> The circuit is centered around a 1:1 pulse transformer. Aside fromthat there are a couple of resistors. The resistors are standard parts but the pulse transformer would be harder to find. Its easier
looking at some old network cards I have here they have pulse transformers for the BNC output.
They might work. They are designed for a pulse width 1/40th as wide as LocalTalk though so it's iffy.
to find used LocalTalk / PhoneNet adapters than it would be to find the pulse transformer. And you end up with a nicer looking, more rugged, and cheaper unit.
Agreed, but I like to know and understand how these things work, so I may try to build a localtalk hub myself, though I will try elsewhere for some second hand boxes too.
Well a hub would just be a bunch of connectors tied together.
A LocalTalk/PhoneNet adapter is quite simple. The pulse transformer isolates the computer from the LocalTalk network. One side of the transformer connects directly to the network. The other side connects to the TxD+ and TxD- lines to the Mac and also to the RxD+ and RxD- lines through 1Kohm resistors. The resistors limit current to the inputs and protect them.
You could simply tie the transmit and receive lines together and connect them to the network. This will work as long as the computers are close enough to each other. The further apart they are the greater the difference in ground voltage (yeah, it does vary).
--
Clark Martin
Redwood City, CA, USA
Macintosh / Internet Consulting
"I'm a designated driver on the Information Super Highway"
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