Switching elements of foreign production. Reference data
Encyclopedia of radio electronics and electrical engineering / Reference materials
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This article introduces readers to a group of microswitches designed for soldering on a printed circuit board, and in terms of pin pitch and shape they are identical to microcircuits in the most common cases with two rows of pins. The manual control of each pair of contacts of the circuit breaker has two fixed positions.
The range of application of microswitches is extremely wide. These are signal units of radio-electronic equipment, where operational switching of circuits is necessary, and address selection devices, and manual code sensors, and alarm systems, etc. Switches are produced in the form of blocks with the number of pairs of contacts from two to twelve. The most popular blocks are eight pairs of contacts for operation in eight and sixteen bit lines and four, eight and twelve switches for use in nodes using binary coded decimal code.
All switches according to the design of the conclusions can be divided into two types. One - the largest in the number of design options - has two rows of pins, the same as for microcircuits in a rectangular plastic case (series K176, K561, for example). Another type also has two rows of leads designed for soldering directly to the printed pads, without holes in the board (surface mount). The conclusions of both types are flat, rigid, but allowing bending.
Switches of the first type can be soldered into the board or mounted in panels like microcircuits. The conclusions of each pair of closed contacts are located one against the other in different rows.
Although the pitch of the leads in a row for switches of both types is 2,54 mm (the so-called inch), the metric marking of the holes and solder conductors on the "seats" of the boards is suitable for mounting; "metric" mounting plates are also suitable - they have a pitch of 2,5 mm.
The material of the housing and controls of the switches is polystyrene, reinforced with glass fiber, UL-94V-0. Leads and contacts are made of brass. The contact surfaces are covered with gold or silver. The switch mechanism of the first type is fixed in the housing with an epoxy compound. In the second type, the case is pressed together with the conclusions. After assembling the mechanism, the case is closed with a lid and glued.
Main characteristics
- Contact resistance, mOhm, not more than......50
- Insulation resistance, MΩ, not less than ...... 1000
- Ultimate test voltage, V, supplied for 1 min......500
- Operating voltage, V, not more than ...... 24
- Operating current through a contact pair, mA, no more......25
- Operating temperature range, °С......-25... +70
- Switching force, g, no more ... 800
On fig. 1 shows the design of a switch with sliding type controls. The leashes of the engines protrude 1,1 mm above the surface of the body. Lead stroke - 2 mm. Switching is performed with tweezers or a screwdriver
The length A of switches with different numbers of pairs of contacts is shown in the table.
The design of such a switch with keyboard-type controls is shown in fig. 2.
The leashes-keys protrude 2,2 mm beyond the side surface of the case. The key stroke is about 3,5 mm (angle of rotation - 30 degrees). Dimension A for the keyboard version of the switches is indicated in the same table.
The surface mount switch option is shown in fig. 3a. In this sliding switch, the leashes are made flush with the upper plane of the housing, which eliminates the possibility of accidental switching. Switching is performed using a thick needle or awl. Lead stroke - 2 mm.
The values of length A are summarized in the table (see above).
A version of this switch is also produced, which differs only in the design of the terminals (Fig. 3, b). It is more versatile - suitable for mounting both in the traditional way (in holes on the board), and - after bending the leads - for surface mounting.
The switches shown in fig. 3 are very convenient when it is necessary to increase the number of pairs of contacts in the block. When mounting the switches "end to end", the pitch of the mounting foil pads of the board remains constant, and the entire line is visually perceived as a single block.
The material was prepared with the assistance of JSC "Brown Medved", Moscow
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