Framed Laser Harp: Need help picking diodes

[Stoney3K]

In the case of using discrete modules, what would be the best choice in the range of 50mW? There are obviously the cheap eBay specials, but those would probably last about 10 seconds.

You won't really need that much power unless you go for the really big gigs. 50mW modules would mean around 0,5W of total STATIC beam power, which would make everything fairly bright. Depends on the stage you will be performing on, though.

I don't know where to start with regards to a scanner system, as all the plans are either in French, or taken off the market (Steven Hobley's). If there are any other tutorials for building a scanning harp, that would be much appreciated. I'm more of a musician than an engineer, but I want to learn.

What it looks like now is:
8 50mw 532nm modules (on custom PSU circuit)
These drive LDR's (I like Carl's idea with the outward beams, that's something I've seen Jarre do), which will be picked up by Steven Hobley's beam detector circuit (using LM324s), with an Arduino handling the A/D.
If there are low-cost scanning systems I could retrofit, I would go straight to a frameless harp, as I don't exactly understand the magic behind the frameless harp, and the framed harp is simple.

Sounds like I should put some information up about building a scanning harp in the near future. I don't have any ready-made circuit boards yet, but my code is based on ATMEGA16 and uses the MCP4921 as a DAC, so it should drop right in with Arduino users. (The Arduino Wave Shield uses the exact same combination of parts). Only some signal level correction is required after that if you want to use the full scan angle of your galvos.

I've also had success by using the ATMEGA's internal PWM to generate audio, but its usability is fairly limited because of the low resolution. Offloading that to a DAC makes a lot of difference when it comes to ease of programming.

The one thing I'm still working on for the frameless harp is detection of the reflected beam. Signal to noise margins are very low, so it's a challenge to make that work.

[dnar]

As mentioned in my post above my framed harp uses a scanner to create the beam's.
At the time of filming the video linked above, the harp had a 500mW laserwave head in it. At the moment I am using Pangolin Livequick to scan the 9 beams scanning 4 points per beam at about 10kpps. I intend to have a circuit built to take over from the software some time in the near future.

Starting with the laser box. This is basically an ILDA projector with only one axis scanner that sends the beam up and out of a slot aperture. A standard ILDA projector could also be used.
Attachment 25050
Attachment 25048

The sensor bar has 9 x 5mm LDR's with pass red bounce green dicro's fitted on to a short pieces of plastic tube cut to 45 degrees and a tissue paper light diffuser on the back of the dicro. Around 95 % of the beam is reflect by the dicro's to send beams over the heads of the audience. The small % of light that passes through the dicro is enough for the LDR to react to. The dicro's seem to filter out all unwanted ambient light. I got these nice, large, cheap dicros from Coloured GU10 halogen spot lamps from CPC.
Attachment 25047

The so called brain's for the harp is the box below.
Attachment 25049
To the top right is the 5 pin MIDI socket and the 15 pin D socket for the sensor bar.
To the bottom are the black and white phono jack sockets that are laid out like the keys of a keyboard. The nine phono plug patch leads go to the N/O contacts of the relays on each of the nine circuits illustrated below.
Attachment 25051
You have to build one of these circuits for each beam.
The black and white phono sockets are connected to a MIDI controller board i managed to buy off the web about 8 - 9 years ago but I have no idea if they are still available. I have found the web page for the manufacturer but the midi board I have no longer seems to be listed. The Board model No is "MIDI 4A". http://www.midi-hardware.com/

A bit of a breef discription but I hope it helps.

Carl

Cool. An opto-isolator or open-collector output would be cheaper, less power and quicker (although the delay with relays is minimal).

[sharksystems]

Ok, I've made some decisions. I'm going to be using a French design, which is frameless. It's a bit simpler, as it uses a stepper motor for drive, and all the digital control logic is done from a PC.

After using my inadequate French skills, I do have a few questions.
The design does not specify certain parts, namely the laser diode, as well as the mirror and phototransistor.

The power supply has a dedicated 5V line for the laser. I was looking at a cheapish 20-50mW green assembly on eBay. I'm looking for something in the range of 30-100mW, green, and inexpensive. If there are any suggestions as to what assembly I should use, that would be great.
Secondly, because I'm not using a galvo, I need a mirror to attach to the stepper motor. What kind of mirror would work? I don't know what to look for. I do know I'm going to need to file down the shaft of the motor.
Finally, the beam pickup is done using phototransistors (9 in series). It does not say the model. Are there any major characteristics to look for?
http://harpelaser.free.fr/
Here's the site. I've done a bit of work so far, in that I've translated all of the control code to English.
Thanks!
Ross

[sharksystems]

A bit of a bump.
I've figured out the phototransistors, mirror and motor. I need help picking out a laser.
I'd like it to run off 5V, I'd like it to be 532nm, and I'd like it to be inexpensive.
Power level can vary, I doubt I'd use anything more powerful than 100mw.
Of course, I know about the eBay specials, but I'm not sure if there are any other inexpensive options.
Thanks!

[Stoney3K]

A bit of a bump.
I've figured out the phototransistors, mirror and motor. I need help picking out a laser.
I'd like it to run off 5V, I'd like it to be 532nm, and I'd like it to be inexpensive.
Power level can vary, I doubt I'd use anything more powerful than 100mw.
Of course, I know about the eBay specials, but I'm not sure if there are any other inexpensive options.
Thanks!

A lab style module will give you more reliability and better beam and power quality than a 'pointer core' type of module. A 100mW of 532nm won't break the bank, around $100-150.

You can also opt for 445nm, an O-like 500mW module will be around $189 and it will give you more power.

[sharksystems]

I was obviously thinking of a lab-style laser, however most of the ones I can find run off 120VAC. To make things a bit neater, I would like something that runs off 5-12v DC. I'm already running two separate 120VAC lines (one is dedicated to the motor, and the other has a 5v line designated for the diode. Could I run the O-Like 100mw module off of 5VDC, and if so, how? If not, are there any options for doing so with another module?
Thanks.

[allthatwhichis]

I have a 100mW CNI that runs off of 5vdc; I don't see any problems with you using the same type of set up. Just find a driver that runs on 5vdc.

[sharksystems]

So I could buy the O-Like 100mw module and drive it with any 5v driver, such as the Aixiz?
Worse comes to worse, I'll run a third 120VAC tap. It wouldn't be the end of the world.

Stoney: that blue laser is tempting, but I think 1W would be a bit much.

[Stoney3K]

Stoney: that blue laser is tempting, but I think 1W would be a bit much.

When it comes to a scanning laser harp: MORE LIGHT IS GOOD. If it is really necessary, you can dial down the power on the blue, but there won't be any situation where you really need to do that.

If you have more laser power (even 300mW instead of 50mW), detection will be much easier. (To be precise: A 300mW laser will give you at least 12dB more useful signal to noise ratio.) A sensing photodiode can't distinguish between 532nm and 445nm, for a detector, they are just as bright where the 445nm would appear more dim for the same power to the human eye.

I know it sounds counterintuitive, but you need all of the power you can squeeze out of this thing. It makes detecting the reflected beam much easier because the circuit needs to be less biased and therefore less sensitive to background lights on stage.

For a framed harp with static beams, feel free to use lower powers though, since the beams will terminate at a fixed point. Therefore you only need to place LDRs or photodiodes at these specific points and make the detection window very narrow.

[Things]

Steven Hobleys harp deign uses an opamp that is very effective at filtering out ambient light. It basically works on the principle that the harp laser will be flickering very quickly, so setting up an opamp to respond to light at high frequency (And not just steady light) helps greatly.

But like Stoney said, you want as much power as you can get. I find the sensor on mine has a bit of trouble picking up the 100mW green I use.