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On 27-Jan-11 06:52, PICdude wrote:
> Need to free up one pin on a 16F project, so looking for ideas a low
> cost, small footprint way to multiplex some I/O pins.  From all the
> options, it seems best to multiplex the 3 outputs that control the
> cathode columns of a 3-digit LED display (via N-channel mosfets),
> using 2 outputs from the 16F instead.  So I need a demultiplexer,
> where only one of the two outputs would be high at any time, and an
> enable pin would sendd both outputs low when the enable pin goes high
> ...(the enable would be the 16F output that directly controls the 3rd
> digit).  I should be able to fit a SC70-6 on the board, so that would
> be ideal, though I'm open to other close suggestions.  This will be
> 5V, btw.
>
> So far, some close, but not complete solutions I've found are NL7SZ18,
> NL7SZ19 (OnSemi), sn74lvc1g2 (TI), etc, but they're not a full
> solution (I'd have to add a transistor or so to invert a signal here
> and there).  Before I go code a 10F do this, anyone know of an
> off-the-shelf demux that would do this easily?  Hoping to have
> something in the $0.10-$0.20/k price range (the 10F solution would be
> about twice that).

Depending on your schematics a passive solution could work. (see attached).

Djula

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