Heart rate detection system and wearable device using the same
Disclosed are a heart rate detection system and a wearable device using the same. The heart rate detection system includes a light emitting unit, a light sensor and a processor. The light emitting unit emits a light to a human body. The light sensor senses a reflected light of the light and accordingly generates a first electric signal. The processor calculates the low-frequency noise signal and the high-frequency noise signal of the first electric signal, and removes them. After that, the processor executes a peak detection with respect to the first electric signal to calculate peak values of the first electric signal, and calculate a heart rate based on the time intervals among the peak values.
1. A heart rate detection system, comprising:
at least one light emitting unit, emitting a light to a user's body;
a light sensor, sensing a reflected light of the light and accordingly generating a first electric signal; and
a processor, coupled to the light sensor and the light emitting unit, configured to:
convert the first electric signal from a time-domain signal to a frequency-domain signal;
calculate a first noise signal according to a first equation, and subtract the first noise signal from the first electric signal of the frequency-domain signal;
calculate a second noise signal according to a second equation, and subtract the second noise signal from the first electric signal of the frequency-domain signal having the first noise signal removed;
convert the first electric signal of the frequency-domain signal having the first noise signal and the second noise signal removed to a second time-domain signal;
execute a peak detection with respect to the first electric signal of the second time-domain signal having the first noise signal and the second noise signal removed according to a first sampling rate, and calculate a plurality of peak values of the first electric signal of the second time-domain signal having the first noise signal and the second noise signal removed; and
calculate a plurality of time intervals among the peak values according to the first sampling rate and the peak values, and calculate a heart rate based on the time intervals;
wherein the first equation is:
Y
[
i
]
=
∑
j
=
0
M
-
1
X
[
i
+
j
]
M
;
wherein Y[i] is the first noise signal, X[i+j] is the first electric signal of the frequency-domain signal, and M is a sampling number;
wherein the second equation is:
S
[
i
]
=
∑
j
=
0
M
-
1
Z
[
i
+
j
]
M
;
wherein S[i] is the second noise signal, and Z[i+j] is the first electric signal of the frequency-domain signal having the first noise signal removed.
2. The heart rate detection system according to claim 1 , wherein the processor is further configured to:
examine a voltage value of the first electric signal of the second time-domain signal having the first noise signal and the second noise signal removed corresponding to each time unit, and the time unit is a reciprocal of the first sampling rate; and
end the peak detection after examining the voltage value of the first electric signal of the second time-domain signal having the first noise signal and the second noise signal removed corresponding to the last time unit;
wherein if one of the voltage values is larger than all of the voltage values corresponding to the last three time units and the next three time units and also larger than an average of the voltage values corresponding to all time units, the processor determines that the voltage value is one of peak values of the first electric signal of the second time-domain signal having the first noise signal and the second noise signal removed.
3. The heart rate detection system according to claim 2 , wherein the processor is further configured to:
dividing a difference between every two adjacent peak values by the first sampling rate to calculate the time intervals among the peak values; and
calculating the heart rate according to the time intervals and a first heart rate conversion equation, and the first heart rate conversion equation is:
BPM
=
2
*
60
T
[
n
2
]
+
T
[
n
2
+
1
]
wherein BPM is the heart rate, T is the difference between two adjacent peak values, and n is the number of the peak values.
4. A wearable device, comprising the heart rate detection system according to claim 1
for instantly detecting the heart rate of the user wearing the wearable device.
5. The wearable device according to claim 4 , wherein the processor is further configured to:
examine a voltage value of the first electric signal of the time-domain signal having the first noise signal and the second noise signal removed corresponding to each time unit, and the time unit is a reciprocal of the first sampling rate; and
end the peak detection after examining the voltage value of the first electric signal of the time-domain signal having the first noise signal and the second noise signal removed corresponding to the last time unit;
wherein if one of the voltage values is larger than all of the voltage values corresponding to the last three time units and the next three time units and also larger than an average of the voltage values corresponding to all time units, the processor determines that the voltage value is one of peak values of the first electric signal of the time-domain signal having the first noise signal and the second noise signal removed.
6. The wearable device according to claim 5 , wherein the processor is further configured to:
dividing a difference between every two adjacent peak values by the first sampling rate to calculate the time intervals among the peak values; and
calculating the heart rate according to the time intervals and a first heart rate conversion equation, and the first heart rate conversion equation is:
BPM
=
2
*
60
T
[
n
2
]
+
T
[
n
2
+
1
]
wherein BPM is the heart rate, T is the difference between two adjacent peak values, and n is the number of the peak values.