Sunday, April 20, 2014

Minima - CPU Module Mods

While building my Minima CPU module, and thinking about the circuit's programming interface components. I started wondering if there was an Off-the-Shelf USB product that could replace and simplify the circuit.

After a little research, I found three likely candidates, all available from Parallax.com;


Each have slightly different header pin-outs for connection to a project. Each uses the same FT232RQ USB-to-Serial chip.

For DYI, the FT232RQ chip is a simple "state machine", which does all of the hard work of USB-to-Serial protocol and signal-level translation. It is simple enough that it could be included directly into a project, all that is necessary is; the FT232RQ, a USB connector, and a few resistors (see the Prop-Plug datasheet with schematic). Note: Parallax encourages use of their schematic for DYI implementation, they will be happy to supply the parts, or as available elsewhere.

If the FT232RQ is included directly in a project, the +5V from the USB connector could also be used by the project, only the off-the-shelf 4D Systems USB Programmer (listed above) provides a fifth pin for a power connection.

The FT232RQ is available in the 28-LD-SSOP and the QFN-32 package. I will use the QFN-32, because I like smaller components. The price of the FT232RQ is about $5.00, but that is cheap for what it does and the components that it replaces.

Also, if the FT232RQ is included directly as part of a project, it is available for generic ASCII I/O for control or output via a standard USB connection.

Because I already have a Prop-Plug, I think I will simplify and re-layout the next Revision of my Minima CPU module with a simple Prop-Plug header. I hope this will work as a generic dumb download interface with the Arduino Interactive Development Environmnet (IDE), but this remain to be tested. Does anyone know?

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Saturday, April 19, 2014

Minima - CPU Module Progress

After making modification to my experimental Minima CPU board layout, I built a board via the Toner Transfer Method, then coated it with solder, and then started installing the via's and a few components. At this stage, the board looks a little rough as the thin layer of rosin coats everything. When complete, the board will be washed with Alcohol and a very thin coat of high tension oil (Corrosion Block) will be applied.

The 11 mil Via holes are Stitched
With Stripped 8 mil Wire Wrap Wire
The new layout is larger than had been previously posted, because I decided to include small push button switches for each of the normally external controls. By including switches on this board other modules or wired connectors are not necessary for full operations, although edge headers (as shown along the near side) are supplied for eventual use of the external controls.

The current board is slightly wider than a 16x2 Character LCD module and other dimension (height) allows the switches and header to be exposed below the mounted LCD. Note: the LCD plugs in via a header across the top of the board, and in normal use, the LCD would typically be mounted remote.

Stitched Loops of Wire Wrap Wire
Installing small via's is NOT a lot of fun, but can be done with the aid of a Microscope. My method starts with drilling the hole in the via that is just big enough for the intended wire used to make the via connection. If the hole just fits the wire, the wire will stand straight through the hole. I stitch all via's together with a single wire, leaving very short loops on each side.

The very thin stripped Wire Wrap Wire is 8 mils in diameter, and the via holes are 11 mils (a tight fit), the via pads are 40 mils. Note: 8 mils are less than the thickness of 3 sheets of typical bond paper, but I really enjoy working on microscopic projects.

Once all holes are stitched together, the loops are bent tight to the board and then cut just out side of the edge of the pad with an X-Acto Knife. Wire Wrap Wire cuts very easily with a gentle wiggle of the knife. The loops on the backside are left in place to hold the wires in place.

After each via is soldered from the first side, the "cut and solder" procedure is repeated on the other side. Care must be taken to avoid heat transfer to the opposite side solder joint, even as small as the Wire Wrap Wire is, it can transfer enough heat to melt the backside solder (if to much heat is applied).

A very-very fine tip soldering iron is used with very fine 15 mil solder.

Because the stitching process is somewhat random, the Wire Wrap Wire is typically bent in to a "Z" shape, with a short flat tail on each side of the board.

I make a Microscope video with a USB camera of the process, but it did NOT turn out. I need to find an adapter for my good low light camera.

About one half of the parts are installed now, but a few (i.e., the 16 MHz Crystal) has not been ordered yet (maybe tonight).

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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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