Optical pressure sensor

1. A pressure sensor, comprising:

an optical source configured to output light to illuminate tissue of a user;

an optical sensor configured to measure reflected illumination from the tissue; and

a compute machine configured to:

output a pressure between a surface of the optical sensor and the tissue, the pressure determined as a function of the measured reflected illumination;

based on the output pressure being outside a range for heart rate detection by less than a first threshold, adjust the measured reflected illumination, and output a heart rate based on the adjusted measured reflected illumination; and

dynamically adjust an intensity of the light output by the optical source based on the output pressure being outside the range for the heart rate detection by more than the first threshold but less than a second threshold.

2. The pressure sensor of claim 1 , where the optical source is configured to pulse on and off.

3. The pressure sensor of claim 2 , where the compute machine is configured to:

compare the measured reflected illumination to a predetermined baseline optical sensor output corresponding to the user; and

output an increased pressure between the surface of the optical sensor and the tissue responsive to an increase in a ratio of the measured reflected illumination to the predetermined baseline optical sensor output during time periods when the optical source is pulsed on.

4. The pressure sensor of claim 2 , where the compute machine is configured to:

indicate whether the pressure sensor is being worn based on the measured reflected illumination during time periods when the optical source is pulsed off.

5. The pressure sensor of claim 1 , where the compute machine is configured to:

indicate to the user to adjust an interface between the surface of the optical sensor and the tissue based on the output pressure.

6. The pressure sensor of claim 1 , where the compute machine is configured to:

based on the output pressure being within the range for the heart rate detection, output a heart rate of the user based on the measured reflected illumination.

7. The pressure sensor of claim 1 , where the compute machine is configured to:

classify the output pressure as representative of a type of predetermined activity.

8. The pressure sensor of claim 7 , further comprising a motion sensor configured to determine movement of the pressure sensor over time, and where the compute machine is further configured to:

classify the determined movement as representative of a type of predetermined activity.

9. The pressure sensor of claim 1 , wherein dynamically adjusting the intensity of the light output by the optical source based on the output pressure being outside the range for the heart rate detection further comprises:

increasing the intensity of the light output by the optical source based on the output pressure being below the range for the heart rate detection; and

decreasing the intensity of the light output by the optical source based on the output pressure being above the range for the heart rate detection.

10. A wearable computing device, comprising:

a pressure sensor configured to determine a pressure between a surface of the pressure sensor and tissue of a user over time, the pressure sensor comprising:

an optical source configured to illuminate the tissue of the user; and

and optical sensor configured to measure reflected illumination from the tissue;

a logic machine; and

a data-storage machine holding instructions executable by the logic machine to:

based on a determined pressure being within a pressure range, output a heart rate based on the measured reflected illumination;

based on the determined pressure being outside the pressure range by less than a first threshold, adjust the measured reflected illumination, and output a heart rate based on the adjusted measured reflected illumination; and

based on the determined pressure being outside the pressure range by more than the first threshold but less than a second threshold which is greater than the first threshold, adjust an intensity of light output by the optical source.

11. The device of claim 10 , where the optical source is configured to pulse on and off, and wherein the data-storage machine further holds instructions executable by the logic machine to:

compare the measured reflected illumination to a predetermined baseline optical sensor output corresponding to the user; and

output an increased pressure between the surface of the optical sensor and the tissue responsive to an increase in a ratio of the measured reflected illumination to the predetermined baseline optical sensor output during time periods when the optical source is pulsed on.

12. The device of claim 11 , where the pressure sensor is further configured to:

indicate whether the pressure sensor is being worn based on the measured reflected illumination during time periods when the optical source is pulsed off.

13. The device of claim 10 , where the data-storage machine further holds instructions executable by the logic machine to:

indicate to the user to adjust an interface between the surface of the pressure sensor and the user's tissue based on the determined pressure being outside the pressure range by more than the second threshold.

14. A wearable computing device, comprising:

an optical source configured to illuminate tissue of a user and to pulse on and off;

an optical sensor configured to measure reflected illumination from the tissue; and

a compute system configured to:

establish a baseline optical sensor output for the user over time based on an output of the optical sensor over a duration including multiple on-and-off pulsations of the optical source;

compare the measured reflected illumination to the baseline optical sensor output;

output a heart rate based on the measured reflected illumination and the baseline optical sensor output;

output a pressure between a surface of the optical sensor and the tissue based on the measured reflected illumination and the baseline optical sensor output;

based on the output pressure being outside a range for heart rate detection by less than a first threshold, adjust the measured reflected illumination, and output the heart rate based on the adjusted measured reflected illumination; and

dynamically adjust an intensity of the light output by the optical source based on the output pressure being outside the range for the heart rate detection by more the first threshold but less than a second threshold.