PRO2020.1

The bank display
is a FND367 using 470 ohm resistors to +5v.  The display driver is a
4511 driven off the SECOND counter in the 4520 package.  Since one of
the segments in a 0-1-2-3-4 counter is always on, it is run (via its
resistor) directly off +5, rather than off of the 4511.
I used rather stiff decoupling (around 100uF in parallel with .1uF)
on the display "module" (4511+fnd367), and the expansion board on both
+5V and +5VBACKUP lines.  This may be excessive, but overkill doesn't  hurt

THE NEXT TIME I'm in there, I will probably switch the 4520 power line
onto the battery backup, so it will power up in the bank I left it in,
rather than at any bank at random as it does now.  If I were doing it
again, I would drive the 4511 off the same lines as the address, rather
than using the second counter in the package, because on power up, the
two halves of the counter chip might have different numbers in them,
causing the bank display to "lie" to you until you go to bank zero (when
both halves get a reset and get synched up again)
I have decided that the scan speed is too slow to make any practical use
of the idea of decoding "20" in the channel number display and using
it to clock the "bank" counter.  With that many channels being scanned,
the chances of catching anything diminish too far.

THE NEXT MOD is to put a fet switch (probably a TIS73 jfet) across the
"speed" switch, with a capacitor from the gate to the switched +5V line
and a resistor from the gate to ground.  This should hold the "speed"  key
on the keypad closed on power up, so the machine starts off in "fast"
speed, rather than in slow.   I havent thought this one out yet, so if
you beat me to it, lemme know how it works.
This mode isn't the best one to send schematics through, so if you
want a schematic of the mod, send me a papermail address.  Mine is:
Mike Kelly, Carleton University, Colonel By Dr., Ottawa, Ontario,
Canada, K1S 5B6.                 73.. mike k. (VE3 FFK)

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