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

Wed Mar 7 11:32:52 EST 2018

Gil,
 I can tell you the way production people do it.  Once tacked in place, flow some liquid flux on the opposite pins.  Then drag your soldering tip (with solder on it) across the pins.  All pins will solder without shorts.  Try it.  
GerryAD6MC

      From: Gil Smith <gil at baudot.net>
 To: nagle at animats.com; greenkeys at mailman.qth.net; aaa-greenkeys <greenkeys at mailman.qth.net> 
 Sent: Tuesday, March 6, 2018 7:05 PM
 Subject: Re: [GreenKeys] Who's still looking at getting John Nagle's, > USB<->CL Board made ?

Yeah, SMT soldering seems scary at first, but it really is not too bad once you give it a try.  
I routinely solder chips in a QFP pack with 0.5mm lead pitch.  The steps are simple:    - put on two pairs of reading glasses (I find a microscope of any sort difficult to use).  - clean the soldering iron tip and get a little solder blob on the end.  - visually line the chip up with the pads and hold it with your fingers in place.  - dab some solder on one or more pins on one corner to tack it.  - rotate the board 180 degrees, line up the chip and hold it, then dab solder on the opposite corner to tack.  - use a 10x loupe to verify that the pins are lining up with the pads, and adjust as needed.  - then, solder each side of the chip in one giant blob (all pins on the side).  Get good joints;  ignore the shorts.  - use a good solder wick to remove the big blob on each side of the chip.      (eg: go to mouser.com and look up 1821-10F; avoid no-brand crappy wick with no flux)  - look with the loupe to ensure shorts are gone;  adjust as needed.  - touch the iron tip briefly to each pin for a final reflow to the pad (then check with loupe)
Passive parts such as 0603 and 0402 are also easy.  0.4mm-pitch chips and connectors are a bit more tricky.
Parts that do not have external pins cannot be soldered with an iron.  For these you need to get a solder stencil (eg: from pcbway for $10 when you get the boards), some solder paste (eg: from stencilsunlimited.com), and a $20 hot-plate or griddle (eg: walmart).
gil

gil smith, AF7EZ
greenkeys moderator
gil at baudot.net

  -------- Original Message --------
 Subject: Re: [GreenKeys] Who's still looking at getting John Nagle's, >
 USB<->CL Board made ?
 From: John Nagle <nagle at animats.com>
 Date: Mon, March 05, 2018 11:52 pm
 To: greenkeys at mailman.qth.net

 > 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
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