Carlovision: Robust Tactile User Interface
(Controls Time Flow)
Robust Rocker Pot
With click detent at center of range.
roll over to see inside
(note: inside mirrored for clarity)
(Controls Scene Change)
(Allows Panel to Communicate with Computer)
USB I/O Board, Phidgets 8-8-8
(for pan within zoomed image)
(controls HDR display: Highs / Mixed / Lows)
(controls info display)
Robust Slider With Detents
Downward gives wider field multi-photo mosaics. Above the "full frame" click stop, a single photo is zoomed and pan joystick becomes active.
(controls admin mode)
(controls gaze direction)
Robust Continuous Rotation Sensor
With 16 detents representing original photograph directions
WHY NOT A MOUSE ?
There are many ways to control an image player, including excellent free ones like the mouse. So it's fair to question the wisdom of a complex piece of custom hardware like the shown "robust tactile user interface".
The justification for building a dedicated physical user interface are
Since only real-world use can inform UI design decisions, these bulky and expensive tactile UIs should be thought of as experiments in ergonomics and robust control design.
- the possibility of more logical controls
- vision undisturbed while controls operated (like driving a car)
- absolute values like gaze direction are obvious by feel
- special values like "time=stop" have click stops
- durability possible
This one-off 12" x 12" panel is designed to control playback of the Carlovision system.
Goal: clear physical correlation to the structure of the photosets.
This device was a substantial diversion from the main project, but served as an education in the making of multiple kinds of tactile controls, and making them able to stand up to rough use in a public setting.
Such robust tactile interfaces - with rotating and linear controls - are not easy things to create, and that largely explains their scarcity, and the prevalence of buttons, which are easier to ruggedize.
It was also an exploration into more general ways to communicate with a computer program beyond the traditional mouse and keyboard.
The sub-parts of this unit are discussed in more detail below.
ROBUST ROCKER POT CONTROL with MECHANICAL DETENT
A rocker pot is a partial rotation control with a horizontal rotation axis.
When deeply recessed behind a panel (as this one will be), they seem more linear than rotational, and give the user a good sense of absolute position.
In this embodiment, the fairly delicate sensor (a potentiometer, the silver cylinder at right), is fully protected from human abuse. It is turned by way of a miniature timing belt. A 2:1 pulley ratio allows more of the pot's range to be used, improving accuracy.
The user handles only the white Delrin disk with red ball, which can travel 90 degrees, no more. The disk is mounted to a 1/4" stainless steel shaft which freely pivots in the black Delrin body, although the action can be damped if desired for a stiffer feel.
The silver cylinder on the left is a roller-plunger, which engages a slot in the white disk to give a clear detent (a click you can feel) at the center of travel. This device is shown disassembled in the photo below.
The rocker pot above has a mechanical detent at its center of travel - red ball up - to tell the user he is at a noteworthy position (in this case "time=stop"). The roller plunger, at left, allows this to happen.
The assembly is essentially a spring-loaded wheel in a housing. The wheel, a tiny ball bearing, rolls along happily until it encounters a rut - the slot machined in the white disk above - at which point it drives into the rut. It takes more force to drive OUT of the rut, which is what causes the detent.
Key to feel of the detent are the ratio of the slot diameter to the wheel diameter, the spring force, and limiting the "wiggle room" of the wheel in its housing.
ROBUST CONTINUOUS ROTATION CONTROL with MAGNETIC DETENTS
In recent years, an interesting type of rotation sensor has come into common usage - the hall effect transducer. One like the example at right is at the core of this control.
These devices allow absolute rotational angle knowledge in continuous (or non-continuous) rotating systems. They are easy to integrate with microcontrollers, have no dead-zones, and, being of a non-contacting nature, have very long lives - 10 million cycles for this type.
Unlike potentiometers, they handle continuous rotation, and unlike quadrature encoders, they know where they are at powerup.
This control gives the user control over, and knowledge of, compass heading of the center of the currently displayed view.
Since the carlovision photosets contain 16 gaze directions, it seemed desirable for the gaze direction control to relate to this with 16 "soft detents" and continuous rotation.
A black Delrin block holds the pieces. The white control wheel (what the user handles) is rugged: mounted to a steel shaft which is ball bearing mounted to the block. The hall effect sensor (hidden, at left) is isolated from user abuse by a timing belt transmission.
The unusual aspect of this device is the magnetic detents. A strong magnet is affixed just below the white disk, which contains a ring of steel pins. As the white disk rotates, it "soft clicks" to 16 preferred positions. The gap between the magnet and pins can be adjusted somewhat to vary the strength of the effect. Compared to mechanical detents, magnetic detents are fuzzier and easier. The magnet is glued into the aluminum tube.
The oscilloscope image at left shows the output of the hall effect sensor as the control is rotated. This voltage gets read by an analog input of the Phidgets 8-8-8 board and converted to a number. Periodically, the player program running on the attached computer requests these (and other) values via USB.
SLIDER CONTROL with MECHANICAL DETENTS
This control gives the user control over, and knowledge of, zoom level of the currently displayed view. As the user pulls back, mosaics are shown with more and more views. There are detents at meaningful points, like "single original photo, full", pushing forward past this puts the system in sub-frame zoom.
Compared to rotating, pushing and toggling type controls, robust translating (slider) controls are expensive and / or difficult. As for the sensors, there are several approaches to turning linear displacement into some measurable electrical value.
It's tempting to use the familiar inexpensive linear pots like those shown in A, but they are not robust: the sensing element is exposed and vulnerable to spills, and the movement is vulnerable to physical abuse.
The industrial-grade version shown in B are quite expensive (several hundred dollars) and that's just for the sensor, not counting the user control. Ditto for the interesting "string pull" sensors like the one shown in C.
My control, shown in the animation and exploded diagrams below, used the not uncommon trick of tying a multiturn pot to the linear control via a timing belt loop. The multiturn pot (blue object in animation below), is fully enclosed and protected from user abuse.
A smooth and durable traveler mechanism takes some care to achieve. This one uses a pair of precision 1/4" shafts and a traveler with teflon bushings.
The traveler has a roller plunger, like the one described above, which allows detents. The placements of the detents are determined by the slots cut on the detent bar.