Artist-photographer-amateur engineer Stephen Hobley make one of these and published a schematic in Makezine issue 15. (Pictures and video of Stephen Hobley's dubbed out one are here.) The harp is a MIDI-based circuit that uses the analog inputs on an Arduino microcontroller with an infrared sensor and photocells. As I roughly understand it: laser pointers send beams into photocells. When interrupted, an Arduino analog circuit is activated, and that circuit sends a MIDI note based on where the laser is broken, using an infrared sensor as a potentiometer to bend the note.

 

 

a) Drill holes for the lasers themselves. Also drill set screw holes. Get set screws. Put set screws in. Replace dud laser. Realign lasers so they point at the right spots.

b) Mount the lasers and wire them up to the terminals.

c) Solder leads to the IR sensors, mount the sensors, wire the sensors to the power terminals and to the microcontroller.

d) Bore holes for the photocells and translucent spreaders. Re-bore holes for transcluent spreaders, aligned correctly this time. Drill set bolt holes to keep the top bridge piece aligned properly.

e) Mount the photocells. Wire them up to the s/r lines. Mount translucent spreaders.

f) Mount the power supply PCBs. Give them a silicone once-over.

g) Mount the detector circuit. String it up to the photocells and the microcontroller..

h) Mount the microcontroller. Hook it up to the photocells and the detector circuit.

i) Connect the power supply to the lasers terminal, IR sensors, and the microcontroller..

f) Run the MIDI test. Troubleshoot.

g) Run the theremin test. Troubleshoot.

h) Run the fully functional multi-note harp. Troubleshoot.

 

Build report and progress as follows:

 

4/3: Spent part of last night doing the s/r lines and then ran the MIDI test. Not surprisingly, it was a bust.

 

3/12: Found a spare pointer I didn't realize I had. Attached it and put in the set screw. Need to pad the lasers so they go the right direction and hit the right points -- have no idea how I'm going to do this yet, perhaps with magic.

 

3/10: Have to backtrack a little due to some problems with laser alignment. Should have seen that one coming, I guess. Wound up just working on the Thingamakit instead because I needed a break from harp stuff. Here are some nice pictures:

 

 

 

Full size shot of the harp. It's tall.

 

 

3/9: Spent yesterday watching hockey and working on the harp. Crossed several things out and have begun seriously mounting things up. Pulling for a completion by the end of the week. I am pleased to announce that the lasers work great, by the way, and apparently leaving the detector circuit alone for awhile has

 

3/6: Happy fun time update: Lasers are wired up. Power supply needs a little bit of reworking and logistical planning -- the variable volt wires broke while I was attaching leads to run to the laser terminal strips. Speaking of, need to get more terminal strips. Going to push and try and finish it this coming week. This will have been three months or so working on this shit.

 

2/24: The laser harp frame is mostly completed -- may require some further tinkering, because I'm a bad woodsmith. The white things with wires coming out of them are terminal strips, for cleanly wiring the photocells down the side to the detector circuit. It did not strike me until I ran out of green stranded wire how much hooking up this project has needed. What a country. Also pictured, on the right side on the speaker are two stuffed Marshmallow Peeps bunnies.

 

 

2/4: I got an M-Audio MIDI-USB adapter. The cheap one. One last Jameco order for a few odds and ends capacitors I need and then it is time to construct the frame and IR filters. Below, the MIDI adapter, which miraculously has an update making it Vista compatible. Further, I installed a copy of MIDI-OX, which is also Vista-compatible.

 

 

1/30: After a lot of unpleasant troubleshooting I diagnosed what was wrong with it -- I wired the 2nd and 5th outs wrong, because they were the bottoms of the first LM324, and it's a symmetrical pinout IC. So a bit of desoldering and resoldering later, we are back in the business. The circuit is still a little wonky and I have to hit the ICs to get all the LEDs to turn on, but I think it's because they are jammed into pretty close quarters and not because of cold solder joints. Either way, fuck it man, it works.

 

1/20: The power supply got a quick rework and is totally functional. See pretty picture!

The detector circuit, after weird issue, is half functional -- two of the channels out of six function reliably. So at least part of it will require a re-work -- not sure what to do about that at this time. Will have to break at least part of it and put it back together, which will be a pain because the wiring got to be a clusterfuck. The LED array belongs in the bottom IC socket but is not installed in this photo.

 

1/12: Put together the power supply only to have it not work right -- it has three output voltages and none of them put out a voltage higher than, like, .3v.  So I desoldered the parts and am in the process of trying again, after testing the working parts (a 7805 regulator and an adjustable voltage regulator).

 

1/6: My order from Trossen Robotics came. Adjustable voltage regulator and six GP2D12 infrared sensors. These were by far the most expensive parts. Also, my uncle got me a second Arduino microcontroller for Christmas so the harp can have a dedicated microcontroller on board, which is nice.