OpenParcelBox/hardware/BOM.md

Bill of Materials (BOM)

This bill of materials lists the components currently required or planned for OpenParcelBox.

Reused Boks One parts are separated from new components to make reverse engineering and PCB design easier to track.

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Main Controller

Reference	Description	Quantity	Status
XIAO-NRF52840	Seeed Studio XIAO BLE nRF52840	1	Validated

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Reused Boks One Parts

Description	Quantity	Status
Front panel	1	Reused
KR-S79 lock mechanism	1	Reused
Battery compartment, 8x AAA	1	Reused
Internal wiring	As needed	Reused when suitable

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Keypad

The original keypad PCB is replaced by a new PCB compatible with the original front panel.

Description	Quantity	Status
Push buttons	12	New PCB
2x6 physical keypad layout	1	Planned production layout
4x4 development matrix keypad	1	Validated for firmware development

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NFC

The preferred NFC design uses the controller integrated in the nRF52840.

Description	Quantity	Status
NFC antenna, 13.56 MHz	1	To design
NFC matching network	1	To design

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Lock Control

The lock opens when a positive 8 to 24 V pulse is applied to the SIG input.

Reference	Description	Quantity	Status
Logic-level P-channel MOSFET or equivalent high-side driver	SIG input driver	1	To select
Bias resistors	According to schematic	TBD	To define

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Indicators and Audible Feedback

The original PCB LEDs are not considered reusable in the current plan.

Description	Quantity	Status
Red LED	1	To select
Green LED	1	To select
Blue LED	1	To select
Active 3.3 V buzzer	1	Validated
Buzzer transistor driver	1	Validated concept

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Power Supply

Reference	Description	Quantity	Status
12 V to 5 V buck converter	DC/DC converter	1	To select
Battery voltage measurement circuit	Battery monitor	1	To design
Power protection circuit	Input protection	1	To define

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Electrical Protection

Reference	Description	Quantity	Status
TBD	Reverse-polarity protection	1	To select
TBD	ESD protection	TBD	To select

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Connectors

Reference	Description	Quantity	Status
TBD	Keypad connector	1	To define
TBD	Lock connector	1	To define
TBD	Battery connector	1	To define

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PCB

Reference	Description	Quantity	Status
OPB-PCB-V1	OpenParcelBox main board	1	In design

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Hardware Constraints

Power Supply

• Power is provided by the original 8x AAA battery pack.
• The lock is powered directly by the battery pack.
• The Seeed Studio XIAO is powered through a 12 V to 5 V buck converter.
• A common ground is used across the whole system.

Lock

• Supply: 8x AAA battery pack.
• Opening command: positive pulse on SIG.
• Opening validation: COM/NC state change.
• A fixed delay must not be used as the only opening confirmation.

Keypad

• Production physical layout: 2x6.
• Development keypad: 4x4 matrix.
• The production keypad will use a custom PCB compatible with the original front panel.

NFC

• Use the NFC controller integrated in the nRF52840.
• Integrate the NFC antenna on the PCB if validation confirms this path.

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Remaining Decisions

High priority:

• NFC antenna design.
• High-side lock driver selection.
• Buck converter selection.
• LED selection.
• Battery measurement circuit design.

Medium priority:

• Connector selection.
• PCB placement.
• ESD protection.

Low priority:

• Power optimization.
• Component count reduction.
• Compatibility with other hardware variants.

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Validation History

V0

• Seeed Studio XIAO BLE nRF52840 selected.
• Zephyr RTOS selected.
• Zigbee communication selected.
• Original front panel retained without irreversible modification.
• KR-S79 lock mechanism retained.
• 8x AAA battery compartment retained.
• Opening validation through COM/NC selected.
• Lock command through a positive pulse on SIG selected.
• Production keypad planned as a 2x6 physical layout on a custom matrix PCB.
• nRF52840 integrated NFC controller selected as the preferred path.
• Active buzzer selected and validated through a transistor driver.
• XIAO power through a 12 V to 5 V buck converter selected.