What is Membrane Switch : Working & Its Applications

Membrane switches are available for five decades. The first membrane keypad was introduced in the year 1970. These switches were designed with polycarbonate-based plastic films which are printed with silver or copper-infused ink to create the electronic circuit. These switches were composed of two conductive layers including one spacer among them. At present, the global membrane switch market has been increasing. In 2015, it is $4.2 billion, so not it is expected to rise to $13 billion by 2024. These switches are widely used in medical, industrial & consumer goods applications. This article discusses an overview of a membrane switch – working with applications.

What is Membrane Switch?

Definition of a membrane switch is, an interface between user & machine is used to allow an operator for communicating with machinery, equipment, or instrumentation is known as a membrane switch. This is a printed electronic circuit that works with force to open & close an electronic circuit.

The circuit of the membrane switch is most frequently screen printed with conductive inks which are normally designed with carbon or silver. Membrane switches are essential parts of devices that are considered user interfaces otherwise HMIs (human-machine interfaces) through mechanical & touch screen switches.

Membrane Switch Design

These switches are designed with different layers which are simply assembled with heat sealing films or pressure-sensitive adhesives. The essential layers of this switch mainly include graphic presentation, graphic adhesive, the PCB layer, circuit layer, adhesive separator, second circuit layer, adhesive layer, and metal domes. Each layer and its function are discussed below.

Graphic Presentation Layer/Graphic Overlay

The graphic presentation layer of this switch is known as a graphic overlay. Generally, these overlays are designed with polyester, the choice of material because of its flexibility & superior chemical resistance as compared to polycarbonate. This switch configuration mainly depends on the function of the device. This layer is normally a printed silicone rubber or polyester material

Graphic Adhesive Layer

This is the second layer in the membrane switch which assists the above graphic presentation layer to the next circuit layer. This layer is designed with polyester material including adhesive on both faces.

Circuit Layer or PCB Layer

The circuit layer is also known as the PCB layer which comprises the membrane switch electronics & dome features. The circuit layer is wherever the paths of the conductive switch are applied and these paths can be generated through two main techniques like screen printing & photochemical etching.

Spacer

The spacer layer separates both the top as well as bottom circuit layers and this layer can be simply created from heat-stabilized polyester among two layers. This layer includes channels in between the empty cavities otherwise the face of the keypad for emitting air. This avoids air from being reduced within the cavity once the key is pressed.

Secondary Circuit Layer

This is an optional secondary circuit or PCB layer that includes an extra circuit necessary for the switch. This layer is normally a polyester-printed and heat-stabilized layer including dielectric and electrically conductive silver-filled inks.

Adhesive Layer

This is the last layer in the membrane switch and it is the adhesive sheet that is arranged at the back side of the switch. This layer helps in assembling the entire switch package to the product enclosure.

Features

The features of membrane switch include the following.

• The surface of this switch is completely sealed so that it can clean & sterilized easily.
• Low Profile – no cracks that can catch contaminants.
• These are less costly as compared to other keypads like capacitive touch & rubber keypad assemblies.
• The thin profile of this switch keeps valuable space within your product design.
• These switches are easily interfaced with existing controllers.
• The graphic interface is versatile.
• Safety by design – these switches are easier to guard against UV radiation.
• These switches are water-resistant.
• Special features can be included in these switches like tactile feedback and lighting options.
• Graphic overlays screen printed or digitally to look like a broad range of surfaces including metal, glass, stone & wood.
• RFI or EMI shielding.
• Display windows are tinted & transparent.
• Support backers are strong like aluminum and FR4 through PEM mounting fasteners.
• Surface finishes are UV hard-coated & Selective textures.
• Backlighting is fiber optic & Electroluminescent.
• Tactile & non-tactile feedback including polyester or metal domes.
• Fixed LEDs.
• Rim-embossed /Pillow graphic overlays.

How Does a Membrane Switch Work?

Membrane switch includes different layers where the top layer is an overlay which includes keys that the user observes and presses. There are two circuit layers under this top overlay layer which are printed within conductive ink like silver, graphite, or copper onto the membrane-like PET or polyethylene terephthalate to make circuits that communicate to the buttons.

A spacer in this switch avoids permanent contact between the two circuits, thus they stay open until the force from a touch otherwise actuator is applied.

As a result, whenever the user presses a button on the membrane switch, then it completes a printed circuit exact to that key. By recognizing the exact circuit that was triggered, the processing unit simply knows which key was pressed; then it produces a suitable equivalent output signal.

For instance; whenever the operator presses key ‘1’ on the switch, then force on the switch simply completes a circuit printed on the membrane just under that button. That printed circuit sends a signal toward the processing unit, which recognizes the key “1” was pressed.

Membrane Switch Circuit

The membrane switch is a numerical keypad that is used in various engineering projects for calculation purposes. These switches are made from thin and flexible materials which are available in different sizes like 4×1, 4×3, and 4×4, but all these switches work in a similar way so they don’t affect the working. Here, we are going to explain how to interface the membrane switch with Arduino UNO.

The working of the membrane switch is not very difficult. Once you push the button on the switch, then it immediately shorts one of the columns to the row lines. So this simply permits the flow of current to flow between these rows and columns.

For example, if you push key 1, row 1 & column 1 get shorted. Similarly, if you push key 2, then row 1 & column 2 get shorted. So an Arduino microcontroller is used to scan those two-row and column lines to work accordingly.

The required components to interface this mainly include; Arduino Uno, USB cable, membrane switch, and jumper wires. The connection of this interfacing follows as;

The D8 to D5 pins of Arduino Uno are connected to R1 to R4 pins of the membrane switch whereas the D4 to D2 pins of Arduino Uno is connected to C1 to C3 of the membrane switch.

By using the above interfacing diagram, we need to connect the membrane switch with Arduino. Uno. Once the connections are made then upload the Arduino Uno code through Arduino IDE.

Once you press the membrane switch key, the Arduino board sets the rows & columns to the input lines. Afterward, it selects the row to set the row high, and next, it checks the column lines.

If the column connection in the switch is low, then there is no key is pressed. So if it drives high, then Arduino recognizes the row. Thus, it understands which key got pressed & displays that on the serial monitor.

Code

The code required for interfacing is shown below.
#include “Keypad.h”
const byte ROWS = 4; // number of rows
const byte COLS = 3; // number of columns
char keys[ROWS][COLS] = {
{‘1′,’2′,’3’},
{‘4′,’5′,’6’},
{‘7′,’8′,’9’},
{‘#’,’0′,’*’}
};

byte rowPins[ROWS] = {8, 7, 6, 5}; // row pinouts of the keypad R1 = D8, R2 = D7, R3 = D6, R4 = D5
byte colPins[COLS] = {4, 3, 2}; // column pinouts of the keypad C1 = D4, C2 = D3, C3 = D2
Keypad keypad = Keypad(makeKeymap(keys), rowPins, colPins, ROWS, COLS);
void setup()
{
Serial.begin(9600);
}
void loop()
{
char key = keypad.getKey();
if (key != NO_KEY)
Serial.println(key);
}

In the above interfacing code, the keypad library is first included. After that, it simply describes the keypad’s number of rows & columns that defines which row is connected to which pin of an Arduino Uno and which column is connected to which digital pin of Arduino Uno.

So now in the void setup, the serial monitor is set by providing the Serial. Begin function. The program was formulated within the void loop if the key is pressed and it will print that pressed key on the Serial Monitor.

Types of Membrane Switches

There are different types of membrane switches available in the market which is used based on the requirement. So these switches are discussed below.

Tactile Membrane Switches

Tactile membrane switches provide a snap action that is visible most clearly to the person while operating this membrane switch. These switches utilize a poly dome or metal dome to offer a physical snap feedback response to the finger of the user by allowing him to recognize that the key has been depressed.

Another kind of tactile membrane switch is “hydroformed poly domes” which offer a gentle tactile reaction as well as narrower operating temperatures as compared to the metal domes.

Due to the short travel of membrane switches, it is frequently essential to provide users with some type of feedback that can be audible, visual, and tactile. Here, both the audible and visual feedback must be a consideration within the design of electronics. Domes can be included in this switch to give tactile feedback. Domes are available in two types which utilize stainless steel, polyester & membrane switches but there is no main difference in consistency between these two types of domes.

Non-Tactile Membrane Switches

Nontactile membrane switches are the most economical & reliable switches but they do not provide direct feedback to the consumer from this switch. So this drawback can be overcome by using a display or an LED indicator. The main benefit of these switches is that they permit simply create custom sizes & shapes of the active keypad region.

Mixed Panels

When the tactile & nontactile switches are combined in a single panel then it is known as the mixed panel. These switches are required where a large active region is required for an exact switch. Another main reason is hidden programming otherwise maintenance switches.

PCB Backed Membrane Switches

These switches are mainly used for the lower circuit which gives structural support by including a variety of surface mount components. This assembly can be connected by a manufacturer to your printed circuit board otherwise sub-contractors can be used to give this kind of construction.

Advantages and Disadvantages

The advantages of membrane switch include the following.

• Moisture & weather resistance.
• Low profile design.
• Low circuitry & voltage requirements.
• Tactile feedback.
• Lighting.
• Reliability.
• Option of tactile or non-tactile.
• Backlighting.
• Shielding.
• Durability.
• Clean surfaces.
• Low profile.
• Affordability.
• Design & ordering flexibility.

The disadvantages of membrane switch include the following.

• These switches are more expensive.
• These are more labor-intensive to design.

Applications

The applications of membrane switch include the following.

• Membrane switches are broadly used in different applications like industrial, domestic, or commercial.
• These switches are found all over like in cell phones; calculators, ovens, door lock systems, etc.
• These switches are used to male simple games and to control the 7-segment display.

Thus, this is brief information on membrane switches. This is one kind of HMI (human-machine interface), designed by using different flexible materials or plastic film layers. These compact & efficient switches are used in a wide range of applications like household devices & equipment interfaces within industries, etc. Membrane switch failure mainly occurs because of cracked overlays, dome collapse, adhesive incompatibility, flexing or bending, and key pressing. Here is a question for you, who invented the membrane switch?