All posts by vk2vjb

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GPSDO Time reference project progressing

IMG_20150809_132613

 

 

The Thunderbolt Trimble arrived during the week, and after 48 hours for the self survey and to calibrate the internal PID loops its delivering a nice level of performance, the only disagreement with my HP 5335 Counter is down in the 10E-15 territory which is outside the resolution of this GPSDO.

The entire ensemble is, however, untidy.  The GPS unit itself is in a small metal box, I have an external laptop power supply to provide the required voltage levels, serial connections, antenna connection, and then the outputs… untidy.   It gets worse when I run a serial cable to monitor it via Lady Heather or similar.

I want to be able to leave this system running all the time, so it needs to go in a box and include its own monitoring.  I also don’t want to spend a fortune here but I also wanted rack mount, and sometimes things just work out with a 2RU rackmount PLA project box at the local Jaycar for $20 😉

The internals for the box are mostly coming out of my ‘junk’ box, bits and peices I’ve collected over the years, including:

* Beaglebone Black

This board will be used to ‘monitor’ the GPS unit and provide network connectivity for ntp etc.   This board will also run the display, keypad, etc so I can monitor the system without using an external PC.

* USB to Serial converter.

An old prolific (PL2303) USB<->Serial converter will be used, while strictly not necessary it removes the need for level conversions here and the BBB has a usb port readily available.

* CM12864-2 128×64 White on Blue Graphical LCD bought for a project several years ago and never used.   This will make a nice display for this project.

* 16 character keypad picked up at a field day somewhere.  I don’t _need_ 16 keys, but it looks ok and will support any additional functionlity I may add later.   Its been sitting in a drawer for years so the price is right 😉

*Amphenol case mount BNC connectors, I picked up a box of ~20 of these for $2 at a field day recently.

* level converters should these be necessary, I suspect they won’t be needed.

I have ordered on additional item:

Sparkfun Graph LCD serial backpack for the display, simply because this will be more convenient wiring the display up to the BBB.

The next steps:

* Code up a parser for the messaging coming from the GPS.

* Wire up the keypad and code up a driver using GPIO pins.

* Wire up the display and see if I can find a driver somewhere, I suspect I can.

* Code away.

all up the boxing project will cost approximately $50 out of pocket given I already have all the key components, and $30 of that is the backpack for the LCD panel to save some time.

 

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… I need to go back to school…

 

The Thunderbolt Trimble GPSDO I ordered finally arrived, after all you can’t possibly have _too_ many time sources.   Of course the first thing I did was set it up, run the position survey and plug it into my HP 5335 Universal Counter which was recently calibrated to a rubidium standard.

Lo and behold after warming up the counter still read:

9.999 999 71 +6   (i.e. 9.999 999 71 * 10E6)

Ok, the trimble will take a while to run the Allan Deviation, I’ll leave it go and come back later.   24 hours later I read:

9.999 999 71 +6

No change, so what’s going on here as I expected exactly (or close to) 10 MHz and I’m reasonably sure the HP Counter is accurate.

I switch to Period mode:

100.000 002 9 -9 (i.e. 100.0000029 *10E-9

Which matches the observed frequency, at 10MHz the period should be exactly 100 nanoseconds…  what’s going on here, lots of fiddling and trying to work out why it wasn’t right, is my counter wrong or there a problem with the Trimble…

What I didn’t facter in is that the ‘002 9′ is in fact ‘2.9 Femtoseconds’ or 2.9*10E-15, the rated accuracy of the GPSDO is 1.16*10E-12.

Aka… timing resolution achieved, and I can forgive the 2.9 femto seconds in either the counter or gpsdo.  In other words, its reasonably accurate as is my counter, and that’s probably as accurate as I’m likely to have… at least until I get my hands on a cesium standard 😉

All I need to do is sit, wait, confirm the results once the GPS has reached its rated resolution, and then use that as my frequency reference.  This will probably take a week or so, but for now it’s not bad.

http://www.vk2vjb.net/2015/08/06/go-back-to-school-nugget/

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First part cut on the New CNC (Roland mdx-20)

I spent a little time today calibrating the desktop CNC mill I’m refurbishing.   A little writeup is available on my site if people are interested.   This CNC will be mainly used to make PCB’s for radio projects 😉

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I spent a little time today in between IT Tasks at work tuning the little desktop CNC I acquired recently. One of the first objectives is to replace the spindle which has an unusual collect design with a more generic ER11 collet so I can use all the small PCB and milling bits I have rather than searching for bits with a 6mm shaft. As part of this upgrade I’ll be moving from the standard 10W DC motor to a brushless RC motor with a little more torque and a lot more speed which is essential when working with small bits.

First up was calibratiIMG_20150612_200817ng the axes, and it turns out the web site I found earlier with the gearing ratio’s on the roland was either incorrect or the one I have is different as all measurements were out by approximately 25%.

A lot of tuning later I have the following (recorded for prosperity):

Step Angle: 3.75 degrees/step
Travel per revolution: 2.36mm (a resolution of 0.02mm)

So the resolution isn’t as good as I’m used to, but sufficient for everything I’ll be using this mill for. There was a little backlash on both the X&Y Axis, which I’ve managed to resolve by tightening the draw wires. I’m really happy I could fix this as the TinyG controller doesn’t actually support backlash compensation.

 

The tuning took a lot longer than it should have as I kept trying to fix the 0.02mm backlash I was seeing without realising that was the resolution of the cnc… Doh!

With the mill all tuned and adjusted, it was time to follow the age old tradition where the first part cut on the CNC should be a part ‘for’ the CNC. In this case in Wax rather than Delrin so I can verify the sizesIMG_20150613_164822 and offsets, good thing too as one of the mounting holes is off by 1.75mm.

This also lead to a little bit of Yak shaving where I needed to render the slab of machine wax down to sizes suitable for this mill. I have a nice little pile of wax ingots now, and still have another batch of wIMG_20150613_164440ax to render down tomorrow.

project

New(ish) PCB Milling Machine

I’ve sold my old heavy duty CNC and acquired an old non working Roland MDX-20 Modela that needed some love.  These little engraver/modelling machines sold for many thousands of $$$ in the past and were widely used in various industries.  Sadly this unit hasn’t had the best life and needed some work to get it going as the original controller board had been (destructively) removed and some seriously hacky working on the wiring left it in a real mess.

With few hours hacking on the weekend I now have all three axis moving they they should using an open source ‘TinyG’ controller board which mates with web based control software.  All that is left to do is build a new spindle as I’m not happy with the runout on the standard setup, I’ll need a little lathe time to make that once the parts (and tools) have arrived (and tidy up the wiring).   Fortunately the local hacker space has a metal lathe that should be up to the task.

This unit is small enough that I can bring it on project day to show off 😉 and maybe even mill some PCB’s.

This CNC will be used to make circuit boards for assorted radio projects, first up will (probably) be a series of RF filters.

http://www.vk2vjb.net/2015/05/30/good-bye-to-one-cnc-hello-to-a-newish-one/

 

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received my sm1000 smart mic today

2015-05-17 17.29.20

The sm1000 is an interesting bit of technology implemented as a microphone to bring digital voice to almost any ham receiver.  The microphone implements the codec2 voice codec designed by David Rowe in hardware, replacing the need for a pc running freedv.

Im looking forward to making some cables for my ic-7100 and ft-857d and trying it out.

It was nice to see David was recently awarded at the WIA conference for his contributions to amateur radio, specifically with Codec2, FreeDV and now the SM1000.

http://www.rowetel.com/blog/?p=3125

 

site updates

What’s in an instance

I’m happy with the performance of the web site on the new AWS Instance.   The initial instance was the ‘t1.micro’ which is the old option from Amazon using para-virtualisation (PVM), unfortunately performance on this instance was terrible as access was capped at 10% of the CPU and the cycles ‘stolen’ exceeded 90%.

Instead of sticking with the poor performing PVM I’ve opted to moved to a HVM instance which allows for bursts in processing capability above the subscription level, providing you have sufficient cpu credits available that is..   A CPU Credit is simply an accounting of when your not using the full amount of CPU your subscribed to, so you can use it to burst later.

I’ve also enabled caching via Amazon CloudFront, which will cost a little extra but delivers all the large content (images, style sheets, etc) via the AWS Cache and Proxy servers reducing load time for the user and reducing performance overheads on the virtual server.

The change in performance with both of these changes is significant with page rendering times down under 5 seconds for all content.   I’m hopeful that this will continue to be the case.

The site has been fully migrated to the new instance, and the mailing list migration will likely occur next week.

If you experience any issues, please let me know.

Jason (vk2vjb).

 

site updates

Web site migrated to new instance

Hi all,

 

The vk2bv.org web site has been migrated to a new AWS instance to provide better performance as the original instance type simply wasn’t adequately resourced.   The new instance is already proving more capable and performant.

If there are any issues please email me at jason AT ball.net and I’ll get onto it ASAP.

Regards

Jason

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Club Merchandise

A quick post to remind people that there is a variety of club merchandise available on Cafe Press. I’ll add a merchandise page to the web site just as soon as I find a cafe press plugin that actually works, in the meantime wander over, have a look, and buy something knowing a little of that purchase comes back to the club.

http://www.cafepress.com/vk2bv