Planet Linux Australia

Syndicate content
Planet Linux Australia - http://planet.linux.org.au
Updated: 39 min 16 sec ago

David Rowe: FSK over FM

Sun, 2014-12-14 10:30

I’m interested in developing a VHF mode for FreeDV. One intriguing possibility is to connect a modem to legacy analog FM radios, which would allow them to be re-purposed for digital voice. One candidate is FSK at 1200 bit/s, which is often used over FM for APRS. This operates through FM radios using the mic/speaker ports on $50 HTs, no special data ports required.

So I want to know the performance of FSK over FM in terms of Bit Error Rate (BER) for a given SNR. That got me thinking. When you send FSK through a SSB radio, it faithfully mixes the tones up to RF and you get FSK over the channel. The SSB radio just adds a frequency translation step. So we can model FSK like this:

However sending a FSK modem signal through a FM radio is very different:

FSK over FM is not FSK when you look at the over the air waveform. The spectrum is no longer two tones bouncing back and forth. So what is it?

I wrote a simulation called fsk.m to find out. This involved building up a FSK modem, and an analog FM radio simulation. The modem took me only a few hours but I was struggling with the analog FM simulation for a week! In particular making my FM demodulator get the same results as the theory. FM is a bit old school for me, so I had to hit the ARRL handbook and do a bit of research.

FSK Modem

It’s a BEL202 simulation (as used for the APRS physical layer); 1200/2200 Hz tones, 1200 bit/s. I’m using the integrate and dump demodulation method and it matches the theoretical curves for non-coherent BFSK. Here is the FSK modem in action. First the FSK time domain signal and spectrum. The spectrum is a bunch of energy between 1200 and 2200 Hz. Makes sense as the modulator keeps moving back and forth between those two frequencies.

The next figure shows the sames signals with a 10dB SNR. Although the time domain signal looks bad, it actually has a BER one error in every 1000 bits (1E-3). The reason it looks so bad is that in the time domain we are seeing the noise from the entire bandwidth (our sample rate is Fs=96kHz). The demod effectively filters most of that out.

This next plot shows the output from the 1200 and 2200Hz integrators in the FSK demodulator for the 10dB SNR case. The height measures the energy of the tone during that bit period. As we would expect, they are mirror images. When one detects a large amount of energy, the other detects a small amount of the other tone.

Analog FM

The next step was to build a simulation of the modulator and demodulator in an analog FM radio. I wrote some code to test the input Carrier to Noise Ratio (CNR) versus output SNR. The test signal was a 1000 Hz tone, and the modulator had a maximum deviation of 5kHz, and a maximum input audio frequency of 3 kHz. After the demodulator I notched out the 1000 Hz tone so I could measure the noise power, the input to the notch filter was signal plus noise.

Here is the spectrum at the FM demodulator input for a 1000 Hz test tone:

The top plot is the tx signal centred on a 24 kHz carrier, in the bottom plot it has been mixed down to baseband and filtered. The FM signal is 16 kHz wide, as per Carsons rule. Here is the output of the FM demodulator:

At the top is a nice sine wave, and the bottom also shows the sine wave. You can see the effect of the output 3kHz low pass filter used to limit the noise bandwidth of the demod output.

When tested over a range of CNR inputs, I achieved output SNRs (red) in line with the text books (green):

At about 9dB the demodulator falls away from theory as the FM demodulator falls over, this is pretty typical. The theoretical model I have used is only valid above this 9dB threshold. You often hear this threshold effect in FM. The blue line is SSB for comparison. Over a certain threshold FM does quite a bit better in terms of output SNR for the same input CNR.

FSK over FM

OK so lets combine the simulations and look at the BER performance:

Oh dear. If my simulations are accurate, it appears FSK over FM is a lemon. About 7dB worse than regular FSK for the same BER. So using a FSK modem over a SSB radio would allow you to use 7dB less power than running the same modem through a FM radio. Coherent PSK is 3dB better again that FSK so that would get you a 10dB improvement. Simple FSK or PSK transmitters are easy to build too, and needing 7-10dB less output power would simplify them again (e.g. 100mW versus 1W).

Here is the spectrum at the FM demodulator input when sending FSK:

Note the FM spectrum looks nothing like regular FSK “over the air”, which looks like this:

So What went Wrong?

Given the plot of analog FM performance (say compared to SSB) above I had expected better results from FSK over FM.

I think I know where the problem lies. The input CNR is a measure of carrier power to noise power in the input bandwidth of the demodulator. Another way of looking at the VHF channel noise is a “floor”, which can be modelled as the average noise power per 1 Hz of bandwidth, called No.

So the Universe has given us a fixed “noise floor”, which will be the same for any modem. The FM demod input bandwidth is much wider, so it’s sucking up much more noise from the channel, which the poor demodulator has to deal with.

Lets plot the analog FM demod performance again, this time against C/No rather than C/N:

This takes into account the noise bandwidth, everything is “normalised” to the noise floor. When the C/No is beneath 48dB SSB looks much better. We can see a 7dB improvement over FM at low C/No values. This also explains why the microwave guys prefer SSB for their long shots.

Here is the BER curve scaled for C/No:

Conclusion

It appears the key to good modem performance is the RF bandwidth of the signal. Given a constant noise floor No, the signal bandwidth sets the total noise power N=NoB the demodulator has to deal with.

This has put me off the idea of a FreeDV VHF mode based on BEL202 FSK through legacy FM radios. I’d really like to come up with a mode that has sparkling BER versus SNR performance. I haven’t spent years making Codec 2 operate at low bit rates just to throw those gains away in the modem!

Couple of ways forward:

  • Take a look at GMSK.
  • Consider developing a version of the SM1000 into an (open source) VHF SDR radio that can do PSK. Not as crazy as it seems. We are already planning a HF SDR version. Radio hardware is getting simple now the signal processing is all moving to software. We can make the modem so efficient that the PA can be modest (100s of mW).
  • Dream up waveforms that can pass through legacy FM radios and have a low over-the air bandwidth. For example FSK that shifts between 300 and 400 Hz. In the past I’ve dreamed up new Codec 2 modes (1300 and 450 bit/s) to suit the properties of HF channels. So why not design a modem waveform to suit us? Go open source!
  • Cop the performance hit and use BEL202 FSK. It might still be useful to use legacy FM radios for DV even with a 7dB loss in modem performance. It seems to work fine for APRS. If your C/No is high (as is often the case) then FSK over FM will have zero errors.

Andrew Pollock: [life] Day 317: Doctor again, final Tumble Tastics, a good deed and general fun

Sat, 2014-12-13 12:26

Zoe slept solidly until 6:48am. It was overcast and cooler, so I dare say that helped. Uninterrupted sleep is always nice. We had a nice snuggle in bed before we started the day.

First up, we had another doctor's appointment so the doctor could have another go at freezing off the wart on her hand. Despite some initial uncertainty, Zoe was much braver this time, and the doctor got to really hit it this time. Zoe was very proud of herself.

After the obligatory Freddo Frog for bravery, we headed home via the Valley to clear my PO box.

After a little bit of TV, we scootered to Tumble Tastics for her final class.

Tumble Tastics has been really great for Zoe. Zoe's always enjoyed gymnastics, and has definitely enjoyed this. She was very fond of Mr Fletcher, her teacher (she seems to really like male teachers) and especially loved the rope swing they had in the classroom. I was personally impressed by the theme that they did each week, and their ability to keep the activities in the relatively small room fresh and varied each week. They use the limited space that they have quite effectively. The fact that it was an easy distance from home was a bonus.

On our way back home, we discovered a stray dog on the side of Hawthorne Road. I checked its collar, and it had a mobile phone number on it, so I gave it a call. It turned out the owner was down at the supermarket, and his wife was at home with a baby, so I offered to return the dog for him.

It was only about a 500 metre walk, but it was very back-breaking, as the dog was pretty dumb and wouldn't follow us, so I head to lead it by the collar all the way, which involved me having to walk bent over all the way. Zoe wanted to help, but he was a bit to big and heavy for her to lead.

He was an interesting cross-breed. He had the markings of a blue heeler, but the head and general body shape of a terrier of some sort.

Due to some ambiguous letterboxes, we ended up at the the wrong house (off by one) and this house had a black Siamese cat that emerged from a boat parked in the front yard when I knocked on the door. Of course the dog decided to chase off after the cat, and I thought all was lost at that point, but he came back after having chased the cat away.

We then proceeded to the right house, returned the dog and went home for a well earned lunch.

After lunch, we went for a walk in the rain to post a letter. Zoe had a great time puddle jumping in her rain boots. We also made an opportunistic Christmas present purchase, and then went home again.

We had an unplanned afternoon of silly play for a while, with lots of running around and tickles and laughter. It was nice. Our downstairs neighbour, Deana, popped up to hang out for a bit as well, which was nice.

Zoe watched a bit of TV after that, and then Sarah arrived to pick her up.

Glen Turner: USB product IDs for documentation - success

Fri, 2014-12-12 23:47
Motivation

In a previous posting I reported a lack of success when enquiring of the USB Implementors' Forum if a Vendor ID had been reserved for documentation.

To recap my motivation, a Vendor ID -- or at least a range of Product IDs -- is desirable to:

  • Avoid defamation, such as using a real VID:PID to illustrate a "workaround", which carries the implication that the product is less-than-perfect. Furthermore, failing to check if a VID:PID has actually been used is "reckless defamation".

  • Avoid consumer law, such as using a real VID:PID to illustrate a a configuration for a video camera, when in fact the product is a mouse.

  • Avoid improper operation, as may occur if a user cuts-and-pastes an illustrative example and that effects a real device.

  • Avoid trademark infringment.

For these reasons other registries of numbers often reserve entries for documentation: DNS names, IPv4 addresses, IPv6 addresses.

Allocation of 256 Product IDs, thanks to OpenMoko

OpenMoko has been generous enough to reserve a range of Product IDs for use by documentation:

0x1d50:0x5200 through to 0x1d50:0x52ff

Note carefully that other Product IDs within Vendor ID 0x1d50 are allocated to actual physical USB devices. Only the Product IDs 0x1d50:0x5200 through to 0x1d50:0x52ff are reserved for use by documentation.

My deep thanks to OpenMoko and Harald Welte.

Application form

The application form submitted to OpenMoko read:

  • a name and short description of your usb device project

    Documentation concerning the configuration of USB buses and devices.

    For example, documentation showing configuration techniques for Linux's udev rules.

    The meaning of "documentation" shall not extend to actual configuration of a actual device. It is constrained to showing methods for configuration. If an VID:PID for an actual device is required then these can be obtained from elsewhere.

    OpenMoko will not assign these "Documentation PIDs" to any actual device, now or forever.

    Operating systems may refuse to accept devices with these "documentation VID:PIDs". Operating systems may refuse to accept configuration which uses these "documentation VID:PIDs".

  • the license under which you are releasing the hardware and/or software/firmware of the device

    The documentation may use any license. Restricting use to only free documentation is problematic: the definition of "free" for documents is controversial; and it would be better if the PID:VIDs were well known and widely used by all authors of technical documentation.

  • a link to the project website and/or source code repository, if any

    Nil, one can be created if this is felt to be necessary (eg, to publicise the allocation).

  • if you need multiple Product IDs, please indicate + explain this at the first message, rather than applying for a second ID later

    Approximately 10.

Andrew Pollock: [life] Day 316: Bike riding play date and picnic

Thu, 2014-12-11 22:25

Zoe woke up at around 1:30am. I think the fact that her nightlight had gotten unplugged didn't help matters, and despite fixing that up, she jumped into bed with me at 1:50am.

We had a slow start to the day, but that said, I did manage to bake a batch of mince pies and make pastry for a quiche before we headed out at 9:30am, so it wasn't an unproductive morning.

I'd organised with Kelley to have a bike riding play date with Chloe at the Minnippi Parklands. I figured that since Chloe can already ride a bike, it might encourage Zoe.

It was a pretty hot morning, and not a lot of attempted bike riding happened before Zoe had had enough. No major breakthroughs happened, but it was very handy having a second adult. I think I need to put Zoe's bike seat up, as she's grown a bit since she first started trying to learn.

After we gave up on the bikes, the girls went and played on the pretend aeroplane and air traffic control tower for the rest of the morning, and we watched a storm roll in.

By early afternoon, the storm was looking a bit ominous, and Kelley had to be back at school, so we dropped them back home, and Zoe played for a bit at Chloe's place before we headed home to get ready for swim class.

In the mean time, the storm hit and appeared to pass, so we drove to swim class, but there was still lightning around, so swim class was canceled.

We headed back home so I could finish making dinner. Zoe was pretty tired from the day's activities, so I'm hoping she has a good sleep tonight.

Andrew Pollock: [life] Day 315: End of Kindergarten

Thu, 2014-12-11 21:25

Well, the day finally arrived. Zoe graduated from Kindergarten.

I started the morning failing to go for a run again. I should just give up until after Summer I think. I had my chiropractic adjustment and did some blogging, before heading out to Zoe's Kindergarten for their farewell morning tea.

The morning tea was nice, and we were free to take our kids home afterwards, so we were out of there by about midday.

The Kindergarten year feels like it's flown by so quickly. I've been really happy with the Seven Hills C&K. I'm grateful my friend Kim told me about C&K while there was still time to get Zoe a place, and that I've been able to have the year off to allow her to go. I think it's definitely a better environment than long day care. The transition statement, which I guess can best be described as an exit report card for Zoe was absolutely lovely. Time will tell, but I think it has prepared her well for Prep next year.

It was also great to be able to serve on the Kindergarten's Parent Advisory Group committee this year. That gave some insight into how the Kindergarten, and C&K in general operate.

Seven weeks of school holidays lie ahead of us, which I'm sure will fly by pretty quickly.

Megan came over with her Mum in the afternoon for a play date, and I prepared some more mince pies.

Zoe and I went out for dinner with my cousin, Renata, to celebrate Zoe's graduation from Kindergarten and we had a nice dinner out.

David Rowe: SM1000 Part 9 – First Betas

Thu, 2014-12-11 18:29

Edwin and his team at Dragino have hand assembled the first two SM1000 Beta units in Shenzhen. I’m working with him to perform some initial tests while we wait a few days for the prototype enclosures to be made. Then Rick and I will both get a SM1000 shipped to us for testing. We’ve found a few little issues so far which we will correct before the Qty 100 beta run later this month.







Stewart Smith: skiboot-4.1

Thu, 2014-12-11 17:26

I just posted this to the mailing list, but I’ve tagged skiboot-4.1, so we have another release! There’s a good amount of changes since 4.0 nearly a month ago and this is the second release since we hit github back in July.

For the full set of changes, “git log” is your friend, but a summary of them follows:

  • We now build with -fstack-protector and -Werror
  • Stack checking extensions when built with STACK_CHECK=1
  • Reduced stack usage in some areas, -Wstack-usage=1024 now.
    • Some functions could use 2kb stack, now all are <1kb
  • Unsafe libc functions such as sprintf() have been removed
  • Symbolic backtraces
  • expose skiboot symbol map to OS (via device-tree)
  • removed machine check interrupt patching in OPAL
  • occ/hbrt: Call stopOCC() for implementing reset OCC command from FSP
  • occ: Fix the low level ACK message sent to FSP on receiving {RESET/LOAD}_OCC
  • hardening to errors of various FSP code
    • fsp: Avoid NULL dereference in case of invalid class_resp bits
    • abort if device tree parsing fails
    • FSP: Validate fsp_msg in fsp_queue_msg
    • fsp-elog: Add various NULL checks
  • Finessing of when to use error log vs prerror()
  • More i2c work
  • Can now run under Mambo simulator (see external/mambo/skiboot.tcl) (commonly known as “POWER8 Functional Simulator”)
  • Document skiboot versioning scheme
  • opal: Handle more TFAC errors.
    • TB_RESIDUE_ERR, FW_CONTROL_ERR and CHIP_TOD_PARITY_ERR
  • ipmi: populate FRU data
  • rtc: Add a generic rtc cache
  • ipmi/rtc: use generic cache
  • Error Logging backend for bmc based machines
  • PSI: Drive link down on HIR
  • occ: Fix clearing of OCC interrupt on remote fix

So, who worked on this release? We had 84 csets from 17 developers. A total of 3271 lines were added, 1314 removed (delta 1957).

Developers with the most changesets Stewart Smith 24 28.6% Benjamin Herrenschmidt 17 20.2% Alistair Popple 8 9.5% Vasant Hegde 6 7.1% Ananth N Mavinakayanahalli 5 6.0% Neelesh Gupta 4 4.8% Mahesh Salgaonkar 4 4.8% Cédric Le Goater 3 3.6% Wei Yang 3 3.6% Anshuman Khandual 2 2.4% Shilpasri G Bhat 2 2.4% Ryan Grimm 1 1.2% Anton Blanchard 1 1.2% Shreyas B. Prabhu 1 1.2% Joel Stanley 1 1.2% Vaidyanathan Srinivasan 1 1.2% Dan Streetman 1 1.2% Developers with the most changed lines Benjamin Herrenschmidt 1290 35.1% Alistair Popple 963 26.2% Stewart Smith 344 9.4% Mahesh Salgaonkar 308 8.4% Ananth N Mavinakayanahalli 198 5.4% Neelesh Gupta 186 5.1% Vasant Hegde 122 3.3% Shilpasri G Bhat 39 1.1% Vaidyanathan Srinivasan 24 0.7% Joel Stanley 21 0.6% Wei Yang 20 0.5% Anshuman Khandual 15 0.4% Cédric Le Goater 12 0.3% Shreyas B. Prabhu 9 0.2% Ryan Grimm 3 0.1% Anton Blanchard 2 0.1% Dan Streetman 2 0.1% Developers with the most lines removed Mahesh Salgaonkar 287 21.8% Developers with the most signoffs (total 54) Stewart Smith 44 81.5% Vasant Hegde 4 7.4% Benjamin Herrenschmidt 4 7.4% Vaidyanathan Srinivasan 2 3.7% Developers with the most reviews (total 2) Vasant Hegde 2 100.0%

linux.conf.au News: Keynote Speaker - Bob Young

Thu, 2014-12-11 07:28

The LCA 2015 team are honoured to announce our third Keynote speaker - Bob Young, founder and chairman of Lulu.com, co-founder of Red Hat and the Center for Public Domain.

Bob's presentation is scheduled for 09:00 am Wednesday, 14 January 2015

Bob Young is the founder and chairman of Lulu.com, a premiere international marketplace for new digital content on the Internet, with more than 300,000 recently published titles and more than 15,000 new creators from 80 different countries joining each week.

Lulu.com, founded in 2002, is Young's most recent endeavour. The success of this company has earned Young notable recognition; he was named one of the "Top 50 Agenda-Setters in the Technology Industry in 2006" and was ranked as the fourth "Top Entrepreneur for 2006," both by Silicon.com.

In 1993, Young co-founded Red Hat (NYSE: RHT), the open-source software company that gives hardware and software vendors a standard platform on which to certify their technology. Red Hat is a Fortune 500 company and chief rival to Microsoft. His success at Red Hat won him industry accolades, including nomination as one of Business Week's "Top Entrepreneurs" in 1999

Before founding Red Hat, Young spent 20 years at the helm of two computer-leasing companies that he founded. His experiences as a high tech entrepreneur combined with his innate marketing savvy led to Red Hat's success. His book, "Under the Radar", chronicles how Red Hat's open source strategy successfully won wide industry acceptance in a market previously dominated by proprietary binary-only systems. Young has also imparted the lessons learned from his entrepreneurial experiences through his contributions to the books to "You've GOT to Read This Book!" and "Chicken Soup for the Entrepreneur's Soul."

In 2000, Young co-founded the Center for Public Domain, a non-profit foundation created to bolster healthy conversation of intellectual property, patent and copyright law, and the management of the public domain for the common good. Grant recipients included the Electronic Frontier Foundation, the Creative Commons, the Free Software Foundation, and the Future of Music Coalition.

In addition to enjoying fly fishing, Young collects calculators and antique typewriters, a nod to his beginnings as a typewriter salesman and can usually be found sporting a pair of red socks. However, instead of red on his head, Young now tips his orange hat.

The LCA 2015 Auckland Team

Andrew Pollock: [life] Day 314: Kindergarten, startup stuff

Wed, 2014-12-10 11:26

I wanted to start the day with a run, but like so many mornings before this one, I just couldn't be bothered. I've really fallen out of the habit.

Instead, I managed to knock over another unit of my real estate licence course by 9:30am. It turned out to be a short and sweet unit, which was great. I'm happy to be down to only four units to go by the end of Kindergarten. It's not the highly optimistic progress that I'd hoped, but being down to the last quarter of the course is still a nice milestone to go into the school holidays at.

To atone for my lack of running, I ended up wandering all over the neighbourhood instead. First in one direction to drop a dish back to Kelley, then in another direction to the post office to mail off the assessment, and then back the other way again to put a brochure in a prospect's mailbox. Google Fit was very happy with me.

After doing a bunch of random stuff at home, I caught a bus into the city for a lunch meeting, and then a taxi home in time to pick Zoe up from Kindergarten.

We popped out to Bunnings to pick up a tap timer for the common area gardens, and then got home before the storm of the day hit.

I did a spot of baking for Zoe's Kindergarten end of year morning tea, and Sarah arrived to pick Zoe up.

The storm didn't really produce much other than a spectacular light show. I haven't seen so much lightning since being back in Brisbane, and it was very impressive. I did miss a good electrical storm living in California...

I closed out the day with a nice yoga class.

Linux Users of Victoria (LUV) Announce: LUV Beginners December Meeting: SUSE Linux

Tue, 2014-12-09 20:29
Start: Dec 20 2014 12:30 End: Dec 20 2014 16:30 Start: Dec 20 2014 12:30 End: Dec 20 2014 16:30 Location: 

RMIT Building 91, 110 Victoria Street, Carlton South

Link:  http://luv.asn.au/meetings/map

Terry Kemp will demonstrate installation and provide an overview of Open SUSE 13.2 and if time allows an overview of SUSE Studio.

Terry is a member of LUV and long-time Linux user from the early days of Slackware -- until one day he saw at a LUV install fest at MLC an install of SUSE, which he has been using since. He was on the committee of the Melbourne PC Users Group and convenor of their Linux and Open Souce SIG.

LUV would like to acknowledge Red Hat for their help in obtaining the Buzzard Lecture Theatre venue and VPAC for hosting.

Linux Users of Victoria Inc., is an incorporated association, registration number A0040056C.

December 20, 2014 - 12:30

read more

Andrew Pollock: [life] Day 313: Kindergarten, errands and podiatrist

Tue, 2014-12-09 12:25

I had a pretty busy morning. Zoe woke up around 12:45am complaining about a sore foot or something. I never quite got to the bottom of it, but I resettled her and got her back to sleep.

She then woke up at 6am for the day, and we managed to breeze through the morning super easily (for a change), with enough time for me to put laundry away and pump up the bike tyres and still arrive at Kindergarten right on opening time. It was all rather amazing.

The Kindergarten director asked me if I happened to have 40 CD sleeves "because I was a computer person", so I offered to go pick some up for her.

I biked back home, and fixed up one of my real estate licence course units that I had to resubmit due to a couple of mistakes, and then headed out in the car.

I debated going to OfficeWorks, which would have resulted in more back and forth, or trying K Mart at Cannon Hill. I ended up going for K Mart, and they didn't have any. Neither did Dick Smith or the post office. I got lucky at one of the cheap shops, and managed to get a pack of 100. I did manage to pick up some cheap plain t-shirts for Zoe to wear under her sun dresses to protect her shoulders, so it wasn't a completely wasted trip.

I dropped the sleeves back into the Kindergarten, and then mailed off the corrected coursework and headed back home.

There was another storm looming at around pick up time, so I drove back to Kindergarten. They've already started end of year clean up stuff, and they've taken down all the stuff from this year from the walls, and the Kindergarten looks shocking stark now.

My health insurance covers podiatry, so I figured I might as well get Zoe checked out before we buy school shoes. I'd made an appointment for 3pm at the myFootDr headquarters over in Camp Hill, where my neighbour Meg happens to work.

Zoe was initially not keen on going, but once we got there, she was fine. They were running a bit behind, so we watched some TV in the waiting room. After watching Wild Vets, Zoe's decided she doesn't want to be a vet any more.

We had a really nice podiatrist, and Zoe was very comfortable with her, and happy to go through the examination. The podiatrist was very impressed with Zoe's physical abilities and general balance, and said she was well ahead of her milestones, which was pretty impressive. I chalk that up to all of the varied physical activities she's done this year.

She said normally she wouldn't try and put a 4 and a half year old on the treadmill for video gait analysis, but given how good Zoe had been, she gave it a shot. Zoe did fine.

I'm really glad that I took her to the podiatrist, because I got some good general advice about what to expect with Zoe's growth given her body shape, and we bought a more appropriate shoe type for her foot than I'd have otherwise bought at the uniform shop. I also got a pair of running shoes for her as well. Zoe had heaps of fun to boot.

The storm hit while we were there, but fortunately there was no hail in it. It had mostly receded by the time we left. We popped in to the post office on the way home, and then the weather turned a bit foul again, and we timed it just right to pick up Anshu from the ferry terminal on the way home.

Sarah arrived not long after that to pick Zoe up.

Andrew Pollock: [tech] A geek Dad goes to Kindergarten with a box full of Open Source and some vegetables

Tue, 2014-12-09 12:25

Zoe's Kindergarten encourages parents to come in and spend some time with the kids. I've heard reports of other parents coming in and doing baking with the kids or other activities at various times throughout the year.

Zoe and I had both wanted me to come in for something, but it had taken me until the last few weeks of the year to get my act together and do something.

I'd thought about coming in and doing some baking, but that seemed rather done to death already, and it's not like baking is really my thing, so I thought I'd do something technological. I just wracked my brains for something low effort and Kindergarten-age friendly.

The Kindergarten has a couple of eduss touch screens. They're just some sort of large-screen with a bunch of inputs and outputs on them. I think the Kindergarten mostly uses them for showing DVDs and hooking up a laptop and possibly doing something interactive on them.

As they had HDMI input, and my Raspberry Pi had HDMI output, it seemed like a no-brainer to do something using the Raspberry Pi. I also thought hooking up the MaKey MaKey to it would make for a more fun experience. I just needed to actually have it all do something, and that's where I hit a bit of a creative brick wall.

I thought I'd just hack something together where based on different inputs on the MaKey MaKey, a picture would get displayed and a sound played. Nothing fancy at all. I really struggled to get a picture displayed full screen in a time efficient manner. My Pi was running Raspbian, so it was relatively simple to configure LightDM to auto-login and auto-start something. I used triggerhappy to invoke a shell script, which took care of playing a sound and an image.

Playing a sound was easy. Displaying an image less so, especially if I wanted the image loaded fast. I really wanted to avoid having to execute an image viewer every time an input fired, because that would be just way too slow. I thought I'd found a suitable application in Geeqie, because it supported being out of band managed, but it's problem was it also responded to the inputs from the MaKey MaKey, so it became impossible to predictably display the right image with the right input.

So the night before I was supposed to go to Kindergarten, I was up beating my head against it, and decided to scrap it and go back to the drawing board. I was looking around for a Kindergarten-friendly game that used just the arrow keys, and I remembered the trusty old Frozen Bubble.

This ended up being absolutely perfect. It had enough flags to control automatic startup, so I could kick it straight into a dumbed-down full screen 1 player game (--fullscreen --solo --no-time-limit)

The kids absolutely loved it. They were cycled through in groups of four and all took turns having a little play. I brought a couple of heads of broccoli, a zucchini and a potato with me. I started out using the two broccoli as left and right and the zucchini to fire, but as it turns out, not all the kids were as good with the "left" and "right" as Zoe, so I swapped one of the broccoli for a potato and that made things a bit less ambiguous.

The responses from the kids were varied. Quite a few clearly had their minds blown and wanted to know how the broccoli was controlling something on the screen. Not all of them got the hang of the game play, but a lot did. Some picked it up after having a play and then watching other kids play and then came back for a more successful second attempt. Some weren't even sure what a zucchini was.

Overall, it was a very successful activity, and I'm glad I switched to Frozen Bubble, because what I'd originally had wouldn't have held up to the way the kids were using it. There was a lot of long holding/touching of the vegetables, which would have fired hundreds of repeat events, and just totally overwhelmed triggerhappy. Quite a few kids wanted to pick up and hold the vegetables instead of just touch them to send an event. As it was, the Pi struggled to play Frozen Bubble enough as it was.

The other lesson I learned pretty quickly was that an aluminium BBQ tray worked a lot better as the grounding point for the MaKey MaKey than having to tether an anti-static strap around each kid's ankle as they sat down in front of the screen. Once I switched to the tray, I could rotate kids through the activity much faster.

I just wish I was a bit more creative, or there were more Kindergarten-friendly arrow-key driven Linux applications out there, but I was happy with what I managed to hack together with a fairly minimal amount of effort.

Andrew Pollock: [life] Day 310: Doctor, shopping, Tumble Tastics and a washed out Movies in the Park

Sun, 2014-12-07 22:25

Zoe slept solidly until 7am, which was lovely.

I'd made an appointment with Zoe's doctor to have some funny looking spots on her chest looked at. The spots were nothing, but the doctor decided to try and freeze the wart off Zoe's hand, which I hadn't been prepared for. Zoe was very brave about it though. The doctor wants to give it another hit in a week.

I've been wanting to get a portable shade tent for the beach for a while, and at BCF it's a seasonal item, so I had to wait for them to come into season. We headed over to BCF after the doctor.

BCF really is a poor cousin to REI. I miss REI. We did run into one of Zoe's Kindergarten teachers at BCF, so that was a bit of a treat for Zoe.

By the time we were done with that, it was getting close to time for Tumble Tastics, so we headed back home to get ready, and then Zoe wanted to go by car because it was hot.

We just chilled out at home after lunch, and I was watching the weather radar while debating the virtues of trying to go to the Hawthorne Markets and Councillor Shayne Sutton's last Movies in the Park night for the year. There was a pretty decent looking storm brewing.

In the end, I decided to wing it, and we headed off to the markets with umbrellas and blankets and camp chairs. I felt like a bit of a pack horse. As luck would have it, it started to rain a little bit half way there, and more earnestly once we arrived.

The upside was the line for free facepainting was non-existent, and Zoe also got to do some free craft activities without too much competition. Santa arrived not long after that.

The movie screening was moved inside the Morningside Panthers clubhouse, but the weather had turned most people away. There were probably only about 40 die hards that bothered to stick around.

The movie was Arthur Christmas, which wasn't something I was familiar with. It was pretty good though, if a little over Zoe's head. She enjoyed it nevertheless.

It was still raining lightly at the end of the movie, so we walked home with our umbrellas, and I got Zoe to bed.