---- START NEW MESSAGE --- Received: from cherry.ease.lsoft.com [209.119.0.109] by dpmail10.doteasy.com with ESMTP (SMTPD32-8.05) id ACF23EA016E; Fri, 30 Jan 2004 11:13:54 -0800 Received: from PEAR.EASE.LSOFT.COM (209.119.0.19) by cherry.ease.lsoft.com (LSMTP for Digital Unix v1.1b) with SMTP id <14.00CC50C4@cherry.ease.lsoft.com>; Fri, 30 Jan 2004 13:11:13 -0500 Received: from MITVMA.MIT.EDU by MITVMA.MIT.EDU (LISTSERV-TCP/IP release 1.8e) with spool id 2851 for PICLIST@MITVMA.MIT.EDU; Fri, 30 Jan 2004 13:11:06 -0500 Received: from MITVMA (NJE origin SMTP@MITVMA) by MITVMA.MIT.EDU (LMail V1.2d/1.8d) with BSMTP id 5586; Fri, 30 Jan 2004 13:10:11 -0500 Received: from ctb-mesg4.saix.net [196.25.240.76] by mitvma.mit.edu (IBM VM SMTP Level 430) via TCP with ESMTP ; Fri, 30 Jan 2004 13:10:10 EST X-Comment: mitvma.mit.edu: Mail was sent by ctb-mesg4.saix.net Received: from workshop (npwn-ip-nas-1-p06.telkom-ipnet.co.za [155.239.199.6]) by ctb-mesg4.saix.net (Postfix) with SMTP id 0727EC0A0 for ; Fri, 30 Jan 2004 20:10:05 +0200 (SAST) References: <004701c3e6cd$db2009e0$7b01a8c0@Paradise> MIME-Version: 1.0 Content-Type: text/plain; charset="windows-1255" Content-Transfer-Encoding: 7bit X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook Express 6.00.2800.1158 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2800.1165 Message-ID: <016c01c3e75b$f39d0520$6700a8c0@telkomsa.net> Date: Fri, 30 Jan 2004 18:27:16 +0200 Reply-To: pic microcontroller discussion list Sender: pic microcontroller discussion list From: gtyler Subject: Re: [EE]: DIAC question To: PICLIST@MITVMA.MIT.EDU Precedence: list X-RCPT-TO: Status: U X-UIDL: 371856540 A pnp and an npn connected like a SCR with a zener between the bases to set the voltage? George ----- Original Message ----- From: "Russell McMahon" To: Sent: Friday, January 30, 2004 3:10 AM Subject: Re: [EE]: DIAC question > > i forgot to attach the circuit so maybe you can take a look at it. > > > > I need a 10v diac for a circuit I want to test and cant get one. > > > can I use 2 reverse zeners in parallel as a diac? > > Presumably the aim is to provide a defined length pulse of relay operation > when a ringing burst occurs. > > D1 provides power from "ringing" signal to operate relay. > D3 blocks input from transistor unto Vin rises to some threshold. > C2 charges. > When D3 fires the voltage across it drops to ~~ 0 and C2 provides a pulse of > energy limited mainly by R3. This sets an on time pulse length. R2 is > intended to be large enough that it charges R2 BUT will not hold the > transistor on. > > Adjustment of R2 may cause other action (eg relay stays on via R2 drive if > R2 too low etc) > > While zeners will give you the hold off action of the diac, zeners will NOT > directly duplicate the diac operation here because they do not break down to > a low voltage when they conduct. > > A circuit that emulates the desired operation could be designed without too > much effort. > If you can specify as closely as possible what you actually want the circuit > to do and the input conditions etc then a cct may well arise. > > eg Input is 50 Hz 20 VAC RMS "ringing signal" with a 1 second on, 2 seconds > off cadence. When ringing input is applied the relay should operate with a > 100 millisecond pulse per 1 second burst of ringing .... or whatever. > > A pair of (gasp) 555 timers could be made to do this job easily. A > CD40106/74C14 also. Other possibilities exist. A minimum change version of > the cct you have now may be the best way. > > > > Russell McMahon > > -- > http://www.piclist.com hint: The PICList is archived three different > ways. See http://www.piclist.com/#archives for details. > -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email listserv@mitvma.mit.edu with SET PICList DIGEST in the body .