Wednesday, April 23, 2014

Minima - CPU Module Mock-up

As stated is the previous post, I was concerned that maybe the JTAG header could interfere with the LCD display. A mock-up would be necessary verify clearance.
Minima CPU
Mock-up to Check JTAG Clearance
The mockup was done with a simple print of the layout, with headers pressed into a Styrofoam block. The display is supported by the header pin at the top and the two nylon screws as legs in the lower corners. Because this is an experimental device, additional constraints are not necessary. The header at the top left, is for BAND switching.
LCD Display Header
The JTAG 6 pin heard (2x3) is located beneath the LCD display. When in the JTAG header is in use, the LCD display will not be used, and therefore removing the LCD will not be a problem. In fact because the JTAG Programming process used a few of the same pins as those used but the LCD, removing the LCD avoids any interaction concerns.

Checking JTAG Clearance below LCD Display
(viewed from the left)
The LCD Display sets at a slight angle forward for the users viewing benefit.

The mock-up revealed an additional concern, the header on the right end of the module should be moved up a little to avoid the nylon screw. The two header on this end are the SSB Mode and Si570 control headers.
The Two Pin Herder Will be Moved to the Right
(viewed from the right)
The spacing between the LCD and front push switches appears about right for easy access. The header at the bottom is (left to right), AUX-CTL for the Minima Audio sections, the Tuning Pot, and the Programming header.
Push Button Switch will be
Mounted in Font of the LCD Display
(as viewed from User Respective)
With much research, I have discovered there are many JTAG header standards in use, some have as many as 20 pins. The high pin count JTAG headers are used for monitoring as well as In Circuit Programming. I will use the simple six pin header and configuration that is used by the Arduino.

With maybe only slight modifications, I am pleased with the layout and mock-up results.


Tuesday, April 22, 2014

Minima - CPU Module Mods - PLus

After chatting with my friend, Jeff - KO7M, I decided to again modify the next Revision of my Minima Controller. Jeff has pointed out that a new raw ATmega328 processor does not have a bootloader.

I guess I knew that already, but I thought that I could use the TxRx pins to download a bootloader similar to downloading an Arduino Sketch. I was wrong.

More research is/was obviously needed.

REV04 of my Minima Control Module
The Backside
The latest addition to my Minima Module Mods is a JTAG connector, which will be used to download the Arduino Bootloader, or other raw mode programs (or sketches). The JTAG connector is under the "locally" mounted LCD display (left of center), but the display will be un-plugged during the JTAG use, because the JTAG and the LCD uses some of the same processor pins. I will have to check that the JTAG connector pins will not interfere with the mounted LCD board.

Once the ATmega328 programmed with the bootloader, the display will be re-installed, and then normal sketch programming will be done via the Prop-Plug TxRx header (lower right).

My previous modifications included; Consolidation of several individual headers into a single AUX-CTL header (lower left), Remove the Minima schematic programming components which will be replaced with a Prop-Plug header. I have also added my own version of EMI suppression by adding 1nF caps to each board edge header pins.

This board is getting complex enough that I am considering having it professionally manufacture, it is about 6.6 square inches and will cost a few bucks, but it now has about 65 via's (which are not exactly fun to do on a Homebrew board). I may still create a prototype board via Toner Transfer, but it will take some time/work.

The goal for this board is to be compatible (but more flexible) with the Farhan Minima Transceiver Project. I also plan to use this board with/for other Test LAB projects.

More project info to follow .  .  .


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;

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?

UPDATE: Apr 21, 2014 14:11
As per the comments, Larry has suggested the "FTDI Friend" - $15 from


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).


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.

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.


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 !


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.


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.


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).


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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