Thursday, 1 March 2018

Rubber belts for 3" Disk Drives

Necessary Preamble:
Back in the 1980's there existed a 3" Disc system championed by Amstrad in its CPC, PCW and Sinclair ZX Spectrum +3, computers as well as a few other more obscure users. The problem is, over 30 years on, and it is very unusual to find one of these drives in functioning order that hasn't been repaired, and the majority of the time, the problem is the flat rubber belt has disintegrated and or turned into a pile of goo in the drive mechanism. Well, there are plenty of places you can find advice on how to replace these belts (you found this, you'll find that), including cleaning up the gooey mess left by the previous belt. The problem is, these belts are hard enough to find; also the belt measurements are hard to find. In order to restore an old drive, I took the old belt, or what was left of it, and measured it then took a gamble with a similar looking belt I saw on CPC Farnell. It worked.


The important bit:
The dimensions of this belt are as follows: 69mm diameter x 3mm width x 0.6mm thick The belt can be found on CPC Farnell's website by searching for AVBELT4. EDIT: I have since found a usenet post from 1996 by the venerable Emmanuel Roussin, here, which says the following:
So the belts I bought, while OK, are a bit on the tight side, however, they do not feel overstretched. CPC do sell a much closer fit in the AVBELT6 which is 72.0mm x 3.5mm x 0.5mm, and a little cheaper. This post is intended to help others find a source of these belts and for me to remind myself.

Tuesday, 29 January 2013

Missing CPU Cores on Quad core CPU

But Nothing's Changed...

Randomly, the other day my computer began reporting only two CPU cores instead of the physical four cores it really has. Forget Hyper-threading, my CPU does not do this; they are real cores, an Intel Q6600 Quad Core CPU. But Ubuntu only displayed two CPUs.
Interestingly "dmesg" did show something unusual, 2 "hotplug CPUs". Somehow the HPET ACPI table had become corrupted (BIOS side) and flipped a few bits resulting in loss of 2 cores; 1 and 3.
Which presented as hotplug CPUs:
After trying lots of noapic, nolapic and other kernel options I decided to reset the BIOS to defaults. On some systems this really requires removing the battery but on mine it was an option in the BIOS itself, which also allowed me to set back some unrelated preferences at the same time. Now dmesg reports 4 CPUs and /proc/cpuinfo agrees.
So although nothing changed, nothing has changed from the user or software side, minor data corruption has caused this behaviour. Machines are not utterly predictable.

Tuesday, 1 May 2012

Strange things in the land of AV

In the land of HD-TV two things I recently discovered that I thought were worth a mention.
One is that 8 years ago or so, Samsung made a HD CRT TV with a HDMI input.
The other is that you can buy a HDMI to RCA RGB component cable which won't work, ever.
The problem is, that HDMI is digital, as in, ones and zeros, but component RGB is a continuously varying analogue signal. The two are fundamentally incompatible without a "Box of Tricks" in-between. This "box" would need to decode HDMI and output it using a Digital to Analogue Converter, one per channel.
Since the cable has no box of tricks then it is unable to do the job. Quite why anyone would make a cable that does not do anything is puzzling but moreover, who is buying them and why have the retailers not been done for Trades Description violations or environmental pollution.

Monday, 23 January 2012

RaspberryPi

An interesting thing is happening.
A UK based Foundation (Charity) has caused quite a stir in the run up to launching their new microcomputer; the Raspberry Pi.

Geeks, Techies and the generally interested have been building up a voracious appetite for what is in essence, probably the most affordable development computing platform made. It is a small device with a lot of capability. For more info go to their website. http://www.raspberrypi.org/
But what I find most interesting is the shear level of interest. It is understandable as the device is amazing and unique; but what is most impressive is this level of interest. It is part viral, part clever use of the press, part genius advertising and part facilitating rumours.

What I am wondering is, if a small startup charity can do this then why can't other businesses. As far as I know, only Apple gets people this worked up.

Essentially, this is it.
This device has gathered the momentum to get a strong development community and will be the most interesting and promising development device of the next few years.
People are already fantasising about planning ideas for its use.

If they'd taken pre-orders I am sure they would be huge numbers. I'd be putting my name down for four.

This should be interesting.

Tuesday, 29 November 2011

Fourier Transform Image Processing.

Image and Photo editors often use various filtering techniques to enhance or degrade an image to the desired effect.
Often these editors do not utilise user controlled Fast Fourier Transform filtering to remove periodic artefacts in the image despite the fact that Fourier transform image processing is used extensively in image files such as JPEG files. It is worth noting that the same technology is used to process most lossy and some lossless audio data formats such as MP3.

Some third party plug-ins exist for image editors which try to bridge the gap, however there is software that exists in the field of Scientific image processing which can do an excellent job with everyday images.
This (unprocessed) image of a Netgem I-Player keyboard has strong diagonal banding which may be a result of the Moire effect. Click to enlarge Image.
The FFT (Frequency domain) image of this image looks like this:
The Low Frequency information is nearer the centre of the image and the high frequency information is nearer the edges. Brighter represents more information, dimmer represents less. The Horizontal and Vertical cross through the centre of the image is representative of the amount of information with strong periodicity horizontally and vertically. (The Keys on the keyboard are arranged in horizontal rows one above another).

The additional crosses in the four quadrants of the image represent the diagonally periodic information which is in the image as diagonal stripes; there are in fact stripes running in both directions with one set stronger than the other. The second set of crosses further out represents a harmonic of the first.

By strategically filtering the frequency domain information to remove these additional crosses then the diagonal lines should be removed from the image when we perform a reverse transformation.
FFT showing Filter.
The image after the inverse FFT has been applied.
The diagonal lines have been severely reduced with a fairly low degradation to the rest of the image. The lower contrast is a side effect of filtering in frequency space as it is representative of power loss or signal loss in these filtered frequency bands.

Notably in the processed image  the number 9 is clearer in comparison to the unprocessed image. The number 5 looks more like a 5 and less like an S in the processed image and, arguably you can read the left "Shift" key more easily than in the unprocessed image.
This processing technique has not magically gained extra information, rather it has removed that which obscured the desired image data.

The software used to process these images is the free, open source and cross platform Gwyddion: http://gwyddion.net/
This software is primarily aimed at Scanning Probe Microscopy image processing; something with which I am very familiar.

I think that there is room for this kind of image processing in image editing software to deal with unusual image artefacts including the Moire effect and vibrational noise sources.

A more technical overview of these processes is given in this link http://homepages.inf.ed.ac.uk/rbf/HIPR2/fourier.htm

Friday, 4 November 2011

Mounting SMB shares from NAS in Linux

When mounting  SMB shares in linux from a NAS box I got this error:

I discovered that the problem is the NAS device's implementation of SMB requires the "nounix" option to be specified.


Hope this helps someone.

Leak Stereo 30 Plus Speaker Plugs

This will only interest you if you already know what it is about.

The Leak Stereo 30 Plus Amplifier has a proprietary speaker plug which is very hard to source.


You can build a functionally compatible part using a terminal block and some pop-rivets of different sizes. I know that the Aluminium rivet is not a high grade contact, but it works very well in this application.
The Spacing is Spot-On, The bore holes fit snugly and the plug performs well with no apparent degradation.

This DIY Leak Speaker Plug will let you get up and running while you source the original or replace the socket with something a bit more useful.