Welcome to the community! I’ll be glad to help you.
My car’s spare tire is a full-sized spare tire rather than the “donut” tire that most cars have. Unlike the donut, my spare tire will very slowly leak air like regular tires since this spare is essentially a regular tire. My four regular tires are topped off with air every time the tires are rotated, which is about every 5,000 miles (every 3-4 months or so).
However, the spare tire is not topped off regularly since most spare tires are “donuts”, the spare is hard to reach (in the trunk), and it is not part of standard tire shop maintenance procedures. As a result, low spare tire pressure can make the spare unusable if not maintained regularly.
Unfortunately, most cars are only set up to monitor the four tires touching the ground and not a fifth tire sitting in the trunk. As a result, I needed another way to know if the spare needed air.
I wanted to monitor the tire pressure in my spare tire with Home Assistant so that I can receive alerts to refill the tire whenever it is needed.
- TPMS sensors
- Home Assistant
- Bluetooth module
When I started this project, I only knew of TPMS (tire pressure monitoring sensors) devices that are internal to the tire attached to the air stem. After some research and posting questions, I discovered some devices that attach externally to the existing valve stem by replacing the existing cap and then communicate using BLE (Bluetooth Low Energy). I ended up purchasing these sensors since someone else has used them successfully.
Home Assistant has thousands of native integrations, but reading TPMS sensors is so niche that there is not yet native support for these devices. Luckily, several people in the Home Assistant community have written ways to read the values of these devices. I went with this integration since it was successfully used by someone else and it was the one most recently updated by the integration creator.
Because the devices communicate using Bluetooth, you will need a Bluetooth receiver close to the TPMS sensors. Initially, I used a standard ESP32 module to run a Bluetooth proxy. This worked, but just barely. Since the sensors are using low-energy signals and the spare tire is now inside a metal box (the trunk of my car), I was getting very little signal to read the values even though my Bluetooth proxy is about twelve linear feet from the spare tire. I have a separate thread that will hopefully overcome this issue.
Once you have all the parts, set up the Bluetooth proxy as shown in the linked instructions and place the proxy as close as you can to where you park your car. Install the integration software using HACS (Home Assistant Community Store) according to the linked instructions.
Once you are ready to install the TPMS sensors onto your tire, do so while being near the Bluetooth proxy module and then complete the Home Assistant configuration with the tire outside of your car. The TPMS sensor should transmit its readings every 5-15 minutes, and if all goes well, Home Assistant should automatically detect the TPMS device within a few minutes of installation onto the tire.
The sensor should show up as a device within Home Assistant and the integration should recognize it as a TPMS data source. You can now put your tire away. From there, name the device as something useful to you and you’re now off and rolling (spare tire pun intended).
The resulting values graph of the tire pressure may have gaps in it depending on the actual integration you used or if the integration hasn’t been updated since I installed it on my setup. With my values for example, the purple line in the graph below is the raw values I received from the TPMS device with lots of holes in the line, while the blue line is a smoothed version of that data (the two holes in the blue line are two times when I rebooted Home Assistant for unrelated reasons). To get this smoother line, use the sensor code provided earlier in this thread as an example for your use.
After that, set up an automation to send you an alert notification when the tire pressure is below a certain threshold for your tire. For mine, I want the spare to be above 32 psi at all times. Once I am alerted the pressure dipped below 32 psi, I will refill the tire to 37 psi.
IMPORTANT NOTE: Follow the manufacturer’s recommended tire pressure range for your specific vehicle.
Hopefully this helps you get started. Good luck and have fun!!