Pulse dialing

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Pulse dialing or loop disconnect dialing, also called Rotary or Decadic dialing in the United Kingdom (because up to 10 pulses are sent), is pulsing in which a direct-current pulse train is produced by interrupting a steady signal according to a fixed or formatted code for each digit and at a standard pulse repetition rate.

Dial pulsing originated with a rotary dial integrated into telephone instruments, for the purpose of signaling. Subsequent applications use electronic circuits to generate dial pulses.

The pulses are generated through the making and breaking of the telephone connection (akin to flicking a light switch on and off); the audible clicks are a side effect of this. As a result, all that is really needed to dial a number with pulse dialing is a switch. With practice it is possible to dial phone numbers by flashing the hook switch (rapidly clicking the receiver switch). Each digit in the number is represented by a different number of rapid clicks. In most countries one click is used for the digit 1, two clicks for 2, and so on, with ten clicks for the digit 0. Two exceptions to this are New Zealand, with ten clicks for 0, nine clicks for 1, and so on, and Sweden, with one click for 0, two clicks for 1, and so on.

Individual digits in a phone number need to be separated with a short pause so as not to bleed into each other and in keypad based pulse dialing digits need to be "buffered" when dialed rapidly. In rotary systems this is taken care of by having the user wait for the rotor to revolve back to the start position before the next digit can be dialed.

Most fixed-line phones now use dual tone multi frequency (DTMF, also called touch tone or tone dialing) rather than pulse dialing, but most telephone equipment retains support for pulse dialing for backward compatibility. Also, some models of keypad phones also have a tone/pulse switch which can be toggled to switch between the two, making these phones usable in areas where DTMF dialing is not accepted, e.g. in most ex-USSR countries. ISDN and GSM mobile phones perform call setup using digital signaling systems.

[edit] Tapping

It is possible to trick a phone system into thinking that a rotary dial is being used. To do this, one finds the little button, switch, or hook that is pushed down when you hang up the phone. To "dial" the digit 1, tap it once. For the digit 2, tap it twice QUICKLY (ten taps per second for UK phones and in North America). For the digit 3, use three taps, etc. The digit 0 is ten taps. (But see above if you are in Sweden, New Zealand or Oslo.)

In the UK it used to be possible to make calls for free from coin-box phones (payphones) by tapping. This was on phones with A and B button boxes. (These were phased out between 1958 and 1979 as subscriber trunk dialling was introduced.) A person caught tapping could be charged with 'abstracting electricity from the GPO'. (several cases of dishonestly using telephones without paying were prosecuted under this offence)