WEARABLE HEART RATE MONITOR
Some embodiments provide a wearable fitness monitoring device including a motion sensor and a photoplethysmographic (PPG) sensor. The PPG sensor includes (i) a periodic light source, (ii) a photo detector, and (iii) circuitry determining a user's heart rate from an output of the photo detector. Some embodiments provide methods for operating a heart rate monitor of a wearable fitness monitoring device to measure one or more characteristics of a heartbeat waveform. Some embodiments provide methods for operating the wearable fitness monitoring device in a low power state when the device determines that the device is not worn by a user. Some embodiments provide methods for operating the wearable fitness monitoring device in a normal power state when the device determines that the device is worn by a user.
1 . A method of operating a heart rate monitor of a wearable fitness monitoring device comprising a plurality of sensors including the heart rate monitor, the method comprising:
(a) operating the heart rate monitor in a first mode while also operating in a second mode configured to detect near proximity of the wearable fitness monitoring device to a user's skin, wherein the first mode is configured to determine one or more characteristics of a user's heartbeat waveform when the wearable fitness monitoring device is in near proximity to the user;
(b) from information collected in the second mode, determining that the heart rate monitor is not proximate to the user's skin; and
(c) in response to determining that the heart rate monitor is not proximate to the user's skin, ending operating the heart rate monitor in the first mode.
2 . The method of claim 1 , wherein the heart rate monitor comprises an optical heart rate monitor.
3 . The method of claim 2 , wherein the heart rate monitor comprises a photoplethysmographic sensor.
4 . The method of claim 1 , wherein the one or more characteristics of the user's heartbeat waveform comprises the user's heart rate.
5 . The method of claim 1 , wherein (a) comprises periodically operating the heart rate monitor in the second mode while continuously operating the heart rate monitor in the first mode.
6 . The method of claim 5 , wherein (a) comprises operating the heart rate monitor in the second mode occurs no more than about 50% of the time.
7 . The method of claim 5 , wherein
operating the heart rate monitor in the second mode comprises pulsing a light source in the heart rate monitor at a second mode frequency and detecting light from the light source at the second mode frequency; and
operating the heart rate monitor in the first mode comprises pulsing the light source in the heart rate monitor at a first mode frequency and detecting light from the light source at the first mode frequency.
8 . The method of claim 7 , wherein the second mode frequency is greater than the first mode frequency.
9 . The method of claim 1 , wherein operating the heart rate monitor in the second mode comprises:
pulsing a light source in the heart monitor at a second frequency;
detecting light from the light source at the second frequency; and
determining whether the light detected at the second frequency has an intensity and/or pattern indicating that the light from the light source has interacted with the user's skin.
10 . The method of claim 9 , wherein the pulsing the light in the second mode source comprises emitting a succession of light pulses, some having variable intensity and others having constant intensity.
11 . The method of claim 1 , wherein operating the heart rate monitor in the second mode comprises:
emitting a succession of light pulses of variable intensity; and
determining whether detected light corresponding to the succession of light pulses has a variable response corresponding to the variable intensity of the light pulses.
12 . The method of claim 1 , further comprising operating the heart rate monitor in a skin characterization mode configured to determine at least one setting for operating the heart rate monitor in the first mode, wherein operating the heart rate monitor in the skin characterization mode comprises:
(i) pulsing a light source in the heart monitor by emitting a succession of light pulses of variable intensity;
(ii) detecting an intensity, a variation in intensity, and/or a pattern in intensity of light after the pulsed light has interacted with the user's skin; and
(iii) determining a response characteristic of the user's skin from the intensity, variation in intensity, and/or pattern of intensity detected in (ii).
13 . The method of claim 12 , further comprising using the response characteristic of the user's skin to adjust the heart rate monitor's gain and/or light emission intensity for operating in the first mode.
14 . The method of claim 12 , wherein the response characteristic is dependent on the opacity of the user's skin.
15 . The method of claim 12 , wherein the emitted succession of light pulses of variable intensity from (i) is used in the second mode as well as the skin characterization mode.
16 . The method of claim 12 , wherein operating the heart rate monitor in the skin characterization mode comprises periodically operating the heart rate monitor in the skin characterization mode while continuously operating the heart rate monitor in the first mode.
17 . The method of claim 1 , wherein the plurality of sensors comprises a motion detecting sensor.
18 . The method of claim 17 , wherein the motion detecting sensor comprises an accelerometer, a magnetometer, an altimeter, a GPS detector, or a combination of any of these.
19 . The method of claim 17 , further comprising:
prior to (c), determining from information output by the motion detecting sensor that the wearable fitness monitoring device has had been still for at least a defined period; and
in response to detecting that the wearable fitness monitoring device has had been still for at least the defined period, performing (c).
20 . The method of claim 1 , further comprising, prior to (a) while the first mode is not operating:
(i) detecting motion of the wearable fitness monitoring device using a motion detecting sensor and/or detecting proximity of the heart rate monitor to the user' skin by operating the heart rate monitor in a third mode; and
(ii) initiating operation of the first mode of the heart rate monitor when the wearable fitness monitoring device is determined to be in near proximity to the user.
21 . A wearable fitness monitoring device comprising:
a motion sensor configured to provide output corresponding to motion by a user wearing the fitness monitoring device;
a photoplethysmographic sensor comprising (i) a periodic light source, (ii) a photo detector positioned to receive periodic light emitted by the periodic light source after interacting with a user's skin, and (iii) circuitry determining a user's heart rate from an output of the photo detector; and
control logic configured to:
(a) operate the heart rate monitor in a first mode while also operating in a second mode configured to detect near proximity of the wearable fitness monitoring device to a user's skin, wherein the first mode is configured to determine one or more characteristics of a user's heartbeat waveform when the wearable fitness monitoring device is in near proximity to the user;
(b) from information collected in the second mode, determine that the heart rate monitor is not proximate to the user's skin; and
(c) in response to determining that the heart rate monitor is not proximate to the user's skin, end operating the heart rate monitor in the first mode.
22 . The wearable fitness monitoring device of claim 21 , wherein
operating the heart rate monitor in the second mode comprises pulsing a light source in the heart rate monitor at a second mode frequency and detecting light from the light source at the second mode frequency; and
operating the heart rate monitor in the first mode comprises pulsing the light source in the heart rate monitor at a first mode frequency and detecting light from the light source at the first mode frequency.
23 . A wearable fitness monitoring device comprising:
a motion sensor configured to provide output corresponding to motion by a user wearing the fitness monitoring device; and
a photoplethysmographic sensor comprising (i) a periodic light source, (ii) a photo detector positioned to receive periodic light emitted by the periodic light source after interacting with a user's skin, and (iii) circuitry determining a user's heart rate from an output of the photo detector, wherein the periodic light source comprises two periodic light sources straddling the photo detector.
24 . The wearable fitness monitoring device of claim 23 , wherein the photoplethysmographic sensor further comprises a housing having a recess in which the photo detector is disposed.
25 . The wearable fitness monitoring device of claim 24 , wherein the housing of the photoplethysmographic sensor further comprises a second recess in which the periodic light source is disposed.
26 . The wearable fitness monitoring device of claim 25 , wherein the housing of the photoplethysmographic sensor protrudes at least about 1 mm above a base surface of the wearable fitness monitoring device and is configured to press against the user's skin when worn.
27 . The wearable fitness monitoring device of claim 26 , wherein the photoplethysmographic sensor further comprises a spring configured to resist compression when the protruding housing presses against the user's skin.
28 . The wearable fitness monitoring device of claim 23 , wherein the photoplethysmographic sensor further comprises an IML film over the photo detector and the periodic light source.