Thursday, January 17, 2019

Holidays over, Getting back to projects

The holidays are over and I am back home from visiting family.  So it is about time to get back to some of my projects.  I am going to start the year with a update to my SNA Jr.   I had started it previously, and ran into problems with my original design.  After looking around the net I found two different designs that have some of the options I want to include in my design.  One is the Antenna Analyzer by IW2NDH and other the SI5351 Network Analyzer by UR5FFR. With a lot of help from Google Translate I was able to get all the information I wanted from their documents.  

My new design will include much of the circuitry from their projects, along with some of the things I developed while working on the 'Test Gadget'.  My earlier design used an Arduino Nano as the processor, but I found I needed more program and storage memory.  This design will use a ESP32 development module, along with a 320 x 240 TFT display.  I will also use a small Joystick instead of a rotary encoder for the user input.  Before the holidays I designed a PCB board and sent it off to one of the Chinese board houses that I have been using recently.  The board arrived shortly after I returned home, and I started building up one so I can test it in sections.

One of the things I want is that the instrument will run off of an internal battery.  In the earlier version of the SNA, I used a pair of 18650 lipo batteries with a separate charge controller board.  This gave me around 7-8 volts that I could feed to a 5 volt regulator on the main SNA board.  I recently found a lipo module that has a built in holder for a 18650 battery, a charge controller,  boost converter and regulators that gives 5 and 3 volts regulated out.  One of these should power the new SNA  board with the ESP32 without having to include a regulator on board.  But,  just in case it does not work out I did include a 5V regulator on the circuit board.

After I got all the major parts in, I could design a case for everything to fit in.  What I really like about having the 3D printer is the ability to design a case to exactly fit the project.  Along with the proper holes for controls and displays, I can also design in all the mounting posts and standoffs for all the major components.  It might take a couple tries to get everything to fir the way I want them.  But it usually costs less than a dollar in plastic to print a part in draft quality.  When everything is the way you want it, print in higher resolution.  
It took a couple tries to get everything exactly the way I wanted, but finally printed the top and have all the parts mounted.  Just need to finish wiring everything up.  Using one of the early attempts as a mounting platform to use while working on the software. The case I have now is in regular PLA, but I have some Carbon Fiber filled filament that I might try.  It should add some RF shielding, but don't know if it will help in the HF range or just at VHF and UHF frequencies. The way I designed the clam-shell case, the top and bottom are symmetrical.  When I get around to designing the bottom half, all I have to do is remove the existing cutouts and mounting posts and replace them with the posts needed for the SNA circuit board itself.