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A project log for Affordable Reflectance Transformation Imaging Dome

A simple and inexpensive way to image and analyze subtle surface details on objects.

leszek-pawlowiczLeszek Pawlowicz 06/25/2016 at 18:440 Comments

Apologies to experienced makers - you probably have/know all of this. This project is potentially of use to many people that might not be makers (like archaeologists and paleontologists), so I'm throwing in a bit of background material on the toolset that's needed. The links are to show you examples of what you'll need (I don't usually own the ones I've linked to) - any equivalent to these tools will be fine.

Absolutely required

If you're going to build this RTI system, you'll definitely need the following tools: buy, beg, borrow or steal.

Soldering tools

The electronics are put together using soldering - for the most part, nothing fancy. If you've never soldered before, it's not that hard. Check YouTube for training videos on how to solder - some are very good. This Adafruit guide is worth a look.

Soldering iron - Don't need a super-fancy one, just make sure it has a point tip on it; I'd recommend 40W or higher, with controllable temperature. You don't want a soldering gun, or an iron with a large chisel tip, as these won't work well for the small-scale through-hole soldering you'll be doing. The linked soldering iron includes a few extras, including some items listed below. I own this one, a bit more control.

Solder - Get the thin stuff, 1 mm (.039") or smaller in diameter; easier to handle, and melts faster. Also make sure it's rosin core.

Brass tip cleaner / sponge tip cleaner for solder - Cleans oxide and unneeded solder of your soldering iron. I prefer the brass cleaner, but the wet sponges work as well.

Wiring tools

Wire stripper - No, the cheap one with the screw adjusted won't work. Get one with fixed holes for AWG wire diameters 22 to at least 26. I use the linked on, but there's a slightly cheaper one by a reputable maker at Digikey.

Flush cutter or diagonal cutter - Used for trimming electrical wires and part leads. The Hakko flush cutter works well and is cheaper, but the diagonal cutter works nearly as well, and you're likely to find it handier for other tasks in the future than the Hakko.

Needle-nose pliers - For inserting parts, bending wires, holding nuts.

Multimeter - Critical for testing the circuits, and measuring/calibrating the output current. Pick one that can handle currents up to at least 1 A (most do up to 10 A).

Alligator leads - Useful for connecting the multimeter to wires; also double as clamps for soldering.

General assembly tools

Crimper - Even with a small dome, you'll be crimping hundreds of Dupont pins, male and female. Technically you could do this with a pair of pliers, but after 50 or so crimps with pliers (and with multiple failures), you will start praying for death.

Electric drill, drill bits - No link for this one, hopefully you have one of these or know someone with one. Largest hole you may have to drill is 1/2" diameter.

1/8" acrylic drill - Acrylic plastic is a pain to drill with regular bits; you'll get lots of chipping, grabbing, and even breaking. This bit has a special design to help eliminate these issues. For larger holes, you can use regular bits after creating a started with this one; just gradually use bits of increasing size until you get to the final size.

Random tools (screwdriver, file, saw, etc.) - A whole bunch of random tools that you may need, but are pretty common.

Silicone adhesive - Used for attaching LEDs to the dome. You won't need a lot of it.

Safety glasses - 'Nuff said.


Optional, but helpful

Head magnifier - If you have young, good eyes, you may not need this. My eyes are old and decrepit, so this magnifier makes soldering and other fine work possible.

Solder sucker / solder wick - If you're a master solderer and never make mistakes, you may not need these - they help fix soldering problems by removing solder. I have both :). Check this video for more info.

Flux - Love this stuff; makes soldering problem connections a lot easier. Cleans off with rubbing alcohol.

Dremel or other rotary tool - Primarily useful for cutting holes in the controller enclosure, as well as general cutting/sanding/filing/milling. You can do all this stuff with other tools as well, it may just take longer.

Heat gun - Used for heat-shrink tubing in this build, special flexible tubing that shrinks when heated to insulate/protect/reinforce wire connections. I don't have a heat gun, but use a hair dryer on the hottest setting put right next to the heat shrink tubing; works, but a bit slow. A lighter or candle flame works on heat shrink tubing as well, as long as you're careful not to melt the tubing or set it on fire.

Anti-static wrist strap - Static discharge is bad in general for electronics, and the P-channel MOSFETs in particular are very static-sensitive. This wrist strap offers a level of protection from static discharge.

Step drill (aka Unibit) - The 1/8" acrylic drill listed above will be good enough for most of the holes you need to drill. However, there are a couple of holes in the dome that will need to be a bit larger. You can drill these by starting with the acrylic drill, and then gradually increasing the size of the drill bit you use until you reach the final size. If you skip too quickly to a larger size, you risk cracking or breaking the dome. A step drill has a conical shape with gradually increasing bit sizes in a single bit - you start with a smaller size, and gradually work your way up to a larger size. I've used these often on acrylic plastic, and as long as you start with a pre-drilled hole, you shouldn't have problems with cracking/breakage as long as you don't apply too much pressure while drilling.

I'm sure I'll think of more tools as I write up the build - watch this space.

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