[sci.electronics] 2 way IR LED systems

edw@wells.UUCP (Ed Wells) (02/19/90)

In article <431@skipper.dfrf.nasa.gov>, rando@skipper.dfrf.nasa.gov (Randy Brumbaugh) writes:
> 
> It seems that each headset would need an independent
> xmit frequency, but all could share a common recv.
> frequency.  This would also allow "listen only"
> headsets.

  Why?  Just have the transmitters fire up like their RF counterparts.
Have the transmitter work on a VOX (Voice operated transmitter) or on
a PTT (Push to Talk).  
 
-- 
=========================================================================
Edward E. Wells Jr., President			    Voice: (215)-943-6061
Wells Computer Systems Corp., Box 343, Levittown, Pa. 19058
{dsinc,francis,hotps,houxl,lgnp1,mdi386,pebco}!wells!edw

tob@cbnewsk.ATT.COM (ted.o.burger) (02/21/90)

> In article <6313@ncar.ucar.edu> hpoppe@bierstadt.scd.ucar.edu (Herb Poppe) writes:
> >How about 2-way data communication (half or fuyll-duplex)?
> I think it's been done.  Some HP calculators have the ability
> to send data to the little HP printer via IR beam.  The printer
> checks for data corruption, and, if it detects an error, requests
> a retransmission.  Of course, this system requires a clear
> line of sight between sender and receiver, which would be a
Bob

Thr HP system is NOT a two way system.  The data is encoded in a (almost) full
error correcting format.  Their goal was to provide the link with minium cost to the
calculator so they could include it on the maximum number of calculators.
The calculator just has a single diode and the reciever is in the printer.
Only the people who want the printer have to spend the bucks to get the
IR receiver.

Ted

johne@hpvcfs1.HP.COM (John Eaton) (02/22/90)

<<<
< Is there any reason Infrared LED systems can't be 
< used for 2-way communication?  It seems like this
< would be easy if different frequency carriers were
< used for transmit and receive.  (I'm not sure how
< those IR headphone systems work - do they use 
< carriers?)
----------
My understanding of the state of the art in optics is that
they are still at the same level as spark gap transmitters
were in the RF arena. The detectors cannot be tuned to different
frequencies of light. 

One system that might work is to have a master station broadcast
a clock and sync signal to everyone in sight. The slave stations
could then jump into selected time slots and send packets up the
the master. 

All this IR talk reminds me of the PCjr. They put an IR "Freeboard"
on a computer designed for the home/education market only to find
that they would not work if you put several in the same room. Talk
about product planning.


John Eaton
!hpvcfs1!johne