Many companies now market 'Vein Finder' products, but these products can cost over $5,000 (depending on quality and utility). That price tag is often outside the means of smaller clinics or facilities. This is a guide intended for hobbyists and DIY problem solvers -- not staff of a large hospital looking for high-end tech to aid in routine venipuncture.
This tool works by using near-infrared wavelength LEDs to illuminate the flesh at the site. The veins will appear as dark bands because they are more absorbent of this spectrum of light than the surrounding tissue. It is similar in principle to holding your hand over a flashlight (something we all did as kids).
Estimated Time to Complete: 3-6 hours (depending on your plastic cutting and soldering ability)
Estimated Cost: ~15-50$ depending on shipping/availability of free samples/if you need to buy solder, spare wiring, misc.
Below is a quick video of it working, moving it up and down my forearm. It's hard to document how clearly the veins appear because of my camera's minimum focal distance, but this ought to give you an idea (imagine no blur!):
Step 1: Required Materials and Tools
Rotary tool, with attachments suitable for cutting through plastic
Needle Nose Pliers x2 (I found these useful)
Blank Circuit board
Rocker Switch, On/Off (I used)
Resistors, 56 OHM, 250mW, 1% (I used) x30
LED 3mm, 20mA, 1.9V, λ 628nm (I used) x30
Plastic Enclosure with battery contacts and PCB screw holes (I used OKW enclosures' Part# A9072129, with Part#s A9190002 and A0304031)
Friendly Plastic, Black/Black (I bought mine here)
Wire (less than 1' needed)
AA batteries x2
Step 2: Cutting Your PCB and Enclosure
Cut an opening on the side of the enclosure, to fit the switch.
Cut an opening on the top of the enclosure, and then again on the bottom of the enclosure. The bottom hole should be wider, so as to allow the LEDs to peek out, while leaving the middle open.
Cut the PCB board into a 'U' shape (almost like a tuning fork), so that the opening will align with the other two openings you made on the top and bottom of the enclosure.
If necessary, cut away some of the PCB to make room for the switch on the side.
Step 3: The Wiring and Soldering
I've also made the mistake of not including adequate room for PCB mounting screws in my illustration. It's very important that you DO account for these before beginning to solder.
This may sound dumb, but it's important to be careful which side you are attaching the components to -- that the side you've cut out for the switch actually line up. For example, in the drawing, although I've shown the components as if you could see them, they are in fact facing INTO the page, and their wiring facing you, out of the page. See the other photo of the real device to see what I mean.
Step 4: Assembly and Friendly Plastics
But it's not ready to use yet.
If you try it on yourself, you'll notice that the sides of the LEDs emit too much light to clearly see the veins -- regardless of how narrow the LEDs' viewing angle. This is where the miracle of Friendly Plastics come in.
You can read more about how to use them on other sites, or on the manufacture's page but the method that I used was to cut small strips and then heat them in near-boiling water. The strips, although 'hot', have very low thermal conductivity so they will not burn your fingers. This allows you to shape the plastics around the edges of the LEDs, so that they do not emit light into the viewing hole -- only down, into the skin.
Step 5: Test It Out
Now try it on the underside of your forearm; press it into your skin rather than merely hover over it. You should be able to clearly see veins as you pass by them, some you may not have known were there.
Unfortunately it is very hard for my camera to capture the exact effect (intense, bright lighting, coming from a small area to focus on), but I've attached a blurry image which hopefully shows some of the results -- I've drawn thin green lines through the veins I was able to see very clearly with the tool.