bcMeter

User Manual

Monitoring Black Carbon

Updated: May 2026

Table of Contents

1. Introduction

The bcMeter is an open-source optical absorption photometer for measuring Black Carbon (BC), or soot, in air. It can be used for ambient monitoring as well as direct emission measurements, for example near wood stoves.

The device has no built-in screen. It serves a local web page that opens on a smartphone or computer in the same network.

A Quick Start Guide / Cheat Sheet is available alongside this manual.

2. Setup & Initialization

2.1 Requirements

2.2 Receiving a Rugged Case Device

If your device is not installed in a rugged case, skip the case-specific steps and continue with Section 2.3.

Figure 2.1: 12V rugged case version as received

Figure 2.2: USB-C or development version as received

1. Open the case latches and check the contents: bcMeter unit, matching power supply, air inlet tube, antenna if supplied, and filter papers in small plastic bags.
2. Inspect the housing, air inlet, outlet hose, power connector, antenna connector, and filter holder. Do not start a measurement if anything is cracked, loose, disconnected, or blocked.
3. Remove loose foam padding or transport protection from the inside of the case. Do not pull on wires or remove fixed foam parts; if the protection is trapped under cables, contact support before powering the device.
4. Connect the air inlet tube to the case-side inlet. The tube should sit firmly and should not be kinked or squeezed by the lid.
5. If the device has a cellular modem, screw the 4G antenna onto the SMA connector by hand. Do not use tools to tighten it.
6. Route the power cable through the cable opening, connect the matching power supply, and close the lid. Once powered, the bcMeter starts its setup hotspot if no known WiFi is available.

Figure 2.3: Remove loose shipping protection before operation

Figure 2.4: Air inlet tube seated in the case wall

Figure 2.5: 4G SMA antenna attached hand-tight

Figure 2.6: Rugged case closed and ready to power on

2.3 Initial Device Setup

Before starting, do this quick check:

1. Confirm that the supplied power adapter matches the hardware (see Section 2.1) and that the device starts without repeated reboots.
2. Place the device away from direct heat sources and sunlight (thermal drift affects optical measurements).
3. If you use a case, check that the hose from bcMeter to the outside air is firmly inserted and not blocked.
4. Insert a fresh filter paper (marked or rough side facing up - see Section 5.1). This is already done for devices bought pre-provisioned from bcmeter.org.

Figure 2.7: Hose from air inlet through rugged case

2.4 Connecting via Hotspot

The device can create its own WiFi network. It does this on first boot and whenever no known network is available. You can also enable the hotspot later in Settings.

1. Plug in the device.
2. Wait 1-2 minutes for the system to boot; the dim blue LED starts to slowly blink.
3. On your tablet or computer, search for a WiFi network whose name starts with bcMeter or eBcMeter.
   Apple Users: If already connected to another WiFi, the bcMeter hotspot will appear under the "Other Networks" submenu. macOS may take up to a minute to scan for new networks even after the device has finished booting.
   

   Figure 2.8: macOS submenu for unknown wireless networks in range
4. bcMeter tries to open its configuration interface directly within a few seconds. If this fails, you should still be connected. If asked, connect using the password bcMeterbcMeter - it is case sensitive.
5. Your computer may warn you that this network has "No Internet Connection." This is normal. Select "Keep Connected" if prompted. Do not choose "use mobile data".
6. Open a browser and type http://192.168.18.8 into the address bar. The device will also open this page automatically. The Welcome screen appears on first use (see Section 2.5).

Blue Status LED

The physical blue LED on the device provides a quick hardware status indication:

2.5 Welcome Screen

On first use, bcMeter shows a two-step welcome screen for email and network setup.

Step 1 - Notification email

Enter the email address where bcMeter should send status messages and alerts. After WiFi setup, the device can send its local access link and connection details to this address.

Figure 2.9: Welcome screen - Step 1: Email

Step 2 - Connect to network

Select your WiFi network, enter the password, and click Connect. Use Scan to refresh the list, or Enter manually if the network is hidden. The device hostname (e.g. bcmeter-0110.local) is shown in the captive-portal note - bookmark it to access your device later on your local network.

Figure 2.10: Welcome screen - Step 2: WiFi with a network selected

After connecting, the setup hotspot turns off and bcMeter joins your network. Check your email for the interface link. Also check spam folders. Devices with a modem can also use cellular connectivity for status, location lookup, or data delivery, depending on the installed hardware.

2.6 Accessing the Interface

When the device is on your network, open it by hostname. The default hostname follows the pattern bcmeter-XXXX. For example:

• Standard Device: http://bcmeter-A3AB.local
• Emission Control Version: http://ebcmeter-A3AB.local

The exact hostname is shown on the device label and in the Welcome email. You can also rename the device in Settings > Device > Device Name.

3. Web Interface Overview

3.1 Dashboard Elements

Use the moon/sun button on the right side of the navigation bar to switch between light and dark mode. The browser remembers your preference for the next visit.

Figure 3.1: Dashboard overview in light mode

Figure 3.2: Dashboard overview in dark mode

1. Navigation Bar: Start and Stop buttons to control measurement sessions, quick access to Log Files, Settings, and Maintenance, and a dark-mode toggle on the far right.
2. Status Panel: Device name, operating state, session start time, and filter loading with a color-coded indicator (see Section 3.2 for details).
3. Statistics Cards: Rolling one-hour BC average, overall session average, and the peak concentration with its timestamp.
4. Live Chart: Interactive time-series graph that updates as new samples arrive (see Section 3.3 for zoom and interaction).
5. Chart Controls: Y-axis parameter assignment, smoothing and resampling controls, log selection, download, and zoom management (see Section 3.3 for details).

3.2 Status Indicators

Device Status

Time Sync Status

Normally, time syncs automatically. If the device clock is not synced, it shows "Time: not synced" in red. Use Maintenance > Time Synchronization to sync the device clock with your browser.

Filter Loading Status

The "Filter" indicator shows how much of the filter strip is loaded. The color changes with loading level:

• Green (0-30%): Filter is clean. Signal quality is optimal.
• Orange (30-70%): Loading is increasing. Mathematical compensation is active and effective. Prepare a replacement filter.
• Red (70-85%): Filter is heavily loaded. Compensation becomes less reliable. Replace filter soon. An email alert is sent every 12 hours when loading exceeds 70%.
• Dark (85%+): Filter is near saturation. Replace immediately for reliable measurements.

3.3 Data Visualization

Figure 3.3: Dashboard with plot controls

Plot Behavior

The interactive chart renders time-series data as it arrives from the device. Because the underlying optical signal is analog, the trace will appear jagged and noisy - this is normal. Smoothed values (Median, EMA) are typically closer to the true concentration. After starting a session the chart remains empty until 3-4 samples have been collected; at the default 5-minute sample interval this means the first data point appears after roughly 15-20 minutes.

Click and drag horizontally on the chart to zoom into a time window. Double-click anywhere on the chart to reset the zoom back to the full session view.

Action Bar

The controls below the chart include:

• Log selector: A dropdown on the left lets you switch between the current live session and any previously recorded log file stored on the device. Selecting an older log replaces the chart data instantly.
• Download View: Exports the currently visible data - respecting any active zoom and filter settings - as CSV, PNG, or SVG.
• Reset Zoom: Restores the chart to the full time range after you have zoomed in.
• Axis Scaling: Opens a panel to manually set the Y-axis minimum and maximum. Useful when extreme peaks compress the rest of the data into a flat line.

Y-Axis Controls

Each axis row (Y1, Y2, and optional additional axes via + Add axis) contains:

• Enable toggle: A switch on the left to show or hide the axis.
• Parameter dropdown: Select which measurement to plot on this axis (see Section 3.4 for the full list of available parameters).
• Smoothing algorithm: A segmented control offering four modes:
  • Raw - unfiltered signal, shows every fluctuation.
  • Med (Median) - removes outlier spikes while preserving sharp transitions. Good general-purpose choice.
  • EMA (Exponential Moving Average) - produces a smooth curve that follows trends but responds slower to sudden changes.
  • ONA (Optimized Noise Average) - adaptive filter tuned for the optical noise profile of the sensor.
• Resample slider: Averages consecutive samples together to reduce noise and thin out the data. Setting it to 2x halves the number of points (each pair is averaged), 5x averages every five, and so on. Particularly useful for noisy data at high sample rates or long sessions where individual fluctuations obscure the underlying trend. "Off" (value 1) shows every original sample.
• Denoise slider: Controls the strength of the selected smoothing algorithm. Low values (1-3) preserve fast transients - ideal for emission monitoring. Higher values (5+) produce a cleaner trace suited to ambient monitoring where rapid response is less critical.

3.4 Plot Parameters

These parameters can be assigned to Y1, Y2, or added axes:

Figure 3.4: Available plot parameters in Y-axis selector

4. Configuration & Settings

4.1 Main Controls

• Start: Begins a measurement session. The device first runs a 20-30 second initialization phase to prime the pump and stabilize the optical chamber. Data points appear after the configured sample interval.
• Stop: Ends the session and saves the file.
• Log Files: Opens the file manager to download or delete session logs.

4.2 Device Parameters (Settings)

Click Settings to configure the device. Settings are organized into tabs: Network, Measurement, Device, and Email.

Network Tab

Figure 4.1: Network settings

The Network tab manages wireless connectivity and is the default view when opening Settings.

Changing WiFi Later

If you skipped WiFi setup on the welcome screen, or need to change the network later, use the Network tab:

1. Navigate to Settings > Network.
2. Select your network from the dropdown. If your network is hidden, choose Enter manually and type the name yourself.
3. Enter your WiFi key and click Connect.
4. The setup hotspot disconnects while the device joins the selected network. Reconnect your computer to your normal WiFi.
5. Wait 1-2 minutes for the device to join your network.

The Network tab also lets you configure the device hotspot. Enable Run hotspot when no WiFi available so the device creates its own access point as a fallback. You can optionally protect the hotspot with a WPA2 key.

Click Forget Network to disconnect from your stored network and force the device to create its hotspot again.

Measurement Tab

Figure 4.2: Measurement settings

These settings define the sampling interval, airflow, location handling, and related measurement behavior. When Auto Flow Control (AFC) is active, a banner shows the current AFC limits.

An Airflow Reference table is displayed below the settings, showing estimated filter lifetime (in days) at different BC concentrations and airflow rates to help choose the right airflow.

Device Tab

Figure 4.3: Device settings

Email Tab (Notifications)

Use this tab for email delivery of log files, filter status alerts, and optional data sharing with the bcMeter project. Provisioned devices already include the required mail service setup. DIY and development details are in the bcMeter wiki.

Figure 4.4: Email settings

4.3 System & Maintenance

Access via the Maintenance button in the navigation bar. The modal is organized into cards for device management, system status, time synchronization, and - when location services are active - geolocation.

Figure 4.5: System & Maintenance modal

Device Management

The Device Management card is split into two columns:

Routine Maintenance

• Calibrate Device: Adjusts LED duty cycles to balance sensor and reference signals. Required after each filter change.
• View System Status: Opens a structured hardware, measurement, system, and network status report.
• Download System Logs: Downloads a troubleshooting report with hardware, measurement, system, and network diagnostics.
• Identify Device: Blinks the device LED for about two minutes, useful when more than one bcMeter is nearby.

System Operations

• Reboot Device: Restarts the device.
• Shutdown Device: Powers down before unplugging. Use this button before disconnecting power. If the device loses power during an active session, it resumes measurement on the next boot.
• Manual Firmware Update: Opens a dialog to upload a firmware file. The device also checks for firmware updates a few times a day and shows a notice when an update is available.
• Factory Reset: Permanently erases all measurement logs, WiFi credentials, calibration data, and device settings. The device will reboot into its factory state. A slide-to-confirm gesture is required to prevent accidental resets.

Figure 4.6: Factory Reset confirmation with slide-to-confirm

System Status

Shows the current device state:

• Device ID: Unique hardware identifier.
• Device Name: Current network hostname.
• Software Version: Installed firmware version.
• Free Memory: Available system memory.
• Last Calibration: Timestamp of the most recent calibration.

Time Synchronization

Accurate timestamps need a correct device clock. Devices with internet access sync automatically via NTP. For offline or hotspot-only devices, use manual sync here.

• Browser Time / Device Time: Displays both for comparison.
• Sync: If the mismatch exceeds 10 seconds, a sync button appears to set the device clock from your browser.

Geolocation

When location services are active (Settings > Measurement > Location), the Geolocation card shows position and altitude data. Available fields depend on the installed hardware modules.

• Location: Latitude and longitude with the source and accuracy indicator. Sources vary by hardware: GPS module (optional), cellular modem cell tower lookup (optional, requires 4G module), or IP-based geolocation (available on all WiFi-connected devices).
• Altitude (barometric): Altitude derived from the pressure sensor. Optional - requires a BME280 pressure sensor.
• Altitude (GPS) & Speed: GPS-derived altitude and current speed. Optional - only shown when a GPS module is installed and has a satellite fix.

Figure 4.7: System Status viewer

5. Maintenance Procedures

5.1 Filter Change Procedure

1. Stop any running session.
2. Unscrew the top cap of the optical chamber.
3. Remove the saturated filter.
4. Always check the unscrewed air inlet chamber for filter residue and remove if present; a soft brush may be used for cleaning.
5. Insert a new filter with Markings/rough surface Facing Up.
6. When screwing the upper air inlet back on, make sure no cables are pinched. Tighten the air inlet chamber only by hand.
7. Check Hose if used: Ensure the air hose remains connected to the inlet port as shown in picture below.
8. It is recommended to run calibration after each filter change but at least every 4 weeks (only with fresh filter)

Figure 5.1: Air inlet where to connect the hose to

5.2 Calibration

Filters may vary slightly in optical density over their surface and signals may slightly vary over time. Calibration balances the sensor signal against the reference signal for the specific filter currently installed.

1. Go to Maintenance > Calibrate Device.
2. Ensure a new and clean filter is installed.
3. Click "Yes".
4. A progress bar will appear. The device adjusts LED intensity.
5. Wait for "Calibration Successful" before starting a new log.

5.3 Data Management

Data is stored on the device's internal storage. To manage your session files:

1. Click Log Files.
2. Logs (>2KB): Valid measurement sessions. Download these for analysis.
3. Logs (<2KB): Failed starts or very short tests. These can typically be deleted.

Figure 5.2: Log files manager

Log files are downloaded as CSV for analysis. The dashboard's Download View button can additionally export the currently visible chart view as CSV, PNG, or SVG. CSV files use semicolon separation with dot as decimal divider.

6. Troubleshooting

7. Best Practices

Environment

• Keep the device away from direct sunlight, radiators, and fireplaces - it is sensitive to temperature and lighting changes.
• Position inlet away from localized emission sources unless intentionally measuring them.
• For indoor use, avoid placement near HVAC vents or drafts.

Sampling Configuration

• Sample frequency: 180-600 seconds for ambient monitoring. For direct emissions from wood stoves (typically much higher concentrations), reduce to 10-30 seconds. Shorter intervals can increase noise.
• Airflow: The user setting ranges from 50 to 750 ml/min; practical limits are hardware-dependent. Increasing airflow improves signal strength but loads the filter faster.
  • Heavy pollution (>2000 ng/m³ average): 50 ml/min works well.
  • Typical urban (~500 ng/m³ average): 100-250 ml/min.
  • Low pollution (<500 ng/m³ average): increase toward 300-500 ml/min if the filter still lasts long enough.

Signal Quality

• Signal-to-noise ratio improves with: higher BC loads, higher air volume, and smaller sample spot diameter.
• Apply median/average filtering to reduce noise - the rolling average is closer to the "real" value than individual data points.
• Calibrate after every filter change for reliable filter status indication.

8. Resources & Contact

• Project Website: https://www.bcmeter.org
• Technical Wiki: https://www.bcmeter.org/wiki/
• Quick Start Guide / Cheat Sheet: bcmeter_cheatsheet.pdf

Contacts

• Technical inquiries & manufacturing: Jonas Dahl, Berlin - jd@bcmeter.org
• Black carbon / Wood stove emissions and air quality: Axel Friedrich, Berlin - af@bcmeter.org