Detecting a telephone RING

(Circuits -> Telephone)
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From: Aurel Boisvert

My computer is in the basement and this device tells me if the phone line is in use. I have inserted a N/O switch in the battery connection so that the batteries will last longer as sometime my sons spend a lot of time on the phone. Prior to using my modem I press the switch to find out if the line is busy.

                         2N3906         33K          2N3904
        2.2 meg            /----------/\/\/\---+      /------+
                         |/                    |    |/       |    ***
Tip o--/\/\/-----+-------|   PNP               +----|  NPN   \    220
                 \       |\                         | \      /
                 / 330K    |                           |     \
                 \         |             +-------------+     |
Ring             |         |             |             |    ---
    o--/\/\/-----+         |             O -           |    / \ Led
       2.2 meg   |         |        3V                 |     |
                 |         |             O +           |     |
                 |         |             |             |     |
                 +-------------------------------------+     |
                           |             |                   |
                           +-------------+-------------------+

** This resistor may have to be lowered to match the led used. Use alkaline battery, they last longer.


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