[GreenKeys] New USB to current loop driver board

[Steve Garrison]

Guys & Gals, this is a fantastic board, but is not for those with even a
little fear of SMD assembly.  There are three chips that I had mounted by a
profession SMD tech.  And there are a couple of tricks I stumbled over, so
if you want to attempt one of these, get in touch.  I may want to do 1 or 2
more of these for myself, so if any others are interested please get in
touch as there is no reason for more than one of us to order 10 boards.  And
I spent more than $50 (including shipping and tax) for my parts since I was
ordering for just one board.  Ordering for multiple boards could save a good
deal.

I'll try to send a picture later of Nagle's new device alongside my cabinet
it replaces.  Quite a difference in size and weight.  And overall cost
savings as well since I did my cabinet through Front Panel Express.

Thanks John for a wonderful project.

Steve G./N4TTY

-----Original Message-----
From: greenkeys-bounces at mailman.qth.net
[mailto:greenkeys-bounces at mailman.qth.net] On Behalf Of John Nagle
Sent: Sunday, December 03, 2017 9:55 PM
To: greenkeys at mailman.qth.net
Subject: [GreenKeys] New USB to current loop driver board

I've designed and built a new board which will drive a 60mA current loop
Teletype from a USB port. This board requires no external loop supply; it's
powered entirely from the USB port.

It fits in a small case 75mm x 125mm.  There are two 1/4" phone jacks for
keyboard and printer, a mini phone jack for a motor power control relay (5V,
100mA max) and a micro-USB connector.  Controls are an on/off switch and a
BREAK button.  A 3-high LED indicates Power On, Motor On, and Data to the
printer.  That's it.  Output current is regulated and will work from 55 to
220 ohm loads with no adjustments.

Steve Garrison just built up one of these boards, and it worked for him.  So
now I'm releasing the design for general use.  Here are all the project
files and documentation:

https://github.com/John-Nagle/ttyloopdriver

The Gerber files and drill files for fabrication are in

https://github.com/John-Nagle/ttyloopdriver/raw/master/board/fab/fab.zip

Send that to a board house if you want boards. I use Seeed in Shenzhen.
They charge $20 for 10 boards, plus shipping, which is about $30.

This is a moderately advanced surface mount soldering project.
You'll need the tools and skills to solder 0.5mm pitch parts.
Parts cost not including the board is about $50 per board.

Usual questions:

- Can you buy a completed board? Not from me. If someone else wants to, it's
all open source.

- Will you modify this to do ...? No, but you have all the design files in
KiCAD and can do it yourself.

				John Nagle
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