Project 2: Serial Communication and Compass Interface

• All components of the project are due by Friday, March 12th at 5:00pm. Note: your 48 hours grace period (with penalty) accumulates over the weekend.
• Discussion within groups is fine.
• Discussion across groups may not be about the specifics of the solution (general programming/circuit issues are fine to discuss).

Project Goals

• implement in code serial communication protocols for interacting with sensors,
• compute errors between desired and actual state variables, and
• convey information about sensors using a set of LEDs.

Project Components

Part 1: Microcontroller Circuit

• Connect power and ground directly to the battery (not to the +5V power supply)
• Connect the compass transmit line to your Mega8 receive line (PD0, pin 2)
• Connect the compass receive line (green wire with a knot) to your Mega8 transmit line (PD1, pin 3)
• Mount the motor amplifier board to your breadboard. Do not wire it in at this time.
• When mounting the compass to your hovercraft, mount it as far away as possible from the motors and from other wires (we mounted ours on the front of the hovercraft).

• Note: you have already mounted a set of 4 LEDs to your circuit (these form a circle). We will use these to display the craft orientation or orientation error (depending on the state of the switch).

Part 2: Serial Interface

Create a software interface to the craft. Implement the following functionality:

• int16_t get_orientation(void) will send the necessary command to request the current heading from the compass device. This function will then wait for the serial response and return the heading as an integer in 1/10's of a degree (so "100" means 10 degrees). Return values must range between -1799 and 1800, with 0 degrees corresponding to North. Use a left-handed coordinate system to be consistent with the compass.

  In order to query the compass, your Mega8 must transmit on the serial line:
  c

  The compass responds with:
  cXXX\n\r

  Where XXX is the ASCII representation of a 3-digit hexadecimal number that gives the orientation of the craft in tenths of a degree. Note that "\n" is the newline character '\n', not the characters '\' and 'n'. "\r" is the carriage return character, not the characters '\' and 'r'.

• Modify the while(1) loop in your main function to:
  • read the current orientation (calling the above function)
  • compute an error (using the function described below)
  • display either the current orientation (Switch state == 0) or the orientation error (Switch state == 1) using the function described below

Part 3: Sensor Processing and Display

Note: this part will count for one personal programming credit

Implement the following functions:

• int16_t compute_error(int16_t goal, int16_t orientation) returns the error between the current orientation and the goal. Specifically, we are asking what the orientation of the craft is relative to a coordinate frame that is defined by the goal. Return values must range between -1799 and 1800. Positive values correspond to the current heading being clockwise from the goal.

• void display_orient(int16_t theta) changes the state of the orientation LEDs to reflect either the orientation or the orientation error (both of which are in a range of -1799 and 1800).

  Note: your display function should only modify the LEDs involved in the orientation display (and no others). Make sure that all of your display functions (including those from project 1) only modify their respective LEDs

Part 4: Hovercraft Layout

• Batteries
• Forward thrust fans
• Breadboard
• Compass
• Distance sensors

References

• Atmel HOWTO
• Hardware in the Lab (including the USB-TO-RS232 converters -- see the FTDI ft232r section)

What to Hand In

• Demonstration/Presentation: All group members must be present.
  • Demonstrate your final product.
  • Present your design and implementation (5 minutes). The group is responsible for assembling a short presentation consisting of 3-4 slides (on computer or in printed form). Describe the design including:
    • which team members were responsible for what components (including the personal programming components),
    • the circuit,
    • your software solution for transforming the ASCII representation of the compass heading into a value,
    • your software solution for computing heading errors,
    • DO NOT include low-level code (only give the general logic)
    • a circuit diagram (not a picture of your circuit)

• Code: Turn in your documented code to the group project 2 digital dropbox on D2L (hand in the ".c" file). Only hand in one copy of the code per group.

  Remember that documentation is about helping you and others looking at your code to understand what it is doing. Therefore, it will generally describe the logic of the code (and not-necessarily the low-level details). For this class:

  1. Each function must be documented (at the top of the function) as to what it does logically, what the meaning is of its inputs, and what the returned value is. If the function has external effects (e.g., commanding an actuator or modifying a global variable, these should also be documented here)
  2. In-line comments should be used to describe logically what is happening at that line or group of lines.

  See an example.

• Personal report: One submission per person to the personal project 2 digital dropbox in text format only (e.g., M$word has a save-as text option in the File menu). In this report, briefly state:
  1. Who performed which personal programming component. Assess the degree to which they performed this task. The ideal scenario is that they performed a large majority (80% or more) of the task.
  2. Of the remaining project pieces, state the relative contributions of you and your group members in terms of percentage of effort. The ideal distribution is equal across all group members. In extreme cases in which effort is not equitable, this distribution will be used to weight individual grades.

Grading

• 40%: Project implementation
• 30%: Demonstration/presentation of working project (to either of the TA or the instructor)
• 30%: Code documentation and group report

Grades for individuals will be based on the group grade, but weighted by the assessed contributions of the group members.

fagg [[at]] cs.ou.edu

Last modified: Tue Mar 2 00:01:19 2010