Thursday, April 17, 2014

Mimima - Minimal Progress

As stated in a previous post, I have started layout of the separate Audio Modules for my experimental Minima Transceiver. I think I have four of the five modules in semi-final form, but I get "bored" working on Audio circuits.

And therefore, I have temporary turned my attention to the ATmega328P Processor Module layout. The original Minima circuits uses an ATmega328P-PU 28-pin DIP package, which is easy to use, and easy to solder on a through-hole PCB, or mounted "Dead Bug" or "Ugly Style". But, I enjoy building my own PCB's.

As with all of my projects, my goal is to make them as small as my eyes, nerves, an abilities will allow, and therefore I will use the ATmega328P-MU which is a small 5x5mm 32-TQFP package on a Homebrew PCB. The pin numbers and layout are a little different, but the functions are the same.

First DRAFT
Minima - CPU Module
The above is the first Draft of the proposed layout, the planned Homebrew Double-Sided board will be 1.4x3.0 inches with only 13 via's. The PCB will be created using the Toner Transfer Method.

The ATmega328P-MU will be mounted on the small diamond shaped pad in the center. The power +5V Power Regulator is on the left, the CPU programming circuit is on the right. The upper long header is for connection to the LCD Display.

I am still considering modifying the layout to use a single combined edge connector for connection to the planned Audio Modules.

This is work in progress, there is still more layout work to be done.

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Tuesday, April 15, 2014

Jaxs and Friends - Needs Our Help

This post is dedicated to Tess (my Dog),  .  .  .  A friend or kin of Tess, is a friend of mine.

The Vet Ranch is making a difference, we can help !


Good luck - Jaxs !

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Monday, April 14, 2014

Minima - Build Continues

I was stalled on my experimental Minima Transceiver build.

The next modules to be built are the Audio section. In general I do not enjoy building Audio circuits as there are just not as interesting. Audio circuits normally use large value caps and large value inductors which can not be wound by hand and therefore less personalized.

I had completed a single layout of all five Audio modules used with the Minima Transceiver as previously posted. But, after following much chatter on the Minima e-mail reflector, where concerns were expressed about low Audio Level, I have decided that maybe five individual modules would be more flexible and more useful than a single combined complex module.

On inspection, it can be seen that the Farhan Minima Transceiver Audio section has several inter dependent connections between Audio modules. ALL modules are required to test any one of the others and therefore flexibility is lost for my desired simple experimentation.

For the last few days, I have left this problem and concerns to my subconscious.

But, I think I now have a plan;

I will layout each module with cleverly placed and matched edge connectors for; power, control, input and output signals. Then the audio modules could be used individually, only the minimal Receive Modules, or the minimal CW Modules, or minimal SSB Modules, would be connected while running tests or experiments. Obviously, module re-configuration would be necessary to change Transceiver modes. Once tested, all modules could be connected together for automatic mode change.

I think this will work, all I need to do is create the "clever layout".

Yes, I know, simple tests could be conducted with simple jumper wires, but I wanted to take the opportunity to find a better solution.

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Wednesday, April 9, 2014

Si5351A Circuit Build - Success

After the Failure as described in previous post, I modifying my Si5351A VFO PCB layout for proper Crystal Pad Pattern, and finished the build.

This circuit will be used as a LAB Test Oscillator and for my experimental Farhan Transceiver VFO and BFO.

Si5351A Module Ready For Test
The 3.3Volt Regulator is the black chip next to the top pin of the power header, the black chip near the bottom header pin is the Si5351A, and below that is the very small 27MHz Reference Crystal. The three BN-47-2402 Binocular Cores provide ground loop isolation for each of the SMA RF Connectors.

Si5351A and Si570 Modules
Ready for Use
One unfortunate aspect of both of these modules is; the Si570 and Si5351A chips do not have options for changing their I2C access address. And therefore, only one of each can be connected to single I2C control circuit without a special I2C switch.

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Sunday, April 6, 2014

Si5351A Circuit Build - Failure

As I have mentioned in previous posts, I want to build an Si5351A RF VFO, which is similar to the Minimal Si570 VFO.

The Si5351A has three RF Outputs that I would like to have available on my LAB Test Bench, and I will also try it as replacement for both the VFO and BFO for my experimental Farhan Minima Transceiver. The Si5351A is programmed via I2C, which is similar to the Si570.

Si5351A Three Port RF VFO
Today, I created the Si5351A PCB via the Toner Transfer Method, and I installed all of the necessary "vias", and 95% of the SMD parts. All that was left to install were the SMA RF Connectors, Power Header, and the Crystal.

I planned to install the Crystal next.

But then, . . . . Failure !

Small Crystal - Big PCB Pattern
(As Viewed Through the Microscope)
Dang, . . . I used the wrong Pad Pattern for the Crystal on the PCB, it is much too big for the Crystal that was purchased for this purpose. The Crystal is shown up-side-down in the photo (pads up) for pad comparison.

According to the Spec Sheet, the size of the CX3225SB Crystal only is 3.2 x 2.5 mm (0.125 x 0.098 inch).  The Crystal is only about as big as one of the Pads of the four Pad Pattern that I used.

I will correct the Crystal Pad Pattern in the layout, and try AGAIN!

This is one of the down-sides of not using "Ugly Style" construction, many time there is NOT an acceptable recovery.

I am getting better-and-faster at creating Double-Sided Homebrew Toner Transfer PCBs, and better-and-faster at connecting the two sides with very small vias. So, . . . I guess when necessary, I can now, Fail Faster :-)


UPDATE: Apr 7, 2014 10:45
For future reference, the Crystal Pad Pattern that I fond that appears to fit is labelled "CFPX-5". It is interesting to note that "Pin 1" is not marked, "Pin 2" is the indexed pin (see the inside filleted corner).

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Friday, April 4, 2014

Minima - VCO Module

New Toner Transfer Paper was received and Ferric Chloride Gremlins are at bay. See previous post.

Without too much difficultly, I finished my Minima VCO Module (see description and PCB Layout on previous post). Currently I do not have a way to program the Si570, but with power connected, the Module outputs its default RF signal.

The board is 1.0 x 1.2 inches, the homebrew vias are 40 mil pads with 12 mil holes. Solder Wipe was used for copper protection.

Minima - Si570 VFO
Backside Traces
As stated in the previous post, I modified Farhan's original circuit to include an output transformer, I want to also use this circuit as a Generic Lab Test Bench RF source where DC Ground isolation would be useful. The output transformer was wound as a 4:4 turns on BN-47-2402 core.

I plan to create an equivalent circuit using the Si5351 chip (as previously posted). It will look similar to this board, but it will have three output SMA connectors.


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Wednesday, April 2, 2014

Ferric Chlroide - with Gremlins

While (still) waiting for my replacement order of Toner Transfer Paper, so that I can continue my Minimal Project, I used some (more) small cut-up scraps for this (yet another) project. Sounds familiar, see previous post.

My Minima Transceiver VFO Module is small and will require very little Transfer Paper, which is ALL that I currently have.

Here is the Si570 VFO layout that I will use. There are vias to traces on the backside.

Minina VFO Layout
(Modified with Output Transformer)
The circuit is a little different than originally published by Farhan. Because I want to use this Module for the Minima, and as a generic Test Bench Oscillator, I included an output transformer on the board to isolate the RF Ground from the DC/circuit ground. The transformer will have a turns ratio of 1:1 and the same turn count as the transformer on the RF Mixer.

With the last scraps of Toner Transfer Paper that I have, I proceeded to transfer and etch the first side of the board. The results looked good with excellent resolution.

The backside Transfer was prepared and lined up with "great care" as to ensure the through-holes and vias would align correctly. I "now" always "Check" and "Re-check" the rotation of the board, because I have, in the past, printed the backside 180 degrees wrong.

Because you can not see through the board at this stage, other image clues are necessary for proper orientation and alignment. Tape on one edge of the PCB is used to maintain alignment while going through the Laminator the first time. After several passes through the Laminator, I dropped the sandwich into hot water to remove the Transfer Backing Paper. Checking it revealed a nice high resolution backside image. It is now ready for the Ferric Chloride Etch.

But, Now for the problem:

About 5 minutes later, when the PCB came out of the etch, I could NOT see through the hole images. DANG, the image on the backside is 180 degrees wrong, AGAIN !

But, I had carefully; checked, re-checked and aligned the image.

So now, I have come to the conclusion that my 35 year old Ferric Chloride Etch has "gremlins" that rotates the image while I am not looking. What else could it be?

This is the third, or forth, time this has happened in the last six months. (I must be just getting old?)

So, now back to waiting for more Transfer Paper.

(Anyone need a well Etched, High Resolution, but useless, I2C Si570 VFO PCB?)

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Sunday, March 30, 2014

A Measurement Fixture

While waiting for my replacement order of Toner Transfer Paper, so that I can continue my Minimal Project, I used some small cut-up scraps for this (another) project.

I have always wanted to build a self calibrating Fixture for my AIM-4170B Analyzer.

Self calibration means to me, that the "Short", "Open" and "50 Ohm Load", which are necessary for calibration, are a part of the fixture.  The "Open" is easy, just remove any parts from the fixture. The "Short" will be a simple push button switch across the analyzer terminals. And, a "Load" is another push button switch in series with a 50 Ohm resistor.

This approach to calibration is NOT exact, but it is good enough for most measurement that I do. For exact calibration, I have three certified (screw on) connectors that can be used.

The fixture as planned is only about 1.4 square inches and provides and SMA connection to an adapter on the AIM-4170B.

SMD parts can be scanned by placing them across the void on the fixture, and a plastic clip can be used to provide clamping pressure as necessary.

Parts with "Leads" can be pushed into the header shown in the center. There are three Ground header-pins, two groups of two header-pins are only shorted together and can be used to string leaded part together for a simple network measurement. And, there is one header-pin (center) that is connected to the analyzer.

Toner Transfer Method was used to build the fixture. As can be seen, only a small scrap of Transfer Paper was needed.


And, a small scrap of PCB material was used, which will be trimmed a little before going into the etch.


For etching, I use Ferric Chloride in a Ziploc Bag while kneading and running hot water over the bag. Only about 1 oz of Ferric Chloride is used.

In the Etch Bag
Almost Finished,
Some Copper (lower center) is Still to be Dissolved,
After cleanup, solder wiped, with switches and header attached, the fixture is ready to be attached to the AIM-4170B Analyzer.

The Analyzer Calibration can be done with the two switches. the upper push button switch connects two 100 Ohm Resistors in parallel across the analyzer terminals. The lower switch "Shorts" the analyzer terminal to ground.

The tapered section (lower center) is where SMD parts can be attached across either of the two voids.  Parts with leads can be plugged into the header.

The Fixture
The Fixture is installed, calibrated and ready for measurements.

Fixture Installed on the AIM-4170B
This fixture will help make sorting and matching Crystals that much easier the next time I build a Crystal Filter.

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Oso Mudslide

In memory of the Oso Mudslide Victims - May you Rest In Peace.

The Mudslide near Oso Washington State is near my home (within 20 miles), I have spent many hours travelling the roads around Oso. I do not know any of the victims, but they are part of our Pacific Northwest Family.

(AP Photo/seattlepi.com, Joshua Trujillo)
For more photos and the full story, see: http://goo.gl/mpDsXl

There is no better place on a Hot Summer Day than in the local Mountains around Oso, running QRP, or down-on the river fishing and playing ball with Tess (my dog).

The mudslide came from a hill; across the River, across the Rail-Road Tracks, blocking the major local highway on the near side, and destroyed lives and homes along its path.

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Saturday, March 29, 2014

Minima - AUDIO Board - Work In Progress

The SMD Caps were received, and therefore layout of my Minima AUDIO and Power Board has resumed.

This initial layout still has a few problems, and it has far too many vias (32) to my liking. I can build vias using the Homebrew Toner Transfer Method, but they are not fun, or at least at the size (40x15 mil) that I want.

This board contains (left to right, top to bottom): On the top row; TxRx Relay and Control, SideTone/CW, Audo PreAmp, Main Power Connector and Regulator (a little lower). On the next row; the KEY Jack, PTT Jack and Mic Amplifier, and the Audio Amplifier and Phone Jack.

My Minima AUDIO and Power Board
Proposed Configuration
If all goes well, the board size will be as shown at 2 x 4 inch. There is still room for additions or modification, but any additions will more than likely mean more vias. :-(

The circuit is a slight modification of the original Farhan Minima Transceiver circuit, I added; the Power Supply with Headers for the other Modules, I included the KEY and PTT circuits on this board because I wanted their Jacks near the Mic and Phone Jacks on the same board. A CPU signal and its Power Header is also included.

I still have to find a suitable Large Cap (500uF - Lower Right), I think the footprint as shown will work.

I just checked, and I need to order more Toner Transfer Paper, I may not have enough to build this board, especially if I make a mistake, Dang !


UPDATE: Mar 29, 2014 12:16

With a little digging, I found a stash of nice 35V 330uF Caps in my part bins, two of which I will use to replace the single 500uF cap as per the original schematic. The caps that I found are stand-up through-hole mount. I moved the connecting traces to the back side so that they could be soldered without the need for front-side solder (underneath the cap).

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