# PlaIMoS: A Remote Mobile Healthcare Platform to Monitor Cardiovascular and Respiratory Variables
## Data Bus Blood Oxygen Sensor
### PlaIMoS Remote Node  
The PlaIMoS remote node, designed and manufactured in Colima, Mexico, uses a 2.4 GHz, 250 Kbps XB24 CZZPIIS-004 transceiver, a 64-Kbyte PIC18F26K22 microcontroller, a 1024-byte EEPROM memory chip, a ADXL345 three-axis accelerometer to detect falls, a MCP73833-AMI battery management (4.2 volt at 1 ampere) to charge a Li-Po battery, a Micro-USB port to charge the battery, \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Package\_id** & **Patient\_id** & **Blood\_oxygen** & **Respiration\_rate** & **Galvanic\_resistance** \\ \hline Int & Int & Float & Smallint & Float \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Fixed measurement station package. Figure 8: PlaIMoS fixed measurement station closed. Figure 7: PlaIMoS fixed measurement station opened. a slide switch to turn the device on and off, a body temperature sensor, and three electrodes to detect patient heart rate and electrocardiogram data [24] (Figure 9). The PlaIMoS remote node is a device that patients use to continuously monitor their vital signs such as temperature, fall detection, heart rate and electrocardiogram. It employs a 12h lithium battery and applies IEEE 802.15.4 wireless technology to transfer data in a WSN infrastructure. This device acquires the electrical signals generated by the heart and provides the corresponding waveform as an electrocardiogram. This information is then processed for later viewing on mobile devices to acquire the patient heart rate. Additionally, to better monitor patients who are suffering from infections, body temperature, and fall detection are also monitored. The final version of the PlaIMoS remote node is shown in Figure 10.  
The received signal is preprocessed by a series of filters and amplifiers to obtain the signal in a range of between 0 and 3.3 V, which is processed analogically and converted to a digital signal by a 10-bit converter. The same analog to digital converter (ADC) is also used to process the electronic signal from a resistive temperature detector (RTD). Using a Wheatstone bridge and a dedicated algorithm [24], it is possible to accurately obtain the patient's body temperature. A digital accelerometer (MXL345) measures acceleration experienced by the user along three axes to determine the user's physical position. Finally, a dedicated algorithm [25] is used determine whether the patient is in a vertical or  
Figure 10: The PlaIMoS remote node device. Figure 9: PlaIMoS remote node hardware. horizontal position. If a possible uncontrolled transition from the vertical to horizontal position occurs, a push package is transmitted alerting persons monitoring the user of a possible fall. Heart rate detection is generated by electrical signals generated by each of the heart's ventricles. The constriction and relaxation of the ventricles as they pump blood through the body generates an electrical wave, which is known as the QRS complex (Figure 11). To obtain the patient's heart rate, it is necessary to know how many QRS complexes are generated per minute. Several methods are described below [26]. The device uses a sampling frequency of Fs = 250 Hz so that each sample is taken at a time interval of Ts = 1/Fs, which is important because it does not need to sample the heart rate for a full minute to produce reliable data. Instead, it only records the interval between two QRS complexes at random and its algorithm extrapolates the beats per minute. However, in order to obtain greater accuracy and eliminate probable reading disturbances, the device compiles a total of 1000 samples to calculate the heart rate, based on an average of RR (ridge peak to ridge peak) intervals (Figure 12). When a thousand samples are stored (n), the absolute value of the first derivative of the samples is obtained in order to provide a precise measurement of the R ridge as shown in Figure 13. Employing this process provides PR and ST intervals that are considerably lower compared to the peaks of the QRS complex and negative values disappear because of the algorithm used.