Tuesday, June 16, 2015

SNA Jr Software update two

I changed the display from a 1.44" 128x128  TFT ti a 1.8" 160.x128 TFT.  Unfortunately they use different driver chips so I had to make some changes to the software , mainly a different driver library and the position of text on the screen.  While I was doing that I also added a couple of
functions to the system.

New circuit board layout moved parts around to make room for the larger display, and added a ERA-3 MMIC amplifier  with attenuator to boost output and present 50 ohm to the DUT. 




After I got the hardware working with the pickup coil to use the SNA Jr. as a Dip Meter, I decided to add a DIP function to the software.  It does a sweep from 1 Mhz. to 50 Mhz. with 50 KHz steps, and looks for the deepest dip in the signal from the RLB.  After that sweep it sets the  range  to 1 MHz.  below and above the dip frequency and then  does a normalized sweep of that frequency range.  Much faster than sweeping through in several ranges.


In the existing sweep functions, they are a single sweep triggered by a short push on the encoder button.  After the sweep is started pressing and holding the button down will enter a setup mode, where you can make adjustments to the gain pots for the sweep range you are using if desired.  Because I added the normalizing  function, I had to do a complete  sweep and then display the data.

video
Moving the coil wound on the pen with parallel cap
in and out of the "Dip Meter" pickup coil


From comments on  QRP-L,  sometimes a continuous reoccurring sweep would be better. This would be useful for adjusting filters, and other alignment procedures.

I added a FAST sweep function that does sweeps at around 1 second per sweep. To get this rate I had to remove the setup functionality, and only did one reading at each point instead of using multiple readings to reduce noise. In this FAST mode I erase the old data point and draw the new datapoint as it is acquired.

Still waiting on some parts to arrive, before I can finish testing the updated circuit board layout.  After the last local QRP club meeting I was asked about the possibility of making kits available.  Still trying to decide if I want to go this route, or just make the design for boards and software available.  If anyone would be interested in a kit of this project drop me a e-mail at duwayne@kv4qb.us   Depending on the response I will decide which way I will go.


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