Raspberry Pi to Arduino Serial USB Communication

0:00 Hi gang! I'm going to show you how I got two-way serial communication to work between a Raspberry Pi and an Arduino. I'm using the Arduino as a motor controller for two eye cameras, but I need something more powerful like a Raspberry Pi for the brains. I used serial over a USB cable so that I can use a PC or anything else if needed for more computing power. For example, the same code works on my NVIDIA Jetson TX1. However, the two-way communication turned out to be tricky to get working and held me back a while. So I thought I'd pass on to you what finally worked. Physically connecting the Raspberry Pi to the Arduino, in my case an Arduino Mega 2560, is easy. Just use the USB cable that comes with the Arduino and is normally used for programming it. I've tested with the Arduino's onboard

0:46 LED. I first wrote some code for the Arduino side. For the setup, I set the baud rate and wait for the serial port to connect. Then for the loop, I check if I've received any serial data. And if I did, then I read one byte of the data. If it's the character 0, then I stop the LED from blinking and send back a letter A over the serial port as an acknowledgement. That's not necessary, but it's good for testing the communication. If instead the character I received was a 1, then I start the LED blinking and also send back a letter A. For any other character, I send back an E, meaning error, since I'm not expecting any other characters. If instead I didn't receive any new serial data, then I just keep the LED blinking. Next came writing some code for the Raspberry Pi. I wrote it in C, and as you'll see later, I tried Python too. Here

1:31 in main, I call OpenSerialPort. It's this function here, which does the open, followed by a bunch of code to set up the serial port. I won't bore you with the details. Then back in main, I next go into an infinite while loop and write the character 1 to the serial port, the one that tells the Arduino to start blinking the LED. Then, to get the acknowledgement that my Arduino code sends back, I call readFromSerial, which is this function here. It simply goes into a loop, reading from the serial port. If the Arduino hasn't sent anything back yet, then it tries again. Remember, my Arduino code sends back an A, so this eventually gets it and returns to main, where I print out the A. I then do that all again, but this time starting with sending the zero character to the Arduino, to tell it to stop blinking. These steps keep repeating every two seconds forever. But it

2:21 didn't work very well. It just sat there. I was stuck for a few months. One day, I stumbled on the solution. I was looking at a project for a four-legged robot on hackaday.io and noticed he was sending successfully in both directions, between an Arduino Mega 2560 and a Raspberry Pi, just like me, but his was working. Looking at his Python code, I realized he was doing an extra step. After clearing DTR, he sleeps for one second and then sets DTR again. Looking back at my open serial port function, I was only clearing DTR. So I added a sleep and set DTR. This time my code worked. The LED started blinking. I decided to see if I had the same problem and solution with Python. So I wrote this code. And without the sleep and setting DTR again, it also didn't work. But after adding the

3:07 extra code, it did work. You can find a link to the Hackaday project in the video description, as well as a link to where you can find the code I've been showing you in this video. I also tried this code on my NVIDIA Jetson TX1 board and am now able to use it to communicate with the Arduino, using the Arduino as a servo motor controller.