I'm looking to use an Arduino Pro Mini to get information from a car's computer and display it on a screen, but both devices work best through serial ports. I hope to use the RX pin to receive information from the computer and use the TX pin to control the screen. I do not need to receive any signals from the screen, and I do not need to transmit anything to the computer. Is it possible to do this, or does using serial require the connection of both channels to a single device? Even if the operation is one-way, do they still need to talk to each other?
Yes you can split the RX and TX like this.
But they have to work at the same baud rate and the same data format. Also your display needs to use TTL levels not RS232.
You also need to disconnect it all when uploading sketches.
chris3145:
Awesome, thanks! If I understand correctly, that means that computer connected to RX can use RS232 as long as the screen uses TTL?
No I believe that is incorrect. The Arduino speaks at TTL levels so you will need a level shifter if the computer output is RS232.
One more thing. If you use the hardware serial in this manner, it is going to limit your ability to debug print to the serial monitor as you build. I am using a 4D display on a project and I am using softwareserial to talk to it so i can still use the serial monitor. In the finished project, the hardware serial will connect to an Anaren 915Mhz radio module.
Are you using the display in SGC or GFX mode? If you are using SGC mode, you will probably want to receive the ACK reply when you send commands. I didn't do this for a long time and ran into a bunch of issues. Once I started looking for that ACK, I found and corrected all of my problems. If you are using GFX mode, this is a moot point. I personally chose SGC mode so I could keep all my code in one place. If you are going to go with the SGC mode, there is a great library already created for these displays. I didn't use the whole library because of ram considerations and I didn't need access to every function included in the library.
that means that computer connected to RX can use RS232
Not sure what you mean by this.
The computer is normally connected through th USB, not RS232.
As Sacman says you need a level converter if you are going to use RS232, something like the MAX202.
The USB to serial converter in the arduino is connected to the chip through 1K seriese resistors, so any signal feeding into the RX pin will have to be strong enough to over ride this.
On the T X side the signal will go to both your display and the computer unless you make some hardware mods.
You need both RX and TX free to upload a sketch.
He is connecting to a Car's computer. When he says computer, I assumed he meant that one. So he wouldn't have any conflict with the 'computer' if he only connects the TX to the Arduino RX. This would also allow him to connect only his TX to the Display with the possible limitations I mentioned above.
I found that you only have disconnect the Arduino RX line to upload a sketch when using these displays because you have to hold the reset pin high. As a result, the display is off and any data sent back to the IDE via the TX (is there any?) during upload would not interfere with the Display.
I've read all your posts, and I like all the information you've given. I wanted to update you guys on how things are proceeding.
It turns out that the ECU (the computer in the car) can output either CAN or serial, but not both. It already has to output CAN for something else, so I'll be tapping into that. My new plan is to run an Arduino Uno R3 with a CAN shield to get all the information (there is somebody else here that has done this before, so I'm not getting in too far over my head). It will do the processing required to convert the CAN inputs into something a little easier to handle, and then it will send this information to an Arduino Pro Mini that is connected serially with the screen. If the CAN shield doesn't interfere with the Uno's serial pins, I may drop the Pro Mini entirely.
Sacman, I tried interfacing with the screen in SGC mode, but I was having a lot of trouble. Installing the libraries and running the sample code only gave me errors (I had to download and rename some additional files, and even then it wouldn't work). I'll be running the screen in GFX mode; it will handle the displaying of all the text and images, and the Arduino(s) will just handle translating the CAN signal into values to pass to the screen. I haven't hooked the Arduino and screen together yet, but both of them are interfacing as expected when connected to a computer.
Hopefully I'll be able to post a video when it's finished. I think it'll be pretty cool.