Print PDF
Favorite
Email
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!"
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!"
Remove these ads by
Signing UpStep 1How 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.
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.
| « Previous Step | Download PDFView All Steps | Next Step » |
I imagine how frustrating it is.
I hope you can find someone to help you so you can upload the instructable.
I think I'll wait for the next one then. =)
I want someone to play "Derezzed" by Daft Punk on this beauty. Or even better, interface it with a solid state tesla coil!!!!!!
Thats all, i would love to make one though
Really, the Prism can be whatever guitar you need it to be... within the confines of four strings, of course. ;)
A bass guitar is just the term for an instrument with all of those qualities, and it is really just a name.
Please do note however, that you do not play "chords" 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.
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.
Just kidding nice project, might work on a variation as a side project =D
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 "darkness" 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...
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 "stick" 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 "blue" toner transfer paper.
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.
Good luck!
The parts came to around $300 I guess, though some are now obsolete and hard to find.
|----- < laser
|-----
|-----
|-----
Like this:
_._._._._
| | | |
| | | | < laser