Waterproof MEMS Audio Logger
Budget: $250 – $750 AUD
Overview
We are building a rugged field recording system composed of multiple submodules.
This project covers only the audio capture + local storage submodule, which will be controlled by a separate master MCU.
Your task is to design a low-cost PCB module that:
• Captures ≥120 seconds of mono audio from one waterproof MEMS microphone
• Stores the audio locally in serial flash as a WAV file
• Exposes a simple digital interface so a master MCU can control recording and download audio data
All triggering, power management, communications, and backend handling are performed elsewhere and are out of scope.
In-scope requirements
Electronics design / mechanical / form factor
• Small PCBA dedicated to audio + memory
o PCB outline provided
• 2 × mounting holes, 85 mm apart
• Designed to be compatible with IP57 system-level sealing
• Mechanical protection, enclosure, foam, magnets, potting: handled by others
• Low power design for energy system (PV + rechargeable battery) (Sub mA consumption in sleep mode)
• Energy budget for 1x acquisition, storage, transfer to master module: xx mAh including communication back to master module within yy seconds. xx/yy to be confirmed.
• Operating temperature –40°C .. +70°C
• Cost effective design
• STM32 family MCU. Alternative selection to be discussed / confirmed.
• 5+ years lifetime
Audio
• 1 × waterproof MEMS microphone (mono)
• Candidate microphone options (you may propose alternatives if clearly better/cheaper):
o PUI Audio AMM-2742-T-WP-R
o Same Sky (CUI) CMM-3424DT-26165-TR
o Infineon IM72D128
o Alternative to be discussed / confirmed
• Record format:
o WAV
o ≥120 seconds
o ≥20 kHz sampling
o 16-bit PCM preferred
Storage
• Onboard serial flash memory
• Sized to store:
o At least one full 120s WAV file
o Plus margin for retries and metadata
• Storage must be brownout-safe (no file corruption if power is removed mid-write)
Interface to master MCU
• Audio module is a slave device
• Interface options:
o SPI (preferred) or
o UART (3.3 V TTL; not RS232 levels)
• Connection via 24-pin connector
• Signals provided by master:
o +3.3 V
o GND
o Interface signals (SPI or UART)
o Optional reset / interrupt line
Control model
The module firmware shall implement a simple command-based protocol, for example:
• Start recording
• Stop recording
• Query file status / size
• Read audio data in chunks
• Delete file / clear memory
Firmware
• Based on existing vendor or open-source libraries where possible
• Responsibilities:
o Configure MEMS microphone interface
o Capture audio
o Package data as WAV
o Write/read serial flash
o Respond to master MCU commands
• No wireless, networking, or cloud logic required
• Modular firmware design
o Hardware abstractions / drivers
o Communication layer (frame layer)
o Command execution
Explicitly out of scope
• Power generation, charging, or battery management
• LTE / cellular communications
• Backend, cloud storage, dashboards
• Heartbeat, scheduling, or system health reporting
• Master MCU firmware
Deliverables
1) Architecture & feasibility
• Block diagram of audio module
• Audio + storage data flow
• Serial flash sizing justification
• Preliminary BOM with cost target
• Firmware architecture
2) Electronics
• Schematics (Altium Designer files)
• PCB layout (Altium Designer files)
• Manufacturing outputs (Gerbers/ODB++, BOM, pick-and-place)
• Bring-up and test plan
• Rough guidelines to PCB dimensions attached.
3) Firmware
• Audio capture → WAV file → flash storage
• Communication interface module (SPI or UART)
• Command execution
• Complete compliable code base
• Documentation of code and architecture
• Documentation of protocol and timing
• DMA drivers used where possible
• Each peripheral abstracted by separate module file. E.g. RAM access/non-volatile storage access, MEMS interface
• Source code preferable in C
Acceptance criteria
• Module successfully records ≥120 s mono WAV
• Audio can be reliably downloaded by master MCU
• No file corruption on abrupt power loss
• Interface protocol documented and demonstrated
Skills required
• Embedded hardware design in Altium Designer (audio + serial flash)
• MEMS microphone interfaces (PDM / I²S / ADC)
• Low-level embedded firmware (C/C++)
• SPI / UART protocol design
• Cost-constrained design
Suggested milestones
1. Architecture + BOM + interface definition
2. Schematics review
3. PCB layout complete
4. Firmware architecture review (record + readback)
5. Documentation + handover
Deliverables
1. Complete schematic, PCB layout and Gerbers.
2. Firmware source with build instructions; compiler / IDE of your choice is fine as long as it’s freely available.
3. Include one physical prototype and validation once the design packages are in hand.
4. Short test report proving the board boots, records, and transfers a WAV file.
We are building a rugged field recording system composed of multiple submodules.
This project covers only the audio capture + local storage submodule, which will be controlled by a separate master MCU.
Your task is to design a low-cost PCB module that:
• Captures ≥120 seconds of mono audio from one waterproof MEMS microphone
• Stores the audio locally in serial flash as a WAV file
• Exposes a simple digital interface so a master MCU can control recording and download audio data
All triggering, power management, communications, and backend handling are performed elsewhere and are out of scope.
In-scope requirements
Electronics design / mechanical / form factor
• Small PCBA dedicated to audio + memory
o PCB outline provided
• 2 × mounting holes, 85 mm apart
• Designed to be compatible with IP57 system-level sealing
• Mechanical protection, enclosure, foam, magnets, potting: handled by others
• Low power design for energy system (PV + rechargeable battery) (Sub mA consumption in sleep mode)
• Energy budget for 1x acquisition, storage, transfer to master module: xx mAh including communication back to master module within yy seconds. xx/yy to be confirmed.
• Operating temperature –40°C .. +70°C
• Cost effective design
• STM32 family MCU. Alternative selection to be discussed / confirmed.
• 5+ years lifetime
Audio
• 1 × waterproof MEMS microphone (mono)
• Candidate microphone options (you may propose alternatives if clearly better/cheaper):
o PUI Audio AMM-2742-T-WP-R
o Same Sky (CUI) CMM-3424DT-26165-TR
o Infineon IM72D128
o Alternative to be discussed / confirmed
• Record format:
o WAV
o ≥120 seconds
o ≥20 kHz sampling
o 16-bit PCM preferred
Storage
• Onboard serial flash memory
• Sized to store:
o At least one full 120s WAV file
o Plus margin for retries and metadata
• Storage must be brownout-safe (no file corruption if power is removed mid-write)
Interface to master MCU
• Audio module is a slave device
• Interface options:
o SPI (preferred) or
o UART (3.3 V TTL; not RS232 levels)
• Connection via 24-pin connector
• Signals provided by master:
o +3.3 V
o GND
o Interface signals (SPI or UART)
o Optional reset / interrupt line
Control model
The module firmware shall implement a simple command-based protocol, for example:
• Start recording
• Stop recording
• Query file status / size
• Read audio data in chunks
• Delete file / clear memory
Firmware
• Based on existing vendor or open-source libraries where possible
• Responsibilities:
o Configure MEMS microphone interface
o Capture audio
o Package data as WAV
o Write/read serial flash
o Respond to master MCU commands
• No wireless, networking, or cloud logic required
• Modular firmware design
o Hardware abstractions / drivers
o Communication layer (frame layer)
o Command execution
Explicitly out of scope
• Power generation, charging, or battery management
• LTE / cellular communications
• Backend, cloud storage, dashboards
• Heartbeat, scheduling, or system health reporting
• Master MCU firmware
Deliverables
1) Architecture & feasibility
• Block diagram of audio module
• Audio + storage data flow
• Serial flash sizing justification
• Preliminary BOM with cost target
• Firmware architecture
2) Electronics
• Schematics (Altium Designer files)
• PCB layout (Altium Designer files)
• Manufacturing outputs (Gerbers/ODB++, BOM, pick-and-place)
• Bring-up and test plan
• Rough guidelines to PCB dimensions attached.
3) Firmware
• Audio capture → WAV file → flash storage
• Communication interface module (SPI or UART)
• Command execution
• Complete compliable code base
• Documentation of code and architecture
• Documentation of protocol and timing
• DMA drivers used where possible
• Each peripheral abstracted by separate module file. E.g. RAM access/non-volatile storage access, MEMS interface
• Source code preferable in C
Acceptance criteria
• Module successfully records ≥120 s mono WAV
• Audio can be reliably downloaded by master MCU
• No file corruption on abrupt power loss
• Interface protocol documented and demonstrated
Skills required
• Embedded hardware design in Altium Designer (audio + serial flash)
• MEMS microphone interfaces (PDM / I²S / ADC)
• Low-level embedded firmware (C/C++)
• SPI / UART protocol design
• Cost-constrained design
Suggested milestones
1. Architecture + BOM + interface definition
2. Schematics review
3. PCB layout complete
4. Firmware architecture review (record + readback)
5. Documentation + handover
Deliverables
1. Complete schematic, PCB layout and Gerbers.
2. Firmware source with build instructions; compiler / IDE of your choice is fine as long as it’s freely available.
3. Include one physical prototype and validation once the design packages are in hand.
4. Short test report proving the board boots, records, and transfers a WAV file.