Add Foot Pedals or Ergonomic Buttons to Your Computer Keyboard

Turn eSmacks sore knuckles into emacs excellence.

tappity-clunk-tappity-tap.

Overview

Pressing a button on a keyboard closes a circuit. Add a longer switch in parallel to a particular button by soldering/copper taping wire inside the keyboard. Use this switch as a foot pedal.

Magic

Because of TTL and long wires this shouldn't work. In fact, I lucked out the first time when adding a ctrl foot pedal. I've gone back and figured out the real trick for getting this to work consistently with any button.

Step 1: Solder Wires to Keyboard Circuit

Unscrew all visible screws. Then unscrew more. The Goldtouch, shown here, is DIY friendly.

Take off the out cover and the metal sheet. Like most modern keyboards, this one has plastic sheets with embedded circuitry, rather than real pcb.

First, the plastic sheets are likely melted together in two places. Depending on which keyboard key you're turning into a foot pedal, the togetherness of the plastic sheets may pose a problem. Simply cut out the offending portion with an x-acto or swiss army knife. or leatherman. or your bare teeth.

Second, to attach wires to plastic sheet circuits without melting the plastic requires copper tape. If you live around Boston let me know and I can hook you up with my massive left overs (I was hooked up by st* --- turn and turn about).

Solder to copper tape, then stick the tape to the circuit.

Where do I put the wires?

There are two plastic sheets with circuitry in them, plus a blank piece of plastic between them to insulate. This middle blank sheet has holes in it wherever the keyboard buttons are (circles), so that when one presses a button it pushes down and squeezes the circuit circles on the top and bottom sheets together, connecting the circuit.

Why does 'a' stop working?

If you obstruct the connection of two circle pads, eg increasing the distance between the pads with a solid object, the keyboard button may cease to work. Position the pads nearby (see TTL below), but not too close, and position the wires carefully. It took me a while to get the keyboard back together while retaining functionality in the entire alphabet. Getting all the sheets to fit together tight is key. Don't tighten the screws too much since you may have to undo/redo a few times.

Camera flash aside

Direct camera flashes have limitations. They give people and dogs devil eyes, and they cause bright reflections. Taping a thin tissue or paper towel over the flash helps a lot. One can also reflect the flash up to the ceiling using thin white cardboard (check your recycling).

TTL - How can this possibly work!?!?

You'll notice that each keyboard button does NOT have its own circuit. The layout is more like a grid, where buttons are part of rows and columns.

The keyboard has a dumb computer in it that sends out voltage across the grid to check which parts are making contact. You can think of this as the computer scanning the keyboard.

How much wire can we add to the circuit before it fails in the scanning?

The following I'm not sure about...mainly because contrary to concerns my pedal works fine with 3-4 ft of wire and poor but attempted twisting... but also because I didn't check this out with a volt/amp meter. Please post a comment if you do!

The scanning process introduces changing current. Changes in current mean we have to think about inductance and capacitance. If we add a bunch of wire, then we could be adding a bunch of inductance and capacitance, which will trick the scanning routine into thinking the pedal is closed when it's open or open when it's closed.

The inductance occurs because changes in current yield magnetic fields. Twisting prevents inductance. Know why? The current flowing down one wire creates a magnetic field that cancels out with the magnetic field created by the current flowing up the other wire.

Unfortunately, wires in close proximity increase capacitance, which is a voltage potential between two charged surfaces. When circuit wires are too proximal the differing charges creates crosstalk. With long wires one wants to spread them out.

When I finally had the foot pedal and was ready to solder it to the wires hanging off the keyboard I was prepared to guess and check to find the right wire length and twisting. It all worked the first time I tried so... maybe I got lucky.

Update

I did get lucky! I added leads for shift and tab in the keyboard, and neither of them work, although 'c' is now behaving like shift and c!

Furthermore, I apparently connect my foot pedal to one of the 'alt' leads and one of the 'ctr' leads hanging out of the keyboard. The first time I did this I didn't mark which of the four wires hanging out of the keyboard came from ctrl versus alt. I guessed and checked to find "the right ones". By chance I found the right ones... but the effects of TTL are definitely making themselves shown.

I will update this with the real tricks for getting this to work on other keys very soon.

Step 2: Make a Foot Pedal

A foot pedal is simply something sturdy and springy that holds a micro switch with wires that connect to the wires hanging out of the keyboard.

A simple pedal can be made by zip-tying a microswitch to something sturdy on the floor.

My third pedal is a switch tied to a loop around my foot. The switch is upside down on top of my foot. A second loop goes from the switch lever to my big toes (it's a sensitive micro switch with a one inch lever hanging off the side). Twitch my toe down for shift.

My first pedal is more of a pedal. This might make it too nonergonomic for some people. Razors make great microswitch bases, though--and there's an extra Razor hanging around MITERS right now!

Clay found a razor on the street the same time I was making this. Razors are kiddie scooters with a back break that is a metal piece with a spring attached. The rider pushes down onto the back wheel to increase friction. I used MITERS's bandsaw to hack the bottom of the scooter in two, salvaging the back part with the break for the foot pedal.

I removed the wheel. I tried putting on the spacers +- wheel bearings and using a switch with a lever arm in order to reduce wear on the switch (the harder one presses the more it rolls). In the end, the clunker of a switch I found fit nicely into the break piece. There's room yet to add a lever. And/or a spring.

I expected to spend a couple days getting used to ctrl-ing with my foot, but I found no problem making the apparently intuitive switch.

Adding shift and tab was immediately intuitive, too.