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Path: utzoo!linus!philabs!seismo!hao!menlo70!sytek!hplabs!sdcrdcf!darrelj
From: darrelj@sdcrdcf.UUCP
Newsgroups: net.micro
Subject: Re: [DRT:  computers turning on when you call them.]
Message-ID: <533@sdcrdcf.UUCP>
Date: Tue, 20-Sep-83 11:02:31 EDT
Article-I.D.: sdcrdcf.533
Posted: Tue Sep 20 11:02:31 1983
Date-Received: Fri, 23-Sep-83 06:00:55 EDT
References: <4948@sri-arpa.UUCP>
Reply-To: darrelj@sdcrdcf.UUCP (Darrel VanBuer)
Organization: System Development Corporation, Santa Monica
Lines: 37

An alternative power on trigger (for a computer which powers on when
telephoned) is the RingIndicator signal provided by many (but certainly not
all) modems on pin 22.  This is  a signal which is active whenever the modem
detects presence of ringing voltage on the phone line, so its a signal on
for about 2 or 3 seconds every 6 seconds or so.  This signal should be
available whenever the modem has power (unlike carrier detect.  Carrier
detect is presented only after the modem has answered the phone and
established the data connection, many modems will not do this unless DTR
(pin 20) is made true; if you have and use RI, the computer can control DTR
and decide whether to turn on DTR and permit the phone to be answered).

To implement this you will probably want three relays:
a 5 volt reed relay, normally open (this will be activated by RI or DCD to
	turn on system
a 5 volt reed relay, normally closed (this will be activated by computer to
	turn system off
a double-pole power relay, normally open (this will actually switch power
	line).

The reed switches and the coil of the power relay should be in series
accross an appriate coil voltage (proably 12, 24 or 120 volts).
The coil of the NO reed relay should have one side connected to +5 volts,
the other side to the output of one section of an MC1489 RS232 receiver IC.
This IC needs +5v and ground for power.
The coil of the other reed relay should be hooked between +5volts and a
buffered output signal from your computer (e.g. the LED drivers for Apple
game paddles).  If the port is an MOS port, buffer it thru a 7404.
Setting the output port to the right value will power off the computer.
(You might need an extra 7404 inverter section, since the state of the port
at initial power-on had better keep power on!

	Darrel J. Van Buer, SDC, 2500 Colorado Ave, Santa Monica, CA 90406
	uucp: {beats me}!sdcrdcf!darrelj
	arpa: vanbuer@usc-ecl.milnet
	tel:(213)820-4111 x5449