Sunday, January 22, 2023

Identify chemicals with radio frequencies - Nuclear Quadrupole Resonance (MRI without magnets)

 

How to build and test an NQR spectrometer, which is similar to MRI, but uses no magnets.  NQR frequencies are unique among all tested compounds, so detecting a resonance indicates a near certainty that a specific chemical is present.





Tektronix 2-series oscilloscope: https://www.tek.com/en/products/oscilloscopes/2-series-mso Video capture was done via VNC client


Zeeman effect shifting optical spectral lines: https://youtu.be/JV4Fk3VNZqs?t=74


Atomic clock calibration using Zeeman effect: https://www.youtube.com/watch?v=xTy1kY_wtsY


W2AEW's RF tutorial on quarter wave transmission lines: https://www.youtube.com/watch?v=A1BAq0KxIdc


Water deflected by electric field: https://youtu.be/NjLJ77IuBdM?t=468


Litz wire only helpful between 50KHz and 1.5MHz - https://youtu.be/FUCRB9UdfUg?t=2010


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Q/A

Why use vacuum variable capacitors? The parallel LC circuit develops well over 1000 volts during transmit, and they are much easier to finely adjust over a large range.




I've spent quite a few hours making this work since late last year.  I failed to detect a signal from urea, which burned dozens of hours.  Switching to NaNO2 suddenly produced a huge signal.


NQR calculations spreadsheet - https://docs.google.com/spreadsheets/d/1pkWlgvEXlANemZt3DR1J5g59S7hsejbvs995Y4FRsl0/edit?usp=sharing


NQR references (many!) : https://docs.google.com/document/d/1XoNUhFceH38nSjAFZoxglNiZlUzn6QMxa6CYTyAM92c/edit?usp=sharing

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Wednesday, November 23, 2022

How to disable auto updates on Windows 10 Home

I've tried all kinds of things to stop auto updates on Windows 10 Home:  Use psexec and disable the items in Task Scheduler, disable the services, run the service as a non-privileged user, edit various registry settings that are intended to influence auto update, try to be creative with "active hours" and play with the clock settings.  Nothing that I found on the internet as of Nov 2022 has worked to actually stop the updates.  I've found that editing the registry values shown below will definitely stop the updates.  As of Nov 2022, this really works.  Simply append ".bak" to the listed .dll filenames in the following registry values.  You can always change them back.  Now reboot or stop the services manually.  The scheduler will attempt to start the services as usual, but the system will be unable to find the nonexistent file, and will log error messages that you can see in the System Event Viewer.

If you end up digging into this, there are three things to monitor:

Window Update (HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\wuauserv)

Windows Update Medic Service (HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\WaaSMedicSvc)

Windows Update Orchestrator (HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\UsoSvc)


Yes, I know OS updates are important.  Sometimes making sure a PC never reboots is even more important.  Use your judgement.

These alterations may lengthen boot time (not sure).  I have not noticed any other effects.







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Thursday, November 3, 2022

How to make precise sheet metal parts (photochemical machining)

 

\
How to make etched metal parts.
-All of the highest quality parts that I made went to the customer, but edge quality and photoresist adhesion is still a problem.

-The photomask dark areas can be expanded, and then the part etched for a longer amount of time to make the edges more perpendicular to the surface. I forgot to mention this clever way to improve the etch aspect ratio called "etch factor" http://www.chemcut.net/wp-content/uploads/2015/03/Chemcut_Thoughts_on_Undercut.pdf



-Special ink and transparencies (films) for photomasks: https://filmdirectonline.com/




-Strange Parts did a great video on metal business cards: https://www.youtube.com/watch?v=83GDV0xsTTs

-https://mymetalbusinesscard.com/product/stainless-steel-business-cards/ 100 cards for $250 could be the cheapest way to get custom mechanical parts: https://www.youtube.com/watch?v=bkZkaT_P0Ck

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Sunday, September 11, 2022

High speed X-ray video: jumping beans, wind-up toys and more!

 High-speed X-ray video captured with a Dectris photon-counting detector. I show how the process works and how this detector is different than normal camera detectors. 


https://www.dectris.com/

https://media.dectris.com/Technical_Specification_PILATUS_100K-S_V1_8.pdf

Mexican jumping beans: https://www.amazingbeans.com/

X-ray timelapse video: https://www.youtube.com/watch?v=j-FHbHoiwNk

ImageJ image format converter: https://imagej.nih.gov/ij/  (the NIH's SSL cert expired?)

Flipping through images fast enough as if playing video: https://www.irfanview.com/

Video editing software: https://www.blackmagicdesign.com/products/davinciresolve/edit

The sequence of tiff files directly from the sensor contain a lot of temporal flicker -- probably because the X-ray tube itself has time-varying output.  This isn't so bad at 60Hz, but quite a problem at 300Hz.  I used Resolve's "color stabilizer" to maintain constant levels throughout a clip, and was impressed how well this removed the flicker.


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Tuesday, May 31, 2022

Drawing on a plasma display with a laser pointer

An orange plasma display will retain an image caused by incident near-UV light. This is an interesting visual combination of photoelectric, hot carrier injection, plasma, and charge trapping effects.



Correction: The orange display is running at 700Hz, 130V in the video.
  I realize that I may have conflated the issues of one-resistor-per-pixel and the display's ability to maintain an image throughout row scanning. They are separate problems that are both addressed by designing the panel to work on AC. Each pixel can maintain its state (on or off) by being supplied constantly with a lower "sustaining" voltage, and can be set or cleared by giving it a momentary higher or lower amplitude. The sustaining voltage allows the pixel to be emitting light or not, and its state remains because of its own impedance until updated on the next scan. In color plasma displays, separate electrodes are used for sustaining and addressing pixels, and the discharge may be sustained between coplanar electrodes instead of plane-to-plane, as in this display.

It's also a possibility that the dielectric and MgO layer only exists on one electrode (the metal), and the ITO is bare. I don't know. On this display, if all rows are electrically connected together, and all columns are connected together, and AC is applied to rows and columns, this effect does not work -- no light is emitted at all! At least some of the electrodes (ie every other column) must be left floating to emit any light, and to show this memory effect. So, driving AC plasma panels requires more waveform tricks that I do not fully understand.

Prior art patents: https://patents.google.com/patent/US7283301B2/en https://patents.google.com/patent/US20060132716A1/en


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