Go Back   Steve's Digicams Forums > Digicam Help > General Discussion

Reply
 
Thread Tools Search this Thread
Old May 31, 2003, 8:38 AM   #1
Junior Member
 
Join Date: May 2003
Posts: 3
Default link car speedo to cam display

Hi

Does anyone know how to link a car speedo to the digital video camera display (like the police). It would be useful for a University project that I am doing.
Thanks in anticipation

Pheonixxx
pheonixxx is offline   Reply With Quote
Sponsored Links
Old May 31, 2003, 5:18 PM   #2
Senior Member
 
Join Date: Aug 2002
Posts: 1,910
Default

You got a few problems with that project to solve. First off the speedometer is a mechanical device, hooked up via a cable to the transmission. Second is those cameras can't be bought in a common electronics store...those are specialized units which can take inputs like the speedometer (probably via an electronic sensor from one of the wheels, the same type that is use for sensing if a wheel is locked/spinning for anti-lock brake/traction control systems), and an input to show that the lights are flashing (in pursuit mode).
Mike_PEAT is offline   Reply With Quote
Old May 31, 2003, 11:39 PM   #3
Senior Member
 
Join Date: Dec 2002
Posts: 5,803
Default

Most modern cars have both an OBD2 port (under the dash) and a separate port which directly hooks into the computer system of the car. I don't believe you can record the speed through the OBD2 port, but I bet you could if you hooked into the proprietary computer port (probably under the hood.) The key word is proprietary. Dealer mechanics know the protocol, the question is if you can get the info.

I would post a question about accessing real time speed information about a given car to a more appropriate web site or netnews/usenet forum (rec.auto.makers.<make> might be a good start.) If you could find a camera which read numeric values through a port and displayed them in real time, then you're only problem is to convert the speed info from the car computer into the proper format for input into the video camera. A phone call to B&H Photo Video in NY (bhphotovideo.com):
800.952.3386
212.444.6711

might help you find the camera. They are a very good camera store that also sells video equipment... I bet they know a lot about that too.
eric s is offline   Reply With Quote
Old Jun 1, 2003, 4:05 AM   #4
Senior Member
 
Join Date: Aug 2002
Posts: 2,162
Default

Many cars now use electronic speedometers. The have asimle permanent magnet transducer (like a multipole permanent magnet dynamo) fitted in the gearbox. The output is a pulse train proportional to the gearbox shaft rotation. Each sensor is usually colour coded to give the same frequency of pulses to the speedo head, for different differential/tyre sizes.

As suggested, the OBD2 port is a way into the engine computer, but I once tried to find out info on the protocols and it was very difficult. You would need lookup tables in your software for each manufacturer type.

There may be ways to determine the speed of a vehicle using GPS, but this might be overkill for you.
voxmagna is offline   Reply With Quote
Old Jun 1, 2003, 5:42 AM   #5
NHL
Senior Member
 
NHL's Avatar
 
Join Date: Jun 2002
Location: 39.18776, -77.311353333333
Posts: 11,545
Default

Excellent idea Eric!... How about setting it up so you can capture both the speedo and the windshield just like the police?
http://www.wirelessvideocameras.com/

All new cars manufactured since the early 90's are required to have OBD-II (some states uses this for emission testing) and it's capable of real-time data capture including speed:
http://www.obd-2.com/dashg.htm
It's based on CAN, Controller(Car) Area Network (some flavor of 8051, 8096, and 68xxx has it built-in) there's optional manufacturer specific code for each vehicle, but the protocol is generic:
http://216.239.39.100/search?q=cache...hl=en&ie=UTF-8

... A caveat though, the standard doesn't cover the physical connectors (it's round on a BMW, rectangular on an Audi, etc...) so a dongle/adapter cable is usually required :P :P :P
NHL is offline   Reply With Quote
Old Jun 1, 2003, 8:50 AM   #6
Junior Member
 
Join Date: May 2003
Posts: 3
Default wow thanks

Thanks all for the replies. I will share all with the board if i get any success with this problem. I should have mentioned that I am in the UK; therefore some of the info given could be different for British cars but, I will look into it further. My car is a Fiat Punto 1997 if that helps any. I will ask on some car related boards to see if I can further my quest
pheonixxx is offline   Reply With Quote
Old Jun 1, 2003, 9:48 AM   #7
NHL
Senior Member
 
NHL's Avatar
 
Join Date: Jun 2002
Location: 39.18776, -77.311353333333
Posts: 11,545
Default

It's pretty much a de-facto standard worlwide if a car has an ECU, or for different subsystems to communicate to one another ie Eaton, Bendix, Bosch etc... and is also use for controlling the cost of diagnostic and repair of modern cars:
http://www.can.bosch.com/content/What_is_CAN.html
NHL is offline   Reply With Quote
Old Jun 1, 2003, 1:15 PM   #8
Junior Member
 
Join Date: May 2003
Posts: 3
Default thanks

Thanks again for the help, its not as straight forward as I had hoped but I will keep you posted if I find the solution. The links were very interesting and food for thought.
pheonixxx is offline   Reply With Quote
 
Reply


Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off



All times are GMT -5. The time now is 12:32 AM.