Build Instructions

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• 1

  Step 1

  Note: I've started converting these instructions into PDF format, and uploading them to my project Files section. These will ultimately be combined into a single large PDF file that will serve as a full manual for building and operating the system. The manual will be kept fully up to date; I will try to propagate updates to these instructions, but can't guarantee how frequently this will happen. And, these instructions are huge, and take a long time to appear in your browser. So, I strongly urge you to use the PDF files as your guide for building a system.

  Addendum: Jean Roc Morreale has created a Read the Docs page that incorporates these instructions. Looks really nice, and I expect I'll try to keep both that site and the PDFs up to date at the expense of these instructions at Hackaday. You've been warned.

  These instructions are going to be excessively, even painfully detailed, especially if you're an experienced maker. Apologies for that upfront. A lot of the people who would benefit from using this system aren't necessarily makers (archaeologists, paleontologists, numismatists, museums), and I'm hoping that by making the assembly process as clear as possible, they'll be more likely to make one of these gizmos.

  Quick note: Clicking on any picture will open it full-screen in browser; if there's a magnifying glass for a cursor, clicking will zoom to full resolution.

  This first section will deal with prepping the dome for installing the LED lights on the inside. This boils down to two operations:

  1. Marking the positions where the LEDs will be mounted on the inside, so that they'll still be visible after you paint the inside of the dome.

  2. Painting the inside of the dome matte/flat black, to minimize scattered light.

  By now, you've hopefully read the two project logs (one, two) on how to select a dome, have ordered it, and now have it sitting before you, like this one:

  (Note: not exactly like this one - I've already marked the LED positions and painted the inside. But I'll use it as a model for this section.)

  When construction is completed, and all the LEDs installed, the inside of the dome will look something like one of these:

  Interior of 12" diameter dome

  Interior of 18" dome

  The LEDs are mounted in rows with shifted columns, with even/odd rows lining up; this is to maximize the variation in angular position. The 12" dome has 48 LEDs in 6 rows/8 columns, while the 18" dome has the maximum of 64 LEDs, 8 rows and 8 columns. 8 rows and 8 columns are the maximum, but you can have fewer than those. It's even OK to have rows with varying numbers of columns, but I don't recommend it - it makes wiring the system and managing the software a real pain. Plus, you want to have the LEDs spaced uniformly in angle for best results, and that can be tricky with varying column counts. So the first thing to do is figure out where the LEDs will need to be mounted inside the dome, and mark those positions. It's best to do this before you paint the inside of the dome black.
  

  Before proceeding, a quick comment about accuracy. While getting the rows and columns laid out evenly will make assembly easier, you shouldn't get too obsessive about accuracy, as small errors won't make that big a difference in the results you get from the system. While the software needs to know the positions of the lights in order to do its calculations, it gets those positions from a calibration file that's generated from the actual light positions. So even if one or more lights are a bit "out of line" with others in their row or column, it won't make a significant difference in the results, since the calibration file will take that into account.
  

  Part A. Determine and mark the angular positions of the columns.
  

  1. To find the angular spacing, just divide the number of columns into 360 degrees. So for 8 columns, the spacing would be 45 degrees; 60 degrees for 6. I wouldn't use fewer than 6 columns, and 8 is preferable to 6.

  2. Place the dome on a sheet of paper large enough to allow you to trace a circle around the edge of the dome flange, then trace the circle.

  Trace circle; dome obscures about half of it.

  3. Find the center of the circle you've just drawn. There are several methods you can use (ask Google), but this one is probably the simplest and cleverest.

  Center found!

  4. Erase all the lines you've drawn except one, which you'll use as a reference. Using a protractor, and the reference line, mark the angles at the spacings you determined in A.1, i.e. 45 degrees or 60 degrees; 45 degrees for the picture below.

  Angles marked at 0/45/90/135 degrees

  5. Draw lines through these marks extending out to the edges of the circle; make an accentuating mark (x, dot, whatever) where the line and circle intersect.

  Lines intercept edge of circle at 8 points (45-degree spacing)

  6. Draw one additional mark halfway between two of the accentuating marks. You can determine the position by eyeball, or more accurately with a protractor used to bisect one of the angles (e.g. 22.5 degrees for a 45 degree spacing as it is in this example, 30 degrees for a 60 degree spacing). Differentiate it clearly from the other marks. The reason for this mark will become clear shortly.

  Extra mark at 22.5 degree angle

  7. Place the dome back on the paper so that it is centered inside the traced circle. Mark the flange clearly at every position where the angle lines intersected the circle. You may find it tough to find something that can temporarily mark acrylic plastic. Sharpies work, and the mark can be removed by rubbing with a paper towel soaked in WD-40; other solvents may work, but test them first to make sure they don't dissolve the plastic.

  Dome flange marked at 45-degree increments

  8. Now take the dome and rotate it in the traced circle until one of the initial marks lines up with the mark created in step A.6. Repeat the process of marking the dome flange at all the positions where the angle lines intersected the circle; try and differentiate this mark somehow from the first set (different color, put a slash through it, etc.). You have now marked the angular positions for all the columns. Half the rows will have their LED columns lined up with the first set of marks, the other half will be lined up with the second set of marks.

  Second set of marks spaced at 45 degrees, located between first set of marks

  Step B. Determine the heights of the rows, and mark the LED positions on the dome.

  1. Using standard RTI guidelines, the lowest angle the LEDs should be mounted is at 15 degrees above the plane of the ground; below this lighting angle, the object you're photographing may be too dim. The highest angle should be somewhere around 65-75 degrees; above this, the object may be too bright. With your desired top and bottom angles, the number of LED rows you'll be installing, and the size of the dome, you can figure out the proper spacing on the rows.

  Example 1: My big dome (18" dome diameter, 8 rows of 8 LEDs, 16 through 72 degrees). With 8 rows, there will be 7 angular gaps between the rows (8-1). The total angular distance between the low and high rows will be 72-16=56 degrees. The angular distance between individual rows will be 56/7=8 degrees. So there will be rows at the following angular positions (where bottom = 0 degrees):

  16
  24
  32
  40
  48
  56
  64
  72

  To figure out the true arc distance up the side of the dome these angles correspond to, divide the angle by 90, then multiply by 1/4 the circumference of the dome. For an 18" diameter, the circumference is 18" x pi, or about 56.4"; 1/4 of that is 14.1". Divide the table above by 90 and multiply by 14.1", and you get (after rounding):

  2.5"

  3.8"

  5.0"

  6.3"

  7.5"

  8.8"

  10.0"

  11.3"

  So these are the row distances above the base of the dome/flange junction. But the columns in adjacent rows will be shifted by half the angular spacing, so you should group the heights into two staggered sets of rows (each set has LED columns aligned with each other):

  2.5"

  5.0"

  7.5"

  10.0"

  and
  

  3.8"

  6.3"

  8.8"

  11.3"

  Example 2: The small dome (12" dome diameter (the size of the dome I'm building here), 6 rows of 8 LEDs, 15 through 65 degrees).
  

  Angular distance between high&low = 65 - 15 = 50.

  Angular distance between individual rows = High&Low / (# rows -1) = 50 / (6-1) = 10 degrees between rows.

  Row angles = 15, 25, 35, 45, 55, 65.

  1/4 circumference = 12" x pi/4 = 9.4"

  Row distances (from bottom) = 1.6", 2.6", 3.7", 4.7", 5.7", 6.8"

  Row distances paired by column alignment = 1.6", 3.7", 5.7" and 2.6", 4.7", 6.8"

  If this isn't 100% clear, just keep reading - hopefully after you see the actual marking operation, you'll understand.

  2. Now you need some way to mark these distances on the dome. Take a piece of string, make one mark on it to indicate the zero reference point, and then measure and mark positions for the first set of row distances on that piece of string (1.6", 3.7", 5.7" in this case). Create a similar second string for the other set of row distances (2.6", 4.7", 6.8"). Taping the ends of the strings down while marking them helps keep them straight.
  

  Marking sets of distances on two string segments. The long marks at left mark the zero point on the right edge of the mark. These are distances for the 12" dome, Example 2.
  

  3. Tape the first string to the dome at the base with the flange at one of the marked angles, so that the zero distance mark is at that base. Tape or hold the other end of the string on the top edge of the hole, making the string as perpendicular to the base as you can. Make marks on the dome next to the marks on the string. Repeat this for all matching marks with the same angular spacing as in A.1.

  Marking the first set of columns

  4. Repeat step B.3 with the second piece of string, on the other set of marked angles (the ones offset by half the spacing of the first set; these should lie exactly halfway between the first set of marks you made).
  

  Marking the second set of columns

  And this is how the dome should look when you're done when viewed from above:

  48 marks on this dome for 8 columns x 6 rows of LEDs

  Step C. Transfer the marked positions to the interior of the dome.

  The marks on the outside of the dome correspond to the positions of the LEDs on the inside of the dome. Thing is, you're about to paint the inside of the dome black, which will make it difficult to figure out what the corresponding position is. So, before you paint the dome, you'll need to put some kind of mark on the inside that will remain visible even after you paint it. There are several options:

  a. Put a blob of paint or nail polish on the inside of the dome at the same position as the mark on the other side.

  b. Drill or scratch a small dimple at the same position as the mark on the other side. Be careful with this approach - I used an electric drill with the dome picture above, and came close to punching through the dome in several spots. Do it by hand and you should be OK.

  c. Put a tiny piece of masking tape in the matching position, and peel it off after you've painted the inside.

  d. Got a better idea? Let me know!

  By the way, this is why I recommend either a clear or white dome; both of those make it easy to see where the marks are on the outside of the dome when you're looking at the inside. A dark-colored dome makes this a lot tougher.

  Once you've marked the interior positions, you can remove all the marks from the outside, including the flange marks. If you use WD-40, take care not to get any on the inside of the dome.

  Step D. Paint the inside of the dome.

  To minimize scattered light, the inside of the dome should be painted flat/matte black. Simplest (and probably best) way to do this is with spray paint. Use a brand specifically labeled as being appropriate for plastic, with the color marked as "flat black" or "matte black" to minimize reflections. Avoid "satin" or "glossy" finishes. My preferred brand is Rustoleum Flat Black Ultra Cover Paint + Primer ; Krylon will work, but seems to require more coats.

  1. Make sure interior of dome is clean and dust-free; use soap and water if necessary, then dry completely. Instructions suggest lightly sanding the inside, but that's not really necessary for this application, as long as the surface is clean.

  2. Cover the outside of dome with masking tape to protect it from stray spray paint. Pay special attention to the hole at the top, as that's the most likely place for paint to leak through.

  3. Follow instructions on paint can. Apply paint to inside of dome in steady back-and-forth motion, overlapping strokes. Not too heavy, or you will get drips/runs inside the dome. You will almost certainly have to apply more than one coat to achieve full light blockage. Allow the first coat to dry for a few minutes, then apply a second coat. I'd even recommend a third coat if you have enough paint left. Let the final coat dry to the touch, then remove the masking tape from the outside. Hold the dome up to a bright light source (the sun works great for this), and check to see if you've put on enough paint to block all the light. If not, re-mask and put on another coat. The Rustoleum instructions say you should put successive coats down less than one hour before applying the previous coat, or after 48 hours.

  4. Set the dome aside to dry. The instructions on the Rustoleum can say that it takes 5-7 days for the paint to fully bond with the plastic, but don't worry too

• 2

  Step 2

  Next few instructions steps will be on building the high-side driver side of the controller. This has the P-channel MOSFETs that control the plus-side voltage to the LEDs, through the columns of the LED matrix. These will be installed on the Arduino Mega Shield, which plugs directly into the Arduino Mega control board:

  On the bottom are the pins that go into the female headers on the Arduino. This shield makes connections with the Arduino so easy and convenient, I had to use it. But there is one drawback: the limited amount of space you have for components. There is just barely enough room for every component needed for the MOSFET drivers, as long as you place them correctly on the board. I will show you where everything needs to go, modify these positions at your own risk.

  The first set of parts is easy, and is good warmup practice if you haven't done any soldering recently. You'll be soldering a female pin header to the right side of the board - this is where the protoboard with the minus-side current controllers will plug in and connect to the Arduino. Then, you'll be soldering eight resistors in that will eventually connect to transistors that control the P-channel MOSFETs (but more on that in the next set of instructions).
  

  First, grab the 20-pin right-angle female header:

  And stick it into the 20 holes on the far right side of the shield. Don't do what I almost did, and stick it in the holes to the left of the correct ones! If you've got something you can use to clamp it in place (binder clips, alligator clips), use those to hold it in place:
  

  
  

  Now flip the shield over, and solder the pins at opposite ends. Once you do that, you can remove the clamps/clips and solder the remaining pins to the holes:
  

  Next, you'll be soldering 8 10K resistors to the shield; these will eventually be connected to the bases of the 2N3904 transistors, which will in turn control the P-channel MOSFETs. One lead of each resistor will go into a hole immediately to the left of the header you just installed, the resistor will straddle another set of soldered pins on the shield (the ones marked 36-52), then most of them will have their other lead go into the holes directly to the left of the number labels. When you solder the resistors, give them enough height that they clear the soldered pins on the left, or you might have problems with shorting. If you like, you can put a thin strip of electrical tape on top of the pins, or paint them with nail polish or rubber paint, to make sure they don't short out the resistors.
  

  Start by putting the leads of the first resistor into the shield, as in the picture below. Note the hole positions - on the left, the hole at bottom right on the shield, on the left, the 4th hole from the bottom:

  Flip the shield over, and you'll see the two leads sticking out:

  Now solder the resistor leads to the holes they're in. Put the next resistor into the next set of holes (above the first set), and continue until you've done all 8 resistors. If you have trouble getting the resistors to stay in place when you flip the shield, you can bend one or both of the leads down to hold it more securely:

  When you're done, the top of the shield should look like this:

  On the opposite side, leave the leads for the first and fifth resistors from the top uncut (you can bend them down to get them out of the way if you like), and trim the leads for the rest to a length of about 1/4":

  Next up: installing the MOSFETs and associated parts.

• 3

  Step 3

  Now it's time to solder in the high-side driver channel components - P-Channel MOSFET, npn transistor, and 10K resistor. Here's a rough schematic for one driver:

  You've already installed the 10K resistor at left, though it still has to be connected to the driver (a future step). So this section will deal only with the MOSFET, the npn transistor, and the other 10K resistor. Here's a pic of the MOSFET; note that the position of drain and source in my schematic are swapped compared to the actual MOSFET (gate is correct):

  And here's a pic of the npn transistor:

  A few cautions before you begin. Some of these may seem obvious, even insultingly so. But I'm including them because I've either come close to making all these mistakes, or have actually made them and had to go through the pain of fixing them.

  1. MOSFETs are notoriously sensitive to static discharge. Make sure you've discharged any static buildup before handling MOSFETs. If you have a grounding wrist strap, now would be a good time to put it on.

  2. Make sure you install both transistors in the correct orientation.

  3. Remember that when you flip the shield over, what was on the left is now on the right, and vice-versa; make sure you're making the right solder connections.

  4. When trimming leads, check to make sure the trimmed lead doesn't wind up wedged someplace where it can cause a short. This has happened to me several times, and can drive you crazy as you try to figure out why things aren't working.

  Here's a picture of the shield board, with the location of the first MOSFET circled in red:

  Insert the MOSFET into the marked pins, with the black labeled side facing to the right of the shield; solder one pin in place to fasten it to the shield:
  

  It can be tough to solder it upright - what I usually do is solder it in place at any angle, then re-melt the solder while pushing he MOSFET until it's perpendicular. Careful - it can get hot.

  Next, the 10K resistor is put as shown in the picture below, with one lead in a hole right next to the source pin, and the other lead two rows up and one row to the left of the gate pin. Pull the leads tight from the underside so that the resistor is flush with the shield board, using needle nose pliers if necessary.

  Flip the shield over, and bend the resistor leads so that the one closest to the source pin is flat and next to the source pin, while the other lead is bent parallel to the MOSFET pins:
  

  Now it's time for the 2N3904 npn transistor. The lead spacing on this resistor is smaller than the hole spacing on the shield, so you'll have to first gently spread the leads further apart until they will fit into the shield. Then insert the transistor with the flat part facing the MOSFET, and the curved part facing to the right side of the shield:

  Note that the three npn transistor pins are in the same rows as the MOSFET pins.
  

  Flip the shield over, and bend the collector pin down over the resistor lead and next to the MOSFET gate pin (better than I did in this pic):
  

  Now solder the collector pin on the npn transistor to the gate pin on the MOSFET; the resistor lead under the collector pin to the collector pin; and the other resistor lead to the source pin:
  

  Trim off the excess lead on the resistor leads, and on the collector pin:

  And that's it - you've created a high-side p-channel MOSFET driver circuit! Hope you enjoyed that, because you'll now have to repeat the process 7 more times for the remaining high-side driver circuits. Here's a picture showing the locations of all the MOSFETs, including the one you just did:
  

  Just follow the exact same steps as the first driver circuit for all the successive ones. It's best to work left to right on the shield when installing the driver circuits, as it gives you the easiest access to the board when installing parts. When it's all done, the shield should look like this on top:
  

  And like this underneath:
  

  
  

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