Tuesday, March 29, 2011

I Need More Magic

I have been building HomeBrew PCBs via the Toner Transfer Method for a long time, as seen in previous posts. I am still trying to perfect my use of this method, where I can expect the same results each time.

There is sill some Magic to be learned.

Currently I am trying to perfect the alignment of the second side of a two sided HB PCB. I am trying circle Targets as common art for alignment guides. So far, I have had limited, and unpredictable success.

The lack of success is not that I can not align the circuit pads for each side, but how to repeatedly do it.

The current difficulty is; My Targets keep falling off of the PCB in the water soak bath, before they can be used.

In an attempt to do everything just right, I created another revision of my QRP QRSS Beacon, which is a two sided board of about 2 inches by 1 inch. The Targets that I am using are about 1/2 inch diameter placed around the edge of the board at random locations.

For this run, I was careful to clean the board as usual, and run it through the laminator several time as before (about 5). Normally, I run PCB and Transfer Paper sandwich inside of a small pocket made from a manilla folder. Successive passes are with the sandwich just setting on top of the folder pocket material, so that the Transfer Paper is in closer contact with the heated roller and the overall thickness is the same.

I have always had a problem getting good transfer results near the edge of the PCB material, and therefore have always provided a boarder of about 1/2 inch around the desired circuit art work. Now with my Targets in that boarder area, they are the art that is being lost.

I tried to get everything just right for this run. All was going well, until I was walking to the sink where warm water was waiting to dissolve the transfer paper release agent.

As I walked, I heard a "snap", from the PCB and Transfer Paper sandwich which I held in my hand. I could see the sandwich starting to separate at the edge. The "snap" that I heard was the targets releasing from the PCB material.

I think cooling and/or shrinkage of the PCB or Transfer Paper is the problem. From previous experiments, I was concerned that this might happen, so I let the sandwich cool naturally after the laminator. But, apperntly it cooled further as I walked to the sink.

As can be seen in the photo, the circuit art in the center of the board transfered perfectly, even with it's small 8/8 circuit traces. Only some of the Targets were lost, but this attempt was all about obtaining good targets.

Three Targets across the top, and portions of the lower targets were lost in the water bath, ghostly outline remains on the copper from where the Targets were previously attached.

I know from previous non-PCB experiments, moisture content has an effect on paper that is put through a laminator. Here in the Puget Sound area humidity levels are high and may be problem that needs to be understood and taken into consideration.

Now, what to do about this heating and shrinking problem, or how to avoid the bad results?

Maybe preheat the Transfer Paper to help stabilize it, by removing moisture?

Maybe moving the sandwich from the Laminator directly into Hot water bath? But I think the Toner has to cool a little before it can be disturbed.

I think if I was working on lager or a more conventional size circuits, all of this would not be a problem, maybe only very thin lines are susceptible to the problem.

I am still working on my HB Double Sided PCB Methods - but so far, the Magic still alludes me.


Sunday, March 20, 2011

RTC DS3231

I have recently been made aware of an interesting temperature compensated Real Time Clock chip, the DS3231. This information is archived here for my later use.

The chip contains its own Tuning Fork Oscillator element, and therefore very few external parts are needed. The chip was introduced in 2005 and available from Mouser for about $10.00 ea.

From the datasheet, the DS3231 provides:
  • Accuracy ±2ppm from 0°C to +40°C
  • Accuracy ±3.5ppm from -40°C to +85°C
  • Battery Backup Input for Continuous Timekeeping
  • Operating Temperature Ranges
  • Commercial: 0°C to +70°C
  • Industrial: -40°C to +85°C
  • Low-Power Consumption
  • Real-Time Clock Counts Seconds, Minutes, Hours, Day, Date, Month, and Year with Leap Year Compensation Valid Up to 2100
  • Two Time-of-Day Alarms
  • Programmable Square-Wave Output
  • Fast (400kHz) I²C Interface
  • 3.3V Operation
  • Digital Temp Sensor Output: ±3°C Accuracy
  • Register for Aging Trim
  • Active-Low RST Output/Pushbutton Reset Debounce Input

For my use in my Beacon Projects; the programmable alarms and once-per-minute interrupt output could be used for the two minute WSPR timing requirements, or accurate QRSS start of signal timing. The Temperature Output could be used for remote environmental sensing, maybe for balloon payload data.


Saturday, March 19, 2011

Macro Lens

In recent months all of by Blogged photos have been taken with my HTC Droid Phone Camera. But it is lacking a little for the small project that I enjoy. Very close-up photos can not be taken with the standard (almost pin hole) style of lens.

I found on eBay a Magnetic stick on Macro Adapter for phone cameras. If you search on ebay, the same lens can also be purchased for less than $10.00 (with shipping) . I decided to give it a try.

The lens comes with a Sticky Back Metal Ring which is placed on the phone camera. The lens has a similar strong magnetic ring that make it easy to attach/remove to/from the camera. When installed, the lens stick out about 1/2 inch.

The following are some of my initial test photos. The shooting stage is a paper towel backdrop on my bench, and the lighting was supplied via overhead florescent tube fixtures about 3 feet away. I think more light from each side would make for better results - I will have to work on that.

This new photo is of a previous (failed) Audio Amplifier project. The macro lens distorts the image a bit, and the near focus (depth of field) could be better, but it was not obvious there was a problem when I took the photo, the camera was trying to auto focus and does not always get it right.

This is a photo of my attempt to create the smallest traces that I could with the Toner Transfer Method. This coil and variable capacitor resonates at 10.14MHz. This photo is planer and therefore did not distorted.

The next photo is of my very early attempts to use solder paste and oven re-flow soldering, the board 1 x 1/2 inches.  This board has been stored with other examples for a long time. Under close full photo inspection, it is obvious the solder paste has flattened and now would short-out if used.

Click on the images, to see the raw camera image detail and photo size.

And of course, this is a test photo of my Partner in all my adventures, Tess my Dog, she is on the work bench next to the computer (Macro not necessary here). She would rather we be outside playing ball.

(5 years old)

It will be fun trying different staging and light set-ups for the photos.


Saturday, March 12, 2011

Ham Fest

I got up at 4:45AM today, to ready,  travel, and attend the Annual Mike and Key Ham Fest at Puyallup, near Seattle.

I just returned - it was great!

There was more stuff than could be viewed. The crowd was large, but we managed to get around to all of the tables.

Several of the local pQRP club members were seen, on one side of the tables or the other.

My purchased treasures include;
  • four each 90deg BNC connectors, 
  • six each 1/8th inch shaft knobs (for a audio adapter circuit that I am building),
  • and, an order for a new MFJ 269 from HamRadio.com, at a very nice discounted show-price, with free shipping to my home.

I am normally a sucker for Large Variable Capacitors, but some how I managed to avoided temptation.

We watched one fellow buy a milk crate full of some very nice Variables for only $20.00

Many older Mike and Keys were available, the D104 was well represented.

The Show Queen was sitting on its own old original box.

It was a great day, now we just have to wait 354 more days for the next event.


Monday, March 7, 2011

Signal Generation

I have been watching Jeff's - KO7M Blog and his current QRSS/WSPR Transmitter project using the DDS-60 as part of the prototype. Jeff had previously done some work with the AD5330 8 bit DAC.

Jeff's efforts have inspired me to look at a previous purchased Si750 SDR-Kit, that I still had not built.

Without much difficulty, I now have put the Si570 SDR-Kit together (only the 3.3v Regulator went in backwards, which I fixed). Testing is still in progress.

While investigating; the kit's circuit and the Si570 datasheet, the DDS-60 and its AD9851 device, I have learned a lot more about micro-controlled frequency generators and DDS's in general.

This may be Old Stuff for some folks, but this is what I have learned, this info is saved here for my future use:
The Si570
The Si750 SDR-Kit is a real neat device with a very wide frequency range of 10MHz to >900MHz and can be controlled via a two wire computer connection (I²C). It's output is square-wave, which is ideal for a mixer LO of a receiver
But, the Si570 has some limitations for use as a general use signal source. The output (square-wave) would require difficult frequency sensitive filtering to obtain a clean sine wave over the entire frequency range.
Obviously for a single frequency, a filter can be easily created, but for that single frequency, a simpler crystal or oscillator circuit could be used instead. 
Once setup, the Si570 output is continuious, without assistance from the computer or micro controller. 
The DDS-60 
More information needed.
The AD5330 
The AD5330 8 bit DAC is a general purpose signal/wave-form source with a frequency range of 1kHz to 36kHz. It uses DDS processor to create the output wave form. Almost any shape of output can be created.
For use as a AF signal source, it's output is normally a stepped waveform, which normally needs a low pass filter to remove the steps.The output can be used with a mixer to create double sideband signals. 
A continuous use computer or micro controller is needed to generate the steps of the intended frequency or wave form.

I need to explore these circuits more, and will update as necessary.


Saturday, March 5, 2011

New Headset

I have been needing a new Computer Headset for a long time. My old set was getting tired and recently one of the plastic brackets/bands broke and was unusable. I had been looking for a replacement for a long time, but could not find anything that I liked.

Must locally available Headsets (in stores) are of the "pad on the ear" type, for radio work and Echolink, I wanted "around the ear" cup type for better noise rejection. Web searches found several, but they seemed expensive and lacked the personal recommendation that I was looking for.

I requested recommendations on the Sunday Night Echolink "QRP" QSO, someone suggested the following:

Stereo Dynamic Headphones

The Headset looked good on the web page and the price was right (only $6.38 with free shipping), but at that low price how could they be of any good?

But, for only six dollars and change, how can I go wrong, my order was placed that night.

I received the Headset on Friday, and have been using the new Headset since. They feel good, sounds good, and are light on my ears and head. The new Headset has an inline volume control, which is nice, as my old set lacked the local control. The slight angle of the ear cups (with respect to the band) and the limited mic boom rotation angle, requires the mic to be located on the left side only. My old headset allowed the mic on either side. I previously used the mic on the right side, I will have to get use to the mic on the left side only.

The Headset is mostly plastic, but if they hold together, I think they will be a good valued addition to my shack.

I talked with John - KB0ADD, he also placed a set on order, it will be interesting to hear his evaluation report.

To the person on EchoLink QRP that suggested this Headset - Thanks.

Interesting: I see the Headset has increased in price, they are now $7.09

I have now been using this Headset for a couple of weeks, I like them and found the inline volume control very useful. The cord is about 18 inches shorter than my previous set, but still very usable. I purchased two additional sets, one for each of my other workstation locations.

A very good value!


Wednesday, March 2, 2011

More PCB Work

Practice has not made perfect, yet.

I thought the new found targets for DipTrace PCB was going help me do the Double Sided Alignment trick, see previous post. The concentric circles looked good on paper, but in practice they are too thin to stick to the PCB for Toner Transfer. The solution is simple make the circles lines thicker - ah, no-can-do with DipTrace. The targets were made from software built-in "Mounting Hole" art (for reasons given before) and the image thickness for circles can not be altered. Too bad, it was a good idea. Other software PCB packages may have more flexibility for creating Targets.

So, back to the drawing board.

I created PAD art for a target. Pads and holes are the only items that DipTrace prints on all layers (Component and Circuit Side of the PCB). My new Target (pad) is 500 mils dia, with a hole 475 mils, which creates a nice circle with a line thickness of about 12 mils. This photos shows the results after Toner Transfer and Etch.

A major part of the lower center Target (circle) was lost in the process. The rest of the circuit looks great.

Now, for the new (maybe hard) part, aligning the second side art with the the first. The Transfer Paper is shown behind the PCB material with the Targets (circles) in alignment. So far, everything has worked as I expected or hoped. Note: the shiny surface on the PCB is clear tape, used to avoid addition etching while the second side is being etched. I inadvertently cut the Transfer paper too short, note the missing targets on the right side, with multiple redundant targets recovery was easy.

The second side did not Transfer or turn out a well as the first, some of the Toner came off in the water soak process. I think when I changed the water in the bath, the water was TOO hot, which "shocked" the PCB material and it expanded faster than of the paper (or vise versa).

A little of the Board Outline Trace and most of the Targets came off the PCB (maybe popped off) near one end of the image. Other than that, the alignment as inspected on the light table looks very good, as shown by light through the center of the pads and VIAs (click on the next image for a good look).

Note: the 60Hz hum bars on the photo were created by the flickering florescent lights of the light Table.

Good alignment can be check by inspecting the small 10 mil holes in the VIAs, five VIAs can be found on the board.

I will not use this PCB to build a project, it will be kept as an example. Due to some of my experimental last minute PCB design edits, the holes on the major PADs had reverted to the default size (35 mils), which is too large for my project (I actually wanted 12 mils holes). I will have to re-make the board.

My next experiment will include more attention to the thermal environment of all processes.


Tuesday, March 1, 2011

Targets for PCBs

It is amazing, how simple ideas can make a world of difference.

As stated in the previous post, adding Targets to the edge of PCB Layout Art will allow me to accurately align both sides of the PCB images for the Toner Transfer Method of building double sided boards.

Use of targets is not new, but my use of them with Toner Transfer is new to me.

I have struggled with image alignment while building double sided boards in the past, Toner Transfer make the task much more difficult compared to Optic Film Exposer Methods. With the optic film method it is easy to see through the art work for alignment and both images can be taped together and/or exposed together in a double side exposer fixture.

I have search the web for ideas regarding Double Side Toner Transfer methods and found nothing that I liked. Some suggest holes and pins to provide alignment, but transferring the resulting sandwich for lamination is problematic.

The Toner Transfer process normally uses non-transparent transfer paper, and therefore alignment of the two images is difficult. But, alignment can be done by adding target around the layout image (similarly as done with optical method) and partly extending them beyond the edge of the intended PCB material.

The etch process becomes a two step process, one for each side. The first etch creates the first side of the intended PCB layout pattern and copper targets that extend beyond the edge of the board. The etched targets on the edge of the board are aligned with the second side target images that extend beyond the edge of the PCB material.  Both target sets are created from the same computer art work.

Circles are used for targets, as your eye is much more sensitive, to slight phase shift (or displacement) of concentric overlapping circles, than as can be seen with just straight lines.

With DipTrace (the PCB software that I use), targets can be created using Mounting Hole images, multiple holes are stacked one on another, and then saved as a library part.

What this means to me

My abilitiy to build much more complex Homebrew PCB has greatly improved.

I have now experimentally used this method to build a PCB with 8 mil traces, 12 mil clearance, and 40 mil "VIA's" pads with 8 mil (or maybe smaller) holes. Solder and tight fitting clipped wires will be used in the VIA's  to provide double sided connectivity.

Note: This is a great tip that I found on the Web; use a single long wire, stitched between all VIA's with loops between, solder the wire at the VIAs and then clip the loops away.

I have found installing (looping) VIAs after all other parts to be helpful, it avoids adjacent part installation dislodging the very sort clipped wire that form the VIA.

Component Side Targets                Circuit Side Targets

The targets are randomly placed around the Layout, the odd number of targets and placement help avoids confusion when attempting alignment. In theory, only two targets are needed, but more targets ensure enough are properly etched and are usable in practice.

For use with PCB Toner Transfer Method, the Component Side image is must be Mirrored via the laser print process.

The example shown here are very small boards (1x2 inch), alignment for larger boards with larger traces should be even easier.

It is interesting, once a long time ago, I was involved with the production of Technical Manuals and their Art Layup, many of the techniques that I used almost 40 years ago find their way into my projects of today.