The Prism is, quite simply, the best laser guitar on the Internet. At least I think so. I hope that you take these instructions and not only make your own, but improve on my design!

I suppose I should clarify what the Prism is: It's a bit like a guitar with some synthesizer mashed in. It has aspects of a theremin and a laser harp thrown in to boot. In short, it's not like anything else, and you can use it to make some really neat sounds. Anything from cold Sine and harsh square waves to heavily distorted noise.

At its heart the Prism features a VCO (Voltage Controlled Oscillator), based around the very shiny XR2206 monolithic function generator. The octave range is selected by blocking one of four laser "strings," and the pitch is controlled by the position of the musician's hand on the fretboard. The musician has the option of selecting a sine, triangle or square wave. The sine and triangle waves can be skewed using a separate Skew control.

It also has two other controllable oscillators, one acting as an LFO (Low Frequency Oscillator) and the other acting as a Sync generator.

I designed the Prism to plug into any regular guitar amp, with no computer required. In fact, there is no programming involved at all in this project! It is just as portable as a regular guitar, and meant to be used at gigs or wherever else an "alternative" instrument is needed!

Here is a video showing the basic functions:

And here I demonstrate the on-board effects:

Visit the Sample page to hear me "jam!"

Step 1: How It Works

I searched the Internet for days looking for the perfect solution. At first I considered making the Prism a MIDI device, controlled by an Arduino (like the Laser Harp seen in MAKE Magazine). Ultimately, I decided to make it completely standalone, like a normal electric guitar, requiring a minimum of external equipment and compatible with everything.

That led me to research various (all-analog) oscillator possibilities. This time simplicity was key, since it all had to fit inside the body of the guitar. There are a number of single-chip voltage controlled oscillators out there, but the only one that is actually in production is the XR2206. This neat little device takes a control current or voltage and produces either a sine, triangle or square waveform that is proportional to that control. The control can be as simple as a potentiometer, or something more complex like the infrared range finder I used. During my search I happened upon a most excellent design by Thomas Henry. It had everything I needed to get started.

The Prism is based on Thomas' design, with a few modifications. I removed some of the control inputs, such as the exponential FM and voltage-controlled Skew. I then added my own custom-designed laser-controlled capacitor bank, a hard-wired LFO generator (based on an XR2206 reference design from the datasheet) and a hard-wired "sync" circuit based on a 555 timer. Oh, and a Sharp Infrared rangefinder to control the pitch.

So how does it work?

Well, I mentioned before that the output frequency is controlled by an input voltage. The three input control voltages, Coarse (the range finder), Fine (a trimpot on the board), and LFO are all mixed together and converted to a current (taking the place of a potentiometer). This current, along with a capacitor from the capacitor bank, determines the frequency produced by the XR2206.

Normally you'd only use a single fixed capacitor, but I wanted each laser "string" to select a different frequency range. The Prism accomplishes this by having each laser trigger a phototransistor, which in turn controls a comparator. If the laser is blocked, the phototransistor turns off and the comparator goes low. This causes a solid state relay to turn on, connecting its corresponding capacitor to the XR2206's capacitor input. When no lasers are blocked, no capacitors are connected and the oscillator produces a frequency above the audible range.

To control the pitch, I used a Sharp infrared rangefinder. You've probably seen this used on autonomous robots, and perhaps some theremin-type instruments. This neat little device measures objects between 10 and 80 cm away, and generates a corresponding analog output between 2.4V and 400mV, respectively. This voltage swing is quadrupled with a simple op-amp on the board.

The desired output waveform is selected by turning a rotary switch, that selects between the sin/tri output and the square output. The frequency and amplitude is the same no matter which waveform is selected.

The skew knob causes the triangle and Sine waves to skew - that is, they get chopped up and lean to one side or the other. For instance, the triangle wave can be made into a ramp for a slightly different sound. The effect is even more pronounced with the sine wave, which goes from a nice clean sound to very harsh and metallic.

The LFO effect can be varied by turning a knob, and turned off by pushing the knob (a very clever design, if I do say so myself!) Its effect can be varied from a slow rise and fall, to a nice vibrato, to a high pitched trill sound.

The Sync only affects the Sine and Tri waves. It is also controlled by a rotary knob, and can be switched off. Each time it transitions it causes the main VCO to reset, chopping up the sound in interesting ways.

There are also a few more on-board trimpots, used for tuning the output waveform. These are only touched once when the Prism is first constructed.

The Prism can be plugged into any regular guitar amp, or it can be modified to control a separate synthesizer setup.

A separate power supply is also needed, that produces +15, -15 and +5V. The lasers are driven by a 3V regulator that "spoofs" the voltage the lasers are expecting.
May be the lazer beam can be smaller to were it's easier to play other strings but my question is can you play bass chords on it or power chords
<p>I think this is a truly great project, but one very bad thing about it, it's that it seem very hard to &quot;pluck&quot; the cord you want to without playing the other. It's not instinctive at all. I'm thinking about making one, but first, I have to resolve this issue because, if I don't, it sure this instrument will end in a box somewhere.</p>
This is a great project and I am currently working on a similar one myself. I see that you have actually made some serious improvements to this guitar in this youtube video http://www.youtube.com/watch?v=4CnRsTaShUU <br> <br> I have watched the above video a bunch of times but I can't figure out what kind of sensor you are using to detect which fret you are on, and how it is precise enough to get the 'bending' within the fret. I see four sensors where you currently have the one on the old prism guitar, but it seems much more sensitive than just four IR sensors. <br> <br> My last question is about how the actual guitar sounds, where it is clearly no longer a sine wave/triangle wave/etc. Did you just program each 'note' to an audio file which would play when triggered? Again, great project and I look forward to hearing how you changed the prism guitar.
Very awesome. How are you using the neck to control the pitch? john_a4321 kinda asked the same thing. The way you described it, the range finders control the pitch, however when I watch the video if you playing, it looks like the range finder is just used to &quot;pluck&quot; the &quot;string&quot; and you are using the neck in a more traditional way to actually get different notes out of the string. What is going on here?
what is the sensor of the neck of the guitar <br>
hey........its been along time since ive seen this instructable <br>im still fascinated with it... <br>just to make it simpiler can you remove most of the stuff and put in an arduino?
can i gt the schmatic circuit diagram of the circuit above
It's right there under the text, called &quot;laser guitar.sch.&quot; You will need Cadsoft Eagle to open the file.
Wow, man. You got skillz!
About how much in total, minus the guitar, does this cost to build? i'm interested in making one as a senior project for school. And is there somewhere i can find the parts list?
my bad, i hadn't read the comments far enough<br>
No problem! But you may want to hold off for a week or two. I've got something coming that I think you'll want to build instead!
I totally failed to get my updated guitar ready in time for the Epilog contest. That, and I was busy building a second storey on my house. It's been finished for a while now, though I couldn't find any musicians who were willing to play around with it for more than an hour or two (somewhat disappointed about that, actually). I needed someone to film showing what it can do since I can't play myself.
:/<br>I imagine how frustrating it is.<br>I hope you can find someone to help you so you can upload the instructable.<br><br>I think I'll wait for the next one then. =)
Whats the word on this alternate build?
This is AMAZING!<br><br>I want someone to play &quot;Derezzed&quot; by Daft Punk on this beauty. Or even better, interface it with a solid state tesla coil!!!!!!
I love the project, and i'm not sure if anyone has called you out on this, but it is a bass, not a guitar, 4 strings!!!<br><br>Thats all, i would love to make one though
Well, it was made from an old bass, but what makes it a bass guitar? The length of the neck? The tuning? The number of strings? A tenor guitar only has four strings, yet it is not a bass.<br><br>Really, the Prism can be whatever guitar you need it to be... within the confines of four strings, of course. ;)
well measure for me the scale length (from the two points the strings touched the bridge and nut.) If it is 34 inches, it is a bass, also it should have about 20-24 frets. Tuning does not matter, because you can tune any instrument to achieve any tone you want.<br><br>A bass guitar is just the term for an instrument with all of those qualities, and it is really just a name.<br><br>Please do note however, that you do not play &quot;chords&quot; in the same was as you would for a guitar. A bass is one note plucked at a time, however sometimes one can play the octave of a note at the same time as the original to achieve the correct tone.
One other thing, your &quot;victim&quot; included standard P-Bass pickups in the hum-bucker layout, also a thumb rest below the strings. Both of these are used in basses, not guitars<br>
Well, it definitely used to be a bass. And it used to have frets, and strings, and pickups, and a thumb rest. Is it a bass if all those have been removed? It's kind of in a gray area, I think. As far as sound is concerned, it's more like a synthesizer or theremin...
I was just curious, what exactly do the connectors in the schematic hook up to? I am currently bread boarding this project and have no idea what to connect each of the plugs to.
Most of the connectors are labeled in the schematic and ought to be self-explanatory (but ask me if they aren't!) The trickiest ones are the two switch potentiometers, which have a switch and pot integrated into a single unit. The steps that describe those components may help.<br><br>If you need full-scale drawings or the original schematic, send me a PM with your email address and I'll send them to you.
I meant what do the &quot;jp&quot; plugs in the schematic get plugged into? Specifically jp3, jp4, jp5.
Also, what does the &quot;Thermal Connection&quot; note in the schematic mean?
The two components must be physically touching, preferably with a layer of thermal paste between them.
Ah! Those go to the rotary switch. It switches between sine, square and triangle waveforms. Step 7 has details on how to wire the switch itself.
Is it me or those schema and part list do not work, it ask me witch program I want to use to see it, have an idea guys?
To view the schematic you'll need Cadsoft Eagle, get it at www.Cadsoft.de. Or is your problem that they are downloading as .tmp files? In that case, try renaming the file to what it was supposed to be.
You would destroy such a beuty!!!!!<br><br>Just kidding nice project, might work on a variation as a side project =D
I cant seem to open laserguitar.brd, laserguitar.sch, &amp; prism parts list! Can U help me out?
.brd and .sch are Eagle CAD files; get a free copy of Eagle at www.cadsoft.de. The parts list is .txt, that shouldn't be a problem... Or are you getting .tmp files? Try renaming them as appropriate. If that doesn't work, let me know and I'll email them to you.
Sorry, I still having trouble with these!
Well, describe the trouble and I'll try to help...
Great man!!
How glossy would the paper need to be because im wondering if i am going to need to buy some very glossy paper online?
You shouldn't need to go online to find the paper. Glossy photo paper works well (I use paper marked &quot;high gloss&quot;), others have had success with glossy magazine covers.
does it matter how long after i print it that i actually iron it onto our copper?
I'm not sure. I always did the transfer within hours, to avoid the possibility of scratching the toner off the paper.
using these exact instructions i did this &quot;laser printer and all&quot; and i ended up with a barely transfered ink. this is very strange... are you sure it doesnt need to be an inkjet printer <br>
100% sure it must be a laser printer.<br><br>However, the toner transfer method can be a bit finicky. There are a number of factors that can affect the transfer - the type of toner the laser printer uses, the &quot;darkness&quot; of the toner, the type of paper used, the cleanliness of the copper clad board, the temperature of the iron, the pressure used on the iron, the amount of time the iron was pressed on the board...<br><br>So, I assume that the toner transferred in some places, but not others? Try cleaning the board really well with fine steel wool. That helps the toner &quot;stick&quot; to the copper. Also try different types of paper. Some people have better luck with photo paper, others with glossy magazine paper. Or, you could try the dedicated &quot;blue&quot; toner transfer paper.<br><br>Another thing to watch out for is air bubbles. I think, but have not confirmed, that air pockets can form between the paper and the copper, preventing a good transfer.<br><br>Good luck!
I wonder if I can get the lasers mounted horizontally, rather than vertically. Also, you've probably been asked this multiple times before, but how much do all the parts come to?<br><br>
What do you mean, horizontally? Like, sticking out of the guitar? It's definitely possible, I'm not sure why you'd do it though.<br><br>The parts came to around $300 I guess, though some are now obsolete and hard to find.
Horizontally as in, instead of this:<br><br>|----- &lt; laser<br>|-----<br>|-----<br>|-----<br><br>Like this:<br><br>_._._._._<br> | | | |<br> | | | | &lt; laser
Yeah, that'll work as long as the sensors are lined up with the laser beams.
I understand if it would be too time consuming, but could you tell me what parts are outdated/discontinued? (And if possible, suitable replacements)<br><br>I'd really appreciate it.
SSM2210 (IC10) and the XR2206 (IC1, IC6) will give you trouble. The rest of the parts are either available or have an easy-to-find replacement.
Thankfully, there is one listing for the SSM2210 on ebay (which I am definitely buying tomorrow) and the XR2206 is, surprisingly, sold at Jaycar (Australia's RadioShack, but with a crappier product range :P)<br><br>Thanks for the help, definitely going to post pics when this is finished.
Well, the spaces didn't work in the second bit of ASCII art, but you get the point.

About This Instructable


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Bio: By day, Jeff is the Jack of All Robots at Clearpath Robotics. By night, a mad scientist / hacker / artist / industrial designer wannabe!
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