Electronic Switch?

Discussion in 'The Projects Forum' started by ajohn, Jun 18, 2014.

  1. ajohn

    Thread Starter New Member

    Jun 18, 2014
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    Forgive me if this is a stupid question, I'm not an electrical person, I'm a mechanical engineer...

    I'm building a system to run some tests, which requires a heater to be automatically turned on and off. The coding is done through LabView, and is is currently running on a NI myDAQ. The problem is the output ports don't supply the current necessary to get the heater to its proper output. I have an external power source I can use. The power source is NOT, however, one that can interface with the computer, just physical controls. Is there any way to build a circuit that will turn the power from the source on and off to the heater using a voltage signal from the myDAQ?
     
  2. alfacliff

    Well-Known Member

    Dec 13, 2013
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    a solid state relay. might help if you told us what the supply for the heater is. either a solid state relay or a plain old relay.
     
  3. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Is this just ON/OFF control?
    Look for an opto Isolator, Opto22, Grayhill, T&B make them.
    They will switch an AC or DC load using a 3-35vdc signal and are isolated.
    Max.
     
  4. ajohn

    Thread Starter New Member

    Jun 18, 2014
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  5. MaxHeadRoom

    Expert

    Jul 18, 2013
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    You could use a Logic Mosfet to switch them, although if you need an off the shelf solution and/or isolation (which you may not need), the Opto22 would do it, DC switching output type.
    Either way you would need a logic output on your Labview card.
    Max.
     
  6. ajohn

    Thread Starter New Member

    Jun 18, 2014
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    So what I have running now is that when a specific condition is met, it outputs 5V from a certain port on the DAQ. So with any of these solutions (the solid state relay, logic mosfet, opto isolator) is this all I would need to be able to run it?
     
  7. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Yes, also if neccesary a small logic (5v) Mosfet,2n7000 could operate a relay, although the cleaner way would be the solutions already mentioned.
    Depending on the logic output capacity you may need a 2n7000 to drive the Opto22.
    Do you require the electrical isolation between the heater and PC?
    If not a logic power Mosfet can drive the heater direct.
    Max.
     
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  8. ajohn

    Thread Starter New Member

    Jun 18, 2014
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    So something as simple as this (https://www.sparkfun.com/products/10213) should do the trick? I'd just hook one wire of the heater to the power supply, the other wire to the drain terminal, the source terminal to my 5V signal, and the signal terminal to ground?
     
  9. MaxHeadRoom

    Expert

    Jul 18, 2013
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    That is rated at 32amps, so as long as your load does not exceed this it should be OK.
    The Drain goes to your load, the Gate to your PC out, and the Source to common (GND)
    You need to bond the two commons (GNDs) together, PC and 12vdc supply common.
    Mosfet Source and PC common.
    See the Bld Tutorial in your link.
    This is the none isolated circuit.
    The PC common is usually at earth ground, so something to be aware of, but not normally a problem if aware.
    Max.
     
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  10. ajohn

    Thread Starter New Member

    Jun 18, 2014
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    Awesome, thank you SOOO MUCH. You just literally saved me at least a day of beating my head against the wall.
    -Alyssa
     
  11. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Your welcome, In case you missed my edit, see the Bldr Tutorial in the link.
    Max.
     
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