Browsing posts in: EagleDecorations

EagleDecorations Ornament Creation Instructions

Thank you for buying one of our ornament kits. These are the generic instructions that apply to all of our ornaments; please look at specific instructions for your kits for more details.

Tools & Supplies

You will need the following supplies:

  • A small soldering iron
  • Solder
  • Needle nose pliers
  • Diagonal cutters or other tool to trim leads and wire
  • A power supply for the kit your ordered – either a 5V USB charger or a 12V power supply.

LEDs and Resistors

To keep LEDs from burning up, we will be including resistors that will limit the flow of current through the LEDs and equalize the brightness between different ornaments.

Depending on the color of the LED that we are using the the voltage we are using for the ornament – either 5 volts or 12 volts – we will be connecting chains of 1, 2, or 4 LEDs to a single resistor. The instructions for your kit will tell you how many LEDs to put in the chain for each resistor. If there are multiple colors in your ornament, each color may use a different number of LEDs in the chain.

Creating chains

Here is an example of creating chains of 2 or 4 LEDs, taken from the yellow star ornament:

IMG_7062

Note that the LEDs are placed with the longer lead towards the outside of the ornament. That is the basic pattern we use for all of the ornaments.

IMG_7063IMG_7064

In these pictures, we are making chains of 2 LEDs. In the left picture, the longer lead on the closest LED is bent towards the shorter LED of the next LED. In the second picture, the short LED on the second LED is bent back towards the long lead from the first LED. Connections between LEDs should always be done in this manner.

Here is what it looks like after creating two chains of 2 LEDs:

IMG_7065

A 4 LED chain looks like this, with 4 LEDs connected in a chain.

IMG_7066

A full set of chains

The outline of an ornament will be a series of chains; it will look like this:

IMG_7068

Adding resistors

After the chains are created, we will need to add a resistor for each chain. The resistors are always connected to the inside (shorter) lead at one end of the LED chain:

IMG_7069

When all the resistors are connected, it will look like this:

IMG_7070

Hooking the chains together

The next step is to hook all of the chains together. We will do the insides first. This is done with some of the bare copper wire included in the kit. Start by taking the wire and bending it into a rough approximation of the template, and then put that inside the wire.

We will be connected the currently unconnected end of each resistor to the bare wire.

IMG_7071

As shown in this picture, you may need to reroute the resistor wire a bit to make it easier to connect to the bare wire. Here’s a close up of that:

IMG_7072

Once all the resistor wires are soldered on, trim the resistor wires. Next up are the outer wires. The outer wires run around the perimeter of the LEDs and are soldered to the remaining unconnected LED lead. Make sure the outer wire does not touch any other wires.

It is very useful to clamp the outer wire down as you are routing it around. I use a little alligator clip:

IMG_7074

Here’s what it looks like when finished:

IMG_7076

At this point we would test by applying the appropriate voltage to the inner and outer bare wires.

Adding the power cord

Locate the power cord – either the USB one with the 5V kit or another one if you are building the 12 volt version.

At the bottom of the ornament, you will find two tiny laser-cut holes. The are for the zip-tie that will hold the power cable in place. Pass the zip-tie from back to front and then to the back again, place the power cable in approximately the location you want and lightly secure it with the zip tie. Solder the power cord wires to the two bare wires, verify that it works, and then tighten the zip tie. Cut off the extra.

Success! You have completed the ornament:

IMG_7080

Protecting the wires

The wires only carry low voltage, so there is little shock hazard.

If you want to waterproof the ornament, I have had good luck with 100% clear silicone sealant. Make sure to cover the base all the LEDs and over and under the resistors and all wires. This approach has survived multiple holiday seasons outside in wet and cold weather, but there is no warranty for outside use.


WS2811 Expander Part 6: of MOSFETS and voltage drops…

After I wrote the stress test article, I decided to put a voltmeter across the drain and source of the MOSFET and figure out what the voltage drop was. I hooked up the output to an LED ornament, watched the brightness cycle up and down, and put my probes on the MOSFET.

What I expected was pretty simple. In the sweet spot of the MOSFET I’m using, it claims a Rds – resistance between drain and source – of 10 milliohms. That means I should expect a voltage drop at 5 amperes of:

V = 0.01 * 5 = 0.05 volts

That low voltage drop is one of the reasons to use a power MOSFET; a bipolar transistor would have a voltage drop of about 0.6 volts, and therefore waste more power and get hotter.

The voltage jumped around a little, and settled down at full brightness:

0.8 volts

Okay, that is really unexpected; I played around with different voltages, and I still got 0.8 or 0.9 volts.

My first thought was that the MOSFETs that I got from Ebay might be counterfeit, so I waited for my order of real parts to show up from Arrow, built a new board, and it read:

0.85 volts

This is really confusing, so I asked a question on Reddit’s /r/AskElectronics subreddit.

The first answer I got was that it might be the base diode because I had the MOSFET backwards.

So, I pulled out the datasheet for the MOSFETS and looked at my schematic and board in Kicad. As far as I can tell, everything is wired correctly.

A deeper answer suggested that if I was doing PWM (I had been testing at brightness = 250 because I knew that would be more stressful for the MOSFET than always on), I should test with always on. It also talked about gate capacitance.

<digression>

This is one of those cases where real devices diverge from ideal devices. FET stands for “Field Effect Transistor” – current through the source and drain is controlled by the field on the gate. You establish a field by the flow of current to charge it up to an appropriate voltage.  The amount of current it takes depends on the gate capacitance (described as “Input Capacitance” on the datasheet). For the MOSFET to turn on, you need to flow enough current to establish whatever voltage you want on the gate.

Or, if you think of the gate as a capacitor, it takes a bit of time for it to charge. In my case, the time it takes to charge will be controlled by the pull-up resistance and the capacitance.

Let’s say we are running at 5V, and our MOSFET has 1nF input capacitance (pretty close), and we are charging through a 10K capacitor.

This calculator says that the time constant is 0.00001 seconds, or 10 microseconds.

</digression>

So, I went and changed the animation code to run all the way to full on – luckily my code is running on an ESP8266 and animations can be changed over WiFi – and rechecked the voltage drop.

Would it surprise you if I told you it was 0.8 volts? Probably not at this point…

Perhaps it’s my voltmeter; I have a nice Fluke but how about if I try using my oscilloscope (a Rigol DS1102D I picked up a while back)?

So, I powered it up, hooked it up, and looked at the waveform across the load. I showed the a nice PWM waveform…

But wait a second… I had updated the animation.

My debugging rule is that when things seem unexpected, back out a level and retest the assumptions. Usually one of those is wrong.

I started with my controller code. I suspected the gamma mapping code, so I added some Serial.println() statements and verified that, yes indeed, the colors were getting set to 255. So, that part was fine.

I next suspected the support library I use (the rather excellent NeoPixelBus). I read through a bunch of source but didn’t seem to be any issues. The code all looks fine…

Was the data getting to the WS2811 correctly? So, I fired up the scope again and hooked it to the data line. On full on, the data looks like this:

NewFile0

The WS2811 uses an encoding scheme where a short positive pulse means “0” and a long positive pulse means “1”.

That is a full string of ones; you can’t see all 24 of them, but trust me when I say they are there. You can see this switch back all the way to all zeros as the animation progresses.

So, the software is telling the WS2811 to go to full bright, but it is still turning off for part of the cycle. Here’s the output straight from the WS2811:

NewFile4

That little positive spike is 29.4 microseconds, which is about 5% of the 536 microsecond cycle time, so full bright is only 95% bright.

The cursors on the capture show the start of two sequential PWM cycles, and the scope nicely tells me that it’s updating at 1.87 KHz. Which is another weirdity, since every source I’ve seen suggests that WS2811s update at 400Hz.

At this point I’m beginning to wonder if I have a WS2811 clone. I thought it might be the same IC used in the SK6812 ICs, but the claim is that they have a PWM frequency of 1.1KHz which is less than I am seeing.

So, it’s off in search of some real WS2811s. It is really easy to buy cheap ICs made in China but is surprisingly hard to find an authorized source. There are lots of sources on aliexpress, some looking pretty shady. Octopart found me a 10-pack from Adafruit for $4.95. I finally found lcsc.com, which specializes in this sort of thing, and ordered some. They look to be WS2811S chips, but I can’t find any information on what the “S” means. More on that when they show up.

Back to voltage drop…

Since the WS2811 wouldn’t go into “full on” mode, I needed a test setup to do my testing. Here’s what I came up with:

image

In the right middle is the MOSFET, with clips connected to the lead and the body. In the picture, it is running only the LED Star, which pulls 145mA of current.

One of the fun things about MOSFETS is the gate holds onto the charge, so if you just touch the gate to 12v, it turns on and stays on. Touch it to ground, and it turns off, and stays off. I measured the voltage drop across the MOSFET.

I next decided to hook up my test load. I started with a single 50 watt bulb, a 4 amp load. I carefully hooked it up in parallel with the led star, and…

There was a loud “crack” and the led star went out. No magic smoke, but the MOSFET was toast. The gate was floating, and there wasn’t enough charge there to put it firmly into full conduction, so it was in the linear zone and quickly overheated, melting the plastic on one of my clamps. So… replace the MOSFET, make sure the gate is attached to positive, and try again. That worked, and the MOSFET was only mildly warm. Let’s try two bulbs for an 8 amp load. That worked, *but* there is no heatsink and it got hot pretty fast, so I unplugged it before it got too hot.

I collected some data and figured out that the Rds was about 90 milliohms, which is a lot higher than the 10 milliohms I expected. That was a mystery for about 8 hours, until I was writing this up and realized that I was measuring the voltage drop at the ends of the leads connected to the MOSFET. The thin leads.

So, I went back and measured right at the MOSFET, and got a Rds of 7 milliohms, a bit better than the 10 milliohms that was spec’d. So, yay!

Faster switching

Returning to our somewhat slow switching, here is what I saw:

NewFile2NewFile3

The negative transition is when the transistor turns on; notice how effortlessly and quickly it pulls the gate voltage down. And when the transistor turns off, note how long it takes it for the gate voltage to charge back up. It’s roughly 10% of the overall cycle time.

Which is a bit embarrassing; I chose the 10K value as a typical pullup value, not thinking about the fact that this was happening on every PWM cycle. It can only supply about 1 mA of current.

The most obvious thing to try is to replacing it with a 1K resistor. That will result in 10mA of current and should switch roughly 10 times faster. Can the transistor handle it? The datasheet says that the 2N3904 can handle up to 200 mA continuous, so that will be fine. Is the base resistor okay? Well, transistor has a DC current gain of at least 50, so that means we need a base current of 10mA / 50, or 0.2mA. The 5V from the WS2811 will push about 4 MA through the 1K base resistor, so that’s way more than enough. It would probably be fine with a 10K base resistor, actually.

I took one of the boards and replaced one of the 10K resistors with a 1K resistor and then looked at the gate drive:

NewFile5

In case it’s not obvious, the top version is with the 1K resistor and the bottom one is with the 10K resistor. More than good enough for my application.


WS2811 expander part 5: 12V stress test…

One of the points of the expander is to be able to drive bigger loads than the 18mA that the WS2811 gives you directly. Much bigger loads.

To do that, I needed something that would stress the system, and I needed to verify that the design worked with 12V.

First off, I needed to cut a new stencil uses the paste layer:

IMG_9501

That’s a bit nicer than the first one; there is adequate spacing between the pads this time.

Aligned it on the board, applied paste & components, and reflowed it. Here’s the result, still warm from the oven:

IMG_9502

All the components self-aligned nicely, no bridges, no missing wires. Perfect.

The only thing I need to do is get rid of the center pad for the MOSFETs, since they don’t actually have a center pin.

How to test it?

Well, I dug through my boxes and found a 5 meter length of 12V LED strip. It says that will be 25 watts. I hooked it up and verified that all 3 output channels are working. It’s running an animation that ramps from 0 to 255 over 2 seconds, holds for 2 seconds, and ramps down for 2 seconds. I chose that because the quick switching is the hardest for the MOSFET to deal with from a heat perspective.

But 2 amps isn’t quite enough. I dug out a 12V power supply that claims it can do 6 amps and hooked it up to one output channel:

IMG_9504

That’s the NodeMCU board in the upper right, powered by LED, the data and ground running to the board, and then some decently-hefty wires running to the board.

More load, more load, more load. I want something that soaks up the 12V. Incandescent car bulbs are nice but I don’t have any handy. But I do have an extra heated bed for my 3d printer; it’s a nice 6” x 6” pc board. Hooked that up in parallel with the lights:

IMG_9505

Ignore the breadboard…

This worked just fine. The board heated up to about 170 degrees, the lights worked fine, and the MOSFET on the driving board just *barely* heats up. My measurements show that it’s switching about 5 amps of current.

The only one that’s not happy is my cheap power supply, which is putting out a nice 10Khz (ish) whine when under load.

I switched over to run it on all the time to see how that affected things. After 10 minutes, the board is up to about 110 degrees, the printer bed is up to 240 degrees, and the 12V power supply is 125 degrees.

I think I’m going to rate it at 6 amps total; that gives a lot of margin, and frankly 70 watts is quite a lot of power for this application.


WS2811 expander part 4: Boards and Parts!

After a bit of waiting, the boards showed up from OSHPark. they looked fine as far as I could tell.

I had all the other parts to do a board, but I needed a paste stencil. I went into pcbnew, chose File->Export, and then chose to export the F.Mask (ie solder mask) layer to a SVG. I cleaned it up a bit to remove non-pad elements, went out to the laser cutter and cut a stencil out of 4 mil mylar:

IMG_9495

Everything looked pretty good; there was good alignment between the board and the stencil. The spacing between the pads looked a little tight, but it’s a fairly fine pitched board, so it was mostly what I expected.

I carefully aligned the stencil and taped it on, got the solder paste out of the fridge, and applied it. Pulled up the stencil and it looked crappy, scraped it off, did it again, and got something that looked serviceable though there was more paste than I expected. Hmm.

Got out the components:

  • 1 WS2811
  • 1 33 ohm resistor
  • 1 2.7k ohm resistor
  • 6 10k ohm resistors
  • 3 1k ohm resistors
  • 3 NPN transistors
  • 3 MOSFETS
  • 1 100nF capacitor

and it took about 5 minutes to do the placement. Here’s the result:

IMG_9496

I didn’t look at the picture at the time, but that’s a *lot* of solder paste.

Into my reflow oven (Controleo 3 driving a B&D toaster oven), let it cycle, seemed fine, here’s the board:

IMG_9499

Not my best work. Frankly, it’s a mess; there are obvious places where there is no solder, and obvious pins that are bridged together. I spent about 15 minutes with my VOM testing for continuity and there were 3 solder bridges and 7 unconnected section.

Something clearly went wrong. And I went back to PCBNew and it was *really* obvious.

The layer you should choose for your stencil is F.Paste, not F.Mask. Here are the two next to each other (Mask left, Paste right):

imageimage

The Mask layer sizes are positively giant compared to the paste ones. So, what happens if you use the Mask layer is that you have:

  • A *lot* more paste on the board, especially the small pads which must have double the amount
  • Solder paste with much reduced clearances.

What that means in reality is that when you put the components on, it squishes the solder paste together and connects pads that shouldn’t be connect. And then when you head it up, you either get bridges or one of the pads wins and sucks all the paste away from the other pad (how it wins isn’t clear, but it is clear that the huge MOSFET pads pulled all of the paste from the transistors next door).

This makes me feel stupid, but it is actually quite good news; it means that the design is fine and I just need to remake a stencil with the correct layer.

Anyway, after a lot more rework than I had expected, I ended up with this:

IMG_9500

It’s still an ugly board, but does it work?

Well, I hooked up 5V, GND, and data in to one of my test rigs and a LED to the LED outputs.

And it works; the LED is on when I expect it to be on and off when I expect it to be off. All three outputs are fine.

The next test will be some testing to see how it fares with switching high current. And I’ll probably want to make another one using the correct stencil and hook it up for 12V operation to verify that.





New kit: LED Candy Cane part 1

My first kit – the Dodecahedral Light Engine – has been selling about as well as I expected a very hard to construct project with limited usages to sell, which is not very well. I primarily did it because I was going to do them anyway for my decoration project and wanted a project I could learn on.

I’ve just started working on my second kit, which is going to be a lot easier to build, cheaper, and more widely useful.

One of my favorite displays is a “tree of lights”, which is a tree with custom LED ornaments on it:

The ornaments are made of small sheets of plexiglass with high-power LEDs inserted into the holes, wired up, and waterproofed.

They are really bright; note in the photo that all of the dim lights are normal brightness LEDs, and even at that level the ornaments overpower the camera sensor. They are bright enough that – and I am not making this up – they cast a shadow about 50 feet away when they were at full brightness, so I dialed them back a little in brightness.

These ones are driven directly from 120VAC as that is what the controller provides.

What I want from this project.

  1. A fun, easy-to-assembly ornament
  2. The ability to run off of 5V or 12V (*maybe* 120VAC with a big disclaimer that you shouldn’t really do it)
  3. Tunable brightness
  4. The ability to drive them as WS2811 nodes (see my WS2811 expander posts…)
  5. A frame/armature that is easy to produce automatically (the originals were done with a 5mm end mill in a drill press and took a *long* time).



WS2811 expander part 3: PCB Revisions again…

More revisions.

I posted the design to /r/PrintedCircuitBoard, and of the comments said:

“Do you need pullups on the outputs of WS2811?”

And of course, I was confident the answer was “no”. For about 5 seconds. And then I measured the WS2811 I have in my breadboard; it gave a nice solid sink when it was on, and when it was off, just a fraction of a volt. Clearly not up to sourcing current to the NPN transistor.

The most likely explanation is that it’s an open collector output:

The collector on the output transistor is just left hanging – it’s only collected to the external pin. The voltage on an open collector can float up above the internal voltage of the IC as long as you don’t exceed the maximum voltage of the transistor

Open collectors are really useful if you want to have a bus architecture with multiple components able to pull the bus low, or if you aren’t sure what voltage of the output is going to be. Since the WS2811 can be used to drive LEDs tied to either 5V or 12V, it makes perfect sense. And it is confirmed by the internets.

Which means that the circuit needs to get a tiny bit more complicated:

image

Another pullup resistor is added to the mix. Really not a problem from the cost and assembly perspective as the design goes from 9 resistors to 12 resistors.

But, can I fit it in the current board layout without making it bigger?

I should probably add a parenthetical note here that says it’s often easier to go with a bigger layout, and in fact if you are going to hand solder a board, you *should* go with a bigger layout. Though I’m not sure how practical it is to solder the MOSFETS by hand since the base pad is so big…

Anyway, here’s what the board looked like before:

I need to put a resistor between each of the traces that head from the WS2811 over to the transistors. Hmm.

I initially just tried to fit them in there, and with a big of rerouting, I was able to make it fit. Technically.

Then I decided that it would be a lot easier if I moved the vertical ground trace underneath the transistors and used that to provide the ground connection to the transistors. That meant I could move the VCC vias around more easily, and could do the following:

image

The fit in reasonably well.

I *think* it’s ready to order the first version of the board, but there’s one more step. I now have on hand the WS2811 ICs and both kinds of transistors. So, I printed out a design with the copper layers shown, and did a test to see if the components really fit on the board.

image

That shows the WS2811 on the left, the MOSFET on the right, one of the NPN transistors and then a tiny 0805 10K resistor at the top. Everything looks like it will fit fine.

I ordered 3 boards for $7.10 from Oshpark, which is my usual supplier for prototype boards if they are small.


WS2811 expander part 2: PCB Revisions

I’ve done quite a few improvements on the board. Let’s look at before and after:

imageimage

My usual flow is to do some changes, and then load the board into OSHPark and see how it previews. And then make changes.

I’ve probably redone the majority of the traces on the board. The big changes are:

  1. I replaced the 0603 resistors with 0805. I’m going to do the components by hand, and the larger resistors are easier to place. And I have a set of 0805s sitting in my drawer.
  2. I realized that I hadn’t planned for chaining together more than one board. After 3 or four revisions, I settled on a single 1×6 header to hold both sections. You can either use two 1×3 headers or one 1×6.
  3. The big headers for power and the LED output were bigger but not a standard connector, since I just wanted them to be easier to solder to. That was stupid. They are now spaced to use standard 3.96 mm spacing (Molex KK line if you want branded stuff), so you can either solder or use a connector. This made the board just slightly taller.
  4. The transistors and resistors have been moved, aligned, spindled, and mutilated.
  5. Added holes for mounting, though it’s probably not needed with a board this small. But I had space.
  6. Added some more labels.

Updated schematic

image

Board shots

I’m thinking this is probably good enough to get my prototype versions built.


WS2811 expander

I’m starting a new decorations project that will involve a fair number of standard LEDs, but not addressable ones. I have a few different use scenarios:

  1. Plug into a standard USB power supply.
  2. Power directly with 120 VAC.
  3. Power either with 5V or 12V and have an easily way to control brightness…

The first two are just wiring, but the third needs something more. My target market is quite used to using WS2812 addressable LEDs, so I’m going to build something that works in that environment.

Quick requirements list:

  1. Runs on 5V or 12V.
  2. Uses WS2812 protocol.
  3. Can drive significant loads (at least 10 amps).
  4. Small and cheap

The second requirement is pretty simple; you can buy the WS2811, which works exactly the same way as the WS2812 lights but is in a separate package. And it very conveniently has a little internal power supply that can use 5V or 12V by changing the value of one resistor. Here’s a typical 5V circuit:

image

Looks very nice, and almost does what I want, except that it’s designed to only sink 18.5 mA, which is quite a bit less than my 10 amp goal. I don’t strictly have a use for 10 amps right now, but I will likely need at least 1 amp for some uses.

So, I’m going to lean on the IRLR7821PbF MOSFET that I used in my backyard controller, which it looks like I can get for about $0.14 each. It’s pretty easy to use:

image

I will just drive the gate of the MOSFET with the output of the WS2811, and when the MOSFET turns on, it will pull the LED1 line low, turning on the LED.

Except… the WS2811 outputs are active low, and the MOSFET in this arrangement is active high. So

image

We add an NPN transistor. If the input is low, the transistor is off and the gate on the MOSFET is pulled high by the 10K resistor. If the input is high, the transistor is on, the gate is pulled low, and the MOSFET is off.

That will be duplicated for all three channels, and we end up with the following:

image

R9 and R10 are really just empty holes; you bridge R9 with wire if you want to use 5V and R10 if you want to use 12V.

I unfortunately generally forget to take snapshots during PCB design, so here’s the V1 state:

image

The MOSFETs have lots of 4s on them – I don’t know why – and to the left are the bipolar transistors and the resistors required for that part of the circuit.

The power input holes and the LED holes are designed to use Molex KK 396 headers and connectors so you can either use those or hand wire.

The lower left shows the jumper locations to set voltage.

All resistors are 0603 sized; that makes them compact but still relatively easy to populate.

The only weirdness are the three through-holes next to the LED terminals. I need to tie that backside ground trace to the frontside MOSFET terminal, but I was having trouble fitting enough vias to carry the current. Instead, I just used the through holes, which will be filled with solder and therefore be able to carry plenty of current.

The board is about 40mm x 28mm in size. I might jump up to 0805 resistors to make it a little easier to fabricate.

Before I send it off to be fabricated, I need to have the transistors in hand so I can verify the layout works.






Connecting the Eagle Controller to a WS2812 strip

To connect the Eagle controller is simple; there are only three connections to make:

image

The following connections need to be made:

  1. The black wire from the strip (or globe) should be connected to the ground pin
  2. The red wire should be connected to the 5V (5 volt) pin
  3. The data wire (purple from the globe) should be connected to the RX pin.

This will be enough for the controller to work if powered through the USB mini jack. This is fine for testing, but has several drawbacks:

  1. Each WS2812 LED will draw 60 mA of current if it is full bright. There are 33 on the globe, which means that full white will draw 60 * 33 = 1980 mA = 2 amps. The USB connector will not be able to supply that amount of power, so you will not get full brightness.
  2. The Eagle controller has a diode so that external power will not power the USB jack. This means that instead of getting 5V to the strip, you get about 4.4 volts to the strip. It also means that there is a lot of power being dissipated by that diode, and it will get *hot*; hot enough that it or other components on the board may fail.

To avoid these issues and enable full brightness, you need an external 5V power supply that can supply sufficient current. It can be connected to the 5 volt and ground connections.

Using the connection board

Newer versions of the controller ship with a small adapter board to make these connections easier.

image

We will start by soldering a male header to the series of pins on the right side of the controller with the pins sticking out underneath. You can get by with just using pins for 5V, ground, and RX, but there’s no harm in soldering all 8 pins. Here’s how I do it:

image

Place the header pins into a solderless breadboard with the appropriate spacing. We put pins in on both sides so the board will sit level, but we are only going to be soldering the ones at the top.

This step may have been done for testing purposes.

It should look like this when the pins are soldered:

image

Now, we need to solder a female header to the adapter board:

image

The header should stick out above the board in this orientation. To do the soldering, I balance the board on the female header and use the other strip of female header to hold the board level:

image

Solder all 8 pins across the top.

image

This is the controller with the male header and the adapter board with the female header. The male header simply plugs into the female header.

image

The wires to the LEDs are then connected to the upper 3 terminals on the adapter board, and the 5V power supply is connected to the lower two terminals.

Compact option

If the controller and the adapter are too thick, there is an option that is thinner:

image

In this option, the female header is omitted and the adapter board is soldered directly to the male header pins.

If you are really tight for space, you can solder the male header, remove the black plastic that separates the pins, and then slide the adapter board right next to the controller.




DLE (Globes of Fire) Part 5 – First Board!

When a new telescope is completed, one of the big milestones is known as “first light” – the first time that the telescope is used as it is intended.

Now that I am the proud owner of a reflow oven – a modified Black & Decker toaster oven fitted with Whizoo’s Controleo3 reflow oven kit – and I have a new version of my boards back – it’s time to think about how to build these things in a reasonable way.

The plan is obviously to switch from hand-soldering to reflow. To do that, the first thing that I need is a stencil that I can use to apply solder paste. Thankfully, kicad makes this really easy; you can modify the solder pad tolerances in the program, and the pcb editor can write out SVG files (thanks to Rheingold Heavy for this post). If I have the pads, I can easily cut a stencil, likely out of mylar because it’s a bit cheaper than Kapton is.

That would give me a way to do a single board if I could hand-align it closely enough. But each of the globes needs 12 of these boards, and hand-aligning is a pain.

So… what my real plan to do is to cut holes in a piece of hardboard (or cardboard) that will hold a number of the boards (12 or 24) and then a matching stencil. If I align the stencil one, then I can put solder paste on all of them.

IMG_9223

So, here’s the test. I took the pad svg and the board edge svg, joined them in inkscape and then cut them on the glowforge. As you can see, the boards fit perfectly into the cutouts, and the solder pads cut correctly. Next I will need to do a better version of this, with different colors for the pads and board edge so I can turn them off and off when laser cutting. I’m also probably going to cut holes for some posts that will give me registration between the board with cutouts and the stencil.

You can also see the first two boards that ran through the reflow oven. I did the solder paste without a stencil and I also skipped baking the LEDs since they showed up in a factory-sealed pack and have been sealed since, and both boards came out fine. And a 10 minute reflow cycle is a lot quicker than hand soldering…


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