DIY LaserBoy Projector

[barold]

barold, Have you compiled the latest version of LaserBoy for Mac OSX? Did I fix the hang-on-exit bug?

James.

It compiled, but still requires a force quit :/

I used 6_19_2008_v2

[James Lehman]

Oh! You just bummed me out.

Oh well. Do you get any specific reason why, that I might do a search on?

Thanks for doing the compile!

BTW How is the sample shifting working for you?

James.

[barold]

I ended up bringing my laser projector to show my brother last weekend. I discovered it was an absolute pain to bring anywhere in its current state. First off, the power supply I am using is a +/-15 V 4.5A cinder block (accurate metaphor for both size and weight). Secondly, I had to take my desktop because of the PCI sound card. I also had to take my monitor because he just has a laptop.

So, I did a couple things to make the whole system a bunch smaller...

1. Laptop power supplies: I used two 15V 4A laptop power supplies to get my +/- 15V for both the scanners and external electronics. They can be found on ebay for about $15 shipped. I didn't notice much of a reduction in quality from the scanners.

2. USB Sound Card: It's all I wanted after I saw drlava's projector. I picked up the same one he had on ebay for $25 shipped. Now I can use my laptop!

Here's a pic of the sound card all hooked up:

RGB moduation signals are strapped off to the side, just in case I need them later

Barold

[James Lehman]

I used two 15V 4A laptop power supplies to get my +/- 15V for both the scanners and external electronics.

So do you have a real, like "third prong" ground anywhere?

James.

[barold]

the laptop power supplies have third prongs, but I wonder if what you are asking has to do with this...

If I try to charge my laptop, my scanners shut off. I can see one of the 2 laptop power supplies I use for +/-15V shut off. I am probably doing something fundamentally stupid, but it goes something like this, and I'm not really sure how I would change it...

The +/- 15V supply "ground" connects to my scanners and my external electronics. The external electronics ground connects to the sound card ground so that I actually get readings from the DAC outputs. The sound card ground comes from the usb ground, which I assume connects to the ground to my laptop. When my laptop gets grounded through the charger, a problem flys all the way back to the +/-15V supply and shuts it off. :/

Barold

[James Lehman]

If you are using 2 plug-in line-lumps together as a differential PS, then you must be connecting the positive of one to the negative of the other; thus making a "new" ground and using the remaining wires as +/- voltage. Right?

Is there continuity from the ground shield of the DC output to the ground on the plug?

I don't think so.

So what is that third prong for anyway?

Hint: Ground Fault Protect, 3 prong outlets are code just about everywhere in the US. So even if you only use the two spades and leave the third prong hangin', the plug still only goes in one way. This shouldn't really matter too much for low current step down transformers encapsulated in plastic lumps, but there are issues to be aware of; like where is the real DC path to Earth? !!!

Ah! And even worse, If I turn-on this brand-new expensive thing, will it become "The-New-Path" to ... POP, FIZZLE, SMOKE ???

I have personally seen some really awful things that happened when someone thought "Hey! Ground is ground! Right?"
(I'm not gonna' say who. )

Meter, Meter, Meter, Meter... ... and then Meter and Meter again!

James.

[barold]

Is there continuity from the ground shield of the DC output to the ground on the plug?

I don't think so.

Right, there is not continuity there on the +/-15V supply. There is only the two 0V and 15V wires

My laptop charger does feed an actual earth ground (from DC plug to thrid prong) as well as 0V and 16V. The earth ground is definitely tied to the chasis of the computer, which is attached to the usb chasis, which is the sound card ground, which eventually hits the 0VDC on the +/-15 V (thus tying one of the +15 to earth, which is probably why it shuts off). Does that sound like the problem?


Barold

[James Lehman]

Does that sound like the problem?

Barold

I think you've got something there!

James.

[barold]

Apparently it was just windoze automatically installing the wrong driver. I've got everything hooked up (and charging) now and it seems to be fine. Weird...

[buffo]

Barold;

Your power supply wiring is fine. If you need a +/- power supply for your scanners, there's nothing wrong with connecting a pair of DC power supplies in series and then calling the center terminal (where the + lead from one PSU meets the negative lead of the other) ground. So long as the outputs of each power supply are completely isolated from earth ground, you can create a new ground point in the DC circuit.

Furthermore, there's no problem bonding that point back to earth ground either. This is *exactly* how I have my scanners powered in my projector. I have a pair of 24 volt power supplies that are connected in series with ground defined in the middle. So long as the circuit is isolated, ground is whatever you decide to call it. (If I had tied the positive end to ground, I would have a negative 48 volt power supply, and if I tied the negative end to ground, I would have a positive 48 volt power supply.)

James;

That third plug on the wall wart is not a "ground fault" plug. The ground plug is simply there to allow a low-resistance return path for current so if the hot wire in an AC appliance touches the case, the current will (hopefully) flow back via the ground prong. (The ground wire is tied into the neutral wire in the breaker panel.) This should draw enough current to trip the circuit breaker before someone gets a shock from touching the case. And if it doesn't trip the breaker, at least it's a low-resistance path that will compete favorably with the (relatively) higher resistance of the human body in the case when someone *is* touching the case and the power is still on - hopefully (but not assuredly) preventing an electrocution.

Ground fault protection, on the other hand, requires extra hardware (normally installed on the circuit breaker or the outlet, but on some high-current-draw devices it can be included in the plug) that senses the current flowing through the both the hot and neutral wires in an AC circuit, and if it detects even a minute difference between the two currents it opens a circuit breaker. It consists of a sensing transformer, a comparator, and a circuit breaker. These devices can sense a difference of a few milliamps between the hot and neutral wires, and they are *very* fast acting. In theory they'll stop the flow of current before any dangerous shock occurs, though you will probably still feel pain for a brief instant.

Adam