Category Archives: project

Bulk upload for Music Magpie and Ziffit

I’ve got a stack of CDs, but it occurred to me that I no longer even have a CD player. I decided to move them on using Music Magpie or one of those we-buy-your-old-stuff services. I didn’t expect to make a pile of cash out of it, but wanted to clear the space, dematerialise a bit, and didn’t want to just throw perfectly good CDs away.


I used barcode2file on my android phone to zap all the barcodes. About 300 items, including a few DVDs.

I looked at:

  • Music Magpie (
  • Ziffit (
  • We Buy Books (

And wanted to compare the prices I’d get from each. Of those, only We Buy Books has a bulk upload option that can take 50 item codes at a time. Even with hundreds of items, that’s easy enough to do manually.

Music Magpie and Ziffit only have a slow one-by-one interface that you wouldn’t ever want to use twice, so I recorded a little selenium script in the Selenium IDE (Firefox), and embellished the Python that came out with the ability to loop through my list of barcodes and record the results.


The code I used is in this gist:

The scripts are probably pretty fragile, and is “just enough” to work. It’s slow too. Successful submissions are written into a tab-separated file.

  1. Upload the entire barcodes list into each service
  2. Tabulate the results in a spreadsheet to give the highest price for each item, and which service will pay it
  3. For each service, produce a list of it’s “winning” items
  4. Upload the sublist into the service, saving the results
  5. Manually, log into each service and complete the trade


We Buy Books give the best prices on average, per item, but also rejected the most items. We Buy Books also gave the widest range of prices; for the items that they did not win, their price was often very low (2p vs 20p from other services for a particular item).

Service Total value Items accepted Average value Bids won Winning bids value Highest bidder
webuybooks £151.00 200 £0.75 74 £73.04 27%
music magpie £184.34 270 £0.68 138 £108.23 49%
ziffit £134.73 246 £0.55 67 £37.22 24%
combined £218.74 £0.66

Comparable items that received bids from all three services:

Where all three services offered bids (178 fairly comparable items), the prices are much higher, which might indicate an element of competition, but given that these things are so hard to compare, I’m not sure this is a factor.

Service Total value Items accepted Average value Bids won Winning bids value Highest bidder
webuybooks £66.97 62 £1.08 62 £66.97 35%
music magpie £71.28 79 £0.90 79 £71.28 44%
ziffit £31.40 37 £0.85 37 £31.40 21%

Average prices are higher. Music Magpie was still the highest bidder most often, but the margin between We Buy Books and Music Magpie has narrowed quite a bit.


Pretty inconclusive. I can’t see a particular pattern that would make me say “Use service xyz always”. If I had less time to do these, and then sort through all the items a second time putting them into different boxes, I’d go with Music Magpie, because although they don’t always give the best prices, they accept a wider selection of items.

With time, a combination approach is most thrifty, and that’s what I did, and it resulted in about 16% extra cash.

What I didn’t do was any kind of breakdown of the types of items: DVDs, CDs, genres etc.

300 items x £10 original price = £3,000.

(Incidentally, £3000 / 20 years of buying media = £150 per year, and I’m paying £95.88 per year to google to host my records now. I suppose the difference is that I have no piles of plastic to show for my money any more. That makes me a bit sad, but also a bit happy.)

Sold for £218.74. That’s about a 7% return of cash value. Over a couple of weekends, it took me about four or five hours to scan, process and box the items. 5 hours x £20 per hour wage = £100 wage for that time, and £118.74 money back.

Well, at least they aren’t just going in landfill.


New 3D printer

I’m building up a new 3D printer, a Mendel Prusa i3.  I ordered a mechanical pack from Greg Colbourn on the eMaker site that included all of the hardware, rods, nuts and bolts, bearings, motors and a set of flat parts in 6mm plywood.  I got a RAMPS electronics pack from the now-ubiquitous reprapdiscount, and was impressed by it.  It included hall-effect endstops and a neat LCD display, and a MK2A PCB heatbed.  I also got a 30A, 12V power supply.

I sanded down the plywood and finished it with some oil (and very handsome it is too) and printed off a set of Prusa i3 parts on my little eMaker Huxley in some nice silver ABS.  I think perhaps the Huxley has detected that it is fabricating the parts for its replacement, and is acting up a bit so a couple of the parts are a bit curled, but fortunately the design of the i3 parts is such that the squareness or flatness does not rely on a good bond to the bed.  Good work.

The mechanical parts went together with a minimum of fettling but I had to print some holders for the LM8UU bearings on the y axis.  These are designed to be simply zip-tied into some slots on the y-carriage, but I found that y-carriage itself collides with the y-axis motor at the far end of it’s travel.  Not by much, but a little, and enough to raise the bed a touch, so I modified the Y bearing holders from the i3-mini variant of the machine and that raises it a mm or so.  Bit of a pain because the hole spacing is so tight, but it works.

I like the three-point heatbed fixing / suspension system on my eMaker Huxley, so I went for the same thing on  this machine.  RepRapPro sell parts separately, so I got the aluminium heat spreader and the MDF insulator from them, along with the spring mounting hardware to go with it.  Of course, this system doesn’t use the four outer corner bolts like the i3 is set up, so I printed some extra pieces that bolt onto the y-carriage.  I lose some z build height, but it’ll do until I get an adapted y-carriage cut.

One of the most troublesome points of failure in my eMaker machine is the termination of the power electronics.  The Sanguinololu board isn’t great for the heatbed because the traces are pretty slim and I think the power handling is close to its rated limits.  That, together with _just slightly too little wire_ for the moving parts has meant that the cable to the heat bed has burnt out a couple of times.  I was determined to make a better job of the wiring this time around to avoid the froth of cabling that surrounds the Huxley.

To this end, I finally got some bootlace ferrules and made up a high-power wiring loom with with ferrules on one end (for screwing into the screw terminals on the RAMPS board), and fork or ring terminals crimped on the other end.  The fork terminals go into the screw-down terminals on the power supply, and the ring terminals are bolted into holes on the PCB heatbed.  I had to drill the holes out a little for that, but there is plenty of contact between the washers on the bolts and the traces on the bed, so it’ll be ok, and it has the benefit of being completely solder-free, and everything is disassembleable and replaceable.  This will make it less brittle, and more reliable.  I don’t know why more people don’t do this.  Soldering trailing wires onto moving PCBs is a really bad idea but this seems to be accepted practice on repraps.

Hot end is a lovely E3D, all-metal device.  Haven’t used it in anger yet, but it builds easily, heats up fast and squirts hot plastic out, and that’s what I look for in a hot end.  It came with a cartridge heater rather than a resistor.  I like it.

Finally is an extruder.  After being used to a bowden extruder on the Huxley, it seems weird to expect to fit a massive NEMA-17-toting extruder on the x-carriage itself, so I’m planning to eventually go with a bowden arrangement again.  It just seems more civilised.  However, E3D are out of stock of the bowden kit, so that’ll have to be a later development.  In the meantime, I’ve got the hardware for an MGS (metal gear system) extruder, and am printing up the RP parts for it right now.  The small gear on my old eMaker, Wade’s-style extruder has always worried me, and has always been deformed.  I just don’t like it, so I was pleased to see a metal system around.  I wonder if a direct-drive is better again, but I’m happy to wait to try that.



CV on Raspberry Pi

OpenCV is a pain.  I guess I’m just being a dolt, but I can’t get it working.

I want to run a piece of software on my pi that will run my slow photo booth at the upcoming Edinburgh mini maker faire.

SimpleCV –

Issue with getting lots of VIDIOC_QUERYMENU: Invalid argument and then a bunch of “Select Timeout” messages:


You can not edit the binary uvcvideo.ko file directly. I advise not trying to compile it yourself. It’s not worth the struggle. You can try various options temporarily on the fly. Attach your webcam, the driver module should be loaded and shown by


. Then you unload the module using

rmmod uvcvideo

. Afterwards you can reload the module with something like

modprobe uvcvideo nodrop=1 timeout=5000

. Fiddle around with the settings.
You can make a set of parameters permanent by editing the file /etc/modprobe.d/modprobe.conf . For the above settings, simply add a line saying

[code]uvcvideo nodrop=1 timeout=5000[/code]



Accessing raspberry pi by name rather than by IP address

I’m using a virgin media superhub that does DHCP, but doesn’t have any kind of DNS stuff in it.  So I can ssh to my pi using it’s IP address, which is inconvenient because it makes me go and look the address up in the router.  For my application (the alarm clock), both devices (the pi and the kobo) need to be able to find each other, or at least the kobo needs to be able to find the pi to register itself.

I’m guessing there’s smarter ways of doing this, but until I am schooled, I’m working on these lines:

So the pi is samba-able now.  I guess samba uses netbios, and that’s the enabler for hostname resolution.

So now I can hit raspberrypi from my windows machine.  However, I suspect, I also need to netbiosify the kobo, and I guess that won’t be as easy.

Put Pronterface on pi.

Get VNC working:

Install pronterface:

Instead of copying the files from github manually, install GIT with sudo apt-get install git then do git clone to get the files.  Skills.


Kobo mini serial port

I’m building an alarm clock that will use a kobo e-ink reader as it’s interface and display, so I’ve been trying to figure out how to interface to it.  I got a kobo mini just after christmas for £50.  It’s a linux box, and I’m actually really impressed by the hackability of it.  It’s very open, easy to get into it (even for a noob like me), and has got busybox and python on it.

Most of the information I needed I’ve got from Mobileread’s Kobo Touch hacking wiki which gives a good guide as to how to get root access.

Prompted by soapy frog’s reports I also cracked up the mini:

Kobo mini mystery optical components

and soldered in some pin headers, then wired in a 3.3v TTL Serial-to-USB adapter board (with an FTDI chip on it), and was delighted to find that I could then PuTTY to that virtual com port (115200 8 N 1) and get root terminal access.

USB to serial adapter being used to connect to the linux console on my kobo mini.