Browsing posts in: Electronics

WPC driver board issues

My WCS 1994 is having some issues; the DMD display is showing static and now the game is behaving strangely.

I’ve been using the guide here, but I’d like to share some other data I’ve gathered since I didn’t find it elsewhere.


Test point Working DC Working AC Problem DC Problem AC Description
TP1 14.7 0.63 13.5 0.08 +12V filtered but not regulated
TP2 4.93 0.01 4.97 0.001 +5V regulated Digital supply
TP3 11.92 0.008 0.758 0.122 +12V regulated digital supply
TP4 0.37 0.63 3.62 0.06 +50V filtered
TP5 0.03 Board ground
TP6 73.2 0.2 – 0.8 75.1 0.01 +50V for solenoids, flippers
TP7 21.7 0.09 21.6 0.04 +20v flash lamps
TP8 15-17 0.2 (ish) 11-14 0.8 (ish) +18 to lamp columns

“Working” values come from my Twilight Zone (working), while “Problem” ones come from my WCS (not working).

What can we tell from this?

Well, a few things. The obvious issue is TP3; it is less than 1 volt when it should be around 12 volts, and it’s letting a lot of AC through at all.

Time to pull out the schematics.

image

Sorry, that was the best image I could pull from a PDF; the paper version isn’t much better.

Basically, we have power coming in from the left side, which should be a nice healthy 18volts (measured at TP8). It goes through two series diodes that will drop the input by a little over a volt, and then it goes to an absolutely-standard 78xx linear regulator circuit; a capacitor on the input, a 7812 (for 12volts) and a capacitor at the output. 78xx regulators are pretty robust, so let’s see if we’re using it correctly…

Like most linear regulators, the 78xx series has some limitations around input voltage; it requires about 2 volts of headroom to be able to give us the output voltage, so we should be looking for 14 volts coming in. We have 11-14 volts – it fluctuates because the lights are flashing in attract mode. That 11-14 volts isn’t enough to consistently give us enough voltage for the 7812 to give us a nice 12 volts.

So, we don’t have enough power coming in, so that is the problem, right? Well, not so fast. Based on what I know about the 78xx regulators, one would expect that if the voltage drops enough so that you don’t have a full 2 volts, you will see the output voltage slowly drop down.

I pulled out a 7809 and hooked it up to my variable power supply, and found that this was mostly true; the dropout voltage was about 1.2 volts (two diode drops). That means I would expect that the 7812 would put out less voltage but something close to 12V.

So, that suggests that we have two issues going on; we don’t have enough voltage coming in for the regulator to work and the regulator looks fried. That is supported by some data I had before this where the game was acting very weird and the voltage at TP3 was fluctuating all over the place. So, a new 7812, and it would be a good idea to replace the 1n4004 diodes and the electrolytic capacitors in this section at the same time, since this board is nearly 25 years old.

Looking at the input voltages at T8, note that there is a decent AC component in the DC voltage – about 0.8 volts. Back to the schematics:

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This is also really simple; we have AC from the transformer coming in, going through a full-wave rectifier, and then there are two honking big 15,000 uF electrolytic capacitors. As these capacitors age, they are going to lose some capacity and have an increased internal resistance; both of those make them worse at filtering, so it’s time to replace those as well. It’s possible that the AC that they are putting out ended up hastening the end of the 7812.

It’s typical to replace both the capacitors and the bridges when the board is reworked, just to make sure, so I will probably do that.

I am a little concerned by some of the values I see on my TZ board; there are some indications that the caps there need replacement as well. I’ll do the WCS and then compare it to the TZ one.



DLE (Globes of Fire) Part 3

 The new boards arrived from allpcb.com. To recap, this, time I went with standard 0.1” (2.54mm”) header pins between the boards. I ordered some angled headers from the Amazon to use for the connections.

IMG_9061

After I populated 11 faces with LEDs, it was time for assembly. Here’s the first approach:

IMG_9063

The first concept was to wire the faces together with short pieces of header on the back. This worked poorly; it took a long time to hook them up and the angles were rarely right. The first half was technically done, but I was unhappy.

For the second half – and keeping in mind that prettiness was not a requirement – I decided to go with another approach. I would use angled headers on the outside, and just solder the pins together where they overlapped.

But first, I needed a better way to set the angle. The led to the following design in TinkerCAD:

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And then a long session of setup to migrate my 3D printer from an absolutely ancient laptop to one that was merely old. I printed up a whole set of these, and then used them to hold the faces at the right angle for soldering. That resulted in this upper ring:

IMG_9068

The alignment clips on the right worked very well; it only took about 30 minutes to do this whole ring. And yes, it’s very ugly.

Time to hook them together, and then attach on the end face. These are attached with small pieces of header pin on the outside.

IMG_9069

Then it’s time to wire up the 5 volts, ground, and data, and take it out for a spin.

The first attempt was not successful; one ring lit and the other didn’t. A quick check discovered that the ground connection between the two rings was not functioning, so I added an additional connection. Which led to this:

IMG_9071

The driver is running some simple rainbow code, so each LED is a slightly different color.

Finally, adding on the requisite acrylic globe gives us the following:

Globe of fire from Eric Gunnerson on Vimeo.

Overall, I’m mostly happy. It would be nice if the header holes were a bit tighter on the pins, and I could clearly get by with 2mm or even 1.27mm pins. The 3d-printed alignment clips could use another iteration to make them easier to use.



DLE (Globes of Fire) Pt 2

A week or so goes by, and I get a package back from allpcb, so I started building one.

Each half has a ring of 5 pentagons plus one the end, so I started hooking 5 boards together:

IMG_9044

The WS2812 LEDs are only 5mm on a side, so the whole board is roughly 15mm x 17mm. That’s tiny, and frankly working on it was a huge pain. I did this, put the boards into a box, and closed it.

Then I came back the next day and decided to have another try. Rather than connect on the outside, I decided to use a much lighter wire and connect on the inside (back) of the boards. Here’s a set of 5 with VCC and GND hooked up:

IMG_9046

Yes, that’s some *ugly* soldering, but in my defense I’d like to note that the spacing on the holes is about 0.05”/1.3mm. This then gets folded into a ring. Eventually, we end up with the top and bottom:

IMG_9050

Next, those two are soldered together with wires to carry VCC and GND between halves, and you end up with this:

IMG_9052

Next was to wire through the data ports. Basically, it starts at one face at the open end, goes around that ring, goes around the lower ring, and finally travels to the bottom. Add in some hot glue to help hold things together, and put the LEDs on, and here’s the result:

IMG_9053

That is one ugly bit of construction, and it took a lot longer than I had hoped.

IMG_9055

After soldering a few hundred WS2812s, you learn how to do it without burning them up. On the left is one face from the 3-LED version that I tested to verify the layout.

V1.1

The first version was technically a success, but only because I so cussedly kept on. I was wondering if I could make something small enough to fit in an ornament ball, and the answer is “yes”, but you really don’t want to do it.

So, it’s practically a failure.

The biggest problem is the connection between the faces; the holes are too hard to solder, and using individually-cut wires is a pain…

So, I’m going to abandon the single-LED version (kindof – more on that later) and work on the 3-LED version. I started by going with standard 0.1” (2.54mm) header spacing, and the plan is to use angled headers. The angled headers will stick out to the side, and two faces are connected by soldering the ends of the header pins together. It’s going to look a big weird, but should be a lot easier to construct.

Here’s the old design and the new one:

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Obviously, the big different is the connectors; they are much larger, though the overall design is only a big bigger. I’ve used the extra space to pull the LEDs a bit farther apart because trying to hand-solder the LEDs in the first version was a difficult. And I added a little bypass jumper; if you solder a wire (or better, a 0805 zero-ohm resistor) across those pads, you can omit the bottom two LEDs and things will work fine.

If you read backwards, you might see that it says “Dodecahedral Light Engine” on the back, which is the new name for the boards.

A fully-populated DLE will features 33 LEDs, pull 2 amps @ 5V with everything on white, and put out quite a bit of light.

I need one more design review pass before I send this one out to have boards made.





Globes of Fire!

The parts for the new controller have started trickling in, but until they all show up I’m a stuck there, so I’ve been thinking in other areas.

In the olden days – pre LED – I had a number of the 50 or 100 light globes in my display:

See the source image

I liked them for their intense burst of light, but the ones I had gradually died, and I haven’t found a replacement.

So… I got thinking again about options. When I built my Animated Snowman, I used WS2182 leds on the faces of 3d-printed dodecahedra. It worked fine, but the hand-cabling was a pain:

IMG_8435[1]

Using the acrylic lamp globes worked great, however. They are cheap, easy to get, and fully waterproof. I just needed a better way to get the LEDs in place.

One of the nice things about dodecahedra is that the faces are all pentagons. I remember a hack-a-day article a couple of years ago when somebody built one by soldering pc boards together, so I decided to do a design of that what that might look like:

image

The concept is that any face can hook to any face. You wire up the ground and VCC connections on all faces to give rigidity to the dodecahedron, and then wire up the DIN and DOUT connections from face to face in whatever pattern makes sense.

This design gives me 12 LEDs (well probably 11, since the top or bottom one will be used for support) in the space of about an inch, so that would easily work in the small acrylic balls (6”, or 4” if I can get them).

Of course, why do one LED per face when you can do 3:

image

Same concept as before; hook up DIN from another face, it will chain through all three LEDs and then head out through DOUT.

This board is roughly an inch in size, so the resulting dodecahedron will be around 2” in size. That will give us 33 LEDs and live up to the title of the post, but it may be overkill, which is why I’m going two versions. I’ll drill a hole through the 12th face and use a threaded rod and nuts to mount the DLE (Dodecahedral Light Engine).

I need to do some design cleanup and then send off for a run of these to see how they work.


Snowflake–custom controller

The Adafruit Huzzah was a nice starting point for the snowflake, but it’s both more expensive and not well-tuned for what I need. To drive the WS2812s, all I need is a single output, and I don’t need dedicated buttons on the board.

I went back and forth on whether I wanted to do two controller boards – one that used the ESP8266 and another that used a cheaper AVR, but the ESP can be had so cheaply that it hardly seemed worth it. I considered a number of different ESP modules – or even building directly from the ESP8266 and adding flash, but the ESP-12 is pretty cheap and it has FCC certification (or is claimed to, at least).

So, basically, I took the Huzzah design and looked at it in Eagle, and then pared off things that I didn’t need and did my design in KiCad. It currently lives here.

The design is pretty minimal; it has a small 3.3 volt linear regulator to power the ESP (I used the same SPX3819 as on the Huzzah), appropriate resistors to put the ESP in the right state, diodes to handle level conversion between the 5V world and the 3.3V world and two headers. There’s a 6-pin programming header that has power, serial connections, and the reset and GPI00 pins on it, and there’s a three pin header for operation that has 5V and GND in to power the board and the data line out for the WS2812 string. Simple and straightforward. There will probably be another version with another sensor; I’m going to need a way to reset these things to handle wireless setup and my new design will be fully encapsulated, so I’ll probably do something magnetic.

Here’s the schematic:

image

Once I had that, it was off to do the PC board layout. That is really my favorite part of the process; to go from a set of random components on the board to something functional (and perhaps even elegant) is a rewarding process. Here’s the layout.

image

I decided that I wanted both sets of connectors at the bottom and the ESP-12 at the top. Basically, the jacks are at the bottom, the 3.3V supply is in the middle, and the resistors, diodes, and LEDs are on the sides. All of the small components are 0805 sized, since I wanted something that I could hand-solder if necessary, and those will also reflow reasonably well if I want. Given the need for two jacks and the space they take up, there’s not a lot of margin in going smaller at this point.

One of these times, I’m going to do snapshots of what it took to get to a decent layout.

The PC boards got finished and sent out to AllPcb.com, who sent me 10 (actually, 11) copies of the board for a total of $5.49 with about a 7 day turnaround. I don’t understand the economics of how that can be profitable, but I’m not going to complain right now.

Initial guesses at the overall costs for the controller:




Part Price
ESP-12 Module $1.78
3819 regulator $0.06
Other parts $0.11
PC board $0.50
Total $2.45

No labor in there yet, but it’s just a matter of putting the parts on there and reflowing them. It should be pretty quick, and I’ll check to see what it would cost to outsource it as well.

The boards have showed up, but I was too cheap to pay for fast shipping of the other components, so they’ll trickle in and then we’ll see if my design works.



Snowball pricing analysis

I’ve been thinking about maybe selling the snowflakes – or a variant of the snowflakes – commercially. Pursuant to that, I did a few calculations on parts costs.

Here’s what it would take to build the prototype in volume (say, 100 units):



Part Price
PC Boards $2.04
55 WS2812 LEDs $3.72
Adafruit Huzzah $7.96
Acrylic $4.07
Printed separators $1.00
Labor @$13/hour $26
Total $44.79

The labor is frankly a bit of a guess; it’s probably quite a bit worse than that.

Assuming I wanted a 50% margin, that would put the retail cost at about $90. The snowflakes are nice, but I’m not sure they are $90 nice.

To reduce the price, we need to look at the places that are the most expensive. Clearly, labor is a problem, so making the design easier and more robust to assemble is going to be critical. And the cost of the Huzzah is a big part of the parts cost, so coming up with an alternative that is easier and cheaper to use makes sense.



Snowflake Final

The snowflakes – five in total – have all been finished.

Well, mostly finished… there are three animating themselves on the gutters of the house right now, while the remaining two (which were on the house until this afternoon) are waiting for their waterproofing to cure.

This post will cover a lot of ground, since I missed a couple of updates along the way. 

Assembly

When we last left our story, we had a PCB in the snowflake form and some laser-cut pieces of translucent acrylic that go on the front.

The next step was to put the LEDs on the board. My hope had been that I could use the hot air rework station to reflow all the LEDs, but a bit of experimentation showed that I was melting the LED cases and hand soldering was faster, so I went that way. I think a cheap reflow oven is in my future.

I used the following approach:

  1. Add solder to all the solder pads on the snowflake (55 * 4 = 220 of them).
  2. Carefully hold an LED in the right position, and touch two of the pads to tack it in place.
  3. Press down hard on that end of the LED, and touch each pad until the LED sinks down even with the level of the board at that end. .
  4. Repeat on the pads at the other end of the LED.
  5. Reheat the first two pads to get rid of the stresses induced when the second end was dropped down.

That was mostly straightforward, except it turns out that if you put the LEDs in backwards, they turn into HEDs – Heat Emitting Diodes – and you get to remove them and put new ones in their place. I put my new hot air rework station – a 9570W+ – to work at that.

Eventually, I got all of them soldered correctly, fixed some connection issues between the boards, and had something I could run my initial animation code on.

It worked.

My original plan was glue the PCBs directly to the acrylic, but I discovered that I liked the result better if there was some space between them. I did tests using pennies as spacers, grabbed my calipers to get some measurements and drew a quick drawing, and then came up with this in TinkerCad:

image

And then printed up a bunch of them in clear PLA. They mostly work pretty well; the only downside is that the connection at the small end needs to be flexible to warp around the board but that also makes it a bit weak, so I’ve broken a few of them. Carefully put them on the PC board and squeeze in the acrylic, and you end up with this:

image

Call this the first prototype. At this point, I was a bit tired of soldering and was waiting for some more parts to show up – and finding out that Amazon’s two-day prime shipping is only aspirational at times – so it was time to write some code.

Code

Both the code and the circuit designs live in GitHub here.

I’ve written four or five versions of color-blending animation code. Last year I wrote a nice abstraction that worked great for the linear strip animations I was doing, but it didn’t adapt very well to what I wanted to do here, so I went back to first principles.

Using polar coordinates, the code knows the location of each LED on the snowflake. For some of the animations, the color is determined by either the angle or distance of the LED from the center, and in these, there is just a simple mapping that says “add the animation offset to that number, and then use it to find a color”.

The nice part of this approach is that is gives me appropriate color blending across the whole snowflake.

I spend a few days on the code, and it’s decent as a first try. It implements four animations:

  • A continuous rotation of all the colors around the arms of the snowflake.
  • An animation of colors based on the distance of the LEDs from the middle.
  • A “sparkle” effect; all the LEDs smoothly and slowly blend between colors, while random LEDs flash full white and then fade back to the current color. I wrote some nice code for this.
  • A bouncing effect called “worm” that is a bit of a take on the Larson Scanner, but across opposite arms of the snowflake, also with color blending.

I had more ideas for animations, but decided to freeze the implementation so I could finish the build.

Autonomous display

For the prototype so far, I was driving it with a ESP that was powered by the serial port, and with a short ribbon cable carrying signals to the snowflake itself.

My plan was to put the ESP remote from the snowflake (so it could be under the eaves and shielded from rain), so I cut two-foot lengths of red/black/yellow wire (for power and signal), wired everything up, plugged it in…

And the LEDs started flashing randomly. Tried decoupling capacitors, tried signal resistors, tried a whole bunch of things, and nothing worked; if I made the signal line longer than about 10”, it wouldn’t work.

Trying to fix that consumed the better part of a day. Ultimately, I decided that the problem was that I was getting a lot of transients, so I decided to run the 5V power directly to the snowflake, and then chain the ESP off of that.

And it worked perfectly the first time, leading to this arrangement:

image

Plus 4 = 5

During the long hours of making four more of the PCBs – cursing my choice to use tiny pads for data connections and not doubling them – I realized that there was a far better way to do the attachment; if I allowed the boards to overlap vertically, I could use through-holes that aligned between the parts and just solder component leads into the holes. My guess is that I could do that basic board in about 1/10th the time, even less than that if I could reflow solder the LEDs. And the boards can probably be (mostly) square, which will make them easily fababble, easily broken apart, and they will fit tighter for better utilization.

Sounds like version 2 to me.

I didn’t take any pictures during this time, but it was a huge pain in the butt to get them all working; the tiny data paths were especially troublesome.

Finally that, was done, and I could turn to other matters. Four more Huzzahs were wired up:

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and were all attached to the snowflakes.

With the Huzzah mounted close, it needed some protection, so a bit more time in TinkerCAD yielded a nice little case:

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That’s a PrintrBot simple metal pro with a custom heated bed on it. I had the usual problem getting tolerances right, but eventually got to here:

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Power

Whenever anybody asks me what the hardest part of these projects is, I always respond “cabling”.

LEDs are power hungry, and unfortunately small wires introduce voltage loss, which means you get color shift. If I had 3 snowflakes on one wire, the last one is going to be dimmer and the colors will likely shift as well. In my previous projects I’ve resorted to powering strips at both ends and using thick landscape lighting wire, but it’s a huge pain.

This time, I got smart.

WS2812s pull about 60 mA max if they are all white, and with 55 of them I needed 3.3 amps @ 5 volts. Since I can live without full white, I decided that 3 amps would be sufficient. And bought 5 of these:

image

One of these will be right next to each snowflake, and then I just need wires that supply something around 12 volts, and everybody will get a nice solid 5V supply and be happy. I reused the 10-gauge wire I had for the project this replaced, but I could easily get by with something like 18 gauge.

I’m not sure powering with DC is the right approach, however; it might be cheaper to go with small 5V AC power supplies and just use standard AC cords.

Waterproofing

I live in the Seattle area, and the holiday season is generally quite wet, and the electronics will need some protection from the elements.

I have quite a bit of West Systems epoxy sitting in the garage leftover from a custom subwoofer enclosure I did a while back, but their website didn’t yield much information about its conductivity. So, I built this:

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and embedded it in a whole lot of epoxy:

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Works fine…

Distractions

About this time, I had a couple of distractions. First off, this showed up from Italy:

IMG_8960

Getting it picked up, legs on it, and ordering parts to recondition it took a bit of time.

And, I had an event where I needed the snowflakes to be part of the display, so I totally finished two of the snowflakes and put them out on the house, trusting that the weather would stay unseasonably dry. Here’s the bench test:

image

You can see the DC->DC converter to the left of the lower snowflake.

I should at this point mention that pictures or video never do these colors justice; they are much more intense than they show up here.

Waterproofing part 2

To keep the attached wires in the right spots, the wires and the Huzzah needed to be supported above the PCB which will be covered in epoxy. Here’s what I ended up with:

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After I carefully poured epoxy over all the parts of the board that needed them, the boards got hung up to cure:

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It being about 40 degrees in the garage, they did not cure overnight and eventually I had to pull them inside to finish curing. They looked like this when they finished curing:

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I retested them. One of them worked perfectly, the other two did not; only some of the LEDs worked.

So, out came the air rework gun to debond the epoxy in an area and then I could trace from there. I ended up replacing about 5 LEDs; from what I can tell they were touching but no soldered, and the cold weather shrunk things enough so that the epoxy could get in there. I also had one pcb trace break (really?). Then, those two got an epoxy touchup to cover over the reworked areas. .

Finally, the huzzah box got hot-glued to the back and silicone was used to plug the hole.

Not perfect, but version 1.

image

You can also see the molex connectors that bring 5V into the snowflake.

Videos:



Snowflake from Eric Gunnerson on Vimeo.



Version 2

*Lots* of ideas for version two, which might be a commercial version.

  • The whole mounting and waterproofing approach is far too finicky and may not work very well. I’m considering vacuum-forming the snowflake out of thinner plastic with both a front and back, and those can then be solvent welded (or siliconed) together to give me something that is truly waterproof. It will also give much better support for the PC boards.

  • The approach of “click-together” pc boards worked, but it required fine-tuning for each and every joint and then detailed soldering for each part. And then rework when the stresses built up. Instead of click-together, I’m going to use overlapping boards that are connected with through-hole wiring. That will take me down to 10 easy-to-solder joints per arm, or about 60 in total. I also think I can get each of the PCs to be rectangular in format, and that will make panelization easier and waste less space. I think.
  • I really need a way to reflow solder all the LEDs, and it may be time to make/buy a tiny reflow oven. Or *maybe* get somebody to do that for me, though the initial quotes I looked at are higher than I expected.
  • Moving the ESP8266 onto the snowflake board, probably on the back. That would require adding a simple 3.3V regulator for power and (probably) programming pins. I’m currently using an ESP-12; I could probably get away with a simpler one but they are pretty cheap already so it may not be worth it.
  • Add more built-in animations. Color wipes in the x/y direction, flash and off animations, concentric rotating color blends could all be done.
  • WiFi coordination between standalone snowflakes, with a dedicated network just for the snowflakes, and *maybe* a separate gateway to connect to an existing wireless network.
  • WiFi connection to an existing wireless network to allow control of the snowflakes. This might encompass setting their default set of animations, being able to download new animations, or being able to do “command control” over the wireless network, either just setting the animation that’s being run or driving every LED independently.


Snowflake update…

Have made decent progress on the snowflake. I have two PCBs assembled and populated. The right way to do it would be to use a reflow oven, but I’ve settled on using my new hot air rework station and solder paste to do the data lines – since the pads that I need to connect are tiny – and hand soldering everything else, including the LEDs. I did reflow on a test LED and it worked, but I had to get things hotter than I would like.

I finished the outline design and cut the snowflake fronts from white acrylic. This was a bit frustrating; the Glowforge is advertised as being able to cut about 11.5″ in the forward/back direction, but they haven’t been able to achieve that, so I had to cut slightly smaller than I wanted.

I used one sheet each of #7328 and #2447 acrylic so I could see which one I liked better:

IMG_8876

After playing around a bunch (something like 15 variants) with both plastics and with keeping them different distances from the LEDs, we settled on 2447 spaced about 10mm away.

Then it was off to Tinkercad to design a clip that would hold the front to the pc boards, which finally led to this. You can see the clips (printed in clear PLA) holding the snowflake at the right distance.

MVI_8888 from Eric Gunnerson on Vimeo.

After a false start or two, I think I have a handle on how I want to structure the animation code; it’s nice and mathy…

Now I just need to order some more Huzzahs to drive the other snowflakes, figure out how I’m going to handle the cabling, and buy some waterproof 12V –> 5V buck converters (I’m tired of worrying about voltage drop).

The video is powering the LEDs from a USB port using tiny wires, and the 5V supply is sagging down to around 4 volts because of the load. So, it will be brighter than this.


Snowflake #2–PCB design

I thought that I was done with the PCB design, but it turns out that I wasn’t close.

Basically, I ran into two big issues.

The first was the wierd angles that I had in my design; they didn’t pack together very well. What I really needed was a way to rotate the two short arms so they were at 90 degree angles.

I couldn’t find anything, so I went and wrote a utility to do it. On the way, I learned a lot about the KiCAD file format. It was a nice little exercise; I’ll note that it’s in pretty rough shape and you would need to recompile it to get the rotation you wanted (and to work on the file you wanted); maybe I will clean it up at some point. It’s C# code because that’s what I speak best.

I guess I should also note that I built a little .pcbnew parser to do it; it parses the file into a bunch of nodes, you change the ones you want to change, and then it writes the file back out the way it was before except for the changes. So, it will likely be useful for other stuff as well.

So, anyway, that gave me everything at increments of 90 degrees, which was good. Then I went off and started trying to understand if PC fab houses could build what I wanted. The answer seemed to be “yes” (though not in the current form), but they would likely charge extra and there was a decent chance they would make a mistake. The problem is that I have 4 different irregularly-shaped boards. You can’t use v-groove panelization because that only works with (mostly) rectangular boards. I was hoping to use the GerberPanelizer, but I couldn’t get any of my boards to show up in it; I suspect it’s because of their shape.

So, I went off and taught myself the requirements and spent a bunch of time coming up with this:

image

This is a hand-panelization of my boards. The idea is to come up with a design that can be fabricated as a single piece by the fab (and assembled/soldered/etc., if you are planning on having somebody do that) but can still be easily separated.

You do this by putting little breakaway tabs with small holes (I used large vias because KiCAD only supports holes in footprints). The idea is that after you get the pcb, you can carefully break off the parts with the weak tabs to separate the boards. The tabs are also called “mousebites”.

To make them breakable, you need to design things so that you have multiple tabs that are in a line and could easily bend. That isn’t even close to possible with this design, so what I’m going to do is cut the boards apart with my Dremel rotary tool or oscillating multitool. The rough edges will not matter for this application. If the design is correct, all the yellow edges will be cut with a router after the PCB is etched.

Oh, and the small boards on the right are little WS2812 breakout boards; I had a bunch of extra space in the square, so I added them in.

My first check is to upload to OSHPark and see what it thinks; I’m not going to order there but it does full visualization of the boards. Here’s what I got for the board and the board outlines:

Yeah, that’s not very good. The design looks fine. However, when I was switching between layers, I accidently chose the “Eco2.user” layer instead of the “Edge.Cuts” layer. They are rendered in the same color. All I needed to do was to turn off that layer, and then I could flip those lines over to the edge cuts layer, and that fixed the issue.

OSHPark still has trouble with the design, but I’ve exported Gerber files (one file per layer in the design tool) and looked at them in other viewers and they are fine. I think the OSHPark viewer is having trouble with the internal cutouts.

Because of the complexity of the design, I’m not sure how to spec it on the online ordering tools, so it is currently out to order.



Snowflake

For the last 5 years or so, I have led a “Holiday Lights Bike Ride” in early December. It’s fun to tour around and look at lights on a bike, and the view you get on a bike is very different than in a car.

One of the houses has a large snowflake with white and blue lights. Very nice and pretty.

After four years of service, I retired the LED strips I had along my gutters. The “waterproof” strips had started shorting out and it was a pain to replace sections. I personally liked the “line of light” look, but the vast majority of people didn’t even notice that they changed color.

My first thought was to replace them with WS2812 strips, so that I could address all of them. I played around with a few designs, but didn’t solve the design problems to my satisfaction; coming up with a way to keep the strips actually waterproof while still supplying them with power (which you need every 2.5 meters) was a hard problem. So, I put that project on the back burner.

A while back, my Glowforge showed up, and that triggered a new thought about the snowflakes. Instead of doing addressable LEDs on the gutter, could I do snowflakes that hung at gutter level? And then do the gutters with some nice traditional C9 LEDs.

Here are the basic parameters that I came up with.

  • Addressable LEDs (probably WS2812s)
  • Snowflake outline in acrylic (because I can cut it on my glowforge), white so that the color spreads out, and something like 12″ across (a little small, but it’s an easy size to deal with, and larger sizes make it harder to deal with the wind storms we always get).
  • Around 50 LEDs per snowflake
  • With local 5V power supply. I’m tired of running 10 gauge cable and worrying about voltage drop, so I want something regulated and local. It will probably be a local 12v to 5v converter, though I might end up with local AC instead.
  • Microcontroller controlled. That was obvious with the ws2812 choice.
  • *Maybe* WIFI controlled. I’m thinking maybe 8 of the snowflakes, and I can do an ESP8266 across that many relatively cheaply. That would let me drive them in sync from the comfort of my office machine.

The snowflake design was pretty simple; it had to be so that I could easily light it with LEDs.

One of the truisms in these projects is that it’s always the wiring that is the most painful part. That almost killed me on the Snowman project; lots of individual wires, and each has to be cut, stripped, and soldered. Not fun.

I’m thinking about doing 8 of these, so that would be 8 * 50 (leds) * 4 (connections), or something like 800 wires and 1600 solder joints. And to compound that, you need decent sized conductors so that you don’t lose too much voltage along the way.

The way to get rid of all the point-to-point soldering is to use a PC board. Since boards are priced based on their area, I explored using APA102 LEDs which are available in a 2020 package.

That’s 2mm x 2mm, or just a little bit more than 1/16” square. I’m planning on soldering with a heat gun (or maybe I’ll pick up a cheap hot air rework station), but the 2020s will be blown right off the board.

So, it was back to the 5050 (5mm x 5mm) package, and at that point the WS2812B won out on cheapness. The APA102s are nicer but much pricier. Oh, and they have separate clock and data, which is one more wire to try to route correctly.

And there I ran into a problem. A run of eight 12″ x 12″ boards would be right around $200, which is a bit pricier than I had hoped, and it’s not clear to me that I could find a fab that would be able to cut such a fragile arrangement of boards; in fact, I was pretty sure I couldn’t find one.

After some thought, I realized that I could do the snowflake as a series of boards; a central board, 6 straight boards that attach to the central board, and 12 arm boards that radiate from the straight boards.

After a bunch of iterations, it ended up looking like this:

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And yes, I did notice the resemblance:

Image result for klingon warbird drawing top view

I took that design, pulled it apart, duplicated parts, and came up with this layout:

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The PC board will be a little bigger because I’ll need tabs between each part, but it will be close. That is about 5” x 5.3” and has all the parts for a 12” snowflake.

But would it work? Well, a trip to the glowforge with a piece of cheap plexiglass and two minutes of time yielded enough pieces to test it out (the rest didn’t cut cleanly because cheap plexiglass):

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The laser loses a bit of material in the kerf, so they are a bit loose, but that will be better with the real design, and it isn’t structural; all of this is supported by the acrylic snowflake, which is thicker and beefier.

It was time to do some board designing. Unfortunately, I don’t have a full license to Eagle, and the free version won’t let me design boards that big (actually looking at the new Autodesk free license, I probably would have been fine), so that meant I had to teach myself KiCAD. Like Eagle, it has a bunch of weird eccentricities which are of course different than the ones Eagle has, and I’ve spent a lot of time researching how to do things that are very simple.

The circuit is really very simple; just power, ground, and a daisy-chained data line. The only big constraints are:

  • I want big traces to limit the voltage drop
  • I need to be able to connect from one board to another

My usual approach for PC board design is to draw the schematic, and then just start playing around with layout. The layout of LEDs is pre-determined, so it’s really just about routing all the conductors.

Here’s a very ugly schematic:

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I luckily forgot to save my early versions because they were pretty bad, but with a lot of refinement and rework, here’s version 0.9.

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The fat green VCC and GND traces are on the underside of the board, and then the thin red traces (or yellow if there are green lines behind) are the data lines. Wherever there are breaks between the boards, the are solder pads that span across the boards; the idea is that those will be soldered to hold the boards together.

The hub on the right was an interesting challenge; I need to design the pads and place the pads for the other 5 arms so that they will correctly align with the one arm that I did design.

Here’s a close-up of the hub:

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The yellow line is the board edge, so what what I have is pads that hang halfway over the board edge and out into space. You will see some small little blue dashes; those are used to align the pads properly on the cutout.

If you look at the little red data line pads, you’ll see that they aren’t so well aligned. I think I’m going to need to redesign those pads with the same alignment marks so they can be better aligned. Then I’ll have to tear out most of the data lines and the old pads, rotate each new pad to the proper angle (each one is different because of the shape of the recess), and then redo all the tracks that run to them.

Such is the nature of PC board design; you think you are done, and then you need to do a bunch of re-routing.

Luckily, the tool helps out a lot; the system knows which pins should be connected to other ones. If I get rid of some of the connections, it looks like this:

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Each of those thin gray lines shows a connection that is made in the schematic, but is not correctly made on the board. The software also has a number of other design rules that help you find mistakes.

At this point, I upload is to OshPark, which I like for small boards, and it gave me this as a final design view:

Which looks pretty nice. 9 LEDs on each arm plus one on the hub gives me 55 LEDs per snowflake.

Given the size of the scrunched together version, I think I can get the boards for 8 full snowflakes made and delivered in 12 days for around $80, which is pretty good.

The downside of this approach is that you spend a lot of time on the pc design, but I’d rather be doing that then spending days straining my eyes and back hand-soldering.

Now the big question is, “how lucky do I feel?” Do I order a whole run at once, or do I order one and verify that it works before ordering the other 7?


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