This Hack Makes Any Blood Pressure Monitor Smarter

There are plenty of smart health monitoring devices on the market today, but the extra tech they pack in can make them quite expensive. If you already have perfectly functional equipment, like a blood pressure monitor, replacing it just to get Wi-Fi connectivity seems like a waste. Maker Tomasz Burzy decided to take a different approach by turning an ordinary, secondhand blood pressure monitor into a smart device with an ESP32-CAM and a little creativity.

The project started with a cheap blood pressure monitor purchased on eBay. Burzy wanted to automatically upload measurements to a locally hosted health tracking application without having to manually enter the numbers. His initial plan was to tap into the monitor's electronics and extract the measurements directly, but that proved to be more complicated than expected.

After opening the device, Burzy discovered a circuit board populated with an Epson microcontroller, pressure sensor, and the electronics responsible for operating the air pump and valve. Using an inexpensive logic analyzer, he began probing the board in search of the data being sent to the display.

Although he managed to capture raw pressure sensor readings, the final systolic and diastolic values were calculated internally by the microcontroller. He even experimented with writing his own blood pressure calculation algorithm with assistance from AI, but the results weren't accurate enough to be useful.

Rather than continue reverse-engineering the proprietary calculations, Burzy came up with a much simpler (if somewhat clumsy) solution: point a camera at the display and read the numbers directly.

An ESP32-CAM module serves as the brains of the upgrade, capturing images of the monitor's LCD and transmitting measurements over Wi-Fi. However, instead of relying on computationally expensive optical character recognition, the firmware takes advantage of the display's seven-segment digits.

Each digit consists of seven segments that can be illuminated in different combinations to represent numbers. By checking predetermined locations within these segments and determining whether they are illuminated, the ESP32 can reconstruct the displayed systolic pressure, diastolic pressure, and pulse rate.

To keep the camera properly aligned, Burzy designed a custom mounting arm in Fusion 360 and 3D-printed it. He also discovered that reflections from the monitor's transparent display window interfered with detection, so he removed the offending plastic.

The finished build includes two additional buttons for selecting between user profiles, along with an LED that confirms the selection. The ESP32-CAM can also enter deep sleep between measurements, waking automatically when the monitor's start button is pressed.

Once a measurement is complete, the ESP32 reads the display and uploads the results to Burzy's private health tracking application. The open source firmware also supports sending measurements to Home Assistant, Node-RED, or other HTTP endpoints.

Burzy has published the firmware, digit-mapping utility, and 3D-printable camera mount, making it possible to give other conventional blood pressure monitors a similar upgrade. Just remember that the camera can occasionally misread a digit, so important measurements should always be checked against the original display.