[Top][All Lists]

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: [gpsd-dev] OBD data, suitable for GPSd inclusion?

From: Jim Thompson
Subject: Re: [gpsd-dev] OBD data, suitable for GPSd inclusion?
Date: Tue, 26 Jun 2012 18:00:34 -0500

On Jun 25, 2012, at 7:28 AM, Derek LaHousse <address@hidden> wrote:

> Hello, GPSd developers.
> I'd like your opinion on whether gpsd should support OBD data from
> automobiles, or if it would be okay to create an obdd in gpsd's image.
> Cars (in the US at least) made in the last decade have an OBDII port,
> where a technician can read error codes and clear them.  It also allows
> a device to ask for the speed, pedal positions, air temperature, etc.
> See for more.  The interface
> to the car is (sometimes) an Elm327-compatible device which converts the
> variety of OBD protocols to a serial connection.

The interface in the car is expressly never an ELM327-compatible device, as 
that would be a violation of Federal law.  The OBD-II specification cites a 
female 16-pin (2x8) J1962 connector, which must be located within 2 feet of the 
steering column.

SAE J1962 defines the pins as:

1. Manufacturer discretion. GM: J2411 GMLAN/SWC/Single-Wire CAN.        
2. Bus positive Line of SAE-J1850 PWM and SAE-1850 VPW  
3. Ford DCL(+) Argentina, Brazil (pre OBD-II) 1997-2000, USA, Europe, etc. 
Chrysler CCD Bus(+)  
4. Chassis ground       
5. Signal ground        
6. CAN high (ISO 15765-4 and SAE-J2284) 
7. K line of ISO 9141-2 and ISO 14230-4
8. -    
9. -
10. Bus negative Line of SAE-J1850 PWM only (not SAE-1850 VPW)
11. Ford DCL(-) Argentina, Brazil (pre OBD-II) 1997-2000, USA, Europe, etc. 
Chrysler CCD Bus(-)
12. -
13. -
14. CAN low (ISO 15765-4 and SAE-J2284)
15. L line of ISO 9141-2 and ISO 14230-4
16. Battery voltage

Now, you might plug an ELM327-compatible device into the OBD-II port, but that, 
as they say, is different.

Given that, as of 2008 all vehicles sold in the US are required to implement 
CAN as one of their signaling protocols, the new sexiness is to read the CAN 
data directly off pins 6 and 14, and for this, you don't need (or want) an 
ELM-327 in the circuit.  The ELM can do it, but it's s-l-o-w.   The CAN bus 
operates at 250 kbits/sec or 500 kbits/sec, and the ELM-327, which is really 
just a pre-programmed PIC, isn't quite up to the task.

So there is nothing technically wrong with your proposal, but as the 1996-2008 
fleet ages out, it will become of less and less use.  

That said, there is some CAN protocol stuff in gpsd for use with NMEA-2000, so 
perhaps that could be studied, if not re-used.

You asked.


reply via email to

[Prev in Thread] Current Thread [Next in Thread]