Laser Harp laser

I dunno if anyone's still gonna see this thread but I figured i'd point out just for anyone trying to figure this out that the schematic for the project actually uses a transistor to turn the laser off and on, so any laser will work as long as you connect the laser to the arduino via the transistor and not directly into the digital output pin. I haven't gotten it to work fully yet but when I do I plan on uploading some pictures or videos for those who are interested.

Umm I might be wrong, but don't laser harps normally have fog in them?

I think they normally use an external fog machine but ive never actually seen one so i dont really know

I've been building a laser harp and am working on this same issue. I am using a continuous laser and I can confirm that's all that is needed, turning it on and off is probably better but adds a LOT of complexity. Here is what I have a continuous beam looking like in a stepper motor:

The laser harp is working! - YouTube

That being said ... I have several pointers, 100mw, 200mw, and 1w. None are particularly visible, not like I would LIKE them to be. If the room's got a lot of fog in it they are fine, but ...

So I see 50mW 532nm suggested earlier. Is that going to be more visible? Why? (And the why is not to argue - I just want to understand what's going on before I spend more money!) --And while I have this working - I have to admit I'm considering switching to that TTL laser suggested on the first page!

Thank you!

For clarity - this is what I've seen that I'm trying for:
Tetris Theme on Laser Harp - Theremin Hero LIVE! Finale - Gamecity 5 Nottingham - YouTube

But then what is THIS?
Laser Harp - Gary Numan / Avicii Mix (Practice Session) - YouTube

Ignore the beginning - that's multiple beams combined. But once they fan out, look how solid they are!

The solid one is probably framed, meaning each laser is firing into it's own light detector. So that's multiple lasers, and much higher cost. But pretty!

The first one, and mine, is frameless - cheaper and smaller, but since the same beam is flickering back and forth it's not quite as pretty.

But my beams never seem quite as visible as those. Maybe I'm just not as good working the fog machine, but ... maybe I just don't have the right laser!

Multiple things can cause it. Back when I ran a few laser harp kits I had an issue where even high powered lasers had very dim beams, it came down to the harp not "sitting" on the beam long enough, and was easily fixed in code.

DPSS green lasers especially don't reach full power right away, so if the harp is only sitting on the beam for a millisecond or so, the laser won't have time to reach full power, and it also appears dimmer to your eye due to persistence of vision.

The best way to combat this is change up your code so you can adjust how long the harp sits/waits on a beam before moving on.

Some lasers are also quite low quality and might not like to reach full intensity for minutes, in which case you're basically limited to getting a new laser.

While you can make pointers work in this case, I don't recommend them as they aren't designed to switch on quickly and you'll have poor results. I'm working on a new self contained, more commercial laser harp at the moment which will provide a simple ILDA interface, so you can use it with any standard laser projector. I'm looking into ways of allowing moving your hand up and down in the beams to allow pitch shifting, but the technology I'm looking at is still a bit hard to come by, so it's still in the pipeline ATM. I'm hoping I may be able to opensource it at some stage too.

My laser is constantly on so I think that's not the issue ... though that makes me wonder if it'd become one if I go to a TTL laser?

I've for the step width and time in external variables, so I've tinkered with those a lot to get where I am now. I didn't want it to sit on a beam TOO long, the end beams stay off for too long a period of time. So it's all a compromise!

And I'm figuring on open sourcing mine too when it's ready ...

As for varying pitch, I have a handle on part of that. I can detect changes in light from my hand going up or down, so that lets me vary pitch - but I have to always start in the middle, I can't tell where you interrupted the beam, only if it gets lighter or darker from there!

(I'm a senior software engineer, so that side I can figure out. It's the hardware side that I'm a rank amateur on!)

While the light intensity approach probably works quite well, in situations where the harp is used with other ambient lighting it can be an issue. My idea is essentially using a camera (but not a regular camera, as I'll still be using a microcontroller to handle everything). I'll still probably keep the regular light sensors for actual triggering for reliability. Lemme know how you get on using the variable light technique.

I think the best way to have a variable pitch would be using a sonar range finder like these Amazon.com: SainSmart HC-SR04 Ranging Detector Mod Distance Sensor (Blue): Car Electronics, they're pretty accurate and responsive and since they're already optimized for arduino it should be alot easier than writing the code for a camera. They also have IR distance sensors but I haven't used those before so I don't know how reliable they are.

They would work, however you'd only be able to play 1 beam at a time, which unfortunately for a lot of people isn't gonna work.

Ooo that's nice and probably better than my variable light idea. I have my harp playing two strings at a time now so that's an issue but ... well ... this is still a pretty sweet thing and I kind of like it!

But then I think my requirements are a lot less stringent than Things - I'm just having fun playing in my basement.

So far though the gist that I've been getting from this thread is that the lightness issue is not a laser power thing, but the time spent with the beam sitting still on a string. So I'm going to have to go test that theory soon!

It can definitely be related to the laser itself, are you using a green/DPSS laser? Maybe give it a shot with a diode laser and see if it improves.

It is a compromise between flickering and beam brightness like you said though. With mine I found flicker was slightly visible if you looked around quickly etc. Worth taking into consideration if you're ever intending on doing performances, as cameras may not capture the harp properly.

That said, using beam brightness is by far the simplest way of doing pitch bending, but it won't work once you go past single colours. Ultrasonic/IR sensors could work given an array of them, but once you're talking 12 beams it could get ... interesting

True, i dont know what the divergance is on those sonar modules, maybe you could hook up another mirror to split the IR beam but since you cant see it it might be hard to adjust, and the sensor may not read it as sell

albuser said:

and the sensor may not read it as sell

Click to expand...

*well, sorry I was typing that on my phone.

Technically you could use an IR distance sensor, but you'd have to use a laser instead of an LED, and also combine it into a beam with a visible laser. Definitely doable and it'd work well, but you'd need to build a specialized projector to do it.

This IR sensor Arduino Sharp Gp2y0a21 Ir Infrared Range Sensor + Cable New: Amazon.com: Industrial & Scientific says it has an angle of >40 degrees, which may be doable for a few beams but when you're talking 12 individual ones thats kind of a stretch. My only concern with using light intensity to control pitch is that ambient light conditions might make it hard to find the right pitch, especially if you're using it at a performance or something like that. I haven't seen a laser based IR distance sensor but i'll definitely keep my eye out in case they already exists. I got my harp to spin and create the beams but I still haven't figured out how to get it to send data to the keyboard to make it actually produce sound, i plan on working on it some more once I have more time, just kind of got sidetracked with other projects.