Posts in Category: offspring

Lasers and MIDI and software… Oh my!

Photo of Jean-Michelle Jarre performing in Helsinki in 2009 © Miemo Penttinen

What happens when a music teacher suggests instrument variety is a driving force behind a child enjoying music, the child says “anything unusual” is good, the other child wants a techie project and the father has far too much 80’s electronica ?

We decide to get a laser harp, of course ! 🙂

And there’s no way at all this could have been due to my obsessive saving of paper-round money to buy Jarre albums on tape to listen to on my Walkman (with Dolby-B, I’ll have you know – quality antiquity !).

A quick Google later and it’s apparent that commercial units run from €500 to £1000 as ‘entry level units’. So that’s not happening. The Wikipedia page does an excellent job of sucking almost all of the fun out of the description, and doesn’t help much (apart from providing a link to the excellent photo by Miemo Penttinen).

There’s a Makezine article by Steve Hobley that is interesting as it includes pitch bend although the harp is framed and uses multiple lasers, but this Instructables article is closer to what I had in mind as it describes (with source) how to create a single laser scanning frameless/infinite harp.

So given that I can’t resist changing stuff I know nothing about, is that $100 estimate what I need to spend ? Well, I have breadboard, an mBed plus application board and soldering kit already. I’m not interested in 5-pin MIDI (plan on using USB MIDI via the application board), and there’s no way I want to have 3 separate PSU’s – I’ll contemplate step-down convertors but it must be a single rail main supply. So time to hit eBay to see what’s there at hobby prices. And the first find is that 10 red 1mW laser diodes cost less than £3 inc. P&P from China… Wow… This might just work.

An afternoon talking this over with Ben, and my initial BoM is as follows:

Item Link Cost
5v 4 phase stepper motor + controller £3.59
10 x 11mm acrylic mirrors £1.65
Laser receiver module £2.99
Laser diode module £3.49
5v 2A DC PSU £3.99
2.1mm DC socket with leads £1.19

Current spend: £16.90 – I could have spent less (or had more spare parts) if I’d have bought direct from China, but given that I a) need to keep the kids attention and b) am way too impatient when being given the chance to play with spinning mirrors and lasers, the above items are all from UK (re)sellers.

Potential pitfalls:

  • no fogging gear so viewing the beams may be tricky
  • low power laser may have high false triggers is the sensor gain is too high
  • no idea if the mBed timing is accurate enough
  • the 5v supply may not have enough current (no idea of the stepper consumption
  • still need to write the mBed software !

Although the pitfalls haven’t made me stop thinking about v2:

  • use green + red lasers to mark out a full tone/semi-tone scale
  • use green + red lasers for an effect/note split
  • put a carrier wave onto the laser and use a doppler detection routine at the sensor to offer pitch bend
  • make the MIDI output via WiFi to link into an iPhone/iPad as sound source for a portable version

Delivery of parts is expected this week, so project updates and pics of parts to follow…

the house of arguments

Excellent conversation with the eldest, E:

E: You know that house on the TV where they have all those arguments ?
N: Big Brother ?
E: No, the Houses of Parliament

halfords: how not to run an online reservation system

I’m probably a little naive given that I work in computing, but after the number of years that Argos have managed to run a nice and simple online reservation/order system I’d have thought it was a simple thing to copy.

It’s not.

Having reserved a bike for my eldest at Halfords one Sunday morning last month, we all went down to collect it with the idea of building it together. The actual reservation was pretty straightforward, and I was quite impressed with the SMS reservation code they texted me within 2 minutes – the bike was in stock and available that day and the next and all I had to do was turn up and pay.

It wasn’t a good sign when the member of staff I showed the SMS to (it was a long number, so thought it’d help him being able to read it) looked very confused and after a long pause wrote down 3 or 4 digits on the back of his hand, ignored the terminal next to him and went off into the back of the shop.

10 minutes later he came back to ask when I’d reserved it, and then tried to tell me it took 3 days to assemble the bike. Eventually he got over his shock that I felt able to build it all by myself, agreed that I didn’t need to wait three days for a flat-pack box and vanished again.

He came back 5 minutes later saying that there was nothing in stock, and I must have seen the display model on the web site.

WTF ? It’s a stock photo, unless they move all their bikes into a perfectly white room with no obvious lighting each time they build one… I cut my losses at this point and left, although perhaps I should have been a typical outraged parent and demanded to see The Manager but I don’t subscribe to the idea that poor service can be cured by shouting loudly at someone else, and more importantly I didn’t want them to have my money: if they can’t even count bikes then what, exactly, is the reservation service for ?

An email to their customer services resulted in a reply a week later – in which, quite incredibly, they acknowledge that their system simply doesn’t work. Of course, they don’t come out and say it’s broken – PR people have been on a course, dontchaknow, and it’s all my fault for trying to shop there (their odd formatting left in):

Dear Mr Spray

Thank you for your recent e-mail regarding our Reserve and Collect service.
Halfords prides itself on offering a range of high quality products and
services and any concerns expressed by customers are treated very


Our Reserve and Collect system is set up to use live data which allows us
to advise our customers of our stock levels right down to the last item.
Our colleagues in store aim to remove the item from sale as soon as the

notification comes through, however there will be the odd occasion where
someone will be purchasing the item at the time of reservation or indeed
the item turns out to be damaged / have a fault. As the accuracy of each

individual stock file is the stores responsibility, we have advised our
store colleagues to contact customers at the earliest possible point if
they believe there could be an issue, and to do anything they can to
rectify the

problem. This may include a suitable alternative or locating another item
from a local store. These guidelines are ‘as a minimum’ in line with other
retailers offering similar schemes.

Please accept our apologies if you feel this hasn’t happened in this case
and be assured that we will make your e-mail available to the Area Manager
for his information.

Kind Regards
<Name Redacted>

Halfords Customer Services

If they can’t manage to subcontract a simple race-free reservation system properly then they obviously don’t need my custom.

Oh wait, maybe they do

pitching in: apple retail store field trips

This is slightly out of character for me but I think there’s an obvious point being missed here:

Apple Retail Store Field Trip:

Whilst at first glance this does make it seem as though “Media Awareness” should now become a pre-school activity, take a step back and ask what passes for ICT in the majority of UK primary schools right now. I freely admit that without children of my own in such a situation I might not know, but unsurprisingly it’s pretty much a Microsoft shop – there are some glimmers of hope (some variants of free software have finally been approved for ‘purchase’) but basically you will be taught the MS way of working.

That’s fine, as a start. What is less nice is the drone-like creation of Word and Excel monkeys – nice skills to have, but not one that I feel is the right approach for generic education in Computing. Keep that as an option in “Business Skills” or something similar – what I want is for my children to be exposed to as much generic Computing as practical, so I naturally oppose any monoculture. A mix of Windows, Mac OS and Linux would be great (although I’d prefer BSD, but that’s my own personal problem…) simply to show that there is more than one way of doing things.

So the crux of the matter is that I pay (indirectly) for my school to buy Microsoft products, and be taught on MS packages. Apple provide for free (to me) an alternative view of the world that is arguably more exciting for the kids (it’s a trip, afterall) and appears from Fraser’s post to be a well thought out tutorial.


(was) small sayings

This is the full version:

N: “What’s the next number in this sequence…”
E (interrupting): “7”
N: “…”
N: “Err, yes.”

The best bit is that she was, indeed, absolutely right…

why, silly me

“Of course it’s nice. It’s got sugar on top”

Aha. I’ll try to remember that then.

iraq redux

Comment from the big one after viewing a trailer for a news documentary on Iraq which opened with the statue of Saddam Hussein being pulled down:

“Some people like that. Some other people don’t”

Possibly the shortest and most unarguably accurate statement on the whole affair so far…

small sayings

head mystery teacher

tukey == turquoise