Showing posts with label Electronics. Show all posts
Showing posts with label Electronics. Show all posts

Thursday, April 23, 2020

Taming an AnyCubic Kossell Pulley 3D Printer

Quick post to note how I got my Anycubic Kossel Pulley basically working.  It took me forever to find how to do some of this, and I know I will forget it if I do not write it down.

  • Use DaHai's configuration video for starters.
    • Upgrade the firmware to Marlin 1.1.9.  I ended up using as of this writing.
    • Use DaHai's files and modify them to work with stock Steppers.  Use Arduino IDE to load the firware after replacing Configuration.h and Configuration_adv.h (which I did not make changes to).  Here are the changes I made to his Configuration.h:
      • Line 624-626: Change these from his upgraded TMC2130_STANDALONE to stock A4988
      • Line 705: I got crazy loud stuttering when first descending to the bed during a print.  Lower this to get rid of that.
      • Line 868: I and several people online have measured and gotten good resulting prints with the Type 2 Probe Offset at -15.88
      • Line 938 to 940: These need to be true for stock steppers.  DaHai's steppers did not need to be inverted.
      • Line 1358-1364: Define your temperature presets. I have used PETG to great success with a preheat of 70C for the bed and 230C for the hotend.  This rises to print at 80C and 245C respectively during the print.
    • When following the leveling instructions, the video shows a "Set Delta Height" option that is absent in the version of the firmware I loaded.  This caused me no end of headaches later when the method of subtracting the bed distance from both the Z-Height and Probe Offset produced weird math and never worked properly.  Instead, I ran auto-calibration, saved the settings, then:
      • Noted my Z after going to Prepare -> Auto Home
      • Brought the nozzle to the bed using Prepare -> Move Axis -> Move Z until a business card wouldn't move when squished between the axis and the bed.  I then noted the height
      • Changed my Z height only by this amount by subtracting the number from the Z height, and a negative Z Height is thus added.
      • Saved and Auto Homed
      • Set my Probe Offset to 15.88 per recommendations online.
      • Checked it again and only touched the Z Height when it was off.  Repeat the Z height move if this is still not right.
  • With the printer calibrated, it was time to print.  I just used Cura because I couldn not get Slic3r or Pronterface to work easily.  Cura does not have the Kossel in it by default, but it can be easily added.  JDHarris on Thingiverse even shared the configuration file they made which can be picked up by Cura after a restart.
  • I printed with PETG which has a high temp but no fumes.  I found hairspray for adhesion worked best thanks to several awesome tips by people connected with the PDX hacker community.  Thanks all!
After this, it just worked and keeps working.  It's magical what a little math and open source firmware will do.  That being said, it's my first printer.  It is bound to break in ways I can't even imagine now.  First order of business?  Print things that make the printer better, as is tradition.

Update: Not all is well in Whoville.  I've developed some Heat Creep with this PETG printing at 245C, and I haven't had the time to troubleshoot it.  Wish me luck!

Sunday, March 24, 2019

The Aviary: Huckleberry

The Aviary, Pg 404

One of the cocktails hailing from The Office, a speakeasy basement bar underneath The Aviary, this seemed simple to assemble with only one bit of complicated machinery: a sous vide.  Also, the presentation alone was intoxicating: a frothy head atop a mauve concoction? Sign me up!

I was able to obtain a chinois at a Goodwill.  The strainer and pestle separates juice from pulp and seeds.  However, the main ingredient is a clove tincture (fancy word for Everclear infused with clove). This required a sous vide as written.  As long as I've heard about them, I have never pulled the trigger on this low temperature wonder-machine (I don't have an instant pot either).  I figured it was time to lay that to rest.

There are plenty of DIY sous vide videos on the internet.  I settled on one that recommended a rice cooker combined with an industrial 110V AC temperature controller instead of a brewer's setup.  The most important part of this setup is the type of heated pot you use.  I couldn't use my crock pot, for example, because it had a digital control.  Every time the power cut off and then back on, it would not return to heating the pot.  My manual-switch rice cooker worked like a charm, however.  Then, for $20 in parts from the hardware store and $20 for the temperature controller on Amazon, I had a safe contraption through which to control my rice cooker and keep a pot of water within 2 degrees of a specific temperature for any length of time (perhaps "safe" is relative; use wire nuts and an electrical box when playing with mains, kids; the picture below shows iteration one with no cover).

The clove tincture was dead simple but extremely smelly.  $1 in bulk cloves and some Everclear got me a half dropper full of the cloviest drops the ever passed your nose. A word of warning: toasting the cloves is a horrendously smokey business.  Do this with a hood on full blast or outside.  We had to open all the windows and run for coffee.  I already had a vacuum sealer so I dumped the toasted cloves into a bag, poured on the alcohol, and dunked it into the rice cooker for an hour.  I decanted the result into an amber bottle with dropper and savored the aroma (which wasn't hard; it was everywhere).

The rest of the recipe was fairly simple.  Huckleberries don't come into season until August, so we went with blackberries from Mexico.  The syrup came together easy with a few gradually finer strainings.  6oz made 166g of juice.  Amaro Averna from Total Wine, Bombay Gin on sale, and Angostura bitters I already had on hand completed the boozy bits.  A quick trip through a shaker came out with a pink foamy pour that gradually separated into mauve and foam.  The bitters and pepper hit our nose, and the herbal hit of the drink completes it.  It's just sweet enough with off-season blackberries to be pleasant without being overpowering.  As we drank, we noticed the colors change and aromas deepen.  Very fun and dynamic drink.

A second round (can't waste syrup, after all) made with vodka toned down the herbal nature.  This will probably be the version I make for myself unless the guests are already gin drinkers.  Too close to 'too much' pine.  A friend suggested ditching the clove and replacing it by painting the glass with Chartreuse.  Either way, this seems to be a reliable cocktail to just have on hand.  Freezing berry syrup during their season in 2oz portions and the huge amount of clove tincture I have left over means it will be quick to assemble with a fun story to tell while we shake it up.

Wednesday, July 25, 2018

Wristband Teardown from Amazon's #FireTVSDCC Event at San Diego Comic Con

A friend returned from San Diego Comic Con 2018 with an RFID bracelet used to track users in the Amazon Fire TV experience (on Twitter, #FireTVSDCC).  This is a teardown of the bracelet after the event.  At this time, I was unable to read from the bracelet.

The bracelet is fairly simple with a cloth band and plastic/paper tab threaded through.  The closure is plastic and one-way.  It bites into and mangles the cloth band if you attempt to remove, but you could probably shim it with tools and practice.  Might be a fun thing for the Tamper Evident Village if it turned out events were trying to use this for access control like plastic self-destructing wristbands.

The back contains a serial number.  I would like to see if this serial number would match the data read off the tag.

Separating the badge by prying them apart, I  spot the prize: an adhesive RFID tag placed between the glossy plastic covers.  It appears to have a model number of "CXJ-040" in the center of the tag.  It uses a circular antenna.  CXJ is the initials of Shenzen manufacturer ChuangxinjiaTheir product pages show many similar wristbands in a few different frequencies.

The tag didn't respond to my Android phone, so it is not a Mifare or similar.  Hopefully I can find a reader at the local Hackerspace or DEF CON 26.

Saturday, June 2, 2018

Fixing Ford AC Head Controller Vacuum Problem

The AC on my land yacht (2009 Mercury Grand Marquis) has been in the fritz for a while. Last winter, it gradually stopped switching from max AC/recirculate (a necessary in Vegas), then got stuck on norm AC until it rested on Defrost/Floor. I was able to fix it with some basic troubleshooting, YouTube sleuthing, and two bucks in o-rings.

This shaky yet informative video by Ian Smith helped me diagnose it as a problem with vacuum only. The AC itself was fine. It blows cool air all day long. It just did so at the windshield. It couldn't be the blend-door actuator.

The same video showed me how to diagnose the vacuum problems. The black hose providing vacuum from the engine seemed fine: I was getting 20 inches of vacuum with the car turned on when I hooked up a bleed pump with a gauge (mine came from Harbor Freight, shown in the video). To test the actuators, all I had to do was hook a 'jumper' pipe from black to the other pipes. Each one seemed to hold air, and the actuators sprang to life once again. For the first time in a year, I had cold air blowing from the vents. The problem couldn't be in the lines. I pulled the controller head for a closer look.

The head itself is a bunch of electronics, a control panel, and one removable plate with four solenoids. The vacuum hoses come into this through a manifold, and the head controls trigger the solenoids to route vacuum from the black hose to the others. This triggers different actuators under the dash. Something was amiss in the manifold.

I returned to YouTube looking for rebuild instructions. I found this extremely helpful video from a Chicago mechanic. The solenoids contain an o-ring that dries out, wears out, and loses the ability to hold vacuum. I obtained close to the recommended o-rings from Lowes (#36, 5/16 OD, 3/16 ID, 1/16 thickness) as I was not willing to wait for Amazon. A little Oatey silicone lubricant made the tight squeeze work a little better. I found I had to seat the solenoid heads at least once before total reassembly. It was too difficult to do so at the end and fight with the other small parts at the same time. 45 minutes later, I had full control of my AC restored.

I can't believe it was this simple to fix the controller. I think I was intimidated by the AC (having spent $1500 last year to have the dealer redo the whole system from seals to refrigerant). I didn't want to break anything. A few targeted troubleshooting steps helped assuage any fears of irreparable harm, and now I have a comfortable cabin once again.

Thursday, April 5, 2018

The Glowhawk: OFBC Gaiden

Update: Plume added, rebuilt using thread and pipe cleaners to keep it upright and separate strands, removed plasticard sticks and zip ties.  Also pulled the EL Wire which is being repurposed in my son's EL Hoodie.

We were only able to print a few OFBC 2.0 cases before DEFCON 26. The leftover parts would have sat in my toolbox for quite a while if not for a serendipitous mistake: I ordered the wrong color LEDs from Sparkfun. This plus a little construction advice from a seamstress helped me cobble together the glowing headgear that is The Glowhawk

My courage and thinning hair prevents me from getting a mohawk while at DEFCON, but I've always wanted one. Instead I started to create one with a networking theme. Pipe cleaners in the color of Cat6 twisted pair served as a thick mane anyone could be proud of. This was wired onto a hat as a test. It looked OK, but it was kind of stubby to wear all on its own.

The LED driver for the OFBC is overdone. A single charge can last 10 hours on the original model. I wondered how much it could handle in terms of output, and a little breadboarding showed me I could wire several of the LED modules together as long as they were in parallel. Now how to use them?

The LEDs are these 3W green modules with attached heat sink. Direct eye contact is not recommended (hence the pains we took to use momentary buttons on the OFBC). On the beer light, we diffused the over-bright light so it could be sculpted by the drink it passed through. I was inspired by a fiber optic dress I saw elsewhere and found fiber optic table centrepieces for dirt cheap on Amazon. Some hot glue joined the disassembled fiber optics to the bright LED. The mane of glowing green was born!

With this fresh take in hand, DEFCON was upon us. I packed my things and thought I might take a crack in the evening. The Richard Cheese show was the perfect venue to solder everything together. The_bozo and I found a better place to work where the hot glue gun could run safely. I transferred the existing Cat6 mohawk to a bright green John Cena hat from Goodwill. Inside the channel that ran between upturned pipe cleaners, I hot glued the modules and fiber optics. Zip ties kept the fiber bundles from flopping around too much.

I consider the Glowhawk a great success, if a tad impractical. It lasted about 2 hours on a charge, and I was able to walk around wearing it with the mobile party crew for that long before it got uncomfortable.  A photo of me wearing it hit the DEFCON Closing Ceremonies, and my son keeps trying to steal my remaining fiber optics for a lamp in his room.

Future improvements include better internal support, googly eyes to cover the logos, and a fifth plume to fill out the front. See you next year!

Tuesday, April 3, 2018

OFBC 2.0

For Toxic BBQ 13 (DEFCON 25), we returned to the OFBC to see if we could improve the design and add some needed table decorations.

The first step was to simplify the PCB creation. I created a new layout in Fritzing that reduced whitespace. It also moved off-board components like batteries and the LED modules to use JST connectors for easy installation and swapping.  OSH Park did a great job with the PCBs. I was able to directly convert the Fritzing designs to printable format. Each board was less than 2 bucks by the time we finished. Never again will I make my own PCBs by hand. 

Sparkfun supplied most of the same components for about 15 bucks per light. Here is an updated BoM for this case:

Next, we redesigned the case. Instead of a three piece design requiring glue to assemble, the two pieces would be a base and a lid with a logo. Everything could be screwed into designed posts and covered with the lid. It was a snap. Production was easier with Shapeways. However, this lead to had longer lead times that prevented us from delivering to the barbecue. The prototyping went well and matched the designs, but the mass printings were so delayed that they didn't arrive in time for the barbecue even with expedited shipping. The resin product looked much better than the filament-printed 1.0 model. The cost at 20 bucks or so each was not prohibitive, but it certainly wasn't mass-market ready.

Design Pics

Updated Lid Design for Toxic BBQ 2018

Monday, August 18, 2014

RadioShack LED Strip Driver

I modified the Pololu RGB LED Strip drivers from version 1.2.0 to support Radio Shack's behind the times model that is 30 LEDs controlled in 3-diode sections.  I had to swap the colors around to match this pinout, and I changed the struct to a class (because why not).

The fix was to physically reorder the declaration of red/gree/blue variables in the struct declaration.  This way, when the information is written to the strip, it is sent in a different (and now correct) order.  You can make the fix yourself by changing the file PololuLedStrip.h:
typedef struct rgb_color  {    
   unsigned char red, green, blue;  
} rgb_color;
typedef struct rgb_color  {    
   unsigned char green, blue, red;  
} rgb_color;

And here it is on GitHub:

I should probably talk to Pololu on licensing concerns here.  I found the license from the original driver and copied it into my repo.  I couldn't figure out how to fork this properly, so I just re-uploaded it until I understand git a bit better.

Friday, August 15, 2014

C3BO: Proof of Concept using Timbermanbot Schematic

This post is part of a series about building electro-mechnical PIN-cracking robots, R2B2 and C3BO.

This is a proof of concept for @JustinEngler's C3BO ( using transistor controlled relays. It was prototyped by modifying Blink from the Arduino sample project.

The schematic was obtained from Timbermanbot ( as seen on Hackaday (

In the video, You'll notice I've replaced the touchpad for your finger with a wire to the headphone jack's ground as the circuit ground. The two pieces of copper tape were no longer sticky enough to stay by themselves, so I am holding them down. They press two and 5 with about 8 key presses per second.

Monday, August 4, 2014

OFBC: Putting it All Together

Note: This is part of the Project Write-up for OFBC: One Fluorescent Beer Coaster

After months of effort, we had a circuit, PCB and shell design to accomplish our goal.  Putting it all together meant solving some unique challenges in the home stretch.  By far the most communal part of the project was finishing the circuit.  Parts were bought by three different people.  It took hours of trial runs and four different nights in my shop to finally get the circuit assembled and ready.  In all, the project taught us to keep moving in spite of obstacles.


The main obstacle was PCB manufacture.  As detailed in that post, uncooperative copper and etchant lead to abominations not fit for solder.  Drill bits broke in PCBs, holes were misaligned, and traces were torn up as we worked and reworked the boards.  The major blunder was the reversed PCBs, but it was tempered by the lack of polar components.  Only the transistor and MOSFET needed to be adjusted when we realized our mistakes.  The quality checks and encouragement as we worked as a definite plus.  There were several times I wanted to just give up and abandon the project.  Truly, I get by with a little help fro my friends.

After the PCBs were in our hands, the task of soldering all the components was a team effort.  One person ran continuity tests on newly etched boards.  Another bridged scratches and pasted down traces.  Buttons (functional and fake) were inserted and crimped at one station while a fourth person began to solder on components.

That moment of truth when the LED lit up was breathtaking all nine times it happened.  When it, more often than not, didn't work on the first try, the scramble to troubleshoot was a team effort as well.  A loose connection, bad trace or through hole in need of a reflow was rooted out in minutes. I can't describe the feelings from closing the box with nine functional copies of the idea sketched out on a picnic table the year before.


Shell manufacture forced choices between what we wanted versus what we needed.  The mechanical ideas at the outset gave way to manufacturing considerations.  Features were pared back to match timelines, work schedules and summer vacation.  Anyone reading this who has worked in an Agile Development environment will recognize similar decisions they make every Sprint.  To borrow a cliché, "Perfect is the enemy of good enough."  With this in mind, we have an eleventh hour compromise ready: should the 3D printer prove a roadblock, we have arranged for a Wednesday night Hail Mary meeting to turn Ziploc Containers into eternal glory.

The Ziploc idea produced 4 "just in case" models.  We stabilized them with glass beads and hot glue.  The containers became the shell and mount for the PCB.  The beverage lid was provided by another ziploc container hot-glued onto the buttons.  Hot glue for grip and stabilization of the platform finished the job.  See the result in the pic below next to the finished shells.

Luckily, the 3D Printer roadblock was cleared just two days before the BBQ.  Poor quality filament lead to clogged extruders.  After a good cleaning, we were back in business.  5 shells total were produced with various upgrades.  We got a top that nested well with the shell, and the mouse-hole in the shell was added to allow the USB to be passed out of the body.  We did not get impressions in the top to get the lid closer to the lens of the LED.  We also did not get any part of the body held together by magnets.

Final assembly took place at Toxic BBQ itself.  The lights stayed on this year, but we started conversations and passed out some business cards with links here.  We placed a few on the tables farther out that didn't have light, and we presented two to the organizer in a Utilikilt.  Furthermore, it went on display in r00tz and the HHV for most of the convention.

Final Word

I left DEF CON for two years running with a profound sense of my own shortcomings.  I saw people around me doing amazing things, but I couldn't point to similar achievements for myself.  Though not terribly complex (most ideas came from Instructables, after all), the process and coordination required to pull off this simple idea has been eye opening.  It all started by pivoting from planning to doing.  It finished with an 80's-montage-worthy string of late nights and high fives.

Already, these efforts are fertile ground from which numerous other ideas have sprung.  Facing another DEF CON, I'm looking for the next big project instead of lamenting my noob credentials.  Only time will tell how many of these work their way to reality.

Sunday, August 3, 2014

OFBC: Shell Fabrication

Note: This is part of the Project Write-up for OFBC: One Fluorescent Beer Coaster


In parallel with the circuit, we designed an enclosure that would be more sturdy than hot glue and disposable containers.  The general idea was a shell with a lid that had some travel.  Our first designs focused on a mechanical clip to lock the lid in place.  Further ideas were a rail to keep drinks stead, a drain channel for condensation, and an interlocking base/top for easy stacking.  Our lack of expertise with the 3D design software and the complexity of the print made us go back to basics.

Similar products used a coaster shape, so we started there. As the whole point of this project is to show off, we wanted to make it easy to disassemble top and bottom. To make this happen, we settled on magnets instead of screws for both top and bottom.

First Full-size Print (with Frenchman Mountain in the Background)


First, the 3D Printer needed to be calibrated, then the extruder needed to be cleaned, then the Kapton tape needed to be replaced.  After a much better test print, we got our first dimensional fit.  Once the PCB was together, we realized two things: 1) the buttons we bought had a much heavier mechanical action than the test buttons and 2) the LED package was too tall for the way we printed the top.  Combine the two, and a lot less light was reaching our girly drinks.  Something had to be done.  The above problems were noted, and various other edits were written directly on the 3D printed shell (a sharpie on white ABS works wonders for clarity).  They were handed off to our man with the printer while the rest of the team worked on PCB fabrication.

Between orders of Kapton Tape - Let's try Painter's Tape!

It was about 10% too small.  Looks like a job for Superm*n!

Not nearly as bright as it should be


The final prototype came together the weekend before DEF CON.  Edits to allow the charging cable to escape from the bottom of the case, a drip cover to prevent condensation from entering the shell, more accurately nested tops and bottoms, and a host of other small changes came together for the final prints. In all, the first run is bulkier than we imagined, but we have discussed ways to miniaturize and reduce costs across the board.  It will be something we are proud of showing off.

The 3D printer was the final obstacle.  From miscalibration to a clogged extruder head to a stepper motor burning out, we had our fair share of problems getting the final package in a physical format.  If the repairs don't come through, we'll be manufacturing stand-ins for the Toxic BBQ.  Nothing can stop us at this point. 

The current Sketchup files will be available on the OFBC project on Github.

Great Size, Less Filling

Tuesday, July 29, 2014

OFBC: Random Design Shots

Note: This is part of the Project Write-up for OFBC: One Fluorescent Beer Coaster

Puzzling Out the Protoboard

Can you Smell the Confusion?

Shell Designs

Initial clip-together design with rails for stable drinks

Circuit, post and spring and modified clip-together designs

Hockey Puck design emerges, Boolean shape building discussions

First practical attempt at dimensional design

OFBC: PCB Fabrication

Note: This is part of the Project Write-up for OFBC: One Fluorescent Beer Coaster

From Protoboard to PCB

The next step along the path was to turn a gawky mess of a protoboard into an elegant example of good design.  This step took a lot less time than I thought it would thanks to Fritzing.  Billed as "Electronics Made Easy", I installed and got up to speed in under an hour.  Conversations with my compatriots helped me tweak and massage the design to our satisfaction.  The end result is a 2" (58mm) PCB for through-hole components.  This will secure the buttons, driver and LED while connecting to the battery.  The experienced among you are probably thinking how absurdly large that it.  It could be a lot smaller, but I consider it acceptable for a first run.  As with other projects, the latest version of the fritzing file will be available on github.

First Run

If I had to pick one part of this project that made me more uncomfortable than any other, it would be the PCB fabrication steps.  I took chemistry in High School and College.  I know the basics.  However, I don't know enough to do it confidently.  I took my queues from MAKE's excellent video tutorial, acquired chemicals at Frys, harvested glass from a recently disabled printer/scanner, and printed transparencies at FedEx Kinkos.  My exposure light was a 26W CFL in a desk lamp.  My red light was a red LED straddling a button cell.

Sneak peek at the Shell prototype

I removed the board from the developer too early or exposed it to too much light. This caused a large region of copper to not develop. There is no way to align and cut a ton of these after the fact. The PDFs exported from Fritzing come out one per page. This means they need to be done one at a time unless you have the skill to post-process the PDF into multiples per page. I pre-cut the PCB's during subsequent runs. My table saw made short work of the big board, and the pre-sensitized copper has a sticker over it that allowed me to cut the board to pieces without compromising its ability to accept an image.


Once the etching was complete, I drilled out the traces.  The prototype board was drilled using a 1/16" bit.  This was way too big.  Out of all the bits I tried, normall through-hole components worked great with a 1/32".  A 1/16" bit was required for the MOSFET, however.  The best set I found was one for the Dremel.

Modern Silk Screening ain't got nuthin' on Sharpies

The only part of the process that ended up being perilous was the disposal of the ferric chloride.  The leftovers are back in the bottle.  I'll take them to the waste disposal place soon.  My driveway has a nice big rust spot on it from where I washed off the etchant.  How am I going to explain that to the HOA?  Ultimately, the problems with Ferric Chloride lead me to a different etchant entirely: Cupric Chloride.  See below.

Production Run 1

With the test run experience in hand, we were set to make an attempt at our first full run.  I chopped the boards on a table saw first.  This was a stunning success.  I also redesigned the PCB to include a slide switch to kill the circuit.  This allows long-term storage as a shifting bag or box won't depress the pressure switches and drain the battery.  You might see on the random design shots how we were planning on mounting the LED to the lid.  This changed before the final production PCB run, and we moved all traces outward to make room in the center of the PCB for the LED module on heatsink.  I also added a copper pad in the center to maximize heat transfer.  Some thermal paste will seal the deal.

The exposure took place in the half bathroom.  With access to water and no exterior windows, it was perfectly suited to etching.  Our supplies were:

  1. Tape, transparencies and pane of glass.  The circuit image is taped to the glass in a double-thick layer.
  2. Positive Developer mixed 10 to 1 in a glass pyrex.  When in doubt, use pyrex to ensure things won't melt through the container.
  3. Desk lamp with a sifficiently bright CFL bulb.
And our steps were:

  1. In darkness, peel off protective layer from light-sensitive copper clad board.
  2. Position the board over the top of your image and tape down.
  3. Flip the glass pane over and double-check the board is positioned correctly.
  4. Expose for 8 minutes using the lamp.
  5. In darkness, remove the board from the glass, and place it in the positive developer.
  6. Swirl the PCB in the solution until the image appears.  If your developer is sufficiently diluted, longer development times will be experienced.  It is better to over-develop and start to lose the image than it is to under-develop and end up with no traces at all.
  7. Wash off the board when it is sufficiently developed,

Final Exposure Workstation (The Guest Bathroom)

After exposure, good boards were placed into the etchant.  The Ferric Chloride was a great big mess.  It was hard to see how the process was coming without fully removing the board.  In addition, it needs to be heated to be truly effective.  Las Vegas has an ambient temperature of 100F/ 38C, and it still took 30 minutes per board.  You can see the etched boards below.  Before soldering, the etch-resist is removed via acetone.

Finished Product on the Plate

Great Success!

Production Run 2

With DEF CON a week away, we didn't have enough boards to complete our goal yet of nine complete lights.  We met for what we thought was our last etching party.  Much like the previous time, we decided to expose and etch using Ferric Chloride.  These boards looked great.  It was obvious we were starting to figure out how to do this effectively.  Unfortunately, we also forgot to check the boards as they were produced.  All 3 good boards were mirror images of what they should have been.  DEF CON loomed large, and we went with the more radical solution: switch etchants and try again.

The new etchant relied on Cuperic Chloride.  Once again, I turned to Instructables for a helpful tutorial.  The key ingredients were muriatic acid and hydrogen peroxide.  As the link shows, the acid and hydrogen peroxide oxidize the copper to form CuCl.  This in turn oxidizes to form 2CuCl by stealing copper from the PCB.  What's better, it needs an acid refresh much less often, and it is completely reusable.  A bubbler or aggressive mixing causes oxygen to oxidize with the 2CuCl and start the cycle again.  We obtained new PCBs (see my rant about Fry's below) and went to town.  We ended up with the 9 boards we needed; we began assembly in earnest.

Lessons Learned

The first board we did had the light placed too close (1-2 inches).  Also, the positive developer was extremely strong.  This caused all of the etch-resistant coating to wash away.  A little more water and moving the light 6-8 inches solved that problem.  When we were doing it right, we waited for the image to appear and then become crisp.  It is extremely difficult to tell in the dark if the image is still cloudy or not.  When in doubt, dilute your developer and leave the boards in there longer.

As with my woodworking posts, the matra is, "Measure Twice, Cut Once."  After every critical step, we had one person check another's work.  This saved us time and again from poorly aligned boards, undrilled holes and bad decisions at the bench.  It didn't save us from all screw-ups (a full crop of mirrored boards), but it saved us other embarrassments.  It also exposed every team member to each point in the process.  In total, five people participated in the manufacture of these boards.  Most have projects lined up that take advantage of things learned along the way.

The boards themselves were a problem, and they highlighted a weakness in the supply chain.  All copper obtained from Fry's failed at least a third of the time.  Online, the consensus was that the boards were old or improperly handled.  The positive developer was much stronger due to being partially evaporated.  The buttons we obtained were stiff and of differing quality that those used in prototypes.  All in all, I would recommend avoiding Fry's if you can help it.  They might have enough materials to get you going, but Amazon or similar suppliers can get you what you need fast enough that it makes no difference.

Monday, July 21, 2014

OFBC: Design and First Prototype

Note: This is part of the Project Write-up for OFBC: One Fluorescent Beer Coaster

Circuit Design

I began the search for parts to fit the Instructable, and I realized I had a lot to learn about each part.  To match the circuit, we searched Frys, Radio Shack, ebay, Mouser and many others online. For an unproven design, going with an unknown module and supplier wasn't an option. Instead, we found all the components we needed on Adafruit.

  • Lithium Ion batteries must be matched to their charger to avoid dangerous heat and combustion incidents.  Capacity is determined by the Amp-hours rating.  The LEDs I was targeting were a max of 350mAh, so I looked for batteries had to be over 1000mAh to get the targeted 3 hour run time.
  • The charger choice was mostly driven by battery choice.  We didn't feel like we could provide a mounted Micro-B port in the time available, but a charging circuit mounted to a full sized USB plug was a good substitute.  With the shell, we would provide an easily removable bottom and 'mouse hole' to allow the charger to live outside the case.
  • Most LED projects online mention heat at one point or another.  To get ahead of this concern, we opted for a heat sink-mounted super bright LED.  This same LED bead was seen on ebay without a heat sink, but we didn't want to screw anything up due to inexperience and opted for the more expensive package for the first run.
  • The Driving Circuit was a simple buy, and the choice also dictated our resistor purchase.  The key value from the MOSFET we purchased was Gate Threshold Voltage.  The voltage drop across R2 with the battery we bought had to match this value.  Using V = IR, R = V/I = 1.5V / 350mAh ~ 4 ohms.

Materials List

Name Description PID
Battery Lithium Ion Polymer Battery - 3.7v 1200mAh 258
Charger Adafruit Micro Lipo - USB LiIon/LiPoly charger - v1 1304
LED 1 Watt Cool White LED - Heatsink Mounted 518
Driving Circuit N-channel power MOSFET - 30V / 60A and NPN Bipolar Transistors (PN2222) - 10 pack 355 and 756
Resistors 100K and 3.5 Ohm Resistors Already Owned

Components, Breadboards and Protoboards, Oh My!

Once the materials were in hand, the breadboard went well.  It worked the first time!  While we waited for batteries to charge, we used a simple brick of 4xAA batteries.  The beauty of the driver we chose is that it can drive LEDs using any voltage source over the target voltage.

Using the breadboard and schematic, we attempted a protoboard version of the circuit.  This was a complete mess, and it took us a lot longer than it should have.  However, by the end of a single prototyping session, we turned a jumble of components into a working light.  One high/low note happened when we wanted to minimize the number of connections but didn't have the right resistor for R2.  We twisted two resistors together to get close to R2's 3.5 Ohms and put them through the same hole on the protoboard.  Instant parallel resistor!

Conveniently, the whole project fit under a Ziploc Container lid.  A little bit of hot glue, another section of protoboard with a hole in the middle, and charged batteries got us our first complete prototype!  It was brighter than the equivalent cell phone flash and had excellent diffusion through some purpose-bought Smirnoff Ice.