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Some PCs serial ports can have levels of -15 volts and +15 volts (while still adhering to the RS232 specification). However, the E3 input circuitry may be designed for levels of 0 volts and 5 volts. If you're feeling protective of your E3, then using the following circuit may put you mind at rest. It works fine for ''my'' E3 and mind. Some PCs serial ports can have levels of -15 volts and +15 volts (while still adhering to the RS232 specification). However, the E3 input circuitry may be designed for levels of 0 volts and 5 volts. If you're feeling protective of your E3, then using the following circuit may put your mind at rest. It works fine for ''my'' E3 and mind.
Line 4: Line 4:
  9-pin 3-pin   9-pin 3-way
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(0V) 5 o----------------+-------------+-------------o Sleave (0V) 5 o----------------+-------------+-------------o Sleeve

Some PCs serial ports can have levels of -15 volts and +15 volts (while still adhering to the RS232 specification). However, the E3 input circuitry may be designed for levels of 0 volts and 5 volts. If you're feeling protective of your E3, then using the following circuit may put your mind at rest. It works fine for my E3 and mind. 

   PC                                               E3
  9-pin                                           3-way
D-connector                                     jack plug 

               100R
(Tx) 3 o------/\/\/\----+-------------+-------------o Ring
             resistor   |             |
                        |           \ |
                       ---           ---
                        ^  IN4148     ^ \ BZY88 4v7
                       / \ diode     / \  zener diode
                       ---           ---
                        |             |
                        |             |
(0V) 5 o----------------+-------------+-------------o Sleeve

(Rx) 2 o--------------------------------------------o Tip

TheEarthWiki: Serial_cable_for_the_paranoid (last edited 2008-02-19 15:39:25 by localhost)