in v1
nRF52840 module (Adafruit Feather nRF52840) $25.00 1 Prototype; custom PCB in v1
LiPo battery 2000 mAh $10.00 1  
USB-C charging board $5.00 1  
E-ink display (2.13”) $15.00 1  
Accelerometer module $3.00 1  
Misc (connectors, wire, headers) $5.00 1  
3D-printed enclosure $5.00 1 Material cost only
Badge total (prototype) ~$129.00    
Ruuvi Tag (equipment tag) $35.00 per equipment unit  

Per crew deployment (5 crew members, 4 equipment units):

  • 5 badges × $129 = $645
  • 4 equipment tags × $35 = $140
  • Total hardware per crew: ~$785

This is prototype BOM. Production PCB integration of MCU + Notecard + sensors will reduce the badge BOM to an estimated $40–$60 per unit at 100-unit volume.