BirdNETMic

Stream to BirdNET. Record to microSD. Control it from your browser.

Web flasher · Published releases · Changelog

Open-source ESP32 microphone firmware with two modes: Streaming sends live audio to BirdNET-Go, BirdNET-Pi, VLC or ffmpeg; Recording saves WAV files to a microSD card, even away from your home Wi-Fi. Use Listen for a quick sound check in either mode. Bird identification runs on the receiving computer, not on the ESP32.

Firmware 2.06 — ESP32-S31 support, optional experimental noise reduction and simpler controls. What’s new in 2.06.

Boards · Quick start · Modes · Battery · Features · Wiring · Help

Select your board and microphone in Device configuration during setup. Saved selections are retained after updating. Optional Adaptive noise reduction (Experimental) is in Audio noise reduction, together with High-pass; it defaults Off and affects RTSP, Listen and SD recordings when enabled. Its benefit for BirdNET recognition still needs comparison on real recordings.

Start with the right hardware

For a new build, choose XIAO ESP32-C5 + an IM73D122 PDM microphone. C5 offers PSRAM for audio/recording buffers and built-in battery voltage measurement, so no external measurement divider is needed. Add the Adafruit microSD BFF #5683 for a standalone recorder. PDM is our preferred microphone choice for new builds; IM73D122 is our quality-focused option. This is a project recommendation, not a measured ranking of every microphone. Existing I2S microphones remain supported.

Supported boards

Five firmware images cover the boards below (including ESP32-S31). Sense and AtomS3U use the S3 image; choose their board variant in Device configuration during setup.

Board	Firmware	Microphone	Streaming	Recording storage
XIAO ESP32-C3	c3	External I2S or PDM	✓	External SPI microSD module
XIAO ESP32-S3 / Plus	s3	External I2S or PDM	✓	External SPI microSD module
XIAO ESP32-S3 Sense	s3	Built-in PDM on Sense expansion board; external I2S also possible	✓*	Built-in microSD slot on Sense expansion board*
XIAO ESP32-C5	c5	External I2S or PDM	✓	External SPI microSD module
XIAO ESP32-C6	c6	External I2S or PDM	✓	External SPI microSD module
ESP32-S31-Function-CoreBoard-1	s31	Built-in ES8311 codec microphone	✓	Not supported; Recording mode remains selectable
M5Stack AtomS3U	s3	Built-in PDM	✓	Not supported

External SD module: Adafruit microSD Card BFF for QT Py and XIAO (#5683) fits directly onto the XIAO pin layout. See SD hardware and wiring. Sense already has a slot on its expansion board and does not need this module.

* Sense remains experimental. Multi-day battery endurance depends on the card, power supply and environment; plan a trial run before unattended use.

Quick start

1. Install the firmware

Connect your board with a USB data cable (AtomS3U plugs into USB-A). For published firmware, open the web flasher in desktop Chrome or Edge and choose Flash. Use the image matching your chip; Sense and AtomS3U share the S3 image.

2. Open the new setup wizard

BirdNETMic now has its own mobile-friendly setup page in place of WiFiManager.

1. On a fresh installation, join BirdNETMic-XXXXXX from your phone or computer. This initial setup network is open.
2. Open http://192.168.4.1 if the welcome page does not appear automatically. Stay connected if your phone reports that this network has no internet.
3. Under Board, select your board. On S3, choose XIAO ESP32-S3, XIAO ESP32-S3 Sense or M5Stack AtomS3U. C6 also offers its antenna selection.
4. Choose Default mode: Streaming or Recording. This is the mode used after power-on; the main UI lets you switch the current mode separately.
5. Choose the connection using the table below.

Your use	Connection	What to do
Streaming to BirdNET	Home Wi-Fi	Press Find Wi-Fi, tap your network, enter its password and press Connect. Wait for confirmation.
Recording with control over your router	Home Wi-Fi	Connect the same way. Audio is saved to SD; Wi-Fi is used for control.
Recording away from a router	Device Wi-Fi — standalone	Connect directly to BirdNETMic. No router or internet connection is needed.

1. Under Direct Wi-Fi access, save the device network name and password with Copy details. This is the device's own Wi-Fi password, separate from your router password.
2. Press Finish setup, then Open controls. For home Wi-Fi, reconnect your phone to that network and use the device address shown. For standalone use, rejoin BirdNETMic-XXXXXX with the saved password and open http://192.168.4.1. The device network becomes password-protected after setup.

Already configured? Open Device configuration at the top of the main UI to change the board, startup mode or Wi-Fi, then Save changes. New Wi-Fi credentials are tested before saving; a failed connection test leaves the saved network intact. Existing installations retain their saved Wi-Fi through the upgrade.

Recording connection is saved separately from the default mode. You can start in Streaming and choose Standalone for later Recording. Switching to Recording keeps an existing home connection; Standalone also opens device Wi-Fi and stops new router connection attempts. After a restart into Standalone Recording, only device Wi-Fi starts. Choose Home Wi-Fi to reconnect through your router. Network → Current connection shows which connections are actually active; device Wi-Fi access details are lower in that section. Explicit Wi-Fi power saving in Recording still turns off both connections after the configured delay. Restart or power off/on to regain access unless a wake source was configured.

Home Wi-Fi unavailable? After about 15 seconds offline, the device opens its password-protected Wi-Fi for local control. Access details are also shown under Network → Device Wi-Fi. Recording can continue offline; Streaming to your home network resumes when that connection returns. In Recording, Home Wi-Fi reconnects automatically; Standalone does not search for the router.

3. Check the microphone

For an external microphone, select Audio → Microphone format using the wiring guide. Review the recommended settings and adjust Gain while watching the signal level. Sense and AtomS3U profiles select their built-in PDM microphone automatically. ESP32-S31-Function-CoreBoard-1 uses its built-in ES8311 microphone automatically; no external microphone is needed.

Press Listen to hear the microphone. The playback Volume control changes what you hear in the browser; Gain changes captured audio. Then follow the Streaming or Recording steps below.

Streaming and Recording

	Streaming	Recording
Main purpose	Live audio for a network receiver	Standalone audio collection
Audio destination	BirdNET-Go, BirdNET-Pi, VLC or ffmpeg	WAV files on microSD
Home Wi-Fi	Needed for the normal network receiver	Optional; direct device Wi-Fi also works
SD card	Not required	Required
Browser Listen	Available	Available independently of SD writing
Bird identification	Performed by the receiver	Process saved files later on a computer

Choose Mode at the top of the main UI. These are separate modes: RTSP is disabled in Recording, and Streaming does not write to SD. Set the preferred mode after power-on in Device configuration → Default mode.

Streaming: connect to BirdNET

In Streams, enable a stream, select BirdNET-Go (TCP) or BirdNET-Pi (UDP), and copy its URL into the receiving system's RTSP audio-source settings.

rtsp://<device-ip>:8554/audio1    Stream 1
rtsp://<device-ip>:8554/audio2    Stream 2

Stream 1 is enabled by default; Stream 2 is optional. Both share the microphone settings. The maximum RTSP client count is configurable from 1 to 3 (default: 2). A .local hostname can replace the IP where your network supports mDNS.

Recording: save to microSD

1. With power disconnected, fit the SD hardware and card. For Sense, fit its expansion board and select the Sense profile.
2. Power on and select Mode → Recording. Check the card status in the Recording panel.
3. Set Recording duration (Until stopped or Set a duration) and Start a new file every (1–120 minutes; default: 60). Press Save recording settings after changing them.
4. Use Listen for a sound check, then Start recording. Check that the SD status confirms recording; hearing audio alone does not confirm that the card is writing.
5. You can disconnect your phone and leave the device recording. To finish, reconnect, press Stop & save, and wait for Saved before powering off or removing the card.
6. Read the WAV files from the card's recordings/ folder on your computer.

Files contain 16-bit mono PCM at the microphone sample rate, including the current gain and high-pass settings. PDM runs at 48 kHz (about 346 MB per hour). The panel shows free space and an estimated remaining recording time. Existing files are never automatically deleted; continuous recording remains limited by card space, power and any errors.

For unattended starts, choose Recording as the default mode and enable Start recording after power-on. File names use the device time when available, or an unsynced prefix when it is not. Test the intended card and power supply before leaving the recorder unattended. See the field recording guide for Wi-Fi-off operation, battery estimates and card capacity.

Recording outdoors: days of sound on microSD

Set the recorder up at home, check the sound, then place it in a suitable enclosure in the woods or garden. No router, computer or internet is required while recording. Protect the electronics from rain and condensation while leaving a suitable acoustic opening for the microphone. A bare board is not weatherproof.

Build inspiration: our first offline recorder (photos)

The first version of our own standalone microSD recorder: an enclosed assembly with an external microphone hood. These photos show one possible build to inspire your own enclosure and component layout.

This build uses:

• XIAO ESP32-C5 with a PDM microphone.
• A microSD card and module for offline WAV recording.
• Four LG MH1 18650 cells in a 1S parallel pack.
• A 1S BMS, output fuse and power switch.
• An enclosure with 3D-printed parts, including the microphone hood.

Outside — enclosure and microphone hood

Inside — microSD module, power switch and wiring

Click either photo for full size. For electrical connections, follow the pinout guide and battery wiring guide.

Wi-Fi off is a one-way action until restart. Start recording and check it first, then use Turn Wi-Fi off until restart. After the configured delay, both home Wi-Fi and the device's own Wi-Fi turn off. SD recording continues, but Listen, remote Stop, status updates and OTA are unavailable. The displayed values freeze. When the offline session definitively finishes (including an error), the device enters deep sleep. A temporary thermal pause awaiting recovery is different. Reset or power off/on is required to reconnect; there is no normal timed wake. Choose a finite duration before switching Wi-Fi off if you want a planned finish. Resetting an active recording can leave its current file incomplete.

At 48 kHz, 16-bit mono, recording uses about 346 MB/hour / 8.29 GB/day:

Card size	Approximate continuous audio capacity
8 GB	23 hours
16 GB	1.9 days
32 GB	3.9 days
64 GB	7.7 days*
128 GB	15.4 days*

These are decimal-capacity calculations before formatting, logs and free-space reserve. *64/128 GB are capacity examples, not qualified card sizes. Use FAT32; do not assume factory exFAT works. Sense documentation specifies up to 32 GB. Our C5 physical recording test used 32 GB. Eight continuous days need over 66 GB of audio space; a 32 GB card fills before a large battery pack runs out.

Battery

Use a protected 1S Li-ion/LiPo pack (3.7 V nominal, 4.2 V maximum). Our C5 measurements at 80 MHz showed 34–50 mA at 5.159 V USB while recording with Wi-Fi OFF (about 0.18–0.26 W), versus 78–95 mA with Wi-Fi ON. The SD card noticeably affects consumption.

Battery example	Rough planning estimate, Wi-Fi OFF
One 3000 mAh 18650 cell	1.4–2.1 days
Four matched 3000 mAh cells in parallel (1S4P, 12000 mAh)	5.7–8.4 days

Estimates assume 3.7 V nominal energy and an illustrative 80% usable-energy budget, using USB-measured power as a proxy. They are not measured battery runtimes: BAT-path efficiency, cold, cutoff voltage, card and cell condition change the result. Four cells must be parallel, never series. Use a properly assembled protected pack.

C5 measures voltage with its built-in divider. C3/S3/C6 and S31 need two external 100 kΩ resistors. Enable Battery monitoring and calibrate against a multimeter if needed. The displayed percentage is approximate, not a runtime prediction. Optional Low-battery protection stops and saves Recording, then stays awake or sleeps; it complements the pack's hardware protection.

Battery diagram, 1S BMS, output fuse and charging · Field recording and estimate assumptions

Features

• Two operating modes: live RTSP Streaming or standalone microSD WAV Recording.
• Browser sound check: independent Listen in both modes, playback volume up to 150%, signal level and microphone health indicators.
• Flexible microphones: I2S and PDM inputs, S3 built-in microphone profiles, adjustable gain, high-pass filtering and recommended audio settings.
• Recording controls: timed or continuous sessions, file splitting, optional power-on start, SD status, free-space estimates and explicit write errors.
• Simple first setup: board, startup mode and Wi-Fi in one wizard, visible network scan results, connection testing and direct Wi-Fi access for standalone use or outages.
• Local Web UI: mobile-friendly controls, light/dark appearance, save/discard feedback, device logs and a JSON API.
• Network audio: two configurable RTSP streams, TCP/UDP targets and mDNS addressing.
• Home automation: optional MQTT and Home Assistant discovery.
• Streaming schedules: local-time windows, including overnight schedules, with optional deep sleep outside the schedule.
• Thermal protection: shared capture protection for both modes and optional recovery after cooling; recording can continue in a new file. Automatic recovery is off by default.
• Board-specific options: C6 internal/external antenna selection, S3/C5 PSRAM audio buffers with an internal-RAM fallback, optional 240 MHz CPU on S3/C5, and up to 320 MHz with PSRAM buffers on S31.
• Firmware updates: USB installation and board-specific OTA with saved settings preserved; guided preparation for older C3/C6 flash layouts.

Stereo, USB audio, Bluetooth audio and Sense camera capture are not implemented. There is no simultaneous RTSP + SD recording, on-device bird identification, automatic deletion of old recordings or guaranteed recovery of an interrupted WAV.

Web UI preview

This screenshot shows the earlier streaming interface; version 2.00 adds Mode, Recording and Device configuration controls.

Hardware essentials

See the linked shopping list for boards, microphones, SD and battery parts.

Our first choice is C5 + IM73D122 PDM, adding the Adafruit BFF for Recording. For a streaming setup without microphone wiring, AtomS3U has a built-in mic. For an external microphone, use a XIAO and one of the microphones in the wiring guide. Sense combines a microphone and SD slot on its expansion board; Sense support remains experimental.

Item	When needed
USB data connection	First installation; USB-C for XIAO/S31, USB-A for AtomS3U
USB power supply	Operation after installation
External I2S or PDM microphone	Standard XIAO boards; see the wiring guide
Board-compatible antenna	Match the board's connector and antenna configuration
microSD card and supported slot/module	Recording mode

Power external microphones from 3V3. Keep microphone wires short. Power the XIAO through USB-C or a regulated 5 V input; never feed 12 V into it or connect two power sources at once.

SD hardware and wiring

Adafruit microSD Card BFF Add-On for QT Py and XIAO — #5683 is the selected external module. It fits the XIAO headers directly and mounts behind the board using soldered headers or removable pin/socket headers. It is not a solder-free connection out of the box. The card is sold separately.

Keep the module's default CS = TX jumper configuration, matching the firmware:

microSD SPI signal	XIAO pin label
CS	D6 / TX
SCK	D8
MISO	D9
MOSI	D10
Power / ground	3V3 / GND

Use printed XIAO labels; underlying GPIO numbers vary by board. Adafruit assembly and pinout guide. This pin mapping is used for C3/S3/C5/C6 with the external module.

Sense: use the built-in slot on the expansion board with its factory SD connection enabled, a FAT32 card up to 32 GB, and the XIAO ESP32-S3 Sense profile. Its SD CS routing differs from the external module and is selected automatically. The camera is not used. Sense selection routes PDM to its built-in microphone; external I2S is also supported. Standard S3 selection uses the external SD mapping.

C6 antenna selection

On XIAO ESP32-C6, Device configuration and Network → Wi-Fi antenna offer External (default) and Internal (built-in). Connect the external antenna before using External. A change requires a restart; there is no automatic antenna detection. Other supported boards do not expose this selector.

Microphones and wiring

I2S microphones

Microphone	Select in Audio → Microphone format	Notes
Adafruit SPH0645LM4H	MSB / left-justified	Supported I2S alternative
ICS-43434	Philips I2S	Supported I2S reference
INMP441	Philips I2S	Supported I2S microphone

Use the printed XIAO pin labels below on C3/S3/C5/C6; GPIO numbers differ between boards.

I2S microphone pin	XIAO pin
VDD / VCC	3V3
GND	GND
BCLK / SCK	D3
LRCLK / WS	D1
SD / DOUT	D2
L/R / SEL	GND (left channel)

Leave D7 unused for these microphones. See the GPIO table and PCM1808 notes for advanced setups. Use 3.3 V, not 5 V, for the microphone.

PDM microphones

IM73D122 breakout shown: CLK → D3, DATA → D2, L/R → GND; leave NC disconnected. Power the microphone from 3V3 and the XIAO from USB-C or a regulated 5 V supply.

IM73D122, Adafruit PDM (#3492 / MP34DT01-M) and compatible MP34DT01 breakouts use different wiring from I2S. Use the PDM selection for all of them; the Web UI label currently names IM73D122. Check each breakout's pin labels:

PDM microphone pin	XIAO pin
VDD / VCC / 3V	3V3 (check the breakout's supply rating)
GND	GND
CLK	D3
DATA / DAT	D2
SEL / L-R	GND (left slot)

Leave D1 and D7 disconnected. Check the module's pin labels before connecting power. Select PDM microphone (IM73D122) in Audio; this sets 48 kHz automatically. Gain and high-pass filtering remain available; I2S Shift does not apply. Use Recommended settings to review the board/microphone profile before saving, or choose Keep saved values and save to retain your tuning.

When upgrading from the v15 PDM firmware, start with new Gain = old Gain × 2^(16 − old I2S Shift), then check the level/clipping. For example, Shift 12 / Gain 1.5 becomes Gain 24. Saved Gain is not changed automatically.

On C3/C5, set Audio → Audio buffer size to 512 samples, and use 160 MHz CPU in Thermal & performance. The default packet size is already 512, but choosing Keep saved values and save preserves a previously saved larger size. The firmware reduces its internal audio reserve when RAM is limited; this does not automatically change the packet-size setting.

S3 uses hardware PDM conversion; C3/C5/C6 use software conversion. Sense support remains experimental.

Everyday use and troubleshooting

Time after startup: with Time Sync on, the device synchronizes when Wi-Fi connects and retries automatically if needed. The UI shows Waiting for Wi-Fi, Waiting for NTP, then YES after confirmation. A valid retained clock remains visible while waiting. Sync Time Now requests a fresh synchronization. See the time-sync and validation guide.

• No sound: check wiring, microphone format and microphone health, then press Listen. For a network receiver, also check Streaming mode and the enabled stream. A flatline warning means the captured samples have stopped changing; it is not a microphone-quality measurement.
• Dropouts: check Wi-Fi signal, check the antenna connection/selection, and start with 512 samples per packet. Use the target setting matching BirdNET-Go (TCP) or BirdNET-Pi (UDP).
• Noise: keep microphone wires short and away from the antenna. Try lower Wi-Fi transmit power when the access point is nearby. High-pass filtering reduces low-frequency rumble (default: 500 Hz).
• Temperature warning: improve cooling or placement. Automatic recovery is optional and OFF by default; repeated or emergency shutdowns need acknowledgement after cooling.
• Browser playback stops: only one browser can listen at a time. Leaving/hiding the page, changing audio settings or updating firmware stops playback; press Listen again when ready.
• SD recording error: check the selected board profile, card, module wiring and power. A missing module, missing card and wiring problem can produce the same error. Stop and save before removing a card.
• Updates: open Firmware update in the device header. Automatic update uses the published image; manual upload needs firmware-app-<board>.bin. Never use a merged firmware-<board>.bin for OTA.

C3/C6: prepare for future updates

Starting with v1.35, XIAO ESP32-C3/C6 devices with the original flash layout need one preparation step to make room for future firmware:

1. Install v1.35 through the usual Automatic update button. This first update works without preparation, even when the old firmware has no Prepare button.
2. On the update page, click Prepare device and confirm once. Keep power connected; the device handles restarts and reconnects the page automatically.
3. Wait for Preparation complete. Your settings are kept, and future OTA updates work as usual.

If you postpone preparation, the microphone keeps working. The new firmware blocks further updates and asks you to use Prepare device first. You do not need to choose files or change settings for this step. S3/C5 devices and C3/C6 devices already using the larger layout do not need it.

A power failure during the brief flash-layout rewrite can require USB recovery. Older devices always receive the small v1.35 bridge first, even if they skip updates until a later release such as 1.40. After preparation, check for updates again to install the latest version.

Keep the device on a trusted LAN: HTTP/RTSP have no built-in user authentication or TLS. For setup details, schedules, MQTT and API examples, see the firmware guide.

Frequently asked questions

Does BirdNETMic identify birds on the ESP32?

No. In Streaming mode, BirdNET-Go or BirdNET-Pi performs identification on the receiving computer. In Recording mode, take the WAV files from the SD card and process them later.

Can I record without a router or internet?

Yes. Choose Recording → Device Wi-Fi — standalone during setup. Use your phone to start and stop recording; it can disconnect while the device keeps recording. The device still needs continuous power and a working SD card.

Can I stream and record to SD at the same time?

No. Select one mode at a time. Browser Listen remains available in both modes for checking the microphone.

Will switching Mode change what happens after the next power-on?

No. Mode changes the current operation. Set the startup choice separately under Device configuration → Default mode.

Build From Source

Use Bash (Linux, macOS, or Windows WSL), Python 3 and Arduino CLI 1.5.0. Build validation also requires size and flock; see the development setup. Run these commands from the repository root. First-time dependency setup:

arduino-cli config add board_manager.additional_urls https://espressif.github.io/arduino-esp32/package_esp32_index.json
python3 tools/check_build_dependencies.py --install

Build a XIAO ESP32-C6 image:

tools/compile_firmware.sh --fqbn esp32:esp32:XIAO_ESP32C6 \
  --output-dir esp32-birdnet-mic/build/c6

For another supported board, replace XIAO_ESP32C6 with XIAO_ESP32C3, XIAO_ESP32S3, or XIAO_ESP32C5 and choose a matching output folder. The helper automatically enables LTO for C3/C6, OPI PSRAM for S3 and PSRAM for C5. Recording releases the RTSP reserve; returning to Streaming releases the SD PCM queue. Listen stays independent in both modes. DMA and capture working buffers remain internal.

For OTA, select esp32-birdnet-mic/build/c6/esp32-birdnet-mic.ino.bin under Firmware update -> Upload compiled file in the device Web UI. Use the image built for your board; OTA needs the app-only .ino.bin, not the .merged.bin USB image. An OTA upload alone keeps the existing partition layout. On C3/C6, complete Prepare device when prompted before another OTA.

Ordinary Arduino IDE or direct arduino-cli compile builds do not automatically enable LTO. See the full build instructions for more details.

Arduino IDE Build Size

Keep esp32-birdnet-mic/build_opt.h next to the sketch. The ESP32 Arduino core loads it automatically in Arduino IDE and arduino-cli; it disables unused C++ exception/unwind metadata. The CLI helper above also applies the C3/C6 LTO settings used for the packaged firmware.

More documentation

• Development workflow, board registry and validation
• Firmware guide and API
• Manual OTA files
• Web flasher and firmware file guide
• Release history
• Field recording guide
• Parts and wiring
• Recording logs and SD journal
• Release workflow
• Hardware validation scope
• Website download statistics

Credits and license

Created by @Sukecz, with thanks to everyone helping improve BirdNETMic. Released under the MIT License.

ESP32-S31-Function-CoreBoard-1

Use the built-in ES8311 microphone without external audio wiring. See the S31 guide for installation, 320 MHz CPU selection, optional battery measurement and the current storage limitations.