Chords-Web#

Overview#

Chords-Web is an open-source web application for real-time visualization of bio-potential signals like EEG, EMG, ECG and EOG. It is an advanced alternative to the standard Arduino IDE serial plotter, made for students, researchers and hobbyists who want to record biopotential data using BioAmp hardware.

Chords-Web runs completely in your browser - there is nothing to install. Open chords.upsidedownlabs.tech, connect your board over USB or Bluetooth, and start visualizing.

Note

Chords-Web is made for educational and research purposes. It is not medical software and must not be used for diagnosis.

Quick Start#

If you are new to Chords-Web, follow these five steps. Each step is explained in detail in the sections below.

Hardware: Connect your BioAmp sensor to a supported development board and place the electrodes on your body.
Firmware: Upload the Chords firmware to your board (see Uploading the Firmware).
Open Chords-Web: Go to chords.upsidedownlabs.tech in a supported browser and click Visualize Now.
Connect: Click Serial (USB cable) or BLE (Bluetooth, NPG Lite only) in the bottom bar and select your device.
Choose a view: Use the app switcher in the bottom bar to open the Chords Visualizer, FFT Visualizer, Rep-Forge or ECG Visualizer.

Requirements#

Browser Compatibility#

Chords-Web talks to your board directly from the browser using these web APIs:

Web Serial API: to connect boards over a USB cable.
Web Bluetooth API: to connect the NPG Lite over Bluetooth Low Energy (BLE).
WebUSB API: to update the firmware of some boards from the browser.

Not every browser supports all three APIs, so some features may not work in your browser:

Browser	Serial (USB)	Bluetooth (BLE)	Firmware update
Google Chrome, Microsoft Edge, Opera	Yes	Yes	Yes (all boards)
Mozilla Firefox 151 or later	Yes	No	Some boards only
Safari	No	No	No

For all features, use the latest version of Google Chrome, Microsoft Edge or Opera. Firefox supports Web Serial from version 151. Older Firefox versions can’t connect to your board and will show the unsupported browser message.

If your browser does not support the Web Serial API, Chords-Web shows a message telling you to switch to a supported browser.

Warning

Using Firefox 151 or later? You can connect your board over Serial and use all the applications. But Firefox doesn’t support Web Bluetooth or WebUSB, so:

The BLE button won’t work, so you can’t connect the NPG Lite over Bluetooth. Connect it over Serial instead.
The in-browser firmware update doesn’t work for boards that are flashed over WebUSB: Arduino UNO R4 Minima, Arduino GIGA R1, STM32G4 Core Board, STM32F4 Black Pill and Raspberry Pi Pico. Update these boards using Chrome/Edge or the Arduino IDE. Other boards can be updated in Firefox, because they are flashed over Web Serial.

Important

Chords-Web works only on desktop/laptop computers. If you open it on a phone, you will see an “Oops! Mobile Detected” message.

Tip

Brave is Chromium-based, but it turns off Web Serial and Web Bluetooth by default. If you use Brave, enable them from brave://settings/content or use Chrome/Edge instead.

For more information, refer to MDN Web Docs on the Web Serial API and the Web Bluetooth API.

Software Requirements#

A supported browser.
Chords firmware on your board. You can upload it in any of these ways:
- Directly from Chords-Web (see Option 1: Update firmware from Chords-Web (Recommended)).
- Using the Arduino IDE and the Chords Arduino Firmware.
- Using the NPG Lite Flasher Web (in your browser) or the NPG Lite Flasher (desktop app) for the NPG Lite or other ESP32 based boards.

Hardware Requirements#

A supported development board (or an NPG Lite, which has a built-in BioAmp).
A USB cable (type depends on your board).
BioAmp Hardware and its accessories (cables, electrodes, gel).

Supported Boards#

Chords-Web detects your board automatically and sets the ADC resolution, number of channels and sampling rate for you.

Board	ADC Resolution	Channels	Sampling Rate	Connection
Arduino UNO R3 / Genuino UNO / Maker UNO (UNO clone)	10-bit	6	250 Hz	Serial
Arduino Nano Classic / Nano clone	10-bit	8	250 Hz	Serial
Arduino MEGA 2560 R3 / MEGA 2560 clone	10-bit	16	250 Hz	Serial
Arduino UNO R4 Minima / UNO R4 WiFi	14-bit	6	500 Hz	Serial
Arduino GIGA R1	16-bit	6	500 Hz	Serial
Raspberry Pi Pico (RP2040)	12-bit	3	500 Hz	Serial
STM32G4 Core Board	12-bit	16	250 Hz	Serial
STM32F4 Black Pill (STM32F401CC / STM32F411CE)	12-bit	8	500 Hz	Serial
ESP32-S3	12-bit	16	250 Hz	Serial
NPG Lite (3 channel / 6 channel)	12-bit	3 or 6	500 Hz	Serial or BLE

Tip

You can also use any other microcontroller, as long as it sends data in the Chords data format.

Setting up the Hardware#

Make all the connections for the hardware you are using:

Connect the BioAmp sensor to the analog input pins of your development board.
Connect the electrodes from the BioAmp sensor to your body.
Connect the development board to your laptop using a USB cable.

You can see diagrams of these connections (cable connections, BioAmp to board connections and electrode placement for ECG and EOG) on the Chords-Web page after you click Visualize Now, before you connect a device.

Uploading the Firmware#

Your board needs the Chords firmware so that it can send data to Chords-Web. Choose any one of the options below.

Option 1: Update firmware from Chords-Web (Recommended)#

You don’t need the Arduino IDE for this option.

Connect your board to your laptop with a USB cable.
Open chords.upsidedownlabs.tech, click Visualize Now and then click Serial.
Select your board’s port and click Connect.
If the board is supported but doesn’t have the latest Chords firmware, a “Your firmware is not updated” dialog opens.
If several boards share the same USB ID (for example, UNO clones and Nano clones), select which board you have.
Click Flash firmware. Chords-Web downloads the latest firmware release and uploads it to your board.
When it shows Firmware updated, Chords-Web reconnects to your board automatically.

Note

STM32 boards: If the board is still in normal mode, put it in boot mode first. Hold BOOT0, tap NRST, release BOOT0, and click Flash firmware again.
Windows: Some boards need a USB driver before they can be flashed (only once per PC). If flashing doesn’t start within 15 seconds, follow the steps in the dialog to install the driver using ChordsDriverSetup.exe or Zadig (choose WinUSB and click Install Driver). Then replug the board and click Flash firmware again.

Option 2: Upload firmware with the Arduino IDE#

Connect your board to your laptop with a USB cable.
Go to the Chords Arduino Firmware GitHub repository, scroll to the supported boards table and open the sketch for your board.
Copy the sketch and paste it into the Arduino IDE.
Go to Tools > Board and select your board.
Go to Tools > Port and select your board’s port. This is the port that disappears when you unplug the board:
- Windows: COM3, COM4, etc.
- Linux: /dev/ttyACM0 or /dev/ttyUSB0
- macOS: /dev/cu.usbmodem... or /dev/cu.usbserial...
Click the Upload button.
Close the Arduino IDE Serial Monitor/Plotter (only one app can use the port at a time) and open Chords-Web.

Option 3: NPG Lite and ESP32 boards#

Use one of these tools to upload the Serial or BLE firmware to your NPG Lite or any ESP32 based board:

NPG Lite Flasher Web: Runs in your browser, nothing to install. Open upsidedownlabs.github.io/NPG-Lite-Flasher-Web, click Connect Device, select the BLE or Serial firmware and click Flash Firmware.
NPG Lite Flasher: A desktop app for Windows, macOS and Linux.

NPG Lite Flasher Web

NPG Lite Flasher

Connecting to Chords-Web#

Open a supported browser and go to chords.upsidedownlabs.tech.
Click Visualize Now.
The images in the center show how to connect your hardware.
The bottom bar has three buttons:
- BLE: Connect an NPG Lite over Bluetooth.
- Serial: Connect any supported board over a USB cable.
- Serial Wizard: Open the Serial Wizard Plotter & Monitor.

Connecting over Serial (USB)#

Click Serial.
Your browser shows a list of serial ports. Select your board and click Connect.
Chords-Web detects your board, and the Chords Visualizer starts plotting your signals.

Connecting over Bluetooth (NPG Lite)#

The NPG Lite can stream data wirelessly over Bluetooth Low Energy (BLE). It has a built-in BioAmp and a 12-bit ADC (ESP32-C6), so you don’t need any other development board.

Flash the BLE firmware: Use the NPG Lite Flasher Web or the NPG Lite Flasher to upload the BLE firmware (3 channel or 6 channel) to your NPG Lite.
Power on the NPG Lite using its on/off switch.
Turn on Bluetooth on your computer.
Open Chords-Web, click Visualize Now and then click BLE.
Select your NPG Lite (its name starts with NPG) from the list and click Pair.
Your signals start plotting. You can now use any of the applications below.

Features over BLE:

Feature	Description
Wireless Streaming	Stream 3 or 6 channels of biopotential data at 500 Hz without a cable.
Battery Indicator	The bottom bar shows the battery level of your NPG Lite. You get a warning when the battery is low and a message when it is fully charged (3CH/6CH firmware only).
Interactive Controls	Select channels, play/pause the stream, apply filters and record to CSV, just like over Serial.

Note

If you don’t see the battery level, your NPG Lite has older BLE firmware. Update it with the NPG Lite Flasher Web or the NPG Lite Flasher.

Note

Checkout our YouTube video for more information:

Common Controls#

These controls are in the bottom bar and work in all the applications, unless mentioned otherwise.

App Switcher#

After you connect, use the app switcher in the bottom bar to move between the four applications. You don’t need to reconnect your board when you switch.

Chords Visualizer: Raw multi-channel waveform.
FFT Visualizer: Spectrum and EEG band power.
Rep-Forge: EMG envelope and muscle strength.
ECG Visualizer: Heart rate with R-peaks.

Note

Filters are reset every time you switch to another application, so a filter you chose in one view doesn’t keep running in another.

Play/Pause and Data Windows#

Click Pause to freeze the screen on the current data window.
While paused, use the Previous Data Window (left) and Next Data Window (right) buttons to go back through up to 5 earlier data windows.
Click Play to continue the live stream.
Changing the selected channels resets the saved data windows.
Pause is not available while recording.

Settings (Zoom, Time Base and Channels)#

Click the Settings icon to open the settings popover:

Zoom Level: Zoom from 1x to 10x to see small signal details or the full signal.
Time Base: Show 1 to 10 seconds of data on the screen.
Channels: Select the channels you want to plot. The number of available channels depends on your board (up to 16). Use Select All to choose all channels and Reset to go back to your previous selection.

Filters#

Click Filter to clean up your signal. You can apply a filter to one channel or to all channels at once using the master buttons at the top.

Filter	Type	Use it for
Muscle	70 Hz high-pass	EMG (muscle) signals
Heart	30 Hz low-pass	ECG (heart) signals
Eye	10 Hz low-pass	EOG (eye) signals
Brain	45 Hz low-pass	EEG (brain) signals
50 Hz / 60 Hz	Notch	Removes power line noise. Use 50 Hz in India, Europe, etc. and 60 Hz in the USA, etc.

Note

A 1 Hz high-pass filter is always applied to remove DC drift, even when no other filter is selected.
The Muscle, Heart, Eye and Brain filters are available in the Chords Visualizer. Rep-Forge has only the Muscle filter and the 50/60 Hz notch filter.

Recording the Data#

Click the Record (red circle) button to start recording in CSV format.
To stop automatically, set an end time: choose 1, 10, 20 or 30 minutes, or type your own time in minutes. You can also record without a time limit and click Stop when you are done.
Recordings can be at most 24 hours (1440 minutes) long.

Recorded files are saved in your browser (using IndexedDB), so they are not lost if you disconnect your board. Click the Files button to manage them:

Download or delete a single file.
Download All as Zip or Delete All with one click.

Each CSV file has a Counter column followed by one column per selected channel (Channel1, Channel2, …). You can plot these files with the Chords CSV Plotter.

Disconnecting#

Click the Disconnect button to stop the data stream and disconnect your board.

Other Options to Explore#

Switch Theme: Switch between light and dark mode using the theme button in the navigation bar.
Version: The navigation bar shows the version of Chords-Web you are using.
GitHub Repository: Open the Chords-Web GitHub repository using the link in the navigation bar.
Contributors: See the list of contributors using the link in the top-right corner of the navigation bar.

Applications#

Chords Visualizer#

The Chords Visualizer is the default application. It plots your raw biopotential signals from multiple channels in real time. Use it to monitor EMG, ECG, EOG or EEG signals, apply filters and record your data.

Features#

Feature	Description
Auto Board Detection	Instantly detects BioAmp Hardware running the Chords firmware and sets the ADC resolution, channels and sampling rate automatically.
Real-time Visualization	Smooth, real-time data rendering powered by WebGL-Plot.
Multi-channel Plotting	Plots up to 16 channels, depending on your board, each in a different color.
Data Windows	Pause and go back through the last 5 data windows.
Zoom & Time Base	Zoom from 1x to 10x and show 1 to 10 seconds of data on the screen.
Filters	Muscle, Heart, Eye and Brain filters, and 50/60 Hz notch filters, per channel or for all channels.
Recording & Data Management	Record data in CSV format with or without a timer. Download or delete files individually or as a ZIP.

Running the Application#

Connect your board (see Connecting to Chords-Web). The Chords Visualizer opens automatically.
Open Settings to select channels and adjust the zoom and time base.
Click Filter and choose a filter for the signal you are recording (for example, Muscle for EMG).
Click Record to save your data, and use the Files button to download it.

Visualizing EMG (Electromyography) signals#

EMG captures the electrical activity produced by skeletal muscles. Use the Muscle filter.

Visualizing EEG (Electroencephalography) signals#

EEG records the electrical activity of the brain. Use the Brain filter.

Tip

To ensure you’re recording a high-quality signal, refer to the detailed guide here: Troubleshooting EEG Signal Quality.

Visualizing EOG (Electrooculography) signals#

EOG measures the electrical potential generated by eye movements. Use the Eye filter.

Visualizing ECG (Electrocardiography) signals#

ECG records the electrical activity of the heart and shows your heart rhythm. Use the Heart filter.

FFT Visualizer#

Overview#

The FFT Visualizer uses FFT (Fast Fourier Transform) to show the frequencies present in your signal and the power of each EEG band. Use it to see your brainwaves and track your focus in real time.