wireless tyre pressure sensor

[jay543_uk]

Hello all

Im a ford technician who like to play around with electronic projects, iv had an idea for a test tool for work and want to no if it would be easy to do.

I want a tool to test tyre pressure sensors without removing the wheels and tyres.

I no the vehicle sends a LF signal to the sensor (i beleive 125khz ) and then the sensor sends its data back at 433mhz.

So i no the car will send out a LF signal every time i turn the ignition on to read the sensors so i shouldnt have to wurry about the LF side of things but can i just buy a 433mhz reciever and captor the data using a PIC and if so how would i no to use a am or fm reciever

 

[shortbus=]

I don't know how Ford does it but I worked for GM/Delphi Electric and their tire pressure sensors used the anti-lock brake reluctor rings to generate the signals. If all 4 wheels where off by the same amount, the system said they were correct pressure.

 

[jay543_uk]

some system use the abs to measeure each wheel speed to work out if a wheel is flat, ie if a tyre deflats more than any of the others then that tyres circufence is less and turns faster than the rest to keep up.

The system i want to be able to test has a sensor in each wheel and a tx in the wheel arch

the tx sends a lf signal to the sensor and then the sensor sends a rf signal to the main reciever in the middle of the car with all the data ( ie pressure and temp ), each sensor is sent a LF signal one at a time so the module in the car no's what sensor is send the data

 

[MikeMl]

If you need a 433MHz receiver, look at **broken link removed**. I just bought some for a data link project.

 

[jay543_uk]

I have a receiver like one of them that i got off ebay but can i just use any 433mhz to receive the signal or do there have to be a matching pair. Maybe ill rig it up to a scope and see what signals are being received.

Has anyone got any ideas on a LF 125khz tx and rx, would it be easy to receive the LF signal and then copy that signal and tx the signal myself to test the sensors, maybe something i would want to do once i have the 433mhz side working first

 

[MikeMl]

The sensors do not transmit a 125Khz signal; they just listen for it and transmit on 433 if they hear 125KHz. A 125Khz oscillator will not be hard to make.

 

[jay543_uk]

the 125khz signal being transmitted to the sensor has to send data, the sensor gets put into different states depending on the information received by the car.
on start up the sensor is told to transmit every 20 seconds or so and after a few minutes it switches to transmiting every 60 seconds, also if the vehicle see the pressure low on one sensor it tells the sensor to transmit every 10 seconds or so. i would need to build something to listen to the commands sent from the car and then transmit the same command to the sensor to get it out of sleep mode and send data to my test receiver.

 

[jay543_uk]

will the sensor on the car be fm or am, can you get fm 433mhz tx/rx as all i can find are am