Re; What to look for in a Model 33 Teletype - a newb's buyer's guide?

drlegendre . drlegendre at
Fri Nov 21 14:54:35 CST 2014

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> 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+
> Pun intended?
> -tony

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