PS: let me modify it a bit.. how silly:


        ,-----------------.---------------- DTR
        |                 |           (low, i.e. +12V)
        |                 |
        \ 100             |
        /                 C
        \          ,---- B    NPN (BC547)
        /          |      E
        \          |      |
        |          |      |
        |    10K   |      |
5 ------*--/\/\/\--*      *---------------- RX
  4N25             |      |
4 ------.          |      |
        |          |      |
        |          |      E
        |          '---- B    PNP (BC557)
        |                 C
        |                 |
        |                 |
        |                 |
        '-----------------'---------------- RTS
                                     (high, i.e. -12V)


Where I will then change that 100 ohm resistor value in order
to balance the current going through the 4N25's phototransistor
(once I manage to measure it).

Thanks!
TPM

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