4 ms·
As I understand it, it's some of the insane backwards compatibility the 'pots' system has to put up with. If you think way back, before dtmf/touch-tone phones,
by soneil 13y ago
As I understand it, it's some of the insane backwards compatibility the 'pots' system has to put up with.
If you think way back, before dtmf/touch-tone phones, when you dialed a number, the line clicked. You press one, the line clicks once. For zero, 10 clicks. This is backwards compatible all the way to rotary phones.
Those clicks are the line being closed and re-opened in rapid succession. You dialled by 'hanging up' repeatedly. So the line can't close the moment you hang up - there's a grace period while it waits for the next click. If the initiating party does't hang up, they emulate this grace period until the exchange times out.
- outworlder 13y agoThat is true, but it doesn't require more than a couple of seconds. I used to dial by hanging up when I was a child, even in modern DTMF phones. Ever see the "flash" key in a phone? Add a few milisseconds to that and a modern phone system should hangup.
- soneil 13y agoThat's the problem; it's not a modern system. eg, the British GPO 332 handset was first issued in 1937 - and still works. It's difficult to demand millisecond timing when you're backwards-compatible with pre-war equipment.
- madaxe 13y agoWay back... I still use a good old GPO rotary phone. Only thing you sometimes have to retrofit is the capacitor on the ringer circuit, as they're usually dead, or not big enough for today's lower voltage lines.