RE: DON'T CUT WIRES
Posted by
Arne Chr. Jorgensen
on 1999-10-13 07:13:13 UTC
Hi,
I am not finished with reading trough everything - yet. So excuse me
if I repeat what others have said.
As you already may have figured out, what I meant was that any
computer will act like a punch tape unit, - just better. In fact it
is what EMC and every others do. So if it has a teletype port, -
many used current loops. ( That is the very best way - noise immune,
easy to work with, will carry signals over large lengths of cable,
etc. )
What I meant about the "old" ISA serial port adapters is:
On the adapter of an original IBM, ( and a bunch of clones ) there
is a socket on the board, with wire wraps. Or an aluminum type of
dual in line pin - device. This one will act as a wire jumper for
the different modes.
( Assuming orig. IBM) - This look a like 16 pin IC has a mark on
the top ( pin 1 ) - If this mark is up, you have a normal RS-232
adapter.
Pull it out, turn it around ( mark facing down ) - you have a
current loop adapter. 0-20mA .
You have +transmit current - on your DB25 pin 9
-transmit current - ....................... pin
11 , this is the current return path.
You have +receive current - on pin 18
and -receive current - on pin 25
-------------------
here is a little trick:
place a 1N4148 or any diode in series with the wire.
wire ------------>|-------------
Now the current will not be affected by this, so you can measure
across the diode with a milliAmp meter. The internal resistance in
the meter will short circuit the diode, and you will read the
correct current anyway. You don't have to clip any wires. Even
during transmission, you will not interrupt the data or disturb
anything by measuring across this control point.
Often you will want to have opto isolation, and this is already
installed on the board. the DB25 pin 18 and 25 is in fact the light
emitting diode in this opto isolator. Note there is no current
limit, that is done on the xmit side. If you would like to wire this
to anything else, like a 5 volt supply, add a resistor of at least
150 ohm to it. ( 220 being very common for 5 volt )
------------------
The rest of the machine, can be upgraded in small steps, ( I have
not looked at the photos, just read what others have told here ) -
but you could win a lot, by taking it step by step. I am not so
familiar with this kind of machines, but I have seen so many stupid
retrofits. In almost each case, the original system was better.
The reason is that they have spent years to match the various
parameters in a machine, and without all that knowledge - you start
on scratch. Many stupid looking, old and nasty things, showed hidden
attributes of wisdom.
By all means, you want something nice and up to date, but I have
rebuilt systems back to it's original status, ( - and some stupid
guy have maybe dumped parts of it ) , - just to find out what was
wrong with the expert system that was put in by very famous makers.
( Siemens, Baily, ABB, GE, - yes, those kind of experts ! )
I don't want to discourage you, but there is so many things you may
learn by just trying out some of it. Even just to get some intuitive
ideas. This can be very helpful later on.
I hope this could be helpful to someone, and I do it just because I
hate to see people disregard old stuff too easy, and making a hell
for them selves.
Best wishes
//ARNE
I am not finished with reading trough everything - yet. So excuse me
if I repeat what others have said.
As you already may have figured out, what I meant was that any
computer will act like a punch tape unit, - just better. In fact it
is what EMC and every others do. So if it has a teletype port, -
many used current loops. ( That is the very best way - noise immune,
easy to work with, will carry signals over large lengths of cable,
etc. )
What I meant about the "old" ISA serial port adapters is:
On the adapter of an original IBM, ( and a bunch of clones ) there
is a socket on the board, with wire wraps. Or an aluminum type of
dual in line pin - device. This one will act as a wire jumper for
the different modes.
( Assuming orig. IBM) - This look a like 16 pin IC has a mark on
the top ( pin 1 ) - If this mark is up, you have a normal RS-232
adapter.
Pull it out, turn it around ( mark facing down ) - you have a
current loop adapter. 0-20mA .
You have +transmit current - on your DB25 pin 9
-transmit current - ....................... pin
11 , this is the current return path.
You have +receive current - on pin 18
and -receive current - on pin 25
-------------------
here is a little trick:
place a 1N4148 or any diode in series with the wire.
wire ------------>|-------------
Now the current will not be affected by this, so you can measure
across the diode with a milliAmp meter. The internal resistance in
the meter will short circuit the diode, and you will read the
correct current anyway. You don't have to clip any wires. Even
during transmission, you will not interrupt the data or disturb
anything by measuring across this control point.
Often you will want to have opto isolation, and this is already
installed on the board. the DB25 pin 18 and 25 is in fact the light
emitting diode in this opto isolator. Note there is no current
limit, that is done on the xmit side. If you would like to wire this
to anything else, like a 5 volt supply, add a resistor of at least
150 ohm to it. ( 220 being very common for 5 volt )
------------------
The rest of the machine, can be upgraded in small steps, ( I have
not looked at the photos, just read what others have told here ) -
but you could win a lot, by taking it step by step. I am not so
familiar with this kind of machines, but I have seen so many stupid
retrofits. In almost each case, the original system was better.
The reason is that they have spent years to match the various
parameters in a machine, and without all that knowledge - you start
on scratch. Many stupid looking, old and nasty things, showed hidden
attributes of wisdom.
By all means, you want something nice and up to date, but I have
rebuilt systems back to it's original status, ( - and some stupid
guy have maybe dumped parts of it ) , - just to find out what was
wrong with the expert system that was put in by very famous makers.
( Siemens, Baily, ABB, GE, - yes, those kind of experts ! )
I don't want to discourage you, but there is so many things you may
learn by just trying out some of it. Even just to get some intuitive
ideas. This can be very helpful later on.
I hope this could be helpful to someone, and I do it just because I
hate to see people disregard old stuff too easy, and making a hell
for them selves.
Best wishes
//ARNE