Car monitor

Hi all,

I am trying to make a car monitor with a 16F876. I have a function generator that I am using to simulate the RPM's and speed while measuring voltage to an analog pin through a voltage divider. Later on I will add some other funtions to make it more interesting. This is all working fine on my bench but I have doubts when I try to implement it into the car. Without trying to develop an OBDII interface, because I don't know anything about it, I was going to tie into the pulses from the speed senor and the engine RPM sensor. If I was trying to make this device for numerous types of vehicles, would the calculation for speed and RPM be different for each vehicle? Does anyone know if the values are different for different models by the same manufacturer? If I am going down the wrong path, please chime in and let me know if there is a better way.

Thanks,

Chris

RPM frequency will be different from a car to another depending if it's a 4,6,8,10,12 cylinder. Worst if it's a 1,2,3,4... coils distributor.

So you can Even build a programmable unit wich will support all motor type tach/coils models.

For the VSS... same thing some will produce 4000,6000.... pulse/miles. That's a real pain. Some after-market Cruise control company have few chart on their website like http://www.rostra.com/

i'd install remote starter, cruise control and about everything electronic in customer car over a decade so i can really talk about that.

Good luck and be sure you can provide the tech-support if it's going to be a commercial product...

I have done a fair amount of OBDII stuff. You are correct it is a pain that being said there is a really easy way to do it. I use ELM Electronics chips in my OBDII projects.

Homepage:
http://www.elmelectronics.com

Direct to chips:
http://www.elmelectronics.com/thehome.html#ELM320

They make individual chips for each type of vehicle or one "super" chip that can be used on any OBDII vehicle. The chip communicates with your PC (or PIC) via serial with ASCII commands. The interface, timing, and protocol to the vehicle is handled by the chip. Makes things really simple! For $14 you can’t really beat it.

Another good resource for software and example schematics using this chip:

www.scantool.net

Enjoy.