Frequency multiplexed optical touchscreen
View Patent ↗An apparatus, methods, systems, and computer program products are provided that can detect touch events on touch panels in a more effective and less costly manner. According to an embodiment, a touch system includes a touch panel and a plurality of radiation sources located at a first edge of the touch panel. The intensity of light emitted from each of the plurality of radiation sources is modulated with a respective modulation frequency. The touch system further includes an optical receiver that is located at a second edge of the touch panel and is configured to receive the light emitted from each of the plurality of radiation sources.
1. A touch system, comprising:
a touch panel;
a first plurality of radiation sources located at a first edge of the touch panel;
a second plurality of radiation sources located at the first edge of the touch panel,
wherein an intensity of light emitted from each of the first and second plurality of radiation sources is modulated with a modulation frequency from a set of frequencies utilized repetitively in varying order between the first and the second plurality of radiation sources; and
an optical receiver located at a second edge of the touch panel and configured to receive the light emitted from each of the first and second plurality of radiation sources.
2. The touch system of claim 1 , wherein the modulation frequencies of the second plurality of radiation sources are uniquely ordered with respect to the first plurality of radiation sources.
3. The touch system of claim 2 , wherein when a first radiation source in the first plurality of radiation sources has a same modulation frequency as a second radiation source in the second plurality of radiation sources, a neighboring radiation source of the second radiation source does not have a same modulation frequency as a corresponding neighboring radiation source of the first radiation source.
4. The touch system of claim 1 , wherein the first plurality of radiation sources and the second plurality of radiation sources are substantially simultaneously excited to emit the light.
5. The touch system of claim 1 , further comprising:
a detector configured to receive the light emitted from each of the first and second plurality of radiation sources and directed by the optical receiver, wherein the detector is configured to generate an analog signal based on the received light.
6. The touch system of claim 5 , further comprising:
an analog to digital (A/D) converter configured to receive the analog signal and convert it to a digital signal; and
a processor circuitry configured to receive the digital signal and determine coordinates of a touch event on the touch panel.
7. The touch system of claim 6 , wherein the processor circuitry includes one of an audio digital signal processing (DSP) and a video DSP.
8. The touch system of claim 6 , wherein the processor circuitry is configured to:
perform a frequency transform on the digital signal and determine an amplitude of the frequency transformed signal for each of the respective modulation frequencies;
determine an attenuation factor for each of the respective modulation frequencies; and
determine coordinates of the touch event on the touch panel based on the determined attenuation factor.
9. The touch system of claim 8 , wherein the frequency transform comprises a Fast Fourier Transform (FFT).
10. The touch system of claim 1 , further comprising:
a third plurality of radiation sources located at a third edge of the touch panel, wherein an intensity of light emitted from each of the third plurality of radiation sources is modulated with a respective modulation frequency and wherein the third edge of the touch panel is orthogonal to the first edge of the touch panel.
11. The touch system of claim 10 , further comprising:
a second optical receiver located at a fourth edge of the touch panel and configured to receive the light emitted from each of the third plurality of radiation sources, wherein the fourth edge of the touch panel is orthogonal to the first edge of the touch panel.
12. The touch system of claim 11 , further comprising a processor circuitry configured to:
determine a first set of coordinates of a touch event on the touch panel based on the light emitted from each of the first and second plurality of radiation sources;
determine a second set of coordinates of the touch event based on the light emitted from each of the third plurality of radiation sources; and
determine an efficiency factor of the touch event based on the determined first and second set of coordinates.
13. The touch system of claim 1 , wherein the plurality of radiation sources comprise a plurality of light emitting diodes (LEDs).
14. The touch system of claim 1 , wherein the modulation frequencies are between about 200 Hz and 20 kHz.
15. A touch system, comprising:
a touch panel;
a first plurality of light emitting diodes (LEDs) located at a first edge of the touch panel;
a second plurality of LEDs located at the first edge of the touch panel,
wherein an intensity of light emitted from each of the first and second plurality of LEDs is modulated with a modulation frequency from a set of frequencies utilized repetitively in varying order between the first and the second plurality of LEDs;
a first optical receiver located at a second edge of the touch panel and configured to receive the light emitted from each of the first and second plurality of LEDs;
a third plurality of LEDs located at a third edge of the touch panel, wherein an intensity of light emitted from each of the third plurality of LEDs is modulated with a respective modulation frequency and wherein the third edge of the touch panel is orthogonal to the first edge of the touch panel;
a second optical receiver located at a fourth edge of the touch panel and configured to receive the light emitted from each of the third plurality of LEDs; and
a processor circuitry configured to detect a touch event on the touch panel based on the light received from the first, second, and third plurality of LEDs.
16. A method, comprising:
receiving radiation beams from a first plurality of radiation sources and a second plurality of radiation sources located at a first edge of a touch panel,
wherein an intensity of the radiation beam emitted from each of the first and second plurality of radiation sources is modulated with a modulation frequency from a set of frequencies utilized repetitively in varying order between the first and the second plurality of radiation sources;
generating a digital signal based on the received radiation beams;
performing a frequency transform on the digital signal and determining an amplitude of the frequency transformed signal for each of the respective modulation frequencies; and
determining coordinates of a touch event on the touch panel based on the determined amplitudes.
17. The method of claim 16 , further comprising:
determining an attenuation factor for each of the respective modulation frequencies.
18. The method of claim 17 , wherein the determining coordinates of a touch event comprises determining the coordinates of the touch event based on the determined attenuation factors.
19. The method of claim 18 , wherein the determining coordinates of a touch event comprises:
determining a set of the modulation frequencies for which the determined attenuation factor is not zero;
comparing the determined set of the modulation frequencies with stored sets of frequencies; and
determining a first coordinate of the touch event based on the comparison.
20. The method of claim 19 , wherein the determining coordinates of a touch event further comprises:
comparing the attenuation factors of the determined set of the modulation frequencies with stored attenuation factors for the determined set of the modulation frequencies to determine a second coordinate of the touch event.