6 May
2005
6 May
'05
1:21 a.m.
I've been thinking about a way to interface a footswitch to my
computer for triggering things like sooperlooper and fweelin. I've
got a sustain pedal for my MIDI controller on the way, but it got me
thinking. I've got a perfectly good serial port on the back of my
computer, doing nothing. I'd like to put it to work, but my hardware
skillz are, well, lacking.
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.
Any hardware hackers out there? Am I crazy? I suspect there's more
to it than what I've said here. Could I wire up a TRS jack and a TS
jack and plug in my amp footswitch (2 switches) and a sustain pedal?
6 May
6 May
1:49 a.m.
Does your computer have a parallel port? There are tons of examples on
the web of how to do simple digital IO on the parallel port. Even if the
port itself is unidirectional, there are a couple of status lines (busy,
paper out) that can be read.
m
On Thu, 5 May 2005, Paul Coccoli wrote:
I've been thinking about a way to interface a
footswitch to my
computer for triggering things like sooperlooper and fweelin. I've
got a sustain pedal for my MIDI controller on the way, but it got me
thinking. I've got a perfectly good serial port on the back of my
computer, doing nothing. I'd like to put it to work, but my hardware
skillz are, well, lacking.
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.
Any hardware hackers out there? Am I crazy? I suspect there's more
to it than what I've said here. Could I wire up a TRS jack and a TS
jack and plug in my amp footswitch (2 switches) and a sustain pedal?
4:59 a.m.
Paul Coccoli wrote:
<snip>
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
anything.
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
Rob
12:24 p.m.
On 5/6/05, Rob Fell <robin.fell(a)ntlworld.com> wrote:
1. RS232 is nominally a +/- 13v (ish) system - you
don't want to ground
anything.
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).
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? Where do the resistors
go? Between DTR and the 3 switches and RTS and the 3 switches?
I'm going to refrain from making an ASCII diagram and hope I've made
myself clear.
Thanks for the suggestions, Rob.
As for the other suggestions, my box does not have a parallel port or
a gameport (Shuttle XPC). I think I can add a parallel port, but that
would cost money. I've seen a number of DIY parallel port digital
joystick interfaces, and apparently some of them even have kernel
support. A joystick port would be great, since it gives you four
analog signals (expression pedals/MIDI CCs). Alas, all I have is the
lowly serial port.
3:50 p.m.
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 :)
Rob
11:37 a.m.
hi
the gameport is another interesting port to use. plenty of schematics
on the web. you can connect variable resistors, not just switches.
maarten
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5 comments
4 participants
participants (4)
-
Maarten de Boer -
michael＠michaelshiloh.com -
Paul Coccoli -
Rob Fell