I recently discovered that the little Radio Shack Piezo Beepers (RS #
273-065), $2.95 or so, run on 3 - 20 VDC and draw an amazingly small 10 MA
while emitting a VERY piercing beep.  Now, the meat of this note is -- they
put out a very satisfactory noise running DIRECTLY off the userport logic
voltage available on the C64/128.  In other words, if you wire the minus
terminal to pin 1 of the C64 userport connector and the + terminal to the C64
userport pin C, then a :PB0 ON (version 2 thru 2.10) or a :MEM $DD01 01
(versions 1.5 thru 3.51A) will turn the beeper on, making a great emergency -
wakeup alarm for those monitoring a field packet station or even a connect
attention alarm:  just include instructions on how to beep it in your CText
or Infotext etc.  Of course, to turn it off once activated just use :PB0 OFF
or :MEM $DD01 00, as required.  73 de Jim WB5AOX@WB2ARS.NM.USA.NA


Here are the kinds of relays and switching devices I've successfully used on
the userport of the C64/128/Vic20:
"Solid State Relays" with switching voltage of 3-20 VDC input, such as Crydom
etc.
"5 Volt Logic Relays" drawing very low current such as the small blue reed
relays sold by Radio Shack. NOTE- ALWAYS use a reverse protective diode 1N914
or such across the coil winding of the relay to prevent spike damage to your
CIA chip in the computer using ANY relay with a coil.
"Any transistor can be base driven on or off from the user port; of course
this includes TTL and CMOS if the CMOS is running on low enough voltage.
"opto-isolators".  These are great little isolation devices that protect your
computer CIA chips as well as switch higher current loads.  They can drive
small loads directly from the open collector outputs or can be used as relay
drivers etc.


Here are some fun/useful functions using DIGICOM that I haven't seen
discussed in other digicom notes.
PB Functions
In versions that permit //MEM and //PB remote access, such as versions 2.00,
2.10, and 3.51/3.51A, the PB pins on the computer's User Port can be accessed
and turned "ON" (TTL hi, approx +3V) and "OFF" (TTL lo, about .2V or less)
for any combination of the 8 PB pins.  This is especially fun and useful for
remotely controlling other electrical items in the shack.  On my home system
I allow others (and myself of course) control of my external RF power
amplifier on the packet station
and even power to the disk drive.  Up to 8 different devices can be easily
controlled in this fashion by using solid state TTL-input relays wired to the
user port connector.  User port pins C thru L are PB0 thru PB7, respectively.
 Thus, if you wire a solid state relay's + input to Userport connector pin C
and the relay's negative input to any of userport pins 1,12,A, or N (which
are all grounds) then if you type :PB0 on (return)  the relay will activate.
Likewise, a remotely connected station can send //pb0 on (return) to activate
the relay.  If this command doesn't work, make sure to type :IO on, which in
versions 2.0 and 2.10 will allow access to the port.  On versions 3.51 and
3.51A you must access the PB pins via the MEM function.  MEM $dd03 should be
set to value FF and MEM $DD01 is then the address of the PB port.  Then, to
turn on your relay attached to userport pin C as before, you'd type:
 :MEM $DD03 FF (return) or remotely //mem $dd03 ff (return)  THEN:
 :MEM $DD01 01 (return) or remotely //mem $ddo1 01 (return).
To turn all PB pins off or low, the command is MEM $DD01 00 (return).
V3.51 MEM/PB pin hex addresses:
 PB0 (userport pin C)    MEM $DD01 01
 PB1 (pin D)             MEM $DD01 02
 PB2 (pin E)             MEM $DD01 04
 PB3 (pin F)             MEM $DD01 08
 PB4 (pin H)             MEM $DD01 10
 PB5 (pin J)             MEM $DD01 20
 PB6 (pin K)             MEM $DD01 40
 PB7 (pin L)             MEM $DD01 80
As you can see, these are hex addresses for Version 3.51.  Any combination of
these pins can be activated/deactivated with the proper hex value.
MEM $DD01 03, for instance, turns on PB0 and PB1 at the same time.  A value
of 00 turns them all low and FF turns them all on.
I think these PB/MEM functions make the DIGICOM systems more powerful and fun
to use than the BAYCOM versions.  C'mon, where are all the other
hardware/software hackers in the world?  73 de Jim W5AOX (jdport@xoommail.com)