Seeking polarity reversing circuit

Discussion in 'The Projects Forum' started by Involute, Jul 16, 2016.

  1. Involute

    Thread Starter Active Member

    Mar 23, 2008
    47
    1
    I'm thinking about using some flipdot, 7-segment digits in a project. Each segment is controlled by a single, 2-pin coil drawing 350 mA @ 19VDC. Send the current through in one direction and the segment flips one way, send it through in the other direction and the segment flips back (no current is necessary to maintain a state, just to change it). I'm looking for a solid state circuit that can do this. The more integrated the better (e.g. ULN2003). Any suggestions? Thanks.
     
  2. AlbertHall

    Well-Known Member

    Jun 4, 2014
    1,964
    387
    If you want to run this from a single 19V supply then you need to be able to reverse the connections - well beyond the abilities of ULN2003.
    An H-bridge driver could do it. The L293D is popular and each IC could drive two segments and could handle those voltages and currents.
     
  3. KeepItSimpleStupid

    Well-Known Member

    Mar 4, 2014
    1,147
    204
  4. ian field

    Distinguished Member

    Oct 27, 2012
    4,415
    784
    The simplest possible switching would be with split rail supplies - or single rail at double the voltage with a capacitor decoupled voltage divider.

    Never used this type of display myself, but I vaguely remember that you only have to pulse the coil briefly to flip the dots. Should be possible to do it with a capacitor charged via a resistor, and a few steering diodes.

    At least one of the hobby magazines published a project to use recycled display boards = possibly EPE or maybe Elektor.
     
  5. Involute

    Thread Starter Active Member

    Mar 23, 2008
    47
    1
    Thanks! All good suggestions, especially that EDN article. Back to research.
     
  6. AnalogKid

    Distinguished Member

    Aug 1, 2013
    4,545
    1,252
    A long-time problem in interface design has been the lack of a true PNP equivalent to the ULN200x series. You can buy a quad 2N3906, but you have to add base resistors and collector clamps. Still, if you can get a dual output, +/-19 V power supply, you can drive each dot single-ended through a capacitor as an alternative to a full bridge drive.

    ak
     
  7. Involute

    Thread Starter Active Member

    Mar 23, 2008
    47
    1
    What would that circuit look like? Ian Field also mentioned a capacitor decoupled voltage divider, which I haven't come across before and couldn't find an example of in a quick search.
     
  8. ian field

    Distinguished Member

    Oct 27, 2012
    4,415
    784
    You could contact the editors of Elektor - I'm fairly sure one or the other has done a flipdot display project in the past few years. Chances are you can get a copy of the original article for a small fee.

    Its the same principle as driving Carpenter relays, circuit examples for that might be easier to find.
     
Loading...