[linux-audio-user] [OT] DIY serial input devices?

Rob Fell robin.fell at ntlworld.com
Fri May 6 03:07:31 EDT 2005

Paul Coccoli wrote:

> I've figured out this much: you can wire a simple loopback by
> connecting DTR to DCD and DSR and connecting RTS to CTS.  What if you
> insert a switch between these?  E.g. connect RTS to the sleeve pin of
> a female 1/4" TS jack and CTS to the tip pin.  Could you then plug in
> a sustain pedal?
> I've seen software that monitors the state of the pins on the serial
> port, so I'm not worried about that part.  I'm just not sure if the
> hardware would work.  Like when the switch is open, do you connect CTS
> to ground?  I don't know enough about this stuff.

Hello Paul

The answer is - it depends a little on your hardware :)

A few points;

1.  RS232 is nominally a +/- 13v (ish) system - you don't want to ground 
2.  It's an I/O port, and should be safe against short circuits, but I'd 
recommend using at least 1K series resistance when you're poking around 
there :)
3.  The RS232 inputs should have pull-ups/downs to bring them to valid 
levels when disconnected.

In summary - with 99% of normal sane hardware, it should work (but I'd 
recommend the precaution of a 1K resistor).

Best of luck

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