Re: TI-H: Power expansion mod done.


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Re: TI-H: Power expansion mod done.




take some pictures and scan them. 

At 12:20 PM 6/1/98 -0500, you wrote:
>
>Greets.
>
>I spent most of my free time this past weekend working on calculator
>mods.  The one I thought might interest people is the power expansion
>port I installed on one of my 85's.  At Radio Shack I purchased a
>package
>of two 'Submini Phone Plugs' the kind with the little switch inside
>(sorry,
>I don't have the part number handy), for $1.50.  The plug is a mono
>plug
>with three solder connectors.  It is constructed such that the three
>connectors
>are arranged like a SPDT switch.
>
>I installed the jack on the lower right side of the calc case.  I then
>removed
>the positive battery terminal from the main board, and ran a wire from
>its
>contact over to the jack.  I installed a new contact into the
>receptacle on the
>back of the case and ran a wire from it to the jack.  Now the front
>and back
>of the case are wired together and battery power flows through the
>jack switch.
>I then connected the final connector on the jack to the negative
>battery lead.
>Now, when I plug in the 2.5mm plug, the main battery is disconnected,
>and
>the power from the plug is connected.
>I considered installing a voltage regulator into the calculator, so I
>could
>operate on any DC supply from about 6v to ~25v, but it didn't seem
>necessary,
>and a standard 7805 was kinda big anyway.
>
>The modification was pretty easy, the only disadvantage of having this
>installed is that without more extensive modifications to the case,
>the
>jack sticks out a bit.  Adding some material to the outside of the
>case
>to mount the switch in would make it look better.  I may attempt this
>when
>I do my main calc (this one is practice model :).  A smaller non-radio
>shack
>jack might work better, something similar to the link port jack would
>be nice.
>
>If anyone is interested, I'll try and get some pictures of the mod on
>my
>web page.
>
>One thing that was interesting is that those unregulated wall
>transformer
>DC supplies (usually consisting of a center tap transformer, two
>diodes
>and a small filter cap) don't work too well as supplies.  When the
>calc
>draws more power (like when graphing), the LCD goes very dim.  This
>might have to do with the bad filtering, but I'm not sure.  I added a
>larger
>filter cap, and it didn't seem to help.  I'll try a larger regulated
>supply
>later and see if that helps.  Another possibility would be to just use
>one
>of those battery holders for 4 D size cells.  A calc ought to run for
>pretty
>near forever on those.  Also, you then have the advantage of a
>portable
>supply, but without a bulky battery extender attached to the calc.
>
>I can provide a wiring diagram if anyone is interested.
>DK
>
>


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