[GreenKeys] New USB to current loop driver board

[John Nagle]

Q and A:

On 12/04/2017 07:32 AM, Jack wrote:> Is a schematic somewhere in all of
the info? I can't find it.
> Thanks, Jack K2TTY

There's an image of the schematic at

https://raw.githubusercontent.com/John-Nagle/ttyloopdriver/master/board/ttydriver01.png

if you don't want to install KiCAD.

 From jpruitt67 at gmail.com:
> Can you tell me what size the board is? Jim Pruitt WA7DUY

75mm x 125mm.  I know there is a price break if you get below
100mm x 100mm, and the board could be shrunk to that size.
All the CAD files are there if someone wants to do it.
I made it that big because it fits a stock enclosure.

Steve Garrison <steve.n4tty at gmail.com>
> 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.

Fine with me.  If you want to do modern electronics, you have to deal
with modern SMT.  The good parts are SMT-only now.  The oscillator part
of this, around U1, only works properly with tight layout. Yes, this
means tweezers under a microscope.  I use a little USB microscope for
this, along with a solder paste dispenser and a reflow oven. Learning
SMT assembly takes practice. There are dummy practice kits you can buy; 
they come with a board and some components that don't do anything.
I went through five of those before I assembled this board.  Also,
this is the seventh rev of the board; it took a few tries to get this
working properly.

If there was a market for 100 of these, I'd have them made by Seeed in
Shenzhen, but it's too small a niche for production.  For production,
I'd reduce the board size, get rid of the daughter board and use a
CP2012N directly, and use smaller solid state relays, so the thing
could be assembled by a pick and place machine except for the connectors.
	
				John Nagle