Collection of Tools & Utilities/Collection of Tools and Utilities.iso/bbsutil/ringdet2.zip/RINGDET2.TXT

Text File | 1988-01-03 | 13KB | 193 lines

                      Ring Detector to Reset a Crashed BBS

                                Designed by Len Busshart,
                                Sysop of PC Plus [phone]
                                Text By Wes Brzozowski

Most every Sysop has to occasionally restart his or her board, because the
board occasionally goes "belly up".  The crash may be caused by power line
noise, thermal problems in a budget computer, the slow degradation of a
component inside the system, or by the actions of immature users who seek to
deliberately bring the system down.  Regardless, this causes extra bother for
the sysop and inconvenience for those trying to call in.  Not content with
simply accepting this, Mr. Len Busshart, sysop of the PC Plus BBS in Endicott
NY, has devised a simple device that will actually allow the next caller to
reset the system.  It works simply but cleverly.

Basically, when the BBS crashes, the computer remains on but it is brain
dead, and is unable to answer the ring signal on the phone line. The circuit
described here will detect a continuously ringing phone line, power off the
system, and then turn it back on. If the computer is able to restart the BBS on
boot-up, any caller can reset the system by simply letting the phone ring for a
while before hanging up. When the BBS is normally running, this circuit will
not be activated, because the computer will answer the phone before the line
has had the chance to ring long enough.

There are a few cases where this device might not be advisable. If the BBS is
not able to restart itself upon boot-up, it won't help at all. If the BBS can
crash, effectively leaving itself "off hook", then all callers will simply get
a busy signal. If they can't send a ring signal, they can't reset the board.
Nastiest of all might be a case where the sysop uses a multitasker so that the
computer can be used for other things while the BBS is running. It's possible
that a user can shut off the computer in the middle of a job. This could also
happen without a multitasker, if no BBS program is running in the system but
the ring detector is still connected to the phone line.

If none of these seems bothersome, then this device will be useful to
everyone involved in the BBS. It would be a good idea to put a short
explanation in the log on message, such as;


    ********************************************************************
    * This BBS employs a Ring Detector Reset Circuit. If the Board has *
    * crashed and cannot answer the phone, just let it ring six times, *
    * hang up, and call back. The board will have reset itself. If you *
    * have to use it, please let us know if it worked properly.        *
    ********************************************************************

With a message like this, most users will quickly learn how to reset the
system if they ever need to. It may also discourage some of the intentional
"board crashers" from doing mischeif. There would seem to be very little
gratification in crashing a board if the very next user can easily undo the
damage.

So much for the good news. The bad news is that you can't just run out and
buy one of these things. At the time this is being written, you can't even
purchase a kit of parts. Although it's not overly complicated, it will have to
be built from scratch, and if you've never worked with power line voltages
before (or if you're not sure which end of the soldering iron to hold!!!) you
should get some help. Fortunately, being a sysop, you can put up a message to
the "hardware hackers" asking for a bit of assistance. Offer a years free
subscription to your board. (If your board is free, be generous; make it a
lifetime subscription!!!)

In any case, you should print out the file RINGDET2.CKT now, and take a peek.
It won't help much to TYPE the file to the screen, because it uses all 80
columns, and so every line will have a blank line after it. Printed on paper,
however, it's quite clear, and a good example of how to express an electronic
circuit in a text file.

The circuit is connected to just two of the four wires in your standard phone
line. Actually, all normal phone systems use only these two wires. It may not
be obvious that this is possible, but it works fine in practice. (And when you
buy your wire by the mile, like the phone company does, you learn to think
of simple ways to do things.) In any case, this circuit will connect to the
GREEN and RED wires only.

When your phone bell rings, a series of plus and minus 45 volt pulses appear
across these two wires. This amounts to a very vicious attack on the delicate
digital circuitry normally found inside a computer. (It can do a fair job of
"lighting up" a standard human body, too.) The 6N139 device is an optoisolator,
which allows the hostile voltages of the phone system to be translated to the
more benign signals that are preferred by digital circuitry.

Every time your phone rings it is responding to a long burst of very short
pulses. As we want to count the rings, we don't count the pulses; we count the
bursts. The first 1-shot converts a burst of pulses into one pulse that's about
the same length as the burst. Essentially, it triggers on while the phone bell
is ringing, and goes off during the intervals when it's silent. The 74193 will
count the rings, and the 7485 will compare the ring count with the preset
number of counts that you must program in to the four switches. When they
match, it triggers a circuit to produce an 8 second shut-down pulse.  This
signal normally controls a Solid State Relay (SSR) that keeps power applied to
your computer. When the shut-down pulse occurs, that power is interrupted for 8
seconds. This shuts your computer off, lets the power supply internally
discharge itself (very important to do!) and then turns it back on.

If you look closely at the circuitry, you'll see some other enabling and
resetting portions that keep ring counts from the previous call from being
added in with those of the present one, and the circuitry is set to ignore any
rings that may occur when the system is temporarily shut down.

The Solid State Relay may need a bit of explanation. This is a solid state
circuit that acts very much like a standard electromechanical relay. They
usually come as a rectangular block with four terminals. The two input
terminals are polarized; that is they have a (+) and a (-), and these are shown
in the schematic. The two output terminals are not polarized; you can use
either one for either connection. These act like a switch that turns on when an
electric current is sent into the input terminals. No part number for the relay
is given. Since they are not as commonly available as the other components
here, you should choose from those you can get. The diagram shows a 10 Amp
relay; this should be enough for your system, but if it needs more, you'll need
one that can carry more amps. (It's always better to have at least %25 more
capacity than you'll need, anyway.)

The diagram also shows that the relay must be able to handle 120 Volts AC;
make sure that the relay you get can do so. (While most all Solid State Relays
will be able to do this, there are a few that instead are made to switch DC,
and these cannot be used in the ring detector. Unlike the old fashioned relays,
the Solid State variety can usually only switch one or the other; not both.)
The mounting side of a Solid State Relay is usually a flat plate of metal. If
you want the relay to carry anywhere nearly as many amps as it's rated for,
this flat plate will have to be bolted down on a suitable heat sink, with
thermal grease sandwiched in between. Solid State Relays are expensive, and you
don't want to burn yours out. If you do burn it out, you may not know it until
you need it. A dead relay usually just stays on all the time, which is what the
ring detector usually does. But when a user tries to reset your computer, the
ring detector will be unable to shut