Forum >Using the OBD- UART for Just Serial
Using the OBD- UART for Just Serial
Beaver_2 2013-07-28 20:44:40 8177 Views5 Replies I do not have an arduino, I just have a netdruino, which is like an arduino except runs the .NET MF.
So I plugged the RX and TX in the sockets, and set the baud rate to 115200, which is the OBD2 baud rate my BUICK 2000 Century uses.
Now the device will echo when its not plugged into the car, but as soon as I plugged it in, it throws back garbage.
Using a seperate OBD2 adapter, that plugs into my laptops USB, I can set up a serial connection of 115200 in putty and just send text commands like "01 0C\r" for RPM.
And it returns the RPM in ASCII Hex form
Is there a way I can get this output from the OBD UART?
I tried 38400 with the OBD UART arduino assembly and it still didn't work.
Thanks for your help,
-Beaver_2
So I plugged the RX and TX in the sockets, and set the baud rate to 115200, which is the OBD2 baud rate my BUICK 2000 Century uses.
Now the device will echo when its not plugged into the car, but as soon as I plugged it in, it throws back garbage.
Using a seperate OBD2 adapter, that plugs into my laptops USB, I can set up a serial connection of 115200 in putty and just send text commands like "01 0C\r" for RPM.
And it returns the RPM in ASCII Hex form
Is there a way I can get this output from the OBD UART?
I tried 38400 with the OBD UART arduino assembly and it still didn't work.
Thanks for your help,
-Beaver_2
2013-08-02 21:33:53 I figured out the problem.
I was powering the Netdruino off the USB and the only wires I had coming from the car kit was the RX and TX.
I plugged in the GND to the Netdruino GND and it started working fine. :-[
Right now I'm getting about 12.7 PIDs per second with just constantly rescanning the RPM.
Now to set this up with Bluetooth for my phone Beaver_2
I was powering the Netdruino off the USB and the only wires I had coming from the car kit was the RX and TX.
I plugged in the GND to the Netdruino GND and it started working fine. :-[
Right now I'm getting about 12.7 PIDs per second with just constantly rescanning the RPM.
Now to set this up with Bluetooth for my phone
Beaver_2 2013-08-01 17:40:47 I don't have one of his boards, so I hope Stanley will pipe in. I'm just a bystander trying to help. Of course it could be defective, but I imagine he tests each one. Are you being careful not to blow the chips, not plugging things together with power on?
What I would try is to first test the adapter with a terminal and eliminate any 'Duino software. It still kind of sounds like a baud rate issue. You probably don't have a glass teletype that would (moreover) work at TTL instead of RS-232 levels. So how are you "sending it" AT or Z? Where are you seeing the "welcome message"?
You could open a terminal on the PC to a USB virtual COM, like using the Development IDE, and turn the NetDuino into a transparent pass-through by coding up a little raw mode (send/receive character by character) loop that doesn't use anything but serial calls on the pins the board is connected to. That would be a useful setup to learn how to talk to the translator chip. If 38400 doesn't work, you could change the baud rate on the PC terminal and in the initialization of your little passthrough app, and see if you can find a setting that works? Is that what you're already doing?
Maybe if you have one of those USB to TTL-Serial boardlets like are used for loading code onto the little Mini-Pros that lack a USB jack, you could try to use that instead of programming the 'Duino to do pass-through, just connecting Ground, TX and RX?
Fernand
What I would try is to first test the adapter with a terminal and eliminate any 'Duino software. It still kind of sounds like a baud rate issue. You probably don't have a glass teletype that would (moreover) work at TTL instead of RS-232 levels. So how are you "sending it" AT or Z? Where are you seeing the "welcome message"?
You could open a terminal on the PC to a USB virtual COM, like using the Development IDE, and turn the NetDuino into a transparent pass-through by coding up a little raw mode (send/receive character by character) loop that doesn't use anything but serial calls on the pins the board is connected to. That would be a useful setup to learn how to talk to the translator chip. If 38400 doesn't work, you could change the baud rate on the PC terminal and in the initialization of your little passthrough app, and see if you can find a setting that works? Is that what you're already doing?
Maybe if you have one of those USB to TTL-Serial boardlets like are used for loading code onto the little Mini-Pros that lack a USB jack, you could try to use that instead of programming the 'Duino to do pass-through, just connecting Ground, TX and RX?
Fernand 2013-08-01 09:26:41 I get the welcome message from ELM when I plug it into the car OBD port.
But every time I send it "AT" or "Z" it doesn't do anything.
It doesn't even echo. I've tried it with the \r and \n and neither have done any good.
Also, the device never lights up like it does in the picture. Could my device be defective? Beaver_2
But every time I send it "AT" or "Z" it doesn't do anything.
It doesn't even echo. I've tried it with the \r and \n and neither have done any good.
Also, the device never lights up like it does in the picture. Could my device be defective?
Beaver_2 2013-07-30 17:17:30 Look up the ELM327 data sheet at Elm Electronics. Look up how to set the baud rate. I imagine that this board is compatible, as the ELM327 has become the industry standard. What do you get if you send it ATI[cr] and [email protected][cr] commands?
The baud rate of your car's OBD connection is immaterial. It uses one of the many protocols and pin sets available for an OBD conversation on the connector. The whole point of these "translators" is that the car's native protocol is converted to a simple common ASCII data stream by the chip on the board. So what you care about is what the translated side uses.
You should be able to set the baud rate with ELM327 AT commands, but although 38400 is very common, and Stanley is telling you it's the default, communications might be more reliable over the wire at 9600 baud.
I wouldn't worry about talking at a slower baud rate at first. It's doubtful the car would be saturating a 38400 baud link in most modes, regardless of the bit rate on the native side, and you control the flow with what you request and how often.
As to your RPM request, I'm not sure, but you might have to start out initializing with an AT sequence, and the translator needs to detect the right protocol for that car, or be told which one to use. Do you know which one your car uses? The chip will tell you which one it detects (ATDP[cr]). Try forming your commands as per the ELM327 documentation and deeper protocol OBD specs, and start out testing with the setup commands.
Let us know how it goes.
Fernand
The baud rate of your car's OBD connection is immaterial. It uses one of the many protocols and pin sets available for an OBD conversation on the connector. The whole point of these "translators" is that the car's native protocol is converted to a simple common ASCII data stream by the chip on the board. So what you care about is what the translated side uses.
You should be able to set the baud rate with ELM327 AT commands, but although 38400 is very common, and Stanley is telling you it's the default, communications might be more reliable over the wire at 9600 baud.
I wouldn't worry about talking at a slower baud rate at first. It's doubtful the car would be saturating a 38400 baud link in most modes, regardless of the bit rate on the native side, and you control the flow with what you request and how often.
As to your RPM request, I'm not sure, but you might have to start out initializing with an AT sequence, and the translator needs to detect the right protocol for that car, or be told which one to use. Do you know which one your car uses? The chip will tell you which one it detects (ATDP[cr]). Try forming your commands as per the ELM327 documentation and deeper protocol OBD specs, and start out testing with the setup commands.
Let us know how it goes.
Fernand 2013-07-29 12:19:35 is there a command I need to send to the adapter to tell it to use my car's baud rate of 115200 instead of another vehical's baud rate? Or is that detected automatically?
Beaver_2
Beaver_2 