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57098Re: Best light-charging, dark turn-on circuit?

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  • chartres456
    Dec 3, 2007

      I appreciate your educating me on the virtues and limitations of the
      FIFO circuit. A reminder of the need for parsimony when placing
      demands on solar engines.

      Thinking in an opposite, and perhaps heretically non-beamish,
      direction, we all have a surplus of 5V DC energy available at our
      desks, often close to where our robots reside.

      Have you seen or developed circuits that could use the USB ports on
      our desktop computers to a) drive a flasher or other load, or b)
      charge a compact ni/cad or lithium rechargeable that's incorporated in
      the 'bot design? (Web searches, surprisingly, haven't yielded credible
      circuits. One might have to purchase and dismantle one of the silly
      USB-powered toys that are widely offered.)

      It seems one would want to incorporate a form of isolation to avoid
      frying the computer if there was a flaw in the peripheral...

      Wilf, thanks for your instructive responses.


      p.s. A couple of inspirations for charging batteries via USB found on
      the web:

      http://www.usbcell.com/ (I've got two of the AAs powering my cordless
      mouse - they work flawlessly)

      The USB Cell people look as if they're developing a USB-charged 3.6V
      phone and device battery that we might find useful; in the meantime I
      found a couple of alternatives:

      Would be interesting to see if these would make interesting platforms
      for both stationary and mobile devices, but it would also be useful to
      adapt other charging circuits (several of which depend on wall-wart
      transformers) for USB input.

      --- In beam@yahoogroups.com, "wilf_nv" <wrigter@...> wrote:
      > couple of problems conspire against solarizing the FIFO.
      > 1) The FIFO LED peak current (30ma) on time is 100x longer than the
      > pummer current pulse.
      > 2) The FIFO does not provide inherent output drive voltage doubling.
      > 3) The FIFO two series 1.5F aerogel caps = 0.75F
      > 4) The FIFO circuit has a narrower operating range.
      > Since the FIFO was designed for 5V and the average current of the
      > circuit is 15ma (please measure), four or five 170mah NiCd batteries
      > in series (4.8V) should work for at least several hours. You can add
      > a resistor in series with the LED to lower the brightness and average
      > current.
      > I can optimize the FIFO circuit for lower voltage (3.6V) operation
      > using a cmos opamp.
      > The SE driver (74AC240) can be combined with the opamp and used as
      > the PWM controlled voltage doubling LED driver and to turn the FIFO
      > on intermittently to extend battery life.
      > Remember the charm of the FIFO circuit is its simplicity and the
      > unusual fade in fade out pattern but not its efficiency.
      > wilf
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