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Thread: Howto: simple Differential Amp + TTL ?

  1. #21
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    , tl07x needs +/- 7V to turn on and swing that high.. its not a rail to rail opamp. according to the data sheet I just looked at. 9V batteries would be a good start, plus a pair of 7805/7905 for the offset pot. 7805 and 7905 need at least 7 volts and -7v to turn on...

    May I suggest "Art of Electronics" by Horrowitz and Hill . Google books has it as a limited preview. Also "Opamps" by David Terrell

    Rules of the opamp:

    The inputs will always try to drive the output so that there is 0 volts between them.
    The inputs in theory will have a impedance of infinity and almost no current will ever flow in them
    The output in theory will have almost no impedance and is a current source.
    Unless its a rail to rail opamp designed for low voltages, opamps need 2-3 volts higher rails then the desired output voltage.
    Inputs should not exceed their common mode range, nor be greater then the rails, see data sheet
    Inverting amplifiers cannot have gains less then one



    Steve
    Last edited by mixedgas; 02-05-2010 at 18:56.
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  2. #22
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    Quote Originally Posted by mixedgas View Post
    Unless its a rail to rail opamp designed for low voltages, opamps need 2-3 volts higher rails then the desired output voltage.
    Steve
    @Xer0: That's what I was referring to when I described powering the op-amps with the +/-12V converter. You just get the 5V to power that from USB.
    Last edited by ElektroFreak; 02-05-2010 at 19:35.

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    Ok, so whats a good R2R opa i could use for?
    The only one i know, [IMG]file:///C:/DOKUME%7E1/TC/LOKALE%7E1/Temp/moz-screenshot.png[/IMG]TS912, istn avaiable in Multisim.

    My idea was to make -5V with a Max768 boost inverter. Is this possbible or cant i use the common Gnd?

    Meh... the ±12V thing creeps me. in need some kind of security that under no circumstances a higher voltage than allowed will pass the x/y output, othwerwiese the galvos go "clonk", 5.1 z diode or so...

  4. #24
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    Quote Originally Posted by Xer0 View Post
    Ok, so whats a good R2R opa i could use for?
    The only one i know, [IMG]file:///C:/DOKUME%7E1/TC/LOKALE%7E1/Temp/moz-screenshot.png[/IMG]TS912, istn avaiable in Multisim.

    My idea was to make -5V with a Max768 boost inverter. Is this possbible or cant i use the common Gnd?

    Meh... the ±12V thing creeps me. in need some kind of security that under no circumstances a higher voltage than allowed will pass the x/y output, othwerwiese the galvos go "clonk", 5.1 z diode or so...
    +/-12V is used by both myself and 300EVIL, and it's necessary IMO. Drlavas version comes with a +/-9V converter. +/-5V will not even power the op-amps as mentioned above. You need at least 7V to the op-amps, which will in turn give +/-4V max to the galvos. And no, your galvos won't go pop if you use a +/-12V converter. I use one every day, and my galvos don't even get warm, 300EVIL has had no problems that I'm aware of.. There's no way for +/-12V to reach the galvos as long as you build the circuit right. +/-4V to the galvos (or +/-7V to the op-amps) will only get you a 15-20deg scan angle. That will get old very fast. We're just trying to tell you how to build this circuit so that you can actually use it. If all you can get out of it is a 15-25 deg scan angle, what's the point?

    I'm not sure where you got the idea that +/-5V is all the galvos can handle.. The ILDA standard is +/-10V, so they at least must be able to handle that. You won't even get +/-10V to the galvos with a +/-12V DC-DC converter. You'll get +/- 9V.

    And on top of all that, why use batteries when by using a DC-DC converter you can get all your power from USB? That's impractical. I believe it's important to try to design things in the most convenient way possible. That way later, when you go to use it, you won't have to worry about dead batteries. Ever. It's all about getting the simplest system with the most functionality.
    Last edited by ElektroFreak; 02-06-2010 at 08:45.

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    Quote Originally Posted by ElektroFreak View Post
    I'm not sure where you got the idea that +/-5V is all the galvos can handle.. The ILDA standard is +/-10V, so they at least must be able to handle that.
    The Datasheet of my Projector says that. see my first Post in the Thread. its symemtrical 10V p-p only.
    So i thought, why generate 12V and then drop them down to 5 again, when i could make -5 with a MAX768 and use them directly. Besides i dont even know yet if it will work with the ±12V DC our Store has. It outputs 2x82 mA at 80% Efficiency, at 5V in this is almost all one port can deliver, so i need a microUSB Y cable too.

    The strange thing is that in Multisim the circuit still not works even iv i give +12V and -12V to the OpAmps.
    And i done ecactly the circuit like weartronics did. so i must missed something, or it works only in real?

  6. #26
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    The ilda standard for galvo amps says it will withstand 10V. Most have a input impedance of 1K to 1 meg in the form of the resistors in the line receiver. 10/1000 = .01A = 10 mA max, hardly enough to cause damage in most cases.

    I owned multisim at one time. Its buggy as can be. Oscillators don't start without help in it and often it doesn't model current flows properly in complex devices. Try the free LTSPICE from Linear Technology and be much happier...

    Get one of these: http://www.vellemanusa.com/us/enu/pr...iew/?id=522032

    and one of these: http://www.velleman.eu/distributor/p...s/view/?id=966, or one with slightly more current capacity.

    Steve
    Last edited by mixedgas; 02-06-2010 at 11:27.
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    Quote Originally Posted by mixedgas View Post
    Get one of these:
    Ok, again, cant find these in Germany...


    Do you think this one of these will work:
    SIM2-0512D SIL7

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    I'm curious why all your parts must come from Germany? I have a spare +/-12V DC-DC converter here that I can send you for the cost of postage if you think it might help.. but I'm not in Germany, so if you absolutely have to have something from Germany that probably won't work.

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    Quote Originally Posted by ElektroFreak View Post
    I'm curious why all your parts must come from Germany? I have a spare +/-12V DC-DC converter here that I can send you for the cost of postage if you think it might help.. but I'm not in Germany, so if you absolutely have to have something from Germany that probably won't work.
    Cause it would take too long... want to have all ready when the Scanner comes, otherwise if i could wait (but i cant ) i would have ordered a complete kit from EVIL300 or James.

    But do you think it will work? Gives 2x82mA at 80% Efficiency.

  10. #30
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    Quote Originally Posted by Xer0 View Post
    Ok, again, cant find these in Germany...


    Do you think this one of these will work:
    SIM2-0512D SIL7
    Yes, that will work.

    I thought you guys can get anything across EU borders duty free...

    Velleman is in Belge...

    Steve
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