LocalTalk/PhoneNet signal compatibility

[robin-fo]

Hi everybody

I recently got a single PhoneNet dongle and now wonder if I could rewire it to use standard Mini-DIN-3 LocalTalk connectors. The transformer appears to be somewhat different... It is however clear that the data (and all the CSMA/CA stuff) obviously is the same but what about the voltage levels etc?

 

[Nixontheknight]

Hi everybody

I recently got a single PhoneNet dongle and now wonder if I could rewire it to use standard Mini-DIN-3 LocalTalk connectors. The transformer appears to be somewhat different... It is however clear that the data (and all the CSMA/CA stuff) obviously is the same but what about the voltage levels etc?

it should be all the same, they sold PhoneNET to LocalTalk adapters way back when

 

[cheesestraws]

The only thing in the box is an isolation transformer and - for the Apple boxes - termination. PhoneNet and official LocalTalk wiring are, as far as I know, totally electrically compatible, and as @Nixontheknight said, they sold PhoneNet to LocalTalk adapters that were just cables with the relevant cables at each end...

 

[robin-fo]

Ok thanks! What about the transformer specification?

 

[cheesestraws]

as far as I know basically the same. I don't think the spec for the PhoneNet one is formally known, but the LocalTalk one is specced in the back of Inside Appletalk, and it's totally unremarkable. AFAIK the resulting voltages on the bus are pretty much standard RS485 in both cases.

 

[robin-fo]

Good. This might be slightly off topic, but did anybody yet find an "off the shelf" replacement for the transformer?

 

[cheesestraws]

No :-(

edit: though I suspect, in practice, using more modern RS485 isolation parts might do. But I haven't tried and I don't think anyone else has, either.

(sorry my messages are a bit terse, half asleep here)

 

[robin-fo]

I already thought about standard Ethernet transformers, but our hardware developer at the office told me they won't work.. :/

 

[cheesestraws]

Your hardware developer probably knows more than I do in this case then! But I'd be looking at standard RS485 isolation stuff to see if that worked.

That's only a theory though, and not one I've examined very closely.

 

[robin-fo]

IIRC the tricky part is to find one with the right inductance for the signal frequency. 20mH is quite a lot for this sort of thing; Ethernet transformers appear to be in the 10...~300µH range

 

[LaPorta]

I have a whole bunch of phoneNet adapters…gonna sell them.