Comment by ralferoo
5 days ago
Accepting 5V over the RJ-11 jack seems asking for trouble. Someone is going to plug it into a regular phone socket at some point, so it needs to be capable of surviving at least 60VAC. Even if a secondary pair is used, there are so many different wiring standards in use, it'll end up plugged into something live sooner or later.
Luckily telephone lines are very current limited. You'd be hard pressed to draw more than 100mA even with a dead short at ring voltages. One zener diode might be all you need.
Also not the most unusual thing I've seen over a RJ11, which includes keyboards, RS-232, other random digital IO and full USB with data. But these are normally on items that are not phones.
>"One zener diode might be all you need."
It would... if you're willing to just let the thing draw up to 0.1W all the time, and fail catastrophically if anything goes wrong with the zener or the supply is more capable than you anticipated (i.e. you plugged into a PoE jack by accident). This is a very bad idea.
also 1-Wire
Dunno about you but I don't know anyone with live RJ-11 jacks in their house anymore.
I have one. It comes from my cable modem.
We still have a landline. It's part of the cable package, but it mostly just gets robocalls.
Didn't know people still had cable packages!
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It's been a very long time since I had a cable modem that didn't have a pair of 4P4C (aka RJ11 or POTS) jacks on the back. These exist to make available the VOIP service that I haven't wanted for decades.
Others using this same enormous, American ISP probably have similarly-equipped gear.
But I must admit that it has also been a very long time since I connected anything there. I don't know if they supply 48v talk battery or not when the modem has a data-only configuration.
I've got them, powered by an Adit 600 in my basement.
What do you use that for?
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I have 4 or 6, I can't recall how many are on my Grandstream. Phones are fun!
I am not normal.