RM> a nearby lightning strike knocked out our power for a while
RM> (according to our neighbour, we were all out). The cables to
RM> the sprinkler solenoids must have acted as antennae

 Ha, ha! Told you so!

RM> or maybe our 240V earth was sufficiently different from the
RM> sprinkler controller earth, because when I got home both of the
RM> serial ports on my pooter were dead, and the RS232 signal from
RM> Drip (the sprinkler controller) was iffy. I replaced the
RM> MC1488/1489 RS232 chips in Drip, but the com ports on the
RM> pooter were still dead.

 How long is it since you built DRIP? It must be five years! And I
told you so!

 As I said then... a good way to isolate long antenna leads from
microchips is an ordinary resistor (they're all spiral cut nowadays)
with a physically small capacitor to ground at the micro end. What
value resistor and capacitor depends on the speed of DRIP (or
whatever), and the slower the better. Ideally I used 10K and 2.2uF
electro, but on a telephone dialler I dropped that to 2.2K and 0.1uF.
Little electros are really good at absorbing sparks. The blue 0.1uF
only last for ten sparks or so. 

 It's important to establish a GROUND on the printed board, so that
if "EARTH" jumps up as you suspect, then the micro and the isolating
capacitors also jump up. You have to watch any other connections you
make to ground. During a lightning strike there is *NO* ground. It all
jumps up in the air by ten of thousands of volts and there is no
way to prevent it... you have to make sure there is an isolating
resistor to limit the energy that flows into the micro, and a
capacitor to tie the micro grounds together.

 I've never actually done it with a computer box, but it you just
wired the capacitors on the back and let the resistors hang out it
should be okay.

RM> A couple of days later, Win98 failed, and would only start in
RM> Safe mode. WinXP would only get as far as its 1st advertisement
RM> page. I took the pooter to a surgery, and it got a motherboard
RM> transplant.

 Yair... that's the problem. Once the spark getsinto the board, there
is no way to know where it will end up. You need the resistor to limit
the energy (it actually sparks over inside), and a capacitor to absorb
the sharp edges of the spark. Even 2.2K and no capacitor makes a huge
difference.

RM> Now its video system is different, and the monitor doesn't want
RM> to know about Win98 screen resolutions greater than 800x600 -
RM> it comes up with a little message that says "Attention:
RM> 67K/74Hz is out of range" (or 68K/84Hz, 64K/59Hz, etc) XP runs
RM> ok at 1024x768, but no higher. So now I'll need a new monitor
RM> as well. Drat.

 That *really* sucks! Every motherboard comes with its own video, and
none of then run the old monitor. Have you tried reinstalling the
video drivers that came with the old board? The monitors are usually
standard...

Regards,
Bob
 
 

--- BQWK Alpha 0.5