ECG is an interpretation of the electrical activity of the heart over time, captured and externally recorded by skin electrodes. It is measured non-invasively by capturing small voltages that are generated on the surface of the skin every time the heart beats.
Two leads are connected to the patient’s body for a single channel ECG and the voltage generated is the differential voltage of two connected leads. The range of the voltage is less than a millivolt in presence of large offsets and high noise from various sources of electrical interference.
The signal has to be amplified by an instrumentation amplifier, filtered, digitized, analyzed and stored for further processing and communication, Figure 3. The frequency range of interest in an ECG is typically between 0.05Hz and 150Hz. The microcontroller used to manage the signal chain can also be used to analyze the data captured.
Figure 3: Block diagram of electrocardiogram
Pulse oximetry is a non-invasive method allowing the monitoring of the oxygenation of a patient's hemoglobin. The level of oxygenation of blood can be found (SaO2) based on the intensity of light attenuated by the body tissue. Oxygen saturation is the ratio of oxygenated hemoglobin to the total hemoglobin. Body tissue absorbs different amounts of light that is passing through it depending on the oxygenation level of the blood.
The system consists of a LED driver and a photo-diode, Figure 4. The output of the photo-diode is conditioned by programmable gain amplifiers and then digitized. This component will have an AC component and DC component. The AC component is a result of absorption by the arteries while the DC component is a result of absorption by tissues and veins. Analog components on PSoC can be used for this application. The external components include LED emitter, detector. The digital data obtained is stored in a non-volatile memory.
Figure 4: Block diagram of pulse oximeter