Functional description
KW40 Heart Rate Monitor Using Bluetooth Low Energy, User's Guide, Rev. 0, 10/2015
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Freescale Semiconductor, Inc.
4.4. Operation
After the device is connected, two types of measurements are reported to the smartphone application,
heart rate and battery level.
4.4.1. Battery level
The battery level reports the percentage of the remaining charge in the device battery. This value is
updated every 10 seconds in the smartphone application.
When the battery level reaches 0%, the device automatically enters the Battery Retention State and the
device cannot be used until the battery has enough energy. Any attempt to begin using the device with a
low battery will result in the red LED blinking three times indicating low battery level. See section
for instructions on how to properly charge the battery.
4.4.2. Heart rate measurements
When the device is connected to a heart rate application, it begins to report the acquired measurements.
The ECG is obtained from the fingertips by placing them in the on-board electrodes. You must carry out
the following steps to ensure accurate measurements.
1.
Place your thumbs on the on-board firmware electrodes (see
). Avoid pressing too hard
to prevent muscular noise interference.
Figure 7. Fingers position
2.
Wait for at least 10 seconds for the signal to stabilize. The red LED will blink every time a
heartbeat is detected.
NOTE
PCB electrodes might not always acquire the ECG signal immediately. If this happens and the
reported heart rate is shown as zero, remove your fingers from the PCB electrodes and repeat steps 1
and 2.