JustinN1

So the board that sparkfun sells has a chip on it that does the OBD II standard instruction sets (there are a bunch that you will find out about as you start digging into things). The arduino (or other microcontroller) communicates with the board via a serial interface (rx/tx) and uses AT commands (if you are old enough you may remember these from early modems). The serial DB9 interface from that board to the obd port is purely the choice of the people at sparkfun who designed it. It probably has to do with it having a sufficient number of pins and being cheap and readily available.

I do have some analog input stuff. In fact I'm doing some of that for my car right now...I've got turbo pressure, oil pressure, oil temp and in some old projects I did some thermistor stuff to get air temps from the engine bay (which is pretty usesless). You can dig around in my github stuff here https://github.com/stirobot . But I'll just paste the functions that read the boost and such values here (there is test code you can comment out or use for when you just want to make sure your display is working):void getBoost() { float rboost = analogRead(A0); //float ResultPSI = (rboost*(.00488)/(.022)+20)/6.89 - atmo; //leave of the /6.89 for kpa float ResultPSI = (((rboost / 1023) + 0.04) / 0.004) * 0.145 - atmo; //by 0.145 to calc psi return (ResultPSI);}void getOilPSI() { float ps...

I do have some analog input stuff. In fact I'm doing some of that for my car right now...I've got turbo pressure, oil pressure, oil temp and in some old projects I did some thermistor stuff to get air temps from the engine bay (which is pretty usesless). You can dig around in my github stuff here https://github.com/stirobot . But I'll just paste the functions that read the boost and such values here (there is test code you can comment out or use for when you just want to make sure your display is working):void getBoost() { float rboost = analogRead(A0); //float ResultPSI = (rboost*(.00488)/(.022)+20)/6.89 - atmo; //leave of the /6.89 for kpa float ResultPSI = (((rboost / 1023) + 0.04) / 0.004) * 0.145 - atmo; //by 0.145 to calc psi return (ResultPSI);}void getOilPSI() { float psival = analogRead(A1); //Serial.print(psival); if (psival > 722) { return (0); } if (psival < 257) { return (110); //110 swings higher than the gauge goes which will alert the user to something being wrong } if ((psival <= 722) && (psival > 619)) { //722 = 1.42 return 174.7 - (psival * 240) / 1000; } if ((psival <= 619) && (psival > 520)) { return 180.2 - (psival * 250) / 1000; } if ((psival <= 520) && (psival > 411)) { return 169.4 - (psival * 230) / 1000; } if ((psival <= 411) && (psival > 257)) { //257 = 100.68 return 141.8 - (psival * 160) / 1000; }}Basically what you want to do is go to a sensor manufacturer (I like autometer and that is what some of my stuff is based on) and ask them for resistance curves for the sensors. A lot of sensors change the resistance based on a change in the environment. You then set these up in a voltage divider circuit (google it, it's fairly straightforward) and that gives you a voltage reading that you read off of one of the analog input pins on the arduino. Then after that it's just a scaling problem to get the right numbers to show up on whatever display you are working with.

Sure...post what errors you are getting (aka why the OBD parts don't compile). I haven't looked at the ELM code in a while and it is possible that it isn't compatible with newer arduino stuff.

This has some ideas: https://communities.intel.com/thread/57555Also this shows a good example (and happens to be what I'm using the edison for now): https://gist.github.com/logxen/ad195ccd31914bab886...

Cool. I'm excited for someone else to build one. I have only run across one other person who build one and it was in a german car forum.The https://www.clusterfsck.io/blog/arduino-elm327-library/ link seems to work for me. Maybe the link is blocked in your country or their server was down for a few minutes. The direct link to the library is here: https://github.com/irvined1982/arduino-ELM327

Here is the link to that german forum: http://forum.gt86drivers.de/index.php?page=Thread&threadID=739