This stethoscope pressure solution consists of a sound as well as pressure recorder. For sound the I2S (Inter-Integrated Circuit Sound) bus is used to communicate with the microcontroller. This interface allows streaming and recording audio to an audio codec board. The Everest Semiconductor ES8388 audio codec was chosen because its supported by Arduino Audio Tools and Arduino Audio Driver and because Espressif created the Lyrat Audio modules with published reference designs. Sound is recorded with pui audio analog MEMS microphones AMM-2742 that are mounted on the printed circuit board. Two microphones are used where one is connected to the stethoscope and the other recording the background. An dual differential amplifier is used to low pass filter and amplify the signal from the microphone, however amplification would not be needed for the ES8388 codec. Pressure is measured with a Honeywell MPR pressure sensor MPRLS0300YG that convers the physiological range of 0 to 200 mm Hg.
| Item | Quantity at Purchase | Costs | Source | Cost per Brick |
|---|---|---|---|---|
| Microcontroller | 1 | $17.5 | Adafruit | $17.5 |
| Display | 5 | $13 | Amazon | $3 |
| Button | 25 | $9 | Amazon | $0.5 |
| Battery | 1 | $10 | Adafruit | $10 |
| PCB | 5 | $45.18 | PCBWay | $9 |
| Parts and Assembly | 2 | $56.55 | PCBWay | $29 |
| MPRLS0300YG (pressure) | 2 | $35 | Sager Electronics | $17.5 |
| Stethoscope | 1 | $25 | Amazon | $25 |
| Arm Cuff | 1 | $17 | Amazon | $17 |
| Assorted Wires | 8m | $15 | Amazon | $1 |
| Assorted Screws and Nuts | 100 | $7 | Amazon | $0.05 |
| Silocone Tubing | 1 | $9 | Amazon | $2 |
| Luer Lock female 3/32 barb | 10 | $9 | Amazon | $1 |
| Luer Lock male 5/32 barb | 10 | $8 | Amazon | $1 |
| Stainless Steel Tubing | 250mm | $10 | Amazon | $2 |
| Assorted 3D printed parts | $3 | |||
| Total with blood pressure | $140 | |||
| Total without blood pressure | $100 |
Electronic components excluding the pressure sensor are $14 per board.
The pressure sensor was mounted in house as the PCB assembly service did not have access to inexpensive source.
Test software is located in the Arduino folder.
| Folder | Description |
|---|---|
| MediBrick_Stethoscope_ES8388_to_CSV | Prints the two channel audio signal to the serial port for visualization with SerialUI application |
| MediBrick_Stethoscope_ES8388_TestSound | Creates test tone in left and right channel for head phones |
| MediBrick_Stethoscope_ES8388_to_Headphone | Plays the recorded sound to the headphone |
| MediBrick_Stethoscope_PressureTest | Test the arm cuff pressure sensor |
Not available yet.
The following files are needed for PCB manufacturing and assembly.
The Bill of Materials is formatted so that its compatible with PCBWay submissions.
These are the links to the OnShape Design files, which you can edit and modify if you have an OnShape account (OnShape has free academic accounts).
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Microphone Housing
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Medi Brick
The software uses a digital high and low pass filter with cut on at 35Hz and cut off at 2kHz to improve sound quality. The coefficients are computed with a python program.
The frequency content of the stethoscope audio was referenced with papers listed in the code's comment.
