2 layers139.7 × 73.7 mm
2 layers69 × 54 mm
Audio and microphone
jamesmu03/tympanometer1A low-cost tympanometer designed to diagnose hearing loss in children, developed as part of the Duke BME Design Fellows program at Duke University's Pratt School of Engineering under the supervision of Dr.
- Size
- 69 × 54 mm
- Copper layers
- 2
- Thickness
- 1.6 mm
- Parts
- 40
- Nets
- 24
- Pads
- 125
- Tracks, vias
- 128, 8
- Pours
- 2
- Routed
- Yes
- KiCad
- KiCad 9.0 (file 20241229)
- Created
- 15 Jan 2026
- Updated
- 20 Apr 2026
Overview
Audio and microphone is an open-source printed circuit board by jamesmu03, from the jamesmu03/tympanometer repository on GitHub. It is a 2-layer board of 69 × 54 mm with 40 parts on 24 nets, routed with 128 tracks and 8 vias.
It is built around the LM4875MM. Its parts include 17 capacitors, 14 resistors, 4 connectors and 3 ICs. It belongs with the audio and music boards and the AVR (ATmega, ATtiny) boards of this library.
Main components
1README
README.mdTympanometer
A low-cost tympanometer designed to diagnose hearing loss in children, developed as part of the Duke BME Design Fellows program at Duke University's Pratt School of Engineering under the supervision of Dr. Mark Palmeri, MD PhD.
- Duke BME Designers Develop a New Tool to Inexpensively Diagnose Hearing Loss in Children
- Preventing Childhood Hearing Loss Worldwide
Team
Iris Ye · Alisha Gupta · James Mu
Repository Structure
This repo has three active branches, one per contributor:
| Branch | Owner | Focus |
|---|---|---|
main | James Mu | Firmware, OLED display integration, microphone PCB |
| (Alisha's branch) | Alisha Gupta | Audio/microphone analog circuit PCB |
| (Iris's branch) | Iris Ye | Isolated microphone PCB and analog filtering |
What We've Built
Firmware & OLED Display — James Mu
Integrated a GME12864-13 (128×64 SSD1306) OLED display into the device running on the nRF52833 DK under Zephyr RTOS. The display renders a real-time tympanogram trace with a split-zone layout:
- Yellow zone (rows 0–15): ear canal volume (ECV), static admittance (SA), and peak pressure (PPP)
- Blue zone (rows 16–63): tympanogram curve plotted from −400 to +200 daPa
The firmware supports all five standard tympanogram curve types (A, As, Ad, B, C) and currently uses physiologically accurate simulated data. Real ADC input will replace the simulation when the analog front-end is complete.
A custom 3×5 bitmap font is used to minimize flash footprint.
Hardware:
- MCU: nRF52833 DK
- Display: GME12864-13 OLED (SSD1306, I2C at 0x3C)
- I2C pins: SDA → P0.27, SCL → P0.26
Analog Circuitry — Alisha Gupta & Iris Ye
First-iteration PCB designs for the microphone and audio signal chain, focused on filtering out 60 Hz noise from the microphone signal. The team has been exploring different analog filter architectures (including a notch filter redesign) to isolate the tympanometry probe tone from interference.
Key components include:
- LM4875MM audio amplifier (SOP-8)
- TLV313IDBVT op-amps (×2, TSOT-23-5) for active filtering
- 0603 SMD passive components throughout
A full bill of materials is in audio_and_microphone/BOM.csv.
Build & Flash (Firmware)
west build -b nrf52833dk/nrf52833
west flashRequires a Zephyr RTOS environment set up with the nRF Connect SDK.
This README was drafted with the assistance of Claude (Anthropic) based on information provided by the team.
Parts
40| Qty | Value | Footprint | References |
|---|---|---|---|
| 14 | 0.1u | footprints:CAPC17595_95N_KEM-M | C1, C2, C3, C4, C5, C6, C9, C10, C11, C12, C13, C14, C16, C17 |
| 3 | Conn_01x02 | Connector_PinHeader_2.54mm:PinHeader_1x02_P2.54mm_Vertical | J1, J3, J4 |
| 2 | 1.0u | footprints:CAPC17595_95N_KEM-M | C7, C8 |
| 2 | 27k | footprints:RC0603N_YAG-M | R9, R12 |
| 2 | 6.8K | footprints:RC0603N_YAG-M | R1, R2 |
| 2 | TLV313IDBVT | Package_TO_SOT_SMD:TSOT-23-5 | U1, U3 |
| 1 | 0.2u | footprints:CAPC17595_95N_KEM-M | C15 |
| 1 | 1.5K | footprints:RC0603N_YAG-M | R5 |
| 1 | 100K | footprints:RC0603N_YAG-M | R4 |
| 1 | 10k | footprints:RC0603N_YAG-M | R10 |
| 1 | 13.3k | footprints:RC0603N_YAG-M | R11 |
| 1 | 150k | footprints:RC0603N_YAG-M | R8 |
| 1 | 22K | footprints:RC0603N_YAG-M | R13 |
| 1 | 300 | footprints:RC0603N_YAG-M | R6 |
| 1 | 6.2K | footprints:RC0603N_YAG-M | R7 |
| 1 | 6.98K | footprints:RC0603N_YAG-M | R3 |
| 1 | 820K | footprints:RC0603N_YAG-M | R14 |
| 1 | Arduino_Uno_R3_Shield | arduino-kicad-library:Arduino_Uno_R3_Shield | A** |
| 1 | Conn_01x03 | Connector_PinHeader_2.54mm:PinHeader_1x03_P2.54mm_Vertical | J2 |
| 1 | LM4875MM | footprints:SOP65P490X110-8N | U2 |
The 39 most common of 40 parts.
Questions
How big is the Audio and microphone PCB?
It measures 69 × 54 mm and has 2 copper layers, 1.6 mm thick.
What parts does the Audio and microphone use?
40 parts, built around the LM4875MM. The full list of its parts is on this page, with links to each part's symbol and footprint where PCBKit's library has them.
Where can I download the Audio and microphone KiCad files?
From the jamesmu03/tympanometer repository on GitHub, at the commit this page was made from: the board is audio_and_microphone/audio_and_microphone.kicad_pcb and its schematic audio_and_microphone/audio_and_microphone.kicad_sch. PCBKit opens the board in the browser, with nothing to install.
Can I use the Audio and microphone design in my own project?
Its repository states no licence, so its author keeps all rights: ask jamesmu03 before reusing the design.
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