Sunday, July 7, 2024

Moxtek X-Ray Tube Controller - Part 3 - Enclosure

Finally, I got around to make an enclosure for the Moxtek X-Ray Tube Controller with a proper control panel.

The complete "X-Ray Tube Commander 2000" Controller in all of its glory.
 This enclosure might be further improved with an angled front panel at some point if I get too bored but for now it serves the purpose just fine.
The faceplate text is currently done "quick-n-dirty" with a Label Maker but I'll print a nice colored laminated front decal for it to get the more refined "lab equipment" look, just the way I did with my N2PK VNA.

The front panel component mounts include large LCD display, 2 backlit control buttons, a rotary encoder /w button, a keylock and small speaker grill.

I designed the enclosure with TinkerCAD - this application is excellent for simple projects such as this one, and it is very fast to work with.
Once the measurements are taken, it literally takes minutes to create the design and output the STL file for printing.

I made the bottom part of the enclosure a bit taller than necessary, just to have some spare room if I decide to change things around or add more connectors. Since it is a just a piece of benchtop equipment, the size is not critical.
 If I ever do another print of this, I will definitely make the box slimmer, round the corners and angle the front panel. 

The X-Ray Tube Controller PCB and components, installed in the enclosure. 

A "Window" on the side exposes the edge of the PCB where all tube interface connectors are located - a DB-9 for connecting to the tube's HV module, supplemental power connector for tubes working at higher power levels (>4W), terminal strip with all interface signals, etc. 
I used this window to feed thru the power cable and temperature sensor cable but I might drill and mount a proper power connector at some point
The keylock is part of the X-Ray safety protocol and prevents engaging the beam without a key. These types of X-Ray tubes create an incredibly high flux right at the aperture and when setting up a sample for XRF the user should remove the key to prevent any accidents. In addition, the XRF enclosure door interlock switch is in-series with the keylock so key must be turned AND door closed for the beam to engage.

The yellow MODE Button serves multiple functions depending on the context.
Single-press is RESET (for Timers, errors, time logging and acts as an Emergency Stop when X-Ray beam is ON).
 Long-press changes operating modes and a double-click switches between memory presets. 
It also acts as a "SHIFT" button while operating parameters are dialed with the rotary encoder (Timer and High Voltage).
The yellow LED is a "READY" indicator showing that the x-ray beam can be engaged at this moment - it turns off if the current conditions disable the x-ray tube - during parameter entry, filament cooling or errors for example.

The push-button on the Rotary encoder is used to enter Parameter Setup mode and scroll thru the different digit positions. 
Tube and Controller Parameters are then dialed in with the rotary encoder at the position of the blinking cursor. 
This button also serves as an "Emergency STOP" button in Timer or Toggle modes, instantly and unconditionally terminating the X-Ray beam.
When the beam is ON and operating in Timer mode, the rotary encoder can be used to add or remove time from the currently running timer by simply spinning the knob.
The BLUE button is exclusively used to operate the X-Ray beam according to the selected mode. 
The blue LED in this button indicates if the beam is ON and it also flashes with 1 Hz period while Timer mode is running.
The status line on the display will show the status of the "Filament heated" signal returned by the tube with a message "X-RAY ON!"

On this picture, the status line displays "Tube ERR!" with Error Code E-111 due to operation with disconnected X-Ray tube.
I also added an option to temporary disable the Tube Error Check.

The 3-digit error code is very easy to read:

First digit on the left shows the "Filament Ready" signal returned by the tube: 0 - signal present, 1 - signal is missing. 

Second digit shows the state of the High Voltage return: 0 means that the tube returns the same voltage as the one requested (Set) by the controller, 1 - returned voltage is lower than requested, 2 - return voltage is higher than requested. 

The third (right) digit is the same as the second but reflects the return of the Emission Current.

Tube Return voltages are monitored within a specific tolerance. Emission current is checked only for Set current >5uA - at very low currents, below 5uA the tube return for emission current might fluctuate more than the established tolerance and could will generate an error otherwise.

Sunday, February 18, 2024

Lightwave portable magnetic stand for Elecraft KX3 and PX3

Elecraft KX3 is a fantastic portable transceiver but one thing I thought could be improved is using a better stand to the stock, foldable legs. 
The built-in foldable feet are a bit annoying as they require the user to manipulate the thumbscrews holding the radio together and because they are opposing, this needs to be done in different directions when standing in front of the radio, not to mention that the front panel sits at too low of an angle for my taste.
I decided to design a lightweight stand that has small footprint, and it can be assembled or taken apart in seconds in the field and will give a good support for the radio without the need to completely unfold the stock legs.
It was a quick and fun half-day project.

The two legs of the stand were designed with TinkerCad and then 3D printed.

All of the components for the stand - the 3 spacer rods and the 2 legs. 
The weight is exactly 2oz. but there is a room to shave off some of it in the next version.

Inside the holes for the carbon-fiber spacer rods, I glued small neodymium magnets (source eBay - 1/4" x 1/8" N42 type). I made a "bed" for friction-fit of each magnet which has a slightly smaller diameter than the main hole, matching the inside diameter of the rod. All magnets are also glued in their "beds" in the same orientation (polarity) by adding a drop of Super Glue before pressing the magnet in place.
The tricky part is to get right the size of the main opening of the arrow-shaft receptacle. Arrow shafts come in different "spine" level or amount of flexing. This is controlled by the manufacturer with the thickness of the arrow-shaft wall or more specifically, the outside diameter - stiffer shaft (lower spine number like 350) will have a larger outside diameter than a 600 spine. Furthermore, when 3D printing the plastic also shrinks as it cools so it takes some experimentation to get the size just right for a snug fit that will also afford smooth and effortless assembly / disassembly.  

For the spacer rods I used scrap cut-offs from carbon fiber arrow shafts. These are very strong and lightweight tubes and bonus they have quite nice finish. 
I have a whole bunch of these pieces in varying lengths leftover from sizing of my archery arrows.
 Inside each of the arrow shafts I glued the same size neodymium magnets, making sure that the polarity is the opposite of the ones in the legs. The glue was applied on the perimeter of the magnet and then inserted into the arrow shaft, making sure it is perfectly flush with the end of the tube.

The stand can be assembled together literally in seconds. The spacer rods just snap firmly in place and hold the entire stand together. Disassembling is just as easy by pulling everything apart. 
The magnet-to-magnet attraction provides just the right amount of holding force without making it difficult to pull apart. 

The original foldable legs of the KX3 can be unfolded ever so-slightly to lock the stand in place so the radio cannot move sideways. This is not really necessary as the stand's legs fit between the stock legs rubber booths, but it can provide additional support if needed.

The angle of the front panel with the radio on the stand is not as low as with the original foldable KX3 legs. 
The radio sits angled at exactly 45 degrees which I find to be more ergonomic.

Short video of one-handed assembly of my KX3 stand.
 A set of shorter rods can turn this stand into a PX3 stand (the KX3's Panadapter). This stand also works great as a portable cell phone stand and I'll be making another one for use during my air travels or when using the cell phone for logging in the field.