12 Ideas for Implementing NFC in Your Design
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Previously, in my Introduction to NFC article and providing some background information on NFC, I mentioned that NFC is an extremely versatile protocol. There are many ways you could implement it in your next product, or build a product around its capabilities. Most applications you would come across day to day are simple tags and readers, such as building access or making payments through Google Pay or Apple Pay, where your smartphone is emulating a tag.
There are many more possibilities for NFC; some of these project ideas are taken from commercially available products or research papers; others are ideas from working through reading the NFC standard.
One of the most common uses for NFC is out-of-band credentials sharing. To share credentials for WiFi, users are likely to already own an NFC-enabled smartphone appropriately configured to their home WiFi network. Through NFC they can share the credentials and SSID with visitors without typing complex alphanumeric passwords or reaching behind their dusty routers to read the label.
Many inexpensive WiFi devices behave like WiFi access points when first powered. If you are building a WiFi connected device, you might also act as an access point to allow your device’s initial configuration. Unfortunately, this feature is not well received by smartphone operating systems, as the device cannot provide internet access and appears wildly insecure in comparison to a modern router. I had to battle with this myself recently, setting up a robotic vacuum cleaner.
NFC can also be used to configure a Bluetooth connection for an audio device, enabling the user to pair it with using just a single “tap” instead of:
- Enable Bluetooth on the smartphone
- Power on the device
- Enable pairing on the device
- Open settings
- Wait for Bluetooth to scan and find the device
- Pair the device
NFC allows eliminating the layer of complexity introduced by having to manually type in WiFi credentials, reduces errors, improve user experience, and allows for easy re-provisioning without resetting the device. An improvement of the user experience when they first begin using your device can go a long way to creating a good first impression.
WiFi-enabled applications usually require a considerable amount of computing power; for this reason, RTL8195AM from Realtek could be a good fit, featuring an ARM®Cortex™-M3 CPU and integrated WiFi and NFC.
Numerous Bluetooth SoC such as Nordic Semiconductors nRF52832, NXP’s QN9090, and QN9030 feature integrated NFC.
Many devices that communicate through mesh protocols such a ZigBee or Bluetooth Mesh may require advanced configuration to join the network. Reaching hidden buttons or power cycling devices installed on walls, such as switches, night lights, and PIR sensors, may be somewhat cumbersome, especially if we want to reconfigure them after the first adoption.
NFC can be utilised for testing and configuring such devices after they have been physically installed by an electrician, without introducing complications needlessly during the early deployment phases. Having wireless communication with the device to perform configuration and diagnostics without the need for potentially insecure protocols that require a relatively expensive IC onboard, you can save installation costs without compromising the device’s security or substantially increasing the bill of materials cost.
For such applications, STMicroelectronics ST25DV-I2C could be a perfect choice thanks to the ease of use, low cost, and intuitive I2C interface.
Configuring devices after manufacturing often requires either a wired debug connection or a temporary wireless network to be provisioned.
NFC allows product configuration while still in the box. For example, you may configure a high-end electronic gift with the user’s name in advance directly at the point of sale.
An electronic device that requires different configuration depending on the country it sells in, for example, radio communication devices, could be configured after packaging and QA. This way, instead of keeping separate stocks for every destination country, you only need a single product: configure it last-minute, add a label on it and ship it to the customer or distributor. This allows a mixture of Just in Time production and warehoused stock, which can save significant capital yet still allow rapid shipping to any region.
This concept could also be combined with the idea above. It allows a device to be pre-configured without unnecessary handling before shipping to the installation site, saving the need for a field applications engineer visit.
Widespread ICs that support double-port memory operation include NXP’s NT3H2111 and the STMicroelectronics ST25DV-I2C.
Analogue components that present unwarranted drift over time or production/supply variances can be extremely frustrating to adopt in mass production. The solution has always been limiting the component usage to a specific sub-assembly of your product, building a custom jig to supply power, testing, and re-calibrate your product afterward.
NFC Tag ICs by some manufacturers offer up to two programmable PWM outputs. With the addition of a couple of passive components, the PWM output can easily be turned into an analogue output.
The lighting industry’s broad adoption to optimise and compensate for various parameters in LED modules has driven down the price ICs with this functionality. The PWM output can quickly be adopted to compensate for the drift or variances in your analog components. Alternatively, such features could be used to program basic product capabilities by using an ADC channel in your MCU instead of I2C or SPI communication if you are short on communication ports.
Examples of NFC Tags offering PWM outputs are the STMicroelectronics ST25DV-PWM and NXP’s NTP5210, the former offering up to 15-bit resolution at 448Hz.
Many embedded devices produce error codes, and most products with properly implemented self-diagnostics features but limited memory and user interface space to display complex messages are restricted in how much information can be provided to a user.
Looking up error codes in a manual that has been thrown out or long forgotten in a basement, has always been impractical and annoying. It just adds to the frustration the user may be already experiencing due to the product malfunctioning.
Through the dynamic generation of an NDEF record, NFC can be used to point the user to a specific web page (or app content) such as http://support.company.com/product/error123.
Additional content, such as a support email address, website, or telephone number, can also be automatically exposed when an error code pops up. By assisting the user in handling the error with a simple tap of their smartphone against the device you can save on support costs and improve user retention.
Assuming your product features an internal debug interface to read the code, LPC8N04 from NXP could be used to implement the modest logic needed to translate such codes to readable URLs.
Cost-Efficient Wireless Power
Implementing an ad-hoc wireless power-transfer technology may be non-viable in many projects due to the risk of not meeting EMC compatibility certification requirements.
NFC is currently the cheapest and easiest way to implement a sub-watt wireless energy transfer using only widely adopted technology.
SIC4310 By Silicon Craft, a lesser-known manufacturer, features up to 10mA and 3.3V output, which is perfect for such applications.
Communication With a Rotating Device
Imagine the following scenario: you have a fixed piece of equipment with a rotating body that has a device mounted on it. Let’s assume you want to communicate with the device on the rotating component of the equipment, from the fixed side.
For example, you want to place a sensor on a crane or piece of industrial equipment. Electro-mechanical interfaces cannot operate reliably for extended periods in conditions, and vibrations and industrial environmental conditions significantly impact the lifespans of mechanical interfaces. If you’re trying to convey data without power, any rotating contact is going to introduce a lot of spurious signals.
Using some form of radio-communication seems the best idea, similar to how pressure sensors mounted to car tyres communicate with the onboard computer.
The NFC protocol is perfect for this application: NFC antennas can be designed to helical, having almost perfect rotational symmetry over the rotational axis. If the sensor or device has a limited power draw, using the wireless power idea above can also allow the sensor/device to operate for extended periods without changing or charging a battery.
NXP Semiconductors offers a dev kit covering this precise scenario, the PN5180.
Communicating Through a Waterproof Barrier
Proving a waterproof seal around a connector can be extremely difficult, especially if the product is exposed to saltwater, plenty of UV radiation that can dry and damage o-rings, and if power has to be provided to the connection, increasing the risk of electrochemical damage. NFC is not affected by such issues, and NFC antennas can easily be hidden behind a sealed plastic wall or embedded in silicone or epoxy potting.
Further elaborating on this idea, NFC can be used to communicate through small amounts of water effectively. Most physical communication layers we use are negatively affected by water. Communicating using electrical potentials makes the product susceptible to corrosion, electrochemical effects, and water penetration due to the difficulty in adequately waterproofing connectors. The use of visible or infrared light for communications is almost always non-viable, as light is scattered and absorbed by water, even though not all frequencies of light are absorbed equally. RF fields are absorbed while electrical fields are shielded in saline water. The 2.4Ghz ISM band, and therefore WiFi and Bluetooth, exists because of the band's effectiveness in microwave ovens to heat the water in food. Acoustic waves, one of the most common means of communication underwater, are affected by multipath propagation, absorption, high power consumption, low bandwidth, and ambient noise.
NFC is based on magnetic induction and thus performs quite well through a significant number of mediums, including a modest quantity of water.
Products exposed to the elements, especially if sealed, are unlikely to receive maintenance and are often designed to be set up and forgotten about. An NFC tag used as memory storage is likely to outlive the product and could be accessed post mortem for diagnostics and failure analysis.
The capabilities of NFC to overcome mediums different than air must be tested experimentally; it would be a mistake to simply look up the magnetic permeability of the material, as the RF field is dynamic (at 13.56MHz) and not static. The NXP NTA5332 IC features Active Load Modulation, a feature primarily used to improve the capabilities of the physical layer allowing for smaller antennas. That can compensate for the attenuation of the signal in less than ideal conditions as well.
Communications for Harsh Environment/Explosion Proof Devices
Some devices must be built to resist high impacts and temperatures. NFC tags are available in a wide range of industrial temperature ranges and can be easily embedded in epoxy or silicone.
With no connectors that could cause a static arc, NFC is friendly to explosion proof designs for use in environments with potentially flammable gasses.
NFC tags can be placed directly on metal through a layer of ferrite; usually, these tags take the name of metal-proof or on-metal tags. Where far-field wireless communication struggles to penetrate a completely sealed metal enclosure, NFC’s magnetic coupling can continue to work.
An industrial application may find the ST25DV series from STMicroelectronics to be ideal, with a temperature range from -40°C to 85°C and up to 400k EEPROM writing cycles at 125°C.
Diagnostic and Configuration Interface
Products often feature a primary interface for the user coupled to a secondary interface for debugging and maintenance; the latter kept as far from the user as possible. A secondary interface may be implemented with a UART, hidden web API, telnet, or an SSH connection, but all the cheapest ways to implement such a feature require placing a dedicated connection internally to the product. For diagnostic purposes, having to open or dismantle the device to access the secondary communications interface can be a considerable time cost. Mixing diagnostic or configuration with the user-accessible connection can provide a potential security hole.
A simple diagnostics interface can be implemented with NFC and accessed without opening the products. The interface can easily be password or encryption key protected and can expose all relevant configurable parameters through NDEF records.
Among the few relevant ICs implementing security features, we can note NTA5332 from NXP, due to being extremely friendly to the electronic engineer and supporting AES encryption standard. Numerous ICs implement comparable measures, but many of them are more geared towards smart cards.
Interacting with Sensors
Many sensors require only limited power and network connectivity, with data gathering intervals weekly or monthly. For such devices, a human operator tapping an NFC-enabled sensor might be the most convenient option. This could be particularly relevant to sensors that are part of a daily checklist spread out through a facility, allowing automated data entry whilst still requiring a human to physically check the equipment/sensor.
The SL13A IC by AMS has been specially designed for this role, adopting a 10 bit ADC and up to 3.4V and 4mA output to power sensors and external circuitry. If coupled with a thin battery, such an IC is exceptionally versatile for environmental data logging.
Implementing firmware updates is hard. By adopting an NFC SoC, such as LPC8N04, you could introduce a low-cost and widely compatible means of performing firmware updates that could be employed by technicians and end-users alike through a smartphone app.
The Power Harvesting feature of NXP LPC8N04 could also help implement firmware updates in systems that are automatically power-cycled, as the NFC SoC would remain powered by the RF field.
More self-sufficient designs could take advantage of EM Microelectronics NF4 extremely high data rates and 64KBytes memory.
How Could You Use NFC?
As you can see, NFC has a wide variety of uses, from implementation to tech support, as well as communications in challenging environments.
In the past, I have built elaborate means of communications in harsh environments where explosive and corrosive vapours, high temperatures, or severe vibrations have made a traditional connector extremely challenging to design in. Far-field radiation-based protocols such as WiFi or Bluetooth are not suitable or capable due to enclosure or security requirements. NFC would have solved many problems for these projects; however, having to supply or design a specialised reader would have defeated many of the benefits.
With the prevalence of NFC readers in modern smartphones and ease of app development for the smartphone, NFC is now a viable option for these challenges. Its versatility allows a wide range of exciting possibilities that were previously impossible or expensive to implement.