Inside a TPMS diagnostic tool

[Stonent]

I had a opportunity to look inside a USB based device for talking to and diagnosing a  tire pressure monitoring sensor.

The issue was that they could read one sensor but it would refuse to read any more.

I took the opportunity to open it up and it was about 90% an arduino inside. It had an Atmega64 and an FTDI chip and not much else.

The communication works by placing against the tire near the valve stem and telling the laptop to read the sensor.

There are two antennas inside. One is a ferrite rod about 1cm in diameter about 5 or 6 cm long that is wrapped with copper wire. It strongly resembled an old AM radio antenna but thicker.  The other one looked like a 1/4 wave ISM band antenna that you might see on a Bluetooth dongle.

I suspect the ferrite rod antenna is to power the sensor and the shorter one to receive the data.

When a reading is initiated the ferrite antenna feels like it very slightly pulls on a screwdriver placed on it.

I don't recall seeing any other ICs on the board so it may have all been done through the PWM and ADC.

If I get a chance ever to look at it again I'll look under the board.

The issue ended up being the USB connection to the computer was slightly loose. I bent the USB cable connector slightly so it gripped a little more firmly and it worked fine after that.

[NiHaoMike]

Pictures seem to be missing...

[Stonent]

Pictures seem to be missing...

Unfortunately cameras were not permitted where I was, so I had to describe it.