Interconnecting classic computers

Tony Duell ard at p850ug1.demon.co.uk
Mon May 5 14:55:51 CDT 2008


As I think most of you know, I have a fairly diverse collection of 
classic computers (I suspect some others do too). 

Quite often I need to transfer data between 2 machines. Maybe to 
download a file from this PC, which I've in turn downloaded from a web 
site, to run on one of the classics. Maybe to print out some listing from 
a classic. Whatever.

My machines vary in size from the pocket computers up to machines that 
it's not practical to move. They're scattered throughout a house. They 
are, alas, not in a machine room. Most of the machines (and all the ones 
I want to consider for this) have an RS232 port, either built-in or as an 
option (which I have). Most of the machines run kermit. Or I can simply 
print to the RS232 port on one machine and capture the incoming 
characters on the other

So, I think the problem reduces to 'how to interconnect RS232 ports'. let 
me add some constraints : 
 
Must work over a distance longer than the RS232 spec allows (i.e. the 
answer is probably not 'A long RS232 cable' :-)). 

Prefereably no cables at all. One solution I've come up with is to use a 
couple of line drivers and a long cable between them. A long cable that 
my parents, or the cat, will get tangled up in :-(

No line-of-sight between the machines

Must work at 300 and 1200 baud. 110 and 9600 baud would be a bonus

I only need one pair of machines linked at a time. I don't need a 
network. So if the solution involves a radio link, the fact that there's 
only one channel available would not be a problem. 

Must not make use of any flow control lines on the RS232 port, since some 
of my machines don't support them.

Using classic, or at least repairable, hardwre is a bonus :-)

I said 'RS232'. I mean asynchronous serial, of course :-). If somebody 
has a solution for TTL or 3.3V level serial ports, I can trivially 
convert the signal levels

I've been looking at some of the license-exempt radio modules, but they 
either are half-duplex or amke use of the flow control lines (typically 
they buffer <n> bytes internally, then de-assert a flow control line 
while they pack up that data and send it to the other end). 

So far the best I've come up with is to link one machine to a palmtop 
(HP95LX), then transfer the data to that, carry the palmtop to the other 
machine and transdfer the data on. It's not ideal, but it does work.

Any other ideas?

-tony




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