Touch surface for mobile devices using near field light sensing
A virtual touchscreen for mobile devices provides a touchscreen area displaced to a side of the display to eliminate problems of a finger blocking the display during normal touchscreen operation. The virtual touchscreen may be monitored by a sensor system looking edgewise from a housing of the mobile device employing as few as two displaced photodetectors and a correspondingly oriented light source constrained to sensitivity within a narrow fan-shaped light-sensing plane. Extraction of the spatial location of a finger touch within this touchscreen area may be performed by a model of reflected light signals of a finger in different locations calibrated to environmental parameters of finger reflectivity and background reflectivity by a simple calibration process.
1. A human interface device comprising:
a housing supporting a graphics display screen positionable against a surface;
at least two photodetectors supported by the housing to receive light along a light-sensing plane extending away from the housing over an area offset from the housing, the at least two photodetectors each receiving light from over a common region of the light-sensing plane and each producing a corresponding light-strength signal being a function of light received from over the common region of the light-sensing plane;
at least one light source to project light along the light-sensing plane; and
an electronic computer communicating with the at least two photodetectors and the at least one light source and executing a program stored in non-transitory medium to:
(1) independently measure the light strength signals reflected from the at least one light source off a finger within the light-sensing plane;
(2) apply values of the light strength signals to a model relating strength of the light strength signals to a distance between the finger and the given one of the at least two photodetectors and converting the distances to orthogonal coordinates defining points within the light-sensing plane; and
(3) control an output on the graphics display screen according to the orthogonal coordinates.
2. The human interface device of claim 1 wherein the graphics display screen provides a display surface parallel to the light-sensing plane.
3. The human interface device of claim 2 wherein the housing provides a greatest dimension along the display surface and a narrowest dimension perpendicular to the display surface and wherein the light-sensing plane is positioned within the narrowest dimension.
4. The human interface device of claim 3 wherein the housing is sized to fit atop of an average human wrist and includes a wrist strap for attaching the housing to the wrist in a manner of a wristwatch.
5. The human interface device of claim 3 wherein the housing provides a frame surrounding the graphics display screen to support the graphics display screen face upward and parallel to the surface during use.
6. The human interface device of claim 1 further including a collimator collimating the light from a fan-shaped acquisition region in the light-sensing plane onto the at least two photodetectors, the fan-shaped acquisition region having its widest dimension aligned along the light-sensing plane.
7. The human interface device of claim 1 wherein the model includes corrections for angular sensitivity variation of the at least two photodetectors within the light-sensing plane and angular sensitivity variations of the light source light output within the light-sensing plane.
8. A human interface device comprising:
a housing supporting a graphics display screen positionable against a surface;
at least two photodetectors supported by the housing to receive light along a light-sensing plane extending away from the housing over an area offset from the housing, the at least two photodetectors each receiving light from over a common region of the light-sensing plane and each producing a light-strength signal being a function of light received over the common region of the light-sensing plane;
at least one light source to project light along the light-sensing plane; and
an electronic computer communicating with the at least two photodetectors and the at least one light source and executing a program stored in non-transitory medium to:
(1) independently measure the light strength signals reflected from the at least one light source off a finger within the light-sensing plane;
(2) apply values of the light strength signals to a model converting strength of the light strength signals t to orthogonal coordinates defining points within the light-sensing plane;
(3) control an output on the graphics display screen according to the coordinates;
further including a collimator collimating the light from a fan-shaped acquisition region in the light-sensing plane onto the at least two photodetectors, the fan-shaped acquisition region having its widest dimension aligned along the light-sensing plane; and
wherein the fan-shaped acquisition region has a width measured in the light-sensing plane with at least 20 times a height of the fan-shaped acquisition region measured perpendicularly to the light-sensing plane.
9. The human interface device of claim 8 the collimator forms the light from the at least one light source into a fan shape having its widest dimension aligned along the light-sensing plane.
10. The human interface device of claim 9 wherein the fan shape has a width measured in the light-sensing plane with at least 20 times the height of the fan measured perpendicularly to the light-sensing plane.
11. The human interface device of claim 1 wherein the output controls an image location on the graphics display screen.
12. The human interface device of claim 11 wherein a motion of the image has a same orientation as motion of the finger within the light-sensing plane.
13. The human interface device of claim 1 wherein the output controls a virtual keyboard for entering characters on the graphics display screen.
14. The human interface device of claim 1 wherein the electronic computer further executes the program to monitor the measured light strength signals to deduce a presence or absence of the finger to control output on the graphics display according to a presence or absence of the finger in the light-sensing plane.
15. The human interface device of claim 1 wherein the electronic computer further executes the program to determine a background signal level when the finger is not within the light-sensing plane and compensating the measured light strength signals according to the measured background signal level.
16. The human interface device of claim 1 wherein the light source is modulated and the measured light strength signals from the at least two photodetectors are demodulated to reject ambient light not subject to the modulation.
17. The human interface device of claim 16 wherein the electronic computer further executes a stored program to change a modulation duty cycle of the light source to decrease power when a finger presence is not detected.
18. The human interface device of claim 16 wherein the electronic computer further executes the program to receive the measured light strength signals during a predefined path of motion of the finger within the light-sensing plane to calibrate the model.
19. The human interface device of claim 18 wherein the model is calibrated to an arbitrary area defined by a specified path of motion of the finger.