Converting the LilyPad to a STRUIX CPU

Converting the Lilypad, from it's fashionista facade to a stackable, number crunching, parallel processing dynamo, is straightforward and just requires a little time.  A lot can be said for having the right tools too! 

Basically we are going to enlarge the existing sewtap pad holes to 3mm and reorient the programming header.  It's necessary to have a new programming header for a couple of reasons.  First the existing header interferes with the A5 pad (part of the TWI bus) when being drilled out.  Second, the new programming header makes it possible to stack other boards (like the XBEE or Protopad II or GPS) that make use of the serial port, on top of the CPU.  The larger holes, and lack of interference, will allow the stack to be built up to any arbitrary depth using M3 standoffs.
 

Here's how to do it:

Off the shelf
 Transformed
 
 

What you'll need:

 
1.
 
An off-the-shelf Lilypad Arduino 328 - of course! (v.18 or later please)
 
 
2.
 
1ea - STRUIX ProtoPad II - This will make alignment of the re-soldered programming header much easier.
 
 
 3.
 
6 x 0.1" right angle pin header - Samtec 1051-06-RA or equal.  This will become the new programming header.
 
- plus -
 
6 x 0.1" header socket - Samtec 1093-06 or equal.  This plugs into the pin header and the ProtoPad II for alignmet.

Project STRUIX stocks this item.
 
 
 4.
 
3mm high speed drill bit and a drill press.  THIS MUST BE A 3mm BIT and NOT "something close"!  Standard high speed bits will work well, but bradpoint bits will center easily into the existing Lilypad sewtap pads.
 
Although it's possible, you probably don't want to drill holes freehand.  Buy, borrow or beg to use a drill press.
 
 
 5.
 
6ea 12mm x M3 M/F standoff threaded fasteners and machine screws.  These may be plastic or metal.
 
They will act as a stand to stabilize the assembly while aligning the new header and make it easier to solder.
 
 
 6.
 
Soldering iron, solder & small (0.075" or finer) desoldering braid.
 
 
 7.
 
Flux remover spray - to clean up the connections after soldering.
 
 
 8.
 
A new (but dedicated) toothbrush & proxibrush.
 
The brushes are used to whisk away the residue left behind by the flux remover.
 
 
 9.
 
Electronic side cutter, SMD tweezers & needle nose pliers.
 
"Sharp" ended side cutters ARE NOT recommended as they can put undue strain on the original programming header pins and lift the pads off the board.
 
 
 10.
 
Plastic adhesive putty.
 
The putty is used to temporarily hold the new programming header in place while soldering.
 
Works like a champ!
 
     
 

Here's how to do it!  The conversion, step by step.

 Step

 Image(s)

 

The longest journey starts with the first step.


Start by unpacking the Lilypad.
 
 

Cut the cord - metaphorically speaking.


Remove the the serial/programming header by clipping as close as possible to the plastic pin carrier.  Make sure the "v" of the clipper is facing away from the plastic carrier. 
 
Clip the pins symmetrically -  outside pins first, then the next set inboard and so on.  Why? because the mechanical action of cutting the header can lift the SMD traces while they are still soldered to the board - and you will have a very difficult time repairing the lifted pad, if you can repair it at all.  Be careful. 
 
The original pin header is a throw away.  If you really care it's a Samtec ####
 

 *** HERE'S WHAT NOT TO DO! ***

A "sharp" side cutter was used along with a improper cutting sequence.  You can see the third pad from the left was lifted.

 
 
 
   
 

Get rid of the old SMD header pins.


Remove the serial/programming header pins from the board.  Rev up your soldering iron and get your tweezers ready.  Carefully flow a tiny bit of solder on each pin to help with reflow - if the pins are stubborn to get started - or - adjust the temperature of your soldering iron. Heat up each pin to reflow the connection and pick it off with the tweezers.
 
 
 
 
 
 

Desolder the header pads.

Clean up the serial/prog SMD pads, first by reflowing a little new solder on the pad, then wicking it off with the desoldering braid - revealing a set of bright and shiny pads.

Don't apply excessive pressure or leave the braid & iron in contact with the board for too long.  You can lift a pad.

 
 
 
 

De-Fluxify.


Spray down the board with flux remover and leave to dry.  Use the toothbrush and proxibrush to clean up the residue after the board is dry.
 
 
 

Drill out the bus pads.

Chuck up your 3mm bit and drill holes in all 22 of the the perimeter pads - using the existing thru holes as a pilot. Using a backing board to prevent tear-out on the back side of the Lillypad, while drilling, is recommended.

One of the pitfalls of converting the Lilypad to STRUIX CPU configuration, is that the drilling will cut the D0/Rx trace on the bottom side of the board.  If needed, it can be repaired by drilling  a small hole just off either tip of the Do/Rx pad and running a wire to connect the bottom trace to the top of the pad.  We'll skip the repair step for now as it can be done later.  Hopefully you won't miss this connection.

 
 
  
 

Trim the new header.


Next the new programming header needs to be cut to size.

Install the header strip on top of the pin header.

Then, using the side cutters, snip your right angle pin header down to size.

A good trick is to use the plastic carrier on the headers to guide the cutters.  This will make it easy to cut all the pins to the same length.


 
 
 
 
 

Make things a bit more stable.


Assemble the Lilypad and three pairs 12mm standoffs - on roughly equal spacing - to make a bit of a stand.  It will get the board off your work surface make it more stable for the rest of the work ahead.

Note:  Looking at the back side of the board, you can see the D0/Rx trace cut by the drilling operation.
 
 
 
 
 

Align the header.


Using the ProtoPad II will make it much easier to make repeatable header alignments - so other boards can plug on top of the CPU.

 Place the right angle pin header on the serial/prog pads - prongs facing outward toward the perimeter pads - and fix in place with a small blob of adhesive putty.
 
Use the header row on the ProtoPad II to line up the pin header assembly.  Adjust the header with tweezers until it lines up straight, then use the adhesive putty to temporarily hold it in place - Then remove the Protopad.

It will make things a lot more stable if you use a blob of putty on both sides of the pin header for better support.

 
 
 
 
 
 

Connect the header.


Use your soldering iron and attach the first leg of the pin header to the board.  When you have a good connection of the first leg, remove the adhesive putty and solder the rest of the legs.  Don't worry if there are imperfect or a bit of blobby solder on the legs, we'll take care of those next.

After soldering, don't forget to remove and save the socket header strip from the pin header.

 

 
 
 






Getting rid of solder blobs.


Using the solder braid, go over each of the connections and wick up any excess solder on each header connection.

Take your time and be careful not to remove too much solder.

You will be left with near perfect SMD style connections.


 

 Soldering iron and braid action to clean up connections

Final Clean Up.

Spray down the board with cleaner and leave to dry.  Use the toothbrush and proxibrush to clean up the residue after the board is dry.

 
 
 
 

And.... You're Done!


That's it!  Successful conversion of the Lilypad to a STRUIX CPU.

Plug it into the USB programmer and give it a try!

Now just repeat the process for a few more Lillypads and you are ready to build your STRUIX.

 
 

 
 
 
 
 






     
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