Earthing Norms DAC...

[rog8811]

I have decided to connect Norm's Dac to my CDS 20k scanner set.

The +15v / Ground / -15v supply from the driver board is a direct connection (once my headers arrive) so input to tha DAC looks fine.

I get into problems when connecting the output from the DAC to the X & Y drivers, the sockets on the leads are 3 pin, centre pin is earth, the output from the DAC are 2 pin, +/-15v (I can cut the centre pin from the header to solder it to the DAC PCB so the socket will fit).

Do I need to somehow get the ground from the DAC to the driver board?

A bit of additional info....The main power supply puts out +/-24v, this goes to the driver board where it is regulated to +/-15v, then goes to the existing DAC (insert Norm's DAC here).

I hope I explained that well enough........ Help please?
Regards rog8811

[carmangary]

First off, Norm's DAC is supposed to output +/-10v so make sure you have that right.

I think the following is correct but double check with someone first:

Norm doesn't use differential outputs so I assume the 3 pins are X, gnd, and Y. Does the 20k set have differential inputs? If not, you need to lower the DAC output to +/-5v. Otherwise, you would connect the DAC X to the + input on the X board. Connect DAC Y to the + on the Y board. Connect DAC gnd to both boards - and gnd connections.

[rog8811]

First off, Norm's DAC is supposed to output +/-10v so make sure you have that right.

Ok the +/-15v on the X Y output was an assumption on my part, looking at the silk screen it just says X+/X- & Y+/Y-, no voltage stated.

Does the 20k set have differential inputs?

Yes, in fact it has +/-,gnd and 2 feedback wires to each galvo (5 wire).

It is probably me but I am having trouble with the explanation of what I have to do......Drawing coming up


I have just shown the main points on the drawing, the red box is where I need to connect, sorry but I still don't understand how (Mech engineer not Electronics engineer ) I will check the voltage out from the Driver board and confirm with Norm the voltage out from the DAC....

The last thing I want to do is to blow something up......

Regards rog8811

[carmangary]

I can't tell for sure without schematics or tech sheets. I'd only be guessing. If you can send me Norm's schematic and the manual for the galvos I can tell you what to do. But, it's just to risky for me to guess and have you break something.

[tocket]

Since Norm's DAC doesn't have a differential output (X- and Y- are just Gnd), what you need to do is to connect either X- or Y- from the DAC (just one of them is sufficient) to X-, Y- and both Gnd on the galvo driver.

To make it extra clear (since you are a mech engineer [I'm a chem engineer myself] ):

DAC       Galvo driver
X+         X+
Y+         Y+
X-         X-,Y-,Gnd (both of them)

Now, looking at how you drew the schematic it seems the two circuits share a common ground, so it might not be necessary to tie X-/Y- to Gnd, but better safe than sorry.

One last thing. Keep in mind that the input polarities on the DAC circuit board were misprinted. You need to connect them in the reverse order, that is, +15V is actually -15V and -15V is +15V. Gnd is Gnd though.

[rog8811]

Thanks, I see what I need to do now, I take it I don't need to reduce the voltage to +/-5v as the outputs to the galvo's are differential?

It seems anti-intuitive that so many lines should be linked

Keep in mind that the input polarities on the DAC circuit board were misprinted. You need to connect them in the reverse order, that is, +15V is actually -15V and -15V is +15V. Gnd is Gnd though.

It is something I picked up on but thanks for the reminder.

Regards rog8811

[tocket]

I didn't bother checking the exact levels on the output of the DAC, just a quick sanity check to see if they were reasonable (within +/- 10V). Then I just hooked them up to the driver and adjusted the size pot on them. My galvo driver also has differential inputs, so it should work just as well for you.

I don't know if it's just my galvo driver being weird, but I found that the x-axis was inverted using Norm's DAC. If you get the same problem you can connect X+ on the DAC to X- on the galvo driver and tie X+ of the driver to Gnd instead. That will invert the x-axis.

[rog8811]

I have at last received all the connectors I ordered and have
connected Norm's DAC.

On my computer I installed userport drive and have selected the address from the LPT port drop down in Popelscan.

I dont have a copy of the ILDA test frame so I set the lissajous pattern
running and enabled the output.

With a bit of adjustment the "X" galvo started to move. I tried adjusting the "Y" galvo with no result.

Just to see where the problem was I swapped "X" for "Y" on the DAC and sure enough, when adjusted, the "Y" galvo was moving.

So it looks like I am only getting one signal out of the DAC.

I have connected the X- and ground together and the Y- and gound together but have not linked the two sets of earths together as they are common on the DAC.

Any help to troubleshoot would be greatly appreciated.

Regards Roger

[tocket]

It seems to be a problem with the DAC then. I would recheck my soldering to make sure there are no jumpers or legs that I forgot to solder. Also check if you've completely missed any components or turned them the wrong way around. If you don't find anything then you need to troubleshoot the board which is a bit tricky without an oscilloscope (you could use your laser projector as one though, even with just one channel working).

You can also contact Norm himself. He has answered all my questions quickly in the past and is very helpful. This is probably your best bet. He did design the circuit after all.

[rog8811]

You can also contact Norm himself. He has answered all my questions quickly in the past and is very helpful. This is probably your best bet. He did design the circuit after all

He has given me a contact in Holland who, it seems, is a bit of a whizz with this DAC. I have e-mailed him more or less what is in my last post, I will see what he says. I am wondering whether to swap the DAC chips to see if that swaps the problem to the other channel.

......I have another thought, when I was trying to set up the DAC that came with the kit I could sometimes get the "X" gavo to run......could it be comunication problem from the computer????

Regards rog8811