yet cost-effective solution for protecting against any user induced ESD events whilst the Littelfuse SIDACtor® devices such as the SEP0xx series that feature low insertion loss, low clamping voltage and log-linear capacitance offer excellent protection against lightening surges. Solid-state relays (SSR) further enhance protection by providing the isolation required between the microcontroller (MCU) and wireless interface. On the important Anti-tamper (3) part of the design, Reed Switches can be employed to prevent any magnetically induced tampering with the unit, and finally in the Auxiliary load output (4) again MOVs and TVS diodes can be specified to protect I/O lines from voltage transients caused by overloading and an SSR can again be used to provide isolation to the MCU.

Gas and water meters differ to electricity meter designs because they will typically be battery powered instead of mains powered, however they still share many of the same functional circuit blocks making the Littelfuse product range equally applicable for these designs as well.

Fire and Smoke Alarms

Similarly modern fire and smoke alarms do much more than trigger a loud alarm when an issue is detected. The latest connected and smart alarms send a message when they detect heat or smoke either directly to the fire service or to an external building management services team via the mobile phone network.

Inside the smart alarm, signal lines link the MCU and digital signal processing to the wireless interface, temperature and gas detectors, test push button, and UART port (used for programming). Designs that receive power from AC mains rather than from batteries also have to convert the power to DC at the correct voltage level. Both the signal and power elements of this design require protection from overcurrent and transient voltage events, again Littelfuse has a wide portfolio of suitably high performance and reliable solutions.

Figure 2 - Typical Fire and Smoke Alarm Block Diagram Figure 3 - Typical Security Camera Block Diagram

The power adapter block (1) shown in Figure 3 will require overcurrent protection fuses along with MOV and TVS Diodes for lightning and transient protection. For the DC Input stage (2a) and RJ-45 Ethernet interface (2b) there will be a requirement for overcurrent fuses and resettable PPTC fuses to protect the power stages along with TVS diodes and arrays to protect data lines.

The Memory Card block (3) on the control board can use TVS diode arrays to protect against ESD events when users insert/remove the memory card. The Motor Drive (4) block will need to be optically isolated from the rest of the control circuit to prevent interference or damage to other components within the system, this can be effectively achieved using a high current SSR such as the CPC1561 series 60V, 1A single pole current limiting relay which incorporates thermal shutdown circuitry for improved survivability in harsh environments.


In this article we have only scratched the surface with a small number of Smart Building application examples, however it is clear that whatever the application requirement for protection, control, or sensing, Littelfuse has a wide range of high-performance products which can meet the design needs.

In addition to the examples shown above Littelfuse have products which are suitable for other smart building and automation applications including smart locks, door and window sensing, garage door, intelligent power outlets, smart thermostats, elevators, home appliances and many more besides.

Design Support

Anglia offer comprehensive support for customer designs on the full range of Littelfuse products, with free evaluation kits and samples of products via the EZYsample service which is available to all registered Anglia Live account customers.

Within the AC/DC power stage (1) of Figure 2, we will find overcurrent protection cartridge fuses and MOVs to protect against voltage transients and lightning strikes. TVS diodes can be used to protect the sensitive semiconductors in the DC-DC converter stage (2), whilst for the Smoke/Fire Detection element (3), Littelfuse have highly accurate temperature sensors such as the economical KW series of NTC thermistors that feature high reliability, small form factor and fast thermal response times. The Alarm block (4) can utilise a Reed Relay or SCR to trigger the alarm, SCRs such as the Littelfuse EC103M series are excellent unidirectional switches for phase control applications and feature a sensitive gate allowing them to be easily triggered with a just few microamps of current directly from the microprocessors to help simplify the design.

Security Cameras

The same thinking applies to the third element of a smart building that we are considering here: security cameras. At its heart, a security camera is an image sensor integrated with a processor and memory. These days, the camera does much more than connect to a console staffed by a local security guard. Smart security cameras communicate with a central computer through Ethernet, Wi-Fi, or a radio band to a wireless receiver, sending event alerts, video images and receiving commands. Often, the system will also include motors for driving a zoom lens and the camera pan/tilt positioning. An AC/DC power adapter and/ or onboard battery pack will be used to power the system.

In addition, Anglia’s engineering team have extensive experience of working with a wide range of smart building applications and can provide valuable product demonstrations, insight, advice, and component recommendations for your application. To assist designers, the Littelfuse Building and Home Automation Application Guide is also available for downloaded free from or by scanning the QR code below. This useful guide details 18 different smart building applications including those covered in this article and provides suggestions for product series which can be used within each design along with links to datasheets and application notes.

Anglia are available to support customers with all aspects of their designs, offering hands on hardware and software design support along with access to an extensive resource of technical application notes and support from Littelfuse experts when required.

Visit or scan the QR code to see the full range of Littelfuse products available from Anglia.

Components in Electronics July/August 2021 9

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