switch relay question

[jasong]

I was wondering if I could use a switch relay from a 600 ohm impedence line? Actually this 600 ohms line is from an interphone that we are using for our paging system.

I'm trying to set up the system so that once somebody will dial the designated number to page, then the relay will automatically switch on the power of the amplifier.

Could anyone give me some feedback about this. Thank you.

[hermanv]

Many telephony switch boxes with a paging output port also offer a "sleeve" lead on that port (sometimes called the "busy" lead), this signal will typically transistion from ground to -48VDC when the channel (or port) becomes active. If you have such a signal then the rest is easy.

If not, some more information is needed: Does the 600 Ohm port also have DC (usually called battery feed)? This voltage again is typically 48V. If it is present, it will change substantially from the idle to busy state and can then be detected with an opto-isolator which can then drive the relay. Use a VOM accross the tip/ring leads to see if this happens.

The last resort is a voice operated switch. This detects the presence of small AC signals on the phone line and operates the amplifier. The voice switch solution often cuts off the leading edge of the voice signal and is not an ideal solution.

[jasong]

hermanv, thanks for your advice. I'm going to try exactly what you advised and get back to you with the results.

Thanks again.