Saturday, January 28, 2017

The problem with gettibg a 3D printer

When I first got my 3D printer, it was with the intention of making parts for my electronics projects. After I found an inexpensive 3D design package, and getting used to it, I was very pleased with what it could do.  Then I made a big mistake, I went to thingiverse.com. This is a huge repository of different 3D printed projects that have uploaded by3D Printer enthusiasts.  After browsing the projects, and a lot  "That's Neat" or "I should try printing that", I realized that I was hooked and now have another hobby.

My printer worked well for what I had wanted it for.  But since it used propriety software I was not able to change the settings to what I would require for some of the things I downloaded from Thingiverse.  While on one of a 3D printing Blogs I was following, I saw mention of a very small inexpensive printer by Monoprice.  
The Monoprice select mini, is a very small printer, but uses most open source slicers such as  "Cura" or "Slic3r".  It comes fully assembled and with a recent price reduction is less tan $200 including shipping.  That day I received an e-mail with a coupon that would bring the price down to around $185, so I ordered one.  It arrived in 3 days, and I quickly unpacked it.   The  machine is almost all metal, and appears to be very solid.  It came with a sample of filament that is too small to do much of anything, you will have to purchase a full spool to do anything useful. 
Using some filament from my other printer, I printed the sample print that came on the micro-SD card along with a couple different software packages.  The print turned out to be very high quality, much better than I had expected from such an inexpensive printer.  Also the printer is very quiet compared to some others I have seen.
Searching the Web I found a series of beginners guide to the printer and some help on initial setup of "Cura" for the machine.  Also found several useful items to print to make the printer a little nicer. 

 I printed up a filament guide and a couple other simple things to use with it.  This printer has a heated bed, so I could use a "PEI" plastic film to cover the print area.  This gives better adhesion to the print surface, and makes it easier to take finished parts off the bed than the blue printers tape that is usually used.
Printing 5  CW paddles at a time
Since I had full control of all the settings, I could use some of the different filaments that I could not use with the first printer. I could also change layer and print options to make some of the items I had designed stronger.  So far the only drawback to the printer I have found is its print volume.  It is only 120mm x 120mm x 120mm, but most thing I want to print will fit in this area.  This might mean that a print job that made 8 pieces at a time, I had to re do and could only print 5 at a time.  

I found a fairly active Facebook Group that covers this printer, and have been finding some useful information on possible modifications I will probably make in the near future.  All in all after less than  a week I am very happy with the little printer.  If someone wants to try 3D printing this would be a inexpensive option to try.
DARN now I have to find time for the electronics projects that are stacking up.

Monday, January 23, 2017

Back to working n the Spectrum Analyzer UPDATE 2/4/17

Now that the BITX is nearly finished, I decided to get back to the Spectrum Analyzer project.  I had did some work on the display and controller using a Arduino Mega and a  3.2" , 320 x 480 display.  It worked well, but was quite large, and the display covered most of the pins on the Mega.  I found a little smaller  2.8" .320 x 240 display that uses a SPI interface instead of a parallel interface.  I wired this up with a Teensy LC micro-controller and started writing some graphics routines.
I decided to keep the waveform display as 300 x 200 to give room for text and cursor values.  The 300 pixel width will work well to give overlapping display ranges in a 1,3,10,30 format.Since the overall range will be around 100 db, using 200 vertical pixels will make it easy to display wave-forms to a .5 dB resolution.
Because I want to have various sweep widths available, I will store the acquired data in a large integer array of 900 elements.  Using this format I can allocate data as one large sweep, or several smaller ones.  Then by designating the starting point in the array and number of points per sweep, I can store multiple sweeps in the same array.  The wave-form drawing routines will work the same way, specify starting point in the array and number of points to display.
 I will be using the same basic data format for storing the acquired data as in the SNA Jr.   The AD8307 log detector has around a 90 dB. dynamic range, and I want to have a 0.1 dB resolution.  I store the data as the dB. value times 10, so all the display routines can work on integer values.  Since I want to have several switched  10 dB attenuators in the system, this will make it very easy to correct the data values.  Just add or subtract 100 to the value to adjust up or down 10 dB. as attenuators are switched in or out.


video To test out the drawing routines, I initialized the array with a triangle wave with values equivalent to 0 to -100 dB.
Then in a loop I display several wave-forms based on that data. These wave-forms start at different points in the array, and display different sweep widths. I am very happy with the display speed I get using the 48MHz. 'Teensy LC', compared to what I had with the Nano in the SNA Jr.  Next to work on the basic controls and menu system.

UPDATE 2/4/17

Did a little work on  the waveform drawing routines to limit to waveforms to the 200 x 300 pixel drawing area.  I plan on using a cheap joystick for the input device instead of a rotary encoder.  Re-wrote a joystick routine I had been working on.  It reads the joystick pots and switch, then sets a flag if a change has occurred. 
It also sets some global variables with the values of these changes,
I use + or - 1 for horizontal and vertical movement depending on direction.  Also set values for either a short or long press of the push button.  I found this to give much faster and easier control than I had with a rotary encoder.
I had been using a 'Teensy'instead of the Arduino Mega that I had started with. I recently bought several cheap stm32 boards I purchased on eBay.  I wanted to see how this ~$3 board compared to a $13 'Teensy'. Speed at 72MHz. is more than adequate for my needs.  It has 8K of SRAM and 65K Flash memory, also enough for my needs.  I pulled out the 'Teensy' and wired in the stm32 board ( usually called the 'blue pill' on the stm32 blogs).  It is just a little bit larger than the Teensy, but brings out more I/O pins.  As they come, they do not have a Arduino compatible boot loader installed.  Programing must be done through a serial converter or a STlink programmer, about $3.  I used the STlink method, and found it very easy and fast.  I changed the Adafruit graphics driver to one modified for the STM processor.  Everything worked as well or better than with the 'Teensy'.  I wrote a little display test routine to scroll through the initialized data buffer.  Scrolling was very smooth with no flicker or hesitation.  By changing the increment I used to step through the data, I could change the rate of scrolling.

All in all I am very pleased with the results, and looks like I will be using the 'blue pill' instead of the 'Teensy' 

A picture of the bread-board using the 'blue pill' with the display running. The stm-32 'blue pill' is just a little bit bigger than the Nano  on the other side of the bread-board.    For about the same price and much more powerful, this might be my choice for any new projects.

















Wednesday, December 14, 2016

Building the BITX 40 v 3 A SI5351 VFO update 1/22/17

Between getting ready for the Holidays and a couple things i need to do around the house, I have not been spending much time working on the BITX.  Except for the drift issues I still have not been able to get resolved, I am very happy with the performance so far.  The simple AGC seems to be working well, and makes listening much more comfortable.  I took a look at the output of the detector on the AGC board, and it looks like it will be usable for a signal strength meter.

With the drift problems, and desire to add a signal strength meter I decided to go ahead and build up a digital VFO. I have a 9850 module left from the SNA Jr.  and a couple  Adafruit SI5351 modules from earlier projects. I had ordered 2 of the BITX boards, and had planned on making the second one into a multi-band rig.  With this in mind I decided to go with the SI5351, because I could use a second clock in the multi-band version for side band selection.


Over a year ago I had built a 5351 based VFO for use with Frog Sounds 40 Meter CW transceiver.  I called it the Canned Frog, because I put it in a canned meat can.

http://kv4qb.blogspot.com/2015/07/canned-frog-part-two.html

I had used a separate clock for the receiver and transmitter LOs, so had about everything I needed in the board I had laid out for it.  This VFO used a Arduino Nano, and a small OLED display.  This will be fine for the single band version, but want a larger display when I get around the the multi-band version.  I used the basic layout I had, and brought out most of the Arduino pins for use with a different display, and other options I am thinking of adding.  When I did the original VFO. I found the regulator on the Nano got quite warm when running on 12 volts.  So, I added a 9 volt regulator to the board to keep the Nano cooler. 
 
I also changed most of the passive components on the board from leaded to SMD versions, that will be mounted on the back.  I have started to try to use SMD components where ever possible.  Drilling holes is the most tedious problem of making my circuit boards.  Only problem with home made PCBs and SMD components is watching out for solder bridges.  I have been playing around with UV curable solder mask, and have gotten the process down to something fairly easy with consistent results.  So after etching and tinning the board, I added a solder mask before drilling.   Everything looks very nice, now to build the board and modify the existing sketch to take care of a IF offset.

12/18/2016 board and software mostly finished

Finished getting most of the board populated except for the filter and attenuator circuits, and the basic software working.  Now I can try setting different levels and filter values on the board to see what values work best.    The software is basically what I had used for the 'Canned Frog', with the CW keyer and CW offsets, and RIT removed.  Since this used a direct conversion receiver, the signal output was on the transmit frequency. The BITX is a super-hetrodyne, and has a IF  frequency around 12M Hz. Therefore the VFO signal must run at a different frequency.   Because you are receiving the Lower Side Band  the exact frequency used is the BFO frequency. Basically the VFO frequency is the BFO frequency minus the operating frequency. 

 For the 7 Mhz. band this is around 4.7 Mhz. to 5 Mhz. The original software used the actual operating frequency for display and setting the si5351.  I measured the frequency of the BFO and used that value in computing the required VFO frequency. This value was used to set the si5351 clock 0 output.

After making the changes to the software, I ended up spending an hour or so trying to find out why the frequency was not changing when I turned the rotary encoder.  I finally looked at signals with a scope, I found I had a bad rotary encoder.  After changing that everything worked the way I expected it to.  

Update 1/2/17

I spent most of the holidays visiting relatives, and did not have much time to work on any of the projects I am working on.  I did bring my laptop along and had some timeto work on a BITX front panel that will work with the SI5351 VFO and Display.  The original front panel was designed to work with a small counter and had a grill opening for a small speaker.  After trying the BITX  receiver, I found that even with an AGC circuit added, the audio sounded much better with a larger external speaker.   This version has a built in bezel for the display, mounting posts for the circuit board. 
I also had to include a recess to provide room for the stacked Display and Adafruit SI5351 board.  To center the display, I had to move the microphone and volume control to the opposite side of the panel.  

 Update 1/22/17


I 3D printed the new design front panel and tested the VFO out when connected to the BITX board. I found some of the same kind of receiver noise I had at first with the frequency counter.  It looks like the BITX board  is very sensitive to any noise on the DC supply line.  I had a reverse polarity diode on the board, that I replaced with a 10MH. choke and added a 100 uF. capacitor across the input to the regulator on the board.  With this I could not hear any noise unless I turn the volume all the way up and disconnect the antenna. 


 The recess I put in the back of the front panel helps keep the display and si5351boards in position, along with reducing the overall depth in the case.

Just a little more work on the software to make sure the RIT is working correctly and possibly add a  S-Meter





Wednesday, November 30, 2016

Building the BITX 40 v 3, receiver portion

12/2/16   Added link to Eagle files for making AGC Board



A couple of things came up and I was delayed in building Farhan's SMD BITX 40.  With the availability and price point on the board, I decided I will stop work on the version I was designing and building.   I will instead spend my time on trying some modifications to enhance the board from Farhan.  
For those who are building with this board, there is a website devoted to different mods for it. 

http://bitxhacks.blogspot.com

Since I haven't gotten around to build a si5351 VFO yet,  I installed a 10 turn tuning pot.  This made it much easier to tune, but I found there was quite a bit of drift during warm up.  Looking over the bitxhacks blog, one of the first mods I made was to change some of the resistor values in the bidirectional amplifiers.  Changing them from 100 to 220 ohms reduces current in those stages,  should reduce heating of that part of the circuit board.  I also coated the VFO coil with several coats of clear nail polish to prevent  coil winding movement.


Another change I made was to cut the short trace going from  switched 12 volt to the  U2 (VFO  9 volt regulator) input pin. Then I ran a wire from the input pin of U2 to un-switched 12 volts.  I also added a .1 uF capacitor from the regulator input pin to ground, and a 47uF and .1uF  from the output to ground.  This keeps the VFO circuit on at all times, and hopefully further reduces warm up drift. 
After all of this it is much better, but I still have some drift, up and down in frequency even after warm up.  Ordering some NPO capacitors to use in the VFO and will see if this helps.

With much of the drift problem solved, I next looked at the audio.  Since the BITX does not have AGC, having to adjust audio level when going from station to station can be aggravating.  Farhan posted a simple AGC circuit on the bitxhacks blog, and I decided to add it to mine.  


I took his hand drawn schematic, and input it
to Eagle and laid out a simple board that can be built as mostly SMD or Muppet style. 




 
After etching a couple boards, I built up one of each to give a try.  For the SMD version I also added a solder mask to make assembly easier.  Adding the AGC board to the BITX took care of leveling the audio, but the added circuitry reduced the audio level.  Replacing the 1 uF. capacitor from pins 1 - 8 of the LM386 with a 10uF. brought the gain back up to where it was.


Link to Eagle files and a .pdf with mirrored top layer image for making toner transfer boards.

https://www.dropbox.com/sh/pg3otf9cwtekkoo/AADGvAfmP_E96njuNP5UX_Y9a?dl=0

Next to add the frequency counter.  With a little change to the gain on the counter pre-amp I had it reading correctly.  Using the setup function on the counter, I measured the BFO frequency, and set the counter mode to subtract the VFO for proper frequency display.  There was some noise introduced on the audio output.  A 220uF capacitor across the counter power supply leads, and a 10mH. choke in series with the positive  supply lead took care of that.

Except for a small amount of frequency drift the receiver portion of the BITX is working.  Now to wire up the microphone and test the  transmitter.  It is starting to look like a transceiver.







Saturday, November 19, 2016

Some nice words about the SNA Jr.

I have been following Paul M0XPD "Shack Nasties"  Blog for quite some time.  This year at FDIM, Paul gave one of the seminar presentations.  I was pleasantly surprised when he mentioned my early version of the SNA Jr. in his presentation.  Later, I had a chance to speak with him about some of our common interests and projects.  I also gave him one of the extra SNA Jr II boards I had had made.  
A week or so ago I received an e-mail from him with a picture of the SNA Jr. that  he had just finished building.  Today I saw that he had updated his blog with a very nice write up about the SNA Jr II.  I want to thank him for his kind words.
http://m0xpd.blogspot.com/2016/11/sna-junior.html
 
If you have not read his blog before, it is one you should follow.  I know I always find something interesting and informative in each post.

Friday, November 11, 2016

Light Weight 3D Printed CW Paddle

I am a member of the North Georgia QRP Club ( NOGA). Many of the members are involved in portable operations such a SOTA.  One of the common discussions involves small light weight CW paddles for field use.  After getting the 3D printer and becoming familiar with its CAD software, I decided to see if I could come up with a small, very light weight paddle.  



The design I came up with is a combination of several different designs I found while searching the Net.  I also decided to customize it with the NOGA name built into the frame.



I printed up a few and gave them out at a recent meeting. The response seemed to be quite favorable. The suggestion was made that this was something we could sell at a upcoming Hamfest.  




I printed up a couple of sets in different colors for the hamfest, and we sold several in each color.  Now we are deciding if we want to make them available, and what would be a good price point including shipping.  I would like to get an idea of the interest in this.  So, if you think you would like to purchase one of these please drop me a e-mail at duwayne@kv4qb.us

Monday, October 31, 2016

BITX 40 v 3

I have been gone for a while visiting family, and have not had a chance to work on the projects I have on the bench.  One of these is a SMD version of the BITX 40, that was only available in India.  Just before I left, I saw that a newer SMD version was available for sale world wide.  And, at only $45.00 including shipping I decided to order one.  A couple of days after I returned home, I received a little box from India.  Inside was a very nice assembled SMD BITX board, and a bag of components needed to build a working transceiver.  Since the local QRP club was going to have a table at a hamfest next week, I decided to quickly build this up for something to display.
I want to make a few minor changes to the kit, first I wanted to use a 10 turn pot instead of the one included in the kit.  Along with that I will add one of the re-packaged DL4YHF counters I designed a couple years ago. I also will use an external hand microphone with PTT instead of the electroet mic. that came with the kit. 

 Next was to come with a case to put it in.  This is exactly what I bought the 3D printer for.  I printed some 6" corner pieces I had designed right after I got the printer, and cut up some double sided circuit board material to use for the sides of the case. I have switched to using .032" PCB material for chassis panels. It is very easy to cut accurate size pieces with a simple paper cutter. The back panel is very simple just two mounting holes for the power and RF connector, and 4 screw holes for mounting the panel.

The front was a little more difficult.  I needed mounting holes for the tuning pot, volume control,a separate power switch, along with a hole for the display. I also decided to add a grill opening for a small speaker to mount behind the front panel.  I went with a panel .2" thick to give room to build in a bezel for the display, and allow enough depth to add a recess to hold the 7 segment display for the counter.
After a couple hours to lay out the design and a few more to do the printing I came up with a very nice looking case for the project. I cleaned up the printed parts, assembled the top and bottom of the case, and gave everything a coat of paint.

 Now to put everything together tomorrow, and see how it works.