The process of selecting switches does not always receive the time and attention it deserves. Given the relatively low cost and simple nature of most switches, often they are selected without full consideration of the features and functionality they offer. Depending on the application, there are certain parameters that will guide a designer to choose a particular switch, but amidst the myriad of options that are available it is all too easy to be led astray.
Here we highlight ten factors that designers should consider when selecting a switch, highlighting why the choice of switch matters – and how, if chosen correctly, a switch can add value to both their product and the overall brand.
Driven by Data
The advent of the Internet of Things (IoT) is generating vast amounts of data across all sectors. This data needs to be stored or, more often, communicated. The necessity of accommodating the required antennas, transmitters and additional circuitry can have a drastic impact on the space available for operational, detection and data collection components, such as switches. Despite this, switches must still interface with the user, while also withstanding harsh environments and aggressive interaction. Manufacturers of medical equipment, for example, are increasingly focusing their investments on developing the systems and platforms to store, correlate and analyze this data. Designers must therefore carefully select switches that are capable of meeting demanding specifications, including miniaturization and low power consumption.
Meeting Physical Demands
With the growth of wearables, the demand for switches is growing. While wearable devices have been around for some time, there are different philosophies when it comes to designing devices for different industries. Components within medical wearable devices, for example, need to be resilient against rough treatment and environmental challenges, while also working the first time, every time. The challenge for designers is to ensure that every individual component is fit for purpose within the demanding environments in which these machines operate. Switches are a vital part of the interface between a user and a device, so when it comes to ensuring consistent performance, long life and quality of the switches, making the correct choice is crucial.
Common switch qualities to meet the requirements of many wearables include sealing against liquids and body fluids and low power consumption in order to preserve battery power. Switches may need to be sealed to IP67 or IP68 and have capability to work reliably with signal currents in the low milliamp range.
Within the industrial sector, for example, switches are used in a variety of applications including CNC machine controls, safety and position sensors, battery chargers, power supplies and gas detection equipment, to name but a few. One thing they all have in common is that space is limited on the PCB, both when it comes to height and footprint. This form factor is becoming increasingly important as the functionality of devices increases, making the real estate on the PCB even more valuable.
Ultra-low-profile switches can ease congestion of components and help reduce the size of end-user devices, making them more desirable in the market. Sub-miniature switches can enable flexibility, allowing electronics designers to add other components on the PCB in space that would otherwise be reserved for a bigger switch. It is not uncommon for many types of automation sensors to require tact switches with footprints of 3.0mm x 2.6mm, with newer tact switches now on the market with footprints under 2.0mm.
Another crucial consideration for switch choice is the required signal current. There is a great variety in electrical requirements depending on the product design, with some switches needing to handle low signal currents for PLCs and microprocessor inputs, while some need to handle higher currents in order to actuate relays.
Tact switches typically handle currents down to 1 milliamp (mA) at 32VDC with some going as low as 1 microamp (µA), while snap acting switches may need to handle up to 25 amps to control a motor circuit. Circuit breaker auxiliary switches present a challenge as they may need to handle a current range from 1 milliamp up to 10 amps with the same switch.
Fit for Purpose
Considering where and how a switch is to be used is vital. Switches are often employed in harsh environments and need to be able to handle any condition they may encounter. Users interact with switches every day, from pushing buttons on a gas pump, opening doors on trains, pressing keypads on ATMs, calling and selecting a floor in an elevator and more; the list is endless. One thing in common is that these publicly accessible devices are far more likely to suffer abuse or encounter harsh environmental conditions.
For these applications, highly rugged switches that are resistant to harsh treatment are needed to create Human Machine Interfaces (HMIs) that stand the test of time. These switches differ from standard switches in terms of their construction materials and methods. For example, most anti-vandal switches will carry an impact rating of IK08 or IK10 (the highest possible impact rating), as well as be sealed to an ingress protection (IP) of IP67. A range of feature options such as LED illumination, function symbols, and termination styles such as solder lugs or quick connect terminals is also needed to accommodate a large variety of applications.
Array of Options
There is nothing worse for a designer than being constrained by a limited selection of switches. Basics such as the number of poles and throws, latching/momentary action and other electrical parameters are all necessary considerations. Also important are environmental characteristics and the reliability of the switch. Getting this correct means defining the right materials, especially for the contacts, and ensuring that the lifecycle is compatible with the expected lifetime of the equipment. A switch’s ergonomics and aesthetics often influence the user’s experience and perception of the equipment.
Common options to consider also include different actuator styles for pushbuttons and snap switches, termination options such as solder lugs, quick connect terminals, or wire leads, straight vs right angle mounting, surface mount vs through hole, and illumination vs non-illumination.
Sound and Feel
The sound and feel of the switch, otherwise known as haptics, are important elements of the switch operation. This provides crucial feedback to the user to let them know that the switch has been operated correctly. Selecting switches with the correct haptics can give a high-quality feel to any product. Haptics have become more important in the automotive industry, for example, as vehicles become more complex and feature rich. In fact, haptics are now crucial to the design of automotive interiors and controls. The look, feel and sound form an important part of the brand identity of the vehicle, and switches are key to this – and successful choices are then often replicated across multiple models from the same manufacturer.
Haptics and acoustics not only position one manufacturer against another – but can also be used to define the position of a model within a range of automobiles from the same manufacturer. It’s important to choose suppliers who are willing to modify switch components and materials (such as the durometer of the actuators and shape of the metal domes) to achieve the correct switch haptics.
Counting the Cost
There is no hiding that cost is an important consideration when it comes to switch selection. The industrial market, for example, is particularly focused on cost and will choose a switch that is “good enough” for the application. This cost-conscious option can be achieved by opting for the most common versions used by the market – ones that do not require a high-performance level and instead deliver economical pricing while retaining rigid quality control. When additional functionality is not required, selecting standard, off-the-shelf variants will prove to be the best strategy.
Cost of Ownership
While it is essential that any solution reflects the needed features and requirements, it must also meet the cost constraints to be commercially viable and meet the needs of the customer. In this context, ‘cost’ refers to more than just the cost of the component; it also must include everything needed to integrate the solution, connection costs and assembly costs – the so-called ‘total cost of ownership’. For example, the realities of today’s automotive industry force automakers to be more efficient in how they produce parts and vehicles; however, at the same time, they must make sure nothing is lost in terms of quality and performance.
Many industrial applications are meant to last for up to ten years in environments which may be dirty, wet, or corrosive. The switches used in these applications need to conduct low signal currents (under 50 mA) at temperature ranges from -40°C to 85°C without oxidation or corrosion of the contacts. Cycle life requirements may range from 50,000 up to 5,000,000. Failure to meet these specifications could result in costly replacement of the end equipment.
When Less is More
Although there may be fewer switches required in the next generation of innovative devices and products, they will still have a vital role to play. The connected, electric and autonomous car of the future, for example, will have more advanced HMIs that need to meet the expectations of consumers familiar with high-quality consumer electronic products such a smartphones and tablets. In future autonomous vehicles, there will be a need to integrate more control functions. The driver will have more time for entertainment or even to work while the vehicle takes them to their destination. This heightened expectation needs to be considered when selecting appropriate switches.
Any product is only as good as the sum of its parts. Whether incorporated into a precision surgical instrument, a sophisticated panel entry system or a car key fob, switches must adapt to the specifics of the product designs they’re used in. By taking these ten design factors into account, design engineers can be sure they are choosing the best switches for their applications.
Mike Bolduc is Global Marketing Manager at C&K, where he is responsible for leading market strategy and global growth efforts for the industrial and medical business segments. Mike has an engineering and business background and over 25 years of diversified experience in the automotive, semiconductor, HVAC, aerospace, industrial, and medical industries working for large global corporations such as Texas Instruments and Stanley Black & Decker.