To help - modification of the S-DOS modem.

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  From the editor: If the reader remembers
WP#2 described the main types of modems,
found application in Tashkent. If you help
thread under modem N2 was presented without
transformer modem. Introducing your -
I would like to add a small modification to it,
which will allow you to more conveniently
use this device.

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           Refinement of the S-modem


  The modem described in WP#2 can perform
Learn only the basic functions: transmission and
receiving an encoded signal through the port
#FE. Call and pick up the phone when
he is not able to call. For implementation
last functions need to be performed
simple modifications:

 1.Plug into the gap between the body and
load 1 kOhm additional transistor
KT940A or similar with Uek max > 160 V.
Connect output line D5 to the base of the trolley
port #FE register through a 1-2 kOhm resistor
and “suspend” it to the +5V bus through a resistor
torus 1.5 kOhm. Transistor KT815 is necessary
replace also with KT940A.

 2.Assemble the call sensor circuit according to the diagram:

    D817A,B 3 kOM D814D
+ ───┤<├──▒▒▒──┬──┤<├──┬──┤
LINE 10 kOhm│10x16V │
          ┌─▒▒▒──┴───┤├──┤ D5-IN
          │ │ ┌─ PORT #FE
          │ B |/ E──┘ │
          └────────|        │ 1.5 kOhmKTZ15B | K─────┴─▒▒▒─ +5V

NOTE:
Part values are approximate.