Re: Amp + Filter sensor circuits

[Tim Vanderhoek <vanderh@ecf.utoronto.ca>]

On Tue, Jan 18, 2000 at 01:39:54AM -0500, Tim Vanderhoek wrote:
> 
> opamp connects to the single amp+filter unit.  The computer turns the
> opamps on/off as necessary.  Total cost: 2*N*little-triangle-thingys.  

Joyce: while modifying the sensors.txt file, a major potential
       problem with this scheme occurred to me.  The implied
       assumption in all our reasonings has been that an op-amp, when
       turned "off", moves its output into a high-impedence state.  We
       have no reason to believe this is true.  We need to test this
       hypothesis ASAP so that we can re-evaluate our scheme if our
       assumption turns-out to be false.

       Can you test it on Sunday?  Or even tonight, if you get this
       email on time.  If you don't have time, I can do the test for
       you pretty quickly provided we have an opamp chip hanging around.

       Urg.  I don't know why I didn't think of this problem earlier.
       I don't know why Dr. Davies didn't mention anything about it.
       I guess I was thinking too much in terms of voltage and not
       enough in terms of current...

I really really want to know by the end of Sunday if our scheme is
dead in the water already or not.  I'm concerned it may be rather
dead, although, if it is, it can still be revived, but at the cost of
slightly more expensive chips to replace the simple drivers...


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