Hi Roy.

18-Feb-04 23:06:47, Roy McNeill wrote to Bob Lawrence


 RM> On (04 Jan 04) Bob Lawrence wrote to Roy Mcneill...

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

 BL>> 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 pooter
 RM>> were still dead.

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

 RM> Nine years, at least. That's the oldest file I can find.

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

 RM> The serial interface runs at 2400 baud.  I think I'd prefer a
 RM> series resistor and a pair of back-to-back shunt
 RM> [zener-in-series-with-a-diode]'s to local ground.  This should
 RM> bother the serial data a bit less.

  why noy just use two zeners back-to-back
  (in series, but facing opposite directions)

 -=> Bye <=-

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