Apush-button telephone is atelephone that has buttons or keys for dialing a telephone number, in contrast to arotary dial used in earlier telephones.
Western Electric experimented as early as 1941 with methods of using mechanically activated reeds to produce two tones for each of the ten digits and by the late 1940s such technology was field-tested in aNo. 5 Crossbar switching system in Pennsylvania.[1][2] The technology at that time proved unreliable and it was not until after the invention of thetransistor that push-button technology became practical.
The Bell System selectedFindlay, Ohio as the first city in the U.S. for marketing tests of touch-tone service and Ohio Bell began installing push-button telephones in Findlay homes starting on 1 November 1960.[3] The next market was inGreensburg, Pennsylvania, starting on 1 February 1961.[4]
On 18 November 1963, after approximately three years of customer feedback, theBell System officially introduceddual-tone multi-frequency (DTMF) technology inCarnegie, Pennsylvania and increased its use in Greensburg, under its registered trademarkTouch-Tone.[5] Over the next few decades touch-tone service replaced traditionalpulse dialing technology and it eventually became a world-wide standard for telecommunication signaling.
Although DTMF signaling was the driving technology implemented in push-button telephones, some telephone manufacturers used push-buttonkeypads to generatepulse dial signaling. Before the introduction of touch-tone telephone sets, the Bell System sometimes used the termpush-button telephone to refer to key system telephones, which were rotary dial telephones that also had a set of push-buttons to select one of multiple telephone circuits, or to activate other features. Digital push-button telephones were introduced with the adoption ofmetal–oxide–semiconductor (MOS)integrated circuit (IC) technology in the early 1970s, with features such as the storage ofphone numbers (like in atelephone directory) onMOS memory chips forspeed dialing.
The concept of push buttons in telephony originated around 1887 with a device called the micro-telephone push-button, but it was not an automatic dialing system as understood later. This use even predated the invention of therotary dial byAlmon Brown Strowger in 1891.[6] The Bell System in the United States relied on manual switched service until 1919 when it reversed its decisions and embraced dialed automatic switching. The 1951 introduction ofdirect distance dialing required automatic transmission of dialed numbers between distant exchanges, leading to the use ofinbandmulti-frequency signaling within the Long Lines network while individual local subscribers continued to dial using standard pulses.[citation needed]
As direct distance dialing expanded to a growing number of communities, local numbers (often four, five, or six digits) were extended to standardized seven-digitnamed exchanges. A toll call to anotherarea code was eleven digits, including the leading 1. In the 1950s,AT&T conducted extensive studies of product engineering and efficiency and concluded that push-button dialing was preferable to rotary dialing.[7]
Initial customer trials for the push-button telephone were conducted by the end of the 1950s in Hamdon, Connecticut, in astep-by-step switching system, and in Elgin, Illinois, in a No. 5 Crossbar central office.[8] In 1960, approximately one fourth of the central office in Findlay, Ohio, was equipped withtouch-tone digit registers for the first commercial deployment of push-button dialing, starting on 1 November 1960.[9][10]
In 1962, Touch-Tone telephones, including other Bell innovations such as portable pagers, were on display for the public to try out at the Bell Systems pavilion at the Seattle World's Fair.
On 22 April 1963 President John F. Kennedy started the countdown for the opening of the 1964 World's Fair by keying "1964" on a touch-tone telephone in the Oval Office, starting "a contraption which will count off the seconds until the opening".[11] On November 18, 1963, the firstelectronic push-button system withtouch-tone dialing was commercially offered by Bell Telephone to customers in thePittsburgh area towns ofCarnegie andGreensburg,Pennsylvania,[7][12] after the DTMF system had been tested for several years in multiple locations, including Greensburg. This phone, theWestern Electric1500, had only ten buttons. In 1968 it was replaced by the twelve-buttonmodel 2500, adding the asterisk or star (*) and the octothorpe or pound or hash (#) keys.[13] The use of tones instead ofdial pulses relied heavily on technology already developed for thelong line network, although the 1963 touch-tone deployment adopted a different frequency set for itsdual-tone multi-frequency signaling.[citation needed]
Although push-button touch-tone telephones made their debut to the general public in 1963, the rotary dial telephone still was common for many years. Sales of touch-tone telephones picked up speed during the 1970s,[14] though the majority of telephone subscribers still had rotary phones, which in theBell System of that era were leased from telephone companies instead of being owned outright.[15] Adoption of the push-button phone was steady, but it took a long time for them to appear in some areas.[16] At first it was primarily businesses that adopted push-button phones.[17]
The touch-tone system required additional equipment at thetelephone exchange to decode the tones. However, most telephone exchanges in the early 1970s only supported pulse dialling based on theStrowger switch system, restricting touch-tone telephones to someprivate branch exchanges (PBX). Tone to pulse converters were later added to linefinder groups in Step by Step offices to allow some subscribers to use DTMF sets.
British companiesPye TMC,Marconi-Elliott andGEC developed a newdigital push-button telephone technology, based onmetal–oxide–semiconductor (MOS)integrated circuit (IC) chip technology. It was variously called the "MOS telephone", the "push-button telephone chip", and the "telephoneon a chip". It usedMOS integrated circuit (MOS IC) logic, with thousands ofMOS transistors on a chip, to convert the keypad input into a pulse signal. This made it possible for push-button telephones to be used with pulse dialling at most telephone exchanges.[18][19]
MOS telephone technology introduced a new feature to push-button telephones: the use ofMOS memory chips to storephone numbers, which could then be used forspeed dialing at the push of a button.[18][19][20] This was demonstrated in the United Kingdom by Pye TMC, Marconi-Elliot and GEC in 1970.[18][19] Between 1971 and 1973,Bell Laboratories in the United States combined MOS technology with touch-tone technology to develop a push-button MOS touch-tone phone called the "Touch-O-Matic" telephone, which could store up to 32 phone numbers in an electronictelephone directory stored onmemory chips. This was made possible by the low cost, low power requirements, small size and high reliability of MOS transistors, over 15,000 of which were contained on ten IC chips, including one chip forlogic functions (such asshift registers andcounters), one for the keypad dial interface, and eight for memory storage.[21] By 1979, touch-tone phones were gaining popularity,[22] but it was not until the 1980s that the majority of customers owned push-button telephones in their homes; by the 1990s, it was the overwhelming majority.[citation needed]
Some exchanges no longer support pulse-dialing[unreliable source?][16] or charge their few remaining pulse-dial users the higher tone-dial monthly rate[23] as rotary telephones become increasingly rare.[24][25][26] Dial telephones are not compatible with some modern telephone features, includinginteractive voice response systems, though enthusiasts may adapt pulse-dialing telephones using a pulse-to-tone converter. Most, but not all VoIP analogue Telephone Adapters (ATA) will only support DTMF dialling.[citation needed]
The international standard for digit signaling by telephones specifiesdual-tone multi-frequency (DTMF) signaling, more commonly known as touch-tone dialing. It replaced older and slowerpulse dial systems.[27][28] The push-button format is also used for allcell phones,[22] but without-of-band signaling of the dialed number.[citation needed]
The touch-tone system uses audible dual tones for each of the digits. Later this was expanded by two keys labeled with a star (*) and a symbol called the square, similar to the pound or hash sign (#), to represent the 11th and 12th DTMF signals. These signals accommodate various additional services and customer-controlled calling features.[7][29]
The DTMF standard assigns specific frequencies to each column and row of push-buttons of thetelephone keypad; the columns in the push-button pad use a set of higher-frequency tones than the rows, both in the audible range. When a button is pressed, the dial generates a combination signal of the two frequencies from the high and low groups, respectively, producing a dual-tone signal, which is transmitted over the telephone line to the central office.[7]
When introduced, the DTMF technology was not immediately available on all switching systems. The circuits of subscribers requesting the feature often had to be moved from older switches that supported only pulse dialing to a newercrossbar, or later anelectronic switching system, requiring the assignment of a new telephone number which was billed at a higher monthly rate.Community dial office subscribers would often find the service initially unavailable as these villages were served by a single unattended exchange, oftenstep by step, with service from aforeign exchange impractically expensive.Rural party line service was typically based on mechanical switching equipment which could not be upgraded.[citation needed]
While a tone-to-pulse converter could be deployed to any existing mechanical office line using 1970s technology, its speed would be limited to pulse dialing rates.[30][31]The new central office switches were backward-compatible with rotary dialing.[citation needed]
The standard layout of the keys on the touch-tone telephone was the result of research of the human-engineering department at Bell Laboratories in the 1950s under the leadership of South African-born psychologistJohn Elias Karlin (1918–2013), who was previously a leading proponent in the introduction of all-number-dialing in the Bell System. This research resulted in the design of theDTMF keypad that arranged the push-buttons into 12 positions in a 3-by-4 position rectangular array, and placed the 1, 2, and 3 keys in the top row for most accurate dialing.[32] The remaining digits occupied the lower rows in sequence from left to right; the 0, however, was placed into the center of the fourth row, while omitting the lower left and lower right positions.[citation needed]
The DTMF keyboard layout broke with the tradition established in cash registers (and later adopted in calculators and computers) of having the lower numbers at the bottom.[33] This was due to research conducted by Bell Labs using test subjects unfamiliar with keypads. Comparing various layouts including two-row, two-column, and circular configurations, the study concluded that while there was little difference in speed or accuracy between any of the layouts, the now familiar arrangement with 1 at the top was the most favourably rated.[34]
The engineers had envisioned telephones being used to access computers, and surveyed business customers for possible uses. This led to the addition of thenumber sign (#,pound ordiamond in this context,hash,square orgate in the UK, andoctothorpe by the original engineers) andasterisk orstar (*) keys in 1969.[citation needed] Later, the hash and asterisk keys were used invertical service codes, such as*67 to suppresscaller ID in the Bell System.[citation needed]
In military telephone systems four additional signals (A, B, C, D) were defined for signaling call priority.[citation needed]
Historically, not all push-button telephones used DTMF dialing technology. Some manufacturers implementedpulse dialing with push-button keypads and evenWestern Electric produced several telephone models with a push-button keypad that could also emit traditional dial pulses. Sometimes the mode was user-selectable with a switch on the telephone. Pulse-mode push-button keypads typically stored the dialed number sequence in a digit collector register to permit rapid dialing for the user. Some push button pulse dial phones allow for double-speed pulse dialing. These allow even faster pulse dialing in exchanges that recognize double-speed pulse dialing.[citation needed]
As telephone companies continued to levy surcharges for touch-tone service long after any technical justification ceased to exist,[35] a push-button telephone with pulse dialing capability represented a means for a user to obtain the convenience of push-button dialing without incurring the touch-tone surcharge.[citation needed]
In the 1950s, the Dutch electronics concernPhilips developed a direct current (DC) signaling method for dialing telephone numbers, for use in the UB-49 private branch exchange (PBX) system. The push-button dial pad used an arrangement of semiconductor diodes to produce a distinct sequence of polarity states for each dialed digit between the two line conductors and ground return, which were analyzed in the exchange by relay logic.[36]
In 1968, the system was used in the UK, in a brief excursion from standards, when the General Post Office (GPO) introduced the first UK-made push-button telephone, the GPO 726 (Ericsson N2000 series).[37][38]
Electronics within push-button telephones may provide several usability features, such as last number redial and storage of commonly called numbers. Some telephone models support additional features, such as retrieval of information and data or code andPIN entry.[39]
Mostanalog telephone adapters forInternet-based telecommunications (VoIP) recognize and translate DTMF tones but ignore dial pulses, an issue which also exists for somePBX systems. Like cellular handsets, telephones designed for voice-over-IP use out-of-band signaling to send the dialed number.[citation needed]
