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A project log for OSPb - An Open Source Lead Tester

An open source design for an inexpensive colormetric test.

Matthew EdmondMatthew Edmond 04/19/2016 at 14:132 Comments

Well this is interesting. I overlooked the fact that the Pi does not have analog in, so a simple photodiode like the I've procured needs a RLC circuit or ADC to work. A quick google search that there are libraries for the RPi to so some image processing using a webcam. Hmm...a webcam measuring incident light rather than a pin diode. Decisions decisions....

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Matthew Edmond wrote 04/19/2016 at 16:10 point

I was hoping to avoid SPI or I2C, but I may bite the bullet and order this. It looks like a good prototype board and as you mentioned lends itself well to scale. Thanks!

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ajlitt wrote 04/19/2016 at 14:58 point

Have you considered using a single source of light and a color sensor like this: 

https://www.sparkfun.com/products/12829 ?  It has ADCs and filters onboard, and could attach to the Pi via I2C.  The chip on that board is about $3 in small quantity, and there are other similar parts from other vendors.  Just add a white LED for the broad spectrum light source.

If/when you want to move beyond prototype, you could put that chip and a surface mount LED down on a single PCB and make a printed or molded sample holder with baffles like your design.  That would make the device smaller and cheaper to build.

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