ODB-II Odometer

**kiwiuser** · 04-11-2007, 07:55 PM

Hi guys,

I have a fairly simple question and I have researched the existing forums already but havnt really been able to find out conclusively whether it is possible.

I want to put a PC in commercial vehicles that measure distances down to a tenth of a meter. (this is only one of many functions).

Currently I achieve this with a wheel probe or proximity sensor - i then run this into a data aquisition board and run it through custom software that I have written. This however requireds a $150 probe and $200 data aquisition board.

What I want to know is...is there a reliable way of getting the odometer reading from ODB-II in most japenese vehicles?

Is so... what is the accuracy?

Has anybody tried interfacing the speed sensor in vehicles directly? If so how did that go?

Any help is greatly appreciated.

Cheers kiwiuser.

**joeyoravec** · 04-11-2007, 09:38 PM

If you're doing this professionally and can afford the ETI membership (www.etools.org) there's probably some way to read the odometer over the network. It isn't cheap, but there's no OBD-II technique so you'd need the manufacturer specific information and ETI is really the only place to get that.

**kiwiuser** · 04-11-2007, 11:30 PM

Thanks for the advice, I will take a look now.

Cheers,

Kiwiuser.

**kiwiuser** · 04-12-2007, 04:22 PM

How about interfacing a speed sensor somehow, does anyone know anything about that?

Cheers,

Kiwiuser

**chewwtoy** · 04-14-2007, 10:59 AM

GPS? This could give you accuracy as far as distance measurement however not in pinpoint accuracy.. but you should be able to get distances... (or at least that's what I've heard).

You said commercial vehicles? What type of vehicles? Heavy Truck Commercial Vehicles, light truck... what?

This could make a difference.

**bbalazs** · 04-15-2007, 03:53 AM

Originally Posted by kiwiuser

How about interfacing a speed sensor somehow, does anyone know anything about that?
Cheers,
Kiwiuser

Yes, I did. In my car (Seicento, FIAT) the wire of the speedometer receives 12V/0V square pulse signals, approx. 16 (I do not remember exactly) on a single wheel turn. I use it with a PIC for measuring the speed and distance.
This data is similar concerning other cars.
I think this accuracy fits your requirements.

You can use a PIC or a frequency/voltage converter ic.

**kiwiuser** · 04-23-2007, 11:27 PM

Originally Posted by bbalazs

Yes, I did. In my car (Seicento, FIAT) the wire of the speedometer receives 12V/0V square pulse signals, approx. 16 (I do not remember exactly) on a single wheel turn. I use it with a PIC for measuring the speed and distance.
This data is similar concerning other cars.
I think this accuracy fits your requirements.

You can use a PIC or a frequency/voltage converter ic.

Hi there,

I would be most interested in how you use it with a PIC for measure distance. can you please provide some more information? Or contact me privately?

Thanks very much.

**bbalazs** · 04-24-2007, 04:34 AM

I wrote a simple program to PIC that count those pulses (it saved the value into EEPROM) and displays it on a small LCD.
Then I zeroed the daily km-counter on the dashboard.
After driving approx 800km, I simply divided the km value with the number of pulses and got a constant, that I use to calculate the speed and distance. I think it is not difficult at all.

I have used 18F4525 with a LCD display.
I have used a serial 4K7 resistor and a 4.7V zener diode in reverse to the ground parallel for the appropriate voltage that fits the PIC ttl level.
The whole electronic was present on a tiny board (I designed a demo panel for practicing with different PICs).
Because the power need is very little of the PIC, for the simplicity I fed it from the cig lighter connector.

So, measuring the distance is VERY simple, just multiple the number of pulses with that constant and it gives the distance.
For measuring the speed I program a timer that makes interrupt in every second (It is more frequent inside, but I divide it internally, of course) and
subtract the previous value of the pulses from the present pulse value.
So, I get the distance within a certain time (half second) so the result is in m/s, then multiply it with 3.6 then the result is in km/h now. For miles/h this value could vary.

You can also gain that constant by different method: Have an exact distance (eg. 10m) and apply a LED on that pulse wire (with a serial resistor, of course). Push your car slowly forward and count the number of periods when the LED light.