Whilst in a self-induced trance, jpero_at_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_at_northernway.net | be your first career choice.
Received on Wed Jul 30 1997 - 23:39:13 BST