LED wiring in line-

[mliptack]

Thanks for the info on the mosfet, is there a particular model I should be looking for? Also isn't the current available to the shutter channel limited by the power supply. I'm sure the DAC limits it, but in the case of the FB3 where you have an external 5v source powering it.... well I guess we wouldn't know without diving into the internal workings of the DAC itself.

The LED idea, isn't REALLY pointless, while I do, and have, see your point. Like I said above

a strobe that will likely blink way too fast to notice (since 30hz is not noticeable)

It is more there for the actual indication that the lasers are Lasing. Of course a small amount of power (like when the lasers are outputting really dim) wont necessarily make the LED emit light... but IDK it was the idea of it that I want to test more than anything.

[buffo]

Thanks for the info on the mosfet, is there a particular model I should be looking for?

Any cheap mosfet that can pass enough current to run your actuator will be fine. (Most of them are rated for at least 200 ma, which is more than enough.) Needs to be N-channel though. That's the only other requirement. Expect to pay around 50 cents for it. (Digikey has them by the truckload, but you can by individuals for 48 cents...)

Also isn't the current available to the shutter channel limited by the power supply.

No. It's limited by the TTL driver (in the DAC) for the shutter output. Depending on the chip used, this could be 8-10 ma, or as much as 25 ma. But it's not designed to drive anything. DAC's are voltage output devices, not current drivers. (And a solenoid is going to pull a lot more than 25 ma.)

The LED idea, isn't REALLY pointless, <snip>
It is more there for the actual indication that the lasers are Lasing.

The shutter signal will give you the same thing, but whatever. I see what you're trying to do. I just think that once you get it assembled, you'll see this pathetically dim flashing LED and wonder why you ever wanted it...

Adam

[mliptack]

Yeah I am sure you're right about the LED... but then I can convince myself to rebuild because I dont like it... and buy all new lasers then...

[DZ]

Your emission indicator should be tied to the shutter. Why? Because any time the shutter is open, you could potentially have output.

I just wanted to clarify that this would not be kosher with the CDRH. For one, the emission indicator needs to be on when the lasers are powered, blanked or not. Another thing, the emission indicator needs to be on a few seconds before any actual emission (built in safety delay). If you allow an external device (QM2K) to control the emission indicator via the shutter line, then the delay would be on the order of a few micro seconds, which would be inadequate.

Now, if you're using something like a GM-20, which has a separate power input apart from the switching signal, then you're OK.

Adam, can you elaborate? Maybe there is a characteristic of the GM-20 that I'm not familiar with.

[mliptack]

SO in this situation how would you have a laser emission LED that always turns on 2 seconds before?!?

Or are you saying a 'Laser Power-On' LED would be adequate then?

-Max

[DZ]

SO in this situation how would you have a laser emission LED that always turns on 2 seconds before?!?

Or are you saying a 'Laser Power-On' LED would be adequate then?

Well, if your lasers turn on as soon as you power on the projector, then the emission indicator should come on first. Alot of the solid state lasers that I've seen have a built in delay already and I suspect this is fine. If there is no delay though, you will need to add a delay circuit to the laser, which is quite easy with a simple 555 timer circuit. In my projector, none of my lasers are powered until the interlock loop is complete. So even when powered there is no emission indicator until the loop is complete, then it comes on when the power supply that powers the lasers turns on, then there is a few seconds before they are able to output. Kinda similar to a gas laser setup, when you plug in the power supply and the interlock loop is complete, the emission indicator turns on, then after about 30 seconds the tube ionizes.

[buffo]

the emission indicator needs to be on when the lasers are powered, blanked or not.

Actually, that's not true David... The standard only requires indication when the laser radiation is "accessible". So if the shutter is closed, the radiation is not accessible, and you don't need an emmision indicator.

However, you are still correct - using the shutter signal as an emmision indicator is not sufficient, because of the delay requirement you mentioned:

Another thing, the emission indicator needs to be on a few seconds before any actual emission (built in safety delay). If you allow an external device (QM2K) to control the emission indicator via the shutter line, then the delay would be on the order of a few micro seconds, which would be inadequate.

I had forgotten about this requirement, but after a quick check of the CDRH site, it came back to me. Here is the relevent section of 21 CFR 1040.10: (Underlining added by me)

(5) Laser radiation emission indicator. (i) Each laser system classified as a Class II or IIIa laser product shall incorporate an emission indicator that provides a visible or audible signal during emission of accessible laser radiation in excess of the accessible emission limits of Class I.

(ii) Each laser system classified as a Class IIIb or IV laser product shall incorporate an emission indicator which provides a visible or audible signal during emission of accessible laser radiation in excess of the accessible emission limits of Class I, and sufficiently prior to emission of such radiation to allow appropriate action to avoid exposure to the laser radiation.

It's the (ii) part that we're concerned with. Since a projector is going to be at least classIIIb, the (ii) part applies, and that's where they state that you need the time delay. Interestingly enough, there is no specified time... It just needs to be long enough to "allow appropriate action to avoid exposure". But you do need a delay, and the shutter line isn't going to give you one. Good catch!

However, if the shutter is closed, you can have the laser running at full power and you do not need an emmision indicator. Still, for practical reasons it makes sense to run the emission LED off your laser power circuit. That way your power-on delay for each laser gives you the time to "allow appropriate action to avoid exposure"...

Only real problem is that you will have times when the emmission indicator is lit and you don't have any accessible laser radiation. Not sure if there's anything wrong with that, but my guess is that it's OK...

Re: the GM-20 comment. I was actually thinking of the GM-20 replacement actuators that Fluff was selling (I've got 3 on order myself), but I couldn't remember the name of those things... (Which is why I said "something like a GM-20".) The ones Fluff has for sale have a power input, a signal input, and a ground conenction. So they don't need any significant current from the controller to actuate. I assumed that GM-20's had the same 3 connections, but apparently they don't. That's unfortunate, because I'm not sure that all controllers can provide enough current to directly actuate a GM-20. How do you actuate the GM-20 shutter in your projector?

Adam

PS: As a result of this thread, it's clear that I need to make a slight wiring change to my projector! (oops!) Good thing I haven't applied for the varience yet...

[DZ]

Actually, that's not true David... The standard only requires indication when the laser radiation is "accessible". So if the shutter is closed, the radiation is not accessible, and you don't need an emmision indicator.

I disagree Adam, I do believe this is one part of the CDRH guidelines that needs to be updated a bit since it seems to be written more for ion's that are on all the time. It would also be helpful if they would consolidate much of the information on thier web site. As you can see, its basically the same info, somewhat re-worded and with the addition of actual time window needed for the delay, though no clear way to calculate a precise delay needed.

The Compliance Guide for Laser Products says and I quote:

"An emission indicator (1040.10(f)(5)) is required on Class II, IIIa, IIIb, and IV laser systems. The indicator can be visible or audible. On Class IIIb and IV laser systems the indication must precede emission by a lenght of time sufficient to allow users and other in the area to recognize that the product has been energized so they can avoid exposure. Depending on the action required and the level of laser radiation involved, the time needed can vary considerably; typical values are in the range of 2 to 20 seconds."

Going from the above quote from the Compliance Guide, anytime the laser/lasers are energized, there needs to be an emission indicator on. The way I read that, is right before I energize my solid state or gas lasers, an emission indicator needs to be lit, blanked or not. It seems rather rediculous, however, thinking about it a bit, I suspect that when writting the compliance guide, the idea is that if you power a laser and for some reason you have a blanked line floating, and a shutter that has failed in such a way that it is open(which also would be a violation, a failed shutter is suppose to only be able to fail to the closed position), then you will already have had a visible or audible warning that emission is imminent.

Re: the GM-20 comment. I was actually thinking of the GM-20 replacement actuators that Fluff was selling (I've got 3 on order myself), but I couldn't remember the name of those things... (Which is why I said "something like a GM-20".) The ones Fluff has for sale have a power input, a signal input, and a ground conenction. So they don't need any significant current from the controller to actuate. I assumed that GM-20's had the same 3 connections, but apparently they don't. That's unfortunate, because I'm not sure that all controllers can provide enough current to directly actuate a GM-20. How do you actuate the GM-20 shutter in your projector?

Oh ok! I have used several GM-20's in the past and knew nothing about what you were speaking of. The GM-20 is basically alot like the G-124, just a scanner with no feedback, so you are just wiring to a coil of wire. Mine is driven from 5VDC through a relay driven by a 2n2222 which is driven from pangolin. The actuators that Fluff is selling, look alot like the STP-8's, which, as I'm sure you know, are not suitable as a shutter, however are great on a beam table.

[buffo]

I disagree Adam, I do believe this is one part of the CDRH guidelines that needs to be updated a bit since it seems to be written more for ion's that are on all the time.

Well, I'm sure you realize that the compliance guide is not the same thing as the actual regulation. The passage that I quoted above was direct from 21 CFR 1040.10. Also, the compliance guide was last updated back in 1989, whereas the actual regulation was just updated in April of last year. (Many of the changes were part of the whole "least burdensome approach" thing they've been implementing lately.)

I think the compliance guide was written with laser projectors in mind, but it doesn't try to cover every possible case, where as the standard does. (Or at least, tries to.) And I do agree that it would be highly impractical to design a laser show projector that would delay opening the shutter for 3 or 4 seconds while the emission light lit up. (That wouldn't allow for proper show timing...) So that's a good reason right there to leave it out of the compliance guide. (No one would ever build a projector that way...)

I also agree that you still need a delay between the time that the emission light comes on and the time that laser radiation becomes accessible. (On the order of 2 to 20 seconds) The standard is pretty clear on that fact.

But assuming that you built such a delay into the shutter (however impractical it might be), I feel you would still be 100% in compliance with the standard, because you would not have "accessible" radiation so long as the shutter was closed.

Remember that you don't need an emission indicator on a class IIIb or class IV laser if the beam can't get out of the housing. (That is also addressed in the standard; it's how DVD burners can get away with having a 100 mw visible diode inside them without any warning labels.) If the laser radiation isn't accessible, there are a lot of the regulations in the standard that don't apply.

You know, this might be an amusing topic to bring up with a CDRH rep. I've been meaning to call them anyway (about other matters), so maybe I'll ask them about it just for grins and giggles.

The actuators that Fluff is selling, look alot like the STP-8's, which, as I'm sure you know, are not suitable as a shutter, however are great on a beam table.

If you add a spring return to them, they'll work just fine as a shutter (which is what I plan to do). But yeah, in their stock configuration they rely on gravity to return to center, which is decidedly not kosher as far as the CDRH is concerned. My original shutter was a spring-loaded solenoid, which worked OK I guess. I thought about using a Ledex spring-loaded rotary solenoid, but they aren't rated for continuous service, and I didn't feel like messing around with a custom circuit to lower the "hold in" voltage once it actuated. (Plus they're loud as hell when they pull in!)

I suppose a GM-20 is the ideal solution, but they're nearly $100 each... That's why I was so keen on those actuators Fluff had. (Eh, we'll see how well they work when I get my hands on them.)

Adam

[mliptack]

Well, I'm sure you realize that the compliance guide is not the same thing as the actual regulation. The passage that I quoted above was direct from 21 CFR 1040.10. Also, the compliance guide was last updated back in 1989, whereas the actual regulation was just updated in April of last year. (Many of the changes were part of the whole "least burdensome approach" thing they've been implementing lately.)

I think the compliance guide was written with laser projectors in mind, but it doesn't try to cover every possible case, where as the standard does. (Or at least, tries to.) And I do agree that it would be highly impractical to design a laser show projector that would delay opening the shutter for 3 or 4 seconds while the emission light lit up. (That wouldn't allow for proper show timing...) So that's a good reason right there to leave it out of the compliance guide. (No one would ever build a projector that way...)

As far as show timing is concerned in that situation you would have to add a 3-4 second delay in the show itself, maybe timing your audio track a few seconds back...

This is definitely a topic I would love to do more research on, and will do, time permitting.... thus far, this conversation is very interesting and thought provoking to say the least.

Remember that you don't need an emission indicator on a class IIIb or class IV laser if the beam can't get out of the housing. (That is also addressed in the standard; it's how DVD burners can get away with having a 100 mw visible diode inside them without any warning labels.) If the laser radiation isn't accessible, there are a lot of the regulations in the standard that don't apply.

In this situation, I think the worst case scenario takes hold, DVD burners would have to be unscrewed and opened... I think that would give anyone considerable warning that it is happening...

However, in the case of a laser show, if something prohibits the movement of the shutter, laser light could be emitted... Like say in an outdoor event a squirrel gets into your projector (hey it could happen) and dies on the shutter in the open position... Let me know your thoughts, I am obviously not as educated on this topic as either one of you are...

If you add a spring return to them, they'll work just fine as a shutter (which is what I plan to do). But yeah, in their stock configuration they rely on gravity to return to center, which is decidedly not kosher as far as the CDRH is concerned. My original shutter was a spring-loaded solenoid, which worked OK I guess.

Adam let me know your results with this and document the process if you wouldn't mind. I also purchased 2 of these units, one for a shutter and one for a diffraction grating.

I was under the impression the STP-8 was appropriate as a shutter, but I am glad you noted otherwise. DZ you said STP-8 I thought there was an x at the end... maybe its a different model?

Is the spring loaded issue the only one concerning the 'not safe for CDRH requirements' or are there other reasons it would be considered not safe?

Of course you can get into the auto beam shutters that Edmunds or others sell but then we're talking lots of cash...

Anyway I look forward to hearing the responses!

-Max