[GreenKeys] i-Telex Coming Soon to N4TTY QTH

[Jeffrey D Angus]

On 11/20/2016 9:43 AM, COURYHOUSE at aol.com wrote:
> ok without the call control unit  is that  still a problem to  on / 
> off  the
> machines  or  has that  been  taken care of?
The way a call control unit interfaces with the TW39 line is dependent on
two things. Line current and polarity.

A minimum "idle" current of 5-7 mA to show the machine is there.
Increasing the current to 40 mA is "off hook"
Once that far connection has been made, the polarity reverses to
show it it connected (and starts the machine motor via a relay.)
For incoming calls, the polarity reverses, the call control unit increases
the line current to 40 mA and starts the motor via a relay.

The simple method, but requires a bit of board surgery, is to jumper the
polarity relay and use the polarity relay control signal to close a motor/
machine power replay.

Setting a command on the TW39 board allows for dialing via the key-
board rather than requiring a pulse type dial in series with the line.

It still requires changing (shorting out) an additional resistor in the 
local
loop to increase the current from 7 mA to 40 mA. Typically a 6200 ohm
resistor.

The call control units do this all automatically.

The TW39 cards on the i-Telex "box" do all the work to emulate a TW39
central office connection to the local loop (usually) via a call control 
unit.







-- 
Jeff-1.0
wa6fwi
http://www.foxsmercantile.com

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