[GreenKeys] Current Loop to RS-232 Conversion on ASR33

Tue Mar 19 18:26:04 EDT 2013

My model appears to be "3320 GWA". I would be curious to know what that
means in terms of likely age, particular characteristics or anything else
that may be of interest.

Regards

Rob

From: greenkeys-bounces at mailman.qth.net
[mailto:greenkeys-bounces at mailman.qth.net] On Behalf Of Don Robert House
Sent: 19 March 2013 02:46
To: r.jarratt at computer.org
Cc: greenkeys at mailman.qth.net
Subject: Re: [GreenKeys] Current Loop to RS-232 Conversion on ASR33

Rob,

ASCII 67 is an 11 unit code.  1 Start, 8 data bits, 2 Stop. However the 8th
data bit is used for parity.

Since your machine is printing in local you must have a nicely operating
machine. 

I have never seen a 33 operate in Full Duplex, but it should certainly be
possible.

The 32, 33, and 38 generate characters in parallel and are serialized by the
distributor.  

Your problem is located somewhere incoming to the selector magnet when the
switch is in the Line position.

Your message reads that the machine is not running open so the selector has
constant current in it's winding.

I have some schematic drawings for the 33, but I need to know what model you
have.

There should be a sticker on the rear of the base near the call control
unit.

Don

K9TTY

On 16 Mar 2013, at 3:19 PM, Rob Jarratt wrote:

It has been a little while since I looked at my ASR33 problem. Just to
refresh everyone: In Online mode I can send characters from the ASR33 to the
computer, but the characters coming back do not print. It works perfectly in
Local mode. I have checked and it is full duplex 20ma, which matches the
setup of my current loop converter and I am using 110bps, 7 data bits, 2
stop bits and Even parity. The ASR33 does not chatter (run open) when
connected to the converter.

Today I tried sending a break from the PC to the Teletype. It did not
chatter when I sent the break. I verified with a multimeter that the current
goes to zero, so I am definitely sending the break.

Does this offer any clues?

Regards

Rob

From: Alf Fisher [mailto:alf_fisher at tiscali.co.uk] 
Sent: 24 February 2013 21:39
To: r.jarratt at computer.org; 'Teletypeparts'; greenkeys at mailman.qth.net
Subject: Re: [GreenKeys] Current Loop to RS-232 Conversion on ASR33

Hi Rob,

I'm sure others will agree but I believe the ASR33 doesn't actually need a
high voltage source as there is a transistor circuit that actually drives
the electromagnet.  I reckon 20 volts with a resistor to limit the current
to 20 mA should work. 

Is it possible with the Westermo, to loop-back the TTY to itself so you can
print what you type? I don't know what is in the converter but another way
may be to bridge the Tx & Rx pins on the Westermo RS232 port  (pins 2 & 3?).
It should work the same as being in Local but you are switched to Line.

Alf

----- Original Message -----

From: Rob Jarratt <mailto:robert.jarratt at ntlworld.com> 

To: r.jarratt at computer.org ; 'Teletypeparts' <mailto:teletypeparts at aol.com>
; greenkeys at mailman.qth.net

Sent: Sunday, February 24, 2013 11:55 AM

Subject: Re: [GreenKeys] Current Loop to RS-232 Conversion on ASR33

I have not looked at this problem for a week or so but will be looking again
today. To summarise, I can send characters from the Teletype to my computer
successfully, but any characters I send from the computer to the Teletype do
not print out.

So far I have verified that the ASR33 is wired for 20ma Full Duplex and that
my Westermo converter works, because I can connect up the current loop
interface into a loopback configuration and I get the characters I send on
the RS232 side echoed back. I am using my RS232 port set at 110bits/sec, 7
data bits, 2 stop bits and even parity. The battery test suggested by
Teletypeparts has not worked though. The only things I have yet to check
are:

1.       Is the mode relay inside the CCU is operating correctly? I used a
multi-meter to test that the contacts were made and broken correctly. It
looks to be making and breaking contacts OK for the most part. One of the
contacts (AM-15) seems a little bent, requiring the relay to close
completely to break the contact. As the bend was such that the contact might
not open correctly, I tried isolating it with some paper, but it didn't seem
to make any difference. A couple of contact pairs showed shorts regardless
of the relay position, but the relay was fully wired in, so this might be
expected. The constantly shorted pairs are AM-9 with AM-8, and AM-1 and
AM-2. Is there a simple way to test the relay with a battery? I am not sure
what voltage and current it would need.

2.       The voltage provided by the converter. I am told it needs to be 80V
and some converters do rather less, perhaps 20V. I have a multi-meter, but
in this case I am not sure where to measure the voltage, I have tried T+ and
T- with respect to the converter's Shield connection and with respect to the
TTY's earth but I don't get any more than about 1 volt, this is whether I am
sending characters or not.

Any ideas?

Regards

Rob

From: greenkeys-bounces at mailman.qth.net
[mailto:greenkeys-bounces at mailman.qth.net] On Behalf Of Rob Jarratt
Sent: 10 February 2013 23:10
To: 'Teletypeparts'; greenkeys at mailman.qth.net
Subject: Re: [GreenKeys] Current Loop to RS-232 Conversion on ASR33

I tried a loopback test on my Westermo converter and that worked fine when
looping back from PC back to PC through the current loop. I tried looping
back from the TTY side via the RS232 interface and there was no echo.

I then tried the battery test you mentioned and unfortunately that failed to
work too.

I think the problem must be inside the 33. L

Regards

Rob

From: Teletypeparts [mailto:teletypeparts at aol.com] 
Sent: 10 February 2013 22:28
To: r.jarratt at computer.org; greenkeys at mailman.qth.net
Subject: Re: [GreenKeys] Current Loop to RS-232 Conversion on ASR33

Rob,

I have heard of the interfaces being bad but I am afraid I have exhausted my
limited knowledge of interfacing.  Some of the guys on Greenkeys may be able
to help you. 

If you want to eliminate the 33 as a problem completely do the following:

Short together 4 and 6 and apply a 9 volt batt to 3 and 7.  Again, if it
runs open reverse polarity on 3 and 7.  Do the test in Line mode.  After you
have the 33 running closed, type a few characters.  If they print OK the
trouble is not in the 33.  I still dont recommend leaving the batt on very
long.  A minute or so.  It may not harm anything, but just to be sure keep
the time short. 

What you have done is make the 33 half duplex (2 wire) and tested it in line
mode.  I do that all the time here to check out the 33 in Line mode.  I also
use a test generator, but before I had that I used the 9 volt batt test. 

Wayne

-----Original Message-----
From: Rob Jarratt <robert.jarratt at ntlworld.com>
To: 'Teletypeparts' <teletypeparts at aol.com>; greenkeys
<greenkeys at mailman.qth.net>
Sent: Sun, Feb 10, 2013 4:28 pm
Subject: RE: [GreenKeys] Current Loop to RS-232 Conversion on ASR33

I do understand about the echo that is needed to get characters to print in
line mode. I am using a terminal emulator on the PC to receive and display
the characters I type on the ASR33, and I type characters into the terminal
emulator to send them to the ASR33 in the hope they will be printed. The
emulator successfully displays the characters I type into the ASR33, but the
ASR33 does not print the characters I type into the emulator, despite the
Westermo LEDs showing activity which suggests it is receiving the characters
from the emulator and sending them on to the ASR33.

I had to re-read about start bits because I had forgotten about them. I
think start bits are always present, so there is no setting to control them.
So basically, I think I am already using 1 start bit, 7 data bits, one
parity bit and 2 stop bits, but nothing is getting printed. I am using a
line speed of 110 bits/sec, which in this case corresponds to 110 baud too.

I suppose the Westermo converter could be faulty and not sending data out to
the ASR33. Unless anyone has any other suggestions I'll try a loopback test
on the converter to see if it is working.

Regards

Rob

From: greenkeys-bounces at mailman.qth.net
[mailto:greenkeys-bounces at mailman.qth.net
<mailto:greenkeys-bounces at mailman.qth.net?> ] On Behalf Of Teletypeparts
Sent: 10 February 2013 18:20
To: r.jarratt at computer.org; greenkeys at mailman.qth.net
Subject: Re: [GreenKeys] Current Loop to RS-232 Conversion on ASR33

Rob,

Read on as I put something important below. 

I guess the voltage doesnt need to be 80 or more.  It may run OK with less.
The norm is 20 MA at 120 VDC. 

I dont know anything about the Westermo, but I know that when you send to
the computer from the 33 the computer needs to be programmed to echo back to
get a copy on the 33. 

When you type in Local, the print is pretty much instant.  When you type in
Line thru the computer you will see a slight delay, not much but enough to
notice. 

The 33 doesnt care about parity on its receive side, it will print whatever
the bits from 1 to 7 are.  The 33 is 110 baud, not sure what that converts
to in computer language. 

Oh and this is important, you need a START bit which is always a zero or a
space or no current which all terms seem to be interchangeable.   The rest
you got correct.  Its one start bit, 7 data bits, one parity bit and 2 stop
bits.  The 33 will run with 1 stop bit, but its normal to give it two when
you can. 

If you put the START bit in, I bet it will work. 

Wayne

-----Original Message-----
From: Rob Jarratt <robert.jarratt at ntlworld.com>
To: 'Teletypeparts' <teletypeparts at aol.com>; greenkeys
<greenkeys at mailman.qth.net>
Sent: Sun, Feb 10, 2013 5:36 am
Subject: RE: [GreenKeys] Current Loop to RS-232 Conversion on ASR33

I made some great progress, with one last hurdle to overcome.

I configured the Westermo to be in active mode (ie supply current) on both
its receive and transmit sides). This cured the problem with the RD light on
the Westermo being on all the time and it stopped the chattering too.

I connected it up to a terminal emulator running on my PC. When I press a
key on the ASR33 the corresponding character appears on the terminal
emulator. However, when I try to send characters from the terminal emulator
to the ASR33 nothing happens. I am using 110bps, 7 data bits, even parity
and 2 stop bits.

As the chattering has stopped, does this mean that the Westermo's transmit
side is set up correctly now?

Am I using the right serial port settings?

Could the Westermo not be outputting the right voltage? It is a 20ma
interface, but the manual does not say anything about the voltage which you
say needs to be 80V or more.

What else might prevent the characters from being printed out?

Regards

Rob

From: Teletypeparts [mailto:teletypeparts at aol.com
<mailto:teletypeparts at aol.com?> ] 
Sent: 09 February 2013 20:30
To: r.jarratt at computer.org; greenkeys at mailman.qth.net
Subject: Re: [GreenKeys] Current Loop to RS-232 Conversion on ASR33

Rob,

The 33 should chatter or run open when in Line mode and not connected to
anything.  The reading of a short is normal as on 3 and 4 you are basically
looking at a switch, the distributor of the 33.  Same reading on 6 and 7 as
I recall. 

Neither side of the 33 generates any current.  The receive wants 20 MA at 80
volts or more and the send will accept whatever the interface gives it,
usually 12 or 15 volts. 

A quick test you can do is wire a 9 volt batt to 6 and 7 while in line mode.
You have a 50/50 chance of getting the polarity correct.  If still running
open, reverse the leads.  The 33 should run closed.  Dont leave the batt
connected for a long time.  You have now verified the 33 will run closed in
Line mode and you need to proceed with the adapter stuff of which I know
very little. 

I believe the Send side of the Westmo should be set to active to generate 20
MA current for 6 and 7 of the 33. 

Dont know about the Westmo receive side. 

Hope this helps,

Wayne

-----Original Message-----
From: Rob Jarratt <robert.jarratt at ntlworld.com>
To: greenkeys <greenkeys at mailman.qth.net>
Sent: Sat, Feb 9, 2013 7:22 am
Subject: [GreenKeys] Current Loop to RS-232 Conversion on ASR33

I emailed this list a little while ago about getting my ASR33 to talk
RS-232. I have since sourced a Westermo MA-21 current loop converter.

I have noticed however, that the ASR33 will "chatter" in line mode
regardless of whether the current loop wires are connected to anything or
not. When I plug it into the Westermo the RD light on the Westermo comes on
even if the ASR33 is disconnected from the mains. The RD light is supposed
to come on when it is receiving data from the line interface (manual here if
you want to see it:
http://www.westermosales.com/pdfs/MA-21manualENGSEDE.pdf), which makes no
sense if the ASR33 is not even connected to the mains.

I have set both the receive and transmit side of the converter to passive
mode for now (ie they don't generate the current), but I think the receive
side of the converter will need to be set to be active so that it generates
the current because the drawings of the ASR33 suggest that the ASR33 receive
side generates current but the transmit side does not. In fact all the
switches are set to the factory settings at the moment.

I tried switching the receive side of the converter to active and when I
switched on the converter (with the ASR33 disconnected from the mains) the
RD light did not come on this time.

I have also noticed that with the ASR33 disconnected from power the screw
terminal pairs 3&4 and 6&7 appear to be shorted (ie 3 shorted to 4, 6
shorted to 7). I suspect this may be expected but I am not sure.

I have wired screw terminals 3&4 on the ASR33 to the Receiver side of the
Westemo, and 6&7 to the Transmitter side.

I wonder if there is a fault in the ASR33, should it chatter in line mode
when it is not connected to anything?

Which side (if any) of the Westermo should be set to active to generate
current?

Regards

Rob

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