Is there a solid state single circuit way to cycle polarity?

Discussion in 'The Projects Forum' started by masked, Jul 1, 2010.

  1. masked

    Thread Starter Member

    Jul 1, 2010
    48
    1
    Hi all,

    My project right now is a simple setup: Three 9v batteries and a 2.64mA current limiting diode all in series. (Okay, sometimes I also add various anode/cathode pairs and the occasional light bulb or ammeter.)

    What I'd like to do is have it automatically reverse the anode and cathode every minute or so. I'm familiar with *mechanical* relays and DPDT switches, but as far as solid-state electronics goes I'm a newbie who's thus far just made up my theory as I repair one bad part of a circuit that someone already designed and built for me.

    I've seen some similar posts but they all involve mechanical objects bumping into toggle switches.

    In theory, it seems like I should be able to wire up a 1-minute bistable 555 chip to a DPDT relay which goes to my cathode and anode.
    However, since the main circuit is 27V I'm assuming that I'll need to isolate a second lower voltage circuit for the timer... and I have no idea how that will affect my overall output.

    So my questions are:
    Is this the right approach?
    Is there a solid-state (non-relay) way to do this within one 27Vcircuit?

    Advance Thank Yous,
    -masked
     
  2. KMoffett

    AAC Fanatic!

    Dec 19, 2007
    2,574
    230
    Google: H-Bridge

    Ken
     
  3. masked

    Thread Starter Member

    Jul 1, 2010
    48
    1
    Thanks so much! :)
    You solved the larger problem of my not knowing what it is that I don't know. Knowing what to look for makes a huge difference.

    Since my last post I'd stumbled onto 4060b counters and read up, but this looks like what I needed!

    thanks again,
    -masked
     
  4. masked

    Thread Starter Member

    Jul 1, 2010
    48
    1
    Hi All,

    I know TexasTony posted an almost identical topic, but I think I'm still failing to understand how to choose my resistors for this h-bridge.

    I've spent days building and simulating dozens of H-Bridge circuits, and I keep running into the same problem.
    I've tried the dual and single pole Tilden style drivers at http://faq.solarbotics.net/BiomechMotorBridges.html
    You can see my simulations at http://www.falstad.com/circuit/index.html by importing (pasting) any of the attached text files. The closest I've gotten was HBridge1.txt
    Basically, everything works with a DPDT relay, but when I try to replace that with solid states, I can not get the second pole to work properly. ....or I can not get the "low" state of the 555 to activate the drive transistors unless I use the +V rail to activate them and then ground it during the "high" state. Like so:
    [​IMG]
    Since the 555 can sink current, I'd like to use the high & low states directly to reverse polarity.

    Anyway, all of my versions work properly in the high state, but then in the low state they only allow microVolts through the driven circuit.
    Can anyone tell me what fundamentals I'm missing here?

    My existing oscillator circuit is:
    [​IMG]

    Continued thanks,
    -masked
     
    Last edited: Jul 21, 2010
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