FAQ English section

[Genesis]

FAQ FRANCAISE ALLEZ ICI: viewtopic.php?f=18&t=15&p=39#p39

Hello folks.
Many of you are asking lot of questions about this project. Here is a FAQ to help you.
if you have any question not listed here post a reply and i will add your new question and answer in this FAQ.

First the technical caracteristics of our Harp:
- Main box dimensions: 220mm x 110mm x 45mm.
- Sensor and remote dimensions: 80mm x 40mm x 20mm.
- Power supply 8 to 30V DC or optional internal 115-230V power supply module .
- Connectors: ILDA, sensor, OSP (firmware download), remote control/footswitch, MIDI IN, MIDI OUT, DC power supply.
- User interface 20 characters 4 lines backlight LCD, 3 illuminated buttons, potentiometer and beeper.
- System core Atmel AVR.
- TTL beam color control give 7 colors (analogue modulation not used at this time).
- Balanced or single ended ILDA signals (depend of the connections) and 12bits DAC.
- Choice between standard Harp and sampler mode.
- Beam numbers can be defined between 1 to 20.
- Memory slots for 20 presets with maximum of 20 beams each beam with his own active and inactive color and with a maximum of 5 simultaneous notes. The instrument is stored too .
- Playlist to choose the presets to be played.
- Works with or without frame.
- Remote control with 3 illuminated buttons and footswitch (option) with programmable button/footwitch function.
- Can be remotely controlled by MIDI commands.
- All the parameters are adjustable by menu.
- The firmware can be programmed and updated by USB.
- It's free!! except the component cost.

1/ What is the Laser Harp?
The Laser Harp is a musical instrument developed and used by Bernard Szajner.
This instrument was made popular by the musician Jean Michel Jarre in his concerts

2/ How it works?
The principe is to use a laser source to create "strings". these strings play a musical note when they are cut by a hand.
Many systems are used to sense the hand in the beam.


the "frameless operation" or light back from hand
a sensor is used to collect the scattered light from the beam impact from the hand glove.

advantages:
- No frame is required over the musician
- Beam reflection to the audiance is allowed


disadvantage:
- Low ambiant light immunity because the sensor must sense the low scattered light fom the hand in high ambiant light. This problem is even more important when the ambiant light is modulated (like neon light and modulated led light which blink quickly near the laser harp scan rate). But i've worked hard to improve the sensor.
This low ambiant light immunity imposes to the Harp to make some iterations in other word to "see" several time the note activated or not before to really play the note. these iterations increase the reaction time.

- Depending on the laser power it ay be required to wear a white glove to increase the signal over noise ratio

- A minimal ceiling height or the use of black duct tape is rquired to avoid the sensor flooded by the back reflection light from the ceiling. Tilt the sensor is also possible.



"frame operation" or beam blink
one or several sensors are installed over the musician and permanently sense the beams. if the hand cut the laser beam the sensor is not illuminated and the note is played.

advantages:
- The ambiant light immunity is highly increased (closed loop) and the Laser Harp reaction time is lower. We can play in this mode under neon light.
- Wear a glove to play is not reaquired because the hand cut the beam

disadvantages:
- A solid frame is required over the musician to install the sensors.
- A sensor is required for each beam (see below our improvement about this point)
- The beams can't be reflected to the audiance



Added modes on our Harp:
To impove the operation we have added several modes to those defined previously.

- the "CEILING" mode"
It's a frameless mode where we take advantage of the reflected light from the ceiling.
The sensors works like in the frame mode because it sense the light from all the scattered beams on the ceiling. if the reflected beam disappear (when the hand is placed between the laser and the ceiling) the note is played

advantages:
- The reaction time is increased and wearing glove is not required to play

disadvantages:
- The ambiant light immunity can cause some problems

- the acrylic light pipe
It's a frame mode and the idea (protected) is to use an acrylic rod as a light pipe. It works better if this rod is colored with fluorescent dye at the laser wavelenght (like rhodamin or fluorescein etc...) so orange or yellow/green color.

avantages:
- the reaction time of the Laser Harp is really increased (closed loop) and wearing glove is not required
- Only one sensor is required whichever the number of "strings"
- Great stage optical effect when a fluorescent rod is used because the rod is illuminated by another wavelenght than the fundamental one (example green laser give a bright orange rod)

disadvantages:
- Higher price
- A solid frame is required with optical adjustments
- Beam reflection to the audiance is no posible (or not the entire beams)


3/ What is required to use our Laser Harp?
This Laser Harp is a MIDI controller connected to a laser through an ILDA (International Laser Display Association) connector.

so a laser is required and it's the highest cost part of the Harp system
You have two solutions:
- You have good technical knoweldge and you buy a laser source with laser scanner pair and you build your own laser (ebay etc....)

- You are a newbie in laser and technical system and you buy a laser from the market but pay attention: with fast scanners (see below) some power and with an ILDA inerfce.(ebay, sound market, etc....)

A MIDI musical instrument is required too because the Laser Harp is like a master Midi controller and can't play musical sound
hre you have two solutions too:
- Use a synthizer (we are using a Juno G from Roland)
- A midi <> USB converter with the right software on the computer to play musical instruments and program the Harp.

4/ which laser model is required?
You must have a laser with enough power. this power depends of some parameters like the operation mode (with frame or not) and if frameless with or without glove. the fluorescent rod is better too.

I've used a BPW21 photodiode with a near linear response to the visible light wavelenght.
Generally the green laser works fine and 250mW is a good minimal power requirement
But if the laser is more powerfull it's better!

About the scanner set you must choose a minimal speed of 24 thousand points per second or 24KPPS and not stepping motor! be aware about the low cost laser which use such type of "scanner"!
the scanner are generally available in a pair but only one is required for the Harp (at this time)

For information we are using a Laseworld Pure Micro 1800 color RGB laser with CT6210 scanners for the development.

5/ The height of the hand in the beam is doing something?
No, nothing happend even if by concept we can access to the photodiode signal and in fact at the scattered light amplitude from the hand. this scattered light is always unstable and depends of the hand tilt, beam position in the hand (in the palm or between the fingers), the color of the beam, the cleanliness of glove etc...
It would be more a "gadget" due to these parameters. but it could be fun. this is why we are working on this feature.

We have another solution in mind too...

The remote control include an analogue input to connect a footswitch to modify the pitch with the foot.

The best solution is to measure the height by the laser itself but with a light speed near 300 000 km per second you can imagine the speed of analysis required to measure a distance of 10 to 1.5m!! it's not posible for a hand made project.

The other solution is to use an infra red camera to track the hand like the Wii remote but the Laser Harp controller will not be autonomous and portable anymore.

6/ Why the firmware is not freely shared?
We have chosen this option after lot of discussion to keep the paternity of this project.
I've started this project with the use of an ILDA laser idea in 2005 and i've shared this idea on the net.
Big mistake! some people have used these informaton to build their harp, make business with it,say to be the inventor, won innovation prices, get on TV etc....i cant give name but it's easy to find in Great Britain.
This person sold these plans to a company which continue to sold this system in serie...but yes with no more support or option available...

So if we share the source code any company will be able to produce the laser harp without problem an easily earn money.

But don't worry the firmware is free and will be sent after you have given to us some informations like your first name, last name, if you are a company (but no commercial use allowed without taking contact with us) and your Laser Harp hardware serial.
These information will be displayed at the Laser Harp startup.

The hardware is free and you can develop you own firmware based on our board. Please Keep us informed if you make modifications on the hardware/schematics and keep us as the original designer.

The Laser Harp team.


to be continued....