Vol. 15: Laser Harp

Play strings of light, using laser pointers, rangefinders, photocells, and Arduino.

Photos by Jacques De Selliers, Stephen Hobley

+ Downloads & Extras:

Analog multiplexor:

AIN Kit (32 analog inputs) from http://www.avishowtech.com/mbhp/mbhp_ainR4.html

This uses 4 standard 4051 analog multiplex chips – documentation is available on the internet on how to use the control lines to connect to each of the 32 inputs.
[www.arduino.cc/playground/Learning/4051]
[http://little-scale.blogspot.com/2007/06/arduino-midi-out-example.html]

Note: With some clever programming you can use just the analog multuplexor to drive the laser harp – connect the outputs of the photocell array directly into the inputs of this board, then you can detect if a beam is broken in software inside the Arduino.

Digital Multiplexor:

DIN Kit (32 Inputs) from http://www.avishowtech.com/mbhp/mbhp_dinR5.html

This kit uses the 74HC165 chips these take the parallel input lines and create a serial stream, you can chain these modules together and have as many inputs as you need. Documentation is available online - the Arduino playground is a good place to start.
[www.arduino.cc/playground]

-=-=-

More than anything this project has been a testament to the collaborative power of the Internet. I could not have done any of this without the help of many people – who were good enough to answer all the questions I posted on a variety of forums. I'd like to take this opportunity to pass on my gratitude - please keep up the good work! If you want to tackle a full sized scanning laser harp – then more information can be found on my website www.stephenhobley.com.

� MAKE: NOISE — Discuss this article

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Showing messages 1 through 8 of 8.

laser pointers
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Could any one tell me which laser pointers I need to get for this project? since it is not specified in the article, I bought some simple ones with <1mW output, but the beam is not visible. I have noticed that laser pointers go up to <5mW output, but I am not sure if their beam would be visible. Can someone tell me?
thanx a lot in advance
Posted by lolarainbow on November 02, 2009 at 07:10:30 Pacific Time

share your work
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Has anyone out there actually built one of these harps? and if so does it work properly? I get the idea I may have used the wrong type of parts. I would love to interface with someone who has a working harp, using the plans in this article.
Posted by looking up on September 30, 2009 at 13:50:12 Pacific Time

harp vs theremin
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Is there suppose to be a pitch change for the harp notes, like in the theremin note. I have constructed the theremin, then the harp, but I don't seem to get the pitch and bend on the harp. I don't even get it on the first note, which is what I used for the Theremin. Help?
Posted by looking up on September 12, 2009 at 13:54:36 Pacific Time

harp vs theremin
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I don't have the code with me, but if I recall correctly the detector output should be sending controller data to change a synthesizer parameter.

MidiOX will tell you if the controller data is being sent.

The effect should be something like this:

http://www.youtube.com/watch?v=Yta0aJrbOxU

Note: A couple of people have written to me to describe problems when chaining large numbers of the Sharp sensors together. When I looked at the sensors I used (that were very old and came from a clearance place) they are not actually marked like the Sharp sensors.

Typical problems are noise on the power lines as each sensor fires. Bypass caps usually help to clean this up.
Posted by shobley on September 14, 2009 at 06:02:47 Pacific Time

laser harp code
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I'm surprised to see only one comment on the laser harp project, but after overcomming many hurdles I have finally completed the project, only to find that it doesn't work. I cannot seem to get the notes to "bend" as I move my hand up and down. When the arduino is programed for the Theremin, it works great, when I reprogram it for the harp, I can get the note on, and off, but there is no variation to the note as I go up or down. I have read the program and have noted that I may have to fine tune it, but I know nothing about programming the arduino, or anything else for that matter, so I am at a loss. If anyone else has experienced this it would be nice to know.Guess I'll start learning how to program the Arduino.
Posted by looking up on June 07, 2009 at 19:23:10 Pacific Time

laser harp code
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Steve,thanks for the info on what to check, the following is some more data that I have collected.

The frame is 2" X 3" wood on top and bottom,Aluminum tubes on the side. It's 37" tall, and 33" wide. the sensors are positioned 4 1/2" apart and recessed into the wood by 1/4".

While a note is played from the "MAKE_THEREMIN.pde" program I get a 30 HZ,pulse train that is 800us of highs and lows (0-5V). I can change the pulse train noticably by moving my hand up and down in front of the sensor. The Range finder input to the Arduino analog pin 0 varies from 2.6V to less than 100mv.

While a note is played from the "MAKE_HARP_CTRL.pde" program I also get a 30 HZ,pulse train that is 800us of highs and lows (0-5V). However as I move my hand up and down in front of the sensor the pulse train does not change, or if it does, it's not noticable. The Range finders 6 inputs to the Arduino analog pins 0-5 still vary independently from 2.6V to less than 100mv but I'm not seeing a change on the scope. All of the notes work, and are different notes according to the data stream on the scope, they just don't bend. The message I get on MIDI-OX output monitor event is "CC: Brightness". I just don't know what it means. If there is anything else I can check, to find out why it's not working I will be overjoyed to check it out. Thank you for your input.
Kim

Posted by looking up on June 13, 2009 at 11:21:56 Pacific Time

laser harp code
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Here are some things to check:

1. The sensors are prone to cross talk. So I would be careful how closely you place them.

2. Check the output with a scope if you can to see that noise on the line is not corrupting your sensor signal.

I looked at the code for the Arduino, and does appear to be correct. Let me know if you discover anything wrong and I will look into for you.

Steve

Posted by shobley on June 08, 2009 at 06:43:10 Pacific Time

how about power source for LM324??
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Hi!
Now I'm making the coolest laser harp.
But I have one question!!

How about power source for LM324?
Should I prepare another power source?
There is no datail about power source in the book "MAKE".

please advice me about specification for AC Adapter.

Posted by fgg0202 on March 09, 2009 at 15:38:48 Pacific Time

Showing messages 1 through 8 of 8.

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