>>-----------------+------+---->> phone line
| |
| o
| /
| / momentary switch
| |
| /
| \ 1200 Ohm
| /
-----____|
/ \
/___\ SCR
|
/
\ 600 Ohm
/
| ^^
----- //
/ \ //
/___\ LED
|
|
>>-----------------+--------->> phone line
Sources
- Terri Barber barber[at]beowulf.ucsd.edu