Minima - VFO Troubleshooting - Cont'd 3

After four days of extreme frustration, while troubleshooting my Minima VFO Module (see previous posts), there is success!

My friend Jeff - KO7M came by today with known working tools (BusPirate) and parts (Si570). We had been troubleshooting my VFO problem via e-mail and over the phone, but we were not getting anywhere.

Jeff at the Microscope

The problem came down to, two (2) simultaneous failures, one in my BusPirate (BP) and one in my VFO Module that I was testing.

1. My BusPirate fails to generate I2C SCL (clock) signals, even though many other functions seamed to work. Without an SCL signal data can not be received by a Device Under Test (DUT), even though the BP can receive Data using the same SCL wire from the DUT.

2. The failure of my VFO was the Si570 itself, it would not accept I2C data or commands, even though it produced RF on the output. It is DEAD.

Before Today

Before today, I had created an Si570 BreakOut Board (see previous post), with just the Si570 and Header pins. My intent was to verify that the BP was working as expected, but because there are also wires, clips and connectors that could have failed results were inconclusive.

Si570 Breakout Board

Si570 Breadout Board

At this point I still could not determine if the failure was in the BP or had I damaged another Si570. So, I built a second Si570 Breakout Board. But alas, still nothing seemed to work.

Today - Jeff to the Rescue !

With Jeff's known working BP we quickly determined my VFO Module (i.e. Si570) was bad. Other I2C devices; the two Si570 Breakout Boards and a Real Time Clock Module (RTC) all work as expected.

Because yesterday I had used my last Si570 on the second Si570 Breakout Board, I could not repair the VFO Module. but we could build an Si570 Breadout Board Adapter  that connects between the Breakout Board to the Minima CPU Module. I had previously designed and did a layout for the Adapter with DipTrace, for just such an occasion. We spent the rest of the afternoon building and testing the Adapter Board.

The Adapter Board tested correctly with Jeff's BP as we hoped. It also tested and worked with the Minima CPU Module.

Adapter Board Connected to the Minima CPU
and a Coax Cable, the Si570 Breakout Board in the Foreground

Stacked and Ready for Testing

Now all Minima Modules worked as expected, we checked for a varying frequency while tuning, we estimated on the oscilloscope 20MHz at the low end, and 50MHz and the high end while Tuning across the (0-30MHz) HF band (for a 20MHz IF).

34.2MHz  (14.2+20) As Shown
with 10X Expanded Sweep Scale

Minima CPU Module and
Temporary VFO Module 

I am a happy camper - Thanks Jeff, for the help !


I can now continue my experiment Minima Transceiver Project.

I need to order a few more Si570's, and a new BusPirate (or troubleshoot and fix it).

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Minima - VFO Troubleshooting - Cont'd

Regardless of what I have tried, my Minima VFO Module does not seem to work, see previous post.  It does not respond to a simple I2C Address Scan from the BusPirate (BP). The problem could be a something simple on the VFO Module, a dead Chip,  the BP, or the connecting wires. I could test the BP and wires if I had a known working I2C device, but I don't.

To fix that, I am going to build a simple stand alone Si570 BreakOut Board, which will only contain an Si570 and Header Pins. If this works, it will be useful for verifying my BP and also it will be useful for other standard ProtoBoard experiments.

Proposed Si570 BreakOut Board

A simple Google search did not suggest a consensus of pin outs for a breakout board, I decided to arrange the pin in Si570 documented order similar to a DIP. The board will be about 0.5x0.6 inches. I guess I should have made the pin row spacing 600mils (not 500mils) so it would fit standard PCB DIP Sockets.

Using standard pin order requires a trace on the backside with the accompanying two via's. Two additional via's will help tie the front and back ground planes together. All soldering for the Headers will be done on the top side, because Homebrew boards do not have plated through holes, and therefore it would be difficult to solder under the Headers on the back side.

I could have included the two required I2C Pullup Resistors, but no, I wanted this to be a generic as possible.

This maybe a very useful board for my future projects, it is a simple task to make several copies while making the first, using the Toner Transfer (TT) Method.

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Minima VFO - Troubleshooting

Last week I was on Jury Duty, and therefore there was little or no time for my Hobby Projects.

But now, I need to continue troubleshooting my Minima VFO which is reporting an error on the LCD display. The error at program reset is: "Si570 comm error".

As programmed, the Arduino Sketch seems to ignore the error and continues with normal execution. If I remove (unplug) the VFO Module the program "stops" and does not get past the initial start-up stage, and therefore it appears that there is "some" communication with the Si570 (or at least the Pullups work).

My friend Jeff - KO7M, suggested using my BusPirate to ensure that the Si570 was set on the correct I2C address as published and working as expected. This will be easy because of the modular construction that I am using, tests can be conducted on only the VFO Module. This testing would be much more difficult (but not impossible) if everything was built on a single board.

Minima VFO connected to the BusPirate

I am glad I blogged my previous use of the BusPirate, it helped me to remember the commands. I think I will expand that post to be more complete.

Well, maybe it is NOT so easy, because so far, I have not found the VFO problem. In fact, I do not seem to be able to do a simple "scan" for the I2C address.

More troubleshooting needed !

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Minima VFO - Under the Microscope

I have been doing some troubleshooting of my Minima VFO, for some reason it is not "talking" with my Minima CPU module. My friend Jeff - KO7M as provided some suggestions for resolution that I am working on.

My Minima VFO
As Built

Just for fun, I took some Microscope Photos while reviewing the circuit and PCB layout for errors. Here are a few for your review.

Si570
From Pins 4 and 5 Perspective

The 3.3 Volt Regulator - SOT-89-3
and Its Output 0805 Filter Caps

Power Indicator with its attending limiting Resistor
The Resistor and LED are size 0603

Binocular Core Output Transformer
This is 32 AWG Wire

SMA RF Output Connector

I enjoy working under the Microscope, there are many things that otherwise we would not see.

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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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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 :-)

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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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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 VFO 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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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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