Laser harp build. Need answers.

[HEXX5]

Ok so im new here and im not entirely sure this is the right place to post this, but i need help with wiring a laser harp. My laser harp is framed and will include absolutely no programming. Im going to have 13 laser modules shining onto 13 respective photoresisters. Also all sound will have to go through an average guitar amp. All i need now is to know how to wire everything.

 

[chuckey]

At a first thought, blocking of the light to a photoresistor should trigger an oscillator at full volume, just removing some of the light, should trigger the same oscillator at a reduced volume.
So you need a trigger circuit that switches on the oscillator at a reduction of, say, 1% of the light. Then you need some circuit that alters the level of the oscillator by the DC corresponding to the light level.
So the first thing, are your lasers too powerful, the output from the photoresistors must drop when the light beam is reduced by 1%. Which makes me think, that the laser should have its optics arranges so the light beam is 10mm in diameter, trying to intercept a beam that is only 2mm will be too difficult. I think for simplicity I would go for a central light source (50 watt DC bulb), feeding optic fibres into each individual lens.
So you need a 12V DC supply. Feed the photoresistor fro +12V, connect a resistor to earth from this junction. Repeat the same arrangement but with a variable resistor in place of the photoresistor. The two junctions go to a comparators inputs. With adjustment of the variable resistor you should then get the output of the comparator to swing from 0V to 12V, which you use as the feed to the oscillator. Now you have to take a sniff of the voltage across the photoresistor and amplify it so the change of voltage form full light to zero light becomes a worthwhile amount , say 0 -> 5V and use this to vary the gain of an amplifier to so feeding the oscillator through it, the level of the note changes in proportion to the amount of light blocked.
Without any data on the photoresistor and its change of resistance due to the light it is not possible to say more.
Frank

 

[HEXX5]

Wow I feel like an idiot lol could someone plz translate to a child's level... Now I know that someone inexperienced probably shouldn't be taking on something this heavy but I really REALLY want to build a laser harp that's simple and easy to use. I'm willing to learn how but I need information and experienced input to do so, and, after all, isn't that what the internet is for?

 

[SteveI]

First, many questions: What kind of sound do you want your harp to make? Do you want it to make a beautiful harp sound, or is a square-wave (i.e. NE555) acceptable? Is it to be polyphonic (interrupt multiple beams at once)? Will the note be played when the beam is first interrupted (edge-triggered) or continuously when it is interrupted? Do you care about MIDI output? Will it use a microcontroller (i.e. Arduino)? Do you want partial output for partial beam blocking (analog)?

 

[betwixt]

I think more fundamental questions have to be asked:

1. Do you realize the danger 13 laser modules will pose? Could you use much cheaper and safer IR LEDs and sensors?

2. Breaking the light beam is like opening or closing a switch. It will not make any more sound than a possible click. How do you convert the switching action to pitch/volume of the harp string?

3. If you are using a summing amp (nothing wrong with that) you need to modulate the lasers with the analog wave shape of the harp note, have you considered how to do that. Hint - lasers are notoriously difficult to precision modulate, IR is easy.

4. Assuming this is going to be hand operated, have you thought about the effects of laser/LED light scattering and falling on the other sensors?

5. Have you considered ambient light falling on the sensors? Unfortunately, almost all artificial light these days carries a lot of noise/interference on it.

Brian.

 

[HEXX5]

The final sound result doesn't matter. I don't want MIDI. Polyphonic. No analog and preferably no microcontroller, however I understand if it MUST have one. Also yes I understand all the dangers of 13 lasers and the difficulties of using lasers in the first place. As for ambient light I was thinking about placing light filters that allow basically just 532nm in front of the photoresisters. Now that I'm reading these posts it's got me thinking that maybe I need to use something other than photoresisters to detect the beams. For instance what is used in a night and day sensing flood-light?

 

[Audioguru]

Why not make an old Theremin device instead that safely uses the capacitance of the player's hands to its volume and a pitch antennas?

https://www.youtube.com/watch?v=K6KbEnGnymk

 

[HEXX5]

Well... Because I don't want a theremin... Lol

 

[Audioguru]

Many years ago when my kids were little I bought them a cheap Chinese toy electronic piano. They learned how to play music, one note at a time on the darn thing. Then I bought them a Casio portable electric organ that plays chords and has 8 different sounds and many effects.

 

[Audioguru]

Well... Because I don't want a theremin... Lol

I found some videos of a laser harp. The player frequently wears gloves and sun glasses to prevent burns.
Ho hum, yawn. Each note has the same volume and there is no vibrato like in a Theremin. Almost every other instrument and voices have vibrato.
https://www.youtube.com/watch?v=WkkhcwXpYy4

EDIT: The sounds can be anything. Voices, car traffic, gun shots etc. A laser harp can play a recording of another instrument that has vibrato.

 

[betwixt]

I still say go with the IR LED idea instead of lasers. All you need is 13 IR LEDS (very inexpensive) and 13 photoresistors (LDRs) or photo transistors. You can narrow the light beam using simple black tubing and if necessary use a plastic IR filter over each of the sensors. It is safe and much cheaper than using lasers with exactly the same results.

I think the real problems you will face are not the mechanical/electrical implementation of the harp structure, it will be making a recognizable sound come out of it afterwards. Don't forget that whether you use laser or LED, the hand action will be reversed. In a conventional harp the finger plucks the string to make the output, in an optical harp the finger blocks the beam, in other words in a 'hands off' situation, all the 'strings' are active at once.

Brian.

 

[HEXX5]

That last point you made Brian is my dilemma. I need to figure out a way to set it up so that when the beam ISNT broken then there is no current, and it's only when the beam IS broken that sound is produced... I know there's a way and I am very, very determined to find it.

 

[Audioguru]

The optical harp makes a sound when the beam is blocked. An LDR or photo-transistor does not conduct anymore when dark. A Cmos transmission gate passes audio when its control pin is high.
So simply use a DC voltage divider with the LDR or photo-transistor so that the transmission gate control pin is high so it passes audio when the optical sensor is dark.

 

[betwixt]

The light level / sound level problem is in theory easy to solve but in practice can be problematic. The theory side says if the LDR is wired as a shunt across the signal and as LDR resistance drops in light, you get more signal diverted down the shunt to ground when the beam isn't broken (= silent). The practical side says the LDR never drops to zero resistance, even if it is highly illuminated so there will always be some leakage of signal in the background.

I suppose the question I have to ask is "is this an analog or digital controlled harp?". An analog one would produce an increasing sound level as the light beam is progressively blocked, a digital one would abruptly turn on at full volume when a particular degree of blocking has occurred. Audioguru's transmission gate idea is ideal in a digital system but of litle use if it is analog.

Brian.

 

[HEXX5]

Well would I still be able to keep the same amount of simplicity with digital? Again I don't want MIDI and microcontrollers (though understandable if needed) are undesirable. Also I guess if a bit of sound is constantly playing (as long as it is generally quiet) it would be ok.

P.s. Reminder that I want 0 programming involved.

 

[Audioguru]

Many years ago a top octave generator was used to produce an entire musical scale but maybe they are not available anymore. Their frequencies were very accurate.
Then you need a separate oscillator for each tone. How many polyphonic tones? To sound musical their frequencies should be accurate.
The laser harps shown in You Tube have a fixed output level. Is that OK or do you need some kind of volume control for each tone while playing it? A Theremin has a volume control antenna.
A Cmos transmission gate is analog, not digital. It simply blocks or passes a tone. A CD4066 IC has 4 transmission gates inside it.

 

[betwixt]

By digital and analog I'm referring to the way the tone is turned on and off. An analog system will change the volume proportionately to the amount of light blocking so the more you interrupt the beam the louder that note becomes. A digital system will work like a bank of on/off switches, nothing at all comes though until the beam is interrupted then it suddenly gets switched on at full volume.

As far as complexity goes, the digital method is easier but aesthetically it will sound like a childs toy organ, you have no control of anything except the absence or presence of a fixed tone and volume per 'string'. It's really up to you which you want to use. On a real harp the volume would be controlled by the force used to pull the string but without the tactile feedback that gives the player it may be difficult to emulate it in an optical system anyway.

As Audioguru points out, you still need something to produce the tones in the first place, all we have considered so far is the method to select those tones and pass them to the amplifier.

Brian.

 

[HEXX5]

Wow you guys are more informative than a high school math class lol I want to thank you for all you've posted so far it's really helping me get things straight. 8)