A Complete Guide to Touch Switches

A touch switch, as the name suggests, is one of various types of activation switches that need only be subjected to some degree of physical contact/pressure from an operator or object in order to actuate. 

Touch switches are, in many ways, the simplest kind of tactile sensor; they are most often a type of binary on/off electronic switch that will only be actuated when there is direct physical contact or some degree of pressure being applied to it.

Thanks to their ability to work when mounted on or behind the surface of numerous panel types and displays (including glass, acrylic and plastic), touch switches are very widely used in a huge variety of different applications, both household and workplace. Multiple touch switches are often arranged in sequence on a single panel or display - for example in a multi-function keypad - allowing for more diverse control inputs to manage various types of applications and tasks.

Although a very wide range of different sorts of touch switches and sensors exists, they all have some basic fundamentals in common.

All kinds of tactile sensors are responsive to some external direct stimulus - be it touch, force or pressure - and their connections are generally made or broken on the basis of responsiveness to light (optical), electricity, magnetism, or some other chemical or mechanical trigger. In other words, they all use a sort of on/off stimulus-to-response pathway.

In some cases, this will be an incredibly simple sequence of inputs and outputs - for example, the individual keys on a computer keyboard are examples of very basic touch switches, which respond to direct physical pressure in order to tell the computer which key is being pressed at which time.

More complex versions of touch switches are found on, say, smartphone screens - often incorporating other features such as capacitive sensing and haptic feedback - but, regardless of the type of sensing/delivery system being deployed, all work along the same basic principles as one another once the actuation has taken place.

As we’ve already noted, touch switches are nigh-on ubiquitous features today, appearing on countless types of different high-end modern devices - but, perhaps surprisingly, they’re actually not that new a technology. While touch switch formats have advanced significantly, and been greatly refined with successive leaps in design and manufacturing methods, the basics of using the human body as a conductor - which it’s very well equipped for - have been understood and exploited for years.

Temperature, resistance and capacitance are all types of touch switch mechanisms that work consistently well when operated by a person, or a suitable switch manipulation object. The way in which a particular touch switch works is entirely dependent on the type of touch switch technology in question, and so in the following section we’ll explore some of the more common kinds of touch switches sold on the market.

Push button switches - also known as ‘momentary’ or ‘contact’ switches - are among the simplest and most widely available kinds of touch switch sold today (although, as noted above, they’re arguably not true ‘touch switches’ at all).

A push button switch is non-latching, meaning it only affects the circuit it’s connected to for as long as it’s being physically actuated (pushed down); as soon as the pressure on the switch is removed, it returns to its default position. This is usually achieved via a basic automatic mechanism such as a spring, and the initial circuit condition will be restored once the spring is released.

The two types of push button switches most commonly sold by suppliers are ‘push to make’ and ‘push to break’ versions. As you’d assume, one breaks the circuit when under a force load (i.e. pushing the button effectively turns the circuit ‘off’), while the reverse is true of a push-to-make connection. Push button touch switches can commonly be designed to offer both functions, depending on how they’re wired up to the circuit.

Capacitive switch technology is one of the two main types that most people would strictly define as a true touch switch. Rather than requiring any sort of actual physical pressure to actuate, capacitive switches function by measuring a small electrical charge that gets transferred from your body to the switch itself. This happens more or less the instant you make a clean contact with it.

A piezo switch derives its name from the piezoelectric effect, which occurs when a degree of mechanical stress - i.e. a bending force, in simple terms - is applied to certain solid materials. These materials include some types of crystals, certain ceramics, and various sorts of biological matter (bone, DNA, numerous proteins).

Resistive touch switches, like capacitive touch switches, also operate by registering changes in electrical current. However, comparatively speaking, resistive touch switches are much more simple in design and construction than the relatively complex capacitive varieties. Resistive switches rely on lowering the resistance - in short, bridging the electrical ‘gap’ - between two conductive metal plates that are laid out with a small but electrically important space in between.

When your finger alights on a resistive touch switch, it makes contact with both plates at the same time, whereupon the water and salts in human skin help to conduct the flow of electricity across this gap, effectively completing the circuit, This actuates the switch, triggering whatever function is has been wired to perform when the contacts are closed.

The simplicity of this design brings with it some obvious benefits - not least that they’re a far more economical choice for the majority of suitable applications, as well as being a fairly robust, consistent and long-lasting option in most scenarios. However, they’re somewhat limited in the range of functions they can perform, due to their extremely binary sensitivities: as a pure on/off touch switch, they don’t support multi-touch operation, for example, making them unsuitable for high-end smartphones and similar devices.