rusefi.com

I've looked around for a good TPMS. Seems these thing vary in price and features. I found I could get 4 tires form a unknown china source for around $80, or I could get a more reputable system that integrates with my smartphone for $179. The $179 device has just come out with an option for a 5th wheel which can be used for my spare tire.

https://my-fobo.com/Product/FOBOXTRA

Most of these systems are using Infineon's SP37 which is a pressure sensor that transmits via 433MHz to a head unit. Tire pressure sensors can be obtained for around $15 to $25 per sensor. So I'd like to add to the pie in the sky wish list a 433MHz receiver that can decode these signals.

https://www.infineon.com/dgdl/SP37_RF_v1.0.pdf?fileId=db3a30433899edae0138c2ade4bb01cf

Last I heard, 433MHz is not allocated for unlicensed use in Regions 2 or 3- colored blue and violet in the image below.
However in Region 1- Europe, Africa, parts of the middle east and northern Asia- i.e. Russia and such, it's okay; colored amber in the same image.

In the SP37 datasheet it notes

The RF transmitter can operate in either the 315 or 434 MHz frequency bands and can be configured for an output power of either 5 or 8dBm.

So I guess the pie in the sky receiver would need to be 315 or 434 MHz. Is 315 OK in non 434MHz areas?

I wonder if a generic receiver can be purchased. I'd kind of like one with I2C. To me it feels like there should be one of these receivers available already.

This seems to be low enough cost https://www.sparkfun.com/products/10533 for 315MHz and https://www.sparkfun.com/products/10532 for the 434 MHz. I wonder if they would work or not, they seem to all be FSK, but I'm not sure if the shift is good. Also I'm not sure if it tries to decode the bits or not. The boards are reasonably low price at about $5 per receiver board.

I got my FOBO tire TPMS today. I installed on them wife wagon and my daily. We can share our data such that I can keep an eye on her car and she can keep an eye on my car, which is cool. As luck has it I have a digital envelope scale that measures down to .1oz. I measured sensor with locking nut. Out of the 5 sensors 3 weighed in at .5oz and two weighed in at .4oz. I would guess they weight .46oz +/- .01oz or something like that. I suspect the battery is 70% of the weight, and I suspect the variation is probably the battery. The rest of the parts appears to be machined well, so I don't expect much for variations.

Any how, .5oz isn't much and you probably won't feel it while driving. However I have stick on weights in .25oz increments, so I installed .5 oz to the other side of the wheel.

About frequency allocations, I purchased from FOBO directly, they are lower cost than if I bought from an USA based ebay store. After my purchase was processed, I got an e-mail from FOBO with FCC certs in case customs inquired. A day later I got an e-mail from fedex customs and replied with the FOBO links to their certs. Then a couple days later I got the sensor kits. One for my car one for the wife wagon.

I also got the "extra" sensor for the spare tire. However I have to weight for a software update until I can work with that. I placed the order when they allowed a pre-buy, and they were kind enough to send it all in one package, but I have to wait a week or two until the software rolls out via play store.

All in all it's been good so far. It has a replaceable battery, they appears to be good build quality, the software has worked intuitively.

Blaine says that using cheap ($30 a set) chinese TPMS sensors and rtl-sdr with a $20 SDR and a $5 Pi Zero would allow for TPMS sensors readable in RusEFI (through CAN, UART, etc)

AFAIK, there are several variations of 30$ chinese TPMS sensors: those operating in 330(?)MHz (or other RF frequences) and those using BLE. The RF sensors are usually supplied with some sort of reveicer. So, it's all possible, but what's the use case? Why would you want to feed it into RusEFI?

Just an idea which goes all the way down the priority list, just preserving knowledge.

I've used a MAX41474 to read FSK data; it can also handle ASK in both 315 and 433 range. That should handle almost any TPMS you'll run across. The downside is it's QFN12 but I was able to solder them using the toaster oven method (the pins are 0.8mm apart, so pretty forgiving as QFN goes).

You'll want an antenna tuned for the frequency range you care about; you could leave a footprint for a Linx "splatch" (ANT-433-SP or ANT-315-SP) but you need a pretty big ground plane. Or use an SMA connector for an external antenna....