To get Obd2 Data via ELM327 C#.NET

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https://burak.alakus.net/en/2011/07/27/to-get-obd2-data-via-elm327-c/

According to me, the most cool part of a CARPC is the part of you’re getting engine data to your touch screen interface. It is really cool. I talked about the protocol called VAN in my previous article. VAN is a sub data protocol of CAN. OBD2 is the way to get data from your engine.

First time when I begin to work on a carpc, I always used free front-ends. But I couldn’t customize the front-end software according to my mind. Because of that I started to write on C#.NET to develop my own CARPC front-end. Multimedia applications, navigation, watching TV via 3G didn’t take my lots of time.

Getting data through my OBD2 port of my car was different. First I tried OBD2 applications like ScanTool.NET, OBDview, etc.

Let me talk about physical connection; In Cars, there is a port with standard 16 pins OBD2 port. This is the port when you get your car to technical service connect to.

The easiest way I know to get data from OBD2 is the OBD2 adapters like ELM327. You can connect that adapter to your PC through USB, and the OBD2 socket to your car. It behaves as a comport through your USB port. This means you can test and also get data from HyperTerminal program or Putty. Its command set is like a modem using AT commands.

So, if you want to get data from your car, connect to your ELM327 adapter through virtual com port using your terminal program. Then send it a AT command. Just it. By knowing this, and if you know just a bit serial programming, do you really need to purchase a Diagnostics application? I answered this question as “NO”.

To start getting informations about your engine status, you need to initialize your ELM327 with your car. OBD2 data protocols varies by car vendors and specs. You need to initialize your OBD2 device according to your car.

Usually, each value in OBD2 (speed, rpm, engine load..) uses 4 digits Hex number to identify themselves. You send the request with their identify number and it responds to you by its identify number. The logic is very easy at all.

Example: Send command “010C”

Receive response “010C001B”

010C is the identifier, 00 1B are the data hex numbers.

the first 00 is the A, and the 1B is the B let’s say.

we will know that the identifier 010C means rpm. To calculate rpm you need to make math between A and B.

rpm=((A*256)+B)/4

Now let’s clarify the initialization process; (C#.NET Code)

serialPort1.PortName = comPort;

            try { serialPort1.Open(); }
            catch (System.Exception excep) {}

            send_data("ATZ");
            System.Threading.Thread.Sleep(2000);
            send_data("ATE0");
            System.Threading.Thread.Sleep(1000);
            send_data("ATL0");
            System.Threading.Thread.Sleep(500);
            send_data("ATH1");
            System.Threading.Thread.Sleep(500);
            send_data("ATSP 5");
            System.Threading.Thread.Sleep(500);
            send_data("01 00");
            System.Threading.Thread.Sleep(500);

The code above, starts sending intialization commands with helping threading. ATSP command is important. ATSP 5… number 5 is the protocol for my car. You need the try it with others if this does not work for yours. To make tries, the best way is to use putty. Use the initialization commands by using your keyboard and try ATSP command from 1 to 5. if the protocol you try is not compatible your car, you get “error” or “no data” response.  It is not a big issue and can be achived by easy movements.

ATZ command; resets the ELM327.

ATE0, ATL0; disables extended responses. When it is disabled it is easier to process the responses programmatically.

ATH1; enables the responses with their headers. It is good to enable it because in responses you can see the identifier of data. So it is easier to understand the response.

We talked about the ATSP command. But as shortly, ATSP1, ATSP2, ATSP3, ATSP4, ATSP5 are the protocols.

0100 command is to test if the connection is OK.

As I talked above, each value of engine has a PID (010C, 010D)

01	0C	2	Engine RPM	0	16,383.75	rpm	((A*256)+B)/4
01	0D	1	Vehicle speed	0	255	km/h	A

To get the other pids meaning you can use the releated wikipedia page; http://en.wikipedia.org/wiki/OBD-II_PIDs

Every car does not response to evey pid. Speed, engine rpm, these are standardized pids. And most cars easily response to that pids.

I can get the ; speed, engine rpm, engine tempature, engine load, engine air flow rate, vehicle battery voltage from my car. (battery voltage is not obd2 releated data, just vc command)

Other thing is threadings.. they are very important because you have to wait for being ready of elm327 before sending a new command. 200 ms is enough for ELM327’s internal process.

Another trick is that you don’t have to try it with your car. there is a simulation application called “obdsimwindows”. It creates a virtual obd2 port

I read about this simulation program in mp3car forum.

http://www.mp3car.com/engine-management-obd-ii-engine-diagnostics-etc/137428-free-software-obd-ii-simulator-redux.html

This is just a obd2 article for geeks not a step by step tutorial.