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…