| ??? 07/12/05 13:57 Read: times |
#97147 - It's a current loop ... Responding to: ???'s previous message |
It's a good idea to keep in mind that the telephone circuit is a current loop.
The ringer voltage is an AC signal imposed on the negative battery level, such that it swings nominally 80 volts about the -48 volts, and more under some circumstances in some localities. This means that (A) the drivers will attempt to source the necessary current, irrespective of what voltage has to be imposed on the circuit to do that, and (B) it is not a balanced signal when viewed from local earth-gnd. Detecting the various states of the line is quite straightforward with several comparators, or, more commonly available, a multichannel ADC. If you look in an old communication systems textbook, you'll be able to find more precise details. RE |
| Topic | Author | Date |
| First:Wiring Error Detection! | 01/01/70 00:00 | |
| It depends | 01/01/70 00:00 | |
| First observation | 01/01/70 00:00 | |
| First observation | 01/01/70 00:00 | |
| Danger of surges | 01/01/70 00:00 | |
| Sort of. | 01/01/70 00:00 | |
| Sort of | 01/01/70 00:00 | |
| Re: Sort of... | 01/01/70 00:00 | |
| Phone line transients | 01/01/70 00:00 | |
| Schematic of a simple filter | 01/01/70 00:00 | |
| Research... | 01/01/70 00:00 | |
| router | 01/01/70 00:00 | |
| gas discharge tubes | 01/01/70 00:00 | |
| GDT | 01/01/70 00:00 | |
| Gas discharge tubes | 01/01/70 00:00 | |
| Oh dear... | 01/01/70 00:00 | |
| Gas Tubes | 01/01/70 00:00 | |
| Or | 01/01/70 00:00 | |
| Ring. | 01/01/70 00:00 | |
| Where's Ring? | 01/01/70 00:00 | |
| I say .. | 01/01/70 00:00 | |
| Telephone systems | 01/01/70 00:00 | |
| Telephone systems | 01/01/70 00:00 | |
| tester | 01/01/70 00:00 | |
| Yep Jan! | 01/01/70 00:00 | |
| Even for testing not allowed | 01/01/70 00:00 | |
| Line simulator | 01/01/70 00:00 | |
| Another Misunderstanding Kai | 01/01/70 00:00 | |
| misunderstanding | 01/01/70 00:00 | |
| Jan | 01/01/70 00:00 | |
| Confusion... | 01/01/70 00:00 | |
| quote from my previous post | 01/01/70 00:00 | |
| It's a current loop ... | 01/01/70 00:00 | |
| Correction | 01/01/70 00:00 | |
| ring? | 01/01/70 00:00 | |
| Yes Jan! | 01/01/70 00:00 | |
| Agreed | 01/01/70 00:00 | |
| it explains a few things, though | 01/01/70 00:00 | |
| Phone Line Ground | 01/01/70 00:00 | |
| Not quite offtopic... | 01/01/70 00:00 | |
| Alternative schematic | 01/01/70 00:00 | |
| Just a simple comparsion !!!!!!!!!!!!!!! | 01/01/70 00:00 | |
please help me (telepone) | 01/01/70 00:00 |