[GreenKeys] Current Loop to RS-232 Conversion on ASR33
Don Robert House
k9tty at dls.net
Mon Mar 18 22:45:33 EDT 2013
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
To: r.jarratt at computer.org ; 'Teletypeparts' ; 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
] 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]
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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