Date: Tue, 11 Nov 2003 22:49:25 -0500
Subject: errata on the board design
From: r <raffi@media.mit.edu>
To: mas863@media.mit.edu
first, a lot of people are having problems programming
their boards after they have stuffed them. if you plug your
board in (from just the schematic you all have) -- you'll
notice it is pulling about 0.062 amps @ 5V. that's way too
much and it is preventing the in-circuit programming from
doing its thing. you need a 0.1uF capacitor (the same as
the other capacitors) from pin 6 on your max202 to ground
(what you have now is that pin 6 on the max202 is shorted
to ground). if you put that capacitor in, you'll see the
current draw go -way- down to something more like 0.028
amps @ 5V and you should be able to program your circuits
in place now. if your trace from pin 6 is visible, you can
just cut it and put the capacitor across it. if its not
visible, you'll have to do some hacking.
second, there seems to be some issues with the db9/serial
connector that i chose. try this for a connector wiring
pin 14 on the max202 -> pin 3 on the DB9
pin 13 on the max202 -> pin 2 on the DB9
the ground line is fine
try these two changes out -- we have one data point that
this fixes all problems with the boards (see the attached
picture for the first working board).
much thanks to bb2 for his help and persistence in solving
what is going wrong with most people's boards.
r