Notecard Carrier Board Design Guide

Notecard can be embedded into a carrier board using a standard M.2 Key E connector. The Blues family of Notecarriers serve as examples of this approach, providing ready-made ways to house a Notecard and expose its key interfaces and features.

As your product grows, you may decide to create a custom carrier board tailored to your specific requirements. This guide walks through the key considerations involved in that process, covering essential requirements, recommended practices, and optional interfaces you may choose to support.

Table of Contents

• Required Items
  • M.2 Connector
  • Keep-Out Areas
  • Power
    • VMODEM
    • VIO
    • Ground
    • Protection
  • No Connection Pins
  • Serial Notecard Request Interfaces
    • UART Serial
    • I2C Serial
  • Cellular Antenna(s)
• Recommended Items
  • Supporting Multiple Notecard Variants
  • Attention Pin
  • External SIM
  • Enable Outboard DFU with ALT_DFU Pins
  • USB Serial Notecard Request Interface
• Optional Items
  • Enable Pin
  • Auxiliary GPIOs
  • Reset Pin
  • GPS Antenna
  • Auxiliary UART Serial Notecard Request Interface

Required Items

The following items are required for any host product that embeds a Blues Notecard.

M.2 Connector

The Notecard plugs into a standard M.2 Key E connector such as Amphenol MDT420E01001. Once inserted into this connector, it is secured along the opposite edge to a grounded standoff by a mounting screw. Blues reference designs use a Würth Elektronik 9774025151R paired with an M2.5x4 metric machine screw.

Keep-Out Areas

Carrier board designs should ensure a 5mm keep-out area around all Notecard antennas in all directions. Ideally, this keep-out area should avoid: ground planes, metal screws, metal components, and metal enclosures to avoid RF interference.

If your design supports multiple Notecard variants, be aware that antenna and u.FL connector placement varies by SKU. See Supporting Multiple Notecard Variants for more information.

Power

Notecard is designed to be powered continuously and should be left powered at all times. Provide constant power to VIO_P and VMODEM_P, and avoid power-cycling or resetting the device after boot. Idle current draw is already very low, and keeping the device powered reduces wear from power cycling and keeps the modem ready at all times. See the Low-Power Hardware Design application note for more on power architecture.

VMODEM

VMODEM_P powers the device's radio and must be applied to pins 70, 72, and 74 of the M.2 connector. Notecard requires 2.5VDC to 5.5VDC, capable of sustained 750mA draw and brief 2A bursts.

VIO

VIO_P powers the device's MCU and peripherals and must be applied to pins 2 and 4 of the M.2 connector. Supply either 1.8V or 3.3V; Notecard is capable of at least 150mA draw.

Blues reference designs provide for a 300mA draw from this supply so that there is a current allowance for peripherals.

Ground

The 12 M.2 connector pins labeled as GND must be connected to the ground of the host system (pins 3, 5, 6, 11, 18, 33, 39, 45, 51, 57, 71, and 73).

Protection

Consider whether your power scheme requires protection such as

• Fuses to protect the host and Notecard from over-current events
• Diodes to isolate power sources from each other, if your host system uses more than one

Note that Blues reference designs do not use protection diodes on some signals to avoid interference with customer low-power designs.

No Connection Pins

The M.2 connector pins whose names begin with NC in the Notecard datasheet must be left unconnected.

Serial Notecard Request Interfaces

To transmit serial JSON commands to Notecard and receive the responses, you may choose either the UART serial interface or the I2C interface, but not both concurrently. Both interfaces are active even in the Notecard's lowest-power mode, and both have on-Notecard pull-ups. These pins may be left disconnected, however in no circumstance should these pins be allowed to be inadvertently pulled to ground by, for example, a powered-off host MCU.

Although only one interface can be active at a time, we recommend routing both the UART and I2C interfaces from the M.2 connector on your carrier. This costs little board area and preserves the flexibility to switch interfaces later without a hardware revision.

Blues provides a collection of open-source firmware libraries for communicating with Notecard over either I2C or UART.

UART Serial

The UART Serial interface communicates at 9600 baud 8-N-1. Host system transmissions are received by Notecard on RX_P (pin 62). The host system receives responses transmitted by Notecard on TX_P (pin 64).

You should provide appropriate termination resistance on these transmission lines. The Notecarrier reference designs use two 100Ω resistors for this purpose.

I2C Serial

The I2C Serial interface uses a Blues-designed serial-over-I2C protocol to implement the same JSON command/response API as the UART Serial interface. Open-source libraries implementing this protocol are available here.

The I2C Serial interface uses the SCL_P (pin 40) and SDA_P (pin 42) signals.

Notecard provides 10KΩ pull-ups on SCL_P and SDA_P - no additional pull-ups are necessary.

You should provide appropriate termination resistance on SCL_P and SDA_P. The Notecarrier reference designs use two 100Ω resistors for this purpose.

Cellular Antenna(s)

Blues Notecarrier A incorporates a PCB-mounted cellular antenna to be connected to the Notecard U.FL connector labeled MAIN. The host system must provide a similar antenna, either PCB-mounted or external.

Host systems using LTE Cat-1 Notecards ("wideband" or "WB" Notecards) may optionally supply a second antenna for receive diversity, connected to the Notecard U.FL connector labeled DIV.

Both the MAIN and DIV antennas should be designed to work for the full range of LTE Cat-1, LTE Cat-1 bis, LTE-M, NB-IoT, and GSM frequencies. Although all frequencies are important, in the US it is particularly important to provide the best coverage on bands 2, 4, and 12.

Please see the Antenna Guide application note for additional information.

Recommended Items

The following practices are recommended for any host product that embeds a Blues Notecard.

Supporting Multiple Notecard Variants

The Notecard is designed to be a swappable component in your embedded product. By designing your carrier board to accommodate variation in Notecard size, you gain flexibility to upgrade to newer devices or swap between radio access technologies based on deployment location, all without requiring a hardware redesign.

While the M.2 mounting screw and standoff are in the same location for all Notecards, Notecard SKU lengths vary between 35mm and 42mm. As such, designs that accommodate Notecard variants should accept a Notecard that is at least 42mm long.

Additionally, designers should not make assumptions about the location of the u.FL connectors on a Notecard. As such, customers are encouraged to source u.FL cables with enough additional length to ensure that they can reach the u.FL connectors at the far edge of the boards.

Attention Pin

The ATTN_P signal (pin 54) is a Notecard output which can be configured 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.

We recommend connecting the ATTN pin to your host MCU, even if you don't plan to use it initially, as having the pin available enables a variety of useful Notecard features.

See the Attention Pin Guide and card.attn API for more details.

Please ensure that there is appropriate termination resistance on this line if connected.

If unused, this pin should be left unconnected.

External SIM

Cellular Notecards have an embedded SIM which provides data connectivity out-of-the-box. An external SIM will not be generally necessary for connection to the cellular network in the countries listed on the Notecard datasheet.

However, we recommend including an external SIM slot in all designs for the following reasons:

• Certification. External SIM slots are required for some wireless certifications, such as FCC.
• Flexibility. Having an external SIM slot enables device usage in regions not covered by a Notecard's internal SIM.
• Fallback. Having an external SIM slot enables cellular fallback capabilities in areas where a Notecard's internal SIM may have sparse coverage.

A Notecard can be used with an external developer-provided SIM via these pins:

• SIM_VCC (pin 8), a Notecard output provided by the Notecard's modem
• SIM_RST (pin 10), a Notecard output
• SIM_IO (pin 12), a Notecard I/O
• SIM_CLK (pin 14), a Notecard output
• SIM_NPRESENT (pin 16), an active-low Notecard input which tells the Notecard firmware that an external SIM is present and should be used instead of the internal SIM. No pull-up should be used on this signal.

If unused, these pins should be left unconnected.

Below are specifications for including both Nano-SIM and MFF2 SIM in your products. We recommend using Nano-SIM as it allows for removable external SIMs.

Nano-SIM Slot

• Connect your SIM ground to the shared Notecard/Notecarrier ground
• Connect Notecard SIM_VCC, SIM_IO, SIM_CLK, and SIM_RST to the corresponding pins on your SIM slot
• Pull SIM_IO up to SIM_VCC with a 15KΩ resistor (R1 in the diagram)
• Add appropriate series terminating resistors to SIM_IO, SIM_CLK, and SIM_RST (22Ω R2, R3, and R4 in the diagram) and place the SIM slot as close as possible to the Notecard M.2 connector
• J1 in the diagram (JAE Electronics SF72S006VBAR2500) contains a physical switch which shorts DSW to CSW when a nano-SIM is inserted, pulling SIM_NPRESENT to GND in order to signal Notecard to use the external SIM. As an alternative to providing such a selector switch, SIM_NPRESENT may be tied to GND in order to always use the external SIM.
• Connect SIM_VCC to ground with a 100nF 16V capacitor, as close as possible to the SIM slot (C1 in the diagram)
• Connect SIM_IO, SIM_CLK, and SIM_RST to ground with 33pF 50V C0G capacitors, as close as possible to the SIM slot (C2, C3, and C4 in the diagram)
• Place appropriate transient voltage suppression on SIM_VCC, SIM_IO, SIM_CLK, SIM_RST, and SIM_NPRESENT lines to prevent ESD damage when touching the slot (the five diodes of TVS1 in the diagram)

MFF2 SIM

• Connect your SIM ground to the shared Notecard/Notecarrier ground
• Connect Notecard SIM_VCC, SIM_IO, SIM_CLK, and SIM_RST to the corresponding pins on your SIM
• Pull SIM_IO up to SIM_VCC with a 15KΩ resistor (R1 in the diagram)
• Add appropriate series terminating resistors to SIM_IO, SIM_CLK, and SIM_RST (22Ω R2, R3, and R4 in the diagram) and place the SIM as close as possible to the Notecard M.2 connector
• SIM_NPRESENT must be connected to GND in order to signal Notecard to use the external SIM. This may be done with a selector switch, or SIM_NPRESENT may be tied to GND (as in the diagram) in order to always use the external SIM.
• Connect SIM_VCC to ground with a 100nF 16V capacitor, as close as possible to the SIM (C1 in the diagram)
• Connect SIM_IO, SIM_CLK, and SIM_RST to ground with 33pF 50V C0G capacitors, as close as possible to the SIM (C2, C3, and C4 in the diagram)

Enable Outboard DFU with ALT_DFU Pins

When designing a host product, we strongly recommend connecting the appropriate pins to enable Notecard Outboard Firmware Update. This capability enables reliable remote updates of host firmware using Notecard, streamlining maintenance and reducing the need for hands-on access to devices.

The standard Notecard supports the Notecard Outboard Firmware Update function on its AUX pins, where their function is multiplexed with numerous other AUX functions. More recent models of Notecard also support five dedicated M.2 pins devoted to Notecard Outboard Firmware Update, referred to as the Alternate DFU (ALT_DFU) pins.

If available, the ALT_DFU pins are the preferred pins to use for Notecard Outboard Firmware Update:

• ALT_DFU_BOOT (pin 32) is used by Notecard to control the BOOT pin of the host MCU during a Notecard Outboard Firmware Update.
• ALT_DFU_RESET (pin 34) is used by Notecard to control the RESET pin of the host MCU during a Notecard Outboard Firmware Update.
• ALT_DFU_ACTIVE (pin 36) is driven low by Notecard to indicate to the host that a Notecard Outboard Firmware Update is in progress.
• ALT_DFU_RX (pin 41) is an input on which Notecard receives data from the host during a Notecard Outboard Firmware Update.
• ALT_DFU_TX (pin 43) is an output on which Notecard sends data to the host during a Notecard Outboard Firmware Update.

Using the ALT_DFU pins for Notecard Outboard Firmware Update allows you to repurpose a Notecard’s standard AUX pins (AUX1–4) for other functionality. See Working with the Notecard AUX Pins for details.

USB Serial Notecard Request Interface

We recommend providing a direct USB connection to the M.2 connector. While not required for normal operation, a USB connection is invaluable for troubleshooting, collecting debug output, and meeting certification needs. It uses the USB_DP (pin 7), USB_DM (pin 9), and VUSB (pin 13) signals to implement a USB 2.0 Full Speed CDC device, and exposes the same JSON serial command/response protocol as the other serial interfaces.

This interface is natively supported by Windows, Mac, and Linux systems, and provides verbose debugging modes useful to developers. Note that the device will not be able to utilize its lowest-power modes while a host is connected to this interface.

If unused, these pins should be left unconnected.

Optional Items

The following practices are optional for any host product that embeds a Blues Notecard.

Enable Pin

Blues Notecarrier reference designs allow a host to pull the EN pin low to disable the regulator which powers Notecard. The large pullup resistor on this signal results in very little current draw when EN is pulled low. This type of indirect power control scheme avoids controlling the line voltage directly; your design may vary.

Auxiliary GPIOs

The AUX1-4 signals (pins 46, 48, 50, and 52) are Notecard input/outputs which operate at VIO_P. They can be configured in software to operate in several optional modes such as GPS Tracking Mode, GPIO Mode, and "button" mode.

If unused, these pins should be left unconnected.

Reset Pin

The NRST signal (pin 67) is an optional active-low Notecard input/output. This pin should never be pulled-up or pulled-down by the carrier. The host system can reset Notecard by momentarily pulling this signal to GND for at least 350ns. Whenever the Notecard might perform its own software-based reset, this line will also be affected. As such, it is important when designing a system that this signal is not "ganged" in parallel with other devices' reset pins or circuits. If a reset signal is to be sent to multiple devices, this signal should be isolated with a transistor so that the Notecard doesn't inadvertently reset other equipment.

For developer convenience, Blues Notecarriers invert this active-low NRST signal into an active-high RESET signal, but this will neither be appropriate nor necessary for most designs.

If unused, this pin should be left unconnected.

GPS Antenna

For applications using GPS, the host system must provide a GPS antenna connected to the Notecard U.FL connector labeled GPS.

We recommend the use of an active GPS antenna, which provides much better performance than a passive antenna by using a Low Noise Amplifier (LNA). Many active GPS antennas are designed to power their LNA via a DC bias voltage applied to their coaxial RF cable. In order to use such an active antenna with Notecard, connect VACT_GPS_OUT (pin 20) to VACT_GPS_IN (pin 22). This will provide a voltage between 3.3VDC and 4.0VDC to power your antenna's LNA, which will vary based upon Notecard SKU and power load. In this active mode, do not connect a passive GPS antenna to Notecard, which will present a DC short, damaging the antenna and possibly your host system.

Please see the Antenna Guide application note for additional information.

Auxiliary UART Serial Notecard Request Interface

The Auxiliary UART Serial connection is an optional interface which implements the same JSON serial command/response protocol as the other Notecard serial interfaces. Host system transmissions are received by Notecard on AUX_RX_P (pin 58). The host system receives responses transmitted by Notecard on AUX_TX_P (pin 60). This interface is only enabled when AUX_EN_P (pin 56) is pulled up to VIO. This interface communicates at 115200 baud 8-N-1.

Verbose debugging modes useful to developers are available on this interface. Notecard will not be able to utilize its lowest-power modes while this interface is enabled using AUX_EN_P.

You should provide appropriate termination resistance on these transmission lines. The Notecarrier reference designs use two 100Ω resistors for this purpose.

If unused, these pins should be left unconnected.