Capacitive touch buttons combined with electroluminescent lighting
A capacitive touch sensor includes a layer of electro-luminescent (EL) material arranged between a first electrode and a second electrode, A controller includes a capacitance sensing circuit coupled to first and/or second electrode and arranged to measure a capacitive coupling associated with the first and/or second electrode. The controller is further operable to apply an EL drive signal across the first and second electrodes to cause the layer of EL material between the electrodes to illuminate. This provides a simple structure that is sensitive to objects adjacent a sensing region defined by the first and/or second electrodes, and which may also be readily illuminated by applying an EL drive signal across the electrodes.
1. A capacitive touch sensor comprising:
a substrate;
a layer of electro-luminescent (EL) material arranged between a first electrode and a second electrode; and
a controller comprising a capacitance sensing circuit coupled to at least one of the first and second electrodes and arranged to measure a capacitive coupling associated therewith, wherein the controller is further operable to apply an EL drive signal across the first and second electrodes to cause the layer of EL material between the electrodes to illuminate, the substrate distinct from the EL material and positioned between the first electrode and second electrode.
2. A capacitive touch sensor according to claim 1 , wherein the controller is operable to respectively apply the EL drive signal and to measure the capacitive coupling associated with the coupled electrode or electrodes in a time-multiplexed manner.
3. A capacitive touch sensor according to claim 1 , wherein the controller is operable to apply the EL drive signal and to measure the capacitive coupling associated with the coupled electrode or electrodes simultaneously.
4. A capacitive touch sensor according to claim 3 , wherein the controller is operable to measure the capacitive coupling associated with the coupled electrode or electrodes at a predefined phase of the EL drive signal.
5. A capacitive touch sensor according to claim 4 , wherein the predefined phase of the EL drive signal is a zero crossing of the EL drive signal.
6. A capacitive touch sensor according to claim 4 , wherein the predefined phase of the EL drive signal is a phase at which a rate of change of the EL drive signal with time is minimized.
7. A capacitive touch sensor according to claim 1 , wherein the EL drive signal includes a blanking period, and the controller is operable to measure the capacitive coupling associated with the coupled electrode or electrodes during the blanking period.
8. A capacitive touch sensor according to claim 7 , wherein the blanking period is a period in which the EL drive signal is maintained at a reference potential.
9. A capacitive touch sensor according to claim 1 , further comprising an EL signal amplifier for amplifying a signal from the controller in order to provide the EL drive signal.
10. A capacitive touch sensor according to claim 1 , wherein the capacitance sensing circuit comprises a drive circuit operable to apply a capacitance measurement drive signal to the first electrode, and a receive circuit operable to measure a component of the drive signal capacitively coupled to the second electrode as an indication of the capacitive coupling between the first and second electrodes.
11. A capacitive touch sensor according to claim 10 , further comprising a switch arranged to selectively couple one or the other of the EL drive signal and the capacitance measurement drive signal to the first electrode in response to a switching signal from the controller.
12. A capacitive touch sensor according to claim 1 , wherein the capacitance sensing circuit is coupled to the second electrode and is operable measure a capacitive coupling of the second electrode to a reference potential.
13. A capacitive touch sensor according to claim 12 , further comprising a switch arranged to selectively couple one or the other of the EL drive signal and either a reference potential, a floating potential, or a facsimile of a signal applied to the second electrode, to the first electrode in response to a switching signal from the controller.
14. A capacitive touch sensor according to claim 1 , wherein the at least one of the first and second electrodes has a shape selected to correspond to a desired illumination pattern for the touch sensor.
15. A capacitive touch sensor according to claim 1 , wherein at least one of the first and second electrodes is transparent.
16. A capacitive touch sensor according to claim 1 , further comprising an insulating panel overlying the electrodes and the layer of EL material.
17. A capacitive touch sensor according to claim 1 , further comprising a decorative mask overlying the electrodes and the layer of EL material.
18. A capacitive touch sensor according to claim 1 , wherein the first electrode has a greater extent than the second electrode.
19. A capacitive touch sensor according to claim 1 , wherein a connection trace to at least one of the first and second electrodes is arranged to run away from the layer of EL material.
20. A capacitive touch sensor according to claim 1 , wherein the controller is further operable to process measured changes in the capacitive coupling to detect the presence of an object adjacent the touch sensor.
21. The capacitive touch sensor according to claim 1 , wherein:
the first electrode is positioned on a first side of the substrate; and
the second electrode is positioned on a second side of the substrate, the second side of the substrate being opposite the first side of the substrate, the EL material positioned between the second electrode and the substrate.