Path: utzoo!attcan!uunet!tut.cis.ohio-state.edu!ucsd!sdcc6!beowulf!barber
From: barber@beowulf.ucsd.edu (Terri Barber)
Newsgroups: sci.electronics
Subject: Re: How Do I Make a Phone In-Use Light?
Message-ID: <11707@sdcc6.ucsd.edu>
Date: 2 Jul 90 21:30:58 GMT
References: <1558@yenta.alb.nm.us> <904@eplunix.UUCP> <4633@milton.u.washington.edu>
Sender: news@sdcc6.ucsd.edu
Organization: CSE Dept., U. C. San Diego
Lines: 40

In article <4633@milton.u.washington.edu> wiml@milton.u.washington.edu (William Lewis) writes:
>In article <904@eplunix.UUCP> raoul@eplunix.UUCP (Nico Garcia) writes:
>>In article <1558@yenta.alb.nm.us>, dt@yenta.alb.nm.us (David B. Thomas) writes:
>>> Another neat phone circuit (VERY simple) uses an scr, a couple of resistors
>>> and a button.  If you wish to switch phones, you hold in the button (gating
>>> the scr), then hang up.  The scr maintains loop current.  An led could be
>>
>>Ummm, can you post this one? Enough of us do occasional phone hacking that
>>I'd like one as well.
>
>
>    I second that. It would be extremely useful around here ...

Okay, let's see if I can remember how to do it (I didn't post the original,
I just want to stick my $.02 in....

Please excuse the ascii graphics....

-------------------+------+----
                   |      |
                   |       /
                   |      /   momentary switch
                   |      |
                   |      /
                   |      \   1200 Ohm
		   |      /
		 -----____|
		  / \
                 /___\  SCR
		   |
		   /
		   \  600 Ohm 
		   /
		   |     ^^
	         -----  //
		  / \  //
                 /___\    LED
		   |
		   |
-------------------+---------