[GreenKeys] A reliable current-loop-to-RS232 converter

Fri Aug 14 17:00:52 EDT 2015

Interesting and simple design. This circuit does away with the buffer transistors I added between the RS-232 interface and the TTY for both transmit and receive.
On transmit to the TTY, I was worried about the +15v swing allowed by the RS-232 input exceeding the Vbe spec of the PNP transistor, so I used input transistors to hide the RS-232 signal from the PNP transistor that drives the TTY receive loop.
On receive from the TTY, I used a transistor to buffer the signal to the RS-232 output. This solution drives it directly from the loop. 
Mike

     On Friday, August 14, 2015 12:45 PM, Jeff Albrecht <jeffa at rodaw.com> wrote:

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