In this article, CUI Devices offers electronics purchasing professionals a detailed insight into tactile switches, including construction, design specs, wiring and more
In essence, a tactile switch is a momentary action device that provides perceptible feedback through touch, reassuring the user the switch has functioned. Additionally, certain models are designed as normally-closed switches, which deactivate the current when pressed and reactivate it on release.
User confusion can arise from tactile switch terminology, often being referred to as push button switches. While both share similarities, it’s essential to differentiate their characteristics.
A push button switch is engineered to permit current flow when the actuator is depressed a specified distance and interrupts the current when pushed again. These switches can be mounted on panels or PCBs. On the contrary, a tactile switch allows current flow when the actuator is pressed and held, ceasing current flow on release, or vice versa. The actuator’s travel distance is minimal. Such switches fall under the ‘momentary action’ category. While certain push buttons are also momentary, all tactile switches fall into this classification.
Notably, tactile switches are typically much smaller than push button switches and often carry lower voltage and current ratings. Furthermore, they offer audible or haptic feedback and are exclusively designed for direct mounting onto PCBs.
A typical tactile switch comprises four main parts: a moulded resin base (4), contact dome (3), plunger (2) and cover (1). This simplicity, with few moving parts, allows tactile switches to typically last longer than other mechanical switches.
The contact dome possesses an arched shape that fits into the base, which houses the terminals and contacts for PCB mounting. When subjected to force, the dome undergoes deflection or shape reversal, which generates the distinctive audible and haptic click. The dome’s flexing also bridges two fixed contacts in the base, completing the circuit. Once force is removed, the dome regains its original shape, breaking the circuit. Domes can be fashioned from various materials depending on the desired level of haptic and audible feedback.
Positioned atop the contact dome is the plunger. This serves to push and flex the dome. Plunger material can be metal, rubber or other, and may feature a flat or raised actuator. The material utilized for the plunger and contact dome significantly influences the tactile click feel and sound.
Resting atop the plunger is the cover, responsible for safeguarding the internal mechanism. Cover material which could include metals or other materials, is contingent on the switch’s intended usage and desired protection level. Certain covers may also incorporate a ground terminal to mitigate static discharge risks.
Selecting the best tactile switch for an application entails more than scrutinizing specifications on a datasheet. Tactile switches, with their distinct ‘feel’ and ‘sound’ can significantly impact the user’s perception of overall product quality. Although challenging to quantify, this perception plays a crucial role in user satisfaction.
The force required to activate the switch and haptic feedback perceived by the user must align with the application and may vary significantly across consumer and industrial products. Hence, it is prudent to test the switch in prototype use, ensuring its characteristics match the intended application. For example, an automotive switch might necessitate a higher actuation force to counteract input errors due to vehicle vibrations, while a switch used in a printer or consumer gaming product could be less sensitive. Regardless of the application, the switch must maintain reliable functionality over the product’s lifetime.
Various design specifications are relevant to tactile switches, including:
Voltage rating: Indicates the maximum voltage the switch can endure when open or closed.
Current rating: Specifies the maximum current a switch can safely carry without damage.
Activation force: Represents the force or pressure required to actuate the switch.
Deflection: Refers to the overall travel distance of a depressed switch.
Contact force: Indicates the force or pressure necessary for the switch to establish a connection between its terminals.
Actuator height: The height of the actuator above the switch’s body, influencing the user’s tactile experience.
Lifecycle range: The anticipated duration of a switch under normal operating conditions, essential for assessing durability.
Temperature range: Specifies the temperature range in which the switch operates optimally and complies with specifications.
Mounting style: Describes how the switch is mounted on the PCB: through-hole or surface mount.
IP rating: The degree of protection against ingress of dust and liquids.
Illumination: Tactile switches come available in a variety of illuminated LED colour options.
Tactile switch wiring
Tactile switches commonly comprise four pins, internally connected in two sets. Four pins enhance stability when mounted on the PCB. Technically, only two pins need to be utilized but it is considered best practice to use all available pins while understanding the pairs are internally interconnected. Tactile switches can be found with just two pins. Moreover, there are five-pin tactile switches available, specifically designed to enable joystick-like control within a compact package.