USB Audio DAC mod + LaserBoy Correction Amp

[James Lehman]

Wooo Hooo!

Lookie here!

I can hook it up any way I want to now!

I soldered in the pins on the output of this board, but I should have soldered in the sockets. Oh well. I just tacked the sockets on the bottom of the board, and went from there. This is what I ended up with. At least this way, I have a set of voltage test pins and output sockets!




Future expandable! Why do those gold pins look like fiber optics? Weird!


James.

[allthatwhichis]

When metal cables get cut nice and straight their ends are real shiney, the flash reflected off the ends and made that effect.

So what did that "kit" there cost to make, or would it cost? And if you happened to have a kit, what would it cost assembled?

[James Lehman]

Yeah, I'll make one for you!

The USB sound card is $25 from eBay. I just ordered another one, for no particular reason. (Probably the same fource that motivates "Dad" from those videos!)

The LaserBoy Correction Amp kit is $40. I have 5 unassembled kits right now. There are more for sale from drlava.

I also have a few more D25F connectors with attached ribbons.

How about a solid $70 for parts plus whatever you want to tip me for making it?

I don't really mind at all. I need some more practice and I like to make stuff.

That offer is for you only, because you asked me! I am not into the idea of making hundreds of these things for peanuts!

Those metal ends are individual gold pins pulled from the plastic pin strips. Yes, they are quite shiny and they have flat surfaces.

James.

[James Lehman]

LaserBoy takes it both ways on the ins and the outs!







James.

[seanharrison]

Its all looking very impressive, I can wait to get mine

[allthatwhichis]

LaserBoy takes it both ways on the ins and the outs!





James.

Eeewwww, so BAD!!!

[James Lehman]

Eeewwww, so BAD!!!

Yeah, I know. But I'm not the one who came up with "male or female" to describe electrical connections. I just went with it.

James.

[James Lehman]

USB DAC settings in Windows for Media Player playback of LaserBoy generated waves!



This is AFTER you have already set the standard Windows sound system mixer to max for both "Speaker" and "Wave". You can mute everything else.

Note, the +0, +2, +3 level settings. This is what it takes to make Media Player play the color channels loud enough for the correction amp to get them up to +5VDC. The X, and Y level settings are up to you and your likes. But, don't get crazy. This DAC has digital gain and digital limiting. If you set it right, it looks perfect!

NOTE: These settings seem to work for me with my O-scope and multi-meter. Your mileage may vary.

I arrived at my color channel settings like this: I maxed out the 50K gain pots and set the level in the USB sound card control to show just over 5 VDC on my meter, while I was playing circle.wav. Then, I backed off the 50K gain pot to set it to exactly +5.00 VDC. If you click right on the little + and - signs you can change the levels by 1 dB per click.

Let's see if I can piece together some emails to make sense of all of this.....

In the original drawing by Dean C. Hammonds, there are three separate pieces. In the new USB enabled design, two of these are irrelevant, but I will explain them anyway. The one that has the zener diode and the 1K resister is a -5.1 voltage reference. This is the -5.1 volts that gets mixed via the 10K trim pot into each channel to do the offset voltage correction. The more of the -5.1 volts you mix with the all positive signal, the closer it gets to being centered over zero volts. There is only need of one negative reference voltage. It is the same for all channels. In the new design we went with a negative 5 volt regulator (pretty much the same difference). The other thing in Dean's drawing is a set of caps that get put on the board, close to the chips power inputs. This is to filter off any noise that may be on the power supply. These are not necessary in the new USB design, because they have been replaced with a DC/DC converter and an appropriate compliment of 10uF tantalum capacitors. That leaves the op-amp circuit itself. This has not changed in any way. You need one of these for every channel. the input to this circuit is the other end of the wire you tacked onto the USB sound card; one per channel. The output of this circuit drives your scanners and your color mods. That's the {X, Y, R, G, B, I} stuff. Each signal is in its own channel.



The LaserBoy Correction Amp is single ended. That means there is one-and-only-one ground and one signal lead for each channel. Your scanners are most likely balanced input. Which means that there is a ground, a positive signal input and a negative signal input. This is so you can run very long lines to the scanners and not pick up noise. It is a lot like an XLR professional audio connection. You don't need to worry about that. If you connect the ground from the LaserBoy amp to the ground of your scanner inputs, then also ground the negative inputs on your scanners, you send the LaserBoy X and Y signals to the positive X and Y inputs of the scanners. If you flip it and ground the positive inputs on the scanners and hook the LaserBoy outputs up to the negative scanner inputs, it will flip and mirror the image.

EDIT: This USB sound card is not an inverter, so in combination with The LaserBoy Correction Amp, the signals ARE inverted! See below as to how to compensate.

NOTE: It's fine if you only want to use one green laser. Just go along with the whole 6 channel thing. You only really need three of them. But this system, as it is described will work fine for you now and let you expand your options in the future.

When you play a 6 channel wave file into a sound card that can do 6 channels or more, you actually are using 6 DACs; one per channel. A DAC is a digital to analog converter. The ones that are on a sound card are made for sound! But that's OK. We just need to get around some of the limitations of that. A DAC takes a stream of numbers in the form of signed 16 bit integers and converts those numbers into proportional voltages. It is clocked. That is to say, it converts a number to a voltage at a rate of so-many samples per second. Since a 16 bit signed integer can be either negative or positive, so can the resulting voltage. BUT! There is one issue right here that I need to point out. There is no law that says that a positive number must always result in a positive voltage. With sound, absolute polarity doesn't really matter (or so they say). So let me tell you right now that some DACs invert and some do not! Not to worry. There is a cure for this! As a matter of fact, the LaserBoy Correction Amp is an analog inverter! That means if you feed a positive voltage into the input it will come out as a negative voltage. It sounds a lot more confusing the it really is. Just think of it like this: any number times negative one is just as far away from zero. It's just on the other side. All you need to do to get it back is multiply it by negative one again. Anyway... Back to the six channels. The analog side of a sound card is DC decoupled, so you have to eliminate the output decoupling caps and then you end up with an analog signal that is all positive voltage. So, you take each one of the six separate, all positive and somewhat puny signals from the USB card and put them right into each one of the numbered inputs on the LaserBoy Correction Amp. The LaserBoy Correction Amp does two things to the signal. It allows you to mix a negative voltage with the all positive signal to bring it down to center over the zero volt line and it gives the signal enough gain (multiplies the voltage) to properly drive your laser equipment.

So now we have the week all positive voltages coming from each channel of the USB sound card, going into each of the inputs of the LaserBoy Correction Amp.

Good!

Notice: We have not hooked up ANY laser stuff yet!!!

Now we need to set the trim pots. The first thing you want to do is set your gain to mid scale. You do this by turning the gain pots (50K) counter clockwise, until you hear or feel a little click. That means that you have run off the low end of the pot. (It's OK. They are made for this.) Now, did you get 25 turn pots? If you bought an official LaserBoy Correction Amp Kit you did! OK. Turn each gain pot from all the way out to mid scale by counting up to half the total turns. If you have 25 turn pots go to 12 full clockwise rotations. Once you have all of your gain pots set, you can set the offset pots.

Here is where you need a meter! With the USB sound card plugged into a computer that is on and has the drivers installed... you will be able to measure the idle state of the sound card. In other words, don't play any sounds. Just let it sit there, like it is supposed to be silent; but fully powered up and ready to go. Set your meter to DC volts (milivolts, if possible) and hook the black lead up to the LaserBoy Correction Amp ground. Now check the output of each channel of the LaserBoy Correction Amp. You are trying to get each output corrected to zero volts. You can check the corespongin input to the amp with the volt meter and see that it is about +2.25 or so volts DC. Now when you put the red meter lead on the output of each channel of the correction amp, you can set the offset pot (10K) to compensate. The more negative voltage you mix (clockwise) into the positive offset, the closer it will get to zero volts. You can go past zero into the negative, so adjust with care. Do each channel this way. Set them all to measure as close to zero volts as you can get (hold your breath!).

Now you are ready to set the gain pots. You know for sure what you need on your color channels (+5 VDC max). So lets do these first.

You need to make a wave in LaserBoy of the white circle.

EDIT: To make waves that will display correctly on an inverting system, hit 'u' from the main menu and toggle option 'd' to on (inverted wave output). Now when you save wave information it will be inverted. There is a tag in the header of the wave that indicates this inversion, so you and LaserBoy will know that it is inverted. If you need to make this wave non-inverted, hit 'b' (LaserBoy wave utilities) from the main menu. Then choose option '7' (invert polarity of LaserBoy wave) and type the name of the wave file [Enter]. Note: The effect of playing an inverted wave is the picture will be upside down and backwards and the color mod information will be useless! Color mod information is supposed to be all positive voltage and therefore would be all negitive.

First hit [Tab] to get to system settings and set the still frame duration in seconds (option 'a') to 300. That's 5 minutes of a still, white circle! Now [Esc] back to the main menu, arrow to frame 9, the circle, and hit 'o' (letter o) to output a file. Choose option '0' (zero) to make a 300 second wave of the current frame. Call it circle.

Now navigate to the LaserBoy\waves folder, find circle.wav and play it in Media Player.

You can get a good idea of how to set X and Y by measuring AC volts. You will have a sine wave in Y and a cosine wave in X. Those settings are relative to what size you want your scans to be. All the other channels should be set to +5.00 VDC. They are supposed to be driving analog color channels to full-on (white). When you stop playing circle.wav, these voltages should drop back to zero.

If anyone has any corrections or additions to this information, please feel free to join in!


James.

[dar303]

You are a hero! I can't wait to try this out, I hope my kit and soundcard gets here soon!

[James Lehman]

Thanks!


Please ask a lot of questions. I've worked with this stuff for way too long. I might assume I've already pointed some things out.

James.