Introduction to the Basics of Key Switches

What this article is going to introduce today is some basic content about key switches , including the introduction, principle, classification, characteristics, and installation precautions of key switches


The first is about the introduction of the key switches:

Introduction of key switch:

The key switch is an easy-to-use combination switch. The key switch is also called an interlock switch and a key switch. They can be interlocked: for example, they can choose the distance between 3 groups: 10MM, 15MM, 12.5MM, 20MM. The mounting holes can choose light control , without holes, with screw holes. Usually there are groups of 4, 6, 8, 12 and 16. But there are also single key switches with only one.


The piano key switch is a switch that can do multi-pole and multi-position combination with a modular structure of building blocks. Most of the key switches are multi-gear combined, and there are also single-gear (commonly used as a power switch). In addition to the difference in the number of switch gears and the number of poles, the key switch also has a locking form. The locking form can be divided into three types: self-locking, interlocking, and non-locking.


The main difference between the key switch and the ordinary button switch is:


  It connects or disconnects one or several groups of electrical contacts by pressing the button, instead of pulling the lever left and right or back and forth;

  It is usually a linkage structure that appears in groups, rather than just a single switch like an ordinary switch;

 The linkage contacts on each of its switches are mostly more than one set of "multi-tool" switches, rather than only one or two contacts;

 When any group of switches is pressed among multiple groups of switches, all the original switches will be reset to the original state (except for self-locking and non-locking structures);

 There are three kinds of structures of interlocking, self-locking and non-locking for users to choose, which is very practical and convenient.

The principle of the key switch:

Long strip, generally there are six welding points, double-pole double-throw, the middle two welding points are input terminals, and the outer four welding points are output terminals; it includes two independent single-pole double-throw switches, and the two groups operate synchronously. After pushing it once, the middle input terminal and the remote welding point are connected, and pushing it again will bounce back, and the middle input terminal and the near-end welding point will be connected.


It is mainly composed of three parts: key assembly, sliding plate mechanism and contact switch group. Each key assembly includes a key, a key lever, a key return spring, and the like. There is a protruding beam in the middle section of the key rod, which is pressed on a trapezoidal insulating block, and at the same time one end of it is pressed on the inclined surface of the sliding pull protruding rod, and the lower part of the key rod is sleeved on the return spring. When a button is pressed, the key rod drives the trapezoidal insulating block to move down, and the insulating block pushes the lateral contact switch reed to close it.


The sliding plate mechanism is composed of a sliding plate, a sliding plate return spring, a gear lock block, etc. There is a tenon at each key rod, with a bevel above it and a groove below it. The beam of the key bar is pressed on the inclined surface, and when the key bar moves down, the beam presses the inclined surface tightly, so that the slide plate moves sideways. When the cross beam falls into the groove of the tenon, the slide plate is reset under the action of the return spring of the slide plate, and the tenon locks the key rod, thereby maintaining the contact closure. At this time, if the second button is pressed, its beam will push the slide plate to move sideways, the first button will bounce (reset) under the action of the button reset spring, and the electrical contact will be disconnected. The second key moves down to close the corresponding contact, and the slide locks the key lever. In order to avoid circuit short circuit caused by pressing the two keys at the same time, the key switch is also provided with a gear lock block, which is trapezoidal in shape and is arranged in the horizontal groove of the slide plate and is located between two adjacent key rods. For example, when the two key rods are pressed at the same time, since the width of the shift lock block is slightly larger than the distance between the centers of the two key rods, the beams of the two key rods are blocked at the same time and cannot be moved down. The position of the contact switch group is inside the plastic shell of the key switch. Each contact switch consists of a moving contact and a static contact. The three static contacts are connected together, and the three movable contacts are respectively riveted on the three strip springs. When the key rod moves down, the trapezoidal plastic insulation under the cross beam of the key rod pushes the movable contact reed to close it with the static contact. When the key lever bounces, the dynamic and static contacts are separated due to the elasticity of the reed, and the switch is disconnected.


Maintenance of key switches:

After using for a long time, the switch performance will become unstable. The main reason is that the contact reed of the switch is loose. By adding a compression spring to the contact reeds, the pressure between the contact reeds is improved, and the reliability of the switch is enhanced.


The manufacturing process of adding a compression spring is very simple. First, take a copper sheet or steel sheet with a thickness of 0.3~0.5mm and good elasticity, make two pieces, and cut the two ends into a circular arc, and use a file to file out some cutting edges on one end. Then use a pair of needle-nose pliers to align the bladed end with the connection between the base of the key switch and the contact reed, and insert it with a little force. It is easier to heat the compression spring on the soldering iron first and then plug it in.


During the production process, care must be taken not to damage the switch base. Through the key switch repaired in this way, the contact reed of the key switch is more reliable to use under the pressure of the compression spring.


The detection standard of the key switch:

   Appearance requirements:

1、The surface of the key cap should be smooth, and the chrome-plated layer should be uniform without air bubbles and pores, and should not fall off;

2、All parts are complete and well connected, and the connection is firm, and there should be no looseness or looseness.

3、The surface of the key plastic parts should have a good appearance, uniform color, smooth and bright, and there should be no  deformation defects such as cracks, lack of materials, and expansion.

   Key operation:

1、The operating mechanism of the switch should be flexible, light, and smooth, and there should be no jamming or incomprehensible deduction.

2、Pressing the second or third gear cannot be locked at the same time (except for the indicator light gear or the special jog light gear).

   Plug-in tension:

The pulling force of the plug is not less than 2kg.

   Technical requirements:

Dimensions and functions of each key: Press to confirm or to close the board. There should be relevant

parameters and certification marks on the surface of the switch, which should be in accordance with the order or

consistent with the sealing plate.

   Withstand voltage:

Apply 2000V between the contact and the keycap, 5mA, 5s without breakdown or flashover

   Plug wire:

It is easy to insert the wire and the card wire is firm, and it is not easy to pull off. The wire should have shark

teeth. (When in doubt, try plugging with a wire of 0.5 to 0.87mm2.)


When the whole machine is powered on, press 12 times per minute, up to 10,000 times in total. After the test is

completed, the switch can still be used (1 per batch)

   ROHS testing:

Whether the six elements of the material used are Cr (chromium), Br (bromine), Cd (cadmium), Hg (mercury), and Pb (lead), whether they meet the ROHS requirements.