Foot pedal for CTRL key

[George]

I would like to modify my PC keyboard so that some of the keys may
be "depressed" with a foot switch. At the moment I need the Control
key to work that way.

There's a 40-pin encoder chip in the keyboard, and with my voltmeter
I found that one of the pins goes from near gound to near +5V when
either Control key is depressed. Is it possible that I could just
connect lines to that pin and the Vcc pin, and bring them out to the
momentary foot switch? Or would that likely make the keyboard
release it's captive smoke?

It's not obvious to me how the key matrix works, but it almost has
to be some kind of polling operation.

The keyboard is your average Keytronic.

 

[George]

Never mind. I found the row and column, and installed the momentary
foot switch across them. Works fine.

 

[Jim Nagy]

Never mind. I found the row and column, and installed the momentary
foot switch across them. Works fine.

But be careful of static discharges that could damage the chip.
Personally, I'd put two 220 ohm resistors at the keyboard, each one in
series with one of the wires that goes to the footswitch. If it still
works bigger resistors, all the better.

 

[George]

But be careful of static discharges that could damage
the chip. Personally, I'd put two 220 ohm resistors at
the keyboard, each one in series with one of the wires
that goes to the footswitch. If it still works bigger
resistors, all the better.

Yes, I've got a 1K on each line, and it still works, which
kinda surprised me. I was also thinking of putting a cap
across the pair on the switch side of the resistors, but
don't know if that really helps anything, or what value to
use.

 

[Jim Nagy]

Yes, I've got a 1K on each line, and it still works, which
kinda surprised me. I was also thinking of putting a cap
across the pair on the switch side of the resistors, but
don't know if that really helps anything, or what value to
use.

Personally, I would just leave it exactly as you have it. I really
think the cap might cause more grief than help.

 

[YD]

I would like to modify my PC keyboard so that some of the keys may
be "depressed" with a foot switch. At the moment I need the Control
key to work that way.

There's a 40-pin encoder chip in the keyboard, and with my voltmeter
I found that one of the pins goes from near gound to near +5V when
either Control key is depressed. Is it possible that I could just
connect lines to that pin and the Vcc pin, and bring them out to the
momentary foot switch? Or would that likely make the keyboard
release it's captive smoke?

It's not obvious to me how the key matrix works, but it almost has
to be some kind of polling operation.

The keyboard is your average Keytronic.

Sounds like a great idea for speed typists. Make a pedal board for
Shift, Control, Alt and Esc keys, frees up the fingers for the actual
typing.

- YD.

 

[N. Thornton]

Sounds like a great idea for speed typists. Make a pedal board for
Shift, Control, Alt and Esc keys, frees up the fingers for the actual
typing.

No sooner is a concepts shown to work, than someone tries to take it
to the max. How could we do that?

Perhaps an additional set of nose operated number keys, along with
elbowed control keys? We could put escape and shift on the eyebrows,
and space on the tongue to save a bit more time. Maybe put some of the
most common letters on toes...

I'm trying to picture our typist of the future Perhaps sticking
with the OP's more conservative plan would be best.


Regards, NT

 

[John Woodgate]

I read in sci.electronics.design that N. Thornton <[email protected]>

I'm trying to picture our typist of the future Perhaps sticking
with the OP's more conservative plan would be best.

Nah! Unimaginative. Think of a five-manual pipe organ, with a pedal
board of course. Specifically designed for multitasking!

 

[TSmith1315]

No sooner is a concepts shown to work, than someone tries to take it

to the max. How could we do that?

Perhaps an additional set of nose operated number keys, along with
elbowed control keys? We could put escape and shift on the eyebrows,
and space on the tongue to save a bit more time.

Escape should be linked to the pucker string!

The mouse gets in *my* way, gotta let go of the keyboard to reach for it...
So, how 'bout an Apache-helicopter-style helmet that monitors eye position to
control the pointer, and blink the R/L eye for the corresponding mouse click?

Tim

 

[Jim Thompson]

I would like to modify my PC keyboard so that some of the keys may
be "depressed" with a foot switch. At the moment I need the Control
key to work that way.

There's a 40-pin encoder chip in the keyboard, and with my voltmeter
I found that one of the pins goes from near gound to near +5V when
either Control key is depressed. Is it possible that I could just
connect lines to that pin and the Vcc pin, and bring them out to the
momentary foot switch? Or would that likely make the keyboard
release it's captive smoke?

It's not obvious to me how the key matrix works, but it almost has
to be some kind of polling operation.

The keyboard is your average Keytronic.

I've used a shift register inserted in series with the keyboard
cabling to capture certain keystrokes to operate monitor switching.

You might modify such an approach to accomplish what you want.

Or simply wire a switch in parallel with the appropriate key?

...Jim Thompson

 

[N. Thornton]

The mouse gets in *my* way, gotta let go of the keyboard to reach for it...
So, how 'bout an Apache-helicopter-style helmet that monitors eye position to
control the pointer, and blink the R/L eye for the corresponding mouse click?

I assume thats what will happen one day, more or less.

Regards, NT

 

[George]

Personally, I would just leave it exactly as you have
it. I really think the cap might cause more grief than
help.

Upon reflection, I think the school-approved solution here
would be to install a 5V zener diode from each line to
ground. That would prevent any excursion outside the range
of -0.6V to +5.1V, and should prevent any static damage
without affecting normal operation at all.