[GreenKeys] Are my mails getting through?

[drlegendre .]

Hi Steve & All.

The answer is pretty simple.

I received an off-list email from John Nagle, which cleared it up.
Apparently, the intention of the 'keyboard loopback' terminals allow the
converter to run as a standalone "dumb" 120V / 60mA loop supply. This way
the keyboard & printer can be connected locally, so the unit functions like
a typewriter.

He referred to the feature as "totally useless" - I'm not quite sure why.
Seems to be useful enough.. certainly worth the two extra terminals.

On Fri, Aug 28, 2015 at 6:05 AM, Steve Garrison <steve.n4tty at gmail.com>
wrote:

> I saw you message yesterday, but didn't have any comment on the keyboard
> loopback terminals, thus no response.
>
> I'm using several of these devices with 100% satisfaction, so I direct
> your question directly to John Nagle.
>
> Steve G./N4TTY
> Sent from my iPhone
>
> On Aug 27, 2015, at 21:35, drlegendre . <drlegendre at gmail.com> wrote:
>
> I sent the following text yesterday, and surprisingly, it met no reply.
> Another member says it never showed up in his inbox.
>
> Did it make it to the list?
>
> -----ORIGINAL TEXT FOLLOWS----
>
> Howdy Gents,
>
> I'm just completing a scratch-build of an RS-232 / 60mA CL converter
> device as described on this page: http://www.aetherltd.com/connecting.html
>
> What is the purpose of the Keyboard Loopback terminals (pins 3 & 4) on
> connector J1?
>
> Pin 4 is a copy of the KB output signal on Pin 5, and Pin 3 is tied
> directly to the 120V DC supply, just downstream of the 2K 10W
> current-limiting resistor.
>
> As I see it, when the converter is connected, but idle, the current loop
> will be closed which would pull both Pins 3 & 4 down to roughly 3.3V DC
> above ground. This is assuming a 55R selector coil. When the loop opens,
> Pin 3 will rise to the nominal 120V DC supply, and Pin 4 will.. I don't
> know.. float? Show some high-Z voltage?
>
> So what's it all about, anyway? As ever, thanks in advance - your help is
> much appreciated.
>
> BTW - I used a very cheap & common 28V AC control transformer for the 120V
> DC supply. Running a standard voltage +tripler+ gives me almost exactly 120
> DC with (what seems to be) very acceptable ripple at 60mA. I used 3X 1000uF
> @ 200V caps, but I'm sure it could be executed with caps of lesser value
> (and voltage as well). In fact, the ESR of the large caps may actually be a
> detriment to the tripler circuit - eh?
>
> -Bill
>
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