Behold the Trommelwähler!


Makes sense - an impulse telephone might interpret a static discharge as another ‘click’, so grounding before releasing each number would be useful. Looks like @orenwolf’s gran could have been misdialling multiple ways!


I approve the Trommelwähler.


I don’t recall a connector at all on our home rotary phone, it was wired directly into the box on the baseboard. The multi-line PBX phones at my mom’s office used something resembling a 36-pin Centronics parallel port but with a much thicker cable. When they replaced their system I got miles of gaily-colored wire to “use” and old telephones to disassemble.

Never managed to put one back together again though. Come on, I was like eight.


haha, at school we did this to bypass the rotary dial lock :grimacing:


I do think the fact of being bomb-proof might be a reason why, as far as I know, they are still used in some environments. I remember visiting an A-bomb shelter a while ago and being told that the phones weren’t just relics from the 70s.

I wonder, however, what happens if you don’t have a dedicated old-fashioned line. The network today would involve a lot of electronics, and internally is already IP-based, as far as I know.


I’m not convinced about that, because I don’t see why an external stop would be any more robust than an internal stop. But the grounding idea seems believable.

I was trying to think if there was a UX reason for it, like if it made it easier to dial without looking. But again, you don’t need the metal claw to feel where the dial stops. And it’s not like the bumps on keyboard home keys, because you only hit the claw at the end of dialling a number, not the start.


The lines are identical in the UK - they use the same plug, and impulse phones are still compatible (but not with all menu systems, a fact which some menu developers have not taken account of). I guess you have to maintain backwards compatibility at the local exchange.


I think it’s probably the mechanically simplest and most effective way to stop a user from over-torquing the dial - even assuming that (were it missing) the rotary system would ‘stop’ once you reached the endpoint. Given the diameter of the dial and the number of mechanical parts between the finger and the rotary component or dial switch, I think a physical ‘stop’ (attached somewhere fairly firmly and directly to the chassis) that interrupts the movement of the finger whilst also giving visual and tactile feedback directly to the user, that they have arrived at the end of travel, is the best solution. Saves a lot of broken dials and wear on the return mechanism!

I had a look at the internals of a few old phones and I’m not sure that the ‘hook’ was earthed - in some models it was plastic!



BOW to the Trommelwähler!


Not for me. The cord doesn’t look UL-approved.


I remember trying to call in to radio program contests on a rotary phone – that worked the side of my finger!

That said, this is awesome. I love a completely different UI to ordinary objects that (a) I never thought of and (b) could have been adopted just as readily as the version that actually was.


I’ve had another think about this, and I’ve realised why it needs to be a physical stop that interacts with the finger of the dialler; it’s because it has to work the same way, irrespective of which number you select. A stop in the dial mechanism could provide a limit to the maximum rotation that the dial could perform, but it would not be able to ensure that for each number dialled, the dial was moved the correct amount and the correct number of impulses were generated.

The impulse telephone is basically like a wind-up monkey, and every time the cymbals clash, a connection is made and an impulse sent down the line. There may be some kind of impulse at the start of each number to tell the system to start listening for a number, but essentially, for 1, you need 1 pulse, for 5, you need 5, and for 0 you need 10 pulses to be sent down the line. So you need each number to ‘wind the monkey’ the correct amount and upon release the little cymbals crash, the requisite number of times. If you were to put your finger in the ‘9’ hole in the dial, but instead of rotating the dial to the stop, you just rotate it to the position of the ‘5’, then you wouldn’t get the correct number of pulses - you’d most likely only get 4 or 5. A mechanical stop wouldn’t be able to do this - since irrespective of which number you selected, the mechanical stop would stop the dial after the same amount of rotation - presumably you would dial ‘0’ regardless which number you chose. I suppose you could have sprung number buttons in the dial face, which protrude downwards when selected by the operator and then interact with a hidden stop hook when you rotate the dial - but all this is doing is adding a layer of complication between the user’s finger and the stop hook, increasing the chance of something breaking whilst delivering unclear benefits. You could also have a coloured ‘end zone’ to indicate to the user that they have reached the end of the rotation and should release the dial, but I think this would be more prone to user error as people dial absent-mindedly.


Okay, now someone needs to hack a rotary telephone into a cymbal-playing monkey. Because such a thing needs to exist.


We have 2 Western Electric rotary dial phones on our landline; they’ve survived while later phones have gone into landfills.

If you dial with a pencil your finger won’t smash against the guard (which exists because the dial is made to go well past 0, that’s how you get the cover with the finger holes off for cleaning).


Wow. What sort of evolutionary pressures produced telephone connectors like those?

It’s not like RJ-11 was a historical inevitability or anything; but some of those things look like they could hide among the higher current mains plugs without difficulty; and would probably be up to the job.


I don’t see how it would be a problem. :laughing:



Half-thinking that with some adafruit kit and a motor or two, you could make an Internet-of-Creepy-Things cymbal-monkey phone-alert that triggers when you receive an e-mail, so you don’t miss those important late-night work mails. :imp:
Fit some LEDs into the eyes so you can see as well as hear it when it goes off.


I figured that out when I was 21, back in the summer of '91. I was working on a movie that was shooting on one of the old soundstages on the Sony lot (formerly the Columbia Pictures studio, which was part of the MGM lot even earlier than that). At the time, Guber & Peters were busily spending a whole lot of Sony’s money upgrading their offices, but hadn’t gotten around to upgrading the soundstages yet. Our stage had two set phones, both rotary phones, but one of them was missing the dial since it was intended only for incoming calls. (Since it was 1991, cellphones weren’t yet ubiquitous in Hollywood, and our 2nd AD was issued a phat-ass DynaTAC brick from the production office that everyone on-set clamored to use when we were on location.) When someone was using the outgoing phone, I figured out how to call out on the incoming phone by pulsing the switchhook. Made me feel like quite the hero when I showed the cast how to do it.