handheld reflectometer

We are building a open source reflectometer… and here’s why

“But wait,” you say, “there are already some out there, and they are pretty well designed and reasonably priced!”  Well, yes – there are full spectrometers like the Spectruino ($411), the Open Source Colorometer ($80 + $20 per LED) from IORodeo, and publications from universities describing open colorometer designs (Appropedia and MTU have a good one, but there are several others – these are DIY so < $100 in parts).  Pretty cheap, and lots of available designs.

Like the seat designed for the average person but usable by no one, product designers should avoid the law of averages.  As in that case, the aforementioned devices are too general purpose to be particularly useful.  The MultispeQ ($600) could work, but was designed for photosynthesis measurements and is over-designed for applications outside of photosynthesis.  For our community partners, none of these devices do exactly they need, which is…

Arborists need a low cost and easy to use chlorophyll meter to add more rigorous sensor data to visual tree assessments.

Consumers + farmers need a way to measure food nutrient density in stores and on farms.

Soil scientists and regulators need to measure soil carbon in the field, quickly and easily.  Doing so could create a massive new pathway for carbon markets to value sequestration of carbon in soil.

Cannabis growers, consumers, and dispensaries need to be able to confirm total cannabanoids and THC levels to comply with regulations, ensure quality product, and identify fraudsters.

These cases require a device which is low cost, easy to use by non-scientists, flexible in what they measure (drops of liquids, cuvettes, leaves, aggregate solids like soil, and whole solids like a pear), usable in field conditions, fast, and open source.  Reflectance is a pretty simple measurement and tells you almost nothing without reference data.  Reference data measures reflectance values and validated lab-based measurements on the same set of samples to build correlations between the two (if they exist!).  But building a reference database can be very expensive.  In the case of food nutrition, measuring a small suite of lab tests for vitamins, minerals and antioxidents can cost $500 or more.  A reference database might contain 100s or 1000s of measurements to have sufficient predictive power.  Yikes!  Expect more on solving that problem in a future post… but for now let’s just get an update on the reflectometer.

Pictures and specs

FYI – We are in the initial stages of design, so everything is in flux and I know this is ugly looking.  Sharing too much too early is in our DNA, sorry 🙂

Our core design is based on the open source MultispeQ (a photosynthesis measurement device), which uses LED supplied light sources at 10 different wavelengths, but is much lower cost.  While this isn’t a full spectrometer, it has the advantage of working independent of ambient light (unlike a normal spectrometer or simple colorimeter where the sample must be in darkness) while being relatively inexpensive (cheaper BOM and less time/cost to make/calibrate).

Ideally, we want users to be able to measure soil carbon, leaf chlorophyll content, brix from extracted sap, and the density of a pear fruit all at the same time with the same instrument.  This not only reduces the cost and increases utility, it also spreads our development costs across multiple applications.  The above design accommodates all of these uses.

This includes a digital tape measure, kind of like the Bagel.  As we validate that design more I’ll post more details.

Here is the link to the 3D design files on OnShape https://cad.onshape.com/documents/849be056da41993fee5440bf/w/fca66e62cdc277f2c4c8e7fb/e/e343e4d4ecd695e477fba916.  The hardware and firmware files will be at the Our-Sci Gitlabs page here https://gitlab.com/our-sci.  It’s a work in progress, so expect to see frequent changes over the next few months.  Much of the hardware, software and firmware has already been tested and validated, so we hope is to have a prototype device ready in only a few months.

We’ll keep the updates going between now and then, so stay tuned or sign up for email updates in the footer of this page.

Posted by gbathree