Optical control system with modulated emitters
An optical control system is described, which employs a series of optical emitters and detectors arranged about a touch area. The emitters are driven by a series of functions, and the system is operable to correlate the signals received at the detectors with the functions to determine the amount of energy received by the detectors from each of the emitters. This system means that all or many emitters can be modulated simultaneously, so the scanning process is accelerated. Also, the energy estimates arrived at by correlation with the functions are largely unaffected by external interference signals as well by each other. An additional benefit of the present invention is that the correlation processing makes use of many detector samples and tends to yield results which have higher resolution than the sample values themselves, due to the averaging of noise over the sample set.
1. An optical touch detection system comprising:
a touch sensitive area within which touch events are to be detected;
a plurality of emitters and a plurality detectors arranged around a periphery of the touch sensitive area, each emitter producing a plurality of optical beams received by a plurality of the detectors, wherein touch events disturb the optical beams; and
an optical control system coupled to the emitters and detectors, the optical control system configured to:
control activation of a plurality of the emitters and detectors simultaneously according to a modulation scheme comprising a plurality of different functions, each function alternating an associated one of the emitters between an activated state and a deactivated at a pattern of times varying from that of each other function in the modulation scheme,
wherein in the activated state the associated emitter is emitting optical beams and in the deactivated state the associated emitter is not emitting optical beams such that the deactivated state consumes less power than the activated state; and
correlate output from the detectors regarding which optical beams have been disturbed by a touch event with the different functions to determine a location within the touch sensitive area where the touch event occurred.
2. The optical touch detection system of claim 1 , wherein the functions are orthogonal functions such that each function is orthogonal with respect to every other function with respect to activated state and deactivated state time periods.
3. The optical touch detection system of claim 1 , wherein the functions are further differentiated using amplitude modulation.
4. The optical touch detection system of claim 1 , wherein at least one of the detectors is positioned to receive optical energy from more than one of the optical emitters.
5. The optical touch detection system of claim 1 , wherein disturbing an optical beam comprises changing an amount of energy received at least one detector relative to an amount of energy transmitted from at least one emitter.
6. The optical touch detection system of claim 1 , wherein each of the functions keeps at least a minimum number of emitters simultaneously in the activated state to reduce a current consumption in the optical touch detection system.
7. The optical touch detection system of claim 1 , wherein each of the functions keeps less than a maximum number of emitters simultaneously in the activated state to reduce a dynamic range of light levels received at a detector.
8. The optical touch detection system of claim 1 , wherein the functions are non-periodic functions over a time period during which they are orthogonal with respect to every other function.
9. The optical touch detection system of claim 1 , wherein the optical control system comprises a memory configured to store the functions, and a drive circuitry configured to access the functions and to control the operation of the emitters and detectors based on the functions.
10. The optical touch detection system of claim 1 , wherein the optical control system comprises a variable timing mechanism configured to vary at least one of the functions with a non-periodic frequency of activation states and deactivation states.
11. The optical touch detection system of claim 10 , wherein the variable timing mechanism is further configured to vary sampling of detector output according to the non-periodic frequency.
12. The optical touch detection system of claim 1 comprising a noise detection mechanism configured to sample detector output before and after one of the emitter activation states to determine a noise level before and after the activation state.
13. The optical touch detection system of claim 12 wherein the noise detection mechanism is further configured to interpolate a noise level during one of the emitter activation states based on the noise level before and after the activation state.
14. The optical touch detection system of claim 13 wherein the noise detection mechanism is further configured determine energy incident on the detectors based on detector output sampled during one of the emitter activation states and based on the noise level during the emitter activation state.
15. The optical touch detection system of claim 13 wherein the noise level during the emitter activation state is used to determine an emitter power level.
16. The optical touch detection system of claim 1 , wherein the optical control system is further configured to:
correlate the functions with output from the detectors regarding which optical beams have been disturbed by a plurality of touch events to determine a location within the touch sensitive area where each of the touch events occurred.
17. A method for determining locations of touch events within a touch sensitive area, the touch sensitive area having a plurality of emitters and a plurality of detectors arranged around its periphery, each emitters producing a plurality of optical beams received by a plurality of the detectors, wherein touch events disturb the optical beams, the method comprising:
activating a plurality of the emitters and detectors simultaneously according to a modulation scheme comprising a plurality of different functions, each function alternating an associated one of the emitters between an activated state and a deactivated at a pattern of times varying from that of each other function in the modulation scheme,
wherein in the activated state the associated emitter is emitting optical beams and in the deactivated state the associated emitter is not emitting optical beams such that the deactivated state consumes less power than the activated state; and
determining a location within the touch sensitive area where a touch event occurred based on which beams have been disturbed by the touch event and based on the different functions.
18. The method of claim 17 , wherein at least one of the detectors is positioned to receive optical energy from more than one of the optical emitters.
19. The method of claim 17 , wherein disturbing an optical beam comprises changing an amount of energy received at least one detector relative to an amount of energy transmitted from at least one emitter.
20. The method of claim 17 , further comprising:
determining a plurality of locations within the touch sensitive area where a plurality of touch events occurred based on which beams have been disturbed by the touch events and based on the functions.