Performance and environment monitoring for cello practice and instrument care.
Photon 2 · PDM Microphone · DHT20 · MicroOLED · Initial State · Blynk · PySide6
The Cello Analyzer is an embedded and cloud-connected device designed to support both musical performance and instrument care. It combines a PDM microphone, a DHT20 temperature and humidity sensor, a SparkFun MicroOLED display, an RGB LED, a buzzer, Particle Cloud publishing to Initial State, and a Blynk mobile interface.
The device has two main purposes:
- Monitor live playing dynamics by estimating sound level, classifying volume into musical dynamic markings (
pp,p,mp,mf,f,ff), and displaying a waveform on the OLED. - Monitor cello storage conditions by measuring temperature and humidity, comparing them to safe ranges, and signaling whether the environment is safe, cautionary, or problematic.
This project helps a musician quickly understand how loudly they are playing while also tracking whether the instrument is stored in a healthy environment.
- Live microphone waveform displayed on the OLED performance page
- Real-time volume estimation from PDM audio samples
- Dynamic classification into
pp,p,mp,mf,f, andff - RGB LED feedback for both performance and environment states
- Buzzer cue when the dynamic crosses between the soft group (
pp,p,mp) and the louder group (mf,f,ff) - Four OLED pages:
- Performance
- Dynamic Trend
- Current Environment
- Environment History
- Particle Cloud variables for remote status viewing
- Particle event publishing for Initial State integration
- Blynk dashboard support, including a virtual page-change button
| Component | Pin | Purpose |
|---|---|---|
| PDM Microphone | A0 |
Microphone clock signal |
| PDM Microphone | A1 |
Microphone data input |
| RGB LED Red | D2 |
Red channel for visual feedback |
| RGB LED Green | D3 |
Green channel for visual feedback |
| RGB LED Blue | D4 |
Blue channel for visual feedback |
| Piezo Buzzer | A5 |
Audio feedback for dynamic transitions |
| Enable Switch | D6 |
Turns the system on or off |
| Pushbutton | D7 |
Cycles through OLED pages |
| MicroOLED Display | I2C |
Displays waveform, dynamics, and environment data |
| DHT20 Sensor | I2C |
Measures temperature and humidity |
| LiPo Battery | JST battery connector |
Portable power supply |
Prototype views:
Connect the Photon 2, PDM microphone, DHT20 sensor, MicroOLED display, RGB LED, buzzer, switch, pushbutton, and LiPo battery according to your wiring diagram.
- Install Visual Studio Code
- Install the Particle Workbench extension
- Sign into your Particle account
- Connect the Photon 2 by USB
- Use
Particle: Configure Project for Device - Select
Photon 2 - Choose Device OS
6.3.5
This firmware was developed and tested on Device OS 6.3.5.
The project dependencies are listed in project.properties:
ArduinoJsonblynkDHT20_I2C_ParticleMicrophone_PDMSparkFunMicroOLED
This project prints:
- startup messages
- raw microphone amplitude values
- volume percentages
- dynamic classifications
- DHT20 warnings
- Blynk page-change debugging messages
You can open the serial monitor from Particle Workbench or run:
particle serial monitor --followThe project uses Particle.publish() to send:
- volume
- dynamic level
- temperature
- humidity
These values are combined into a single JSON payload and forwarded to Initial State through a Particle webhook.
Create a Blynk template and device, then copy:
- Template ID
- Template Name
- Auth Token
Paste those into src/celloanalyzer.cpp, then configure Blynk datastreams to match the virtual pins used by the firmware.
The OLED interface includes four pages:
Performance- live waveform
- current dynamic label
- current volume percentage
Dynamic Trend- percentage of time spent in
pp,p,mp,mf,f, andff
- percentage of time spent in
Current Environment- current temperature
- current humidity
Environment History- temperature high/low
- humidity high/low
The waveform is drawn on the first page by drawPerformanceScreen() in src/celloanalyzer.cpp.
This project uses Particle.variable() to expose live device values to the Particle Cloud and Particle.publish() with a webhook to send data to the Initial State dashboard.
The project publishes data every 2500 ms using millis()-based timers.
The event name is:
Cello_Analyzer
The JSON payload is built in publishInitialStateData() and has this structure:
[
{"key":"volume","value":42},
{"key":"temperature","value":23.2},
{"key":"humidity","value":55.4},
{"key":"dynamic","value":"pp"}
]
| Tile Name | Tile Type | Details |
|---|---|---|
| Humidity | Gauge Tile | Displays current humidity with a visible safe-range region |
| Temperature | Gauge Tile | Displays current temperature in Celsius using a thermometer-style visualization |
| Volume | Line Graph Tile | Displays historical trend of volume percentage over time |
| Current Dynamic | Summary Tile | Displays the current dynamic label such as pp, mp, or f |
| Most Frequent Dynamic | Summary Tile | Displays the most commonly occurring dynamic over recorded history |
| Humidity | Line Graph Tile | Displays historical humidity trend over time |
| Temperature | Line Graph Tile | Displays historical temperature trend over time |
| Event Name / Variable | Details |
|---|---|
Cello_Analyzer |
Particle event published to Initial State; includes volume, temperature, humidity, and dynamic |
mode |
Current page or operating mode |
dynamic |
Current musical dynamic label |
volume |
Current volume percentage |
raw |
Smoothed microphone amplitude before normalization |
temp |
Current temperature in Celsius |
hum |
Current relative humidity percentage |
alert |
Environment alert state: OK, WARN, ALERT, or ERROR |
celloHealth |
Descriptive cello health message such as Cello safe, Dry air, Humid air, Too cold, Too warm, or Sensor err |
The Blynk mobile app provides a phone-based dashboard for monitoring and controlling the Cello Analyzer remotely.
| Datastream Name | Virtual Pin | Data Type | Suggested Range / Notes |
|---|---|---|---|
| Switch Mode | V0 |
Integer | Min 0, Max 1 |
| Current Mode | V1 |
String | Displays current OLED mode |
| Dynamic | V2 |
String | Displays current musical dynamic |
| Current Volume | V3 |
Integer | Min 0, Max 100, unit % |
| Current Temperature | V4 |
String | Displays current temperature |
| Current Humidity | V5 |
String | Displays current humidity |
| Current Health | V6 |
String | Displays cello health message |
| Current Environment | V7 |
String | Displays environment status |
| Dynamic History | V8 |
String | Displays recent dynamic history summary |
| Temp History | V9 |
String | Displays temperature high/low summary |
| Humidity History | V10 |
String | Displays humidity high/low summary |
| Virtual Pin | Purpose | Suggested Widget |
|---|---|---|
V0 |
Virtual page-change button | Button |
V1 |
Current mode label | Labeled Value |
V2 |
Current dynamic label | Labeled Value |
V3 |
Current volume percent | Display |
V4 |
Current temperature | Display |
V5 |
Current humidity | Display |
V6 |
Cello health message | Display |
V7 |
Environment alert level | Display |
V8 |
Dynamic history summary string | Display |
V9 |
Temperature high/low summary string | Display |
V10 |
Humidity high/low summary string | Display |
Mode and dynamic are sent to Blynk as strings because they are text labels. Temperature and humidity are also currently formatted as simple display values, though they could be converted to numeric datastreams for gauges and charts.
The firmware is organized into the following major sections:
- Variables and Libraries
- Microphone and Volume Processing
- RGB LED and Buzzer Feedback
- OLED Functions
- Environment Sensing
- Setup
- User Input and Mode Changes
- Cloud and Mobile Output
- Main Loop
The code is located in src/celloanalyzer.cpp.
Important timing values in the current firmware:
- OLED update interval:
2500 ms - Blynk update interval:
2500 ms - Initial State publish interval:
2500 ms - DHT20 read interval:
2500 ms - Serial raw print interval:
1000 ms - Button debounce interval:
200 ms - Dynamic max decay check interval:
8000 ms
A PySide6 desktop version of the project is included in desktop_dashboard.
It provides:
- live waveform visualization
- current volume and dynamic display
- temperature and humidity monitoring
- an OLED-style preview panel
- mock data mode for UI testing
- serial data source scaffolding for Photon 2 integration
- session recording and CSV export
Run instructions are available in desktop_dashboard/README.md.
- src/celloanalyzer.cpp
- main firmware
- project.properties
- Particle project dependencies
- desktop_dashboard
- PySide6 desktop dashboard application
- Add manual calibration for different instruments
- Improve cloud update speed while keeping webhook reliability
- Use a more specialized platform for richer audio signal analysis
- Test more microphone sensors
- Expand the environment system to control external hardware such as humidifiers or dryers
- Improve battery efficiency and power management
- Replace prototype wiring with a custom PCB
Acknowledgements:
- Professor Robert Parke and the TAC 348 teaching team
- Lincoln, Fion, Ilce, and Matt for debugging and setup help through Spring 2026 semester
- The Particle community PDM microphone discussion
- The
Microphone_PDMlibrary repository
Copyright (c) 2026 wuisabel-gif. All rights reserved.