I’ve been meaning to hack my blood pressure monitor for a while, and I finally got around to doing it! So, the idea is to mod a regular electronic blood pressure monitor to make it wireless and connected to the Internet, much like iHealth BP5 or Withings’. That makes detecting trends in your blood pressure much easier, since you can chart the data and even correlate it with other health data, such as how much sleep you’ve been getting, your weight or your level of activity. The model I have is the EW3106 from Panasonic. It’s quite old but from what I’ve seen the design hasn’t changed much throughout the years. The other part of the solution is the ESP8266. It’s an awesome little Wi-Fi module. It has a TCP stack and only uses about 20% of it’s CPU resources, which means you can run your own software on it, with no need for an external MCU. Some cool guys have added support to the Arduino environment, which makes it really easy to use. And when you consider it costs little more than $4 it’s really a no-brainer. Since the unit has a feature to store measurements (the blue M/R button), I figured it would probably have a memory chip connected to an I²C bus. My idea was to, whenever the user decided to save a new measurement, retrieve the data stored by the MCU, make sense of it and push it to the cloud.
Should you choose to attempt this project on your own, keep in mind you’re modifying a medical device and that CAN interfere with it’s accuracy and reliability. Remember that a Wi-Fi device emits RF which can affect other devices. If you choose to modify it, don’t use it as a medical device anymore. Use this information and code at your own risk. I cannot be held liable if, knock on wood, your house burns down or your your dog dies!
The insides of the the EW3106
This type of blood pressure monitor is known as an oscillatory blood pressure device. The way it works is it inflates the cuff so the pressure around your brachial artery is high enough that it collapses, completely blocking the flow of blood. Then, it starts slowly releasing the pressure until the unit can hear the blood “whooshing” through the compressed artery. That’s your systolic pressure. It then keeps on releasing the pressure until it cannot hear it anymore. That’s your diastolic pressure.
The unit was quite a hassle to open. I hate these plastic hooks, it’s hard to open without breaking them or damaging the plastic, even though they make a lot of sense from a manufacturing point of view. Some elbow grease and a bit of patience and it came off. This is how the monitor looks inside. There’s a PCB with the LCD on top, two switches, an air pump (the metal part in the left upper corner) and a valve (yellow thing, lower right corner). When you press the button the valve closes and the pump inflates the cuff, while the MCU samples a pressure transducer connected to the cuff. The MCU can be seen on the top side of the board, along with two smd potentiometers, which are probably used to calibrate the unit.
Read More: Hacking a Blood Pressure Monitor