Tuesday, July 29, 2014

Autonomous Robot with Zynq

In an earlier post, I talked up the Xilinx Zynq (an IC with both FPGA and Microcontroller). In my Advanced Embedded System Design course, we had to build an autonomous robot that can navigate around with some form of intelligence and seek out certain objects to 'destroy'. Now the term 'destroy' was really left up to the students to define; for our robot a laser pointer was used to mark enemies. Identifying 'enemies' was a challenge, so we incorporated a camera so the robot could see and track on its own. Meet our robot (below):

Equipped with:

  •  Zybo
  • OV7670 Camera
  • Arduino
  • Sabertooth Motor Controller
  • IR Proximity Sensors
  • LiPo Batteries (12V + 7V)
  • Pan/Tilt Servo motors
  • Laser
Custom logic was designed onto the FPGA portion of the Zynq, in order to maneuver the robot, control the pan/tilt bracket, capture frame data from the camera, and lastly - 'fire the laser'. The ARM portion of the Zynq was used as the algorithm prototyping environment (in C) to make use of the custom FPGA interfaces. The Arduino was used to configure the OV7670 over the I2C-like communications. The following diagram shows how all components were interfaced.

The reason the OV7670 was chosen was its parallel data interface and low cost ($20), allowing us to obtain an image capture rate of 30fps. However, you get what you pay for in terms of ease of interfacing. I had to design custom logic in VHDL to perform frame captures and store them in block-ram on the FPGA. It's hard to debug what you can't see. None the less, after days of toying around, the Zybo was finally able to see. In order to view what the Zybo saw, I wrote a quick program to transfer images from the Zynq to my laptop over a serial connection (using Processing). Below is the process flow for debugging the images.

The custom FPGA logic which interfaced to the OV7670 was designed to either stream frames into the block-ram, or take a single snapshot and leave it in the block-ram. The FPGA had to interface/synchronize to the vsync, href, pixel-clock, and 8-bit data of the OV7670. It also needed to interface with the ARM processor and to FPGA-based block-RAM. Below is the block model of the custom camera control as shown in Vivado.

We couldn't have done it without camera register settings provided by this source: Hamsterworks - OV7670

Otherwise the images didn't turn out so well:

I'll post some videos of the robot in action soon...