[GreenKeys] Problem with Current Loop to RS-232 Converter on ASR33

[Rob Jarratt]

> -----Original Message-----
> From: greenkeys-bounces at mailman.qth.net [mailto:greenkeys-
> bounces at mailman.qth.net] On Behalf Of Dave
> Sent: 20 January 2013 19:42
> To: greenkeys at mailman.qth.net
> Subject: Re: [GreenKeys] Problem with Current Loop to RS-232 Converter on
> ASR33
> 
> On 20/01/2013 18:29, John Nagle wrote:
> > On 1/20/2013 2:07 AM, greenkeys-request at mailman.qth.net wrote:
> >> Date: Sat, 19 Jan 2013 18:31:05 -0000
> >> From: "Rob Jarratt" <robert.jarratt at ntlworld.com>
> >> To: <greenkeys at mailman.qth.net>
> >> Subject: [GreenKeys] Problem with Current Loop to RS-232 Converter on
> >> 	ASR33
> >>
> >> The ASR33 I got came with a little box that I assume to be a Current
> >> Loop to
> >> RS232 converter.
> >      More detail on the provenance of the device would be useful.
> 
> It was rescued from a dump truck by a friend of mine. Rob persuaded me he
> was going to use it.



And hopefully I am fulfilling the promise! :-)




I didn't  know any thing about its provenance....
> 
> >> The ASR33 behaves rather oddly when I plug the RS232 connector into
> >> anything. When the connector is not plugged into anything the ASR33
> >> ticks over as I believe it should. However when I plug the connector
> >> into a socket, even if the socket is not connected to anything else,
> >> the ASR33 starts acting a little as if it receiving characters, the
> >> cylinder with the characters embossed on it "vibrates" but does not
> >> print anything. If I plug it into my breakout box, with the other end
> >> not connected to anything, it acts in this way and I notice the Rx
> >> light come on, which of course it shouldn't as nothing is being sent
> >> to it. It is almost as if there is a short to the Rx line. I have
> >> checked the connector for shorts but there don't seem to be any.
> >>
> >> Has anyone ever come across behaviour like this?
> >       RS-232 is supposed to have an input that swings from -12V to +12V.
> > Most modern devices (last 20 years or so) accept 0 to +5V as input.
> > Some older devices may not do that.  Also, RS-232 inputs are supposed
> > to have some load on them; an input resistance of 3K to 7K is
> > specified for RS-232 inputs, so that random electrical noise isn't
> > sensed as data.
> >
> >       Does your device work when attached to some proper RS-232 data
> > source?  If the only problem is that it behaves badly when unplugged,
> > just put a 5.6K resistor across the input to sink the noise.
> >
> > Read this: http://www.arcelect.com/rs232.htm And this:
> > http://www.maximintegrated.com/app-notes/index.mvp/id/723
> >
> > 					John Nagle
> >
> >
> >
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