Forum >Replies by Fernand
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- You Reply: 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? - You Reply: 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.