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A project log for The Optical Inch

A tiny, ultra low profile wideband spectrometer for everyday needs (test lamps for color temperature & CRI, UV-A /UV-B dosimetry, ...)

helgehelge 01/13/2017 at 16:481 Comment

In the previous log it was shown that half of the ADC turned out to be non-functional. Luckily it wasn't the last board so another one was grabbed.

A few hours later we have a modified PCB with 1.27mm headers (perf board circles cut in half to yield 1.27x2.54 grid pads

and thanks to quick delivery from China also a big pack of u.fl cables and connectors (sculpting the pads-to-be for U.FL was something that made me want to redo the PCB - Rev1E PCB on the right is for reference so you can see the GND polygon)

Here's the fun part: soldering the U.FL cables and attaching 0.635mm wires to route the connections to the diodes

and it's done. Let's mount the PIN diode array (it's hard to see but there are 2 diodes on each of the 8 chips, 16 pixels in total, only the upper half is in use right now)

I haven't bothered to get the pinout right so the channels are out of order but you can convince yourself that

* all channels are working to spec

* no shorts

* gains are compatible

test setup: reset and acquire background for dimmed laptop monitor showing a black image with a 1px white line, move diode array across the screen, illuminating one pixel at a time as they pass. Note also that the zero line is noisy due to brightness fluctuations in the backlight an that the LCD is not completely dark, so some jaggedness is to be expected.

coming up next:

* electrically shielded housing, provisions for x-ray aperture

* systematically redo PCB mods for noise mitigation and quantify significance

* measure some stuff!

You may have noted that we're diverting a bit here. That's be cause the hardware developed here will be used in an x-ray backscatter imaging experiment. Apart from that we're still on track with the Optical Inch.

Discussions

esot.eric wrote 01/13/2017 at 17:47 point

Nice work, that "fun part" looks real fun :)

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