December 12th Meeting: Better than Blinky

blinkinglightsfromgoogleimagesPaul MacDougal will talk about alternatives to the classic Arduino beginning program and shares this summary:
“Blink is a great first example for Arduino programming, but a really bad example of embedded programming. With 99.9% of its time spent in delay(), nothing else can happen. This talk will show how to rewrite blink in several different ways to allow it to play nicely with other functions.”

Join Paul and others at NCSU for the regular meeting. More details on the “at NCSU” meeting page.

Notes about OSH Stencils

A few notes from listening to Brent of OSH Stencils: on The Amp Hour:

  • Planning to offer 1.6mm jigs to eliminate the error vis a visa common PCB thickness (hurray)
  • For those that didn’t know:
    • Offering high quality Kester solder paste (in checkout cart, as with the jigs)
    • Offering stainless steel as well as kapton (stainless steel are common 4mil thickness).
  • 5x5mil smallest feature size possible with kapton stencils. Minimum feature size for steel stencils is ONE MIL!
  • They see 70/30% split between 3mil and 5mil thickness of kapton. The 3mil is best for ordinary work, while the 5mil is appropriate for high power devices with large thermal pads, etc. where a lot of solder is needed. I can vouch for the fact that 5mil is a total disaster for fine pitch parts like a QFN package. Kapton in 4mil is unobtanium, which is why they don’t offer that thickness.
  • Name is OSH Stencils because Brent was originally going to collaborate with Laen of OSH Park, but a change in Laen’s circumstances caused them to remain separate entities and Laen was totally OK with the similarity of names.
  • Can reduce kapton stencil curl by “counter-rolling” the material and this will give temporary relief.
  • Started with hobby laser: That “exploded” the first week after starting business. Switched to Epilog 24 (roughly $30k)
  • Stainless steel stencils made with approx $300k LPKF fiber-based “flagship model” laser cutter
  • Have maintained 24 hour turn time from the beginning. They went with high end laser to be able to make *the best* stainless steel stencils. They are competitive by avoiding framed stencils and using a proprietary material loading system into the LPKF. Basic cost of framed stencil material is 5X the cost of raw. Could use “pneumatic frame” to simulate real frame, but that didn’t allow sheet sizes that were large enough to be cost effective.
  • Brent said their charter as they began making steel stencils was to offer the top quality at reasonable prices. He invited people to compare their metal stencils to Chinese stencils under a microscope as they consider potential “cost savings” by going off shore. (OSH Stencils is in the Salt Lake City area of Utah). The metal makeup is different. Most offshore vendors use “inexpensive stainless steel”. Looking at the apertures (the cutouts) you often see grooves to do with the kerf (diameter of laser beam). With low quality metals the edges of apertures have grooves making them look like washboards.  Also see minor warping and ripples in the Chinese metal.
  • Look for “exciting announcements” to do with the stencil process to be offered by OSH Stencils in coming months.
  • OSH Stencils makes stencils for customers that have nothing to do with electronics. Art projects, special “plates” for mechanical components, etc. They’re open to queries about whether your creative application can be handled by their equipment.

Latest Reflow Progress


Solar Power Management/Charger rev 2B, Trail Counter rev 9
Stainless Steel Stencil from OSH Stencils
Stainless Steel Stencil from OSH Stencils

Here are Chip McClelland’s latest Trail Counter and Solar Charger boards, together with a shot of the stainless steel stencil now offered by OSH Stencils. The metal stencil makes it hugely easier to get perfect pasting and confirms that the curve that comes with  polymide stencils has been at least one root cause of that type being so challenging to use.  There was no paste bleed through to the back of the stencil, and the fine pitched power controller and Simblee BLE chip lands were perfectly formed. To get a sense of the cost difference some existing board specs were plugged into the OSH Stencils web site: a roughly five square inch battery charger, a three square inch decade counter/divider, and sub-square inch 6-axis breakout board. The steel stencils would be almost exactly double the cost of polymide, averaging about $12 each. By the way,  multiple PCB designs can be grouped within one stencil. This can greatly reduce the cost difference depending on the areas involved.

These are OSH Park boards: very deep blue/purple, sitting on a sky blue antistatic mat. This is a tradeoff with the very bright, high color temperature LED flood lights used to illuminate the bench.

New in the Meeting Archive

Traffic Intersection Lights

Traffic Intersection Lights

August’s meeting included a project retrospective and demo of Brian Grawburg’s Raspberry Pi/Python driven traffic light simulation. This is part of a set of teaching tools Brian has developed for teaching Python to area youths at the Imagination Station in Wilson, NC Brian’s project is described in his article in the December, 2014 MagPi magazine (page 4) as well as on his project page.

For a handy set of links to this and other TriEmbed presentations visit the meeting archive page.