This is what the system looks like:
The Raspberry Pi talks to the Arduino via USB serial. The movement commands are sent from the Pi to the Arduino, currently, 'w', 's', 'a', 'd' to toggle movement, and ' ' (space) to stop. there are also ASCII numbers 1-6 that correspond to PWM values to control the speed of the motors. While it would be possible to control the motor driver with the GPIO pins of the RPi directly, I had that other circuit all hooked up from a previous project, and all it required was a single USB cable to the Pi, so I went with that instead of rewiring everything.
This time, we want to start doing something a bit more fun. Here's a preview of the end result:
The premise of the example is quite simple: get too close to the robot, and it runs away from you!
We use Python this time to implement the sensing behaviour. The source code that implements the above is available here. I call this one the PyPiBot as it runs on Python... ;)
Basically, what it does is the following:
1. Open SPI device for getting sensor data from the PiShield
2. Open serial port (for sending commands to the motor driver)
1. Get data from sensor port
2. If sensor value is greater than a certain threshold trigger a move forward routine:
- send a 'w' to the robot, which puts it in forward mode
- wait a second (sleep)
- send a ' ' to make it stop
3. Check for ctrl+c and quit the program
What you notice about this particular script is that it is blocking, which means that while the robot is in the move forward mode and the script sleeps, you can't respond to anything else. We'll tackle that in another example in the future!