Bench Talk

LTE-M for Hobbyists

(Source: bublik_polina – stock.adobe.com)

It used to be that only large corporations with deep pockets and a lot of design resources could tackle designing products and devices that could connect directly to cellular networks. Small companies, hobbyists, and do-it-yourselfers typically could not even get cellular RF semiconductors.

The term Long Term Evolution (LTE) part of the cellular connectivity world is often used interchangeably with 4G, the dominant cellular communications network. Still, a new and simpler LTE-M (Machine-Type Communication) is making it more feasible for designers and hobbyists everywhere to create IoT-based systems that connect directly to the cellular world. 

But now, modular cellular hardware and firmware solutions are available to just about anyone. Hobbyists, budding innovators, and students now have a simple and cost-effective way into this once-exclusive club.

LTE-M is a machine-to-machine communication protocol ideal for IoT designs and applications. Compared to LTE, LTE-M provides faster data rates, lower latencies, and quicker internet connection times. LTE-M is also more power efficient and provides a better range at the expense of a little bit slower data rates. While this may seem a bit of a drawback, it is not for IoT devices that typically exchange smaller amounts of data.

Sensors, actuators, control and monitoring systems, traffic lights, etc., don’t require high bandwidth streaming data rates, so LTE-M is a better choice for these types of designs. Many other applications can leverage the simpler design approach, longer ranges, and sufficient data rates like seismic sensors, distributed weather monitors, and remote facilities management and security.

Commercially, LTE-M is used in applications like Cold Chain, which tracks and monitors temperatures of sensitive cargo that must be kept below a threshold temperature (like vaccines and foods). Smart AG holds the promise of enabling farm optimization through functions such as soil monitoring and automating agricultural equipment. Asset tracking is another commercially viable use of IoT LTE-M. While BLUETOOTH^® and Wi-Fi^®-based asset tracking can do an excellent job within the confines of a facility, the ability to connect to a global cellular network means there is no place to hide.

If only there were development kits and evaluation platforms that hobbyists and gizmologists could use to allow them to take advantage of this globally accessible technology. There is!

Microchip Technology is universally known for its microcontrollers, but there is so much more technology they have to offer. In addition to simple and sophisticated microcontrollers, Microchip Technology also provides power electronics (SiC), FPGA technology (Polar Fire SoC with FPGA), Automotive and CAN technology, DSP, and now, communications solutions like LTE-M.

Of specific interest is the Microchip Technology EV7ON78A development board used to develop IoT applications for direct LTE-M connectivity to the cellular network (Figure 1). Using a 'feather' form factor, it is easily breadboard compatible and hobbyist friendly. Easy to work with 100mil spaced signal headers provide easy access to all the boards I/O and signaling.

Figure 1: The EV70N78A LTE-M development kit makes it easy for anyone to develop IoT applications directly connecting to the cellular network. Breadboard friendly and compatible with Arduino, Adafruit, Sparkfun, and SEEED development environments. (Source: Mouser Electronics)

The development platform is based on the company’s AVR128DB48 AVR MCU. This 24MHz 8-bit powerhouse includes on-chip Op-Amps, A/D converters, D/A converters, and UART and SPI ports and includes the ECC608B Security and Authentication IC. This unburdens the designer from dealing with all the encryption and decryption functions needed for device-to-device authentication.

Key is the Sequans Monarch 2 cellular modem module. This ultra-low power LTE-M (and NB-IoT) certified iSIM module contains its own embedded MCU and provides global band support. Using a familiar embedded processor makes it easy to construct your own breadboard. One hundred mil spaces header ports offer all the access to I/O ports and critical signals.

For quicker development, the EV7ON78A is compatible with the Adafruit ecosystem. In addition, it easily interfaces with Arduino, Sparkfun, and Seeed, which can act as a host platform. This module even contains a Li-Ion/LiPo battery charger, which routes to the battery connector.

The open-source DxCore is readily available for all, and the EV7ON78A comes with a built-in library, including LTE connectivity drivers. Web page serving is also supported using the included HTTP web page drivers. For brokered communications, the EV7ON78A includes an MQ telemetry Transport driver, allowing edge of network devices to communicate through an access point broker.

Microchip Technology makes it easy to develop and interface firmware to the outside world (Figure 2). Simple I²C ports can be used as a sensor bus, for example. I²C is also used to communicate with the ECC608B security element. The UART talks to the cellular modem, and SPI can be leveraged for higher-speed data needs. An on-module color sensor, temperature sensor, buttons, and LEDs can be used to test signal chain and indicate status.

A PC can be used as a development workstation connecting to the on-chip debugger through USB. UART framing is used to talk to the AVR processor. An IDE is included for direct Arduino integration, and the EV7ON78A can run as a self-hosted Cloud service (AWS) for Amazon cloud connectivity.

Figure 2: The simple but elegant architecture lets designers and hobbyists access all the LTE-M functions and interface with their own IoT subsystems. (Source: Mouser Electronics)

While design engineers, hobbyists, and innovators have always been able to design IoT devices that communicate in a self-contained world through Wi-Fi or Bluetooth, connectivity to the cellular network has been a tougher nut to crack. Wi-Fi and Bluetooth are useful for some applications but are location dependent. LTE-M is more global in nature and allows location freedom.

Thanks to Microchip Technology, anyone can now design cellular connectivity into their projects, especially IoT applications. And don't forget about the many other developments and evaluation boards Microchip offers for wired and wireless applications. We hobbyists live for these things.

After completing his studies in electrical engineering, Jon Gabay has worked with defense, commercial, industrial, consumer, energy, and medical companies as a design engineer, firmware coder, system designer, research scientist, and product developer. As an alternative energy researcher and inventor, he has been involved with automation technology since he founded and ran Dedicated Devices Corp. up until 2004. Since then, he has been doing research and development, writing articles, and developing technologies for next-generation engineers and students.