Switching anode/cathode

Discussion in 'General Electronics Chat' started by coder, Jun 7, 2006.

  1. coder

    Thread Starter New Member

    Jun 7, 2006
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    Hi,

    I'm working on a prototype which uses a latching solenoid (coil) to move an armature. To change between positions I need to reverse the anode/cathode of the coil and supply 3V for 100ms. My problem is that I write software and don't get into hardware much, so although it seems simple in concept I'm not sure how to design a circuit that allows me to control, via two IO pins, the solenoid. Originally I was thinking some kind of electronic DPDT switch but, guess what, in order to control it I need to reverse the anode/cathode! (kinda an infinite loop for me)

    Any help would be appreciated.
     
  2. Papabravo

    Expert

    Feb 24, 2006
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    A diagram of your starting point would be helpful.
     
  3. billbehen

    Active Member

    May 10, 2006
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    1

    Sounds like a DPDT relay and a couple of diodes would do the trick -- a sort of backwards rectifier, that would conduct current one way through the solenoid when the relay was thrown one way, and the other when it was thrown the other! The DP aspect of the relay would let you reverse both connections to the solenoid at the same time; the diodes would prevent a short circuit.
     
  4. Papabravo

    Expert

    Feb 24, 2006
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    A picture would be worth several more paragraphs anyway.
     
  5. Ron H

    AAC Fanatic!

    Apr 14, 2005
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    See this thread. It solves basically the same problem. It's 3 pages long, but there are some answers and schematics there if you take the time to read it.
     
  6. coder

    Thread Starter New Member

    Jun 7, 2006
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    Thanks Ron. I read through the thread which turned me onto mosfet drivers. After looking at a few schematics I came up with the attached schematic. AFAIK it should work, although I noticed one schematic had diodes to protect from under/over voltage (from the motor they were driving).
     
  7. Ron H

    AAC Fanatic!

    Apr 14, 2005
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    Notice that the output resistance is around 7-10 ohms, so your series resistor should be changed to 47 ohms. Also, the chip will burn up if you accidentally leave it on for too long. I don't know if 100ms is too long. :(
    EDIT: power dissipation shouldn't be a problem with 200mA and 100ms. I was using 400mA when I made that conclusion.
     
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