From news.media.mit.edu!grapevine.lcs.mit.edu!olivea!decwrl!decwrl!koriel!news2me.EBay.Sun.COM!rampart.EBay.Sun.COM!handler.Eng.Sun.COM!pepper!cmcmanis Wed Jan 19 08:54:13 EST 1994
Article: 7817 of comp.robotics
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From: cmcmanis@pepper.Eng.Sun.COM (Chuck McManis)
Newsgroups: comp.robotics
Subject: miniboard hack
Date: 19 Jan 1994 09:29:23 GMT
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While the robot-board list is down I figure I'd post this here.

So I got this mondo-cool IBM thinkpad 750C to carry around and I'm
thinking "hey, robots on the road" right? Wrong. Turns out the 750C
uses a "low power" RS232 setup in its serial port and the Miniboard
"use a transistor to make the transmit work" hack fails to function
reliably. Most notably during downloads, eventually the miniboard
can't "see" the characters being sent by the 750C. This was actually
similar to a situation I had with the wizard palmtop which has the
same problem. What to do? An RS-232 buffer of course. So I took a
MAX233 chip (Maxim 5v only RS-232 chip, internal capacitors), a 7805,
a 1uf tantalum cap, and a 9v battery. Put them into a Radio Shack
"transmitter" case using some cheesy RS prototyping board added a
RJ-11 jack and a pigtail ending in an RJ-11 plug. And voila! A
buffer. Now I connect the computer/wizard to the buffer using the
standard miniboard setup (DB25 -> RJ-11) then plug the buffer into
the miniboard's RS232 plug and it works. Since the ground pin
is connected through this doesn't completely isolate the MB from
the host, but it does allow it to work.


-- 
--Chuck McManis			     All opinions in this message/article are
FirstPerson Inc.                     those of the author, who may or may not
Internet: cmcmanis@firstperson.COM   be who you think it is.