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DIY Comparatron Helps Trace Tiny, Complex Objects

Hackers frequently find themselves reverse-engineering or interfacing to existing hardware and devices, and when that interface needs to be a physical one, it really pays to be able to take accurate measurements.

This is easy to do when an object is big enough to fit inside calipers, or at least straight enough to be laid against a ruler. But what does one do when things are complex shapes, or especially small? That’s where [Cameron]’s DIY digital optical comparator comes in, and unlike commercial units it’s entirely within the reach (and budget) of a clever hacker.

The Comparatron is based off a CNC pen plotter, but instead of a pen, it has a USB microscope attached with the help of a 3D-printed fixture. Serving as a background is an LED-illuminated panel, the kind useful for tracing. The physical build instructions are here, but the image should give most mechanically-minded folks a pretty clear idea of how it fits together.

So how does it work? One places the object to be measured onto the illuminated bed, and the software shows a live microscope view, with a tiny cross-hair in the middle of the video. By jogging the microscope around — which the platform is capable of doing in increments as small as 0.1 mm — one can visually mark a series of points on the object, creating a sort of point cloud.

Because the distances between these points are recorded by physically moving the microscope in known, real-world amounts, the resulting “point cloud” accurately reflects real-world points on the actual object. From there, one simply exports as a DXF, then imports into the CAD software of one’s choice. The last step is essentially connecting the dots. It requires some patience from the operator, but it’s highly accurate, and the price is certainly right.

The popularity of 3D printers has helped make CNC hardware cheaply accessible to hobbyists, and their precision makes them attractive foundations for projects that measure small distances. You can see [Cameron]’s Comparatron in action in the video below.

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