Medical Applications User Guide (pdf) - Freescale Semiconductor
Medical Applications User Guide (pdf) - Freescale Semiconductor
Medical Applications User Guide (pdf) - Freescale Semiconductor
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8.2<br />
Electrocardiography<br />
(ECG) Acquisition<br />
The heart rate calculation is performed using<br />
the ECG signal. The heart beat frequency is<br />
determined by measuring the time between<br />
QRS complex intervals. The ECG signal<br />
is acquired using two finger sensors, one<br />
on each side of the device. The first one<br />
takes the signal from the left index finger.<br />
The second one is divided in two parts: one<br />
takes the signal from the right index finger,<br />
the other works as reference.<br />
The signal is amplified using an<br />
instrumentation amplifier built by using the<br />
internal op amps of the Flexis MM MCU<br />
or the Kinetis K5x MCU, which has a high<br />
common mode rejection ratio (CMRR) that<br />
allows it to work as an initial filter. Then,<br />
the signal must go through a 0.1 Hz – 150<br />
Hz band-pass filter in order to remove the<br />
environmental noise. A second filter must<br />
be applied. In this case, a 50 Hz – 60 Hz<br />
notch filter, depending on the country’s<br />
electrical service frequency. This second<br />
filter is intended to remove the power<br />
line noise, which equals 50 Hz or 60 Hz,<br />
depending on the region. Finally, the signal<br />
must be acquired by an MCU using an ADC.<br />
Optionally, the MCU can perform digital<br />
filtering algorithms in order to have a more<br />
reliable signal.<br />
8.3<br />
Pedometer<br />
The pedometer counts the quantity of steps<br />
taken by the user while the activity monitor<br />
is activated. Accelerometers can be used<br />
to determine the overall activity level of the<br />
user. This module uses an accelerometer to<br />
determine device movement, and it must be<br />
able to detect when a step has been taken<br />
or whether the user starts running. The<br />
acceleration measurements recorded by the<br />
accelerometer are sent to an MCU either<br />
by using analog voltages to represent the<br />
movement, or by using digital methods such<br />
as I2C to send previously processed signals.<br />
Figure 8-1: Activity Monitor Block Diagram<br />
Magnetic Sensor:<br />
eCompass<br />
Heart Rate<br />
Monitor<br />
USB<br />
Mini-AB<br />
Power Management:<br />
Battery Charger<br />
Inertial<br />
Sensor:<br />
Pedometer<br />
OPAMPS<br />
TRIAMPS<br />
<strong>Freescale</strong> Technology Optional<br />
External<br />
Bus/GPIO<br />
Touch Sensing<br />
freescale .com/medical 45<br />
VREF<br />
Pressure<br />
Sensor<br />
Altimeter<br />
MicroSD<br />
Card<br />
I 2 C I 2 C SPI 1 SPI 2<br />
MCU/MPU<br />
GPIO<br />
USB PWM<br />
Li-Polymer<br />
Battery<br />
Display<br />
Figure 8-2: ECG Acquisition Block Diagram<br />
Figure 10-3: Block Diagram ECG Acquisition Block Diagram<br />
LA<br />
RA Ref<br />
Finger Electrodes Instrumentation Amplifier<br />
<strong>Freescale</strong> Technology<br />
Home Portable <strong>Medical</strong><br />
0.1 Hz – 150 Hz<br />
Band Pass<br />
Wireless Communication:<br />
ZigBee ®<br />
50 Hz – 60 Hz<br />
Band Reject<br />
Buzzer<br />
MCU
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