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1. (WO2019027555) ACTIVE STYLUS
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CLAIMS

1. Apparatus for determining user operation of an actuator, the apparatus comprising: a state circuit having a characteristic time constant that may assume each of a plurality of different magnitudes;

an actuator operable by a user to change the magnitude of the characteristic time constant from a first to a second magnitude of the plurality of magnitudes; and

a popup and test (POP AT) circuit operable to access the state circuit to acquire data useable to determine whether a user has operated the actuator to change the magnitude of the characteristic time constant.

2. The apparatus according to claim 1 wherein the state circuit comprises for each of the plurality of magnitudes a resistor having resistance R and a capacitor having capacitance C that determines the magnitude of the characteristic time constant as a resistance-capacitance time constant.

3. The apparatus according to claim 2 wherein for each of the different RC time constants, capacitance C is the same and resistance R is different.

4. The apparatus according to claim 2 or claim 3 wherein the POP AT circuit comprises a charger operable to charge the capacitor to a test voltage Vj to determine the magnitude of the characteristic time constant.

5. The apparatus according to claim 4 wherein the POP AT circuit comprises a first switch configured to receive a signal that operates to connect the charger to the capacitor.

6. The apparatus according to claim 5 wherein the charger comprises a second switch configured to receive a signal that operates to disconnect the charger from the capacitor and initiate at a first time discharge of the capacitor and relaxation of voltage Vj.

7. The apparatus according to claim 6 wherein the POP AT circuit comprises a sensor that generates output signals based on voltage across the capacitor as the voltage relaxes from Vj.

8. The apparatus according to claim 7 and comprising a controller that receives the output signals generated by the sensor and processes the signals to determine a second time at which the voltage across the capacitor decreases to a voltage less than a relaxation voltage VR and wherein the controller is configured to determine the magnitude of the characteristic time constant of the state circuit based on the output signals and the second time minus the first time.

9. The apparatus according to claim 8 wherein the controller controls the POP AT

circuit to repeatedly access the state circuit to acquire the data.

10. The apparatus according to claim 9 wherein the controller controls the POP AT circuit to periodically access the state circuit to acquire the data.

11. The apparatus according to claim 10 wherein the period of the periodic access is less than or equal to about 1 second.

12. An active stylus having different states and comprising apparatus according to any of the preceding claims wherein change of the magnitude from a first magnitude to a second magnitude operates to change a state of operation of the stylus.

13. A method of determining user operation of an actuator, the method comprising: connecting the actuator to a state circuit having a characteristic time constant that may assume each of a plurality of different magnitudes so that operation of the actuator operates to change the magnitude of the time constant from a first to a second magnitude of the plurality of magnitudes; and

determining the magnitude of the characteristic time constant.

14. The method according to claim 13 wherein the time constant is a resistance-capacitance (RC) time constant determined by a resistance R and a capacitance C and wherein changing the magnitude of the time constant comprises changing the resistance R.

15. The method according to 13 or claim 14 and comprising changing a state of operation of an active stylus based on determining the magnitude.