Smart Locks Use Smartphone NFC to Unlock—All Without a Battery

Smart locks reinvent the age-old door lock by making them interconnected and electronically controlled. However, smart locks suffer from one major pitfall: they require an energy source to work. The “smarts” in a smart lock only work as long as their battery is charged. Otherwise, they lose their functionality. To address this issue, Infineon has announced a new solution to do away with batteries in appliances like smart locks.

Infineon has designed a chip that allows battery-less smart locks to open and close via a mobile phone. 

In this article, we’ll look at Infineon's new energy-harvesting chip for battery-less smart locks and assess how the company intends to use it to help develop true passive smart locks and other appliances.

Infineon Unveils an NFC Actuation Controller

To help solve the battery limitations of devices like smart locks, Infineon has released the NAC1080.

The NAC1080 is described as an NFC (near-field communication) actuation controller, which is designed and optimized for NFC communication-controlled actuation. Specifically, the integrated circuit consists of an NFC transceiver with associated energy harvesting modules and an integrated half-bridge capable of peak currents up to 250 mA for motor control and actuation. At the system's core is a 28 MHz, 32-bit Arm Cortex-M0 MCU that also features 16 kB of integrated SRAM and 60 kB of Flash memory.

Block diagram of the NAC1080. 

One unique feature of the NAC1080 is its ability to work in two different power supply modes. The first mode is called active supply mode, where the device is powered by an external 3 V source such as a battery. The other mode is passive supply mode, where the chip uses harvested energy from the external NFC RF field.

In passive supply mode, no external power source is required. Instead, the device requires the presence of an NFC field. The chip harvests the nearby NFC energy and stores the harvested energy in external capacitors, which are sized to store the amount of energy necessary to initiate an actuator, such as a motor.

Designing a Passive Smart Lock

With the NAC1080, a smart lock can be designed without batteries—instead using the IC in passive supply mode, according to Infineon. In this way, the lock can work directly with a smartphone: the phone taps the smart lock and the lock then harvests the phone's incident NFC energy to unlock or lock the door.

Example schematic of a NAC1080 smart lock system.

For this type of design to work, Infineon asserts that the most important consideration is the energy storage needs of the system. Namely, designers must consider both the energy required to power the MCU (the high-priority supply) and the energy required to physically actuate the motor (the low-priority supply). Here, the total energy harvested by the system must exceed the needs of the MCU and the actuator. Meanwhile, the storage capacitors must also be sized appropriately to provide the required energy.

Energy balancing in a NAC1080-based smart lock system. 

Other design considerations in smart lock applications include antenna impedance matching, the coupling coefficient between the transmitter and receiver antennas, and the electrical-to-mechanical power transformation efficiency of the motor itself.

Can Some IoT Say Goodbye to Batteries?

By integrating NFC harvesting, H-bridge control, and an Arm core into a single device, Infineon believes it may have opened the door to IoT devices that don’t require a battery. This chip includes an integrated AES128 accelerator and a true random number generator. These features offer data encryption and decryption with low power consumption.

Infineon reports that this technology may be useful for low-power locks in gyms, hospitals, office furniture, bicycle locks, and mailboxes. The new chip may also be used in more complex locks—for instance, those to secure front doors. 

All images used courtesy of Infineon.