I built the functions of a mouse into a footrest so I could compose and edit text without breaking my train of thought and taking my hands off the keyboard to fumble with a conventional mouse or trackball. Commercial foot operated mouses are available for up to $1500, but I do not care for the way they are implemented. My version can be built for under $30. Disclaimer: I am not actually a computer geek, I just play one on the Internet.

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Step 1: Components and Tools

Components
PVC architectural plastic sheet for foot board, 1/2 inch thick (actual 0.470), 17 inches by 22 inches, chosen because it is slick and because I had some scraps.
1 optical mouse; Targus model PAUM004U because it was on sale nearby for $10; reconditioned ones are available for that price via the internet.
2 roller lever switches, Radio Shack #275-017A, $4 each, order or find walk-in store that stocks them at radioshack.com.
7 feet clear plastic tubing, 1/2-inch inside dia, 3/4-inch outside dia.
Screws for fastening tubing to foot board, 1-inch long #6 phillips pan head, and washers.

Tools
Woodworking tools. If motorized tools are used on plastic, they should be run at very slow speed.

Step 2: Background

I have long wanted to make a foot operated mouse, but a conventional ball mouse can send unwanted pointer commands if its body is jiggled, as would happen with foot movements. An optical mouse does not, and they have recently become cheap. I wanted the feet to perform mouse functions using gross foot movements that would not cause fatigue. Each foot has a defined rest position that allows for some fidgeting without sending mouse commands. Sliding the left foot forward from the rest position makes a left click, and rotating that foot and sliding it forward makes the less-used right click. Pointer motion is achieved by lifting the right foot slightly and moving it over the upturned mouse. I had no need to implement the scroll wheel.

The mouse is oriented the same as if used conventionally, with its wire tail aimed away from the user, but rolled over belly up. Sliding the foot left causes the pointer to move left across the screen, and sliding the foot forward causes the pointer to move down. This latter may be disorienting for some users, and the vertical movement can be reversed using the mouse control setting offered by some operating systems. You can also download Sakasamouse, which will allow you to change the direction of either or both mouse axes, and restore them, anytime you wish http://hp.vector.co.jp/authors/VA026826 . I adjust the pointer speed to the lowest setting.

I operate my footmouse with slippers that slide easily because their plastic soles have become slick with use. The same effect could be achieved by pulling XXL size men's cotton socks over slippers or even street shoes (You know what they say about men who have big feet. That's right, it means they have big socks). Size of the foot board and locations of the elements depend on the size of the user's feet and their comfortable rest positions.

Step 3: Foot Board Layout

I outlined my dainty size 8 men's slippered feet on paper, at their rest positions and also where they would fall when operating the click buttons and pointer. I marked the openings for the left- and right- click switches and the spot for the pointer sensor. The left-click switch is actually a half inch to the left of the foot centerline, and the right-click switch is a half inch to the right of the foot centerline. One inch of foot travel would click a switch, and another inch and a half of travel would hit a bumper. Together these determined the shape and location of the plastic tubing rails that would confine my feet and guide their movements by feel. I replicated the curve at the left foot toe onto the right front corner of the foot board, for symmetry and stability then drew a half-inch edge outside the tubing. The blue object is a handy drawing aid that will hold a curve once bent, Alvin Curvex 1022-24. The paper pattern was cut around its perimeter and used to transfer positions of all the elements onto the foot board by poking through the paper with a sharp stylus.

Step 4: Foot Board Openings

Switch slots
photo 1: With switch located at correct depth in this material, tops of switches' mounting holes align with bottom surface of foot board.
photo 2: Location of a slot and its axes marked on tape
photo 3: Material is removed by drilling
photo 4: Slot is cleaned up using Dremel tool with spiral bit and router attachment. Wood blocks cut and sanded to length define the width of the slot as 0.25 inch, for a sliding fit with the switch, and the distance between them defines the slot's length at one inch. I filed down two small pips on the sides of the switches to make them even with the bosses that surround the switches' mounting holes.
photo 5: The upper edges of the slot are rounded over using small flat and round hand files.
Mouse cutout
photo 6: The opening is drilled and the plug sawn out then it is cleaned up using big-boy router having speed control, spiral bit and pattern-following collar. For aesthetic reasons I had hoped to install the mouse in a recess in the bottom surface of the foot board, with its magic navel peering up through a small opening. This did not work because the foot must be very close to the mouse's tummy to engage the optical pointer control. I did not make provision in the opening to accommodate the rubber plug that provides strain relief for the mouse's cord, I just stuffed the entire plug up the mouse's wire hole.

Step 5: Mouse Modifications

photo 1: Removing one screw allows that end of the cover to be lifted then snapped off the base. Note the green rectangular click switches and the switch under the scroll wheel axle. The circuit board easily lifts out, which allows the scroll wheel to be removed.
photo 2: The cord reel can be discarded if desired by removing a screw and prying it open.
photo 3: Excess plastic parts snap off of the cover.
photo 4: Two1/4-inch dia hex-head bolts, one-inch long, washers inside and outside, fit through existing openings, the square one drilled to size.
photo 5: Bottom of the circuit board shows the two outboard solder connections of each click switch. A length of stranded hookup wire is soldered to each. Switches may be left in place, but I unsoldered and removed both, plus the scroll wheel switch, for possible use in another project.
photo 6: Scraps of the foot board material aid bending two mounting brackets from sheet metal strip 1 inch wide, 0.080 inch thick. The brackets, shaped with the mouse assembled, will position the mouse's magic navel just below flush with the foot board's upper surface. Lock washers and nuts attach the brackets to the mouse's cover.

Step 6: Switch Mounting Clips

Switch mounting clips are heavy coat hanger wire, which exactly fits the switches' mounting holes, bent around two nails clamped vertically an inch and a half apart in a vise.

Step 7: Assembly

Mouse and switches are attached from beneath using sheet metal screws. The switches are mounted such that when the foot is slid forward, the toe will pass over the switch's body before hitting the roller. Wires from mouse switch solder pads are soldered to the common and normally-open terminals of the foot click switches. The two wires from the mouse's original left-click switch go to the foot left-click roller lever switch, right goes to right.

My foot board sits higher than it needs to, but I could not resist these white metal door stops for legs. Prying off the rubber tip reveals a screwdriver slot that aids in installation. I pre-drilled holes in the underside of the board, without going through, partially screwed a doorstop into each hole to create threads, then backed it out. I then ground the tip off the auger of each doorstop so they would not go through the foot board, then screwed them snugly into place.