If you already have a camera then this project will cost less than $50 to complete. If you like to shop on AliExpress you can probably build it for around $30. If you like to support your local middleman, more power too you, but it will cost a little more. The giant screw shown above was made from a regular drywall screw captured using this scanner and a Nikon DSLR.
Desktop 3d scanning has made great leaps in recent years but it still has great limitations. Scanner hardware is built around a specific scan volume and resolution. You can get decent results, but only if your object fits that sweet spot. If your object is too small, or too detailed or your scanner is just having a bad day your scan will look like a potato. Luckily there is another approach. Photogrammetry uses a set of regular 2d photographs taken from all angles around an object. If a point on an object can be seen in at least three pictures then its location can be triangulated and measured in three dimensions. By identifying and calculating the location of thousands, or even millions of points the software can build up an extremely accurate reproduction. Unlike a hardware based scanner there are no size or resolution limitations to this process. If you can photograph an object you can 3d scan it. It works from molecules to galaxies, or it would if they would ever approve my Hubble time.
The limiting factor with photogrammetry is the quality of the photographs and thus the skill of the photographer. Photos must be well exposed and in razor sharp focus. They must also be spaced around the object so they capture every part to be scanned and they overlap enough that the software can figure out where each shot belongs. With large objects this can be done manually with some practice, but it is virtually impossible to do it well with a small object. This scanner automates the process.
A high quality photogrammetry scan requires high quality photos of the subject from all angles. The easiest approach for scanning small things is to rotate the subject while photographing it. This scanner uses a stepper motor controlled by an arduino board. The stepper turns the object by a fixed amount and then an infra red LED fires off fiendishly clever series of blinks which mimics the camera's wireless remote. The camera being rather gullible and wishing to please takes the picture.
An lcd display shield with a set of buttons allows the user to control the arduino. Using the buttons the user can select the number of pictures to be taken per revolution. The scanner can run in automatic mode where it takes a picture, advances the stepper and repeats until it has completed a whole revolution. There is also a manual mode where each push of the button takes a picture, advances the stepper and waits. This is useful for scans where each picture needs to be framed and focused manually.