30 Jul
1997
30 Jul
'97
4:39 p.m.
Whilst in a self-induced trance, jpero(a)mail.cgo.wave.ca happened to blather:
> I know that this really doesn't fit here,
since I only bought this calc
> yesterday, but I figure that someone here may know...
>
> I bought a TI-85 graphing calculator, and it has a 3-wire computer
interface.
> It seems that for $40, you can buy a cable adapter
to hook it to a PC's
COM
> port. Software can be gotten from TI's Web
site.
>
> I don't want to pay $40 for a DB-9 connector and a 3-wire headphone
jack.
I'm
> guessing that the interface is a
software-handshaking 3-wire RS-232
setup, but
> before I hook something up to the calc, I wanted
to ask if anyone has this
> calc and can shed some light on it.
Sorry to throw wet towel on you...those
"dongle" interface kit guess
what has little complex board inside. Real sucker really.
We did that this year to see if we can do that too. :)
Hold on there, pardner! This isn't nearly as complex as you think. If the
TI is anything like my Casio FX9700G graphic calculator, with the funky
3-wire headphone hookup, you can most likely do it with 1 or 2 chips or
even just some diodes and resistors. What it is, is the interface is an
*almost* standard RS-232 interface. Speed and all is normal, but it prolly
only works on TTL levels. The PDDs (Portable Disk Drives) from Tandy to be
used on their old, non-MS-Dos laptops did the same thing... used RS-232 but
only at +5V and 0V levels.
Use a diode to change the -12V to 0V, and resistors to change the +12V to
+5V .. it helps to have a cable to test first for that one, tho. On the
Tandy PDDs, the resistor value was 22K Ohms IIRC and any cheap .6V drop
diode would do (read: 1N914 -- everybody's buddy)
Otherwise, just design a small, self-powered 1488/1489 box to convert the
levels, and you're off and running. I was planning on doing this for my
Casio, but haven't had the time just yet.
(Maybe I can just use my TPDD cable... hooking up the appropriate wires???
Something to think about.)
Anyway, I hope this helps!
Roger "Merch" Merchberger
--
Roger Merchberger | If at first you don't succeed,
Programmer, NorthernWay | nuclear warhead disarmament should *not*
zmerch(a)northernway.net | be your first career choice.