[Luc]

That actually worked? I thought you had to tap the line switch (the switch the receiver pressed down on when not in use), not the receiver. Which would make sense, to reduce interference from sound coming through the receiver while dialling.

Supposedly pulse dialling still works on (most?) new telephone equipment. That's what the vendors of classic phones I've been looking at are saying, anyway.

[anigbrowl]

It does (or at least did) - try it if you know someone with a landline. I was surprised too, as I just tried it on a whim one day. I grew up with pulse telephones and particularly loved the chunky sounds of old models so I used to play with the phone a lot as a kid.

You had to have a good feel for the timing of the pulses or the trick didn't work. Taps and clicks broadband noise with a very sharp transient so it would have to be a very noisy environment indeed for the ambient noise to interfere. I've never played with any analog exchange equipment but the electronics to detect and count pulse dialing doesn't need to be very sophisticated.

[stcredzero]

I once heard that years ago at MIT, they used to vandalize the physical switch on campus by dialing a number, then rigging the handset mic wires to the wall outlet. Since there was an actual physical connection of conductors from one handset to another, the increased current would sometimes somehow stick all of the relays in place, and the phone on the end would keep on ringing loudly until something burnt out.

[Luc]

But the electronics would be different if you did it by tapping the line switch, than if you did it by generating a sharp noise on the line. After all, pulse dialing is also called 'loop disconnect dialing': http://en.wikipedia.org/wiki/Pulse_dialing

"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."

It's confusing.

[anigbrowl]

Well, if you think of it in terms of voltage rather than switching, the audio transient will cause similar spikes in the voltage amplitude. I think that the analog circuits in exchange hardware are only interested in the shape rather than the origin of the pulse but as I said I've never looked at such equipment directly.

I have a modular synth here and have managed to rig up a patch that counts audio pulses (incoming signal goes through a rectifier and an envelope follower and on to an accumulator) and generates an appropriate tone for the counted number after a ~1/4 second pause, and doesn't much care whether I'm opening and closing the circuit or just tapping the front of the microphone. It's not a very complex circuit so maybe analog exchange switching works on a similar principle.