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

Rob Fell robin.fell at ntlworld.com
Fri May 6 13:58:06 EDT 2005

Paul Coccoli wrote:

> Hmm...so if DTR is set to +13V (0) and RTS is set to -13V (1) for
> example, then I can use switches connected to CD, DSR, and CTS so that
> each pin can read 0 or 1.  Is that correct?  

That sounds correct.

 > Where do the resistors
> go?  Between DTR and the 3 switches and RTS and the 3 switches?

I'd be inclined to put series resistance onto each DB9 pin you utilise. 
  In the event of a damaged cable this would limit any short circuit 
currents to levels which shouldn't cause irreparable harm.

If it were my motherboard/serial-port, I'd find the highest value 
resistance that reliably works between DTR and an input (hint: use a 
variable resistor and measure it's value when disconnected): I'd then 
use fixed resistors of at most half that value.

> Thanks for the suggestions, Rob.

You're welcome.  I look forward to seeing a footswitch-virmidi app soon :)


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