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DangerousThing
04-12-2014, 01:54 PM
Hi:

This is a sub-project of my steampunk themed robot, SA-Groucho and friends) I am thinking of making a harp that has "strings" of light that can be interrupted by a hexapod's legs (the hexapod would be Harpo). I could cheat and have everything be run by Bluetooth, but I would prefer to do this such that the hexapod would be truly playing the instrument and that the strings could be seen if there is enough steam in the air.

Currently I'm thinking of this as a strange form of midi keyboard that could be fed into a simple synth to get the kind of sound I want. Everything in this project, both hardware and software, will be released as full open source.

Enough explanation: the question is what should I use for the "strings?" Would a laser diodes spaced about 1/4th inch apart be seen as individual sources? Or is there a better way to detect where a robot's limb intersected a 2d plane defined by the harp without actual contact?

jwatte
04-13-2014, 12:08 AM
This has been done by others; you could Google.

What I would use would be cheap red laser modules on one end, and red-sensitive phototransistors (or other such photodetectors) on the receiving end. Use black straws or something to get an inch of isolation between the detectors, and individual separation should be perfect.

DangerousThing
04-13-2014, 01:29 AM
This has been done by others; you could Google.

What I would use would be cheap red laser modules on one end, and red-sensitive phototransistors (or other such photodetectors) on the receiving end. Use black straws or something to get an inch of isolation between the detectors, and individual separation should be perfect.

I will google. But of course it's been done by others. I should have thought. For one thing it was a Star Trek instrument, so others would have wanted to do it for that reason alone. But if the mechanism was that obvious to me, it should have come to a few others over the last ten years or so. :(

Do you think that laser module will be needed, or that a laser diode might be enough?

Thanks much!

CasperH
04-13-2014, 02:35 AM
Maybe:

http://www.slipperybrick.com/2009/07/the-prism-a-laser-synth-guitar/
http://www.instructables.com/id/Simple-Arduino-Laserharp/?ALLSTEPS

A bit too commercial, but cool nonetheless: http://www.laser-harp.com/site/wiki

tician
04-13-2014, 03:05 AM
One of my first thoughts was a neato lidar since it would give all legs and beyond with a single sensor and it uses a plain red laser pointer. Not sure it would be strong enough or slow enough to give a really nice visual effect. Maybe Xevel will know more about that...

DangerousThing
04-13-2014, 07:19 AM
I remember trying to use a doubled diffraction grating so that the patterns are both horizontal and vertical so I could measure the pattern with a camera to determine distance and basic object information. This was about the time I stopped doing robotics for a decades so I no longer have my notes or my code. Basically I just looked for dots of the correct color and pattern.

DangerousThing
04-13-2014, 07:20 AM
Maybe:

http://www.slipperybrick.com/2009/07/the-prism-a-laser-synth-guitar/
http://www.instructables.com/id/Simple-Arduino-Laserharp/?ALLSTEPS

A bit too commercial, but cool nonetheless: http://www.laser-harp.com/site/wiki

Thanks much!

jwatte
04-13-2014, 12:20 PM
One of my first thoughts was a neato lidar since it would give all legs and beyond with a single sensor

Or you could use a Kinect sensor.

For the "laser harp" type application, it's easier with one emitter/sensor per key you want to sense. For two octaves, you need 25 such pairs.
One of the first users of laser harps was Jean Michel Jarre -- since 1981!
https://www.youtube.com/watch?v=dpOX1XCgzJo
The fancy ones work by reading reflection, rather than the simpler version of just shining the beam into a detector and detecting breaking.

tician
04-13-2014, 12:34 PM
The neato lidar mounted under the body gives you 360 degrees of sensing and the close range needed to sense the legs of a phantomX size robot. A kinect cannot do that unless mounted on a mast above the robot to look straight down on all the legs.

DangerousThing
04-13-2014, 09:55 PM
Or you could use a Kinect sensor.

For the "laser harp" type application, it's easier with one emitter/sensor per key you want to sense. For two octaves, you need 25 such pairs.
One of the first users of laser harps was Jean Michel Jarre -- since 1981!
https://www.youtube.com/watch?v=dpOX1XCgzJo
The fancy ones work by reading reflection, rather than the simpler version of just shining the beam into a detector and detecting breaking.

Yes, I was thinking of using one emitter/sensor pair to get the individual notes. I was only going for 8 notes per octave along with a sensor to change the key of the instrument. Since this can be done on the fly, as well as stretching a note, I think I can get away with just 8 notes. I will also want a sensor/emitter pair between each and every note that will be used for gestures.

So now I need to experiment to see of I can find an inexpensive sensor that will work. Adafruit has laser modules for $6 which makes a two-octave instrument a bit pricey for silliness. Do you know of a better price elsewhere?

Thanks.

jwatte
04-14-2014, 10:41 AM
$10 for 60 ?
http://www.ebay.com/itm/Lot-of-60Pcs-Mini-650nm-3V-6mm-5mW-Laser-Red-Dot-Diode-Module-Laser-Copper-Head-/390819613877?pt=LH_DefaultDomain_0&hash=item5afeaa0cb5

DangerousThing
04-14-2014, 10:48 PM
Again, thank you. I haven't gotten anything from eBay in over a decade, so it's off my radar. Well, if 3 of these are good, then the price is better than Adafruit. If half of them are good, then I've got enough to build the harp after I find some sensors as Digikey or Mouser or even Jameco.