[GreenKeys] Who's still looking at getting John Nagle's, > USB<->CL Board made ?

[John Nagle]

> From: Sam Stinson<samstinson at gmail.com>

> Subject: Re: [GreenKeys] Who's still looking at getting John Nagle's
>  USB<->CL Board made ?

> The simple fact is, there are no through-hole versions of some of the
> components used in John Nagle's design. Or at least, none that I 
> could find after a few hours spent casually going over the schematic 
> and looking up data sheets and such. Unfortunate, but it is what it 
> is.

     Yes, that's correct. The LT3750 is surface mount only. It's usually
used to charge the capacitor for the flash in cameras.

> Also the layout of switch mode power supplies is entirely
> non-trivial (I would go so far as to call it voodoo)...  a simple
> parts swap conversion from SMD to through-hole is highly unlikely to
> work without significant re-design.

    No way would that work. It won't even work if the layout has
significantly longer traces.  I tried. The layout is from the LT3750
data sheet.

>> On 3/5/18 1:50 PM, Pete Lancashire wrote:
>> 
>> Nothing to taking his CAD, changing the parts to thru hole and 
>> laying out a new board.
>> 
>> Well, that's entirely up to them giving you the original CAD files 
>> that they developed.

     It's all on Github in KiCad format at

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

> From: On Behalf Of drlegendre .
> 
> Now beggars can't be choosers and all that, but I don't get why John 
> elects to design these circuits with SMD parts, knowing that the 
> primary user base will be a group of DIYer's. Can you work with SMD 
> parts? I can't. I mean to say, I might be capable to some degree,
> but sheesh - why?! Are the required parts simply not available in
> legacy form-factors or something?
> 
> Normally I'd be all over this, but the SMD requirement just takes
> all the wind from my sails. So what's the deal? For the record, I
> built one of his earlier designs (RS-232 -to- 120V / 60mA) on
> perfboard with some parts chassis mounted, and that all went just
> fine.

     I tried some through-hole designs. You can see them all in the
earlier revs on Github.  I built a switching power supply
using a 555 timer, and it worked.  It could charge a 1uf cap to
120V in one bit time.  But then I discovered that Model 14/15
selector magnets have more inductance than previously thought,
and 1uf isn't enough.  It couldn't get a 2uf cap up to 120V in
one bit time (22ms), given the available 5V power from a USB
port. Ran out of power budget.

     If you want to run from a wall wart, I'd suggest getting 5 of those
little 24 VDC DC-DC converters I mentioned previously and putting them
in series. They're about 4mm x 12mm and $5 or so each.
A board like that would be all through-hole, and would satisfy
the wants of some of the people here.  Just take my previous
design, which requires a 120VDC power supply, stick on 5
DC-DC converters, use the same USB to serial daughter board
as the new model, and you'd have something about the same size
as my new board. You'd just have to plug in a 5V wall wart that
could deliver about 10-12 watts.  You could build that on perf
board and it would work; there's no high-frequency stuff.

     To run from a USB port, I needed to get the efficiency up.
That meant building a  reasonably efficient switcher, which
requires a good control IC. Such ICs don't come in through
hole. I had to learn how to do SMD, and it's a huge pain
at first. Then it ends up being easier than through-hole.

     Yes, SMD means tweezers under a microscope. I use a
$30 USB microscope for placing, and a binocular stereo
microscope for inspection and removing solder bridges.
As Steve Garrison pointed out, soldering the LT3750 is
difficult. I'd like to have a directly soldered on
CP2102N USB to serial converter, but that's even worse, 0.4mm
pad spacing, and it's QFN, with the pads under the IC,
so you can't fix solder bridges.

     I did this partly to get up to speed on modern electronics.
I'm in Silicon Valley, and I should know this stuff.

			John Nagle