21 Nov
2014
21 Nov
'14
12:54 p.m.
Pun unavoidable, more or less.
So at least we're on the same page so far as RS-232 -> 20mA converters are
concerned. I've been looking at that stuff today.. and here's something
that seems too easy.
Is there any reason that I couldn't pick up a cheap, common RS-232 to TTL
converter module (like eBay item 310624019670 - about $5) and connect the
TTL side to an opto-isolated transceiver pair like the HCPL-4100 / 4200?
The DIY schematics I've seen are essentially RS-232 to TTL converters
(using the MAX232 IC) that directly drive the 4100/4200 pair.
Like I said, seems too easy.. but why wouldn't it work?
On Fri, Nov 21, 2014 at 2:35 PM, tony duell <ard at p850ug1.demon.co.uk> wrote:
Sure, I get all that.. but what on Earth does it have to do with the
thread
topic - which concerns what to look for when
acquiring a Model 33
Teletype?
I think we're assuming you are going to connect this ASR33 to something
else.
ASR33s have a 20mA (or 60mA, link selectable, I think) current loop
interface. Not
RS232 (OK, I mentioned the Data Dynamics machine that used ASR33
mechanisms,
but strictly that's not an ASR33). The most common machine (I think) with
a 20mA
current loop interface is a Unibus PDP11. Hence all the comments, if you
had
one of those, you could easily link the ASR33 to it.
That said, a quick google search for 'RS232 current loop' (no quotes)
throws up
a number of commerical units and built-it-yourself schematics to convert
the current
loop interface to RS232.
All of that info seems peripheral, at best. And
no, I don't have +any+
PDP
Pun intended?
-tony