Laser Projector (Red, Green, Purple) "Laser 3D Party Light" from Spencer's

[james]

In the interest of history, I starting working with laser display in late 2003.

The main reason I wrote LB was exactly because laser software was very expensive and didn't do many of the things I wanted to do as an artist.

I am well aware that there are other applications out there that used a DC modified sound device.

I am also aware that there were no inexpensive sound devices that could do 8 channels (Dolby 7.1) until VIA and C-Media introduced some PCI sound cards about that same time.

I found drivers for specific chips in the Linux Kernel.

It would be a few more years until C-Media came out with the CM 6206 chip that an inexpensive USB 8 channel device would be available.

I have worked with several professional laserists who have used LB to convert ADAT transcriptions to ILDA files.

All anyone has to do is contact me and ask.

I tend to be very helpful and I am willing to advance the development of LB to incorporate new features.

If you don't know how to do something and you are not willing to ask, that's on you.

James.

[mixedgas]

The correction amp is a level shifter and amplifier. The sound card chip on a 20$ USB sound device is a monolithic device that handles everything, the USB interface, signal processing, levels, ant-aliasing filter and the analog output.
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Typically external sound devices run off a single supply of 5 volts from the USB cable with no negative voltage available. Because of this design driven lack of current sourcing, the output is typically biased to one half of the chips internal voltage as it can only sink current. In other words the DAC output is single ended and can only go positive, it cannot go below ground level. This shows up as a DC offset on the output. Audio signals from the card thus swing above and below a DC voltage. But the signal cannot pass below zero and become negative. As human hearing is not so great below 20 Hz, a capacitor is mounted on each channel to block the DC and act as a high pass filter to the AC audio signal.
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The AC coupled audio sounds fine, but a galvo would wander around as the audio changes without a DC return to the source. So the correction amp synthesizes a signal that is grounded and can swing below zero.
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The modification to the card removes the "blocking" capacitor so the card passes DC. The "correction" amp then acts as level shifter to remove the fixed 1.2 volt DC offset and create a signal that swings above and zero, as the Galvo amp wants to see minus five to plus five volts for full deflection. As the audio is typically 2.4 V peak to peak or something similar, the "correction" amp also has a gain of about 2. It also buffers the signal so the cables and galvo amp do not load down the DAC chip.
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So its done with opamps, resistors and a few potentiometers. If you don't have a source of +/- 12 volts handy, the correction board also has a tiny power supply module on it that takes 5V from the USB and generates the needed voltages for the op-amps. You have +/- 12V in the Spencer's projector, so it can power the correction amp.
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This is a link to Dennis Draheim's site has a very good drawing of the usual inverting summer correction amp. The common TL082 or TL084 needs split supplies of +/- 12V to work well. The site credits Dean Hammonds for the basic design:
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http://wiki.milwaukeemakerspace.org/...rojects/layzor
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The Spencer's projector has a single ended amp input for both X and Y, so you do not need the differential ILDA standard signal with three wires per amp. Just +/- 5V for X deflection and +/- 5V for Y deflection.
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If your going to start from scratch, its better to just get a dual or quad SPI based DAC chip and skip the sound card.
About 5 years (er make that 10 years) ago I helped Steve Hobley with the TLV5618 and Arduino when he asked a similar question. Link to his page:
http://www.stephenhobley.com/build/lh_arduino.html
Its the same DAC chip Elm Chan uses, and is known to have the speed to 30K pps, but yet have a low cost. You'd need one of X and two more for color.

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Steve

[colouredmirrorball]

... Processing graphics library ...

On it. The biggest hurdle is real time DAC output. All DAC APIs or SDKs or APKs or whatever the term is come with a .dll file which requires native (Windows-specific) C++ code. I have not succeeded in getting JNA or JNI work and my C++ attempts always result in a headache. That's why I'm so optimistic about IDN (Ilda Digital Network): it does not require OS-specific drivers. My hope is to get it to work with Processing in the near future. If each DAC producent or maybe even the community provides a bridge between IDN and the DAC then nobody needs to suffer the eleventy billion different APKs out there.
I can, however, output Ilda files. (If I manage to un-break the library after some recent "fixes", that is :P)

[james]

If you build a correction amp from Dean Hammonds' original design and parts values and try to pair that with the CM 6206 USB sound device, it will not work.

The CM 6206 has a DC offset of only about +1.2VDC.

Dean's original design was for sound devices that have a DC offset of around +2.5VDC.

It uses a 5.1V zener diode to create the negative voltage that gets added to each channel of DAC output.

It's too much. There simply isn't any way to adjust the offset trim pots to compensate.

There is also a design out there with a fixed -5V regulator. Same problem.

That's the number one reason I redesigned the correction amp to use a variable negative voltage regulator and different parts values for much finer control over the offset trim and to provide more gain needed for sound devices that have a lower DC offset and less peak to peak voltage.

My design works with any DC modifiable sound device that needs a correction amp.

James.

[JohnYayas]

I've got some of the RIYA Lites left. $100 + shipping is all you need to move on in life.

[james]

" 15 characters"

I see Laser Wizardry has retracted his inaccurate comments.

James.

[swamidog]

no. laser wizardry deleted his posts globally. it had nothing to do with laserboy.

I see Laser Wizardry has retracted his inaccurate comments.

James.

[james]

no. laser wizardry deleted his posts globally. it had nothing to do with laserboy.

Oh! Well, I don't know him. But I know of him. I hope he's OK.

[czyzczyz]

So I finally went and purchased the projector and the blue laser module. Once I get that all up and running I'll play with making shows and putting 'em on the SD card and then I'll start to think about a DAC and analog drivers.

At that point, I'll probably want to find a way generate realtime graphics and text via programming; Displaying tweets, maybe lissajous and other graphics dynamically generated via processing or nodebox (if I can get it to output svg sequences and hack together some svg to ILDA conversion), currently playing song lyrics, etc. I'm not sure the best way to go about this, but the Laserboy amp combined with a cheap C-Media 6206-based sound board seems (here's one for $14) like it'd meet my open-source hackable needs as well as be of sufficiently low cost that it won't kill me if I later want to use an alternate DAC (EtherDream looks interesting). And it'd be fun to play with lasermame even though I know these galvos around going to be fast enough to really display vector games more complex than asteroids.

I'm looking forward to spending some of my paltry free time looking at colored lines on the wall and trying to bend them to my will.

[hakzaw1]

BTW & FYI
you can buy the Spensers new version-already has 450nm blue for a little more.
any w/ 405 are surely old stock. but still no ilda----


time spent reinventing the wheel would be better spent learning QS or LX and buying a nice 800mW pure diode PJ-strickly for home use- (not 100% compliant)

hak's dos centavos solo