At 08:37 PM 12/17/97 -0800, you wrote:
>At 10:03 PM 12/17/97 -0500, Wynn Rostek wrote:
>>For US POTS, if you add a series resistor (100 ohm max) in each line, and
>>then place a pair of zeners (20-30 volt) across the line (both polarities)
>>you can clip the ring signal at that phone so it will not ring.  It won't
>>ever ring.
>>
>>----------/\/\/\--------|-------|--------
>>                        |       |
>>                       ___      V
>>                        ^      ---
>>                        |       |
>>                        |       |
>>---------/\/\/\--------------------------
>>
>>By cliping the ring voltage below 30 volts, you prevent the ring detect
>>circuit from being activated.
>
>Unfortunately, the circuit drawn here will clip the voltage down to about
>0.7 volts.  You have forgotten that zeners still are normal diodes in the
>forward direction....  Simply place the zeners in series instead of
>parallel, and your circuit should work fine, however.
>
> - Rick "Go with the flow" Dickinson
>
>

Rick, you are absolutely right, but I think that one more clarification is
in order, the zeners should be in series, but the series combination of
zeners should be placed in parallel with the line:

<copying an ascii drawing because I am so bad at ascii drawing>

----------/\/\/\------------|--------
                           ___
                            ^
                            |
                            V
                           ---
                            |
                            |
---------/\/\/\----------------------

Hope you don't mind my clarification,

Sean



+--------------------------------+
| Sean Breheny                   |
| Amateur Radio Callsign: KA3YXM |
| Electrical Engineering Student |
+--------------------------------+
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