Sunday, May 28, 2023

Multi-layer reactive foil: no fuel, no oxygen, tons of heat

This unusual sheet metal is made of hundreds of nano scale layers of aluminum and nickel. A spark initiates a self-propagating reaction that creates NiAl compound, and lots of heat! This material is used to solder items so fast that the base material doesn't have time to draw heat away from the joint. The technical data sheet indicates that this process is fluxless, and I suspect trying to include flux would cause rapid gas expansion that would blow the solder joint apart. I'm not sure how the solder wets the surface without flux. 

Sunday, April 9, 2023

Temperature-sensing RFID tag in magnetic stir bar

I describe an old project in which a few friends and I designed an RFID tag that fits into a magnetic stir bar and measures temperature wirelessly.  We decided to open-source the project, and you can see the PCB design and tag firmware at the github repo below.  I don't think I have the firmware for the base station, unfortunately.

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: Video capture was done via VNC client

Zeeman effect shifting optical spectral lines:

Atomic clock calibration using Zeeman effect:

W2AEW's RF tutorial on quarter wave transmission lines:

Water deflected by electric field:

Litz wire only helpful between 50KHz and 1.5MHz -

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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 -

NQR references (many!) :

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.

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"

-Special ink and transparencies (films) for photomasks:

-Strange Parts did a great video on metal business cards:

- 100 cards for $250 could be the cheapest way to get custom mechanical parts:

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