Inside a Cheap $70 USB Spectrometer
Back on Oct 26, 2017 ago I ordered a "USB Spectrometer" from a company called Thunder Optics in Beauvais, France. The order took so long to arrive that I figured I'd been ripped off and mentally wrote off the purchase. However, just today, 5 months later, my order finally arrived (I guess the $29 shipping charge doesn't buy you much when shipping from France.)
So, what does the inside of a USB Spectrometer that costs only $99 ($70 plus $29 for shipping) look like. Here's what I found when I opened the case:
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Yes, that 's right... The things is put together with "hot snot" from a glue gun. It consists of what looks like a webcam module attached to an aluminum "U" bracket that also positions the plastic grating film in front of the camera's lens.
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Based on the USB Vendor Id of 0x1908 and the Product Id of 0x2311, I concluded that the camera module is probably the same one used in a GemBird USB camera dissected in this article, which says it's based on a Galaxycore GC0309 640 x 480 @ 30 fps 1/9″ sensor with pixel array size 648 × 488 pixels. Or, "probably the cheapest on on the market ever," as the author of that web page says, as he states he was able to purchase the complete USB camera for $3 from an eBay seller.
Light enters the unit through a crudely-cut "slot" in the front plate on the opposite end of the box:
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And, there's a bit of photographic film on the opposite side of the slot that forms the "slit" for the light to pass through:
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As you can see in the following image, the alignment of the camera and grating section with the slot where light enters is at an angle. Perhaps this is needed in order to get the spectrum to fall on a particular area on the sensor, but I found it made it hard to get an image to show up on the sensor when I was shining a light at the input slot.
Needless to say, I'm feeling rather underwhelmed by this "spectrometer's" design and execution. Perhaps I'll feel differently once I figure out how to install the software and plot a spectrum. However, now that I've identified all the components, I imagine that just about anyone with moderate electronic and mechanical skills could easily replicate this design and probably do a bit better on the aesthetics, too. Here are a few other observations based just on taking the unit apart and inspecting it that could be improved:
The film with the input slit tends to come loose from the inside of the front panel (see side view photo above.)
Not only is the input slot cut very crudely, it's also cut at a slight angle.
The only thing in the box I received, was the unit itself. No manual was included, or information of any sort was included.
The box is not exactly light proof. There was a bit of black hot snot around the slot cut for the USB cable, but the front and back plates can seep light where the two plates butt up against the case box.
In retrospect, I'm sorry I didn't investigate a cheaper USB Spectrometer kit available from Public Labs. While the housing is made from black craft paper, the internal design and layout seems better and more flexible and the paper housing could easily be replaced with something more substantial.