Tagpcb

Nanino Upgrade

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4 months ago, I read about Johan’s Nanino on Hack-A-Day, and thought it would be a great way to teach some folks how to etch their own circuit boards.  Although I’m increasingly shipping PCBs off to China, being able to etch your own boards is a valuable skill to have.  I’ve taught workshops on it in the past, and I’ve described the process on this blog.  Today, I set out to make a copy of Johan’s Nanino, but was almost immediately frustrated by the inability to manipulate and print the board file in a way that worked well for my process.  In the end, I redrew the thing using DipTrace.

Nanino ImprovedThe only change made to the original is the addition of a .1 uF capacitor on the DTR line of the FTDI header.  Some of the traces are a little closer together, but they’re still spaced out enough that etching this board is a cinch.

Here are the files:

Diptrace Schematic for Nanino

Diptrace PCB for Nanino

PDF of Nanino from the Back

You can use this PDF to etch directly.  No mirroring is needed.

Can be printed.  1200 DPI.
Can be printed. 1200 DPI.
Can be printed. 1200 DPI.  No mirror needed for etching.
Can be printed. 1200 DPI. No mirror needed for etching.

DXF of Nanino

And, because the original Nanino is licensed CC-BY-NC-SA, this one is also:
Creative Commons License
This work is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 Unported License.

 

It works!
It works!
Good toner transfer
Good toner transfer
The etch was drama-free
The etch was drama-free

Creating SVG files for solder paste stencil stencils from KiCad

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Eventually, hand soldering surface mount components becomes a pain, especially if you’re doing small manufacturing runs. It’s much easier to work with solder paste and a hotplate.  Joints are higher quality, and you can manufacture more boards at once.  If it was good enough to get Sparkfun started, it’s certainly good enough for us! Working with solder paste does require a stencil, though.  The stencil contains precisely sized holes which allow solder paste to be precision applied to the metal pads on your PCB.  There are many companies which will provide cheap and high quality stencils, but if you have access to a laser cutter, there’s no reason you can’t do this yourself.

There are a lot of guides out there for creating SVG stencils from Eagle, so I’ll be covering KiCad in this tutorial.  Additionally, the laser cutter I have access to at the LVL1 Hackerspace is a Full Spectrum laser which can cut directly from Inkscape, so I’ll be basing this tutorial on Inkscape.

Step 1

Generate gerbers from your completely routed KiCad PCB project.  There are a lot of good guides out there for getting to this point in KiCad.

http://reprap.org/wiki/KiCad

http://code.google.com/p/opendous/wiki/KiCADTutorialCreatingGerberFiles

and a collection of resources here: https://meatandnetworking.com/w/Kicad_Resources

Step 2

Open your PCB in a program like Gerbv.  Any gerber viewer capable of outputting to SVG is alright for this, but I like gerbv the best.  You’ll want to open the solder paste layer, which KiCad names by default to something like “pcbFileName-SoldP_Front.gtp”.

Export to SVG, put the file anywhere you like. In Linux, you have to manually add the SVG file extension.

Step 3

Open the file in Inkscape.

Ungroup the objects by right-clicking on a pad or line and selecting “Ungroup.”

Open the “Fill and Stroke” menu.

Clear the “Fill”.

Turn on “Stroke” and set it to a color that your laser cutter likes.

Our full spectrum laser will try to cut the inside and the outside of the stroke if it’s too thick.  .1mm is thin enough that our laser cutter software will only cut the outside of the stroke.

Step 4

Before proceeding, you can delete the board outline, since it’s unnecessary.

Select all the objects, and open the “Transform” menu under “Object.”  Under the “Scale” tab, MAKE SURE that “Apply to each object seperately” is CHECKED.  This maintains the centroids of all your pads.  You’ll have to play around a little bit to get this value just right. Decreasing the size of the features is necessary due to the thickness of the stencil material.  The thicker the material, the more you’ll need to reduce the size of each feature.  For overhead transparency plastic, 90% is just about right.

Now you’ve got a finished stencil SVG, suitable for lasering.  In a future post, I’ll show off how to soldering using paste and a hotplate.

A Tiny Balloon Computer

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Another PCB design gets shipped off to China for manufacture!

This is a tiny balloon computer.  Without battery or GPS, it weighs less than 40 grams.  It can transmit RTTY or CW at 25 mW on the ham 2M and 70cm bands, and will last up to 16 hours on a single AA.

This board will be Arduino compatible, and the primary goal will be to support White Star‘s superpressure balloon experiments.  A superpressure balloon maintains some pressurization above ambient in order to maintain altitude.  In order to figure out how to design the balloon envelopes, and to verify our math, we need to know what’s going on inside the balloon.  It’s difficult to pierce the balloon without generating leaks. The ideal solution is to place a second balloon computer inside.  Both will transmit pressure to the ground, and we’ll be able to compare pressure inside the balloon to ambient pressure for model verification.  The pressure sensor can sense a change as small as 4×10-4 PSI, so this should work.

This is my first attempt at real RF design.  Fortunately, operating within the ham radio bands means I don’t have to worry too much about spurious transmissions or leaky harmonics.

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Toner Transfer and Muriatic Acid Etchant: Making PCBs at LVL1

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LVL1 is great.  A place for creative and motivated people to get together and goad each-other into doing more creative things.  It’s also a great gathering place for tools, as well as knowledge.  A few months ago, the spoiled electrical engineer that I am, I never would have considered making my own PCBs.  Any project worth taking off the breadboard was worth sending to China to get made “right.”

Of course, there isn’t always time and money to send something to China.  Today’s installment is the Sumo-bot board I’m trying to put together for the Hive13 sumobot competition.  Unfortunately, it doesn’t look like poor Snoopy bot will make it to the ring, but the board making process itself is worth talking about.

Laying out a PCB using software like Eagle is beyond the scope of this post.  If you can follow the appropriate Sparkfun Tutorial, it’s pretty easy to pick up.  Something to note:  for single sided home-made PCBs, put all traces and surface mount components on the BOTTOM layer.  Put any necessary jumpers on the top layer.  When you’re ready to print, just turn off all the layers you don’t want turned into copper.

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