Transducer/Odometer

[carlosdesa]

Hi everybody! I would like to know how a transducer work with the odometer of a car. How does the odometer get the miles from the wheels? Who sends the information to the odometer and how does that information is collected?

Thanks!

[maxwedge]

Depends on the car and the type of speedo, a signal from a speed sensor in the trans is sent to the pcm, then is converted and powers a stepper motor in the speedo head.

[carlosdesa]

Originally Posted by maxwedge

Depends on the car and the type of speedo, a signal from a speed sensor in the trans is sent to the pcm, then is converted and powers a stepper motor in the speedo head.

I want to know about GM chevrolet Celta 2003 transducer and odometer.

[maxwedge]

What ever that is ,not here in the USA.

[carlosdesa]

Originally Posted by maxwedge

What ever that is ,not here in the USA.

Ok, tell me an example about a car that you know about. From year 2000 forward.

[maxwedge]

Any fwd GM car with a analogue speedo uses this method. My 2003 Buick Lesabre for example.

[carlosdesa]

Originally Posted by maxwedge

Any fwd GM car with a analogue speedo uses this method. My 2003 Buick Lesabre for example.

Depends on the car and the type of speedo, a signal from a speed sensor in the trans is sent to the pcm, then is converted and powers a stepper motor in the speedo head.

Can you explain it with details? I want to build a taximeter...

[shorod]

Maybe the easiest way to do this for you would be the either start with a vehicle that has a hall effect speed sensor already and tie in to that, or to place a magnet on a drive axle with a hall effect sensor fixed to particular point (this is probably easier on a RWD vehicle with a larger driveshaft), determine how many units of distance apply to a single pulse, build your circuit to count the pulses and multiply that by your "cab fare" for the given distance. Using the hall effect sensor and square wave allows the use of digital circuits and avoids the need of an A to D converter.

If the vehicle you choose has anti-lock brakes, you likely will already have access to a pulse from a tone ring and hall effect sensor system. The downside to this is there will be many tones per axle revolution so your counter will need to be capable of registering the tones coming in at a much higher rate.

-Rod

[jdmccright]

I can delve a little more into the details on the sensor and how it registers the signal from the "tone ring" that is on the axle.

As mentioned, the sensor utilizes the Hall effect to detect rotation of the axle. The sensor is basically an electromagnet (EM for short) that is fed a low voltage from the ABS or PCU modules. The result is a current signal that can vary between 4-20 mA (milliamperes). Left alone and away from other metallic items, the EM will generate a constant current. This current (any current actually) induces a tiny magnetic field around the wire. The sensor is a wire wrapped into many loops to amplify this field.

Now the Hall effect occurs because the magnetic field can be altered by other magnetic objects that come near the sensor's magnetic field and alters it...say the big tooth of a tone ring. Any change in the magnetic field also causes a change in the current running through that wire. So, as the tooth passes through the sensor's field, it causes a momentary change in current through that circuit. As the tone rings spins, the sensor will detect a pulsing current equal to the number of teeth on the tone ring for each full rotation of the axle. Do some math and you can determine the distance the tire rolls for each axle rotation.

You can certainly try to build one of these but if you're looking for something easy to rig together, I'd find a small speedo/odo unit for a bicycle and adapt that rather than building a whole electronic circuit from scratch. Around here they're around US$20-30 and would be good enough for tracking mileage. I do not know if your gov't or other business regulating bodies will accept this if they require trip meters.

Good luck!