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Wi-Fi Device-to-Cloud Data Pump

For developers looking for the ability to expand their wireless connectivity options beyond cellular without sacrificing the simplicity and power of the Notecard.

The Wi-Fi Notecard is a version of the Blues Notecard with Wi-Fi connectivity in place of cellular. The device is the same size as all cellular Notecards and follows the same m.2 pinout. What's more, the Wi-Fi Notecard uses the same powerful JSON-based programming interface, meaning that developers can easily add Wi-Fi as a deployment option for their IoT solutions, with minimal impact to their existing host applications.

Functional Description

As an embeddable device-to-cloud data pump, the Notecard eliminates all complexity and friction that exists with existing IoT solutions. It enables development and rapid iteration of production-quality secure cellular or Wi-Fi IoT solutions at an extremely low, fixed cost. With as little as two lines of code on the controlling MCU, and with no external libraries or dependencies, data can be sent from device to cloud.

Notecard is:

  • A drop-in embeddable data storage and transport module for Wi-Fi IoT products, pumping JSON-formatted or binary data ("Notes") bi-directionally between device and cloud:

  • JSON from/to MCU application using I2C, Serial, or USB.

  • JSON to/from your cloud app using HTTPS.

  • JSON is auto-tagged with date/time, tower, and GPS locations.

  • A removable and field-upgradable 30mm x 35mm system-on-a-module (SOM).


  • Low-power. Designed to operate on battery power, be "always-on", maintain time & location, while typically drawing less than ~8µA when idle.

  • MCU-agnostic. Will support any MCU or single-board computer as your app processor - even low-memory, 8-bit microcontrollers.

  • Secure. Integrated STSAFE Secure Element with hardware crypto, true hardware random number generator, and a factory-installed ECC P-384 certificate provisioned at chip manufacture.

  • Simple. Uses a JSON command interface over I2C, UART, or USB. Allows you to connect your 3.3V MCU, while eliminating complex AT commands and state to manage.

  • Power-conscious. Mostly-offline data sync mode for low power, and always-online mode for low latency.

  • Efficient. Battery-powered Wi-Fi without the complexity of managing connections, queues, or storage.

  • Integrated. Utilizes an extremely thin cloud infrastructure that directly routes your data to where it belongs: AWS, Azure, GCS, or your own cloud.

  • Built for data. Data routing and simple "no code/low code" visual data stream analysis through (SaaS), or host and integrate Notehub functionality into your own app (OSS).


The performance of the STM32 microcontroller onboard the Notecard may be affected in the presence of extremely bright light including, for example, direct sunlight. Bright light may interfere with the semiconductor's operation by generating unwelcome electrical currents, performance degradation, malfunction, or shutdown.

If you anticipate that bright light may shine on your Notecard in its deployed setting, we recommend you mount the Notecard in a shadow, or that you cover the STM32 microcontroller with an opaque tape to reduce light levels that may affect the semiconductor.

Package Configuration


  • Module: Silicon Labs WFM200S Wi-Fi Transceiver Module

  • Radio: 2.4 GHz 802.11b/g/n

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Module Datasheet

Block Diagram

The Notecard is packaged using a compact removable form factor, 30mm x 35mm.

Open hardware schematics for both the Notecard and Notecarrier boards are available on GitHub, making it a straightforward task to embed the Notecard into a broad variety of host device designs.

The Notecard can interface with the host MCU at 3.3v levels.


Typical Application

As shown below, Notecard is not an application processor and hosts no customer application code. It can be used as data pump peripheral that is focused on bidirectional, asynchronous, secure data staging and transfer of JSON notes. The Notecard can also be configured as a low powered, autonomous, asset tracking device, in which case it does not require a host processor.


Key features

  • Security

Modern services require that the cloud and the device perform bidirectional authentication so that neither can be spoofed. For many applications it's important that over-the-air and over-the-wire data is encrypted. For this reason, the Notecard integrates an STSAFE Secure Element which contains symmetric keys manufactured into the chip. Neither the manufacturer of the Notecard nor the manufacturer of the customer's product has any need to handle or manage secure key material. The keys generated by STMicroelectronics for the Notecard use ECC with the NIST P-384 curve, and the signature algorithm is ECDSA-with-SHA384.

  • Low Power Consumption

The Notecard has sophisticated power control and makes heavy use of variable clock speeds. This enables the Notecard to have a typical idle current consumption of ~8uA at 3.3V, while still supporting active UART and I2C communication.

Power Information

The Notecard's main supply voltage (VMODEM_P) is used for the cellular modem and associated circuitry. The Notecard has on-board regulators designed for direct connection to a battery, so any voltage in the range of 2.5V to 5.5V may be provided.

The Notecard typically sits in an ~8µA idle mode waiting for a request from the host MCU, however the Notecard current draw increases to the ~250mA range when the modem is active. Furthermore, when in a region requiring the use of GSM, it can spike to up to nearly 2A for a few milliseconds. The modem also draws 10's of mA when the GPS is receiving or the CPU is performing session encryption. As such, it's recommended that VMODEM_P be directly connected to a battery or other supply that is capable of such brief spikes. It is also recommended that PCB traces for VMODEM_P and GND be designed to handle such current.

The Notecard's logic voltage (VIO_P) is provided by the Notecarrier or host system for digital communication; it will be either 1.8V or 3.3V. Although the Notecard typically draws very little current, this supply should be designed with a 150mA budget allocated to the Notecard.

Pin Name
Pin Numbers


In order to take advantage of various Notecard features pertaining to "dynamic line voltage detection" (both now and in the future), or establish a USB Serial connection to the Notecard, you must connect the VUSB power pin and support the USB power design aspects of the Notecard.

Features include:

  • Continuous mode behavior with the usb flag.

  • Triangulate mode behavior with the usb flag.

  • Monitor mode behavior.

Antenna Requirements

The radio on Wi-Fi Notecard has an embedded antenna, though an external antenna can be used when connected through the u.FL connector on the Notecard. Any external antenna must support a 2.4 GHz frequency band.

The antenna included on the Notecarrier-A Series as well as the external antenna provided with the Notecarrier-PI support 2.4 GHz and have been tested with the Wi-Fi Notecard.

Cellular Service

This section does not apply to the Wi-Fi Notecard.

Pin Name
Pin Description

Pin Description

Notecard M.2 Key E, Edge Connector Pinout

Pin #
Pin Name
Func. Interface
Func. Interface-1
Pin Name-1
Pin #-1

Link: Digi-Key part number of the connector - Both Digi-Key and Mouser have pictures for this part number that show a component with a different key, but both have links to datasheet/drawing/CAD models.


All pins whose Functional Interface is marked "Power" must be connected.

All pins named NC MUST have no connection and be left open because they are reserved for future use. Furthermore, any pin not used in a design MUST also be left open.

Those pins ending with _P may be optionally protected from anomalous external conditions on some Notecarrier designs, depending upon use-case specific requirements.


Technical Details

Host Microcontroller API

Notecard supports an extremely rich, simple API whose syntax is standard JSON. The developer can communicate requests to Notecard, generally by using little more than printf function available in most programming languages.

Serial Communication

JSON requests and responses (the Notecard's Application Programming Interface "API") may be sent over any of the following interfaces:

  • USB Serial Interface

  • UART Serial Interface

  • I2C Interface


If NOT using a Notecard firmware library, you may unintentionally send requests to the Notecard so fast that you overflow the 1500 byte buffer used to receive data (whether it be I2C, Serial, or UART). The solution is to pause 250 ms after every 250 bytes sent and ensure the total size of each NDJSON object sent is no more than 8KB.

API Reference

For API usage, names, and parameters, please refer to the Notecard API Reference.

USB Serial Interface

The USB Serial Interface appears to the host as a USB 2.0 Full Speed CDC device. You can access it from Linux, Windows 10 or macOS without a device driver using terminal emulation software. Newline-delimited JSON requests may be sent directly as UTF-8 text over this port, or you may use the open-source Blues libraries for C, Python, Go, and Arduino.

Pin Name
Pin Number

UART Serial Interface

The UART Serial Interface operates at VIO_P at a fixed baud rate of 9600 using eight data bits, no parity bit, and one stop bit. Newline-delimited JSON requests may be sent directly as UTF-8 text over this port, or you may use the open-source Blues libraries for C, Python, Go, and Arduino.

Pin Name
Pin Number

I2C Interface

The Notecard acts as an I2C secondary device operating at VIO_P, and it implements a simple Serial-over-I2C protocol. You can access it from an embedded host using open-source Blues libraries for C, Python, Go, and Arduino.

Pin Name
Pin Number

Host Microcontroller Hardware Interface

Attention Interrupt

Using software, you can optionally configure Notecard to use the ATTN output pin to:

  • Inform the host MCU of certain asynchronous events (such as incoming data availability, or Notecard motion) in an interrupt-driven manner rather than just polling.

  • Place the host MCU into a power-off sleep state and wake it back up again.

Pin Name
Pin Number

Note: This pin operates at VIO_P. If it is unused, it can be left disconnected.

Auxiliary Ports

An optional Auxiliary UART Serial Interface is available on the AUX_RX_P and AUX_TX_P pins. This interface is inactive unless enabled by raising the AUX_EN_P pin since this UART consumes extra power when in use. It operates at VIO_P at a fixed baud rate of 115200 using eight data bits, no parity bit, and one stop bit. If this interface is unused, the three pins can be left disconnected.

The AUX1-4 pins operate at VIO_P and can be configured in software to operate in several optional modes such as GPS Tracking Mode, GPIO Mode, and Internet Button Mode. If these pins are unused, they can be left disconnected.

Pin Name
Pin Number

Note: The auxiliary serial port is normally disabled because it consumes up to 100µA of power when enabled.


Use of this pin is optional. If the host system has a global reset line, caution should be used when connecting this pin to the host system's reset because the Notecard may independently pull the line low in software. Restrictions on this pin are:

  • If this pin is not used, it must remain not connected (NC).

  • The pin is active-low. It must be held low for at least 350nS for a clean reset.

  • This pin must never be pulled-up. A pull-up would interfere with the Notecard's own internal watchdog timer and thus will prevent reliable operations.

  • Some Notecarriers may invert this signal to be active-high.

Pin Name
Pin Number

Network Communication Behavior

The Notecard includes a built-in connection to (specifically and communicates over SSL. Outbound connections speak directly with the Notehub session load balancer (or "Discovery Service") for provisioning and device authentication. By default, the TLS connection is unidirectional, but can operate bi-directionally, if needed. The keys and certificates for each device are provisioned by STMicrosystems inside the STSAFE secure element present on every Notecard. Once the Discovery Service has provisioned or authenticated a device, it issues a "ticket" and a Handler IP address that the Notecard can use to make subsequent requests.

The Notecard can also connect to the Handler to do a constrained set of remote procedure calls related to synchronization. If the Notecard determines that the data queued for transmission to or from the Handler should be encrypted, it opens a session to the Handler on port 8086. Otherwise, an unencrypted socket is opened on port 8081.

The over-the-wire data transmitted on both sockets is highly byte-optimized, which is why raw SSL and TCP sockets are used, and not unoptimized HTTP/HTTPS transactions.


Electrical Characteristics

Absolute Maximum Ratings


Ordering Information

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Security and Vulnerability Scanning

As a part of our regular audit and scanning process, Blues Inc. performs full vulnerability scanning every six months. Any identified vulnerabilities will be analyzed, reported, and patched in a timely fashion, where appropriate.

Revision History


Contact Information

Blues Inc.
50 Dunham Ridge Suite 1650
Beverly, MA 01915

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