DIY LaserBoy Projector

[James Lehman]

I know what a GFP outlet is! My point was that if you do any new house wiring today, that IS up-to-code, you have to use them, at least in places like the bathroom!

My other point was that there are a lot of AC cords on things that have the third prong and don't use it. This is a strong indication that it should only be plugged into an outlet with all three holes present and that it will only go in one way. Of course there is also the fact that sometimes one of the two spades is wider than the other. This has the same effect.

Most home stereo equipment is only two prongs.

My Fender Twin Reverb, all-tube guitar amp has three prongs and a switch to choose which way to ground the chassis. So do other guitar amps. Yes, I have gotten zapped from touching the bass player!

James.

[buffo]

I know what a GFP outlet is! My point was that if you do any new house wiring today, that IS up-to-code, you have to use them, at least in places like the bathroom!

GFI protection for outlets within 6 ft of a water source have been required by the US residential wiring code for the last 20 years. They're not new by any means. (And yes, I have done both residential and commercial wiring.) More to the point, GFI protection is irrelevant to Barold's PSU setup.

My other point was that there are a lot of AC cords on things that have the third prong and don't use it. This is a strong indication that it should only be plugged into an outlet with all three holes present and that it will only go in one way. Of course there is also the fact that sometimes one of the two spades is wider than the other. This has the same effect.

No, it doesn't have the same effect. One spade is wider than the other because it prevents you from swapping the hot and neutral. This is a different standard that is completely separate from the GFI requirements. If you swap the hot and neutral, you can *still* get shocked by a faulty appliance if you don't have the GFI outlet. On the other hand, even if the hot and neutral are reversed, the GFI will still protect you because it senses the *difference* between the two currents.

As for the ground prong; just because it's included on a lot of devices doesn't mean that it it's a "strong indication" that it should only be plugged into a grounded outlet. There are a number of devices that gain little if any benefit from the ground prong. A wall-wart transformer with an isolated secondary and an all-plastic case is an excellent example. What is that ground plug protecting you from? Where is it connected inside the device? There are no metal parts on the case that you can physically touch, so you *can't* get shocked. Furthermore, there is no connection from ground to the DC output. The ground prong is useless in that application.

So why do they have the prong? Standardization, mostly. And the fact that a third prong helps to hold the thing steady in the outlet. Also, to be in compliance with the electrical safety standards for appliances, you either have to include a ground plug *or* you have to double-insulate the internals. In most cases adding the ground prong is easier and cheaper. (Even if it's not actually protecting you from anything.) Bottom line: There are a large number of completely enclosed, all plastic devices that include the ground prong on the power cord even though it's not really needed.

Most home stereo equipment is only two prongs.

Yes, for a completely separate reason: elimination of ground loops. You'll notice that most home stereo equipment has a metal chassis. Thus there is a significant risk that you could be shocked when touching the case if a hot wire happened to work loose and came in contact with the case. Yet there's no ground plug...

It's a textbook example of a situation where a ground plug would be ideal. But the risk of creating a ground loop (and the annoying 60 cycle hum that comes with it) is too great, so most stereo manufacturers decide to double-insulate instead. Slightly more work, yes, but it ensures that you won't have any hum...

My Fender Twin Reverb, all-tube guitar amp has three prongs and a switch to choose which way to ground the chassis. So do other guitar amps. Yes, I have gotten zapped from touching the bass player!

If you got shocked touching the base player, and it wasn't a static shock, then something is *seriously* wrong with either the wiring in your amp or in his. Even if both cases (or even just one) were ungrounded, there shouldn't have been any way for current to flow between them unless you had a wiring fault that made one of the cases hot.

Was it a low-voltage tingle, or a "holy shit!" 110 V shock? If it was low voltage it's not nearly so bad and could have been caused be a number of things (maybe induced voltage in your case from the filament transformer), but if it was a big shock then you've got 110 volts on the case of your amp (or his), and that's *very* bad.

Adam

[James Lehman]

If you got shocked touching the base player...
Was it a low-voltage tingle, or a "holy shit!" 110 V shock?
Adam

It was of the "holy shit!" variety. It was in the basement of a house I used to own that was built in 1904. There was a very interesting mix of styles of electrical house wiring; some tube and knob, 2 wire and some three wire Romax. I think _that_ is exactly why that switch for chassis ground is there!

I think we agree on everything here. I'm just going from personal observation and you're going from training and experience. I don't think anything I wrote is so wrong that it's dangerous. Read it again. I pose more questions, really.

James.

[buffo]

It was of the "holy shit!" variety. It was in the basement of a house I used to own that was built in 1904. There was a very interesting mix of styles of electrical house wiring; some tube and knob, 2 wire and some three wire Romax. I think _that_ is exactly why that switch for chassis ground is there!

Ahhh... Starting to make more sense now. My guess is that one of the outlets in that house was wired backwards (hot and neutral reversed). It's conceivable that the neutral wire was connected to the chassis ground, and if one outlet was wired backwards, that would make the chassis hot. Pity you can't go back there with an outlet tester and check the wiring. Would be a good thing for the current residents to know about.

I think we agree on everything here. I'm just going from personal observation and you're going from training and experience. I don't think anything I wrote is so wrong that it's dangerous.

I'm not trying to bust your balls. Just fleshing out the post with more info. If I sound like I'm being an ass, I apologize. It's been a busy week (20 hrs OT, and lots of nightshift too) and my "stop being a pedantic dickhead when you post" filter probably isn't working as well as it should. I get that way sometimes... Sorry!

Adam

[James Lehman]

"stop being a pedantic dickhead when you post" filter probably isn't working as well as it should. I get that way sometimes... Sorry!

Adam

Oh Man! You and me both! I thought I was the only "know-it-all" here on the PL. I rely on the fact that others will correct me if I am totally off and in the danger zone. That's the beautiful thing about a public forum like this.

No offense taken. I appriciate the information fill-in.

Take care. James.

[barold]

Thanks for all the grounding information from both of you. I'm glad to know that I am not doing anything stupid

Turns out my external electronics were mostly the problem, they were getting a little unhappy from being thrown around. There were a couple loose connections and my zener diode died. I fixed it up and put it into a project box for safe keeping. That also made the whole thing look a lot nicer, and more portable. My projector and everything I need to control it now fit in my backpack!

Barold

[buffo]

Hey Barold;

Any chance of you making the trip to SELEM this summer? I know it would be a long trip (14 hours or so), but you'd be able to show us your home-built projector and also meet the guy (James) that wrote the software you're using! Plus it's going to be a *great* weekend. Plenty of lasers, lots of geeks, and one hell of a dinner party Friday evening to kick it all off.

Give it some thought anyway... Sure would be cool to see you there.

Adam

[allthatwhichis]

Yea, you have already made your projector portable. All the hard work is over... except the drive.

[barold]

I would really like to head to SELEM. I might be able to make it. I've got friends in DC that I could visit to split the drive in half. We'll see, at this point I really cant commit to it :/

Barold

[James Lehman]

Just as soon as I get my current "job" project is out of the way, I want to really dig into LaserBoy and not come out till it's all working!

It's going to take some time. I need to get my old pure Linux system going again to be able to generate correctly shifted waves.

I will also be doing some REAL LASER testing this time.

And I want to get drlava's stuff going and see Laseroids!

James.