Why did early telephones use a rotary dial instead of 10 individual buttons?

  • I was watching a video of little kids trying to figure out how to use a rotary phone, and it was not immediately clear to any of them how the rotary mechanism was supposed to work. That got me thinking: why was the rotary mechanism used in phones at all? It seems like individual buttons would be more intuitive to everyone and might even have less mechanical problems than a thing that has to rotate thousands and thousands of times over it's lifetime. Why was that design choice made, why were they popular, and why did they stick around so long even after phones with buttons came on the market?

    edit: The first touch tone phone was introduced by AT&T in 1963. Even though integrated circuits weren't practical for commercial use at that time, apparently transistors were:

    By the early 1960s, low-cost transistors and associated circuit components made the introduction of touch-tone into home telephones possible. Extensive human factors tests determined the position of the buttons to limit errors and increase dialing speed even further. The first commercial touch-tone phones were a big hit in their preview at the 1962 Seattle World's Fair. (1)

    The fact that Bell Labs had invented the transistor probably helped that process along. And I understand that the change in how telephone networks worked (from pulse dialing to DTMF) drove a change in the electrical design of phones. But while transistors let them make that protocol change, was it really impossible to implement pulse dialing using buttons but not transistors? From Wikipedia:

    In the 1950s, AT&T conducted extensive studies of product engineering and efficiency and concluded that push-button dialing was preferable to rotary dialing (2).

    That suggests the designers did not know that buttons were better than a dial (if they did know, why would they have done such extensive studies?). It also suggests that it WAS possible to make a phone with buttons. They would have had to build button prototypes for their studies, right?

    (1) http://www.corp.att.com/attlabs/reputation/timeline/64touch.html

    (2) https://en.wikipedia.org/wiki/Push-button_telephone

    You dang kids get offa my lawn! Next you'll want to know about party lines, or why it was illegal to own your own phone!

    I bet he's never even dialed a phone number by tapping on the handset cradle, or whistled a 300 baud handshake tone. All these n00bs!

    I've protected this question because it's getting pretty much the same answer repeatedly - because the technology at the time could only handle pulse dialing. That answer has already been stated multiple times so any more ways of saying the same thing is just noise.

    I don't think the technology answers which have already been given answer the final part of the question though..."and why did they stick around so long even after phones with buttons came on the market?"

    Interesting story. When I was learning to program digital telephone exchanges 30 years ago. I learned that the first automatic exchange (which accepted loop make/break pulses from rotary 'phones) was invented by http://en.wikipedia.org/wiki/Almon_Brown_Strowger He was an undertaker & we were told that there was another in town, who's sister worked at the switchboard. When people called for Strowger, they were "accidentally" connected to the other undertaker (the brother of the switchboard lady). This prompted Strowger to invent the automatic telephone exchange.

    "early telephones"... never did a statement make me feel so old. I fully expect to see a question one day on why 'early computers' didn't have touchscreens, or understand voice commands, or have neural interfaces.

    @PhillipW Probably a combination of if it's not broke, don't fix it; and rotary phones being cheaper than touch tone for some time after the latter were first available.

    @RobertB you don't even need to tap the handset cradle; I've managed it once just by clicking my tongue into the receiver.

    When *touch-dialling* phones first came into use, they were still pulse-dialled rather than tone-dialled in most areas. In Bell Canada jurisdictions in the 1960's subscribing to *touch-dialled* service was extra, and subscribing to *tone-dialled* service was another hefty additional amount. Like long-distance service before deregulation, all the premium services were treated as a cash-cow by the Phone utilities. Also, many of the pulse-dialled exchanges had not yet been paid off as tone-dialling became capable.

    @PhilH Or "Why did early phone keypads have a #hashtag key, when there wasn't an Internet?"

  • Adam Davis

    Adam Davis Correct answer

    7 years ago

    The main reason was that it replaced hand crank telephones, and thus was a familiar interface.

    In the hand crank phone system, several houses were connected on one line, and each house was assigned a different ring pattern. For instance you might have been assigned one short ring, then a long ring.

    Your phone had a hand crank, a bell, a mouthpiece and a speaker.

    When the bell rang one short ring then a long ring, you picked up the phone and answered it. You ignored other ring patterns, unless you were a nosy neighbor.

    To call someone else on your circuit, you cranked the hand crank according to the pattern of the person you intended to call. The hand crank was on the side of the phone, and was essentially a small crank generator that sent an AC signal on the line, which the bells would react to on all the phones on the circuit.

    If you wanted to call to someone not on your line you would ring the operator - typically one long ring - they would answer and patch your call into other circuits and other operators if need be. The final operator in the chain would put the correct ring pattern on the correct circuit for the intended recipient.

    Thus, the hand crank was the original user interface for indicating who you wanted to talk to.

    When automated selectors were introduced, there were many attempts to provide a reasonable user interface. One involved using two buttons, similar to telegraph keys, which had to be pulsed a number of times each to select rows and columns of relays. This was deemed too expensive because it required additional wires, and most systems instead moved to pulse dialing. This meant no new wires had to be pulled to customers, just an equipment change in the telephone plant and in the user's homes. Further, it was backwards compatible, and you could have both old crank style and new pulse style phones on the same circuit.

    The first pulse dialing phones included some that had a button you would press a number of times, but individuals using the system couldn't easily time the pulses correctly. The first rotary dial phones were better, but they still depended on the user rotating the dial smoothly. Eventually a rotary dial with a spring and speed governor that created the pulses after the user let go was introduced to the market, and this is the one that took off with consumers.*

    People who were used to crank dialing phones and patterns found it easy to understand and use. It was no longer a crank, and it was on the face of the phone, but it was very similar to the long and short rings of the crank phone - a 0 was the longest (10 pulses) and a 1 the shortest (1 pulse) and it was essentially a crank dial phone with more than a few pulse styles.

    So while there are technical and cost reasons behind the pulse dialing technology (explained by other answers) the main reason it succeeded in the market where other techniques failed was that it was a familiar interface for those used to the prior telephone interfaces.

    *Keep in mind that the phone system was a monopoly at the time, you not only paid for the line, but rented the phone as well, and were not permitted to connect your own phones to the line - only phone company owned equipment. Further, the phone company provided all the electricity needed to run the phone system. The newer pulse dial phones could have been made with buttons and electronics, rather than a mechanical system, but that made the phone more expensive, and power hungry. They could have passed the cost along to the consumer, or used the mechanical method and made more money from phone leases.

    First answer, that really answers the question.

    You hit upon the _real_ answer: The rotary dial was a significant improvement over the previous user interface.

    @MichaelHampton: Which came first--the rotary dial or the telephone? I haven't found any patents prior the telephone which precisely resemble a phone dial, but there were a variety of devices that used wind-up motors to generate pulse trains many decades before the telephone was invented, and something like a stock ticker (which predates the phone) might work well with something like a phone dial.

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Content dated before 7/24/2021 11:53 AM