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RE: [beam] Hexapod

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  • Wilf Rigter
    The gate delays are not a problem since short h-bridge glitches have low energy. Anyway the turnon / turnoff times of the h-bridge are also different so only
    Message 1 of 10 , Sep 27, 2000
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      The "gate delays" are not a problem since short h-bridge glitches have low
      energy. Anyway the turnon / turnoff times of the h-bridge are also different
      so only a deliberate deadtime can cure all glitches.

      By the way, your original post with the 139 "reversing" Z-bridge idea was
      quite brilliant. You almost got it right but because it does not tristate,
      you have to use a resistor to isolate the HC139 output to the h-bridge input
      . In other words, use 2 input resistors for each h-bridge input as shown in
      the PNCfree microcore with "reversing" 74HC139 h-bridge. Note the nifty
      control of the enable line.
      <<u139CORE.gif>>
      There are several other variations on your hexapod circuit worth pursuing.
      For example, your design uses a grounded master bicore and two slave
      branches to generate a pair of waveforms each delayed from the master bicore
      output waveforms by 90 degrees. These branches act as a slave bicore but
      have independent delays and independent pulsewidths. However there is no
      particular advantage to using branches compared to a slave bicore. In fact,
      as you noted with branches you can get overlapping waveforms so then you
      need a HC139 to avoid frying the h-bridge. Still independent control of the
      slave wave could be useful.

      So how about a bi-phase slave circuit similar to that Nv/Nu circuit used in
      the powersmart head. It can be made phototropic with the addition of some
      photodiodes just like a suspended master bicore as shown.

      For a complete Hexapod circuit combine all these elements: the single ended
      bi-phase slave output can be connected to the two halves of a HC139 and two
      h-bridges each with independent reverse. This design gives you a complete
      hexapod control circuit in TWO chips!

      enjoy

      wilf

      <<hexapod1.gif>>


      > -----Original Message-----
      > From: Richard Piotter [SMTP:richfiles@...]
      > Sent: Tuesday, September 26, 2000 7:50 PM
      > To: BEAM
      > Subject: Re: [beam] Hexapod
      >
      >
      >
      > Also, I have an aditional question. There is a slight, fraction of a
      > second, delay between when an input enters an Nv and the output changes.
      > With the two branches, there can be substancial delay, between loading
      > and variations in component value. If I were to put an additional
      > inverter at the end of one chain and cut the other, will the delay time
      > of the second inverter switching after the first have an adverse effect
      > on power coonsumption while the H-Bridge has the same signal for a split
      > second (with no 139 installed). Is it a low enough effect to not
      > adversely effect power consumption or the safety of the H-Bridges over
      > an extended time?
      >
      >
      > I think I'll do the PCB tommorow or the day after. Depends how bored I
      > get and if I have enough dry transfers left for it.
      >
      >
      >
    • Wilf Rigter
      Here is the detail on the biphase slave.
      Message 2 of 10 , Sep 28, 2000
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        Here is the detail on the biphase slave.

        <<biphase.gif>>
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