Push Button Switches

Chapter 1: What are the principles of push button switches?

This chapter will explore the function and operation of push button switches.

What are Push Button Switches?

Push button switches, or pushbutton switches, are electrical devices that activate or deactivate circuits when pressed. They are commonly used to control a wide array of electronic devices and systems.

Push button switches come in various forms, including buttons and keys, and can be categorized as either maintained or momentary. The most common type of momentary switch is the push button. A normally closed push button switch, often called a push-to-break switch, interrupts the circuit when pressed, while a normally open push button switch, known as a push-to-make switch, completes the circuit when pressed.

Maintained push button switches, in contrast, latch into one position and stay there until pressed again, alternating between held and released states. Most push buttons are designed with two states, though configurations with more than two states are possible but less common. Push button switches find extensive use in various applications, including computers, crosswalk signals, telephones, industrial machinery, security systems, ATMs, military equipment, slot machines, fitness equipment, and many other devices.

How Push Button Switches Work

Push button switches, like other electrical switches, are used to modify the electrical circuits they are connected to. An open circuit prevents electricity from flowing, which halts the operation of the connected device. When a push button switch closes the circuit, it allows electricity to flow freely, enabling the device to function. Push button switches can be designed for either sustained or temporary circuit closure. Some push buttons are equipped with springs that cause the switch to return to its original position when not pressed, thereby keeping the circuit open.

A brief circuit interruption can enable the transfer of power from one point to another. Some push buttons can maintain electrical flow, featuring on and off positions that are toggled with each press. Regardless of their specific application, push buttons are crucial components in controlling electrical current. Their ability to reliably conduct and interrupt electricity as needed by the operator is essential. Typically, breaking the circuit involves creating an air gap between two contacts, which must be opened quickly to achieve the desired effect. Most electronic switches alter the connection state by adjusting the effective resistance within the circuit.

The resistance of a switch can be adjusted to create a high resistance for an open circuit or a low resistance to close the circuit effectively. Push button switches typically lack physically moving components. A crucial aspect of these switches is their ability to respond to the actuator, which may be manual or automatic. The actuator's role is to open or close the circuit by altering the connection state.

Actuation can be triggered by physical actions, such as a lever or slide, or by other events like overvoltage or changes in light intensity. For added protection, a fuse is often included with the switch to safeguard the connected equipment. Given the wide range of electronic devices, a variety of circuitry solutions are needed to support them.

For instance, a simple electric light requires only wires, a switch, and a power source to function. In contrast, a computer keyboard relies on a complex network of circuits on a circuit board to transfer signals to the CPU. Despite the complexity, switches are essential for controlling the circuitry in both simple and sophisticated applications.

Chapter 2: How can push button switches be designed and customized?

Push button switches are some of the most fundamental electric switches, similar to toggle switches in their basic function of changing circuits. Both types of switches are user-friendly. Operating a push button switch involves pressing it to achieve the intended result. Many push button switches include tactile feedback to help users confirm that the switch has been activated successfully.

Push button switches come in various configurations: flush, recessed, or elevated. Recessed buttons are set below the surface of the device to prevent accidental activation. Flush switches are level with the surrounding surface, providing a sleek appearance. Elevated buttons protrude above the surface, making them easy to locate and press.

Relays in Electric Switches

Relays are electrical devices designed to control a circuit using a separate, often low-power, signal. Essentially, a relay acts as an electrically operated switch. It typically consists of an electromagnetic coil. When an electrical signal energizes the coil, it attracts a metal contact, altering the circuit by either making or breaking a connection. Once the electrical signal is removed, the relay includes a mechanism to return the contact to its default, de-energized position. While the coil is energized, the metal contact remains in its attracted state, making the relay function similarly to a momentary switch.

The latching relay is a type of switch that operates more like a maintained switch. It typically requires signals of opposing polarity to open or close the circuit. Unlike other relays, the absence of power does not affect the controlled switch's state; it remains in its last position until deliberately changed. Latching relays are used when a circuit needs to stay in one state (on or off) for extended periods without continuous power to the coil. They are commonly employed in electrical power supplies to operate circuit breakers.

Previously, telecommunication systems extensively used electromagnetic push button switches for applications such as analog switching, railway signaling, and transceiver selection. The solid-state relay, an alternative to the electromagnetic relay, uses semiconductor components to control separate circuits. A common example of solid-state relay technology is the optocoupler, which connects a light-emitting diode (LED) with a photodiode.

Actuator Mechanisms

Actuator mechanisms in switches are responsible for manually toggling a circuit on and off. In push button switches, these actuators are essential components that control the switch's operation. Essentially, the actuator is responsible for opening and closing the circuit. It is a mechanical part that moves to enable the electrical switch to function properly—without it, the switch cannot operate.

There are several types of actuators, each with its own unique operation. For instance, a toggle actuator features a lever that is manually engaged. Depending on its configuration, the switch either opens or closes when the lever is moved. This simple and practical manual operation makes it an effective method for controlling an electrical switch.

Rotary actuators are another type, equipped with a handle that can be turned to open or close the circuit. Users rotate the handle to adjust the switch's state. Until the 1970s, rotary actuators were primarily used in televisions, but today they are more commonly found in radio control devices and measuring instruments.

Biased actuators operate using a spring-based mechanism, offering a straightforward way to control an electrical switch. The actuator contains a spring that, when pressed, either opens or closes the circuit. Their simplicity, ease of use, and durability make biased actuators a popular choice among engineers and businesses.

Connectors and Contactors in Electric Switches

A contactor is an electrical circuit component designed to act as a switch. Its primary function is to establish and interrupt electrical contact. When the contactor is engaged, it closes the circuit, allowing electrical flow. When it is disengaged, it opens the circuit, stopping the flow of electricity. By making and breaking contact, contactors control the flow of electrons, thereby regulating electrical power and signals within a circuit. Contactors are typically constructed from metal or other conductive materials.

The following materials are commonly used in the production of contactors:

Copper and Copper Alloys: Copper is an excellent conductor of both electricity and heat, second only to silver in conductivity. Brass, a popular copper alloy, is frequently used in contactor manufacturing.

Silver and Silver Alloys: Silver offers superior electrical conductivity, potentially the highest among all metals. Additionally, silver and its alloys are resistant to oxidation, making them valuable for contactor applications.

Gold and Gold Alloys: Gold is an effective conductor, following copper and silver in conductivity. It also exhibits excellent corrosion resistance. However, due to its scarcity and high cost, gold is rarely used in contactors.

Platinum Group Metals: Platinum is one of the most expensive materials used in circuitry. Given its high specific weight, the value of platinum for contactors is often questioned, especially since volume considerations typically outweigh weight.

Carbon as a Conductor: While carbon is a nonmetal, certain forms of it can conduct electricity. Although it is less effective compared to metals, carbon is used in specific industrial applications, such as in certain batteries and renewable energy systems, as well as for experimental and recreational purposes.

Other Metals: Various other metals also conduct electricity and are used in different applications where resistance is less critical. Examples include:

• Chromium alloys
• Steel alloys

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Chapter 3: What are the different types of push button switches?

Push button switches are typically categorized as either normally open (NO) or normally closed (NC). Normally open switches remain open and break the circuit when not pressed, completing the circuit and turning "ON" when activated. Conversely, normally closed switches are closed and maintain the circuit when not pressed, breaking the circuit and turning "OFF" when activated. The functionality of push button switches can be further specified by their switching circuit configurations, including single pole, single throw (SPST); single pole, double throw (SPDT); double pole, single throw (DPST); and double pole, double throw (DPDT), which are among the most commonly used circuits.

Normally Open

An electrical switch is typically designed to be open when in its default state. A normally open switch remains off until it is activated, as its internal contacts are separated. When a normally open switch is off, the contacts are open, severing the electrical connection and keeping the switch in the off position. In contrast, normally closed switches have their contacts closed by default, maintaining an electrical connection and keeping the switch in the on position until it is activated. Normally open switches can be further categorized into momentary types, which only remain in their activated state while pressed, and latching types, which stay in their activated state until pressed again.

A momentary switch requires continuous pressure to remain activated, while a latching switch only needs to be pressed once to change its state. Most switches are designed to be turned on with a single press. Here are some common examples:

Light Switch – Light switches are typically normally open latching switches. They remain open until pressed, closing the circuit to turn the light on. The light stays on until the switch is pressed again to turn it off.

Medical Bed Controls – Medical bed controls, which can be footswitches or hand controllers, often use normally open momentary switches. The switch remains open when not pressed, requiring continuous pressure to move the bed to the desired height. Once the pressure is released, the switch opens and the bed stops moving.

Medical and Industrial Equipment – Many medical and industrial devices use normally open switches, such as footswitches that allow operators to keep their hands free. Pressing the footswitch closes the circuit, enabling the machinery to function. Examples include:

• Sewing machines
• Medical machinery
• Metal cutting machines
• Metal bending machines
• Tattoo machines
• Optical instruments
• Hair removal devices

Normally Closed

A normally closed contact remains in the closed position when no external force or energy is applied. It requires an input of energy—either mechanical or electrical—to open the contact. This applied energy creates the necessary force to actuate the switch, causing the normally closed contact to change to an open state.

A switch with a normally closed contact remains closed without the application of any external force, energy, or interaction. This type of switch is often used for emergency stop functions. When the switch is not engaged, the circuit remains closed, allowing current to flow. When the switch is pressed, it opens the circuit, cutting off the power and stopping the current flow.

Single Pole, Single Throw

The single pole, single throw (SPST) switch has one input and one output, directly connecting the input to the output. Its primary function is to control the circuit by toggling it ON or OFF. When the switch is in the closed position, it completes the circuit and turns it ON. When the switch is open, the circuit is interrupted and turned OFF. Examples of SPST switches include those used in 25kV railway DC power systems and domestic lamp switches.

This switch features two types of connections: normally open (NO) and common (C). When the switch is activated, the circuit closes, allowing current to flow from the common (C) terminal to the normally open (NO) terminal. When the switch is deactivated, the circuit opens, stopping the flow of current. Essentially, this switch operates as a simple on/off mechanism. Pressing the switch button connects the internal contacts, completing the circuit and allowing current to flow. For instance, SPST switches are commonly used to control room lighting. When the switch is OFF, the circuit is interrupted, turning the light off. When the switch is ON, the circuit is completed, turning the light on.

Some benefits of the SPST switch include:

• Simple circuit design
• Simple wiring
• Reduced cabling
• Lower costs
• Increased ability to function with high voltages & currents
• Reliability

The drawbacks of the SPST switch include:

• Possible confusion in its usage
• Lack of durability

Single Pole, Double Throw Switch

The single pole, double throw (SPDT) switch enables the control of two separate circuits using a single common input. This type of switch can be operated either manually or through an automatic mechanism, such as an electromagnetic coil. A practical example of a single pole, double throw switch can be found in the output terminal relays of ACS 550 or 800 VFDs. In this setup, the relay switch functions as one input with two distinct outputs.

The SPDT (Single Pole Double Throw) switch functions as an ON/OFF switch that either connects or disconnects two terminals. When the switch is in the closed position, it connects the terminals, allowing current to flow between them. Conversely, when the switch is open, the terminals are disconnected, preventing current flow. SPDT switches are classified into two types based on their operation: BBM (Break Before Make) switches and MBB (Make Before Break) switches.

Break Before Make (BBM) Type Switch

Transfer switches are designed to quickly switch electrical power sources. An open transition, also known as a break-before-make transfer, involves the transfer switch disconnecting from one power source before connecting to another. During this transition, no power is supplied to the downstream load.

A BBM (Break Before Make) SPDT switch is typically connected to the closed throw circuit and disconnected from the open throw circuit by default. When the BBM switch is actuated, it first disconnects from the closed circuit and then connects to the open circuit.

In devices with the BBM function, the input control logic alters the signal path so that the link between two multiplexed pathways is never electrically connected at the same time. This isolation is crucial in multiplexed applications to prevent signal distortion when transferring a signal from one channel to another.

Make Before Break (MBB) Type Switch

Another type of transition is the make-before-break (MBB) switch, which temporarily bridges two positions. In this configuration, the second connection is established before the first connection is broken. The switch blade, controlled by a selector switch, connects to the first power source and then switches to the second position to load the electrical contact. T-shaped and V-shaped blades are commonly used for this type of switch.

In an MBB SPDT switch, the pole is connected to the normally closed (NC) throw circuit by default and disconnected from the normally open (NO) throw circuit. When the MBB switch is activated, it first connects to the normally open circuit before disconnecting from the normally closed circuit.

The MBB feature ensures that when the signal path is altered by the input control logic, the connection between two multiplexed paths is never electrically severed. This prevents situations where a high impedance output could occur, which is crucial when a feedback node requires a continuous load.

Double Pole, Single Throw

The Double Pole Single Throw (DPST) switch features two inputs and two outputs, with each input corresponding to one output. Each terminal on this switch can be set to either ON or OFF. In this context, "pole" refers to the number of circuits controlled by the switch, while "throw" denotes the switch's position. Essentially, a double pole switch manages two independent circuits with a single throw mechanism that controls both circuits simultaneously.

A DPST (Double Pole Single Throw) switch is designed to control two distinct circuits simultaneously, with a single actuator such as a push button or toggle. In this switch, both circuits are either turned ON or OFF together. It features four terminals: two for inputs and two for outputs. Although a single DPST switch can handle multiple voltages from separate sources, it manages two inputs and drives two separate outputs in a circuit. Essentially, a DPST switch is like having two SPST switches combined, controlling different circuits but operated by the same actuator.

The DPST switch offers the following advantages:

• Two unrelated circuits can be opened or closed at the same time.
• There is the usage of two independent circuits.
• There is a simultaneous function of the input-output pair.

Some potential drawbacks of the DPST switch are:

• The switching work of both circuits must simultaneously be ON or OFF.
• The DPST switch is a more sophisticated, but more expensive ON/OFF switch as it connects or disconnects two circuits at the same time.

Double Pole, Double Throw

A DPDT (Double Pole Double Throw) switch is an electromechanical switch that builds upon the SPDT switch by adding an extra pole. This switch is easy to install thanks to its locking system, which enables secure mounting in a remote cabinet without the need for nuts, bolts, or screws. The DPDT switch features two inputs and four outputs, with each input corresponding to two outputs. Its versatility comes from the fact that each terminal can be set in one of two positions. By connecting the inputs to four distinct outputs, the DPDT switch can toggle a circuit between two different modes of operation. Essentially, this switch combines the functionality of two SPDT switches into one unit.

DPDT (Double Pole Double Throw) switches can break or split the conductors of two independent circuits. The "DP" in DPDT refers to the switch's ability to control two distinct circuits, while the "DT" indicates that the switch can alternate between two positions. These switches feature six terminals: two inputs and four outputs. They are available in both momentary and maintained contact configurations. Essentially, the DPDT switch combines two SPDT (Single Pole Double Throw) switches, allowing for dual ON-ON or ON-OFF-ON settings. This design enables the switch to handle four circuits with two separate circuit systems, allowing all circuits to be turned on simultaneously.

Consequently, when the switch is activated, two appliances connected to the same circuit can be powered simultaneously. However, only two of the four circuits within a DPDT switch can be active at any given time. The switch uses polarity reversal to alternate between the two powered circuits.

The DPDT switch offers the following advantages:

• The DPDT switch conveys two unrelated signals.
• It can function with high voltages & currents.
• They provide failover capabilities for computers.
• It can work on drive motors, pumps, and control relays because of their high current capabilities.
• The DPDT switch can be used in numerous areas.
• They provide an user the ability to control multiple appliances with the push or flick of a single button.
• The DPDT is economical when compared to installing multiple switches where each one only controls a single operation.
• This switch weighs less in comparison to multiple switches.

Some drawbacks of the DPDT switch include:

• The switch is expensive as compared to bridges.
• It is hard to trace network connectivity issues with the DPDT switch.
• There is a difficulty in broadcast traffic.

Chapter 4: What are the applications, benefits, and drawbacks of push button switches?

This chapter will explore the applications, advantages, and limitations of push button switches.

Applications of Push Button Switches

Push button switches are used in a variety of commercial and domestic applications. Some of the most common applications include:

Calculators: Push button switches in calculators are tactile switches that complete an electric circuit when pressed and break the circuit when released. This requires physical interaction to turn the button on or off. Calculators, which often feature numerous small push button switches, use these buttons to input data. The logic circuit within the calculator regulates power supply connections based on the state of these push buttons on the keypad.

Doorbells: Doorbells are commonly used worldwide and are designed for intermittent use rather than continuous operation. Historically, doorbells used electromagnets to activate a hammer that struck a bell to produce sound or melody, with the sound continuing until the circuit was de-energized. Modern doorbells incorporate push button switches that can become annoying if pressed continuously, as they trigger the doorbell's sound mechanism.

Push Button Telephones: Telephones feature numerous buttons or push switches for dialing numbers. Modern push button telephones often include electronic controls that offer additional functionalities, such as last number redial and storage of frequently dialed numbers, enhancing their usability. Some models also provide advanced features like data coding, information retrieval, and PIN entry.

Advanced Machine Controls: Push button switches are designed to facilitate complex control systems, making them user-friendly for operators. These systems can be equipped with various software programs and color-coded buttons to indicate their status. For instance, in many systems, a red button typically denotes the power function, while a yellow button may indicate a pause. These color codes are standardized internationally for a broad range of industrial applications.

Push button switches have a broad range of applications beyond those mentioned. They are commonly found in casino games, high-security systems, fitness equipment, and many other diverse settings.

Benefits of Push Button Switches

Push button switches have transformed switch design, enhancing their efficiency. Some of the key benefits of using push button switches include:

• Push buttons save space in any equipment or switchboard.
• The buttons are significantly stronger and more user-friendly.
• Because the buttons are attached to the machine or switchboard, they cannot be simply stolen.
• Push buttons are significantly less expensive than other switches.
• The buttons are small, which makes them easy to fit into any space.
• The buttons can withstand greater voltages or short circuits and not be destroyed.

Additional benefits of push button switches include:

Push button switches are designed with special sealing techniques, making them waterproof, oil-proof, resistant to pollutants, anti-static, and capable of withstanding contamination and interference.

They are also cost-effective to manufacture; some membrane switches can be produced for just a few cents each. This low cost provides significant commercial advantages for versatile electronic components.

Another advantage is their compact and lightweight nature. Illuminated push button switches are particularly easy to transport and install due to their minimal weight.

Moreover, push button switches offer excellent electrical conductivity. They can use copper foil, silver paste, or carbon paste to print the circuit, and their unique membrane design can handle higher voltages and allows the conducting layer to be folded without performance degradation.

Push button switches also provide a long service life and an appealing appearance. While many electronic switches have a good look and durability, these features are especially notable in push button switches.

Drawbacks of Push Button Switches

However, there are several drawbacks to using push button switches, including the following:

• Touching the metal button switch too frequently can cause its metal shrapnel to lose its elasticity, causing the push-on switch to become inoperable. This is a common issue with electronic switches, and frequent usage of any electronic component can hasten inoperability.
• Furthermore, the push-on switch cannot create functions on its own; rather, the push-on switch requires additional PCB boards to work together to build a comprehensive switch control system.

Conclusion

Push button switches are electrical actuators that, when pressed, either close or open an electrical circuit. The actuator of a push button switch is a button or key, which can be permanent or temporary. Push button switches are normally open (NO) or closed (NC). When triggered, they complete a circuit. When closed, they break a circuit. They can be characterized by their functionality and the switching circuit they use, which can be:

• Single Pole, Single Throw (Spst)
• Single Pole, Double Throw (Spdt)
• Double Pole, Single Throw (Dpst)
• Double Pole, Double Throw (Dpdt)

Push button switches are used in a wide range of applications, including computers, crosswalks, telephones, industrial machinery, security systems, ATMs, military equipment, casino gambling slot machines, fitness equipment, and gadgets.

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