[sdiy] Expo question and unrelated dumb matrix idea

[Scott Gravenhorst]

Yes and the inverse function can be implemented with an opamp with a diode in
the negative feedback loop.  I've never tried it, but I'm told it's anything
but accurate and has all of the temperature wonderfulness that an expo
converter suffers.

AN-30 (application note 30) which is about log converters might interest you.

David Moylan <dave at westphila.net> wrote:
>Inverse of expo is log.
>
>Dave
>
>Tom Arnold wrote:
>
>>First, the expo question.
>>
>>Is there such a beast as an inverse expo converter, or is there a different
>>name for this that I'm not thinking of at 2:30am?  I'm doing a pot to
>>current->voltage converter and the responce I'm getting acts very Expo (
>>lots of movement for not much voltage change and them whammo ).  The pot
>>*is* linear.
>>Unfortunatly I'm trying not to modify the control the pot is in, so
>>connecting it across the supply rails and taking a voltage from the wiper
>>isnt an option.  I dont need to be exact, just need to compensate in a rough
>>way for the crappy curve I'm seeing.
>>
>>Next, the dumb matrix idea.
>>
>>Since I obviously have too much spare time and too few projects, I played
>>with something else tonight too.  I want to build a small pin matrix with
>>small being the operative word ( I'd like 15x15 in about 2" square ).  The
>>idea I tried that actually seems to work is taking strips of machinepin
>>sockets for SIP IC's, trimming the pins off then grinding the bottom lightly
>>with a dremel until I hit the cavity.  I was afraid the contacts might pop
>>out the bottom once it was open but in this case ( Augat sockets ) they did
>>not.  Now an actual sewing pin goes right through the top socket and can be
>>lined up on a second set of SIP sockets which are unmodifed to provide the
>>second contact.  Its less work then it sounds although I only made a 5x5 as
>>my test matrix.  May be cool for matrix patching a noise box or something.
>>
>>Next run to the surplus places I'm going to try and find some older
>>microprocessor sockets that are solid pins across the bottom unstead of
>>having an empty area around the die as this would give me a solid top and
>>bottom structure to play with.
>>
>>I did mention it was a dumb matrix idea... but it may be a fun toy for
>>someone.
>>
>>  
>>
>

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-- Scott Gravenhorst | LegoManiac / Lego Trains / RIS 1.5
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