[GreenKeys] New USB to current loop driver board

[Jack]

Thank you!

Jack


-----Original Message-----
From: John Nagle [mailto:nagle at animats.com] 
Sent: Monday, December 4, 2017 1:21 PM
To: Jack <wa2hwj at att.net>; Green Keys <greenkeys at mailman.qth.net>; drlegendre . <drlegendre at gmail.com>; jpruitt67 at gmail.com >> Jim Pruitt <jpruitt67 at gmail.com>
Subject: Re: [GreenKeys] New USB to current loop driver board

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