

        ================================================================

               D A S (DTMF ACCESSORY SQUELCH) APPLICATION NOTE 1

                  OPERATING WITH FEWER CONTROLS AND INDICATORS

                                  951105/Iss-1
        ================================================================


                               Paul Newland, ad7i
                              Post Office Box 205
                               Holmdel, NJ  07733
                                 ad7i@tapr.org


           ----------------------------------------------------------
           |        Copyright (c) 1995 by Paul Newland, P.E.        |
           |   All Rights Reserved.  This guide may be reproduced   |
           | by radio amateurs for their own personal use, provided |
           | this copyright notice is included in any reproduction. |
           ----------------------------------------------------------

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      *                             NOTES                               *
      *                                                                 *
      *  SPECIAL TYPESETTING FUNCTIONS (I.E., FOOTNOTES, ITALICS,       *
      *  ETC.) ARE MARKED WITHIN THE TEXT USING A DOUBLE SLASH (LIKE    *
      *  THIS //).                                                      *
      *                                                                 *
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      INTRODUCTION
      ------------------------------------
        DAS (DTMF Accessory Squelch) acts like a switch connected in
        series between the speaker output of your VHF or UHF transceiver
        and an external speaker.  DAS will monitor a radio channel for
        you, with the speaker switch open so the speaker remains silent,
        until someone sends one of the DTMF sequences you have selected.
        When DAS hears your your personal Touch-Tone ID sequence on the
        radio channel it will light a LED, sound an buzzer and close the
        series speaker switch so that you can hear the audio of the
        calling station.

        An introductory discussion of DAS was published in //QST//,
        December, 1995, pages 25-31.  The "DAS Configuration Reference
        Guide", available from the TAPR FTP file server as well as the
        ARRL BBS//1, provides a more complete description of each
        programming option, the purpose of the option and how the various
        options may interact.

        This document, DAS Application Note 1, "Operating with Fewer
        Controls and Indicators", describes how to do just that for DAS



      DAS-AN1: OP W/FEWER CON & IND   -2-                     951105/Iss-1


        SELCAL operation, without significantly reducing functionality.
        Most users don't need all the switches and LEDs that DAS provides.
        Some users may not want any of those things.  This may be due to
        panel space limitations or just the desire that the operator face
        less stuff.  This application note describes how to get by with
        less in the area of DAS controls and indicators.


      DELETING THE MONITOR SWITCH
      ------------------------------------
        There's a simple work-around to avoid using (or even providing)
        the monitor switch.  Consider using the MICUP signal for monitor
        control.  Have two hangers -- one connected to MICUP and the other
        not connected to anything.  When the microphone is in the MICUP
        hanger DAS will be in the normal SELCAL mode with the speaker
        quiet.  When the microphone is in the other hanger (or in your
        hand) DAS will be in the monitor mode.  It's that simple.


      DELETING THE CLR SWITCH
      ------------------------------------
        As with the monitor switch, there's a simple work-around to avoid
        using (or even providing) the CLR switch.  CLR is only used to
        enter/exit the CONFIG mode and to clear the LEDs and relays.

        For configuration, you don't need the CLR switch -- you can simply
        press a clip lead to the correct contacts on TB1 in order to enter
        the CONFIG mode.  To exit the CONFIG mode issue the DTMF command
        "*0#".  That will get you out of the CONFIG mode just the same as
        pressing CLR.

        To clear the LEDs and the relays, you can configure DAS to treat
        every occurrence of the microphone leaving the MICUP hanger as a
        brief press of the CLR switch.  This function is active whenever
        the MICUP IS CLR option is set to ACTIVE.  To ACTIVATE this
        feature enter the CONFIG mode and issue the command *4161#.  After
        the command accepted flash code is displayed issue the command
        "*0#" to leave the CONFIG mode.

        With DAS so configured, when you want to clear the LEDs or relays
        just take the microphone out of the MICUP hanger.  That will be
        just like pressing and releasing the CLR switch.


      USING JUST ONE LED
      ------------------------------------
        You may not have noticed but the various detected SELCAL events
        (Personal, Group, LiTZ) are represented by different LED flash
        codes.  If the user doesn't need to easily and uniquely
        differentiate between all the various detected events, consider
        connecting all the LED driver outputs together to drive just one
        LED, instead of four separate LEDs.





      DAS-AN1: OP W/FEWER CON & IND   -3-                     951105/Iss-1


      DOING WITHOUT LEDS
      ------------------------------------
        If you don't care that you received a SELCAL call while you were
        out of the room (or car) you don't need to use any LEDs with your
        DAS unit.  In this case, if you hear audio from the speaker you
        know that either (a) you left DAS in the monitor mode (the
        microphone out of the MICUP hanger or monitor switch set to MON)
        and/or (b) your DAS unit detected one of the DTMF sequences that
        you configured into the system.  If that's all you need to know,
        you don't need LEDs.  One or two LEDs might be helpful during
        configuration, but they are not essential.


      NOTES
      ------------------------------------
        1.   TAPR FTP File Server ftp.tapr.org, look in /tapr/das.  TAPR
             on the Web at "http://www.tapr.org".  ARRL BBS, +1 860 594
             0306, 8-N-1, look in the FILES area, search on DAS.


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