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Thread: +/- 10v, or +/- 5v which is it?

  1. #1
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    Default +/- 10v, or +/- 5v which is it?

    I've just ordered a parallel port DAC kit from "Norm".

    The circuit diagram shows X+ (and y+) ranging from +10v to -10v. X- and Y- are connected to ground.

    If I understand differential inputs correctly, then if I connect the X-and GND on the galvo amp to X- on the dac (GND) and then connect the X+ to the X+ input on the amp I should be OK.

    Differential inputs on the galvos are like balanced audio line drivers, that is, in the galvo X- is inverted, added to X+ and the result divided by 2 (in my case (-GND + 10v) / 2 = +5v out).

    Do you concur?

    Steve

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    Yea, you are right. As long as your galvo amps have differential inputs then you are ok. Wouldn't work with those 15K scanner amps though.

  3. #3
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    Hmmm...

    You mean the lasershowparts ones? I have some of those, and they do have an input labelled as differential.

    So you're saying that they don't do the /2 on the inputs?

    Steve

  4. #4
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    The 15K ones I got from lasershowparts don't have a differential input. At least I don't think they do. I'll have to double check next time I look at them. They are currently stuffed away in a box unused. Does anyone want to buy them?

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    Quote Originally Posted by carmangary View Post
    The 15K ones I got from lasershowparts don't have a differential input. At least I don't think they do. I'll have to double check next time I look at them. They are currently stuffed away in a box unused. Does anyone want to buy them?

    The 20k's Steve bought do have differential inputs...
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  6. #6
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    Norm's markings are NOt differtial compliant, he uses galvo + to mean a single ended output and galvo - to mean good old circuit ground. His board is single ended!!!!

    So you get a 10-0-10 signal out of each + pin, for amps with a 5-0-5 single ended input that may be too hot, you can always use a potentiometer on the NLS boards output to cool that down. for a modern standard scanner amp with differntail, youd ground one input, tie norms galvo- to ground and tie galvo + to the non grounded input and you should be fine. Although I'd use the potentiometer on each galvo just to be sure.....

    Stev eRoberts

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    It's OK. Just hook is (-) gnd to the - on the scanner input and it should be ok. The scanner amp expects +/- 10v and that's what Norm's DAC outputs. But, it isn't a differential output so it will be subject to noise.

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    Couldn't you just put a resistor in to drop the voltage? Checked the manuals for the 10k set from lasershowparts and it says the scanner imput is -5v to +5v(10vp-p), what does the "p-p" mean?

  9. #9
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    p-p is peak to peak. I bet that there is a pot on norm's dac that you can use to scale back the output voltage to +-5v p-p. If not, you should email him and ask him where to put it. It would be better to put it before the op amps (bias) instead of afterwards I think.

  10. #10
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    Well if it says -5v to +5v(10vp-p) doesn't that mean it can take the 10v signal? I'm busy building a DAC and it takes 5v, but gives a output of 10vp-p, will it work on a scanner set that takes -5v to +5v(10vp-p)?

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