Maker Faire 2014 - The Light Harp
Pass the Oven Gloves
The Light Harp was an attempt to replicate Jean-Michel Jarre’s Laser Harp without the dangerous eye-blasting lasers and the need to wear protective gloves just to play the instrument. Even though the design was little more than a first prototype and therefore fairly crude, the instrument proved astonishingly popular.
The design was simple enough - a simple frame was assembled from electrical trunking. The upper cross beam was fitted with eight very bright LEDS whilst the lower beam was fitted with twelve light-dependent resistors (LDRs). The voltages from the LDRs were sampled by an Arduino Mega 2560 and converted into MIDI Notes. To make a sound, the player interrupted the beams of light and an attached synthesiser - a Yamaha EX5 for those interested in such things - made all sorts of interesting noises.
The software did a little bit more than just sample the inputs. We also included :
- an eight-point rolling average filter to reduce transients typically from people taking photographs
- A force-to-scale module that guaranteed the instrument would only play notes in a Major key
- A hysteresis loop on every input prevented (but didn't entirely eliminate) multiple triggers
- Auto-cutoff / Midi reset when no input activity had been detected to eliminate stuck notes i.e. drones
- A built-in sequencer with MIDI transport auto-start/stop
We still had people queuing up to play this instrument long after the centre had closed.
What would I do differently next time? One of our visitors said he'd made much the same kind of instrument for his wife as a Christmas present. He recommended the following:
- An ultrasonic transducer to measure the distance between the player's hand and the sensors as an analogue of the note velocity
- Micro-lasers are better and more reliable than LEDs as a light source
- Shrouds around the LDRs to cut out extraneous lighting
- Shorter cable runs
- Better screening on the cable runs
- A common PCB for mounting the LEDs i.e. more even lighting
- A common PCB for mounting the LDRs - simplify the wiring harness
- Screen everything to reduce cross-talk
- Calibration system per LDR
This is another of my very favourite projects and one that I plan on revisiting now that we have children of our own who will love this device as much as we did.