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Design Goals
Design Goals
Contactless
Accurate
Cost-effective
Device Design
Device Design
Our design solution consists of an under-sheet device that uses a piezoelectric sensor to measure a patient’s ballistocardiogram and respiration rate. The sensor generates an electric charge in response to the mechanical motion of the heart and lungs that will be converted into a voltage output. The ballistocardiogram/respiration signal, once digitally processed, will provide information about respiratory rate, heart rate, heart rhythms, and cardiac output. The device will be able to visualize relevant data and allow the doctor to quickly analyze a patient’s progression.
Overall Schematic
Overall Schematic
Physiological movement is recorded by the piezoelectric sensor as the raw analog signal, which is then filtered and amplified by the circuit. Arduino has an analog-digital (A-D) converter that converts the analog signal to the digital signal. Raspberry Pi serves as a microcontroller to store, digitally process, and transmit the self-explanatory BCG data to physicians and patients.
Circuit Design
Circuit Design
The hardware component of our device consists of a piezoelectric sensor which is connected to an active high pass filter and inverting amplifier with a gain of 3. We used a single ended operational amplifier, LM 7041, so enough voltage source can be supplied. C1 is the capacitance of the piezoelectric sensor itself, which is 7.3 nF. Rounding out our charge amplifier circuit are components that include a 2.2nF capacitor and a 100MΩ resistor. A voltage divider with 2 100kΩ-resistors in series powered by the 5V DC output from Arduino is connected to the non-inverting end of the op-amp to create a 2.5V DC offset to the ground. The circuit output is then connected to the input of the Arduino to monitor BCG signal changes. Therefore, the Arduino can clearly detect the signal change within the Arduino 0V-5V readable range. With our current circuit, we have a lower limiting frequency of 0.1Hz, which provides the best BCG signal in the Arduino monitor window.
BCG signal
BCG signal
This is an example of the raw digital BCG signal collected by the Arduino.
Parts, resources, and cost
Parts, resources, and cost
Total cost for the project: $424.97
Total cost for each home health monitor: $234.35
By: Haoming Shi
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