Bald SENSE is an open-source FeatherWing that measures temperature, humidity, color and light, and provides hardware for sound sensing, timekeeping, and removable storage. It needs a compatible Feather microcontroller board to operate. In the documented build, an Unexpected Maker FeatherS3 supplied an ESP32-S3, Wi-Fi, and Bluetooth; CircuitPython brought up the board’s sensors, MQTT transmitted readings, and Grafana graphed them. Its microSD socket also supports logging without a network connection.
What is the Bald SENSE FeatherWing?
Bald SENSE is an environmental-monitoring expansion board made to mate with nearly any Feather microcontroller. It is not a standalone logger: the Feather host supplies the processor and, depending on the model, wireless connectivity. The documented project used an Unexpected Maker FeatherS3 with an ESP32-S3.
The PCB combines several sensing and logging components:
- SHT31: measures temperature and humidity.
- APDS-9060: provides color and lux sensing.
- PDM microphone: hardware for sound sensing, subject to host and firmware support.
- DS3131 real-time clock (RTC): keeps time and has a coin-cell holder for backup power.
- MicroSD socket: provides removable storage for data logs.
The board is designed for the Feather ecosystem, but verify the fit and software support for the specific Feather you choose. Adafruit’s FeatherWing library documentation covers FeatherWing-specific CircuitPython classes and recommends installing the Adafruit CircuitPython library bundle along with required drivers.
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- � 3% relative humidity measurements with a range of 0�80% RH
- �0.4 �C temperature accuracy at a range of -10 to +85 �C
- Uses I2C for data transfer so it works with a wide range of microcontrollers
- PTFE filter to keep the sensor clean
Which Feather board works with Bald SENSE?
The project report’s build used an Unexpected Maker FeatherS3. Its ESP32-S3 provides 2.4 GHz Wi-Fi and Bluetooth, allowing the assembled system to transmit data as well as record it locally. Other Feather boards may be suitable, but wireless features vary by host; check the selected board’s interfaces, CircuitPython support, and compatibility with the Bald SENSE connections before building.
A compatible Feather board is a separate, required companion to the Bald SENSE Wing. For example, the official CircuitPython board directory entry for Feather Bluefruit Sense describes that Feather as compatible with the Feather form factor, battery-charging, Bluetooth/BTLE-capable, and breadboard-friendly. Those attributes describe that board; they do not establish that it has Wi-Fi.
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- PCB dimensions: 22.9mm x 50.9mm / 0.9" x 2"
- Display area: ~25.8mm / ~1.0"
- Weight: 4.8g
- On 32u4 or M0 Feathers, buttons A, B & C connect to 9, 6, 5 respectively
- On Huzzah ESP8266 Feather, buttons A, B & C connect to 0, 16, 2 respectively
How does the CircuitPython logging workflow work?
The documented workflow uses CircuitPython to communicate with the Bald SENSE sensors and integrated circuits, MQTT to send IoT readings over a network, and Grafana to graph collected data. Local microSD logging provides a separate storage path when the network is unavailable.
- Choose and install a Feather host. Select a compatible board with the connectivity and interfaces your project needs; attach the Bald SENSE Wing according to the board and Wing documentation.
- Set up CircuitPython and libraries. Use the CircuitPython build appropriate to the Feather, then install the Adafruit CircuitPython library bundle and any required drivers described in the FeatherWing documentation.
- Bring up supported sensors and ICs. The documented build used CircuitPython for the Bald SENSE sensors and integrated circuits except the PDM microphone. The project report says the ESP32-S3 had hardware PDM support but that CircuitPython did not support that interface in that build.
- Choose a data path. Write readings to the microSD card for offline logging, publish them through MQTT when the host has an available network connection, or use both paths if your implementation supports them.
- Graph transmitted readings. The project used Grafana to graph data collected through its MQTT workflow. The project report does not specify broker configuration, topic names, or a complete installation recipe, so those details depend on your software setup.
PDM microphone support is version-sensitive. Check the current CircuitPython support for the chosen Feather and its PDM interface rather than assuming the limitation in the documented build still applies—or that it has been resolved.
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Can Bald SENSE send data over Wi-Fi or log offline?
Wi-Fi transmission depends on the Feather host, not just the Wing. With the ESP32-S3-based FeatherS3 used in the project, the host supplied 2.4 GHz Wi-Fi and Bluetooth. Pairing a different Feather does not guarantee Wi-Fi; confirm its connectivity before planning remote telemetry.
For offline collection, the Bald SENSE microSD socket provides removable storage. The RTC can supply timekeeping, with a coin-cell holder for backup power. The project description does not provide RTC accuracy figures or a quantified battery life, so those should not be assumed for a time-sensitive deployment.
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- For charging single Lithium Ion/Lithium Polymer 3.7/4.2v batteries (not for older 3.6/4.1v cells)
- 100mA charge current, adjustable to 500mA by soldering a jumper closed
- If you want to add an On/Off switch, we also made that really easy. The two 0.1" holes with a box around them are the battery output line. Carefully cut the trace between them with a hobby knife and replace with two wires from a switch like this slide switch, or this pushbutton one, for example.
- Please note that for the Itsy nRF52840 this backpack covers the reset/user buttons (you could use 3 wires instead of having it sit on top.
- Skill Level: Assembled and Tested
What did the garden test reveal about heat and readings?
The project author tested MQTT and data-logging code in a small garden. Grafana graphs showed the plants received at least six hours of sunlight. The same test reported enclosure ambient temperature reaching 70 C, at which point the ESP32 ADC drifted significantly. These are observations from that project, not independently replicated laboratory measurements, and the report does not establish a universal threshold for every ESP32 board or enclosure.
The reported drift is an important design warning: an enclosure’s internal temperature can affect measurement reliability. For deployments that may heat up, monitor the temperature near the electronics, validate readings under the actual enclosure conditions, and treat ADC values near the reported condition with caution. The source does not quantify the amount of drift or identify a correction factor.
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- Durable Construction: Made from rugged plastic for long-lasting use
- Flexible Range: Can detect objects up to 80cm away
- Easy Installation: Includes 10cm cable for quick and simple setup
- Compact Size: Measures just 6.5mm diameter for space-saving design
- Reliable Performance: Consistently accurate readings for reliable operation
What to check before building
- Host compatibility: confirm your Feather physically and electrically works with the Wing and offers any interfaces your application needs.
- Network needs: verify Wi-Fi or Bluetooth on the specific host; neither is guaranteed by the Wing alone.
- Firmware support: check current CircuitPython support for all sensors and the PDM interface on your chosen board.
- Logging and time: provide a microSD card for removable logging and confirm the RTC backup setup suits your needs.
- Thermal conditions: evaluate enclosure heat and validate sensor and ADC behavior in the installation environment.
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