Help with multiple power supplies

Discussion in 'The Projects Forum' started by seokeefe, Feb 25, 2014.

  1. seokeefe

    Thread Starter New Member

    Feb 25, 2014
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    Hello...

    I've uploaded a sketch of what I would like to successfully connect: 1) an Arduino controller, 2) a LM7805 regulator circuit, and 3) a MOSFET circuit to switch a 12 soleniod.

    When the 24V input is received, the LM7805 outputs a 5v signal to the Arduino. The Arduino responds by sending an output signal which is fed into the MOSFET, which turns on the MOSFET, ultimately switching the 12V solenoid. If I connect the Arduino ground to the 12V supply ground and test just the MOSFET circuit, the solenoid switches as expected. However, if I intend to use the 5V LM7805 signal, I can no longer connect the Arduino to the 12V ground, correct? I must connect the Arduino ground to the 24V ground if I want the 5V signal, correct?

    Is there a way to use the two power supplies together with the Arduino? I tried to omit the 12V supply by utilizing only the 24v supply. I tried this by using a LM317 circuit to get from 24v down to 12V. However, when I connected what I had measured (no load) to be 12V up to the MOSFET circuit, the voltage dropped from 12V down to 4V and would no longer fire the solenoid.

    Any suggestions? I'm stuck using the 24v supply.
     
  2. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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    all the grounds should be tied together..
    and what do you even need the 5V supply for.. Arduino has a little one already built it..
     
  3. Bernard

    AAC Fanatic!

    Aug 7, 2008
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    Could then use a buck regulator for 24V to 12V for solenoid, but will need a logic level FET or a secondary FET driver.
     
  4. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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    It "could" all just be done with the 12V supply.. Arduino can accept 12V.. solenoid needs 12V.. arduinos regulator will give 5V if needed..
     
  5. seokeefe

    Thread Starter New Member

    Feb 25, 2014
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    so I can safely tie together the ground of the 24v supply and the 12v supply?

    I don't think Arduino can read a 24V signal, which is why I need to bring it down to 5V.

    Thanks for the help.
     
  6. seokeefe

    Thread Starter New Member

    Feb 25, 2014
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    The 24V is my input signal. It is the trigger for everything else. Arduino is responding to that signal.
     
  7. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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    ?? what do you mean "read".. what are you trying to do with that 24V supply..
    you can typically use a voltage divider to measure higher voltages..
     
  8. seokeefe

    Thread Starter New Member

    Feb 25, 2014
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    I'm not trying to do anything with the 24V supply. The 24V feeds a heater. When that heater turns on, I want my Arduino to perform a function. the Arduino needs an incoming signal as a trigger to perform the function. I'm not sure, but I don't think I can use a 24v input signal on Arduino, which is why I'm bringing it down to 5v.
     
  9. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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  10. seokeefe

    Thread Starter New Member

    Feb 25, 2014
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    Thanks for the help.
     
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