Monday, 1 June 2015

"System repair disc could not be created. The parameter is incorrect. (0x80070057)"



The simple answer to this error is I was using a CD-R disc instead of a DVD-R disc.

I got stuck for almost 30 minutes googling around and trying out all kinds of suggestions. Then after downloading ISO image and trying to burn it to the disc using ImgBurn, I got an error message in human language telling me the disc has incorrect format. Could be better, but I got the hint.

Developers, we need error messages that a human being of average intelligence can understand.

Sunday, 26 April 2015

Cleaning Roomba's front wheel

You learn something new everyday.

I have been using the Roomba for the past 5 years at least without realizing that the front wheel needed cleaning. I clean the side wheels and the brushes religiously, occasionally using the air compressor, but front wheel, nah.

That's until one of the Roombas started making a funny noise. When it runs, it would sound like it's going over a hump every second. I have heard that before when the bottom brushes are not properly fitted, but this time the problem is not that.

I finally traced it down to the front wheel. I noticed it does have quite a bit of hair stuck in the axle. After struggling on my own for awhile to figure out how to clean the damn thing properly, I turned to YouTube:

 

Turned out it was pretty easy. You just pull the wheel carrier right off with a bit of force, then pop the wheel off with a flat blade screwdriver. Then I found the culprit:


It's a tiny bead from my daughter's DIY necklace toy set, stuck right between the wheel and the carrier. Problem solved.

Of course, pull all that hair and debris off the front wheel axle makes for much cleaner operation overall. So one more thing to add to the Roomba cleaning checklist!




Friday, 9 May 2014

Strange problem on KVM VPS

This one for the X-Files.

I have been helping a client migrate his web server from one VPS to another because he needed more disk space. His previous VPS is based on Xen, and the migration is to a KVM-based VPS.

Everything was smooth-going at first. I installed Debian 7 x64, all the usual packages: nginx, php, mariadb etc. Easy. Configured and tested the setup. Easy.

Then I migrated his database and web server over and asked him to do some business-side testing. That was when we hit an unusual snag. His PayPal IPN wouldn't work.

At first, I traced the logs, thinking it was some kind of PHP code incompatibility. Nothing. The code will break at this point:

   $fp = fsockopen('ssl://www.paypal.com', 443, $eno, $estr, 30);

and never return.

I was stumped. So I wrote a simple test program that retrieves the HTTP and the HTTPS version of google.com. Lo and behold, the HTTPS fetch breaks right at that point with:

    Illegal instruction

I looked up what that means and found that it is just another name for the good ol' core dump. Shocked, I ran the same code on the Xen VPS (running the same Debian 7 and PHP version) and the code ran OK.

A number of searches did not turn up anything useful on this problem. It doesn't seem anyone else has encountered this. Having run out of ideas, I reported the details back to my client and suggested that he migrate to a Xen-based VPS instead.

I hope one day I will find out what this was all about...

Bluetooth headsets: Samsung HM1700 vs Plantonics M25

I had been using a Samsung HM1700 headset for over a year now. Recently, the Plantonics M25 was on sale. It looks a lot smaller, lighter and sleeker than the Samsung HM1700, it supports A2DP, it has long battery life, so I bought one to have a try.

The thing about Bluetooth headset is that you can never tell how well it works for you from the specs. You have to live with it for a week or two before you can tell if the two of you are compatible, sorta like a roommate or girlfriend. So I lived with the M25 for a week.

Samsung HM1700

Pros:
  • Long battery life
  • Great reception
Cons:
  • Bigger and heavier
  • Ear loop is not as comfortable
Plantonics M25

Pros:
  • Long battery life
  • Sleeker, smaller and lighter
  • Ear loop is fitting and comfortable
Cons:
  • Too many A2DP dropouts for my liking. By that, I mean the A2DP stream will drop out for a second or two being picking up again. This happens when I turn or bend my body, pick up a tool etc. It happens with the HM1700 too, but much less frequently.
So it seems like I will be sticking with the HM1700 for now and returning the M25. Let's hope something better comes along later at the same price point.

Friday, 14 February 2014

Bitcoin - Figures on transaction cost

Here are some figures on transaction costs in cross-border transactions.

Currently the de-facto reference currency in cross-border transactions is the USD.

A recent purchase of USD186 using the credit card resulted in the following line items in AUD:
  • AUD (from USD) - $202.00
  • Currency conversion assessment fee: $0.40
  • International transaction fee: $3.00
  • Cross border assessment fee: $1.60
Ignoring the spread used in the currency conversion, the transaction cost is about 2.5%. The actual transaction cost taking the spread into account is probably about 3+%

A recent purchase of USD700 using PayPal incurred a fee of $23 (buyer or seller pays). The transaction cost is a whooping 3.3%. I happened to have some USD in my account, so I didn't need to perform currency conversion. PayPal's spread in forex rate is notoriously poor compared to other avenues.

A purchase of 1.45BTC (approximately USD1085 at that time) incurred a transaction fee of 0.0002BTC, which is negligible. Speed rivals that of PayPal. Again, I happened to have some BTC lying around, otherwise conversion from fiat to BTC will incur additional charges, typically in the 2% range.

So if BTC (or some other crypto-currency) replaces USD as the de-facto reference currency for transaction, it should drastically lower the transaction cost. However, the price volatility of BTC is one factor that prevents this from happening. BTC needs to be relatively stable against other currencies before it will be widely adopted for cross-border transactions.


Friday, 7 February 2014

Bitcoin - Micropayment system for the Internet?

I have been dabbling with crypto-currencies, specifically Bitcoin and Litecoin, over the past 12 months. Everything from mining to e-commerce to currency exchange. I think I "get" the magic of the whole idea now.

For better or for worse, crypto-currencies drastically reduces the friction of money flow. You probably won't be able to find another means of moving money at a lower transaction cost, especially when small amounts are involved.

In addition, the speed of transfer is excellent for a distributed system. With Bitcoin, it takes a few minutes. With Litecoin, it takes a couple of seconds. The low transaction fee and fast transfer speed respect no geographical boundaries. It applies whether you are moving money within the same country, or between two countries on opposite ends of the Earth. Which probably freaked more than a few legislators out.

Plus this is a distributed system with no central authority to slow things down or screw things up. PayPal is fast, but try talking to the people who have had their PayPal accounts frozen at a whim and had to jump through hoops to unfreeze their account, sometimes without success. Also, PayPal's transaction fees are notoriously high (Visa/Mastercard's fees are even higher) and they have to impose random rules required by the powers-that-be of the countries they operate it. For example, in certain countries, PayPal now charges a fee for transferring money between two individuals regardless of amount, even though PayPal started out as an easy way for people to email small sums of money to one another!

It is therefore clear that crypto-currencies like Bitcoin have unique features to offer over existing systems, so it is not entirely frivolous. It has the potential to solve problems such as micropayment on the Internet, which until now has not taken off due to the high transaction cost and lack of standard, so we pay for content with our privacy via online ads. If one of the crypto-currency becomes de-facto standard, it should be quite straightforward to have a browser that will automatically tip the author when content is accessed, made worthwhile due to the low transaction fee.

Which is not to say there aren't teething issues to be resolved. The idea of keeping all the transactions that ever existed in a monolithic blockchain makes it huge, and it is unclear whether such a system can accommodate micro-transactions of this scale without also raising the transaction fee. But there are ideas such as making the blockchain itself distribtued, which should eventually make its way into the mainstream.

There is also currently a heated debate between inflationary versus deflationary crypto-currency. Quite a few crypto-currency are intentionally deflationary, and standard economic theory tells us that people will tend to hoard deflationary currencies, which is probably what is driving the massive speculative activity behind Bitcoin right now. For a crypto-currency to be used instead of hoarded, it probably needs to be mildly inflationary. And some kind of clever algorithm to dynamically adjust the rate of inflation based on economic activity would be nice!

Still, like other P2P technologies, I think the cat is out of the bag and there is no turning back the clock. The concept of distributed crypto-currency is here to stay and it will only evolve at the speed of software. Eventually, I think most, if not all, of the kinks will be ironed out, one or more standards will emerge, and there will be widespread adoption by netizens. The next few years will be interesting to watch in this space...

Thursday, 15 August 2013

110GB+ worth of photos/videos on a microSD memory card #2

In my previous post, I talked about wanting to write a script to see how far I can squeeze 110GB worth of media (photos and videos).

I wrote the script the quick-and-dirty way, in PHP. When people think of PHP, they think of web pages, but PHP can equally be used for writing your everyday scripts, just like Perl or Python.

The script resizes all photos to a maximum width/height of 1024. I found this provides maximum size reduction for the photos without sacrificing the viewing quality in full photo mode on my tablet (screen resolution: 1280x800). Obviously it will affect the quality when zooming in, but I rarely do that when flipping through the photos. Since I haven't got a tablet with retina display yet, I am not sure how that will fare, but for this exercise, I am sacrificing quality for size.

For videos, I use handbrake-cli to transcode all of them to MP4 with a maximum width of 640. Again, this reduces the size drastically, improves compatibility (since all Android tablets/smartphones I have come across so far can play MP4 with no problems) and looks OK quality-wise on my tablet.

The script takes a source directory and replicates the folder structure in a target directory. It transcodes all files with certain extensions (configurable in config.php) and places them in the corresponding target subdirectories. If the file has already been transcoded, it will not be transcoded again, so it will be relatively quick to update the target directory after adding more files to the source directory.

The script took 1.5 days to transcode my 110GB collection (bear in mind this is a older, slower AMD Turion II laptop). The result was only 29GB and fits easily into a 32GB microSD card.

I popped the microSD card into my tablet and viewed the files using QuickPic. The result was awesome.Check it out in the video below:



Note that this video was produced with the microSD card inserted into an al-cheapo single-core tablet bought for the kids during a sale. I was pleasantly surprised by how quick and smooth it was. Needless to say, on my own 10" quad-core tablet, the result was even better.

QuickPic is a better app than Gallery for this purpose because:

1. It allows you to set "Include Folders" to include only the media files from the microSD card

2. It lets you set the 'Explorer View" to browse through the folders/subfolders in a hierarchical manner.

3. It has "Stack", "Grid" and "List" views for different visual summaries of the folder content.

4. It is quick and has tons of other options.

The result of the transcoding operation exceeded all my expectations. I have a snapshot of 110GB worth of media on a tiny memory card, ready to be popped into any tablet or PC to view. At only 29GB, there's lots of room for growth, especially on a 64GB microSD card (which no doubt all tablets will support in the future, even cheapo ones).

If you think you might find this useful, you can download the script below. It includes the PHP and Handbrake-CLI binaries so it should be ready to run under Windows. It shouldn't be too difficult to adapt the script to work under other platforms as well.

After download, unzip into another directory and edit config.php. You only need to change $srcdir and $tgtdir. Then bring up a command prompt and run transcode.


Once you verify that everything works correctly, you may want to schedule it to run periodically via the Task Scheduler.

Download: Batch Media Transcoder V1.0 (ZIP 25.2MB)

Download: Batch Media Transcoder V1.0 (7-ZIP 17.1MB)