> Michael Rigby-Jones > > Russell McMahon [SMTP:apptech@PARADISE.NET.NZ] wrote: > > > You can send bidirectionally SIMULTANEOUSLY on a single wire plus > ground > > > by using a "hybrid" as used in all telephones to convert the 2 wire > line > > > signals to and from a receive signal to the earpiece and a transmit > signal > > > from the microphone. Googling on hybrid and telephone will probably > give > > > enough information. > > > > Only if you use a modem though. For direct logic level signaling a > hybrid > > won't be much use. > > -----Original Message----- > From: Dave Tweed [SMTP:pic@DTWEED.COM] > Sent: Wednesday, December 04, 2002 5:45 PM > To: PICLIST@mitvma.mit.edu > Subject: Re: [PIC]:Communication on a single line > > Why not? Hybrids work just as well at DC as they do for audio; you just > need a receiver with balanced inputs, like an RS-422 buffer: > > Tx >---+---+ +---+---< Tx > driver | | | | driver > R R R R > R R R R > R R R R > | | | | > + <-------+--------------------------------------+-------> + > Receiver | | Receiver > - <---+ +---> - > | | > R R > R R > R R > | | > V V > > All resistors are the same value (e.g., 4700 ohms) and the transmit driver > needs to be a voltage source (low impedance). > > If the transmitter switches between, say, 0V and 5V, the opposite receiver > will see a voltage differential of 0V and 2.5V, respectively, while the > local receiver will just see 0V. > > For long lines, you'll probably want to use lower resistances and you'll > want to limit the slew rate of the transmitter so that the receiver > doesn't > produce glitches on the transistions of the local transmitter. > I thought that a true hybrid used transformers, or at least some tricky transformer simulation with op amps to ensure the transmitted signal did not appear on the receive port? Mike -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.