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Parts, Parts, Parts

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 06/21/2016 at 03:570 Comments

Well, I think I've got the components list done. But wouldn't surprise me if I missed an item or two; will update on the project log if that happens. Just for reference purposes, I'll talk about elements of the components list here with a description of what every part is supposed to be used for; hopefully, that will make the design and assembly process more understandable. Check the original components list for required quantities.

A few comments on parts suppliers. For many of the discrete components, I link to a Tayda Electronics page. These guys have great prices on discrete components even in small quantities, they ship fast, and the shipping costs are very reasonable. For parts/items they don't have, I use Digikey - great service and fast shipping, but prices tend to be somewhat higher for many components. I also link to pages on eBay, AliExpress, Amazon and other vendors for various items not found on Tayda or Digikey. But feel free to use your own favorite vendor.

Three general categories: controller parts for the main control unit, dome parts for the RTI dome itself, and camera parts for the odds and ends that you'll need to connect your camera to the controller for automatic shutter control.

Controller parts

Arduino Mega 2560 R3 Controller - Main control unit. I've used several brands of less-expensive clones without problems. R3 is the most recent model, with the fastest processor, but if you have an older non-R3 unit, that will work as well.

Power supply - Any Arduino-compatible power supply should work, as long as it's rated for at least 2A current (9-12V OK but 9V recommended, 2.1mm x 5.5mm barrel jack, center-positive.

Battery power supply (optional) - Required for portable operation. Uses 6 AA alkaline batteries. The linked item already has a standard Arduino jack (2.1mm x 5.5mm barrel jack, center-positive), but you can certainly hack together your own as well. If you plan to use rechargeable NiMH batteries, you'll need a holder that takes 8 AA batteries, since NiMH batteries have lower voltages than AA (1.2V vs. 1.5V each).

Arduino Mega protoshield - A handy protoboard that plugs into the Arduino Mega, and has room on top to solder in the high-side driver components (albeit just barely). Make sure the one you buy looks like the one I link to.

11 x 8.5 cm protoboard - I highly recommend the one I link to, as it's cheap, the right size, and the metal goes all the way through the holes producing a secure solder hold. On cheaper protoboards, the metal is often just a little disk on top, and has a tendency to fall off.

10K linear taper potentiometers and knobs - Control the duration of the light, and the delay to allow the camera time to process and save the image before taking the next picture. 5K will work fine as well, and feel free to choose any style knobs you want.

Momentary push buttons (red and black) - Activate key functions, and one red button also resets the Arduino.

Toggle switches - Set options: sound on/off, manual/auto mode, shutter hardwire or IR/Bluetooth mode.

Red LED, panel LED holder, 560R resistor - For power indicator that hooks up to 8-12V power supply. I use a 560R resistor because 8 of those are needed for another purpose, and minimum resistor order from Tayda is 10. If you have a 470R resistor, you can use that instead.

USB Female A Panel Connector - Main jack for hardwired camera shutter connections, and also for the IR LED if you use a camera with LED remote capabilities.

Ethernet RJ-45 panel jack - The controller connects to the dome through Cat5E cables, which plug into these panel jacks.

RJ-45 Jack and breakout board - One RJ-45 jack is mounted internally, and the breakout board is needed to mount it to the protoboard.

CAT4101 LED Driver and breakout board - CAT4101s are the main switch/drive/current controller on the low side. They are surface-mount devices, so breakout boards are needed to use them on the through-hole protoboard.

0.1 uF disc capacitor - Use to suppress noise on input of CAT4101.

560R resistors and 5K trim potentiometers - CAT4101 use a resistor to set the desired currrent, with lower resistances yielding higher currents, up to 1 A max. The 560R resistor sets the maximum allowed current of 1 A; the trim pot is in series with that resistor, allowing you to set lower output currents if desired, as well as allowing you to fine-tune the output of all eight CAT4101s so that they match.

10K-ohm resistors - Used in several locations to limit currents.

IRF9540 P-Channel Power MOSFET - High-side switch to LED matrix; controls columns.

2N3904 NPN transistor - Controls IRF9540 MOSFETs.

Power strip protoboard - There are a lot of ground and +5V/+9V connections required, more than are available on the Arduino itself. The power strip protoboard adds extra female pin headers to accommodate those connections.

100 uF capacitor - Smooths out any major variations in the 9V input.

Piezoelectric buzzer - For audio feedback of several functions. Can be turned off in hardware or software.

Heat sinks (7mm x 7mm to 10mm x 10mm) - These probably aren't necessary. The MOSFETs are rated to operate continuously at up to 13A at 100C, and they will never see more than an amp for a few seconds at a time at much lower temps. The CAT4101 drivers will need to burn off more voltage, but even they won't be on for long periods, and have a thermal shutdown at 150C. Still, just to be safe, I use small heat sinks on both. I recommend getting heat sinks that come with tape adhesive in place - makes installation a lot easier.

Various headers - Used for wiring connections.

Dupont pins (male and female) - Used primarily for the LED wiring connections, but also in a few other locations. Housings needed for the female pins. If you live near the sea and corrosion is an issue, consider getting gold-plated Dupont pins, available on eBay; just slightly more expensive.

Black and red 22 AWG solid hookup wire - used for making connections inside the controller. Red and black to keep track of hot and ground connections, respectively. I say 10 ft. of each, which is probably more than you'll need, but it's cheap.

Black Kynar insulated 24 AWG solid wire - The main wire for connecting LEDs inside the dome, and protoboard interconnections. One 100-foot roll is probably enough for domes up to 24" in diameter; larger domes may require a second roll.

The next set of parts is for the enclosure that will hold the electronics, and into which will be installed switches, pots, LEDs, panel jacks, etc. Feel free to design and construct your own, using my model as an example.

Plastic enclosure box - This was the only pre-made one I could find that was big enough to hold everything. It's a nice box, but kind of expensive- shipping almost doubles the price.

Rubber feet - To put on the bottom of the enclosure box, to keep it from sliding around,

Mixed nuts, washers, bolts, screws, spacers - Attach the main control electronics to the box.

RTI Dome Parts

What you need to build the RTI dome, to light up the object from multiple angles and take photographs through the top.

Dome - I've already posted here and here on what's required for your dome. Deviate from these recommendations at your own peril.

Flat/matte black spray paint for plastic - Used to cover the inside of the dome, to minimize scattered light from the interior. Make sure whatever black paint you choose dries with a "flat" or "matte" non-reflective finish - avoid "satin" finishes, and "glossy" is totally unacceptable. Also make sure the paint is specified as working with plastics. I found Rustoleum works best; Krylon also works, but requires more coats.

Black reflective sphere - This will be used to calibrate the dome LED positions. I reference a high-quality silicon nitride bearing, but any decent black reflective sphere will work. This includes black marbles, stainless steel ball bearings dipped in black ink, or obsidian spheres for larger systems. For proper calibration, the sphere must have a diameter of at least 250 pixels when photographed from the top of the dome.

LEDs - The system was designed to handle up to 3W LEDs mounted on star bases for heat sinking. I highly recommend Cree LEDs, and I also highly recommend buying from a reputable source. I made the mistake of buying "Cree" LEDs at bargain prices from Chinese vendors, which suffered from non-uniform intensities and wildly varying color balances. Official Cree LEDs are binned to match fairly closely in intensity and color balance. My vendor of choice is LED Supply - decent prices, volume discounts, and they ship quickly. Buy a few more than the minimum you need, in case you have problems in assembly, or wind up with a bum LED or two. New models of LED come out on a regular basis - my current choice is the 3W neutral white XP-E2 variety, 1up star. For domes 12-14" diameter, I recommend no more than 48 LEDs; 15-17", 56 LEDs; 18" and up, 64 LEDs (the maximum number the controller can handle).

2mm heat shrink tubing - To insulate LED wiring connections.

Cat5e 24 AWG Ethernet patch cables - These are used to connect the dome to the controller. I spec 24 AWG to maximize the current capacity and reduce resistive heating - I've run 1 A through the individual wire strands continuously for up to an hour without any significant heating. Monoprice is an awesome source for these, as well as any additional USB cables you might need. I spec 5 ft., but choose a longer length if you want more flexibility; you'll be cutting one end off of these, so you can always shorten them if necessary during the system build. I strongly recommend that one of the cables you buy be red, to be designated as the positive/high connection to the dome. For the other cable, pick any other color - I usually choose a color to match the dome (black or white for all the ones I've built to date).

4" cable/zip ties - Used to tidy up cables inside the dome. Available everywhere; I usually pick a color that matches the exterior of my dome.

Camera cables

If you haven't already, read my log on camera considerations for additional background on these parts. I highly recommend Monoprice for all your USB cable needs.

Canon camera with CHDK:

All you need is the standard USB cable that plugs into the camera on one end, a female USB jack on the other. Depending on your configuration, you may want to get a longer cable, or a USB extension cable.

Camera with IR remote capability:

940 nm IR LED

47R 1/2-W resistor

USB cable

Assembly is easy - just wire the resistor in series with the LED, connect to the USB cable; more complete instructions down the road. Software supports cameras made by Canon, Nikon, Olympus, Pentax, Sony, and Minolta that have IR remote capability. I recommend this option heartily for any camera that supports IR remote; cheapest, easiest and most flexible option.

Camera with hardwired remote capability:

4N35 Optoisolator

220R resistor

Remote connector plug compatible with your camera. You may have to buy a cheap hardwired remote on eBay or Amazon, and then cut off the connector plug.

USB cable

More explicit instructions down the road.

Dome stand

I'll cover this in a separate post - lots of options here, as well as the freedom to set it up anyway you want.

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