toddi@beaver.cs.washington.edu (Todd Inch) (11/29/90)
Someone (oops, lost the article) requested a phone-line simulator with some special needs which amounted to one side dropping current when the other side went on-hook. Ringing wasn't a requirement. Here's my favorite, assuming you don't need dialing to do anything in particular, don't need ringing of any sort, and don't need dial tone. (Yes, that limits its application a bit!) To phone, speakerphone, fax, other device | | | | 9 Volt ------- | Battery --- | | | | | To other phone, speakerphone, fax, etc. This works for everything I've ever tried. I've heard it'll even work for a couple of "dumb" FAX machines that don't listen for dial tone. If your speakerphones need lots of voltage, you might put a few 9 Volt batteries in series to increase voltage as necessary. On some (especially older) touch-tone equipment, the polarity has to be correct, so just reverse the wires if it goes "clunk" instead of "beep" when you press the buttons. (Not that the tones will actually DO anything with this circuit.) Turn those old phones you've got laying around into "field sets" for the kids to play with. Sorry, no ringing. Todd Inch, System Manager, Global Technology, Mukilteo WA (206) 742-9111 UUCP: {smart-host}!gtisqr!toddi ARPA: gtisqr!toddi@beaver.cs.washington.edu
dgc@math.ucla.edu (David G. Cantor) (12/01/90)
In Telecom V10, #854, Todd Inch <gtisqr!toddi@beaver.cs.washington. edu> suggests a circuity for a simple phone line simulator: Here is (in my opinion) a minor improvement: | | This differes from the original by the | | addition of the (load) resistor. The | | "battery" can be any DC supply from about | | 6 volts to 50 volts and the resistance | Line 1 | should be chosen so that about 20 ma | | flows when the lines are shorted. That is, | | R = 50 V, where R = restance in ohms and | | V = voltage of supply. Note that the telco | | standard has V=48 and R around 2400. None | | of this is critical. A slightly better --battery-\/\/\/ | simulator is made if the batter is shunted | | by a capacitor, on the order of 10 microfarads. | | | | | | | | | Line 2 | | | | | | |