Telephone keypad
A telephone keypad is used to dial the number on telephones , fax machines and similar devices. Beginning in the 1970s, it almost completely replaced the rotary dial previously used in devices from the 1990s onwards.
Recommendation ITU-T E.161
The arrangement and labeling of the keys on telephone keypads is standardized by Recommendation ITU-T E.161 of the International Telecommunication Union " Arrangement of digits, letters and symbols on telephones and other devices that can be used for gaining access to a telephone network ". The standard is published in three languages (English, French and Spanish) and thus also standardizes the symbol designations in these languages.
- Arrangement of the digits on telephone keypads: The arrangement of the numeric keys does not correspond to that of many other device keyboards, for example on pocket calculators , adding machines , cash registers , or the numeric keypad of computer keyboards . Numbers 1, 2 and 3 are at the top. This is due to the fact that the digits were arranged in such a way that, like on a previously common rotary dial, the 1 is above and 9 and 0 are below.
- Assignment of letters to numbers: In addition to the numbers, three to four letters can be embossed per key. The assignment for Latin letters is fixed and came up long before the existence of cell phones and SMS in connection with the choice of letters , which is particularly common in North America. There phone numbers originally contained the first two or three letters of the name of the exchange , e.g. For example, connections belonging to the "Lakewood" exchange had telephone numbers in the form LA-1234 . Later, when the letters were abolished, it came up to come up with sequences of letters for whole (7-digit) numbers that make a word that is easier to remember. The letter assignment was originally not uniform with regard to the rarer letters O , Q and Z.
- The symbol placed at the bottom left
is called “star” in German (according to the designations in the standard: English star , French astérisque , Spanish estrella ). It consists of three rectangular bars of equal length, one of which is horizontal and the other two cross in the middle at an angle of 60 °. In Unicode , no character code is directly assigned to this symbol, similar characters are ⚹ U + 26B9 sextile " Sextil " (which as an astrological symbol can, however, have different forms depending on the font) and ? U + 1F7B6 medium six spoked asterisk (which, however, has a vertical bar and thus appears rotated by 90 ° in relation to the ITU symbol). The often used " asterisk " * (U + 002A asterisk ) is less suitable for a standard-compliant rendering, since many of its glyphs have five instead of six spokes, which often do not correspond to the rectangular shape; In addition, it is usually not shown in uppercase letters in the running text , but as a superscript character . - The symbol ⌗ (English square "square", French dièse " Kreuz (musical notation) ", Spanish cuadrado "square") placed at the bottom right is contained in Unicode as U + 2317 viewdata square , but is often used with the similar pound # (Unicode: U + 0023 number sign ), as this is available on standard computer keyboards. The German designation “Raute” corresponds to the standard in that it allows alternative designations and is applicable to the extent that the edges must be of the same length (so that the inside is actually a geometric diamond ). With the square shape, the line ends must protrude between 8% and 18% of the edge line length on each side, with the inclined shape (interior angle 80 °) always by 18%.
- To support the visually impaired, the number key “5” must be marked with a tactile mark.
The star and hash keys do not have to be present.
Standard keyboard
Standard keyboard with letters
Alternative key arrangement
Alternative key arrangement
technology
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The dialed digits are usually transmitted using the multi-frequency dialing method . Each row and each column is assigned a specific tone frequency. When a key is pressed, its line and column tone is transmitted at the same time. In older keyboards there was a slider for each row and column which, triggered when a key was pressed, switched on the corresponding tone generator (in an integrated circuit (IC)) via a switch . Today the keys are connected directly to the tone generator IC via a matrix. For reasons of compatibility, most keyboards can also be switched to the pulse dialing method derived from rotary dial technology.
A total of 16 transferable characters are defined. In addition to the numbers, there are asterisk ( 
), hash (⌗) and the letters 'A' to 'D', but the latter can hardly be found on any keyboard.
There were also telephone keypads with pulse dialing. These were used in telephone networks that were not capable of multi-frequency dialing in order to still be able to use the convenience of a button telephone. Almost all of the early keyboards used by the Bundespost telephones were only capable of pulse dialing. In private branch exchanges there were also telephone keypads based on the diode-earth method (DEV). Here a third conductor or earth was needed to evaluate the keystrokes. This method has not proven itself in public networks.
See also
Individual evidence
- ↑ E.161: Arrangement of digits, letters and symbols on telephones and other devices that can be used for gaining access to a telephone network. International Telecommunication Union, August 12, 2014, accessed March 18, 2015 .
- ↑ Phone Key Pads. DialABC, December 11, 2012, archived from the original on March 15, 2015 ; accessed on March 18, 2015 .
- ↑ ITU-T E.161 (02/2001), English edition, p. 4: The symbol may be referred to as the square or the most commonly used equivalent term in other languages. In some countries an alternative term ... may be necessary for this purpose ...
Web links
- Rotary dial or keyboard? bayern-online.com, accessed on March 18, 2015 (description of a study on the key arrangement from 1968).