Denny’s OpenBSD Newbies blog

Those of you who are hearing mplayer for the first time
should certainly see this article.

It is the best multimedia application out there and it is
written in pure C. It is amazing stuff. A grand old project
with an amazing cornucopia of features.

Those of you who have not heard of the footpedal do
not need to worry. It is a footrest with three buttons
which you can press with the toe.
Here is a picture.

Foot Pedal

It connects via the 9 pin serial connector to the serial port
of the computer. Before we get to the technical details we
do need to know something about the medical transcription
industry.

Every technical problem needs a business goal to meet.
Sometimes it is not very obvious as in the case of academic
UNIX tools, but without having an appreciation of the real
purpose of the project, one cannot do well in business.
Technical solutions do not exist in isolation.

Medical transcription is the process of converting a doctor’s
voice recordings into English text. The doctor would have
spoken at varying speeds and with different accents. A
medical transcriptionist has the job of translating his spoken
words into the written word.

I am sure you can imagine that this is no easy task. The
transcriptionist has to listen to the dictation multiple times
at various speeds to figure out what on earth the doctor is
trying to say.

His/her fingers are typing the message in the audio, and you
wish to be able to rewind, pause/play and fast forward the
recording with the foot. That is where a footpedal comes in.
You can’t use the mouse or keyboard for this since the hands
are busy typing out text.

While the hand is typing the foot will be interacting with the
audio player to help the transcriptionist to accurately translate
the dictation into English text.

The footpedal is a passive device with no power and no moving
parts. There are 3 switches as you can see above. The left pedal
is connected to the DSR pin(8), the middle pedal is connected to
the CTS pin(6), and the right pedal is connected to the DCD pin(1).

I figured this out using a perl script given here.

use Device::Modem;

  my $modem = new Device::Modem( port => ‘/dev/tty00′ );

        /*
        if( $modem->connect( baudrate => 9600 ) ) {
            print “connected!\n”;
        } else {
            print “sorry, no connection with serial port!\n”;
        }
        */

        my %sig = $modem->status();
        for (‘CTS’,'DSR’,'RLSD’)
        {
                if($_ =~ /RLSD/) {
                       print “Signal DCD is: “, ($sig{$_} > 0 ? ‘on’
: ‘off’), “\n”;
                } else {
                       print “Signal $_ is: “, ($sig{$_} > 0 ? ‘on’
: ‘off’), “\n”;
                }
        }

The next thing to do was figure out a way to do this in C.
That was the hard part but I got there. Check out the code
in this page to interface with the serial port on Windows
and OpenBSD to recognize the pedal presses.

Okay now we are halfway through. We can recognize
the pedal presses. But how to interface with the
audio player?

Before that we have an even more important question
to tackle.

Which player should we use?

I started working on audacity but quickly realized that
it does not have the rewind and forward feature. Plus
I realized that most audio players don’t have this at all.
Except of course mplayer. But before that I considered
and rejected sox and vlc.

I looked at the mplayer input.c file, the way it interfaced
with the joystick and LIRC remote control. I know I could
copy the semantics and match it with key presses. I did the
project first on OpenBSD and then got it working under
Windows. It was a great project, I thoroughly enjoyed it.

All the code in beautiful syntax highlighted fashion with
black background is here.

However the work is not over yet. You need to recognize
the pedal presses with more care. Right now it is too
sensitive so to speak. It has to have some back pressure
and hysteresis. I need to understand the needs of the
medical transcriptionist better. I shall finish this project
and add these details later. At the moment, I can say
that the project is nearly over.