B i o m e t r i c - E X P E V B
6
Rev. 0.4
Figure 5. Biometric-EXP Demo Modes
*Note:
SpO2 Monitor mode is not available when using Si1143-M01-PS or Si1147-M01-PS.
3.2. Heart Rate Monitor Mode
When heart rate monitor demo is idle, the LCD will show the word “Pulse” followed by a message instructing the
user to place his/her finger on the optical sensor. In idle mode, the sensor is not continuously sampling. Rather, it
executes one sample every two seconds by performing a forced measurement. That sample is then analyzed to
determine if there is skin contact with the sensor. Only when the application detects skin contact does it begin
sampling continuously and running the HRM algorithm. It will remain in run mode (continuous sampling) until skin
contact is removed for greater than two seconds. This approach significantly reduces power usage when idle.
When the application is acquiring the heart rate, it will display the word “Wait” on the LCD. It typically takes five to
seven seconds to acquire a valid heart rate. Once a valid heart rate is measured, the display will show the heart
rate. If the heart rate is not displayed within seven seconds, it is likely that the algorithm cannot get a valid pulse
rate. When this occurs, the user should remove his/her finger and try it again adjusting the position of the finger
and the finger pressure as needed.
Proper finger position in relation to the sensor and LEDs as well as proper finger pressure is essential for accurate
measurements. The finger should fully cover both LEDs and the sensor. As illustrated in Figure 6, the finger should
be lightly placed on the sensor. Too much pressure will restrict blood flow in the finger and, therefore, not allow the
sensor to measure a heart rate.
Figure 6. Proper Finger Placement
Heart
Rate
Monitor
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