Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Path: utzoo!watmath!clyde!cbatt!UCBVAX.BERKELEY.EDU!SPGDCM%cmsa.Berkeley.EDU
From: SPGDCM%cmsa.Berkeley.EDU@UCBVAX.BERKELEY.EDU.UUCP
Newsgroups: mod.telecom
Subject: Hold Circuit
Message-ID: <8612110705.AA22744@ucbvax.Berkeley.EDU>
Date: Fri, 5-Dec-86 01:45:44 EST
Article-I.D.: ucbvax.8612110705.AA22744
Posted: Fri Dec  5 01:45:44 1986
Date-Received: Sun, 14-Dec-86 10:48:14 EST
Sender: daemon@ucbvax.BERKELEY.EDU
Organization: The ARPA Internet
Lines: 33
Approved: telecom@xx.lcs.mit.edu


 Years ago I saw (I think in an electronics hobbyist magazine) a very simple
 circuit which one could add to any phone to gain an illuminated "hold"
 function. It worked on regular twisted-pair phones; it worked only on the
 phone you wired this way. As best I remember it, it was something like a zener
 diode, a resistor, a temporary-connect push-button, and an led; maybe a neon
 light instead but I think not.

 The concept was that once your button made the connection, the zener diode
 effectively shorted the line enough to hold onto the circuit (one would need
 to draw the voltage down to say 10v). Then if any other extension went
 off-hook, it would draw the line down to 5v. which somehow dropped the zener
 out and it let go, as a good hold should. The LED got activated properly
 somehow so that it glowed on the held instrument until an intercept or that
 instrument went off-hook and dropped hold.

 Now I am really sad I lost the diagram, because I want to add hold to all my
 phones. Costs too much to upgrade them all when I could add this instead for
 say $2-4 each.

 Anybody know the circuit? Especially useful would be the exact component
 values, preferably within the set widely available such as Radio Shack, or if
 necessary with a source of supply if the values are rare.

 P.S.: unfortunately many commonly-sold phones still don't offer hold, but even
 worse, many offer what I would like to see called "false-hold": you can flip a
 dumb toggle or slide switch on the phone to "hold" the line, but must shut
 that particular switch off to unhold; really a mute toggle, not a hold. Some
 store's ads (such as San Francisco Macy's) call this hold, and you waste a
 visit to the store. Some mail-order houses have had to resort to calling the
 correct feature "true-hold". Hmmm... as if you had to see words like "real
 food" or "true-movies" in ads or else get cheated...
 Thanks, Doug