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ArcticMyst Security by Avery

need help with dac/scanner build

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May 13, 2010
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already posted in tutorials section, but figured nobody would see my post


so i got my "modified" 6 ch usb soundcard from midwest lasers and plug it in to find my scanners are still putting out jibberish when i can get it to drive the scanners at all. the test pattern (the only recognizable image i could get it to project) in spaghetti (lfi was totally unresponsive) has blanked areas that travel all around the design? now i find that i need another component called the "correction amp". ok... i kin find 1 of those eventually.

but im going through the steps outlined in 1st post and opening the .wav file provided in the link just to confirm all 6 channels work using headphones to listen for a sound(groovy trak btw, a real toe tapper) : front L and front R ok- white noise, volume of both channels change appropriately when i move volume slider, but rear R and rear L behave unexpectedly as i move the volume slider in media player to max. the sound goes from one channel to the next and fades completely out when the slider reaches max volume.(the only way to get full volume on both channels is to park it precisely in the middle)and the same with the jack for center and bass. is this normal or is there something seriously wrong with the mods or the soundcard itself? the only mod i can see that was done to the soundcard would be some new caps next to the output jacks, where im gathering i would connect the leads to the correction amp.
oh yeah 15kpps scanners if that matters.

HHHEEEELLLLPP! i got 12 days to figure this out.(we got a memorial day gig that , properly executed , will allow us to fire the boss/owner of our outfit) the best tech support i could get from the seller was to "just play with it and figure it out" for myself.
thanx
stvn


been doing my research, got the 2007 revision for variance filled out, my projector should be assembled by the time we get it back. applied for slightly higher power than i expect to actually be running by then , but just how else would yer propose plans for a constantly evolving beast?

ok so i have edited once already as my reading was very productive tonight, witch leads me to better questions, its prolly a good time also to share wot i have to work with at this point: i have a red dpss(?) the beam looks like a tem 30 on the transverse mode chart i found, and another red diode slightly higher wavelength but in a tiny housing and 2 adjustable lens that im guessing are the collimator. after removing the first of the 2 lenses the beam went from nice-n-round to a narrow stripe(found a thread here describing this very thing saying these r bad)beside the fact that the diode seemed to strobe at @40-60 hz and i believe i killed it trying to push the wrong voltage and current through it trying to figure why it was flashing so.(strobing still- so it was not the power and likely crap to start with) but i believe the driver/power supply looks like its all on 1 board and is potentially still useful(can post pix as soon as i learn how).now the dpss(allegedly, i havent taken it apart yet, but ist packaged like the dpss green yag)as i said resembles the traverse mode diagram labeled TEM 30 can this be made nice-n-round like the other with those 2 lenses? and when folks speak of a multimode laser do you mean it can go back and forth between TEM 10, TEM 33, TEM 31 etc. or is it referring to anything other than a single spot TEM 00?
now we also have an argon ion tube putting out @.25 watt(when we replace the power supply, will ask for leads at another time)but im not sure we can incorporate this into an rgb as the "blanking" method would be drastically different?
i have also just purchased an external usb soundcard with 6 channel out that im using to control a set of 15k scanners and blanking.(thanx 2 steve @mid-west) still using freeware, spaghetti,laserboy,lfi player. got a test pattern in spagh. but the areas where the laser is "off" seem to wander around the image??? as of this minute its still giving me fits, but im sure there is another place on the forum where i can beg for someone to walk me through that mess.



thanx so much for all the help,
stvn
 
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well i tried to make my own correction amp and let me say just dont. pay the man and dont think twice.
i broke my first sound card by building my amp wrong so yeah....
http://hacylon.case.edu/ebay/laser_diode/LaserBoy_Correction_Amp.php
As far as what coming out of your sound card i would not know once you get that correction amp you will need a volt meter you cant just judge on noise.
i got very similar scanners most rated at 15k can do 18k at around 8 deg mine can write up to 8 letters before starting to look weird.
and as long as you are only doing one channel then you only need 3 of them to work also make sure you got the right drivers by getting the ones from the sound card tut.
 
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ok (plz try not to laugh)so im able to get the blanking to work. connected output to TTL leads (youre gonna love this) BY LICKING MY FINGER AND HOLDING THE CONNECTIONS TO BOTH LEADS SIMULTANEOUSLY!!!!!
THE (oops) the output measures quite short of the required 5v described in this tutorial and elsewhere. needless to say ive already boxed it up and its going back to the seller FIRST thing monday ... C.O.D.
im sooo cheezed off right now, not because i was sold something unfit for the purpose it was sold for but because i screwed around with it for a week before i found out, so the chances of getting something that will work in time for the all important gig are slim to nil!
DAMMIT!!! "oh just plug it in and itll work" he says. BS!
ok i feel a lil better , thanx for all the helpful info


and speaking of helpful, there a guy on the PL forum wrote a sweet little ild file browser/viewer. theres a couple bugs but still very functional... you know youve wanted something just like this.
 

Benm

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Er.. you tried to supply an input signal using wet fingers, and are surprised the output signal isnt at 5 volts?
 
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yes , the blanking output from the soundcard does not and never has measured 5v. after playing with settings for a couple days with no success, i moved the whole deck to another room to try another computer.

set the whole thing up and instead of twisting the wires from the soundcard to the TTL leads on the laser, just squeezing them together,success! blanking lines gone.

so i twisted the wires, blanking lines return.
what was different? sweaty fingers!

well i cant make sweat appear instantly at will...
...nor am i going to pay for a piece of equipment that requires me to hold a connection and perspire.

had it not been hot and humid while i was working, had i not been squeezing the leads together between thumb and forefinger very hard to make the tentative connection, i may have never figured it out.

ben, are you suggesting that replacing the caps in front of the output jacks on the soundcard is the only mod necessary and no correction amp is needed? or is it that you think my method of investigation was unsound? because it worked!
if you wish i can explain how the moisture caused the blanking lines to disappear, i dont mind and i have the time.
 
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Benm

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ben, are you suggesting that replacing the caps in front of the output jacks on the soundcard is the only mod necessary and no correction amp is needed? or is it that you think my method of investigation was unsound? because it worked!
if you wish i can explain how the moisture caused the blanking lines to disappear, i dont mind and i have the time.

You need to both bypass the capacitors on the soundcard and use a correction amp.

For the X/Y signals you can just use the correction amp to get to an ilda-compatible signal which drives the galvo's, no problem there.

Blanking can be a bit different: There is the ilda specification of +/- 2.5 volt differential, and there is TTL. While both operate at a 5 volt difference between on and off, they are not necessarily compatible. The problem is ground: TTL expects a signal 5 volts above ground, while ilda specifies 2.5 volts above or below ground.

Perhaps this is where your sweaty fingers come in: You might have completed a ground circuit with your fingers without realizing. As the impedances of TTL inputs -can- be very high, its quite feasible for something odd like this to happen.

You could investigate by interconnecting the grounds using a resistor of about 10k. This should be safe if you make a wrong connection, yet conduct at least as well as your hands did.

Personally i get the blanking signal from the soundcard in a different way: I use a comparator and just tune the value such that it switches on and off at the correct point. This only allows TTL modulation, not analog like the ilda standard, but is quite simple to build with just a single opamp.
 

drlava

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If you need this working reliably for a show in a few days, I'd suggest getting a RIYA micro instead of messing with this. The sound card DAC isn't meant to be a plug and play system. Also, you bought it from WHERE? :)
 

Benm

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I think it can be rigged reliably, but you need time and/or equipment to diagnose problems. The most vital tool is a scope, so you can actually see what your signals are doing, and exactly at which point things go wrong.
 
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yeppers , ben,
you not only nailed it but gave a much better explanation than i could have mustered up. kudos! :bowdown: i also thought @ the bridge resister thing but my haed already hurt and didnt feel like doing the math. additionally, it didnt feel completely safe and comfortable (borrowed laser and all):whistle:
btw, i saw the pix of your rgy project, looking spiffy.

and now dr. L,
it was midwest lasers and their"modified usb soundcard" Assembled - Item #: LPSND2 $47.75 link: http://www.midwest-laser.com/html/computer_controlled_laser_show.html
i will DEFINITELY be contacting you when i get closer to a shopping spree. im still compiling a list of things to buy.
however, right now my partner just called me to tell me he broke the mirror off his scanner...AGAIN!!!:cryyy::mad::banghead::cryyy:and superglued the galvo trying to fix it :scowl::banghead: and smoked the scanner amp:banghead::banghead::banghead::banghead: at least we got a half dozen or more pick-offs 1 set of scanners and 2 good dpss greens. thats if by some uncanny miracle they arent DESTROYED in the next 8 days!!!:rolleyes:

not to mention Sam McCaslin of "retro records" has apparently reneged on the agreed fee and offered us half.:tsk: this recent development has me wondering if i would be participating at all in the event. my first instinct is to throw some beams and projections for every OTHER band that hits the stage, so when the guys come off their set asking "what happened ? why no 'wow' effects?" :wtf: simply say sorry, but sam said it just wasnt in the budget. may be a real schnitzel move, but so is making an agreement a month in advance and offering half of the agreed fee 8 or 9 days before the event.

if i show up on setup day its gonna take a stak o' greenbacks to get me to set up, i think this cat has already ruined his chances of getting by with cutting a check. of course payment in advance as well as a signed agreement so if it rains we are as dry as the Gobi desert, or we pack up until we are and keep our fee.
any fool from this neck of the woods knows better than to schedule an outdoor event on memorial day as we always get HEAVY rain to full blown flooding conditions on memorial day weekend.:crackup:
oh, the folly
 
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Benm

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Sorry to hear about all the other problems, but i hope you'll be able to sort the electronics bits from now on.

I'm currently going from prototypes to permanent installation on several pieces of electronics, like compensation amps and drivers. I'll make sure to post the final schematics on LPF once done.

For me the electronics aren't that much of a challenge, but the optical path setups and such are something rather new... lets try to combine some knowledge here to make a good and complete tutorial in the end :)
 
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You can built a better red laser with an aixiz housing and DVD burner diode and you will end up with a lot more power with very little effort or cost.

That diode driver you linked to seems to be only good for laser pointers. It doesn't appear to support any type of modulation. I recommend a die4drive driver or flexmod driver.
 

Benm

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I'd recommend building the drivers yourself, its not all that difficult to do. I have some analog-ready TTL circuits under construction, but gotta draw out the schematics for those. They are fairly easy builds based on CA3140 opamps and BD139 transistors, and they can do analog modulation with 0-2.5 or 0-5v input singals depending on changing resistors. Both ranges obviously also function as TTL modulation, as long as your TTL zero is actually close to 0 volts, which it usually is.
 
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There is nothing wrong with building drivers yourself if you like that sort of thing. But, I prefer to use something like a die4drive that is nice and neat and only about the size of a couple postage stamps.
 

Benm

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I can imagine going for a small form factor driver when building something portable, but with scanners the size of the LD current sources often isn't much of a problem - at least compared to the other components.

Personally i prefer circuits where i know what every single component does, and with opamp based drivers that isn't all that hard to do, as long as you keep the practical limitations of the components in mind.

Also, you get to know the limitations of your hardware. I build drivers that will take 100 kHz modulation without a hitch, so there are no odd things to solve in terms of blanking delays required.
 
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doesnt ttl blanking give up artifax more readily when using 20kpps + scanners, isnt it difficult to get a decent color blend for true color or even 256 color palletts on anything but a static beam? so i would wanna go with analog for projecting more complicated colors of animations at higher speeds, right?
 
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