Decoding radio pH capsules with rtl_433
Recently I was implanted with a wireless capsule to monitor stomach pH (specifically, the Medtronic “Bravo Reflux Capsule”). It’s a sensor that’s temporarily attached to your lower esophagus, in order to measure the pH in-situ. This is a pretty common procedure ever since it supplanted the previous gold standard of cathether-based ambulatory pH monitoring, with a cathether running through your nose.
Aside: Unfortunately you do lose intraluminal impedance measurements with this type of small wireless sensor, but that’s a separate story.
Because the capsule transmitted wirelessly, it gave me an opportunity to see if I can capture the data myself, given that when I examined the patient demo capsule, it seemed to be a very small, very low-power transmitter with 2 watch-battery-sized coin cells as a power source. This likely meant that this device is:
But how did it communicate wirelessly? The medical tech described the communication as “Bluetooth-like”, which would likely be a no-go for data capture depending on the version of Bluetooth. Plus, there are a plethora of specialized low power transceiver chipsets these days in the license-free ISM bands (which you may know as Wi-Fi and Bluetooth), due to the thriving mobile and IoT markets. But the first thing that caught my eye was the manufacturer’s image: “433”.
