[GreenKeys] New Loop Converter Prelim specs

[gil smith]

Hi folks:

Thanks to all who responded with feature requests -- I hope I have them all
covered here.  This interface is sounding a lot like the one I did a couple
of years ago.  Many of you got these boards, and a few of you even built
them up:

http://www.vauxelectronics.com/gil/tty232/tty232/

I think all we need is a second-generation of this board;  some thoughts:
I will get rid of full-duplex, since it seems to be rarely used and it will
simplify things.  I will get rid of the rs-485 and X10 ports.  I want to
try a constant-current HV loop to replace the big-frickin'-resistors (maybe
a TO-3 on a heatsink).  I need to investigate the snubber, since it
interfered with the loop sense, and had to be disconnected in half-duplex.
I will keep the optional low-voltage loop, since even though no one here
needs it, there are applications for hanging a 33 onto a computer with
speed conversion (I have such an application, so it stays).  I can use up
to maybe 200 bytes of internal pic memory for speed-conversion buffering,
but I want to investigate adding an sram chip -- adding a 32K, 128K, or
512K chip should handle your buffering needs, I would think.  Jack tells me
the speed-converting versions of dovetrons used 200-char fifos, so the sram
may only be needed for streaming text.

So some prelim specs:


1)  External box with loop supply transformer, DB-9 232 connector, loop
jacks...  But it could still mount inside a dovetron if desired, and take
advantage of the HV winding and power supply voltages.  Otherwise a special
cable with a couple of BNC plugs and a DB-9 will be needed to connect to
the dovetron's POLAR (232 in) and OUTPUT (232 out) jacks.  Or a straight
DB-9 cable to connect to a PC.  I might just put a DB-9 on my dovetron to
make cabling easy.

2)  High-Voltage (120-150V), 60- or 20-mA loop, and four insulated 1/4"
jacks for one to four TTYs (M15, M28...).  Half-duplex only.

3)  Low-Voltage (30V), 20-mA loop, and one insulated 3.5mm jack (M32, M33...).
Half-duplex only.

4)  RS-232 interface using fully opto-isolated connections to either HV or
LV loops.

5)  Optional PIC microcontroller -- provides configurable options such as:
baud-rate conversion, ascii-to-baudot conversion, auto-CR-CR-LF-LTRS at N
chars (default 72), auto-line-feed insertion after CR, etc.  If PIC is not
installed, jumpers connect the 232 port directly to the tty loop interface.

I did the baud-rate conversion and ascii-to-baudot conversion code already
on the TTY232 pic, but it only had a small internal pic buffer, and relied
on serial port xon/xoff flow control to throttle data.  Flow control is not
an option on a TU, so need to add ram chip as well.  The code for the
TTY232 pic was ascii-only input, and baudot or ascii out.  I need to
provide for baudot input as well. 

6)  Auto-power the TTY, by detect incoming data, buffering it, turn on a
TTY motor relay, delay for spin-up, then let data flow.  Some sort of
SelCal is possible here as well, if you help me define a string to watch
for (programmable, but perhaps default of ZCZC).  Shutdown string would be
handy too (perhaps default of NNNN).  Input appreciated.

7)  A char counter might be more work than it is worth, but I could likely
activate a signal line at N chars (default 70).  This could be used for a
bell, or could activate a light until CR entered.  Let me know what might
be handy. 

8)  Store and replay test messages?  Answerback string?  Lots of
possibilities for stuff stored in eeprom.

9)  Provision for an externally-powered loop, instead of an internal loop
supply?  Let me know.

10)  Commonly-available parts, of course.  Bare-boards, or full kits will
be available.


thanks,

gil



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