WATCH D3-Inspired Cuff-Based Blood Pressure Monitor: Oscillometric Systolic and Diastolic Measurement with ESP32

Blood pressure is one of the most measured vital signs in the world, yet most students have never seen how a monitor actually finds its two numbers. This monitor makes that measurement visible. An arm cuff inflates around the upper arm, a pressure sensor watches the cuff as it deflates slowly, and the small pressure pulses caused by blood pushing past the squeezed artery grow and then shrink into a curve called the oscillometric envelope. The point where that curve peaks gives the mean arterial pressure, and two fixed ratios along the curve give the systolic and diastolic readings. The whole process runs on an ESP32, and a local dashboard draws the cuff pressure trace, the envelope, and the final reading together, so a student can point at the exact curve that produced each number.

This monitor works by squeezing an artery and listening, through pressure alone, to how blood fights its way past the squeeze, in four stages that all run on the device. First, the pump inflates the cuff above the expected systolic pressure, which fully closes the brachial artery and stops the oscillation pulses. Second, the valve lets air out slowly, and as cuff pressure falls below systolic pressure, blood starts to push through in spurts, producing small pressure pulses in the cuff that grow as more blood gets through. Third, the pulses reach their largest size when cuff pressure equals mean arterial pressure, then shrink again as the artery stays open through the whole heartbeat. Fourth, the firmware reads the envelope of those pulses, marks the peak as mean pressure, and applies the systolic and diastolic amplitude ratios to report the two familiar numbers with a pulse rate counted from the pulse spacing.

1. The cuff is wrapped snugly around the upper arm at heart height, with the sensor line connected to the pump, valve, and pressure sensor manifold.
2. The pump inflates the cuff to a target pressure of 180 mmHg, then stops, and the firmware confirms a stable hold with no fast leak.
3. The solenoid valve opens in short pulses to release air at a controlled deflation rate of about 3 mmHg per second.
4. The pressure sensor samples cuff pressure at 100 Hz while the firmware high-pass filters the signal to extract the arterial oscillation pulses.
5. The firmware builds the oscillation-amplitude envelope across the deflation and records the cuff pressure at the envelope peak as mean arterial pressure.
6. Systolic pressure is read where the envelope reaches 55 percent of its peak on the rising side, and diastolic pressure where it falls to 85 percent of its peak on the falling side.
7. The dashboard displays systolic pressure, diastolic pressure, mean pressure, and pulse rate, logs the reading with a quality flag, and the student repeats the measurement to compare readings.

Tech stack:

• ESP32-S3 microcontroller
• MPX5050 piezoresistive pressure sensor
• Mini DC air pump · solenoid valve
• Upper-arm cuff with air bladder
• OLED display module
• ESP32 web dashboard
• CSV reading log
• Rechargeable battery pack

This monitor is built around four capabilities a student can demonstrate live: an automatic inflation and controlled-deflation cycle driven by a pump and a solenoid valve, a pressure-sampling chain that separates the slow cuff pressure from the small arterial oscillations, an oscillometric algorithm that finds systolic pressure, diastolic pressure, mean pressure, and pulse rate from one deflation curve, and a local dashboard that draws the pressure trace and the envelope next to the reading. Around those core capabilities, the software keeps a reading log with timestamps and a result quality flag, exports readings as a CSV file for the report, and repeats the same measurement on demand so a student can compare consecutive readings and see real measurement variation between sittings, which turns a single number into a repeatable experiment the student can defend in review.

• [Automatic cuff cycle] A mini DC air pump inflates the cuff to a set target pressure, then a normally-closed solenoid valve releases air at a slow controlled rate, so the full measurement runs from one button press with no manual pumping. Implemented in the base prototype.
• [Oscillometric pressure sensing] A piezoresistive pressure sensor samples cuff pressure at 100 Hz, and the firmware separates the slow deflation trend from the arterial oscillation pulses riding on it. Implemented in the base prototype.
• [Systolic and diastolic detection] The firmware builds the oscillation-amplitude envelope, takes its peak as mean arterial pressure, and applies fixed amplitude ratios on the rising and falling sides of the envelope to find systolic and diastolic pressure. Implemented in the base prototype.
• [Local reading dashboard] A web dashboard on the ESP32 shows the live cuff pressure trace, the oscillation envelope, the latest reading with pulse rate, and the reading log, served over the local network with no cloud account. Implemented in the base prototype.
• [Reading log and CSV export] Every completed measurement is stored with a timestamp, systolic pressure, diastolic pressure, mean pressure, pulse rate, and a quality flag, and the log exports as a CSV file for the report. Implemented in the base prototype.
• [Measurement quality flags] A reading is flagged when the cuff leaks faster than expected, when motion corrupts the envelope, or when too few oscillation pulses are found, so a bad reading is labelled as bad instead of being reported as a number. Implemented in the base prototype.
• [Repeat-measurement comparison] The dashboard keeps the last readings side by side, so consecutive measurements on the same arm can be compared and the natural variation between readings becomes part of the demonstration. Implemented in the base prototype.

• Working prototype: ESP32-S3 controller, MPX5050 pressure sensor, mini air pump, solenoid valve, upper-arm cuff, OLED display, and battery pack, wired and tested
• Complete ESP32 firmware for inflation control, controlled deflation, 100 Hz pressure sampling, envelope detection, and the ratio-based systolic and diastolic calculation
• Local web dashboard with live pressure trace, oscillation envelope, reading display, reading log, and CSV export
• Circuit and wiring documentation with labelled connections for every wire
• Component list with the exact parts used in the build
• Calibration and demonstration procedure, including the static pressure check against a reference gauge and the repeat-measurement comparison
• Project report PDF (background, oscillometric theory, methodology, results format, limitations)
• PPT presentation for final review
• Viva Q&A preparation document (oscillometric method, envelope ratios, pressure sensor operation, pump and valve control, why a student monitor is not a medical device)
• Builder note: keep the sensor, pump, and valve manifold airtight with short tubing, because even a small leak steepens the deflation curve and shifts the envelope ratios enough to move the reported readings