m21198@mwvm.mitre.org (John McHarry) (11/21/89)
A couple weeks ago there was some discussion here of how to force an answering machine off the line when another extension is picked up. There was mention of a device from DAK that will do the trick, putatively using some sort of thyrister device. A simple resistor- capacitor circuit was also contributed. My circuit is even simpler than the RC solution, and has some slight advantage. All that is necessary is to hook a 9 volt, 1 watt zener diode in series with the answering machine, or other device one wants to be able to over-ride. This works because phones drop somewhat less than 9 volts when off hook, effectively shutting off the zener. My answering machine tends to continue to blare until it has finished its announcement: The turned off zener provides enough isolation that it cannot be heard from the far end, and you have to listen for it on the other extension. Of course, there are a couple of caveats: If you are on a very long loop, this may not work due to the extra 9 volts drop across the zener. Also, some electronic phones drop close to 9 volts themselves. In that case, a 10 volt zener might do the trick. Also, I think it was stated that you can cascade the DAK devices: I don't think that would work well with zeners as the voltage drops would add, but the zeners are less than 50 cents each. I guess you get what you pay for, at most. The usual disclaimers: This is my own hack, and not endorsed by my employer or anyone else. Also, I'm not Drano: Your pipes are on their own! *************************************************************** * John McHarry (703)883-6100 M21198@MWVM.MITRE.ORG * ***************************************************************